

[RP1.002] Experimental Plan and Recent Results from HSX
F. S. B. A. Anderson, A. Abdou, A. Almagri, D. T. Anderson, J. Canik, S. P. Gerhardt, W. Guttenfelder, K. M. Likin, S. Oh, J. Radder, V. Sakaguchi, J. Schmitt, J. Tabora, J. N. Talmadge, K. Zhai (HSX Plasma Laboratory, UW-Madison), D. Brower, C. Deng (UCLA)
In the HSX QHS configuration, significant reductions in
direct loss orbits, parallel viscous damping and
neoclassical thermal transport are predicted compared to a
conventional stellarator. The quasi-symmetry can be broken
through the introduction of a toroidal mirror term in the
magnetic field spectrum. The mirror term phased to give the
highest trapped-particle fraction at the ECH launch gives
poor power absorption and low stored energies; the opposite
phase gives absorption and stored energies similar to the
QHS case. Experiments on 2nd harmonic ECH at B=0.5 T have
been extended to up to 100 kW injected power. Diamagnetic
loop measurements of the stored energy are now augmented by
Thomson scattering, with Te as high as 700eV observed.
Biased electrode experiments have shown reduced damping of
flows with symmetry. The DEGAS code has been used to model
neutral distribution. Recent results and the future program
plan for investigating these configuration differences will
be presented.
[RP1.003] Electron Cyclotron Heating at B=0.5T in HSX
K.M. Likin, A.F. Almagri, D.T. Anderson, F.S.B. Anderson, S.P. Gerhardt, J.N. Talmadge, K. Zhai (HSX Plasma Laboratory, University of Wisconsin-Madison), C. Deng (UCLA)
Second harmonic X-mode ECH produces and heats the plasma in
HSX. Ray tracing calculations predict 40% first pass
absorption at a plasma density of 1.5 x 10^18 m-3 and T_e of
400 eV. A set of absolutely calibrated microwave detectors
is installed to measure the wave absorption,. The absorption
efficiency is very high (about 0.9) in the QHS and Mirror
configurations and drops to 0.6 in the Anti-Mirror mode
where deeply trapped particles have direct loss orbits.
Neutral gas breakdown studies show factors of five higher
density growth rates in QHS compared to anti-Mirror. For
QHS, the stored energy increases linearly with launched
power and plasma density. The radiated power (mainly OII at
the edge) increases linearly with absorbed power. Teo
measured by Thomson scattering also rises linearly with
heating power and reaches ~600 eV at 100 kW of launched
power. A four channel ECE system has been implemented on HSX
to provide information on the electron temperature profile.
[RP1.004] Characteristics of Electrode Biased Discharges in HSX
S.P. Gerhardt, D.T. Anderson, J. Canik, W.A. Guttenfelder, J.N. Talmadge (The HSX Plasma Laboratory), C. Deng (UCLA)
The quasi-helically symmetric (QHS) configuration of the HSX
stellarator has strongly reduced parallel viscosity compared
to conventional stellarators. We use a fast switching biased
electrode system to induce plasma flows and a set of Mach
probes to measure the flows. Results show that the flow
evolution at bias turn on involves two time scales and two
directions. The radial electric field is formed on the
electrode voltage time scale (».001 msec.) and one component
of the flow rises on or near that time scale. A second
component of the flow takes longer (».5 msec.) to establish
itself. The measured damping times of the bias induced flows
are reduced in the QHS configuration by a factor of
approximately two compared to configurations with the
quasi-symmetry intentionally broken. We model the
experiments using neoclassical theory involving parallel
viscosity and ion-neutral friction, including a newly
developed numerical calculation of the Hamada basis vectors
for the 3D HSX geometry. The experimental results agree well
with these neoclassical predictions.
[RP1.005] Neutral Density Modeling and Measurements in HSX
J. Canik, D.T. Anderson, F.S.B. Anderson, S.P. Gerhardt, J.N. Talmadge (HSX Plasma Laboratory, University of Wisconsin-Madison), C. Deng (UCLA), L. Owen (ORNL)
The neutral density and particle source rate have been
measured experimentally in the Helically Symmetric
eXperiment (HSX) using an absolutely calibrated set of 15 Ha
detectors. Nine of the Ha detectors make up a poloidal array
at one toroidal location, with the other six distributed
toroidally around the device. The neutral distribution has
been modeled using the Monte Carlo code DEGAS1. 3-D
simulations have been normalized to the Ha brightness at the
central chord of the poloidal array. The calculations show
good agreement in the line-integrated profiles from the Ha
arrays when the gas puff is located at the same toroidal
plane as the poloidal array. The toroidal Ha array reveals a
significant asymmetry in the emission, with the brightness
at the gas puff a factor of five greater than the signal on
the other side of the torus. Results of simulations of
different operating regimes will be presented [1] Heifetz,
D.B. et. al., J. Comp. Phys. 46, (1982) 309
[RP1.006] Characteristics of Edge Turbulence in HSX
W.A. Guttenfelder, D.T. Anderson, J. Canik, S.P. Gerhardt, J.N. Talmadge (HSX Plasma Laboratory, University of Wisconsin-Madison), C. Lechte (TJ-K Laboratory, U. of Kiel, Germany)
Langmuir probes have been used to characterize the edge
plasma and turbulence in the Helically Symmetric eXperiment
(HSX) stellarator. Power spectra of ion saturation current
and floating potential (measured on the low field side of
HSX) display broad frequency content. Electrostatic particle
transport spectra deduced from these signals show a
significant contribution for frequencies up to 300 kHz.
Total electrostatic particle transport in the edge is
approximately 10^16 cm-2s-1 in the outward radial direction,
increasing with decreasing radius. Within r/a \sim0.7, a mode
at 40-50 kHz is apparent and is responsible for a fraction
(<20%) of the particle transport. Phase velocities of the
fluctuations are calculated via the two-point correlation
technique to be in the ion diamagnetic direction and
decrease as the E´B velocities (also in the ion diamagnetic
direction) decrease. First electrostatic transport
measurements from a probe with access to the high field side
of HSX will be presented
[RP1.007] Particle Transport and Density Fluctuations in HSX
C. Deng, D. L. Brower (UCLA), J. Canik, S. P. Gerhardt, D. T. Anderson, F. S. B. Anderson (The HSX Plasma Laboratory, University of Wisconsin, Madison)
Initial estimates of particle transport in the
quasi-helically symmetric stellarator, HSX, are carried out
using a multichannel interferometer system which has 9
viewing chords with 1.5 cm spacing. Density perturbations
are produced by modulating the plasma gas fuelling and the
particle source is measured by a multi-channel Ha system.
The total radial particle flux is estimated by solving the
continuity equation. Diffusion coefficient D and convection
velocity V are modeled. Preliminary estimates indicate a
diffusion coefficient De\sim1 m2/s. Investigation of fast
oscillations evident on the interferometer time-series
traces reveals the existence of high-frequency density
fluctuations in the range of 25-100 kHz. These fluctuations
are noted to have an m=1 nature and are only observed in
quasi-helically symmetric plasmas in HSX. Observation of
these fluctuations is made during the ECRH pulse when the
resonance position is near the plasma core suggesting they
may be driven by gradients in the plasma pressure.
[RP1.008] First Thomson Scattering Results on HSX
K. Zhai, F.S.B.A. Anderson, K.M. Likin, D.T. Anderson (HSX Plasma Laboratory)
First results using the Thomson Scattering (TS) System on
HSX have been obtained. Based upon the GA divertor TS system
design, the HSX TS system consists of several interdependent
subsystems; YAG laser, beam transportation, collection
optics, fiber optics, polychromators, and data acquisition.
It is capable of providing a 10-point radial profile. The
central channel is now operational and the rest of the
channels will soon be implemented. HSX is currently using
28GHz ECRH at the second harmonic x-mode for plasma
production and heating. It is found that the central
electron temperature rises linearly with heating power from
30 KW to 100 KW at a fixed density of 1.5\times 10^12cm^-3; in the
QHS mode from 300eV to 700eV, and in the Mirror mode from
200eV-600eV. At 40KW heating power, the electron temperature
decreases with increasing plasma density, consistent with
the diamagnetic measurement of the stored energy. The
operation of the system and the detailed results of density
scan and power scan for both QHS and Mirror modes will be
presented.
[RP1.009] Soft X-Ray Tomography in HSX
V. Sakaguchi (vsakaguc@wisc.edu), A.F. Almagri, D.T. Anderson, F.S.B. Anderson, K. Likin (The HSX Plasma Laboratory)
Under certain discharge conditions, HSX plasmas exhibit a
sudden loss of stored energy followed by fluctuations of the
order of few kHz in both the stored energy and the soft
x-ray (SXR) signals. These are measured by a diamagnetic
loop and a set of PIPS detectors respectively. To help
understand the origin of these crashes and the nature of the
oscillations, as well as to measure basic plasma properties
such as position and shape, a SXR tomography system is under
development in HSX. A single array of 20 silicon p-n
junction photodiodes is installed on the device and, in the
near future, the diagnostic system will be expanded to
several arrays in order to obtain tomographic
reconstructions of the SXR emission. Initial SXR and stored
energy measurements during these crashing discharges as well
as the results of the one-array reconstruction will be
presented. Implementation details of the complete
tomographic system will be shown as well.
[RP1.010] Study of Hard X-ray Emission in HSX
A.E. Abdou, A.F. Almagri, D.T. Anderson, J. Radder, J.N. Talmadge (HSX Plasma Laboratory, University of Wisconsin-Madison)
A hard x-ray system employing a CdZnTe detector has been
implemented on HSX. The magnetic configuration has been
altered between QHS and Mirror mode in order to determine
the effect of magnetic ripple on the spectrum and densities
of fast electrons. Pulse height analysis of the hard x-ray
signals (HX) show the presence of x-ray photons with energy
up to 1 MeV. In the QHS mode, the hard x-ray intensity
decreases monotonically over two orders of magnitude as the
central line averaged density increases from 0.2 to 1.0 x
10^12 cm^-3. In contrast, in the mirror configuration the
intensity level is small at the lowest density, peaks at a
density of 0.5 x 10^12 cm^-3 and then falls at higher
density. In QHS the tail of the spectrum extends to higher
energies than for the mirror mode. Increased intensities
correlate with the highest stored energies as measured by
the diamagnetic loop.
[RP1.011] High ion temperature discharges after Ne glow discharge cleaning in LHD
Shigeru Morita, Yasuhiko Takeiri (National Institute for Fusion Science), LHD Team
Ion heating experiment has been extensively carried out in
LHD. Using Ne NBI discharges the central ion temperature
reached 5keV as a result of the increase in Pi/ni. However,
the ion density was dominated by the residual hydrogen. In
order to displace the hydrogen to neon, Ne glow discharge
cleaning was done. As a result, the ion temperature up to
7keV was obtained in combination of Ar puff. Higher ion
temperature was also obtained for C pellet injection. During
these discharge a large increment of toroidal rotation was
observed. The observed toroidal rotation speed indicated a
good correlation with the ion temperature. In the
conference, effects of the Ne glow discharge, Ar puff, C
impurity pellet and toroidal rotation are discussed.
[RP1.012] Extension of the HINT code and equilibrium computation of LHD with zero rotational transform surface
Takaya Hayashi, Ryutaro Kanno, Hideaki Miura, Noriyoshi Nakajima, Masao Okamoto (National Institute for Fusion Science), Yasuhiro Suzuki, Yuji Nakamura (Kyoto University)
The three dimensional MHD equilibrium code HINT, which does
not assume the existence of nested magnetic surfaces, is
modified to extend functions and usabilities. Possibility of
a Large Helical Device equilibrium with a zero rotational
transform surface is exmined by HINT. The rotational
transform profile is assumed to be controlled by amount of a
net toroidal current. In the equilibrium, we find existence
of the equilibrium but formation of two n=0 islands
composing the homoclinic-type structure near the center,
where n is a toroidal mode number. As further increase of
beta, three n=0 island structure is formed, while the
homoclinic-type nature is retained. A maximum in the
Shafranov shift is observed as the increase in the amount of
the net current.
[RP1.013] Eigen surface cyclotron modes of the stellarator plasma column
Ivan Pavlenko, Volodymyr Girka, Igor Girka (Kharkiv National University)
The eigen surface modes of magnetically confined plasma
column can be excited during the ion cyclotron resonance
heating (ICRH) in stellarators plasma. These modes can be
localized in a narrow region at the plasma edge. Therefore
the essential part of the ICRH power will be absorbed at the
plasma edge without the effective plasma heating in the
center. Due to this reason the ICRH system has to avoid
operating in the range of the parameters which provide a
high probability of the surface mode excitation. As an
example, the eigen surface modes of LHD have been studied to
estimate the penetration depth of wave field into plasma
column and calculate their radial distribution. The
calculations have been carried out for the nonuniform radial
density and temperature profiles. The eigen wavelength of
the surface perturbations at harmonics of the cyclotron
frequency are reported. The dependence of the eigen
wavelength on the plasma density gradient has been studied.
[RP1.014] Development of Heavy Ion Beam Probe System in CHS
Shimizu Akihiro, Fujisawa Akihide, Ohshima Shinsuke, Nakano Haruhisa, Isobe Mitsutaka, Suzuki Chihiro, Nishimura Shin, Nagaoka Kenichi, Minami Takashi, Yoshimura Yasuo, Okamura Shoichi, Matsuoka Keisuke (National Institute for Fusion Science)
Heavy Ion Beam Probe (HIBP) is a very powerful tool that is
able to simultaneously detect potential, density, magnetic
field and their fluctuations in interior of high temperature
plasmas. In CHS, so far, the HIBP has revealed interesting
behavior of the plasma interior, such as bifurcation,
internal transport barrier, MHD phenomena, by observing
potential profile and density fluctuation. Now we are making
efforts to make a full use of the other abilities of HIBP,
that is, to detect potential fluctuation and magnetic field
fluctuation. In order to study potential fluctuation, a new
ion source has been developed to increase beam current
density. With the new ion source, we have obtained current
3~5 times larger than the previous one. This improvement
allows us to detect the potential fluctuation, and also
density fluctuation with higher S/N ratio. As for the
magnetic field fluctuation estimated from the beam
displacement, the interpretation of the signal is quite
difficult because of 3D magnetic field configuration of CHS.
In the first place, a numerical calculation has been
performed in axisymmetric toroidal field i. e., tokamak
configuration, in order to obtain a basic perspective of the
relationship between the beam displacement and local
magnetic field fluctuation. In our presentation, we will
describe the resultant progress of HIBP measurements, and
the recent results of density and potential fluctuation
measurements in the CHS stellarater.
[RP1.015] Progress in Analysis and Construction of NCSX.
M.C. Zarnstorff, G.H. Neilson, D. Mikkelsen, N. Pomphrey, W. Reiersen, J. Schmidt (PPPL), J.F. Lyon, B.E. Nelson (ORNL), NCSX Team
The National Compact Stellarator Experiment (NCSX) is being
developed to explore the high-\beta stability and
confinement of a quasi-axisymmetric stellarator with average
aspect ratio 4.4. It is designed to be passively stable to
the ballooning, kink, vertical, Mercier, and neoclassical
tearing modes for \beta > 4% without the need for
external feedback or conducting walls. The bootstrap current
generates only 1/4 of the magnetic rotational transform at
\beta = 4% (the rest is from the coils). As a
consequence, stability properties are relatively insensitive
to the pressure profile shape. The quasi-axisymmetric
magnetic field produces thermal neoclassical transport
similar to equivalent tokamaks and adequate fast-ion
confinement. It also produces low damping of flows in the
toroidal direction. The consequence of the low toroidal flow
damping on the expected turbulence will be discussed. The
coils have been designed to provide good flux surfaces and
to flexibly investigate the predicted MHD stability and
transport properties. Prototypes of the coils and vacuum
vessel are under construction. Fabrication of the production
coils and vessel is scheduled to start next year.
Development of a national team for research and diagnostic
development will also begin next year.
[RP1.016] Progress in Technology Research and Development for NCSX
G. Neilson, J. Chrzanowski, P. Heitzenroeder, S. Raftopoulos, W. Reiersen, M. Viola (Princeton Plasma Physics Laboratory), P. Goranson, J. Lyon, B. Nelson, D. Williamson (Oak Ridge National Laboratory)
The physics mission of the National Compact Stellarator
Experiment imposes demanding requirements on the
manufacturing technologies for the modular coils and vacuum
vessel. These components must satisfy complex
three-dimensional shape specifications to high accuracy
while meeting their performance requirements. A research and
development program is being carried out by PPPL, ORNL, and
industry to demonstrate the necessary technologies. Advanced
numerical modeling, metrology, and manufacturing methods are
being developed to optimize the fabrication of the modular
coil winding forms (by casting and machining) and vacuum
vessel (by forming and welding). Coil winding developments
include flexible cable design, epoxy impregnation of
complex-shaped windings, metrology, composite materials
properties, and dimensional control during the winding
process.
[RP1.017] Two-Fluid Steady States of High Beta Stellarators
Linda Sugiyama (MIT), H.R. Strauss (NYU), W. Park, G.Y. Fu (PPPL)
Stellarator steady states and stability obtained from
two-fluid nonlinear relaxation are very different from MHD
predictions and may allow higher beta. Numerical simulations
of the NCSX high beta stellarator with the M3D two-fluid
code show that a strong equilibrium pressure gradient near
the plasma edge (``H-mode'') creates a region where
diamagnetic drifts and related effects drive a steady state
poloidal flow on fast MHD-like time scales, well before the
neoclassical parallel viscous stress acts to reduce
v_i\theta. The flow in the strong \nabla p region is
similar over a large range of p_e/p_i, in the
ømega_*i-direction with magnitude significantly smaller
than an average diamagnetic velocity based on (p_e+p_i)/2.
The flow robustly stabilizes high mode number resistive
ballooning/interchange modes that limit MHD stability in
simulation, but generally not in experiment. In addition,
electron two-fluid effects can increase magnetic island
growth rates on interior rational surfaces. These effects
increase with \beta and p_e/p_i, suggesting that the
best stellarator confinement may exist in hot-ion operation.
The beta limit may be a gradual one due to the overlap of
large, although contained, magnetic islands that destroy the
effective plasma confinement, rather than catastrophic
instability.
[RP1.018] Neoclassical transport in NCSX
D.R. Mikkelsen, M.C. Zarnstorff (Princeton U.), C.D. Beidler, H. Maassberg (IPP), W.A. Houlberg, D.A. Spong (ORNL), V. Tribaldos (CIEMAT)
Neoclassical viscosities and cross-field particle and heat
fluxes are presented for projected NCSX conditions.
Calculations based on full 3-D magnetic configurations are
compared with predictions for equivalent axisymmetric
configurations and an analytic model for neoclassical
helical transport. The transport matrix for 3-D
configurations is based on monoenergetic diffusivities,
obtained here from the DKES code, and from MOCA, a Monte
Carlo orbit code. The pitch-angle-scattering collision
operator does not conserve momentum, so we use a procedure
proposed by Sugama to obtain the corrected transport
parameters. The magnetic geometry of NCSX can be varied by
changing the internal bootstrap currents and the
independently driven currents in the external modular field
coils. To obtain efficient estimates of the neoclassical
transport for each new configuration, the monoenergetic
diffusivities are represented with physically motivated
basis functions. We also compare to predictions of the
ambipolar radial electric field and the neoclassical helical
particle and energy fluxes given by the analytic
Shaing-Houlberg model (with an improved treatment of the
\nu regime).
[RP1.019] Eliminating islands in high-pressure free-boundary stellarator magnetohydrodynamic equilibrium solutions.
Stuart R. Hudson, D.A. Monticello, A.H. Reiman, M.C. Zarnstorff (Princeton Plasma Physics Laboratory), A.H. Boozer (Columbia University), D.J. Strickler, S.P. Hirshman (Oak Ridge National Laboratory), Princeton Plasma Physics Laboratory Collaboration, Columbia University Collaboration, Oak Ridge National Laboratory Collaboration
Magnetic islands in free-boundary stellarator equilibria are
suppressed using a procedure that iterates the plasma
equilibrium equations and, at each iteration, adjusts the
coil geometry to cancel resonant fields produced by the
plasma. The coils are constrained to satisfy certain
measures of engineering acceptability and the plasma is
constrained to ensure kink stability. As the iterations
continue, the coil geometry and the plasma simultaneously
converge to an equilibrium in which the island content is
negligible. The method is applied with success to a
candidate plasma and coil design for the National Compact
Stellarator eXperiment [Phys. Plas., 8(5),2083 2001].
[RP1.020] Heat Load on the NCSX First Wall
T. B. Kaiser (University of California, Lawrence Livermore National Laboratory), D. N. Monticello (PPPL), D. N. Hill, M. V. Umansky (LLNL)
We have used magnetic field data generated by the PIES 3D
MHD equilibrium code(M50 coil set) and a new vacuum field
code(Michael Drevlak Max Planck Institute for
Plasma Physics, Greifswald, Germany, private communication),
together with the latest numerical model of the first wall
(Art Brooks, PPPL, private communication) to
compute wall heat loading in the National Compact
Stellarator Experiment (NCSX) as a function of position.
Field lines originating just outside the last closed
magnetic surface are followed until they intersect the wall
by integrating the field-line equations of motion in
cylindrical coordinates using the LSODE integrator. Magnetic
field values are interpolated with arbitrary-order splines.
The local (nonuniform) heat flux is estimated from the
density and incidence angle of escaping field lines.
