Session BP1 - Poster Session I.
POSTER session, Monday morning, October 29
Exhibit Hall B,

[BP1.001] Transport Modeling

[BP1.002] Dynamic Evolution of Electron and Ion Channel Transport Barriers

A wide variety of magnetic confinement devices have seen transitions to an enhanced confinement regime. A simple model incorporating the nonlinear interactions between the turbulent fluctuations and the sheared radial electric field coupled to a transport model is able to capture much of the observed dynamics. Adding to this simple model an evolution equation for electron fluctuations, such as a simple ETG model, one can investigate the interaction between the formation of the standard ion channel barrier and the somewhat less common electron channel barrier. It is found that the barrier formation in the electron channel is even more sensitive to the alignment of the various gradients making up the sheared radial electric field then the ion barrier is. The electron channel heat transport is found to significantly increase after the formation of the ion channel barrier but before the electron channel barrier is formed. This increased transport is important in the barrier evolution. The electron dynamics, added to evolving flows and beam deposition, allows a wider variety of dynamics to be investigated and more initiation/control schemes to be explored.

[BP1.003] Model for L-H transitions based on finite beta drift waves including transport

A set of equations is derived that describes the slow and fast evolution of a tokamak plasma, for finite \beta drift waves. We follow an approach described before [1] in which the relevant equations are first separated in axisymmetric and fluctuating parts and then transformed to a twisted flux-tube geometry. This reduces the problem to 2D. The fast equations, which have been shown to predict the L-H transition threshold [2] for several experiments, are coupled to the slow equations which describe the transport. In this way it is possible to relate this threshold, which is given in terms of the mode parameters \alpha_MHD and \alpha_D that meassure ideal stability and diamagnetic effects, respectively, to the quatities that are experientally controlled and determine the transition. The full system of equations are numerically solved to get a self-consistent description of the L-H transition.

[1