[RP1.021] Overview of the QPS Experiment.
J.F. Lyon (Oak Ridge National Laboratory.), QPS Team
The Quasi-Poloidal Stellarator (QPS) is a
very-low-aspect-ratio (R/a = 2.7) compact stellarator in
which the dominant magnetic field components are poloidally
symmetric in flux coordinates, which leads to large
reductions in: neoclassical transport at low collisionality;
bootstrap current; and poloidal viscosity, which allows
large E x B poloidal flows for suppression of anomalous
transport. The magnetic configuration is relatively
insensitive to increasing beta. The experiment under design
has R = 0.95 m, a = 0.35 m, B = 1 T for a 1.5-s pulse, and
P(heating) = 2-4 MW. Nine independent coil currents allow
varying: neoclassical transport by a factor \sim25, degree of
poloidal symmetry by a factor \sim10, and poloidal viscosity by
a factor of 530. QPS can study regimes in which either the
anomalous transport or neoclassical transport is dominant,
ballooning stability limits at beta = 2.5%, and equilibrium
robustness at finite beta. Recent progress on physics
issues, the relationship to other stellarator concepts, the
QPS project status, and the proposed experimental program
are presented.
[RP1.022] Design of the QPS Experiment.
B.E. Nelson (Oak Ridge National Laboratory.), QPS Team
The Quasi-Poloidal Stellarator, QPS, is a low-aspect-ratio
(R/a = 2.7), compact stellarator under design at ORNL. The
device parameters are R = 0.95 m, a = 0.35 m, and B = 1 T
for 1.5 s with 2 MW of ECH and 3.5 MW of ICRF for plasma
heating. A nonplanar modular coil set provides the primary
magnetic field configuration. It has two field periods with
ten modular coils per period. Due to stellarator symmetry,
there are only five different coil types. Flexible copper
cable conductor will be wound on a stainless steel form,
vacuum impregnated with epoxy, and canned for vacuum
compatibility. The coil form allows the coils to be
connected into an integral structural shell. Unlike most
stellarators, a vacuum vessel surrounds the coils rather
than fitting inside the coils, allowing excellent access for
plasma diagnostics and heating. In addition there are
external vertical field and toroidal field coils and an
ohmic current solenoid for configuration flexibility. First
plasma operation is planned for the end of 2007. Details of
the engineering design and analysis will be presented.
[RP1.023] Confinement, Flow Damping and Flexibility of Quasi-Poloidal Stellarators
D. A. Spong, S. P. Hirshman, L. A. Berry, D. J. Strickler, J. F. Lyon (Oak Ridge National Laboratory), D. Mikkelsen, D. Monticello (Princeton Plasma Physics Laboratory), A. S. Ware (Univ. of Montana)
Quasi-poloidal (QP) stellarators have achieved levels of
optimization that significantly suppress neoclassical
transport relative to anomalous levels. QP symmetry also
allows poloidal flow damping to be less than toroidal flow
damping. This ordering (reversed from that of tokamaks)
should allow more efficient control of the radial electric
field with less required momentum input. An analysis of flow
dynamics in such systems has been initiated using viscosity
coefficients that can be derived from the usual transport
coefficients (density/energy diffusion, bootstrap current.
resistivity enhancement). The dependencies of these
coefficients on plasma parameters such as collisionality and
electric field will be analyzed and implications for flow
evolution discussed. By varying the modular and vertical
field coil currents in proposed QP systems, substantial
flexibility has been demonstrated theoretically with respect
to neoclassical confinement, quasi-poloidal symmetry, flow
damping, and magnetic island widths. Variations of a factor
of 20 in low collisionality neoclassical transport rates and
a factor of 5 in quasi poloidal symmetry can be achieved.
Work supported by U.S. Department of Energy under Contract
DE-AC05 00OR22725 with UT-Battelle, LLC.
[RP1.024] Impact Of Plasma Current Profile And External Coil Currents On Ideal Mhd Stability In The Quasi-Poloidal Stellarator
E. Barcikowski, A. S. Ware (University of Montana), L. A. Berry, S. P. Hirshman, J. F. Lyon, D. A. Spong, D. J. Strickler (Oak Ridge National Laboratory), G. Y. Fu (Princeton Plasma Physics Laboratory)
This work examines the impact of both the plasma current
profile and external coil currents on ideal MHD stability in
the Quasi-Poloidal Stellarator (QPS) [1]. The reference coil
set for QPS contains 20 modular coils with 5 different coil
shapes with each of the 4 coils of a given shape forming a
group with a separate power supply. In addition to the
modular coils, there are also a set of toroidal field coils
and 3 pairs of vertical field coils. This coil set allows
for flexible variation of the magnetic configuration. QPS
has been designed to run with a bootstrap aligned current
profile but will also have the capability of driving Ohmic
current. By varying both the external coil currents and the
plasma current profile, the ideal MHD stability properties
of QPS can be greatly impacted. The infinite-n ballooning
\beta limit can vary by a factor of ~2. The marginal
ballooning \beta limit is lowest with an Ohmic current
profile, highest with a bootstrap current profile, and can
be varied between these limits with a combination of Ohmic
and bootstrap current. As expected, finite-n ballooning
modes (for n up to 19) have higher \beta limits, roughly
50-100% higher than the infinite-n limit for QPS. Kink
and vertical modes are stable in QPS to much higher plasma
\beta (> 5%). [1] J. F. Lyon, et al., “Physics and
Engineering Design of a Very-Low-Aspect-Ratio Quasi-Poloidal
Stellarator”, in preparation for Nucl. Fusion, (2003).
[RP1.025] A Breeder Algorithm for Stellarator Optimization
S. Wang, A. S. Ware (University of Montana), S. P. Hirshman, D. A. Spong (Oak Ridge National Laboratory)
An optimization algorithm that combines the global parameter
space search properties of a genetic algorithm (GA) with the
local parameter search properties of a Levenberg-Marquardt
(LM) algorithm is described. Optimization algorithms used in
the design of stellarator configurations are often
classified as either global (such as GA and differential
evolution algorithm) or local (such as LM). While nonlinear
least-squares methods such as LM are effective at minimizing
a cost-function based on desirable plasma properties such as
quasi-symmetry and ballooning stability, whether or not this
is a local or global minimum is unknown. The advantage of
evolutionary algorithms such as GA is that they search a
wider range of parameter space and are not susceptible to
getting stuck in a local minimum of the cost function. Their
disadvantage is that in some cases the evolutionary
algorithms are ineffective at finding a minimum state. Here,
we describe the initial development of the Breeder Algorithm
(BA). BA consists of a genetic algorithm outer loop with an
inner loop in which each generation is refined using a LM
step. Initial results for a quasi-poloidal stellarator
optimization will be presented, along with a comparison to
existing optimization algorithms.
[RP1.026] Development of a Prototype Three-Dimensional Equilibrium Reconstruction Code
S.P. Hirshman, E.A. Lazarus (Oak Ridge National Laboratory), J.D. Hanson, S.F. Knowlton (Auburn University), L.L. Lao (General Atomics)
An initial step toward developing an efficient equilibrium
reconstruction code for three-dimensional (3D) plasmas has
been taken. The 3D magnetics diagnostics codes V3RFUN and
V3POST can be used to rapidly compute the expected magnetic
signals in external loops arising from both external coil
currents and internal stellarator plasma currents. The
V3RFUN code is executed once initially (for a prescribed set
of stellarator coils) to generate a database of diagnostic
responses valid for arbitrary plasma currents. Then, the
V3POST code is executed repeatedly from within the 3D
optimization code STELLOPT to compute diagnostic signals
arising from the MHD pressure and iota profiles. The
optimizer determines the profiles which best match the
measured external diagnostic signals. The relative
computational efficiency of the V3POST evaluations renders
this procedure numerically feasible and will provide a
prototype for the eventual development of an optimized 3D
reconstruction code (V3FIT). The prototype code will be used
to examine numerical features of the reconstruction process
- such as the level of convergence needed to estimate the
signal gradients - which will guide the development of the
optimized V3FIT code.
[RP1.027] Reconstruction of 3D Equilibria from Flux Surface Knowledge Only
H.E. Mynick, N. Pomphrey (Princeton Plasma Physics Laboratory)
Using the properties of the Grad-Shafranov (GS) equation, Christiansen and Taylor (CT) have shown(J.P. Christiansen, J.B. Taylor, Nucl.Fusion) 22, 111 (1982). that complete MHD equilibria may be obtained for axisymmetric tokamaks with noncircular cross-sections, provided that one initially knows only the shapes of the flux surfaces. Starting from a 3D generalization of the GS equation(L.M. Degtyarev, V.V. Drozdov, M.I. Mikhailov, V.D. Pustovitov, V.D. Shafranov, Sov. J. Plasma Phys.) 11 22 (1985), we have recently demonstrated(H.E. Mynick, N. Pomphrey, Phys. Plasmas) 9,1050 (2002) that this remarkable result can be extended to 3D systems like stellarators.
A code to practically implement this earlier formal result
is nearing completion. For testing, the code takes plasma
shapes from VMEC equilibria, and the predicted profiles are
compared with those from VMEC. With it, we will test if this
extended CT method may be used as a practical diagnostic to
use emissivity data from stellarators, and what the
sensitivity of the results are to uncertainties and
sparseness of the experimental data.
[RP1.028] Construction Progress of the Compact Toroidal Hybrid
G.J. Hartwell, S.F. Knowlton, J. Armstrong, J. Peterson, C. Montgomery, J. Fullerton, M. Krefting, J.D. Hanson (Auburn University.)
The Compact Toroidal Hybrid (CTH) is under construction at
Auburn University. CTH is a stellarator/tokamak hybrid
device that will use an ohmic current of I_p\leq 50kA to
investigate both ideal and resistive current-driven
instabilities in low aspect ratio stellarators, and to carry
out 3-D plasma equilibrium reconstruction tests. The edge
vacuum rotational transform in CTH is variable from
t_V(a) = 0.2 to 0.5 with a current-generated transform
t_J(a) \leq 0.5. The average plasma major radius is
R_o = .75m, the vacuum vessel minor radius is a_v =
0.29m and the maximum average plasma minor radius is a_p
= 0.20m. CTH is a low \beta (\leq0.005) machine and will
operate at magnetic fields B_o \leq 0.5T. Target plasmas
for ohmic current stability studies will be generated by an
18GHz klystron operating at ømega=2ømega_ce. The CTH
vacuum vessel has been cleaned, and outfitted with heater
pads and magnetic diagnostics. The poloidal field coils have
been wound and helical field coil winding will begin shortly
after delivery of the helical coil frame. The CTH device is
scheduled to be completed and operational in mid-2004.
Supported by US DoE Grant DE-FG02-00ER54610
[RP1.029] High Beta Helical Equilibrium
David Smith, Allan Reiman (PPPL, Princeton University)
An analytic solution of the helical Grad-Shafranov equation
subject to the constraints \beta=2\mu_0p/B^2\sim O(1) and
q=d\Phi_T/d\Phi_P\sim O(1) is presented. The pressure
profile p(\psi) and the safety factor profile q(\psi)
are specified. The solution takes the form of a boundary
layer problem with the inverse aspect ratio \epsilon=a/r_0
as an expansion parameter. In the core region, \psi is a
function of only the major radius so the flux surfaces are
vertical lines. The boundary layer is located at the wall
and the Shafranov shift is of the order the minor radius. A
solution with vanishing toroidal current is also presented.
This condition imposes a constraint relating p(\psi) and
q(\psi) such that only one profile may be independently
specified. DOE Contract Number: DOE-AC02-76-CHO3073.
[RP1.030] The effect non-linear wave-particle interaction on ECRH with helical ripple stellarators
JaeChun Seol, C.C. Hegna (University of Wisconsin-Madison)
Particles trapped in the helical ripples in stellarators
bounce back and forth along the magnetic field line. Trapped
particles get energy from the wave repeatedly. When the
turning points are far from the resonance region, the
heating process is stochastic and the wave-particle
interaction makes a small perturbation on the distribution
function. The rate of velocity-diffusion for the leading
order distribution function is proportional to the sum of
squares of the wave amplitudes. This is the, so called,
"quasi-linear diffusion theory" since linear absorption and
quadratic diffusion are used. However, quasi-linear theory
is not valid when the turning points are very close to the
resonance region and the particles stay in the resonance
region such as in second harmonic X mode ECRH. When this is
the case, the wave and particles are correlated and the
stochastic process is not viable. To obtain ECRH heating in
this nonlinear regime, collisions need to be explicitly
accounted for. Nonlinear wave-particle interaction for
deeply trapped particles has been described in previous
work. In this work, the equivalent diffusion term when
nonlinear wave-particle interaction dominates will be
derived. It is desired to look for steady-state solution of
the Fokker-Planck equation when the heating term and the
Coulomb collision term are balanced in order to analyze
power deposition.
[RP1.031] JET
[RP1.032] Real-time profile control in JET for steady state advanced tokamak operation
D Moreau, F. Crisanti, X. Litaudon, D. Mazon, E. Barbato (EFDA-JET, Culham Science Centre, Abingdon, OX14 3DB, UK), EFDA-JET workprogramme contributors Collaboration
Real-time control of the plasma profiles (current, pressure
and flows) is a key issue to sustain steady state discharges
with internal transport barriers (ITB) and a large bootstrap
current fraction. In order to simultaneously control the
current and pressure profiles in JET ITB discharges, a
multi-variable model-based technique has been proposed. It
is based on a truncated singular value decomposition of an
integral model operator and retains the distributed nature
of the plasma parameter profiles. The related algorithms
have been implemented in the JET control system, and applied
to the control of the current profile in reversed shear
plasmas using three actuators (neutral beam injection, ion
cyclotron heating and lower hybrid current drive).
Successful control of the q-profile has been achieved in
quasi steady state conditions with a significant fraction of
bootstrap current. In these experiments the strength of the
ITB's was marginal during the control phase, due to the
chosen q-profile setpoints and to the moderate heating power
which was requested by the controller. Hence, further
experiments aiming at the simultaneous control of the
current profile and of the normalized ITB temperature
gradient are being pursued and first results will be
reported.
[RP1.033] Edge Transport Barrier Behaviour in JET ELMy H-mode Plasmas
Mark Kempenaars, Marc Beurskens, Marco de Baar (Associatie EURATOM-FOM, FOM Rijnhuizen, P.O. Box 1207, 3430 BE, Netherlands), Alberto Loarte, Arne Kallenbach (EFDA Close Support Unit, Garching, MPI fur Plasmaphysik, Garching, Germany), Chris Gowers, Klaus Günther, Anatolii Korotkov, Phil Morgan, Robin Prentice (EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB, Abingdon), JET EFDA contributors Collaboration
The ELMy H-mode plasma configuration is the most likely candidate, at the moment, for ITER and fusion based power plants. Hence it is very import to understand the workings of these plasmas. Recently on JET a large database of edge transport barrier, ETB, data has been gathered using the edge LIDAR Thomson scattering Diagnostic. This had been impossible before, due to system resolution limitations. Now a plasma configuration has been designed (DOC-U) with the last closed fluxsurface tangential to the edge LIDAR laser line of sight, effectively increasing the spatial resolution to ~ 2 cm. The results obtained from this database are shown [1] to be contradictory to expectations and other experiments [2,3]. It shows that the ETB gradients decrease with an increasing Greenwald density fraction and the pedestal width increases. In this paper these results are expanded and further analysed, to achieve a better understanding of the ELMy H-mode plasma edge behaviour in JET.
[1] M. Kempenaars, et al, 30th EPS 2003, St. Petersburg,
5-11 July 2003 [2] G. Saibene, et al, Plasma Physics and
Controlled Fusion 2002 [3] A. Kallenbach, et al, 30th EPS
2003, St. Petersburg, 5-11 July 2003
[RP1.034] Modeling effects of local surface properties on heat flux deposition in the JET divertor
Y. Corre (KTH Royal Institute of Technology, Stockholm, Sweden), J. Hogan (Fusion Energy Division, ORNL), E. Gauthier (CEA-Cadarache), P. Andrew (Culham Science Centre), T. Eich (IPP-Garching), S. Jachmich (Laboratory for Plasmaphysics, ERM, Brussels), T. Loarer (CEA-Cadarache), G. Matthews (Culham Science Centre), P. Monier-Garbet (CEA-Cadarache), Contributors to the JET/EFDA Workprogramme Collaboration
Understanding heat flux deposition from ELMs is an essential
issue for a next step fusion device. A high time resolution
infrared system is used in JET to measure the surface
temperature distribution and its evolution on the divertor
target plates. Previously, an empirical technique was
developed, based on a flexible 1D model calculation, to
assess possible complications due to surface layer
properties, such as poorly adhered a-C:D layers [1]. The
model validation used data from JET DOC-L discharges (DOC-L:
inner and outer strike points positioned for optimized
infrared measurements) with programmed constant L-mode power
steps. The effect of layers was identified for the inner
tile surface. In this paper we compare the 1D model for
surface temperature evolution with results of 3-D modeling
with the CASTEM-2000 thermal code, for these DOC-L power
step cases. The 1-D values are shown to approach the 3-D
results as the model power deposition width increases,
showing that there is a absolute 30% accuracy for the 1D
model along with a well-supported validation for its use in
scaling studies. Additional modeling describing the role of
layers and also of small localized heat sinks (dust), as is
suggested for similar cases [2], will be presented. [1] Y.
Corre et al, EPS 2003, St. Peterburg [2] E. Delchambre et
al, J Nucl Mater 2003
[RP1.035] Deuterium to Helium Plasma-Wall Change-over Experiments in JET with Reversed Toroidal Field
D.L. Hillis (ORNL, Fusion Energy Division), T. Loarer (CEA-Cadarache, France), R.A. Pitts (CRPP-EPFL, Association EURATOM)
The deuterium and helium dynamics in the plasma and
subdivertor regions of JET are compared during a sequence of
similar ohmic and NBI pulses where 100% He gas is injected
into the JET vacuum vessel, whose graphite walls were
previously saturated with deuterium. After the first six He
fueled change-over discharges, only He plasma operation was
performed. The He concentration is measured in the
sub-divertor with a species selective Penning gauge.
Comparison of the time dependence of the divertor
concentrations with those at the edge and strike point shows
significant differences during the first six discharges.
Data has been obtained for both the normal and reversed
toroidal magnetic field direction. These differences along
with a global He particle balance is used to assess the
status of the wall saturation over the initial 6 - 7 He
change-over discharges.
[RP1.036] Resistive Wall Mode studies on JET
M Gryaznevich, C G Gimblett, T C Hender, D F Howell (EURATOM/UKAEA Fusion Association, UK), S Pinches (Max-Planck IPP, EURATOM Association, Germany), R J La Haye (General Atomics, USA), Y Liu, A Bondeson (Chalmers University, Sweden)
It is important to determine the scaling of the stabilising
requirements for RWMs to extrapolate to ITER and beyond. The
underlying damping determining RWM stability has been probed
with applied error fields on JET; similar to the methods
used on DIII-D. Experimental results show good agreement
with modelling with the MARS code, in particular on the
amplification of the applied error field as beta increases
towards the ideal limit. Analysis of old data has also
revealed instabilities with many RWM characteristics,
possibly giving another route for cross machine comparison.
(Funded by EURATOM under EFDA)
[RP1.037] Core and Edge MHD Studies in JET Reversed B Experiments
M.F.F. Nave (CFN, IST, Portugal), S. Coda, J. Graves, R. Pitts, O. Sauter (CRPP EPFL, Switzerland), R. Buttery, C. Challis, P. Lomas, G. Matthews, M. Stamp (UKAEA, UK), R. Koslowski, C. Perez (FZ Juelich, Germany), M. Marascheck, S. Pinches, W. Suttrop (IPP Garching, Germany), A. Loarte (EFDA ITER, CSU Garching, Germany), and JET EFDA Contributors Collaboration
JET operation with reverse B changes the NBI heating to
counter injection, while the normal field has co-NBI. One
consequence is to change NBI induced rotation and its effect
upon MHD has been studied. Shorter sawtooth periods were
obtained with counter-NBI. With co-NBI, the sawtooth period
increased with power, while with counter-NBI, the sawtooth
period reduced to a minimum at 4 MW. A candidate mechanism
consistent with the salient features of this trend is the
dependence of kinetic internal kink stabilization on sheared
toroidal rotation and central energetic ion penetration in
reverse B plasmas. ELMs and Washboard modes in high density
ELMy H-mode plasmas, as well as edge MHD modes in the
quiescent H-mode (QHM) regime were studied. Although the QHM
was not obtained, an edge continuous n=1 mode (with several
harmonics) was observed during ELM-free phases. The edge MHD
features were similar to the "edge harmonic oscillation" of
DIII-D and also similar to earlier JET counter-NBI
experiments where the n=1 external kink (outer mode) was
found to be more unstable than with co-NBI.
[RP1.038] Size Scaling on Carbon Screening by a Tokamak Divertor
J.D. Strachan (PPPL, Princeton University, USA), G. Corrigan (UKAEA, Culham, UK), A. Kallenbach (IPP, Garching, Germany), G.F. Matthews, J. Spence (UKAEA, Culham, UK), and JET EFDA Contributors Collaboration
Plasma impurity content depends upon impurity sources,
fuelling efficiency, and confinement. In JET, carbon is the
primary impurity, and its fuelling efficiency has been
studied using methane gas injection. In this poster, EDGE2D
modelling of the JET experiments and similar AUG experiments
are extended to ITER. For carbon injected at the mid-plane,
screening depends upon: the SOL temperature, the carbon
ionisation depth, the thermal force near the divertor
entrance, the parallel distance to the divertor, and the SOL
flux expansion. For carbon injected at the strike points,
the carbon screening depends upon the carbon ionised in the
region where the thermal force is strong. In JET, carbon,
originating inside the divertor, had typically 5% chance of
reaching the main chamber SOL, but from the main chamber SOL
had about 10% chance of contaminating the core plasma. By
contrast, carbon originating in the main chamber, was
typically 95% ionised inside the main chamber SOL but had
only 4 to 10% chance of contaminating the core. Since the
ITER SOL will be hotter, and the ITER divertor will be
larger than JET, the calculated carbon screening is much
better.
[RP1.039] Testing of the JET ITER-Like ICRH Antenna High Power Prototype
F.W. BAITY, R.H. GOULDING, G.H. JONES, B.E. NELSON, D.A. RASMUSSEN, P.M. RYAN, D.O. SPARKS (Oak Ridge National Laboratory), J.C. HOSEA, G.D. LOESSER, J.R. WILSON (PPPL), F. DURODIE, P.U. LAMALLE (ERM/KMS Brussels), I. MONAKHOV, R. WALTON, EFDA-JET workprogramme contributors Collaboration (EFDA-JET/UKAEA)
A High Power Prototype (HPP) of the JET ITER-like ion
cyclotron resonance heating (ICRH) antenna has been
constructed and tested in a joint collaboration between Oak
Ridge National Laboratory, Princeton Plasma Physics
Laboratory, and EFDA-JET/UKAEA. The HPP consists of one
quadrant of the full JET-EP ICRH antenna. Internal matching
capacitors are utilized in a circuit that maintains a
voltage standing wave ratio at the input < 1.5 over a factor
of ten range in resistive loading. The HPP is being tested
in vacuum at full capacitor design voltage and current for
up to 10-s pulses. The HPP design and status of the test
results will be reviewed. Measurements of the currents,
voltages, input impedance, and temperatures will be
discussed including low power measurements of the tuning
range and sensitivity to capacitor position. Measurements
will be compared to circuit analysis and modeling codes. The
impact of HPP results on the design of the final JET
ITER-like ICRH antenna will be discussed.
[RP1.040] Simulations and Stability Analysis of JET H-mode Triangularity and Power Scans
T. Onjun, A. H. Kritz, G. Bateman (Lehigh University, Bethlehem, PA, USA), V. Parail, H. Wilson (Euratom/UKAEA, Culham Science Centre, Abingdon, UK), J. Lönnroth (EURATOM-Tekes, Helsinki U. of Tech., Finland), G. Huysmans (Euratom-CEA, Cadarache, France), A. Dnestrovskij (Kurchatov Institute, Moscow, Russia)
Four JET H-mode discharges in a triangularity scan and three
JET H-mode discharges in a power scan are simulated using
the JETTO code. The simulation results are analyzed using
the HELENA and MISHKA stability codes. In the JETTO
simulations, periodic ELM crashes are triggered either by a
pressure-driven mode or by a current-driven mode. For the
triangularity scan, the variation of the pedestal height,
which is caused by the variation in MHD stability of
finite-n ballooning/peeling modes with triangularity, is
consistent with experiment. For the power scan, it is found
that ELMs are triggered mainly by current-driven modes,
where a significant part of the edge current is the
bootstrap current that is driven by the edge pressure
gradient. As a result of inductive effects between ELM
crashes, higher-pressure gradients are achieved in the
pedestal, as the heating power is increased, consistent with
experiment.
[RP1.041] Ignitor, Fire, and ITER
[RP1.042] The Ignitor Experiment: Fusion Burning Phase, Isotopic Control and Optimal Injected Heating
A. Airoldi (CNR, Italy), G. Cenacchi (ENEA, Italy), B. Coppi (M.I.T.)
Ignitor^1 has been the first experiment proposed and designed to reach ignition conditions, and remains unique in preserving this goal. At ignition where plasma heating due to the fusion reaction products compensates for all forms of energy loss, the thermonuclear instability sets in and an appropriate set of two nonlinear equations that include the tendency of the plasma temperature to explode^2 and the quenching due to pressure gradient driven modes, is introduced to describe the resulting (oscillatory) burning phase. Quasi-stationary subignited regimes are identified using the JETTO transport code by controlling the isotopic composition of the plasma and applying appropriate pulses of ICRH heating to the plasma column. When the DT mixture is optimal (50-50), the ICRH power needed to shorten significantly the approach to ignition can be as low as 3MW if applied at the time when the ideal ignition condition is reached.
^1B. Coppi et al., Nucl. Fusion 41, 1253 (2001)
^2A.C. Coppi and B. Coppi, Phys. Plasmas 6, 1470 (1999)
[RP1.043] Optimal Temporal Evolution of the Magnet Currents of the Ignitor Machine
A. Coletti, R. Coletti, M. Ramogida, M. Roccella, M. Santinelli (ENEA, Italy)
The Ignitor Magnet System is comprised of 24 Toroidal Field
Coils (TFC) and 12+2 pairs of Poloidal Field Coils (PFC),
including the Central Solenoid and the EM Press. Currents in
the TFC and each of the PFC are regulated by dedicated
thyristor converter units. Starting from a first possible
scenario for the magnet currents and voltages evolution, an
iterative optimization process of the total installed
electrical power has been performed, by taking into account
several elements: smoothing of the current evolution,
reduction of the voltage step variations by switching on
proper resistors, modifying the coil turns and the coil
current consequently, connecting in series coils with
similar current behaviour, eliminating coils if poorly
effective on the plasma, using converter schemes (sequential
control or internal feedback control) suitable to reduce the
reactive power requirements and ac current harmonics. In
this way the total installed power in the Ignitor Power
Supply System is about 2200 MVA instead of about 3400 MVA
calculated before the optimization process. In addition the
power requirements (max active power, max reactive power,
max active power negative/positive steps) result compatible
to the 400 kV Grid operational requirements.
[RP1.044] Load Assembly of the Ignitor Machine with 3D Interactive Virtual Reality
S. Migliori, S. Pierattini (ENEA - ITC Dept), ENEA Advanced Visualization Technology Team
The main purpose of this work is to assist the Ignitor team
in every phase of the project using the new Virtual Reality
Technology (VR). Through the VR it is possible to see, plan
and test the machine assembly sequence and the total layout.
We are also planning to simulate in VR the remote handling
systems. The complexity of the system requires a large and
powerful graphical device. The ENEA?s "Advanced
Visualization Technology" team has implemented a repository
file data structure integrated with the CATIA drawing cams
from the designer of Ignitor. The 3D virtual mockup software
is used to view and analyze all objects that compose the
mockup and also to analyze the correct assembly sequences.
The ENEA?s 3D immersive system and software are fully
integrated in the ENEA?s supercomputing GRID infrastructure.
At any time all members of the Ignitor Project can view the
status of the mockup in 3D (draft and/or final objects)
through the net. During the conference examples of the
assembly sequence and load assembly structure will be
presented.
[RP1.045] The Fast Pellet Injector Program for Ignitor
A. Frattolillo, S. Migliori, F. Bombarda (ENEA, Italy), S.L. Milora, L.R. Baylor, S.K. Combs (Oak Ridge National Laboratory)
The characteristics of a fast pellet injector for the
Ignitor ignition experiment have been identified. In order
to produce sufficiently peaked density profiles during the
initial phase of the current ramp and to sustain them along
the flat top phase, a multiple injector capable of shooting
pellets of variable sizes will be developed. The program
involves the collaboration of the ENEA Laboratory at
Frascati and the Fusion Technology Group of Oak Ridge. The
initial activities will be devoted to the development of a 4
barrel, double stage gun able to reach speeds up to 4 km/s.
The compact size of the Ignitor machine makes injection from
the high field side unpractical, while it is unclear that a
vertical injection close to the magnetic axis will be
beneficial. Simulations performed with the PELLET
code(W.A. Houlberg, et al., Nuclear Fusion)
28, 595 (1988), on the other hand, indicate that
pellet speeds of 3-4 km/s would allow a sufficient particle
penetration from the low field side, particularly during the
initial current ramp up phase, when the plasma temperature
is still relatively low and good control of the density
profile is most desirable.
[RP1.046] Disruption Scenarios and their Effects on the Ignitor First Wall
F. Bombarda, G. Ramogida, M. Roccella (ENEA - UTS Fusione), F. Lucca, A. Marin, G.L. Zanotelli (LTcalcoli sas, Merate, Italy)
The 2D simulation of the reference plasma disruption in
Ignitor (a fast current quench following a Vertical
Displacement Event - VDE), has been performed using the
MAXFEA code. The resulting excitation loads have been used
in a detailed 3D model to evaluate the electromagnetic loads
in the first wall and its supports. The model of the most
loaded region of the first wall has been performed using a
zooming procedure that allows the replacement of the
out-of-model plasma, poloidal coils and passive structures
with current filaments surrounding the modeled region. To
identify the most stressed tiles under the effect of the
electromagnetic loads due to the VDE, a preliminary
structural analysis has been carried out using a simplified
model. Then a more detailed model has been performed for
these tiles, with the aim of evaluating the stress on the
screw and the pre-load needed to avoid detachment between
the tile and the tile-carrier. The thermal loads on the
tiles are evaluated independently and the implications of
possible other disruption scenarios are discussed.
[RP1.047] First Wall of the Ignitor Machine
Antonio Cucchiaro (ENEA, Italy), Bruno Coppi (M.I.T.)
The design of the first wall of the Ignitor machine^2 involves a system of Molybdenum tiles that constitute a “continuous limiter” surrounding nearly all of the plasma column. Sets of tiles are connected to tile carrying plates that can be replaced by an appropriate remote handling system. The adopted solutions for the attachment of each tile to the tile carrier and of the tile carrier to the plasma chamber on the inboard side and to the appropriate supporting structure on the outboard side are described. The relevant structural analysis is presented.
^2B. Coppi et al., Nucl. Fusion 41, 1253 (2001)
[RP1.048] Advanced Design and Construction of Toroidal Magnet Plates
G. Celentano, A. Capriccioli, A. Cucchiaro, A. Pizzuto (ENEA, Italy)
The main elements of the toroidal magnet Ignitor^2 are normal conducting plates each carrying up to 357.5 kA. According to the machine design these plates are to be cooled at 30 K that is the optimal temperature for the material that has been chosen (Copper OFHC) Given the properties of this material a new solution for the cooling of each plate has been adopted. The construction of two prototypical full size plates is underway taking into account the experience gained in the previous construction of 10 plates that were assembled into a full toroidal field coil. The toroidal magnet of Ignitor is made of 24 coils.
^2B.Coppi, A.Airoldi, F.Bombarda et al., Nucl. Fusion
41,1253 (2001).
[RP1.049] Advances in the Structural Design of the ICRH Antenna for the Ignitor Experiment
Muzio Gola, Teresa Berruti (Politecnico of Turin), Matteo Salvetti (M.I.T.)
The Faraday shield (FS) and the strap array are the
in-vessel elements of Ignitor’s ICRH antennas. Detailed
non-linear and 3-D finite element analyses were performed to
analyze their thermal and structural behavior. Dynamic
disruption loads are superposed to quasi-static thermal
loads relying on the different time scale of the two
phenomena. Disruption loads on the FS are computed by using
an inductive-resistive lumped parameter circuit and those on
the straps by using a resistive circuit. Disruption loads on
the Faraday shield bars are minimized by electrically
insulating one side of the bars. The effects of induced eddy
currents on the straps are taken into account. Moreover, the
latest simulations model the thermal loads over the straps
taking into account the presence of the FS. The mechanical
design of each component is optimized in order to facilitate
the full remote handling installation, to minimize the
stresses induced during plasma pulses and to guarantee a
high degree of reliability. Finite element analyses show
that the FS and the straps will be able to withstand the
expected loads.
[RP1.050] Analysis of the Connection of Ignitor to the Rondissone Node of the European Electrical Grid
M. Sforna (GRTN, Grid Department, Rome, Italy), B. Coppi, M.F. Salvetti (M.I.T.)
The basic requirements for the power supply of the Ignitor
machine and the effects of its connection to the electric
node of Rondissone, in the North-West of Italy, are
described. This study identifies the possible technical
restrictions associated with a flexible and meaningful
operation of the Ignitor experiment. The study was carried
out by GRTN, the Italian Independent power System Operator
(ISO), taking into account two typical extreme conditions of
the grid, at the highest (winter) load and at the lowest
(summer) load. The worst scenario generates peak power
consumption of about 1095 MW and 860 Mvar, as well as a peak
power delivery of 428 MW. Results show that when the Ignitor
machine operates at its normal conditions it doesn’t
generate disturbances on the system frequency that exceed
the allowable range +/- 0.2% (50%) prescribed by the GRTN
grid code. The generated voltage interferences at the
substation of Rondissone are acceptable. Local systems of
reactive power compensation (SVC) are envisaged to minimize
voltage disturbances.
[RP1.051] Design Criteria for the Columbus Experiment
M.F. Salvetti, B. Coppi (M.I.T.)
In principle, it is possible to scale up the parameters of Ignitor, the only experiment proposed and designed to reach ignition, but within a narrow range preserving the ability to maintain this goal with reasonable margins against the onset of macroscopic instabilities, given the high plasma pressures required. A strong ohmic heating is to be maintained so that ignition can be reached even in the case of a failure of the ICRH system. The Columbus experiment^2 is proposed as a parallel US project to the Ignitor program carried out in Italy and is geometrically self similar to this, the dimensions being increased by 25/22 (R_o=1.50 m) and the volume by about 50%. The most important parameter design guideline is the value of the mean poloidal field (\sim3.4T ). The plasma current I_p\sim12.2MA is close to that of the ITER-Feat concept for the same value of the safety factor q_95(\Psi)\sim3.6. As in the case of Ignitor and ITER-Feat, the plasma current redistribution time and the duration time of the plasma burning state are comparable. Columbus incorporates all the technological solutions developed for Ignitor.
^2B. Coppi and M.F. Salvetti, MIT (RLE) Report PTP 02/06
(December 2002, Cambridge, MA)
[RP1.052] Preliminary Thermal Analysis of the Toroidal Field Coils in the Columbus Machine
Sebastien Febvay, Matteo Salvetti (M.I.T.)
The Columbus experiment^1 is geometrically self similar to Ignitor, the linear dimensions being increased, roughly, by the factor 25/22 (R_o=1.50 m) and the volume by about 50%. Characterized by decreased current densities in the toroidal and poloidal magnet systems, Columbus allows for longer plasma pulses relative to Ignitor. We identified a reference current pulse in the toroidal magnet that has a flattop extended to about 7.6s (disregarding the contribution of high energy neutrons). The Toroidal Field System is made of 24 OFHC copper coils. Similarly to Ignitor, the highest current flowing in each of the coil plates is 357.3 kA (the total magnet current being I_M=94.38 MA-turn), and the acceptable temperature in the magnet ranges from 30 K to about 240 K. We carried out coupled electromagnetic and thermal 3-D finite element analyses to determine the temperature distribution within the magnet and we compared our results to those obtained by using the 2-D FORTE code. The magneto resistive effect is presently being included in our model.
^1 B.Coppi and M.F.Salvetti, MIT (RLE) Report PTP 02/06
(December 2002, Cambridge, MA).
[RP1.053] Continuity of Confinement Regimes in High Field Experiments
G. Cenacchi, F. Bombarda (ENEA, Italy), B. Coppi (M.I.T.), A. Airoldi (CNR, Italy)
High magnetic field experiments have shown consistently that under ohmic heating conditions, the energy confinement time tends to increase with density as long as its profile is significantly peaked. This peaking can occur spontaneously as for the Alcator A and FT experiments or be produced by injection of pellets as for the Alcator C and FTU experiments. When the profile is not peaked, the confinement time saturates as the density is increased above a value which is an increasing function of the plasma current. The values of the saturated confinement time correspond to those of the so called L-regime. Pellet injection to prevent saturation in the Alcator C experiments was suggested on the basis that Ion Temperature Gradient driven modes were responsible for most of the observed energy transport and were preventable by peaked density profile. Recent experiments by the FTU machine^2 are shown to be consistent with those performed by Alcator C originally.
^2A. Frigione et al., paper EX/P4-02, 19th Fus. Energy
Conference (Lyon) 2002, publ. IAEA-CN-94.
[RP1.054] Issues for Burning Plasma Experiments and Fusion Ramp;D Metrics
Dale Meade (Princeton Plasma Physics Laboratory), FIRE Design Team
Attractive magnetic fusion based on the tokamak will require
significant progress in: plasma confinement for
self-heating, MHD stability for high plasma pressure,
self-generation of the confining magnetic field, and high
power density exhaust through the plasma edge. A burning
plasma experiment faces the challenge of first being able to
access burning plasma conditions, and to then extend
dimensional and normalized plasma parameters toward the
fusion plasma regimes described in the ARIES studies. The
ARIES plasma regimes also require the plasma to evolve to a
largely self-organized plasma state that will present a
grand challenge for magnetic fusion science. ITER, an
international collaboration on a reactor-scale facility to
demonstrate the scientific and technological feasibility of
fusion, and FIRE, a national design study of a next step
experiment to explore and optimize burning plasmas, are
being pursued to address the issues described above. The
dimensionless (e.g., H, beta, f_bs, Q, etc.) and normalized
(e.g., fusion power density, P_loss/R, etc. ) metrics for
fusion Ramp;D that can be accessed on ITER and FIRE will be
described. Additional information is available at
http://fire.pppl.gov. Work supported by DOE Contract #
DE-AC02-76CH0 3073.
[RP1.055] Beryllium/Tungsten Mixed Material Analysis of FIRE Plasma Facing Components Including Convective Transport
D.A. Alman, D.N. Ruzic (Plasma-Material Interaction Group, University of Illinois at Urbana-Champaign)
Extensive computer modeling for the Fusion Ignition Research
Experiment (FIRE) design study focused on Be/W
mixed-material erosion issues, combining several computer
codes. Since the FIRE design calls for a beryllium first
wall and tungsten divertor, Be can be sputtered and
transported to the divertor, forming a Be/W mixture. The
goal is to determine the amount of Be deposited on divertor
surfaces and to model the mixture's erosion/redeposition
properties. Sputtering is calculated from deuterium neutral
fluxes (obtained from DEGAS2) and D^+ flux from the
plasma. The ion flux includes both the diffusive flux from
the UEDGE fluid code and approximations of convective
(non-diffusive) transport. The sputtering of Be is
determined by VFTRIM-3D. WBC+, part of Argonne's REDEP
impurity transport package, calculates the transport of Be
to the divertor. Results show that convective transport
dominates, increasing Be sputtering to 8x10^21 s^-1,
with 4x10^21 s^-1 reaching the divertor plates. The
next step is analysis of the erosion properties of the Be/W
mixed material with the ITMC code at ANL.
[RP1.056] RWM Feedback Control in ITER
G. A. Navratil, J. Bialek, A. H. Boozer, O. Katsuro-Hopkins (Columbia University)
Achieving the advanced tokamak plasmas in ITER that are
necessary to realize long-pulse/steady-state burning plasma
goals depend critically on the control of the resistive wall
mode (RWM) at and above the no-wall beta limit. We have
carried out a broad study with the VALEN code in both
eigenvalue and time-dependent analysis of RWM feeedback
control using the base ITER design error field correction
coils and find this system quite limited in performance,
reaching only 203D analysis of the passive stabilization properties of the
double wall ITER vacuum vessel and internal blanket modules,
show substantial improvements in RWM ideal wall
stabilization limits from the effect of the blanket modules.
VALEN modeling shows this improved ideal limit can be
achieved with active feedback control using only six
internal coils (arranged as three n=1 pairs) with dramatic
reductions in the stabilization power requirements.
[RP1.057] Calculation of beam ion distributions in ITER and their impact on alpha-particle measurements by collective Thomson scattering
J. Egedal (Plasma Science Fusion Center, Massachusetts Institute of Technology), H. Bindslev (RisøNational Laboratory, Denmark), P. Woskov (Plasma Science Fusion Center, Massachusetts Institute of Technology)
Collective Thomson Scattering (CTS) has been proposed as a
viable diagnostic for characterizing fusion born
alpha-distributions in ITER. However, the velocities of the
1MeV proton heating beam ions in ITER are similar to that of
fusion born alpha particles and may therefore mask the
measurements of the fusion products. To estimate the impact
that beam ions may have on the CTS measurements, a fast
general code is being developed for calculation of beam ion
phase-space distributions in Tokamaks. For the present ITER
beam injection design and magnetic geometry the code first
calculates the beam deposition profile in constant of motion
(COM) space. The slowing down process is then modeled taking
into account the spatially non-uniform drag by the electrons
and pitch angle diffusion by the ions. Our investigations
show that there are CTS scattering orientations where the
alpha particles will not be significantly masked by the
presence of the beam ions.
[RP1.058] Results from the US-EU Collaboration on mixed-material PMI effects for ITER
R. P. Doerner, M. J. Baldwin (Center for Energy Research, University of California – San Diego), K. Schmid (Max-Plank Institute for Plasmaphysics, Garching, Germany)
A beryllium-seeded deuterium plasma is used to conduct experiments in PISCES-B to investigate mixed-material erosion and redeposition properties of materials relevant for next step burning plasma devices. The experiments are designed to reduce uncertainties in the prediction of tritium retention in redeposited mixed-materials. A small (0.15plasma onto a carbon target is seen to have a dramatic impact on the carbon chemical and physical erosion rates. The surfaces resulting from the bombardment of graphite with D+Be plasma are measured to contain a large fraction of beryllium coverage on the surface, a result that can be explained by redeposition of eroded material. The implications of these experiments for ITER will be discussed.
Work performed as part of a USDOE-EFDA Bilateral
Collaboration and supported under DOE contract
DE-FG03-95ER-54301.
[RP1.059] High Power Microwaves
[RP1.060] Heating of Thin Films on High Power Microwave Windows
Herman Bosman, Y. Y. Lau, R. M. Gilgenbach (University of Michigan, Ann Arbor, MI)
Thin film coatings of conductive materials with low
secondary electron emission (SEE) yields, such as Ti, TiN or
Cr_2O_3, are deposited on the windows to prevent the
occurrence of multipactor. Contaminants may also
inadvertently contribute to patches of conducting thin films
on the millimeter wave diamond windows. The ohmic losses in
these films can be severe, and may cause unexpected window
failures. This paper provides a quantitative analysis of the
power absorbed by such films, and the accompanied
temperature rise. It is found that up to 50% of the
incident power may be absorbed in the protective films of
nanometer thickness [1]. We will also report our analysis of
some recent measurements on the effects of contaminants on
diamond windows [2,3]. [1] H. Bosman, Y. Y. Lau, and R. M.
Gilgenbach, \textitAppl. Phys. Lett. \textbf82, 1353
(2003). [2] H. Jory, private communication (2003). [3] R.
Heidinger, G. Dammertz, A. Meier, and M. K. Thumm,
\textitIEEE Trans. Plasma Sci. \textbf30, 800 (2002).
[RP1.061] Development of 1 to 1.5 MW CW Gyrotrons
K. Felch, M. Blank, P. Borchard, P. Cahalan, S. Cauffman, S. Chu, H. Jory (CPI)
High power mm-wave sources provide electron cyclotron
heating, current drive, and instability suppression in
fusion plasmas. CPI has delivered three 110 GHz, 1 MW
gyrotrons for ECH and ECCD experiments on DIII-D, each of
which has demonstrated reliable operation at 1 MW for pulse
lengths up to 5 seconds. CPI has also delivered a 140 GHz, 1
MW gyrotron to IPP for use on W-7X. This gyrotron has
produced a peak output power of 900 kW, and pulse lengths up
to 700 seconds at 500 kW. Ten consecutive 500 kW 600 second
pulses were demonstrated without fault at 25CPI's test facilities could not support long pulse operation
at full power, such operation is planned at IPP. The 140 GHz
system employs a diode magnetron injection gun, a
TE_28,7 cavity interaction mode, an internal mode
converter to produce a Gaussian output beam, a low-loss CVD
diamond output window, and a single-stage depressed-voltage
beam collector to enhance the overall electrical efficiency
of the device. Currently, under a DOE development program,
CPI is fabricating a 110 GHz, 1.3-1.5 MW CW
depressed-collector gyrotron to deliver improved reliability
at power levels above 1 MW.
[RP1.062] Electron-cyclotron Heating on TCV with 118 GHz Gyrotrons
L. Porte, S. Alberti, G. Arnoux, T.P. Goodman, M.A. Henderson, J.P. Hogge, Y. Martin, E. Nelson-Melby (CRPP-EPFL, 1015 Lausanne, Switzerland)
Three 118GHz, 0.5MW, 2 sec. gyrotrons have been installed on
TCV for the purpose of electron cyclotron heating at the
third harmonic in the X-mode (X3). The radiation is
vertically launched. In this way, the absorption is
maximized because the electromagnetic beam traverses the
length of the cyclotron resonance; a curve nearly following
a vertical line in the poloidal plane. The plasma facing
mirror can be steered, during a pulse, in the poloidal plane
and can be shifted, radially, between pulses. This allows
one to control the absorption in real time during a pulse.
The resonance is very narrow and coupling of the beam to the
resonant electrons can be lost due to refraction and/or
plasma movement. As a result it is necessary to use real
time control of the launcher mirror to maintain absorption.
The real time control system will be described and results
from its useage will be described. The vertical launch
allows the X3 system to be used as a ‘probe’ of fast
electrons. By moving the radial position of the launcher
from shot to identical shot it is possible to selectively
heat non-thermal electrons at energies commensurate with the
shift toward the high field side from the cold resonance.
Experiments studying this possibility will be described.
Using X3 allows access to densities above the cut-off for
second harmonic ECRH. In particular X3 gives access to core
heated H-mode plasmas in TCV. Results from attempts to heat
H-mode using X3 will be presented and in particular, the
effect of X3 heating on ELMs will be presented.
[RP1.063] An explosive emission cathode in a thermionic cathode environment
Charles Schlise, Ryan Umstattd (Physics Department, Naval Postgraduate School, Monterey, CA 93943)
Present-day high power microwave devices suffer from a lack
of reliable, reproducible cathodes for generating the
requisite GW-level electron beam in a vacuum. Standard
explosive emission cathodes have been limited to 10’s or
100’s of ns due to the expansion of cathode-generated plasma
and the ensuing impedance collapse that debilitates
microwave output. Traditional thermionic cathodes do not
suffer from this drawback of plasma generation, but have not
yet been demonstrated to provide the required emission
current densities. It is expected that if the plasma could
be made cooler and less dense, explosive emission would be
more stable. Cesium iodide (CsI) has been found to slow the
impedance collapse in many explosive emission cathodes.
Herein we will examine diode impedance collapse, gas
production, and cathode conditioning in an effort to perform
an evaluation of explosive cathode performance in a typical
thermionic electron gun environment. These results will then
be used to help demarcate the parameter space over which
these CsI-coated carbon fiber cathodes are viable candidates
for the electron beam source in next-generation high power
microwave devices.
[RP1.064] Secondary Electron Yield Measurements
N. Zameroski, T. Svimonishvil, M. Gilmore, E. Schamiloglu, J. Gaudet, M.O. Manasreh (University of New Mexico)
One of the major problems affecting the efficiency of high power microwave devices is that of secodary electron emission. It is a well-known fact that efficiency can be greatly improved by using depressed collectors comprised of low yield materials. This experimental research benchmarks existing material yield curves and classifies yields of new material for use in depressed collectors. Secondary Electron Yield is defined as \delta=I_s/I_p where I_s is the secondary electron current and I_p is the primary electron current. Since I_p = I_s+I_target yield can be obtained from delta=1-I_target/I_beam. Beam current is measured using a Faraday Cup connected to pico amp meter and target current is measured directly by pico amp meter. Beam spot size is kept minimal at 1-2mm. Results show that the secondary electron yield curve is dependent upon the incidence angle of the primary electrons.
* Work supported by a grant from AFOSR
[RP1.065] Cloud Turbulence Correlation Functions and Power Spectra Measured using a Gyroklystron-Powered 94 GHz Radar
Arne Fliflet, Wallace Manheimer, George Linde, Winjoy Cheung, Mai Ngo, Vilhelm Gregershansen, Bruce Danly, Karen St. Germain (Naval Research Laboratory, Washington, DC 20375)
The Naval Research Laboratory (NRL) has recently developed a
high power 94 GHz radar called WARLOC. This radar has unique
advantages for cloud research stemming from the fact that
the return from clouds scales inversely as the fourth power
of the wavelength. Clouds are largely invisible to
conventional radars and opaque to lidars, whereas
millimeter-wave radars produce strong signals from cloud
water droplets. Thus W-Band radars can be used to sense the
internal structure of clouds. The WARLOC transmitter has
about three orders-of-magnitude more average power than the
W-Band radars used in previous cloud studies and greatly
improved resolution and scanning capability. Here we report
initial results on cloud studies. The new capabilities of
WARLOC have allowed us to produce high-resolution images of
the internal structure of clouds. Regions many square
kilometers in area can be scanned with 15 m resolution in
about a minute even through intervening cloud layers. The
scanned cloud reflectivity yields two-dimensional cloud
turbulence correlation functions and power spectra directly
from spatial measurements for the first time, and with
higher resolution than previously possible. We find that in
the inertial range, the Kolmogorov spectral index (-5/3)
agrees reasonably well with the data, but the assumption of
isotropy does not. Interestingly, in two clouds studied, at
longer scale lengths, the fluctuations appear to be wavelike
in the vertical direction, but not in the horizontal
direction.
[RP1.066] Microwave Noise Reduction Experiments in kW Magnetrons
V.B. Neculaes, R.M. Gilgenbach, Y.Y. Lau, M.C. Jones, W.M. White (Intense Energy Beam Interaction Laboratory University of Michigan, Ann Arbor, MI 48109)
Nonrelativistic magnetron (4 kV, 300 mA, 2.45 GHz, kW
microwave power) experiments are performed on commercial
oven magnetrons for an in-depth investigation of
crossed-field injection-locking and noise. Injection-locking
is demonstrated by utilizing an oven magnetron as a
reflection amplifier. Microwave noise generation is explored
as a function of injected signal and cathode conditions. Our
experiments confirm that the microwave noise can be reduced
when the cathode heater power is decreased. We also
investigate the influence of reducing the cathode heater
power on the microwave output power and magnetron
efficiency. Noise reduction is also observed when a weak,
low noise microwave signal is injected into the reflection
amplifier. Experimental and simulation results will be
reported for innovative, new techniques for reduction of
microwave noise in magnetrons.
[RP1.067] Analysis of Mode Growth in Relativistic Magnetrons with Extractor Loading
Keith Cartwright (Air Force Research Laboratory), John Luginsland (Science Applications International Corporation), Laurence Merkle (Rose-Hulman Institute of Technology, Department of Computer Science and Software Engineering), Michael Haworth, Peter Mardahl (Air Force Research Laboratory), Jack Watrous (NumerEx), Tony Murphy (Air Force Research Laboratory), Air Force Research Laboratory Collaboration, Science Applications International Corporation Collaboration, NumerEx Collaboration
Relativistic magnetrons are a promising source of high power
microwaves, combining high power and repetition rate with
the potential for high efficiency. Although they have been
actively investigated for over three decades, much of the
theoretical work has focused on the performance of the
source itself, typically without the complication of power
extraction schemes. Experimentally, however, it has been
observed that the loading of cavities due to extraction can
greatly increase the potential for mode competition, as well
as complicate the resonant structure of the device. In this
work, we develop a circuit model for a relativistic,
cylindrical, N-cavity magnetron with M extractors. In order
to predict the growth rates of the modes the beam is
prescribed as either a cycloidal electron flow or Brillouin
electron flow. The impact of these two models for the
electron dynamics with be compared and contrasted. Detailed
analysis of the hot tube, small signal, growth rates for the
magnetron modes will be examined with both a simple analytic
space charge model and a semi-empirical model found from 3-D
particle-in-cell simulation. Implications on extractor
design, mode competition, and optimization of the
relativistic magnetron will be discussed.
[RP1.068] Initiation of a Relativistic Magnetron
D.J. Kaup (University of Central Florida)
We report on recent results in our studies of relativistic magnetrons. Experimentally, these devices have proven to be very difficult to operate, typically cutting off too quickly after they are initialized, and therefore not delivering the power levels expected [1]. Our analysis is based on our model of a crossed-field device, consisting only of its two dominant modes, a DC background and an RF oscillating mode [2]. This approach has produced generally quantitatively correct values for the operating regime and major features of nonrelativistic devices. We have performed a fully electromagnetic, relativistic analysis of a magnetron of the A6 cylindrical configuration. We will show that when the device should generate maximum power, it enters a regime where the DC background could become potentially unstable. In particular, when a nonrelativistic planar device enters the saturation regime, the DC electron density distribution could become unstable if the vertical DC velocity would ever become equal to the magnitude of the vertical RF velocity [3]. We find that during the initiation phase, for the highest power levels of our model of the A6, near the cathode, the DC vertical velocity does become just less than, and definitely on the order of the magnitude of the vertical RF velocity. Consequently, any localized surge in the currents near the cathode, could easily destroy the smooth upward flow of the electrons, drive the DC background unstable, and thereby shut down the operation of the device.
[1] Long-pulse relativistic magnetron experiments,
M.R. Lopez, R.M. Gilgenbach, Y.Y. Lau, D.W. Jordan, M.D.
Johnston, M.C. Jones, V.B. Neculaes, T.A. Spencer, J.W.
Luginsland, M.D. Haworth, R.W.Lemke, D. Price, and L.
Ludeking, Proc. of SPIE Aerosense 4720, 10-17,
(2002). [2] Theoretical modeling of crossed-field
electron vacuum devices, D.J. Kaup, Phys. of Plasmas
8, 2473-80 (2001). [3] Initiation and Stationary
Operating States in a Crossed-Field Vacuum Electron Device,
D. J. Kaup, Proc. of SPIE Aerosense 4720, 67-74,
(2002).
[RP1.069] Mode Control, RF Breakdown and Innovative Cathodes in Long-Pulse, Relativistic Magnetron Experiments
M.R. Lopez, R. M. Gilgenbach, W.M. White, M.C. Jones, Y.Y. Lau (Intense Energy Interaction Laboratory, Dept. of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109), T.A. Spencer, M.D. Haworth, K. Cartwright, P.J. Mardahl, T. Murphy (Air Force Research Laboratory, Kirtland AFB, NM), J.W. Luginsland (SAIC), D. Price (Titan Pulse Sciences, CA)
Research is underway on a 6-vane, Titan relativistic magnetron powered by MELBA-C (Ceramic insulator) at parameters: V = -0.3 MV, I = 1-10 kA, and \tau = 0.5 \mus at 10^-7 Torr. This experiment has generated peak microwave power levels of 300-500 MW near 1 GHz. Time-Frequency Analysis (TFA) indicates mode competition between pi mode and 2/3 pi mode during operation. Experiments to investigate the effect of extractor symmetry on mode competition have utilized two vs three waveguides distributed symmetrically on the magnetron structure. In agreement with AFRL simulations three-fold symmetry tends to improve pi mode operation. Ongoing research involves efforts to prime this device with a MW magnetron source. RF breakdown has been observed in a window/waveguide system filled with atmospheric pressure air. Microwave power and pulselength are both increased with SF6 fill gas. Innovative, new, high-current cathodes are being explored utilizing laser-ablation.
* Research supported by AFOSR and AFRL.
[RP1.070] Vortex Structure in a High-Density Non-Axisymmetric Crossed-Field Equilibrium Flow
John Davies (Clark University), Chiping Chen (MIT, Plasma Science and Fusion Center)
It is shown that vortex structures exist in high-density
non-axisymmetric crossed-field equilibrium flow in a
crossed-field device. With the aid of perturbation theory
and the guiding-center approximation and assuming a constant
electron particle number density in the electron layer, we
determine equipotential surfaces, electron trajectories, and
the corrugated boundary of the electron layer. As the
electron density approaches the (critical) Brillouin
density, a vortex structure with regions of negative
potential forms near the cathode surface.
[RP1.071] Compact Relativistic Magnetron with Output Mode Converter
Andrey Andreev, Mikhail Fuks, Edl Schamiloglu (Department of Electrical and Computer Engineering, University of New Mexico)
We consider a relativistic magnetron in which all of the
resonators of the anode block are smoothly continued onto a
conical antenna up to the radius corresponding to the cutoff
frequency of the radiated wave in a cylindrical waveguide.
Such a magnetron is capable of high output power, is
compact, has a high resistance to microwave breakdown, is
able to work with extremely high currents, and has the
possibility of forming desirable output radiation patterns.
The magnetic field can be provided by a small solenoid over
the resonant system, which is a much smaller volume than is
required for the Helmholtz coils used in traditional
relativistic magnetrons. The maximum size of this magnetron
is the aperture of the horn antenna. The unique aspect of
such a design is the possibility of using the horn antenna
for conversion of the operating mode to lower order modes,
including the TE_11 mode, which is radiated as a narrow
wave beam. For a magnetron operating in \pi-mode, the mode
converter comprises a continuation of the resonantor blocks
onto the horn for those resonators that correspond to the
symmetry of the output mode. For example, in order to
provide Gaussian mode output only two diametrically opposite
resonators of even-numbered resonators must be continued
onto the horn. In this case the aperture of the horn antenna
can be close to the cut-off diameter for the TE_11 mode,
and the output power is limited only by breakdown of the
output window. In this presentation results of preliminary
calculations of the magnetron with output mode converters
are presented.
[RP1.072] Laminar Electron Flow Solutions for Two-Dimensional Electrode Geometries
Ronak Bhatt, Chiping Chen, Mark Hess (Massachusetts Institute of Technology)
Numerous microwave devices (such as magnetrons and sheet
beam devices) utilize geometries which are invariant in one
dimension. In order to minimize noise and beam loss, one
seeks conditions under which two-dimensional laminar
electron flows may exist in such devices. In this work, a
non-relativistic fluid equilibrium theory for these electron
flows is developed which takes into account self-fields,
image fields from the electrodes, and externally imposed
electric and magnetic fields. Several special cases are
examined within the theory, including the Brillouin flow
limit.
[RP1.073] Three Dimensional Modeling Of Electron Guns Using MICHELLE
John Petillo, Kenneth Eppley, Dimitrios Panagos (Science Applications International Corporation), Eric Nelson (Los Alamos National Lab), Norman Dionne (Raytheon), John DeFord, Ben Held, Liya Chernyakova (Simulation Technology and Applied Research), James Burdette, Xiaoling Zhai (Boeing), Mark Cattelino (Communication and Power Industries), Khanh Nguyen (Beam-Wave Research, Inc.), Baruch Levush (Naval Research Lab)
MICHELLE, which is a new two-dimensional (2D) and
three-dimensional (3D) electrostatic equilibrium
particle-in-cell (PIC) code, has been designed to address
the recent beam optics modeling and simulation requirements
for vacuum electron devices, ion sources, and
charged-particle transport. Problem classes specifically
targeted include gridded-guns, multi-beam guns, sheet-beam
guns, and depressed collectors. The focus of the development
program is to combine modern finite-element techniques with
improved physics models. The code employs a conformal mesh,
including both structured and unstructured mesh
architectures for meshing flexibility, along with a new
method for accurate, efficient particle tracking. New
particle emission models for thermionic beam representation
are included that support primary emission, and secondary
emission is handled with an advanced model. One of the key
features of the MICHELLE code is its ability to model
fine-scale features in a large volume. This has made it
valuable for performing sensitivity studies and generating
manufacturing tolerance specifications. The MICHELLE code
has been released, and has been employed in the design and
verification of electron guns and collector designs over the
last several years. Much emphasis has been placed on
validating the code against other models and experimental
data. An open issue for validation concerns secondary
emission. MICHELLE has a new extensive secondary emission
model, however data is sparse for many beam energies and
materials of interest. The application of MICHELLE to
multi-beam guns, gridded guns, and multistage depressed
collectors will be presented, along with an update of the
MICHELLE development regarding the areas of particle
tracking, temperature-limited and space-charge-limited
emission, and secondary emission.
[RP1.074] Numerical modeling of breakdown in high-power waveguides
Scott Hendrickson, John Cary, Peter Messmer, Peter Stoltz (Tech-X Corporation)
Unwanted electron emission from metal walls influences the
operation of vacuum waveguides. If the electron density
becomes large enough, the electron plasma can reflect the
electromagnetic waves that are supposed to be transmitted.
Numerical simulations of the generation of electrons in
high-power vacuum waveguides are presented. In particular,
the parameters relevant to the high-power waveguides at the
Stanford Linear Accelerator Center (SLAC) are modeled.
Modeling is done with the VORPAL code from the University of
Colorado. Results are shown comparing experiments from SLAC
to a thermal gas desorption and ionization model.
Researchers have used this model to successfully explain
results from ion diode breakdown.
[RP1.075] Ion Beams
[RP1.076] Recent results from the High Current Experiment for Heavy Ion Inertial Fusion
Peter Seidl, David Baca, Frank M. Bieniosek, Christine M. Celata, Andy Faltens, Lionel R. Prost, Jean-Luc Vay, William L. Waldron (LBNL), Alex Friedman, Michel Kireeff Covo, Arthur W. Molvik, Steven M. Lund (LLNL), Heavy Ion Fusion Virtual National Laboratory Collaboration
The High Current Experiment (HCX) is exploring heavy-ion
beam transport in an alternating gradient quadrupole
focusing channel at a scale representative of the low-energy
end of an induction linac driver for fusion energy
production. A primary mission of this experiment is to
investigate aperture fill factors (F = diameter of maximum
beam excursion / aperture diameter) acceptable for the
transport of space-charge dominated heavy-ion beams at high
space-charge intensity (line-charge density \sim 0.2\mu C)
over long pulse durations (> 4 microsec). We present the
phase space evolution of a K+ ion beam transported (F>0.5)
through the matching section, 10 electrostatic transport
quadrupoles and 4 magnetic quadrupoles. Transverse phase
space is measured including beam halo and particle loss.
Space charge waves are also studied along with their
influence on the transverse beam evolution. New data on beam
energy and phase space projections better constrain beam
parameters and improve agreement with simulations. The
consequences for beam control and fill-factors in future
induction accelerators will be discussed.
[RP1.077] Progress in Measuring Electron Cloud Effects in HIF Accelerators
A.W. MOLVIK, R.H. COHEN, A. FRIEDMAN, M. KIREEFF COVO, S.M. LUND (LLNL amp; HIF-VNL), F.M. BIENIOSEK, E.P. LEE, L. PROST, P.A. SEIDL, J-L. VAY (LBNL amp; HIF-VNL), M.A. FURMAN (LBNL)
Accelerators for heavy-ion inertial fusion energy (HIF) have
an economic incentive to fit beam tubes tightly to beams,
putting them at risk from electron clouds produced by
secondary electrons, and ionization of gas from walls (a
problem in accelerators for high-energy physics). We are
using two complementary approaches with the High-Current
Experiment (HCX): (1) Measure the electron emission and gas
desorption coefficients from 1 MeV K^+ ions incident on a
target, at angles near grazing incidence, to understand the
processes and develop mitigation techniques. (2)
Characterize electron production, accumulation, and the
effects on ion beams in quadrupole magnets where we are
commissioning a variety of charged particle diagnostics to
measure net charge, gas density, and secondary electron
production. These data will be compared with predictions of
theory and simulations.
[RP1.078] Recent developments in diagnostics for Heavy Ion Fusion experiments
F.M. BIENIOSEK, A. FALTENS, W.B. GHIORSO, J.W. KWAN, L. PROST, P.K. ROY, P.A. SEIDL (Lawrence Berkeley Laboratory and HIF-VNL), A. FRIEDMAN, A.W. MOLVIK, G. WESTENSKOW (Lawrence Livermore National Laboratory and HIF-VNL), S. CHAWLA (UC-Berkeley)
We discuss progress in diagnostic development for the Heavy
Ion Fusion program in the HIF-VNL at LBNL and LLNL. Typical
HIF beams are high current (up to 1 A), and the energy range
is 60 keV to 2.0 MeV, increasing up to 10 MeV in the near
future. Beam parameters of interest include current, density
distribution, energy, energy distribution, emittance, and
space potential, in injector, transport, and final focus
sections. Optical diagnostics based on a scintillator screen
and a gated intensified CCD camera have been implemented and
provide full 4-D transverse information on the experimental
beams. Current work includes development of a compact
optical diagnostic and improved algorithms for data analysis
and interpretation. A longitudinal diagnostic kicker has
been implemented for generating longitudinal space-charge
waves. Comparison of the waves with a simple 1-D fluid model
of the beam will be presented. Time of flight of the space
charge wave and an electrostatic energy analyzer provide an
absolute measure of the beam energy. These and other new
diagnostics will be described.
[RP1.079] Progress in Modeling Electron Cloud Effects in HIF Accelerators
R.H. Cohen, A. Friedman, A.W. Molvik (LLNL amp; HIF-VNL), A. Azevedo, J.-L. Vay (LBNL amp; HIF-VNL), M.A. Furman (LBNL), P.H. Stoltz (TechX)
Stray electrons can arise in positive-charge accelerators
for heavy ion fusion (or other applications) from ionization
of gas (ambient or released from walls), or via secondary
emission. Their accumulation is affected by the beam
potential and duration, and the accelerating and confining
fields. We present electron orbit simulations which show the
resultant e-cloud distribution; ion simulations with
prescribed e-clouds which show the effect on ion beam
quality; a gyro-averaged model for including electron
dynamics in ion simulations, and its implementation status;
and progress in merging the capabilities of WARP (3-D PIC
code for HIF) (D.P. Grote, A. Friedman, I. Haber,
Proc. 1996 Comp. Accel. Physics Conf., AIP Proc. 391),
51 (1996), with those of POSINST (e-clouds in high-energy
accelerators) (M.A. Furman, LBNL-41482/CBP Note
247/LHC Project Report 180, May 20, 1998).
[RP1.080] The CMEE Library for Numerical Modeling of Electron Effects
Peter Stoltz (Tech-X Corporation), Ron Cohen, Art Molvik (LLNL), Miguel Furman, Jean-Luc Vay (LBNL), Andreas Adelmann (Paul Scherrer Institut)
The CMEE (Computational Modules for Electron Effects)
library is a collection of computer routines for numerical
modeling of electron effects in accelerator and plasma
physics codes. The goal of this library is to make these
numerical models available to any code in need of electron
effects modeling, including high-power microwave codes,
fusion wall interaction codes, laser-plasma codes, proton
accelerator codes, and HIF codes. CMEE includes routines to
model secondary electrons, neutral gas desorption and
ionization. The secondary electron routines are based on
routines from the POSINST code. The neutral gas desorption
routines are based on a thermal binding model similar to the
model in ,e.g., the LSP code. The ionization routines are
based on the IONPACK library from Tech-X. This poster
discusses the latest state of these routines, specifically
implementation in the WARP code and comparisons to data from
the High Current Experiment (HCX). In particular, recent
comparisons between the CMEE routines and neutral gas
desorption measurements from HCX are presented.
[RP1.081] The Integrated Beam Experiment-- The Next Step for Heavy Ion Fusion
C.M. Celata, J.W. Kwan, E.P. Lee, M.A. Leitner, B.G. Logan, J-L. Vay, W.L. Waldron, S.S. Yu (Lawrence Berkeley National Laboratory), J.J. Barnard, R.H. Cohen, A. Friedman, D.P. Grote, A.W. Molvik, W.M. Sharp (Lawrence Livermore National Laboratory), D.V. Rose, D.R. Welch (Mission Research Corporation), R.C. Davidson, Igor D. Kaganovich, H. Qin, Edward A. Startsev (Princeton Plasma Physics Laboratory)
The U.S. Heavy Ion Fusion Program is completing a 2-decade
effort of small-scale experiments and analysis to explore
the beam manipulations and non-neutral plasma physics of the
intense beams necessary for a driver. The next step, a
proof-of-principle experiment called the “Integrated Beam
Experiment” (IBX) is in the design stage. It would
integrate, for a single beam, all the beam physics from
source to target, including beam production, acceleration,
interaction with electrons and gas, compression,
neutralization, and final focus. Present designs call for a
K+ beam accelerated in an induction linac to 5-10 MeV. We
present design studies, including PIC code studies of beam
behavior.
[RP1.082] Simulation Studies of Temperature Anisotropy Instability in Intense Charged Particle Beams for IBX Parameters
E. A. Startsev, R. C. Davidson, H. Qin (Plasma Physics Laboratory, Princeton University)
The Integrated Beam Experiment (IBX) is a proof-of-principal
experiment for heavy ion fusion designed to test
source-to-target beam physics using a single beam of K^+
ions of duration 0.2 - 1.5 \mu s, accelerated to energies
~ 5-10 MeV, and driver-scale normalized perviance in the
range 10^-5 -10^-3. An important physics issue to be
addressed by IBX is the effect of longitudinal-transverse
coupling on the beam transport and focusibility of the
driver. Our previous numerical and theoretical studies of
intense charged particle beams with large temperature
anisotropy [E. A. Startsev, R. C. Davidson and H. Qin,
Phys. Plasmas \textbf9, 3138, 2002] demonstrated that a
fast, electrostatic, Harris-like instability may develop.
This paper reports the results of recent simulations of the
temperature anisotropy instability using the Beam
Equilibrium Stability Transport (BEST) code for IBX
parameters.
[RP1.083] Moment Equation Approach to Chromatic Aberrations in Final Focus Systems for Heavy Ion Fusion
John J. Barnard (Lawrence Livermore National Laboratory), Edward P. Lee (Lawrence Berkeley National Laboratory)
Ordinarily, the envelope equations provide adequate accuracy for rapid design calculations of rough layouts of a set of magnetic quadrupoles arranged to focus an ion beam to a small spot (for example, for the final focus system of a Heavy Ion Fusion driver.) Typically, such systems consist of four to eight large aperture quadrupole magnets preceded by a drift section. However, chromatic aberrations (depending on momentum spread) and other non-linear terms in the equations of motion may contribute significantly to the final focal spot size. We present here a moment equation approach which includes terms through second order in particle transverse position, angle and fractional momentum spread, (but which drops terms higher than a specified order) and which treats space charge by assuming it is distributed uniformly over an elliptical cross section. Integrating the derived set of moment equations allows rapid determination of the contribution of chromatic aberrations to spot size. We compare the results of integrating moment equations with an analytic theory, as well as with Particle-In-Cell simulations.
[RP1.084] RF Plasma Source for Heavy Ion Fusion
Glen Westenskow, David Grote, Robert Hall (Lawrence Livermore National Laboratory), Jonathan Kapica, Joe Kwan, William Waldron (Lawrence Berekely National Laboratory)
We are developing high-current ion sources for Heavy Ion
Fusion (HIF) applications. Heavy ion driven inertial fusion
requires beams of high brightness to deposit the necessary
high energy in the target to obtain high gain. Our proposed
RF plasma source starts with an array of high current
density mini-beamlets (of a few mA each at \sim100 mA/cm2) that
are kept separated from each other within a set of
acceleration grids in order to minimize the space charge
expansion. After they have gained sufficient kinetic energy
(>1.2 MeV), the mini-beamlets will be allowed to merge
together to form a high current beam (about 0.5 A) with low
emittance. We are performing experiments on RF plasma
sources. A 80-kV 20-µs source has produced up to 5 mA of Ar+
in a single beamlet. We have measured the emittance of a
beamlet, and the fraction of Ar++ ions. The plasma chamber
has 26-cm inner diameter with multicusp permanent magnets to
confine plasma. RF power (\sim11 MHz, >10 kW) is applied to the
source via a 2-turn, 11-cm diameter antenna inside the
chamber. We have started testing a 80-kV 61-hole
multi-beamlet array designed to produce a total current >200
mA. In this stage of the experiments the beamlets will not
be merged into a single beam. A 500-kV experiment where the
beamlets will be merged to a produce 0.5 A beam is being
planned.
[RP1.085] Particle Simulation Schemes for High Intensity Charged Particle Beams
Wei-li Lee, Edward Startsev, Hong Qin, Ronald C. Davidson (Princeton Plasma Physics Laboratory)
Numerical schemes for the electromagnetic particle simulations of high intensity charged particle beams have been developed. The purpose of devising these schemes is to avoid the numerical difficulties associated with the direct calculation of the time derivatives of the vector potential, \partial A / \partial t, in the Darwin model, for which the transverse induction current in Ampere's law is neglected. The first scheme requires the calculations of higher order velocity moments of the distribution function to obtain the time derivatives for both the scalar potential \Phi and A, similar to the method used for shear-Alfven waves.[1] The second uses the canonical momentum P = p + q A/c in the equations of motion as a means to eliminate the troublesome time derivatives.[2] The use of these schemes for physics problems in heavy ion fusion systems will be reported.
[1] W. W. Lee, J. L. V. Lewandowski, T. S. Hahm, and Z. Lin, Phys. Plasmas 8, 4435 (2001).
[2] W. W. Lee, E. Startsev, H. Qin and R. C. Davidson,
Proceedings of 2001 Particle Accelerator Conference 1906
(2001).
[RP1.086] Beam Loss and Halo Formation Induced by Image-Charge Effects in a Small-Aperture Alternating-Gradient Focusing System
Jing Zhou (MIT), Bao Liang Qian, Chiping Chen (MIT, Plasma and Fusion Center)
It is shown with a test-particle model that image-charge
effects induce a new mechanism for chaotic particle motion
and halo formation in an intense charged-particle beam
propagating through an alternating-gradient focusing channel
with a small aperture, circular, perfectly conducting pipe.
While our model allows for nonuniform beams with elliptic
symmetry, the effects of image charges on halo formation are
illustrated with a uniform Kapchinskij-Vladimirskij (KV)
distribution. Halo formation and chaotic particle motion are
studied for various choices of system parameters: filling
factor, perveance and vacuum phase advance. Furthermore, the
percentage of beam loss to the conductor wall is calculated
as a function of propagating distance and aperture size.
[RP1.087] Ionization Cross Sections for Ion-Atom Collisions in High Energy Ion Beams
I. D. Kaganovich, E. A. Startsev, R. C. Davidson (Plasma Physics Laboratory, Princeton University)
Knowledge of ion-atom ionization cross sections is of great
importance for many accelerator applications. When
experimental data and theoretical calculations are not
available, approximate formulas are frequently used. Based
on experimental data and theoretical predictions, a new fit
for ionization cross sections by fully stripped ions is
proposed. The Born approximation and classical trajectory
calculations are frequently used to estimate the cross
sections. Neither approximation is expected to be valid over
the entire range of projectile ions and target atoms.
Aspects of both models must be included in order to address
the shortcomings in the underlying assumptions. A large
difference in cross section, up to a factor of six,
calculated in quantum mechanics and classical mechanics, has
been obtained for 3.2GeV negative ions of iodine and
positive ions of cesium. Because at such high velocities the
Born approximation is well validated, the classical
trajectory approach fails to correctly predict the stripping
cross section at high energies for electron orbitals with
low ionization potential.
[RP1.088] Symmetric Neutralized Ion Beams - Experiments and PIC Simulation
N. K. Hicks, J. Chen, A. Y. Wong (University of California, Los Angeles)
Experiments with symmetric neutralized ion beams consisting
of H^+ and H^- ions are being conducted. The H^+
and H^- beams are transported and merged in RF
quadrupoles and are then injected into a magnetic field. The
ability of the beam to propagate across the magnetic field
due to the formation of a polarization electric field that
cancels the magnetic field deflection is being explored.
Approximate quantities for the proof-of-principle experiment
are: beam energy 1 keV, beam current density 10^9
mA/cm^2, magnetic field 100 G. 3D PIC simulation of the
cross-field propagation process is also being carried out,
with particular attention to the effect of a background
plasma and other loss mechanisms such as beam expansion. The
injection of arrays of higher energy beams of this type into
magnetic fusion devices for heating, fueling, current drive,
and diagnostics is being considered.
[RP1.089] RF Plasma Source for Heavy Ion Beam Charge Neutralization
P. C. Efthimion, E. Gilson, L. Grisham, R. C. Davidson (Plasma Physics Laboratory, Princeton University), S. Yu, B. G. Logan
Highly ionized plasmas are being employed as a medium for
charge neutralizing heavy ion beams in order to focus to a
small spot size. Calculations suggest that plasma at a
density of 1 - 100 times the ion beam density and at a
length ~ 0.1-0.5 m would be suitable for achieving a high
level of charge neutralization. An ECR source has been built
at the Princeton Plasma Physics Laboratory (PPPL) in support
of the joint Neutralized Transport Experiment (NTX) at the
Lawrence Berkeley National Laboratory (LBNL) to study ion
beam neutralization with plasma. The ECR source operates at
13.6 MHz and with solenoid magnetic fields of 0-10 gauss.
The goal is to operate the source at pressures ~ 10^-5
Torr at full ionization. The initial operation of the source
has been at pressures of 10^-4 - 10^-1 Torr.
Electron densities in the range of 10^8 - 10^11
cm^-3 have been achieved. Recently, pulsed operation of
the source has enabled operation at pressures in the
10^-6 Torr range with densities of 10^11 cm^-3.
Near 100% ionization has been achieved. The source has been
integrated with NTX and is being used in the experiments.
The plasma is approximately 10 cm in length in the direction
of the beam propagation. Modifications to the source will be
presented that increase its length in the direction of beam
propagation.
[RP1.090] Modeling Drift Compression in an Integrated Beam Experiment for Heavy-Ion-Fusion
W. M. Sharp, J. J. Barnard, A. Friedman, D. P. Grote (LLNL), C. M. Celata, S. S. Yu (LBNL)
The Integrated Beam Experiment (IBX) is an induction
accelerator being designed to further develop the science
base for heavy-ion fusion. The experiment is being developed
jointly by Lawrence Berkeley National Laboratory, Lawrence
Livermore National Laboratory, and Princeton Plasma Physics
Laboratory. One conceptual approach would first accelerate a
0.5-1 A beam of singly charged potassium ions to 5 MeV,
impose a head-to-tail velocity tilt to compress the beam
longitudinally, and finally focus the beam radiallly using a
series of quadrupole lenses. The lengthwise compression is a
critical step because the radial size must be controlled as
the current increases, and the beam emittance must be kept
minimal. The work reported here first uses the moment-based
model HERMES to design the drift-compression beam line and
to assess the sensitivity of the final beam profile to beam
and lattice errors. The particle-in-cell code WARP is then
used to validate the physics design, study the phase-space
evolution, and quantify the emittance growth.
[RP1.091] A Proposal for an Initial Fusion Materials Testing Facility
Douglass E. Post, James L. Anderson, George P. Lawrence, Paul W. Lisowski, Kurt F. Schoenberg, Richard L. Sheffield, Bailey R. Stults (Los Alamos National Laboratory, Los Alamos, New Mexico)
As pointed out in the Fusion Community "35 Year Plan"
presented at the APS DPP in 2002 in Orlando, fusion
materials that are low activation, have long lifetimes and
can withstand high neutron fluxes are essential for fusion
energy for both MFE and IFE fusion power systems. The
present US 35 year proposed strategy for fusion materials
development calls for building a test facility within the
next ten years. Initial estimates put the cost of the
International Fusion Material Irradiation Facility (IFMIF)
at nearly $1B. We report the possibility of an initial,
smaller scale fusion material testing facility built for a
significantly lower cost utilizing the existing
infrastructure of the $150M LEDA facility located at LANL.
While the test volumes would be much smaller than the full
scale IFMIF, there are significant advantages to beginning a
smaller scale testing program sooner than the planned start
of operations for the full scale IFMIF.
[RP1.092] Preliminary Results of Proton Collimation Experiments
George Miley, Robert Stubbers, Jason Webber (Fusion Studies Lab, University of Illinois at Urbana-Champaign), Hiromu Momota (NPL Associates, Champaign, IL 61820)
Proton Collimation involves the conversion of an isotropic
source of highly energetic protons from a source, such as an
inertial electrostatic confinement fusion reactor, and
forcing the particles into a highly focused channel where
they can be utilized in a direct energy converter as a
possible spacecraft power source or possibly used as a
high-Isp, low-thrust particle rocket. These experiments are
to verify the proton collimator effect, its reciprocal
process, and to provide an evaluated database for use in the
design of a proton collimator for an IEC fusion reactor. A
low energy electron beam is used to simulate an energetic
fusion proton beam in the current experiments. Sensitivity
experiments will provide the database needed for
constructing an optimized collimator. In particular, the
effect of collimator operation to source asymmetry will be
tested using the adjustable-position source feedthrough. In
the process of completing the collimator construction and
testing, several minor modifications, such as filament
structural design, have been made. Testing of device
settings and collimator principles is underway and initial
results will be presented.
[RP1.093] ICF Hohlraums and Implosion Physics
[RP1.094] Investigation of M-band Gold Spectra in Hot Halfraums at HELEN and OMEGA and in EBIT plasmas
M.J. May, M. Schneider, B. Heeter, J. Scofield, K. Reed, B. Wilson, K.B. Fournier, P. Beiersdorfer (LLNL), K. Oakes, M. Stevenson, G. Slark (AWE)
The determination of the charge state distribution (CSD) of
highly ionized gold in high-density plasmas (\sim
10^21 cm^-3) is critical for ICF experiments.
Predictive calculations of the CSD have produced widely
varying results. Previous experiments on NOVA have had some
success in guiding the models at 2 keV. Here, CSD’s have
been investigated in Hot Halfraum experiments (T_e >
5keV) at OMEGA and HELEN by comparing the n=5-3 and n=4-3
X-ray transitions in Ni-like to Kr-like Au to HULLAC line
emission modeling. CSDs at low density (\sim 10^12
cm^-3) and T_e = 2-2.5 keV have been inferred in
plasmas created at the Livermore electron beam ion trap
(EBIT) facility (Wong, et. al., PRL 90, 235001-1 (2003)).
One uncertainty in these CSD measurements is the collisional
excitation cross sections. To reduce this uncertainty, some
of the relevant n=3-4 and n=3-5 cross sections have been
measured at the EBIT facility and are compared with
theoretical predictions. This work was performed by the
University of California LLNL under the auspices of the DOE
under contract W-7405-ENG-48..
[RP1.095] Simulations of the effects of foam ablators on shock propagation and implosion stability in ICF capsules.
Lee Phillips, John Gardner, John Sethian (Naval Research Laboratory)
We have performed a series of detailed simulations of shock
propagation through two-dimensional models of foam ablators,
using NRL's FAST radiation hydrodynamics code (J.H. Gardner,
A.J. Schmitt, et al., Phys. Plasmas 5, 1935 (1998)). These
models differ from those used in previous simulations in
incorporating the effects of radiation, heat, and detailed
equations of state for the components of the foams (CH, DT,
and RF). It was found that the selective absorption of
radiation by the CH or RF fibers dramatically changes the
structure of the foam in front of the shock, which in turn
has a large effect on the characteristics of the propagating
shockwave. We attempt to draw some preliminary conclusions
for the design of high-gain direct-drive ICF targets. We
also reexamine the results of experiments, performed at
NRL's Nike laser facility, on the propagation of shocks
through foam ablators, in light of our simulation results.
[RP1.096] Experiments on Ablation Front Features
S. G. Glendinning, F. J. Swenson, J. H. Hammer (Lawrence Livermore National Laboratory)
Structures at a non-accelerated ablation front evolve in a
Richtmyer-Meshkov-like manner, but differently from those
shocked at an embedded interface [Velikovich et al., Phys.
Plasmas 5, 1662 (2000); Robey et al., Phys. Rev. Lett. 8908,
5001 (2002)]. We report on simulations and experiments on
nominally hemispherical features initially imposed on a
TiO_2 foam, density 1.8 g/cc. The features were
ablatively driven with x-rays from a gold hohlraum, 2.26 mm
diameter by 1.68 mm long. The radiation temperature peaked
at about 140 eV, for about 3.3 ns. The features were
typically 50 \mum diameter by 10-20 \mum deep. The
initial studies described concentrated on diagnostic
techinques, including addressing the issues involved in
backlighting along the axis of a hohlraum during the
stagnation of gold on axis.
[RP1.097] Interpretation of X-ray conversion efficiency in hohlraums on Omega
Laurence Lours, Michel Naudy, Jean-Paul Jadaud, Bruno Villette (CEA, BP 12, 91680 Bruyeres le Chatel, France)
Since 1999, CEA performs experiments on Omega in
collaboration with LLNL. One of these experiments (may '03
empty hohlraum shots with 3 cone LMJ-like irradiation) is
interpreted here. In order to understand former symmetry
experiments, the target is oriented so that the
backscattering diagnostics are along the inner cone. The
influence of the polyimide foil holding the foam ball in the
center of the hohlraum is observed.
[RP1.098] Diagnosing Dynamic Hohlraums Using Tracer X-ray Lines
J. P. APRUZESE, R. W. CLARK, P. C. KEPPLE, J. DAVIS (Naval Research Laboratory), T. W. L. SANFORD, T. J. NASH, R. C. MOCK, J. E. BAILEY, R. J. LEEPER, T. A. MEHLHORN (Sandia National Laboratories), J. J. MacFARLANE (Prism Computational Sciences)
A dynamic hohlraum is a unique, nearly Planckian x-ray
source that is produced by imploding an array or arrays of
high atomic number wires onto a cylindrical hydrocarbon
foam. Its ability to generate a desired x-ray spectrum
symmetrically from both the top and bottom of the foam
depends critically on the plasma conditions attained in its
interior. In a series of experiments performed on the Z
generator, Al and/or Mg tracer layers were embedded in the
foam target at various distances from its ends. Their
K-shell lines were observed mostly in absorption. In the
present work, we show how the relative intensities and
depths of these absorption lines are controlled by the foam
plasma temperature, density, their gradients, and top/bottom
symmetry. Calculations using detailed configuration atomic
physics and radiation transport models with up to 4000
frequency groups are employed to diagnose specific Z
experiments by analyzing their tracer spectra.
[RP1.099] Improved drive symmetry via integrated 3D simulations of NIF ignition targets
M.M. Marinak, G.D. Kerbel, N. Gentile, P.A. Amendt, O.S. Jones, S.M. Pollaine, S.W. Haan (Lawrence Livermore National Laboratory)
The baseline NIF ignition target design has been improved with the aid of 3-D integrated HYDRA simulations, incorporating a number of modifications to accommodate realistic illumination geometry. We describe these refinements, which include a laser pointing geometry optimized to reduce the m=4 azimuthal variation associated with the inner laser ring. Integrated simulations show the capsule implosion exhibits improved symmetry and greater overall robustness than previous designs. We will also simulate the coupled effects of multimode surface perturbations and intrinsic drive asymmetry in high-resolution capsule only simulations. Perturbations initialized on both the inner and outer surfaces encompass the full spectrum of the most dangerous modes, yielding the most complete model of the ignition capsule performance.
[RP1.100] Investigation of radiation diffusion in a thin Au wall using x-ray backlit imaging
R. G. Watt, R. E. Chrien, G. Idzorek (Los Alamos National Laboratory)
Radiation diffusion occurs in the hohlraum wall in Inertial
Confinement Fusion (ICF). ICF hohlraums come in both thick
and thin wall versions. The thick wall hohlraum contains the
laser produced drive radiation efficiently, but precludes
direct observation of the laser-wall interaction region The
thin wall hohlraum (TWH) allows an x-ray image of the
interaction region to be observed through the wall, with
minimal impact on the hohlraum energetics. The TWH typically
consists of a 2-3 um Au layer surrounded by a supporting
wall of plastic or Al. Energy loss by diffusion through the
thin Au layer can have a significant impact on the
energetics of the hohlraum, but the losses have never been
directly examined. The present work examines the radiation
diffusion through a 1 um Au wall with a 25 um Al support
layer by imaging the expansion of the Al under the influence
of the radiation diffusing through the Au layer. 6.7 keV
x-ray backlit imaging is used to examine the outer Al
surface location as a function of time, and to compare the
resultant trajectory to that predicted by a radiation
hydrodynamics code. The experiments are done on the Sandia
National Laboratories Z accelerator, using the dynamic
hohlraum as a radiation source to drive the expansion of a
small TWH. Images and simulations will be compared.
[RP1.101] Electron Transport In Magnetized Laser Hohlraum Plasmas
Lorien Friesen, John Edwards, Richard Town (LLNL), Robert Kingham (Imperial College,London), Wojciech Rozmus (University of Alberta)
The plasma conditions we expect to encounter in hohlraum experiments on the National Ignition Facility span from the familiar, relatively benign conditions of Nova and Omega to much more hostile environments in which electron temperatures may be 10s of keV. In any of these situations simple estimates indicate that heat flow is very non-local, making the local diffusion approximation typically used in hydrocodes invalid. However, large, mega gauss magnetic fields which are generated primarily at the wall and fill the body of the hohlraum will tend to localize the electron transport. In this paper we use the Fokker-Planck code IMPACT to study heat flow as a function of plasma scale lengths compared to the electron mean free path, and as a function of magnetization and compare the results with local and non-local theory for plasma conditions of relevance to hohlraums driven by the National ignition Facility.
This work was performed under the auspices of the U.S.
Department of Energy by the University of California,
Lawrence Livermore National Laboratory under contract No.
W-7405-Eng-48.
[RP1.102] Design and characterization of hohlraum targets for long-pulse radiation drive in early NIF operation
Juan C. Fernandez, S. Robert Goldman (Los Alamos National Lab.)
The National Ignition Facility (NIF) at Lawrence Livermore
National Laboratory is undergoing a complex process of
simultaneous commissioning of ever increasing capability for
experiments, and laser construction. This process will
continue until full capability with 192 beams is available
late in the year 2008. Two key milestones are the
availability of 4 beams (1 quad) starting this year and the
availability of 12 quads in 2006. With merely one quad, NIF
is the facility that provides the highest laser energy that
can be coupled to a class of cylindrical hohlraum targets
known as a "halfraum''. Halfraums have only one
laser-entrance hole and are ideal for single-sided
illumination geometries and experiments requiring
radiation-driven planar packages. Twelve quads allow
suitable single-sided illumination of a much larger and more
capable halfraum. Another key advantage of early NIF is the
relatively long (> 10 ns) laser pulses available, which can
be exploited with a suitable target design. Los Alamos, as a
principal participant in the NIF, is developing plans for a
multi- institutional team to commission 1-quad and 12-quad
hohlraums suitable for NIF experiments requiring long-pulse
radiation drive. This paper describes: 1) the experiments
necessary to characterize and commission these hohlraums; 2)
the scientific understanding that this campaign is expected
to add for the pursuit of ignition; 3) concomitant
diagnostic development; and 4) the timetable for this
campaign.
[RP1.103] High Magnification X-ray imaging of Indirect Drive Implosions on Omega
Robert Turner, Peter Amendt, Sam Dalhed, Otto Landen, Lawrence Suter, Russell Wallace, Bruce Hammel (Lawrence Livermore National Laboratory), Keith Thorpe, Gregory Pien (Laboratory for Laser Energetics)
Ultra high magnification x-ray images of ICF imploded fuel
cores can be used to diagnose higher order modes of
time-integrated drive symmetry. We will show time-resolved
x-ray images obtained at 87x magnification and 8 to 9 keV
photon energy, using target-mounted pinholes. This technique
should easily transfer to NIF implosion experiments. We will
discuss steps taken to reduce strong background levels, and
experiments aimed at identifying the source of the
background. We will show a direct comparison between an 87x
image and a more conventional 12x image when looking at a
highly distorted implosion. Finally, it has been observed
that the introduction of the argon dopant to increase x-ray
brightness reduced yields more than expected from
simulations. We will report on progress in understanding the
atomic physics which is responsible for the reduced yields
that are observed. We will also show that simulations for
high convergence (18X) implosions are in good agreement with
experimental yields when the argon dopant is removed.
[RP1.104] Measurements of thermonuclear neutrons in dynamic hohlraum experiments on Z
C.L. Ruiz, J.E. Bailey, G.A. Chandler, S.A. Slutz, T.A. Mehlhorn, R.J. Leeper (Sandia National Laboratories, Albuquerque NM 87185-1196), G.W. Cooper, A.J. Nelson (University of New Mexico, Albuquerque NM 87131), J. Franklin (K-Tech Corp, Albuquerque NM 87110), L.H. Ziegler, C. Hagen (Bechtel Nevada, Las Vegas NV 89030)
Dynamic-Hohlraum ICF experiments are currently being conducted at Sandia National Laboratory's Z facility to address the implosion of thin, deuterated (D2) gas-filled capsules. Of particular importance is the demonstrated production and measurement of thermonuclear neutrons. We will discuss the integrated use of an array of neutron diagnostics being used in these experiments. These diagnostics include active neutron time-of-flight detection schemes and passive activation detection schemes (indium samples and lead and beryllium detectors). The basic concepts and sensitivity calibrations of these detectors will be described. Data from current D2 capsule experiments will be presented.
Sandia is a multiprogram laboratory operated by the Sandia
Corporation, a Lockheed Martin Company, for the U.S.
Department of Energy under Contract No. DE-AC04-94AL85000.
[RP1.105] Calibration of a detector for measuring dd fusion neutrons based on the 9Be(n,a)6He Reaction
A.J. Nelson, G.W. Cooper (University of New Mexico), C.L. Ruiz (Sandia National Laboratories), J. Franklin (-Tech Corp), L. Ziegler, C. Hagen (Bechtel Nevada)
A detector based on the threshold reaction 9Be(n,a)6He has been developed to measure bursts of dd fusion neutrons. The 6He activity produced can be directly related to the neutron yield. To measure the activity of the 0.8-second half-life, pure-beta emitting 6He a photomultiplier/scintillator system is used in which the scintillator is closely coupled to the Be. The detector consists of six, 16cm x 16cm x 0.6cm, Be plates alternately sandwiched between seven 16cm x 16cm x 1.25 cm plates of plastic scintillator. The output signal of the 12.7 cm diameter photomultiplier tube is passed through a constant fraction discriminator to a multichannel scalar. The sensitivity of this detector to dd neutrons as a function of discriminator setting and applied voltage will be presented.
Sandia is a multiprogram laboratory operated by Sandia
Corporation, a Lockheed Martin Company, for the United
States Department of Energy under contract DE-AC04-94AL8500.
[RP1.106] The utility of knock-on D, T, and P for diagnosing NIF implosions
M.J. Canavan, J.R. Rygg, J.A. Frenje, C.K. Li, F.H. Séguin, R.D. Petrasso (MIT), V.Yu. Glebov, D.D. Meyerhofer, T.C. Sangster, J.M. Soures (LLE, U. of Rochester), S.W. Haan, S.P. Hatchett, J.A. Koch, O.L. Landen (LLNL)
Recent experiments at OMEGA have produced the most complete
spectra of D, T and P knock-ons, spanning nearly the entire
energy range. We examine how such measurements could be
effectively used to diagnose NIF implosions. For example, KO
protons will give direct information about the ablator
\rhoR and any asymmetries (by using multiple
spectrometers). This method will complement the measurements
of scattered neutrons by the Magnetic Recoil Spectrometer.
(See Frenje \emphet. al., this conference). This work was
performed in part at the LLE National Laser Users' Facility,
and supported in part by the US DoE (contract W-7405-ENG-48
with LLNL, grant DE-FG03-99DP00300 and Cooperative Agreement
DE-FC03-92SF19460), LLE (subcontract P0410025G), and LLNL
(subcontract B313975).
[RP1.107] Design of an Experiment to Test Shims to Improve Symmetry in Indirect Drive, ICF Capsules
Debra Callahan, Max Tabak (Lawrence Livermore National Laboratory)
We have been exploring the use of shims as a technique for
fixing asymmetries in ICF capsules. The shim is a thin layer
of material placed on or near the capsule surface to block a
small amount of excess radiation. By varying the thickness
at different locations around the capsule, we have been able
to fix early time asymmetries of \sim 9% in pressure. To
test this concept, we have designed experiments that use the
double Z-pinch hohlraum[1,2] on Z. We will discuss these
designs as well as the application of shims to high-yield
capsules for inertial fusion energy. [1] J. H. Hammer, et.
al., Phys of Plasmas, 6, 2129 (1999). [2] R. A. Vesey, et.
al., Phys of Plasmas, 10, 1854 (2003).
[RP1.108] Integrated calculation of a high gain target for NIF with burn through foils
Max Tabak (Lawrence Livermore National Laboratory)
Burn-through foils have been proposed as a technique to reduce the asymmetry of the radiation incident on the implosion capsule. This technique is currently being explored for ICF targets driven by heavy ion beams or Z-pinches. This work applies this technique to laser-driven designs. We begin with an earlier design of Suter that produced gain near 40 for 2.3 MJ of laser light. A more optimum 1-D implosion design( a scale of the base design for heavy ion fusion) leads to approximately a doubled gain from the coupled energy. However, in integrated designs this design fails due to a large P4. A burn-through foil is designed to remedy this problem. Generalization of this scheme to more complicated radiation asymmetries will also be discussed.
[RP1.109] Burn Dynamics of Plasma-Jet Magnetized-Target Fusion
John F. Santarius (Univ. of Wisconsin)
In magnetized-target fusion, an imploding, conducting liner
compresses a magnetized plasmoid, such as a spheromak or
field-reversed configuration. The increasing magnetic field
of the target reduces thermal conduction and the liner's
inertia provides transient plasma stability and confinement.
This poster explores the burn dynamics of using plasma jets
to form the liner [1]. The investigation uses the University
of Wisconsin’s 1-D Lagrangian radiation hydrodynamics code,
BUCKY, which solves single-fluid equations of motion with
pressure contributions from electrons, ions, radiation, and
fast charged particles, using either ideal-gas or
table-lookup equations of state. BUCKY includes ion-electron
interactions, PdV work, and fast-ion energy deposition. For
this research, the code has been extended to include the
magnetic field evolution as the plasmoid compresses plus the
dependence of the thermal conductivity and fusion product
energy deposition on the magnetic field. [1] Y.C. F. Thio,
et al., ``Magnetized Target Fusion in a Spheroidal Geometry
with Standoff Drivers,'' in Current Trends in International
Fusion Research, E. Panarella, ed. (National Research
Council of Canada, Ottawa, Canada, 1999), p. 113.
[RP1.110] Alpha particle fusion reaction product modeling in DRACO
Gregory Moses, Jiankui Yuan (Fusion Technology Institute, University of Wisconsin-Madison)
Alpha particle fusion reaction product transport in DRACO is computed using either multi-group flux-limited diffusion theory or continuous energy Monte Carlo particle tracking. Both of these transport models incorporate the same basic slowing down model of Li and Petrasso. Detailed comparisons of particle transport and energy loss predicted by the two models will be presented. Results of 2D lagrangian fusion burn simulations will be compared for the two models. The Monte Carlo model can be used in either an “adiabatic” approximation on each time step or a time dependent model where in-flight particles are remembered for the next time step. Both models are implemented using parallel computing algorithms using the MPI parallel programming interface.
Work supported by the Laboratory for Laser Energetics,
University of Rochester.
[RP1.111] Analysis of cryogenic DT target yield degradation due to vapor-ice interface roughness
T.A. Heltemes, G.A. Moses (Fusion Technology Institute, University of Wisconsin-Madison), T.J.B. Collins, P.W. McKenty, P.B. Radha, S. Skupsky (Laboratory for Laser Energetics, University of Rochester, 250 East River)
We use the DRACO 2D Lagrangian radiation hydrodynamics code to examine the effects of vapor-ice interface roughness on cryogenic DT target yield. The simulation modeled the effects of a uniform laser pulse on a spherical DT target with a vapor core encapsulated by a solid DT shell. This uniform target simulation produced a DT neutron yield of 1.97616E+19 neutrons. Surface roughness was modeled by perturbing the vapor-ice interface. This paper examines cosine shaped perturbations with amplitudes of 0.5 microns to 12.0 microns in 0.5 micron increments and l-modes of 2 through 10 for each of the perturbation amplitudes. The resulting DT neutron yields are then compared to the uniform case to determine the effect of vapor-ice interface roughness on target yield.
[RP1.112] Spectroscopic Modeling of Ar K-shell spectra from Z-pinch-driven capsule implosions.
I.E. Golovkin (Prism Computational Sciences, Madison, WI 53711), J.E. Bailey (Sandia National Laboratories, Albuquerque, NM 87185-1196), J.J. MacFarlane, P.R. Woodruff (Prism Computational Sciences, Madison, WI 53711), S.A. Slutz, G.A. Chandler (Sandia National Laboratories, Albuquerque, NM 87185-1196), R.C. Mancini (University of Nevada, Reno, NV 89557)
Emission spectroscopy of Ar-doped DD capsule implosions is
an important diagnostic for inertial confinement fusion
experiments. In these experiments, time- and space-resolved
Ar K-shell emission spectra were recorded during the
collapse of the implosion driven by up to 40 kJ of 200 eV
x-rays. Targets were 2.1 mm CH capsules filled with 10-20
atmospheres of DD and 0.085 atmospheres of Ar. We will
present details of spectroscopic analysis and
temperature/density inferences for these experiments, based
on a uniform-core approximation (PrismSpect code) and on
postprocessing 1D hydro simulations (Spect3D code).
Hydrodynamics simulations were performed with the code
HELIOS, that includes an inline collisional-radiative
radiation transport model.
[RP1.113] Direct Drive Double Shell Target Implosions on OMEGA
G. A. Kyrala, N. Delamater, D. Wilson, R. Watt, J. Guzik, W.M. Wood, W. Varnum, D. Haynes, G. Pollak, M. Gunderson, K. Klare (Los Alamos National Laboratory), W. Garbett, A. M. Dunne, P. Graham (AWE)
Imploding direct-drive double shell targets may provide an
alternative, non-cryogenic path to ignition on the National
Ignition Facility (NIF). Experiments are being pursued at
OMEGA to understand the hydrodynamics of these implosions
and the possibility of scaling to NIF designs. We have used
40 beams from the OMEGA laser to directly drive the
capsules, and we have used the remaining 20 beams to
backlight the imploding shells from two different directions
at multiple times. We will review the recent experiments to
measure the zero-order hydrodynamics of the targets using
two-view x-ray radiography of the capsules. We will present
data on measured yields from the targets. We will present a
measured time history of the implosion, and we will discuss
the effect of externally applied radiative preheat on the
implosion hydrodynamics. We will review the method used to
radiograph the targets and the techniques used to extract
useful information to compare with calculations. The effect
of imperfections in the target construction will be shown to
be minimal during the initial stage of the implosion, and
the yields were observed to be uniformly low compared to
indirect-drive.
[RP1.114] Progress with double shell implosions on Omega
N Delamater, G Kyrala, D Wilson, J Guzik, M Wood, D Haynes, W Varnum, M Gunderson (Los Alamos National Lab)
Recent calculations indicate that double shell targets may
provide an alternative, non-cryogenic path to ignition on
the National Ignition Facility (NIF) and experiments have
been pursued at OMEGA to understand the hydrodynamics of
these implosions and the possibility of scaling to NIF
designs. We will review recent results obtained with double
shell implosions using direct drive. The initial direct
drive results gave observed yields about 0.1 to 7 percent of
clean 1-d calculated yield. It was learned in these direct
drive experiments, however, that capsules which performed
best were those which had a thin outer layer of gold. This
effectively causes radiative preheat effects giving
implosion hydrodynamics and performance closer to the
indirect drive case. Yields were observed to be uniformly
low compared to indirect drive, possibly due to mix seeded
by the structure of the foam or drive asymmetries. The
results we present, include implosion core images for Al and
Au coated targets, backlit images of the implosions which
show the full implosion history, neutron yields and
comparison to calculations. This work was performed at Los
Alamos national Laboratory under the asupices of the US
Department of Energy under contract No. W-7405-ENG-36
[RP1.115] Shear amp; Compression Plasma Viscosity In Spherical ICF
Richard Morse (X-1, LANL)
In (1) the exceptional viscosity of DT plasmas (Braginskii)
was estimated to reduce by orders of magnitude growth rates
of the most threatening m=0 modes in liner implosions of
cylindrical Z-pinch plasmas that reach a thermonuclear
T=10keV. Here in spherical B=0 implosions shear viscosity is
estimated, by numerical(2)(implicit in t) amp;
analytic(Chandrasekhar) methods, to reduce similarly the
growth of R-T modes in DT plasmas reaching 10keV, where
\mu\sim5.E4 poise, or higher T. Surface plasma
interactions with the confining pusher shell(3) amp;
Knudsen(large mfp) limitation of the viscous effects are
discussed. Compression viscosity(Zel'dovich) adds noticeably
to irreversible heating(reduced to quadratures) in such
systems, esp. with final T>10keV amp;/or implosion
velocities >10E7cm/s. Here double implosions, as suggested
in (4), can increase significantly entropy production prior
to final implosion amp;, consequently, heating efficiency.
(1)Bull. APS 44-7 Nov99 BP189 (2)McCrory et. al.
Nuc.Sci.amp;Eng. 64,163(77) amp; references (3)Montierth et al.,
PFB 4(4) Ap92 amp; references (4)Two Stage Heating Of Theta
Pinches, Freidberg amp; Morse, Proc. '71 Garching Conf. On
High \beta Plasmas
[RP1.116] ICF capsule mix issues for DT ignition
Erik Vold (Los Alamos National Laboratory)
In ICF capsule implosion, it has been hypothesized that
mixing of the fuel (DT) and the capsule material degrades
the hydrodynamic compression thus reducing the convergence
ratio. Additionally, prediction of capsule ignition in
transient simulations requires a detailed knowledge of how
the materials are mixed at the atomic level and how they are
mixed at sub-grid scales which in turn evolve to atomic mix
by plasma diffusion processes. Modeling the fuel heating due
to the slowing down of the alpha particles requires coupling
a ‘kinetic’ process to a fluid simulation, while
incorporating a sufficiently detailed description of the
mixed fluids. An approach based on a volume-of-fluids
computational framework is described to formulate the
necessary physics and to accomplish these goals. The models
are used to investigate DT ignition physics issues,
including the partitioning of alpha slowing down energy in
atomically mixed regions compared to regions of dispersed
mixed materials characterized with an average scale length
for the sub-grid size distribution. Results account for the
ratio of this dispersed material scale length to the
reaction zone thickness, in this case, equal to the range of
the alpha particle.
[RP1.117] Application of time-resolved Ti K-shell spectroscopy to the study of mix in directly driven spherical implosions
D. Haynes, M. Gunderson, D. Wilson (X-2, LANL)
A submicron layer of Ti-doped CH inserted at the fuel/pusher
interface would provide a useful diagnostic of mix in
current ICF relevant spherical implosions. The emission from
this layer would afford a clear signal of mix if the Ti
reaches the central core. For ~900 micron outer diameter, 20
micron thick CH microballoons filled with 3Atm of deuterium
imploded using 23kJ of ultraviolet light from the Omega
laser system, the conditions anticipated for the Ti in the
absence of mix are such that the Ti H-like resonance lines
are calculated to be more than an order of magnitude less
intense than the He-like resonance lines. With mix as
calculated using a multi-fluid mix model, the Ti-dopant
reaches to central core and the H-like resonance lines
increase in intensity to levels comparable to the He-like
resonance lines. Thus, the timing and intensity of the
H-like resonance lines can be provide data to constrain mix
models. This work was performed at Los Alamos national
Laboratory under the auspices of the US Department of Energy
under contract No. W-7405-ENG-36.
[RP1.118] Code Validation Utilizing Spectral Data Analysis of ICF Implosion Experiments on OMEGA
Mark Gunderson, Donald Haynes Jr., Norman Delamater (Los Alamos National Laboratory, Los Alamos, NM), Sean Regan (LLE, Rochester, NY)
Time-resolved spectral data from recent ICF implosion
experiments of plastic microballoons containing deuterium
fuel doped with argon is proving quite useful in checking
the corresponding 1D and 2D simulation results from the
multi-dimensional hydrocode RAGE [1]. Comparisons with
experimental density and temperature determined by fitting
theoretical argon line shapes generated by MERL [2] to
experimental data show that the simulated density and
temperature in the fuel are too large unless some seed for
mixing is incorporated. We use a nonuniform drive as a seed
for mix. The need for mix is further supported through
simulations using the 1D Lagrangian code HYADES (no mix)
that give neutron yields an order of magnitude larger than
that seen in experiment. This work was performed under NLUF
grant DE-FG03-01SF22224 and DOE contract No. W-7405-ENG-36.
[1] Gittings, M.L., SAIC's adaptive grid Eulerian hydrocode,
DNA Numerical Methods Symposium, Apr 1992. [2] Mancini,
R.C., Kilcrease, D.P., Woltz, L.A., and Hooper Jr., C.F.,
Comput. Phy. Commun. 63, 314-322 (1991).
[RP1.119] hydrodynamic simulations of direct drive ICF experiments
philippe nicolai, guy schurtz (celia-university of bordeaux FRANCE), laurent disdier (CEA FRANCE)
The indirect drive scheme is the approach to the inertial
confinement fusion chosen by the leading laboratories - the
LLNL for the NIF and the CEA for the LMJ. The direct drive is
considered as an alternative choice. It allows a higher
yield at a lower energy cost if all physical processes are
understood and controlled. Our goal is to identify the most
severe constrains of the direct drive scheme by comparing
the integrated hydrodynamic simulations and the experiments.
Our 2D radiative-hydro code, accounts for heat flux
inhibition due to the non local effects and self generated
magnetic fields. The simulations were compared with the
series of experiments carried out at the Omega facility at
the LLE.This comparison allowed us to identify the physical
processes which are described correctly and those which need
to be improved in the code.
[RP1.120] Defect-Driven Hydrodynamics and Mix in Convergent Geometry
G. R. Magelssen, N. E. Lanier, S. H. Batha, J. Fincke, R. L. Holmes (Los Alamos National Laboratory, Los Alamos, NM), A. M. Dunne, C. Horsfield, K. W. Parker, S. D. Rothman (AWE, Aldermaston, United Kingdom)
Understanding the effect of defects on mix for inertial
fusion capsules is an important goal for the National
Ignition Facility. Recently, we have completed a series of
defect experiments in compressible, convergent, miscible
plasmas on the OMEGA laser facility. Two types of defects
have been studied, an axial and an azimuthal gap in an
aluminum marker. In cylindrical geometry, the marker was
placed between an epoxy ablator and low-density CH foam. The
cylinder was imploded by direct drive with 50 laser beams.
Experiments showed significant penetration of the defect
into the foam. We will present detailed comparisons between
expeimental results and RAGE simulations
[RP1.121] Spherical Implosions Using a High Density Cone and One Sided Illumination
John H. Gardner (LCPamp;FD, Naval Research Laboratory), Stephen P. Obenschain (Plasma Physics Division, Naval Research Laboratory)
For many years planar targets have been used to experimentally measure the RM-RT growth in targets of similar design to those needed for direct drive inertial confinement fusion. The advantages were the lower laser energy requirements and ease of diagnostic access. Planar geometry is a reasonable approximation to the behavior of a small section of a spherical pellet as long as the distance moved is small compared to the pellet radius. Obviously at some point spherical convergence will become an important effect. We would like to take advantage of the geometry advantages of the one sided illumination while at least approximately including spherical convergence effects. One possible way of accomplishing this is to use a truncated cone of high-density material to contain the sideways expansion of the target and force it to converge as it accelerates down the cone. We will report on some numerical simulations that we have performed to look at some novel target designs that will simultaneously allow diagnostic access and let us look at the effects of spherical convergence on the RT instability.
[RP1.122] Simulations of ignition capsule implosions, and of Omega Rayleigh Taylor experiments
Steven W Haan, Peter A Amendt, Gilbert W Collins, Thomas R Dittrich, Abraham J Fetterman, S Gail Glendinning, Mark C Herrmann, Omar A Hurricane, Marty Marinak, David Munro, Jay D Salmonson, George A Strobel, Larry J Suter (Lawrence Livermore National Laboratory)
Simulation results are presented on several ignition targets
proposed for the National Ignition Facility. The most recent
work has emphasized beryllium-ablator targets in which the
level of copper dopant varies with radius. These
graded-dopant targets have been designed at 250 eV and 300
eV peak drive temperature. The targets are significantly
more stable with respect to Rayleigh-Taylor growth than
uniformly doped targets. Rayleigh-Taylor experiments on the
Omega laser will also be discussed. This includes convergent
Rayleigh-Taylor experiments, and planar Rayleigh-Taylor
experiments with CH(Br) and polyimide foils. The planar
experiments have been especially interesting because of
significant disagreement between simulations and experiment.
[RP1.123] Measurements of Laser Imprint on Targets Irradiated by the Nike KrF Laser.
Max Karasik, J. L. Weaver, A. N. Mostovych, V. Serlin, J. W. Bates, S. P. Obenschain (Plasma Physics Division, Naval Research Laboratory, Washington, DC), Y Aglitskiy (SAIC, McLean, VA), J. H. Gardner (Laboratory for Computational Physics amp; Fluid Dynamics, Naval Research Laboratory, Washington, DC)
Accurate quantitative simulations of hydrodynamic
instability seeded by laser non-uniformity (laser imprint)
are important in predicting performance of direct-drive ICF
targets. In order to benchmark such simulations, we are
carrying out experiments on imprint on planar plastic as
well as cryogenic deuterium wicked foam targets. Most of the
imprint occurs during the initial low-intensity part of the
pulse, called the ``foot'' of the pulse, which is necessary
to compress the target to achieve high gain. In the
experiments, the amount of imprint is controlled by changing
the uniformity the foot of the pulse as well as the
bandwidth of induced special incoherence (ISI) laser
smoothing. Measurements of the resulting Raleigh-Taylor
amplified areal mass non-uniformity are made by face-on
x-ray radiography using Bragg reflection from a curved
crystal coupled to an x-ray streak camera. We will present
the experimental results and comparisons with 2D simulations
using FAST hydrocode. Work is supported by the U. S.
Department of Energy.
[RP1.124] Laser shaping pulse contributions to mass perturbation reduction during imprint and acceleration phases
N. Metzler (SAIC, McLean, VA, and Physics Department, NRCN, Israel), A. L. Velikovich, A. J. Schmitt (Plasma Physics Division, Naval Research Laboratory), J. H. Gardner (LCPamp;FD, Naval Research Laboratory)
Some time ago,(N. Metzler et al., Phys. Plasmas
\bf6), 3283 (1999);\bf9, 5050 (2002);\bf10, 1897
(2003). we proposed and demonstrated analytically and
numerically that tapering the density of the outer layer of
an ICF target can reduce laser imprint significantly.
Because of the difficulty in manufacturing such targets, we
suggested producing the density grading dynamically “on the
fly” with a short Laser Shaping Pulse (LSP) preceding the
drive pulse. Our recent numerical simulations showed that
LSP significantly reducing the perturbation growth in an
imploded target could be incorporated into a high-gain
direct-drive target design. A short “picket” or “spike”
hitting the target before the drive pulse can also be used,
together with (or even instead of) the foot of the main
pulse, to tailor the target adiabat in order to reduce the
RT growth rate in its outer layers while keeping the inner
side of the target at low adiabat suitable for ignition or
high gain.(V. N. Goncharov et al., Phys. Plasmas
\bf10), 1906 (2003); J. Perkins et al., Bull. Am. Phys.
Soc. \bf47, 101 (2002). We report a numerical study of
the relative roles of laser imprint mitigation due to
density gradients and the RT stabilization due to adiabat
gradients. We also discuss the design of some experiments
intended to verify the numerical predictions of perturbation
evolution in laser targets irradiated by a short spike
before the drive pulse.
[RP1.125] Reduction of Rayleigh-Taylor Instability Growth with Multi-Color Laser Irradiation
K. Otani, K. Shigemori, T. Sakaiya, S. Fujioka, A. Sunahara, M. Nakai, H. Shiraga, H. Azechi, Y. Izawa (Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871, Japan)
We proposed a novel scheme to reduce the Rayleigh-Taylor
(RT) instability growth rate with simultaneous irradiation
of longer wavelength laser. The longer wavelength laser
irradiation is expected to enhance the effect of non-local
electron heat transport because of the electron temperature
at the cut-off density for the longer wavelength laser is
higher than that for the shorter wavelength laser, resulting
an enhancement of ablation velocity and reduction of RT
instability. Planar polystyrene targets were irradiated by
shorter (\lambda= 0.351 \mum: 3ømega) and longer
(\lambda= 0.526 \mum: 2ømega or \lambda= 1.053
\mum: ømega) wavelength laser simultaneously. We
measured the target trajectory, the target density, and the
RT instability growth rate for 20- and 50-\mum
perturbation wavelength targets. We have also done a
spherical implosion experiments with CD (carbon-deuteron)
shell targets irradiated by twelve beams of GEKKO-XII laser
mixed two wavelengths (ømega and 2ømega)
symmetrically.
[RP1.126] Stabilization Mechanism of Ablative Rayleigh-Taylor Instability Growth at Medium Wavelengths
T. SAKAIYA, H. AZECHI, H. SHIRAGA, M. NAKAI, K. SHIGEMORI, S. FUJIOKA, Y. TAMARI, K. OTANI, A. SUNAHARA, H. NAGATOMO, Y. IZAWA (Institute of Laser Engineering, Osaka University), N. OHNISHI (Department of Aeronautics and Space Engineering, Tohoku University)
For high-gain design of inertial confinement fusion targets,
it is critically important to obtain good understanding of
the Rayleigh-Taylor (RT) instability. We have investigated
experimentally the RT instability of CH targets with the
laser-drive. From those experimental results, it has been
found that the growth rates of the RT instability at medium
wavelengths (\lambda = 30-100 \mum) are reduced compared
to those calculated from the result of the one-dimensional
simulation coupled with the Takabe-Bodner formula. One of
the stabilization mechanisms is the modulation of the
cut-off surface (laser-absorption region) due to the lateral
motion of the ablative flow. Since the ablation pressure is
enhanced by the modulation of the cut-off surface (enhanced
dynamic overpressure), the RT growth rate may be reduced.
[RP1.127] Instability of isolated planar shock waves
Jason W. Bates (U.S. Naval Research Laboratory)
The hydrodynamic stability of an isolated, planar shock wave
in an arbitrary, inviscid fluid medium is investigated by
analyzing the linearized solution of an appropriate
initial-value problem. Our approach generalizes the work of
Roberts (Los Alamos Scientific Laboratory Report No.~LA-299,
1945), whose methodology was restricted to a perfect-gas
equation of state. We find that when j^2(dV/dp)_H < -1 or
j^2(dV/dp)_H > 1-2|M_1| --- where j^2=(p-p_0)/(V_0-V) is
the slope of the Rayleigh line, (dV/dp)_H is the slope of
the Hugoniot curve in the pressure-volume (p-V) plane, and
M_1 is the downstream Mach number --- perturbations on the
surface of a shock front grow exponentially with time and
the system is unstable. The former instability criterion is
well-known, and agrees with earlier predictions by D'yakov
[Zh.~Eksp.~Teor.~Fiz.~27, 288 (1954)] and Erpenbeck
[Phys.~Fluids 5, 1181 (1962)], but the latter is
apparently less restrictive than previously thought. We
discuss the correspondence between our theory and these
alternative analyses, as well as possible implications for
inertial confinement fusion research.
[RP1.128] Novel Diagnostics Development for Ablative Rayleigh-Taylor Instability
Hiroshi Azechi (Institute of Laser Engineering, Osaka University)
The Rayleigh-Taylor (RT) instability with material ablation
through the unstable interface is the key physics that
determines the success or failure of inertial fusion energy
generation. Our strategy to reach proper understanding of
the ablative RT instability is to measure all necessary
quantities (growth rates, gravity, wave-number of the
perturbation, mass ablation rate, density profile) without
invoking simulation. This allows us to rigorously test our
understanding of the RT instability. We will present RT
growth measurements as well as the ablation density
measurements based on recently developed novel techniques of
high spatial resolution: Moire interferometry, penumbra
imaging, and Fresnel-phase-zone-plate imaging. We will
further present intended reduction of the RT growth by two
independent ways: induced non-local electron transport by
irradiating long-wavelength lasers (1/2-um or 1-um) in
addition to the short-wavelength lasers (1/3-um or shorter)
as a drive; and increasing ablation velocity and density
scale length by double ablation in high-Z doped targets.
[RP1.129] Experimental Design for Studies of Beryllium Ablator Microstructure
T. E. Tierney, J. A. Cobble, D. C. Swift, N. M. Hoffman, D. L. Tubbs, R. D. Day, A. Nobile, D. Schmidt (Los Alamos National Laboratory, Los Alamos, NM 87545)
Target designs for the National Ignition Facility include
hohlraum-driven, beryllium alloy ablator capsules. In this
type of design, a 1-2 Mbar shock preconditions the capsule
wall before the main implosion pulse. Continuum mechanical
simulations of the microstructural response have shown that,
under certain conditions, the anisotropic behavior of
beryllium can seed Rayleigh-Taylor instabilities
irrespective of surface smoothness. We will perform
experiments to shock and accelerate planar and wedged
beryllium samples using a 180-eV gold wall halfraum. This
talk will present the experiment design and initial results
from Omega laser experiments, where we have tested drive and
diagnostic techniques.
[RP1.130] Microstructure, Shock Waves, and Stability: The Initiator of Mixing?*
Nelson M. Hoffman, James A. Cobble, David L. Tubbs, Damian C. Swift, Thomas E. Tierney (Los Alamos National Laboratory)
Many metals are anisotropic polycrystals, especially in their initial state. In some applications [e.g. fusion capsule implosions at the National Ignition Facility (NIF)], the first shock traveling through the capsule's ablator could have an intensity (\sim 1 Mbar) that is in the regime where anisotropic strength has important effects. Recent discrete- element simulations* show that shock waves traveling through an anisotropic microstructure generate strong fluctuating velocities behind the shock. To investigate whether such flow fields can seed ablative Rayleigh-Taylor instability in NIF capsules with beryllium/copper ablators, we will carry out experiments at the Omega laser in which we shock and accelerate planar beryllium(0.9 % copper) samples in an indirect- drive hohlraum. Face-on x-radiography will reveal the extent to which perturbations appear and grow in the samples. Our first experiments, scheduled for July 2003, will use intentionally perturbed samples in feasibility tests.
*Y. Horie and K. Yano, LA-13936-MS, May 2002
[RP1.131] Calibration of Numerical Simulations to Initial Experiments for Assessing the Effects of Material Properties in Ignition-Capsule Designs
David Tubbs, Nelson Hoffman (Applied Physics Division, Los Alamos National Laboratory)
Hoffman* discusses our motivation to assess empirically the effects of anisotropic material properties on the stability of capsule ablators planned for the National Ignition Facility. Of specific concern is the possibility that the polycrystalline microstructure of beryllium (with copper admixtures) will provide the seed for Rayleigh-Taylor instability growth. In July 2003, we conduct initial, indirect-drive experiments using the OMEGA laser at the University of Rochester to qualify our hohlraum and laser-pulse designs and experimental diagnostics. Subsequent experiments will attempt to determine the extent to which beryllium microstructure can be represented by an equivalent surface perturbation. We discuss the calibration of numerical simulations to data from the initial experiments.** Specifically, we assess the hohlraum temperature data and the impact of hohlraum radiation on radiographic imaging of the beryllium-copper samples.
* Nelson M. Hoffman, et al., “Microstructure, Shock Waves, and Stability: The Initial Conditions Leading to Mix,” submitted to this conference.
** T. E. Tierney, et al., “Experimental Design for Studies
of Beryllium Ablator Microstructure,” submitted to this
conference.
[RP1.132] NEW ICF/HEDP Target Development
Tom Walsh, Diana Schroen (Schafer Corporation), Abbas Nikroo (General Atomics), John Varadarajan (Schafer Corporation)
The GA/Schafer team has produced targets for Inertial
Confinement Fusion (ICF) and High Energy Density Physics
(HEDP) programs for over ten years. During that time we have
seen requirements for targets change significantly, nearly
always toward more complexity, new materials, and increased
requirements for precision. Sometimes, completely new
materials or assembly techniques are required for new types
of targets. Additionally, characterization requirements have
increased as diagnostic capabilities have improved. When new
materials and target geometries are developed, they often
require new characterization capabilities rather than
improvements in existing capabilities. This poster will
describe GA/Schafer experience with respect to the time
required to develop new HEDP and ICF targets. Factors that
affect development time are complexity of the targets,
assembly requirements, material development, and
characterization. We examine each factor for various types
of targets, in each case considering the entire development
cycle from pre-order discussions between experimenters and
target fabricators to target delivery. The targets that we
will examine include SNL Capsule Implosion Targets, NRL EOS
Targets, NRL Patterned Foam, LLE Doped Foil, and LLE Shells.
These targets each involved one or more of the factors
enumerated above and are useful to demonstrate the way these
factors affect development time. Because the time between an
experimenter’s request and the fabricator’s delivery can be
over a year in extreme cases, it is very important that the
target fabricator becomes involved as early as possible in
the experiment design process. We will also present ways
that the experimenter/modeler/target fabricator team can
reduce the time required bring a target from idea to
hardware.
[RP1.133] Michigan Target Fabrication Facility for High Energy Density Experiments
K.K. Dannenberg, R.P. Drake, A.B. Reighard, C.K. Kuranz, D.J. Kremer, R. Gabl, M. Grosskopf, P. Susalla, E.C. Harding, E. Roesler (University of Michigan), Joe Riley (Newport Corporation)
Target fabrication is essential for high energy density
experiments and is a good educational experience for
students. The Michigan experimental astrophysics group has
designed and constructed a modern laboratory facility to
fabricate and metrologize targets. The Michigan station
allows for both metrology and fabrication at one station.
Using three systems of stages, targets are constructed and
measured. System one, the component manipulator system, uses
seven motorized stages to place targets and components in
specific locations with respect to a spherical and Cartesian
coordinate system. System two uses four motorized stages to
hold target pieces at specific locations and angles. System
three is a gluing system. We describe how this system was
designed, constructed, and used for target fabrication and
metrology in recent experiments. Work at Michigan supported
by the U.S. Department of Energy under grants
DE-FG03-99DP00284, DE-FG03-00SF22021, and other grants and
contracts.
[RP1.134] Propagation of an intense 0.527~\mum laser pulse through an underdense aerogel target
K.B. Fournier, L.J. Suter (Lawrence Livermore National Laboratory, Livermore, CA 94550), M. Stevenson, G. Slark, K. Oades (AWE, Aldermaston, UK), G. DiPeso (Lawrence Livermore National Laboratory, Livermore, CA 94550)
We have measured the propagation of 2ømega (0.527 \mum)
laser light in underdense aerogel targets at the HELEN laser
(AWE). Our targets were 2~mm long SiO_2 foam cylinders
that had a fully ionized density of 0.07n_crit
(n_crit = 4.4\times10^21 cm^-3 for
2ømega). The targets were irradiated with one beam of the
HELEN laser with energies of 200--400 J in 1~ns square
pulses. Spot sizes ranged from 40~\mum at best focus to
500~\mum, phase plates were used to smooth the beam
intensity. The resulting intensities on target were
1.5\times10^14--2.8\times10^16 W/cm^2. The
axial propagation of the laser beam, as given by Si K-shell
x-ray emission (h\nu \sim~1.7keV), was observed with a
differentially-filtered framed x-ray imager (FXI); pinhole
size was 10~\mum, and time resolution was
\approx~200~ps. In addition, backscattered energy (SBS and
SRS) was measured with streaked spectrometers, and hot
electrons and energy transmitted through the target were
also measured. Temperature in the target is estimated by
either Thomson scattering of the 2ømega beam or from the
Si K-shell spectrum. Results are analyzed versus laser
filamentation parameter, Q = I\lambda^2(n_e/n_
crit)(3/T_e). This work was performed under the auspices
of the U.S. Department of Energy by University of California
Lawrence Livermore National Laboratory under contract No.\
W-7405-Eng-48.
[RP1.135] Comparison between delocalization and beam deposition models for thermal electron transport
Denis Colombant, Wallace Manheimer (Plasma Physics Divison, Naval Research Laboratory, Washington, DC 20375), Michel Busquet (ARTEP Inc., Columbia, Md 20145)
Delocalization models have been around for 20 years now and have not yet replaced the widespread use of thermal conduction flux-limiters in radiation-hydrodynamic codes for laser target studies. We have recently proposed a beam deposition model^1 which looks promising and would also bridge the gap between a full Fokker-Planck calculation and a flux-limiter treatment. We present here results from a comparison between a delocalization model^2 and our beam deposition model for several cases involving implosion calculations.
[RP1.136] Electric Propulsion, Plasma Thrusters
[RP1.137] Ion Heating Experiments in a Supersonic Plasma Flow for an Advanced Plasma Thruster
Akira Ando, yohei Hosokawa, Motoi Hatanaka, Tsuyoshi Yagai, Hiroyuki Tobari, Kunihiko Hattori, Masaaki Inutake (Department of Electrical Engineering, Tohoku University)
In the Variable Specific Impulse Magnetoplasma Rocket
(VASIMR) project in NASA, the combined system of the ion
cyclotron heating and the magnetic nozzle is proposed to
control a ratio od specific impulse to thrust at constant
power. By now, few attempt of a direct ion heating for fast
flowing plasma by waves has been done. Ion heating in a fast
flowing plasma might be difficult because of the short
transit time for ions to pass through a heating region only
once and the modification of ion cyclotron resonance due to
the effect of Doppler shift. Ion heating experiments are
performed in a fast flowing plasma produced by
Magneto-Plasma-Dynamic Arcjet (MPDA) operated with an
externally-applied magnetic field. RF waves with an ion
cyclotron range of frequency is excited by a pair of loop
antennas or a helical antenna. An increase of plasma stored
energy measured by a diamagnetic loop coil is observed when
the waves are excited with various azimuthal mode numbers in
several magnetic nozzle configurations. It is most effective
to heat ions to excite the waves with an azimuthal mode
number of m=\pm1. Dispersion relations of the propagating
wave are obtained and compared with theoretical ones.
[RP1.138] Early Results of ICRH Experiments in VX-10
F. R. Chang-Diaz, J. P. Squire, A. V. Ilin, A. J. Petro, V. Jacobson, G. McCaskill, A. G. Tarditi, D. S. Winter (Advanced Space Propulsion Laboratory, NASA Johnson Space Center), R. D. Bengtson, B. N. Breizman (University of Texas at Austin), F. W. Baity, M. D. Carter (Oak Ridge National Laboratory), P. Colestock, M. Light (Los Alamos National Laboratory), E. A. Bering (University of Houston), T. W. Glover (Rice University), C. Davis (University of Michigan), D. G. Chavers (NASA Marshall Space Flight Center)
The Variable Specific Impulse Magnetoplasma Rocket (VASIMR)
is an open-ended RF-heated propulsion concept currently
under development by NASA. Current experiments (VX-10) focus
on the demonstration of significant ion acceleration by ion
cyclotron resonance. Theoretical and plasma simulation
predictions are used to define the parameter space of
interest in these experiments. Early results show
significant ion energy absorption with concomitant plasma
acceleration and agree well with predicted values. Plasma
diagnostics include Mach, triple, RF and emissive probes, a
momentum sensor, retarding potential analyzers, a
spectrometer and a 70GHz microwave interferometer. An array
of thermocouples monitor heat deposition to the walls of the
discharge tube. A baratron sensor and a fast ion gauge
provide time-tagged background pressure. Early results from
these diagnostics will be presented and discussed.
[RP1.139] ICRF Plasma Loading Comparison of Calculations to Measurements in VX-10
J. P. Squire, F. R. Chang-Diaz, A. V. Ilin, V. T. Jacobson, T. W. Glover, G. E. McCaskill (Advanced Space Propulsion Laboratory, NASA Johnson Space Center), F. W. Baity, M. D. Carter, R. H. Goulding (Oak Ridge National Laboratory)
The VASIMR propulsion concept accelerates ions using ion
cyclotron resonance. ICRF power is applied to an antenna on
the high field side of the fundamental resonance. The
antenna is designed to launch the Ion Cyclotron Wave (ICW)
primarily downstream to the resonance in the flowing plasma.
Such an antenna has been installed in the VX-10 experiment
for low power testing on a flowing helicon discharge with a
high degree of ionization. Plasma loading measurements at
about 2 MHz are made with a tuned resonant high Q circuit
and an HP network analyzer. Measurements with up to 1.5 kW
of applied power are also made. Plasma conditions are held
constant from shot-to-shot while the tuned frequency is
scanned. This scan is repeated for several different
parameters, e.g. magnetic field strength, magnetic polarity,
discharge species (D2, He and Ar), and plasma density.
Results from a reduced order calculation agree well with
experiment and illustrate the significance of the Doppler
shift. Measured plasma loading as compared to calculation
will be presented and discussed.
[RP1.140] Spectroscopic measurements on VX-10
E. Sciamma, C. Lee, R. D. Bengston (University of Texas at Austin), F. R. Chang-Diaz, V. T. Jacobson, T. W. Glover, J. E. McCoy, J. P. Squire (Advanced Space Propulsion Laboratory, NASA Johnson Space Center)
We have spectroscopic measurements of VX-10 in the visible
and near IR spectral region at several locations in a helium
fueled helicon discharge. The He II line is weak. Trace
impurities are carbon, oxygen, and hydrogen. Temperature
measurements at several locations along the axis of the
discharge will be presented
[RP1.141] MHD Simulation of Plasma Flow through the VASIMR Magnetic Nozzle
A. G. Tarditi, J. V. Shebalin (Advanced Space Propulsion Laboratory, NASA Johnson Space Center)
The VASIMR (Variable Specific Impulse Magnetoplasma Rocket, [1]) concept is currently in the experimental development phase at the Advanced Space Propulsion Laboratory, NASA Johnson Space Center. The current experimental effort is mainly focused on the demonstration of the efficient plasma production (light ion helicon source, [2]) and energy boosting (ion cyclotron resonance heating section). Two other critical issues, the plasma detachment process and the collimation of the plasma plume in the magnetic nozzle, are essential for the near term experimental development and are being addressed through an MHD simulation modeling effort with the NIMROD code [3,4]. The model follows the plasma flow up to few meters from the nozzle throat: at that distance the plasma exhaust parameters reach values comparable with the ionospheric plasma background [5]. Results from two-dimensional simulation runs (cylindrical geometry, assuming azimuthal symmetry) aimed in particular at testing the effectiveness of different open-end boundary condition schemes are presented.
[1] F. R. Chang-Diaz, Scientific American, p. 90, Nov. 2000
[2] M. D. Carter, et al., Phys. Plasmas 9, 5097-5110, 2002
[3] http://www.nimrodteam.org [4] A. Tarditi et al., 28th
Int. Electric Propulsion Conf., IEPC 2003, Toulouse, France,
March 2003 [5] A. V. Ilin et al., Proc. 40th AIAA Aerospace
Sciences Meeting, Reno, NV, Jan. 2002
[RP1.142] Characterization of Plasma in a Miniaturized Cylindrical Hall Thruster
A. Smirnov, Y. Raitses, N.J. Fisch (Princeton University Plasma Physics Laboratory)
Conventional annular Hall thrusters become inefficient when scaled to low power. Their lifetime decreases significantly due to the channel wall erosion. Cylindrical Hall thrusters that have lower surface-to-volume ratio and, thus, seem to be more promising for scaling down, exhibit performance comparable with conventional annular Hall thrusters of the similar size [1,2]. Plasma potential, ion density, and electron temperature profiles were measured inside the 100 W cylindrical Hall thruster (channel outer diameter 2.6 cm) with the use of stationary and slow movable emissive and biased Langmuir probes. Potential drop in the 100 W cylindrical Hall thruster is localized mainly in the cylindrical part of the channel and in the plume, which suggests that the thruster should suffer lower erosion of the channel walls due to fast ion bombardment. Plasma density has a maximum of about (2.6\sim3.8)x10^12cm^-3 at the thruster axis. At the discharge voltage of 300 V, the maximum electron temperature is about 21 eV, which is not enough to produce multiple ionization in the accelerated flux of Xe+ ions [3]. This work was supported by grants from AFOSR and DARPA.
[1] Y. Raitses and N.J. Fisch, Phys. Plasmas 8, 2579 (2001).
[2] A. Smirnov, Y. Raitses, and N.J. Fisch, J. Appl. Phys.
92, 5673 (2002). [3] A. Smirnov, Y. Raitses, and N.J. Fisch,
J. Appl. Phys. 94, 852 (2003).
[RP1.143] Regime of electron temperature saturation in Hall thrusters with ceramic walls
Yevgeny Raitses, David Staack, Nathaniel Fisch (Princeton Plasma Physics Laboratory, Princeton, NJ 08543)
A discharge voltage threshold has been observed in a
laboratory Hall current plasma thruster. This threshold
separates two different plasma regimes of the thruster.
Below this threshold, which in our experiments was 400 V,
the length of the closed electron drift region is
insensitive to the voltage but the maximum electron
temperature increases linearly with the voltage. Above this
threshold, the electron temperature saturates and the drift
region expands. This behavior at high discharge voltages
appears consistent with predictions of the charge-saturated
sheath regime due to strong secondary electron emission from
ceramic walls of the thruster channel. The dominant
mechanisms of the electron mobility and electron energy
losses are likely different in these two regimes. For
example, a role of the secondary electron emission appears
to be less important below the measured threshold.
[RP1.144] Basic Energy Equation for Hall Thrusters
David Staack, Yevgeny Raitses, Nathaniel J. Fisch (Princeton Plasma Physics Laboratory)
In the PPPL 2kW laboratory Hall Thruster, the plasma
potential and electron temperature was deduced from emissive
and cold floating probe potential profiles. These
measurements were obtained with only small probe-induced
perturbations for discharge voltages in the range of 200V to
600V. The electron temperature gradient appears to scale
with the electric field in the thruster's acceleration
region and the near field plume. This relationship suggests
an energy loss term proportional to the electric field,
independent of any effect of the channel wall. These results
raise questions regarding the mechanism of energy balance in
magnetic layer Hall thrusters.
[RP1.145] Investigation of Fluctuation-Induced Electron Transport in Hall Thrusters with a 2D Hybrid Code in the Azimuthal and Axial Coordinates
Eduardo FERNANDEZ, Noah Borelli (Eckerd College, Saint Petersburg, Florida), Mark Cappelli, Nicolas Gascon (Stanford University, Stanford CA.)
Most current Hall thruster simulation efforts employ either
1D (axial), or 2D (axial and radial) codes. These
descriptions crucially depend on the use of an ad-hoc
perpendicular electron mobility. Several models for the
mobility are typically invoked: classical, Bohm, empirically
based, wall-induced, as well as combinations of the above.
Experimentally, it is observed that fluctuations and
electron transport depend on axial distance and operating
parameters. Theoretically, linear stability analyses have
predicted a number of unstable modes; yet the nonlinear
character of the fluctuations and/or their contribution to
electron transport remains poorly understood. Motivated by
these observations, a 2D code in the azimuthal and axial
coordinates has been written. In particular, the simulation
self-consistently calculates the azimuthal disturbances
resulting in fluctuating drifts, which in turn (if properly
correlated with plasma density disturbances) result in
fluctuation-driven electron transport. The characterization
of the turbulence at various operating parameters and across
the channel length is also the object of this study. A
description of the hybrid code used in the simulation as
well as the initial results will be presented.
[RP1.146] Experimental Study of the Anode Sheath in Hall Thrusters
Leonid Dorf, Yevgeny Raitses, Nathaniel Fisch (Princeton Plasma Physics Laboratory)
An interesting phenomena observed in the near-anode region
of a Hall thruster is that the anode sheath changes from
negative to positive, at the same thruster operating
conditions, after the thruster has been operating for a long
time. It is expected theoretically that the anode sheath is
a function of thruster operating conditions. However, the
observed behavior of the anode sheath is likely to be
associated with a dielectric coating, which appears on the
anode surface in the course of operation. Preliminary
measurements of discharge current oscillations indicate that
thruster operation becomes more stable when the anode sheath
is positive. The effect of the anode collecting surface area
on the anode sheath and stability of thruster operation were
studied experimentally using biased and emissive probes.
This work was partially supported by the US DOE under
contract No. DE-AC02-76CH03073.
[RP1.147] ECE Radiation Analysis of the Hall Thruster
M. Kim, G.A. Hallock, J.C. Wiley (The Univ. of Texas at Austin)
The Hall thruster is a plasma propulsion device being
developed for stationkeeping and orbit transfer of
geosynchronous communication satellites. Recently [1],
measurements on a Hall thruster being qualified for flight
identified strong electromagnetic emission in the 1-5 GHz
range. We have identified this radiation as
electron-cyclotron emission(ECE). Several broad peaks with
harmonic relationship occur. The ECE frequency is similar to
satellite communication frequencies(1-20GHz), so the ECE
radiation may interfere with the communication signal. These
emissions were more than 20 dB above MIL-STD 461E, and 40 dB
above spacecraft designers limits. To predict the effect of
the plasma on the various subsystems and mitigate risk
associated with introducing of the Hall thruster, the
analysis of ECE radiation is performed with the magnetic
field, plasma density, and plasma electron temperature.
Preliminary results are consistent with the experimental
measurements. In addition a simulation code for ECE
radiation annlysis is being developed with finite element
analysis to predict the effect of the radiation for a given
thruster and satellite geometry. [1] E.J. Beiting, et al.,
IEPC-03-129.
[RP1.148] Asymmetry of Zeeman Peaks in MNX
Xuan Sun, E.E. Scime (Physics Department, West Virginia University), Mahmood Miah, S.A. Cohen (Princeton Plasma Physics Laboratory)
A steady-state argon plasma, produced by a helicon antenna
in a 0.6-m long, 15-cm dia. chamber in a Helmholtz
magnetic-field geometry, exits the chamber through a
co-axial magnetic nozzle coil with 1-cm bore hole and enters
a Pyrex tube termed the expansion region (ER). Laser-induced
fluorescence (LIF) measurements in the ER shows two
co-existing ion populations, one with directed supersonic
(\sim 30 eV) flow, the other with a thermal ( \sim 1 ev)
distribution. Due to the Zeeman effect caused by the
magnetic field, the observed Doppler-shifted LIF lines are
further split, into minus and plus \sigma components. The
\sigma minus and plus amplitudes are equal for the thermal
ion population and independent of field strength and
distance from the nozzle coil. In contrast, a \sim 50%
asymmetry appears for the supersonic ion beam. The asymmetry
strongly depends on the magnetic field of nozzle but has no
clear relation to neutral pressure or magnetic field in main
chamber. Furthermore, the measured FWHH of -\sigma and
+\sigma peaks are also not equal. Possible mechanisms for
the asymmetry are discussed. This work was supported by DOE
contract No. DE-AC02-76CHO3073.
[RP1.149] Increasing Mass Flow Rate in the Magnetic Nozzle Experiment
Mahmood Miah, S.A. Cohen (Princeton Plasma Physics Laboratory), Xuan Sun, E.E. Scime (West Virginia University)
Langmuir probes, microwave interferometry, laser-induced
fluorescence, and gas pressure gauges are used to diagnose
the plasma in the main plasma formation region and expansion
region of the Magnetic Nozzle Experiment (MNX). The
dependence of plasma parameters in both regions of MNX is
studied as functions of main and nozzle magnetic-field
strengths, RF power, and neutral-gas pressure, in order to
increase the total mass flow rate from the main region into
the expansion region at maximum specific impulse. This work
was supported by DOE contract No. DE-AC02-76-CHO-3073.
[RP1.150] Plasma fluctuations in an MPD thruster
Mario Bagatin, Matteo Zuin, Carlo Regnoli (Dipart. Ing. Elettrica, INFM), Vanni Antoni, Roberto Cavazzana, Gianluigi Serianni, Monica Spolaore, Nicola Vianello (Consorzio RFX), Fabrizio Paganucci, Paola Rossetti, Mariano Andrenucci (Centrospazio), Dipart. Ing. Elettrica Team, Consorzio RFX Collaboration, Centrospazio Collaboration
An investigation of magnetic and electrostatic turbulence
has been carried out on an MPD thruster with an externally
applied magnetic field. Several arrays of Langmuir probes
and magnetic field coils have been inserted in the plasma
plume and inside the thruster close to the cathode. The
investigation has been performed in a wide range of external
magnetic field strengths (from 0 to 100 mT) and in a range
of arc currents from 2 to 8 kA. It shows that the
fluctuation amplitude increases with the external magnetic
field strength. The degradation in the thrust performance,
which is known to characterize this kind of thrusters at
high power, is found to be related to plasma turbulence. A
further consequence of the application of the external field
is the appearance of a pulsing m=1 mode in the azimuthal
direction at the higher values of the electric power of the
MPD thrusters. The frequency of this mode increases almost
linearly with the arc current and its phase velocity results
very close to the Alfvén velocity. The properties of
magnetic and electrostatic turbulence are found in agreement
with the hypothesis of an Alfvénic nature of these
instabilities.
[RP1.151] Evaluation of Electromagnetic Force and Magnetic Laval Nozzle Acceleration in an Applied-Field MPD Thruster
Hiroyuki Tobari, Ryuichi Sato, Kenji Harata, Kunihiko Hattori, Akira Ando, Masaaki Inutake (Department of Electrical Engineering, Tohoku University)
A magneto-plasma-dynamic thruster (MPDT) is expected as one
of the promising electric propulsion systems owing to
features of a relatively large thrust, high specific impulse
that is unattainable by conventional chemical or nuclear
propulsion required for space missions such as a manned Mars
mission. To clarify the electromagnetic acceleration
mechanism of a plasma flow in an applied-field MPDT,
detailed flow field and electromagnetic force field are
evaluated experimentally with spectroscopic technique and
magnetic probe array. It is found that an axial drag force
generated by an interaction between azimuthal plasma current
and radial magnetic field cancels an acceleration force in a
uniform magnetic field. A thermal energy component is much
larger than a flow energy component in Bernoulli's equation
and ion acoustic Mach number is limited less than unity in
the muzzle region of MPD arcjet. In order to convert the
thermal energy to the flow energy, magnetic Laval nozzle
acceleration with a local magnetic coil is attempted. The
ion Mach number after passing through the nozzle throat
exceeds unity and a production of supersonic plasma flow is
achieved. An optimum magnetic nozzle configuration is
discussed with the experimental results.
[RP1.152] New Ideas for Confined Alpha Diagnostics on ITER
R.K. Fisher (General Atomics)
Understanding the dynamics of a burning plasma will require development of adequate alpha particle diagnostics. Three new approaches to obtain information on the confined fast alphas in ITER are proposed. The first technique measures the energetic D and T charge exchange (CX) neutrals that result from the alpha collision-induced knock-on fuel ion tails undergoing electron capture on the MeV D neutral beams planned for heating and current drive. CX neutrals with energies >1\,,MeV would be measured to avoid the background due to the large population of injected beam ions. The second technique measures the energetic knock-on neutron tail due to alphas using the lengths of the proton recoil tracks produced by neutron collisions in the film. The range of the 14 to 18 MeV recoil protons increases by \sim400 microns per MeV. The third approach would measure the CX helium neutrals resulting from confined alphas capturing two electrons in the ablation cloud surrounding a dense gas jet that has been proposed for disruption mitigation in ITER. Jet Charge Exchange (JCX) could allow measurements in the plasma core, while the Pellet Charge Exchange (PCX) technique that provided much of the data on confined alphas in TFTR, will likely be limited by pellet penetration to measurements outside r/ a\,, \sim\,,0.5 in ITER.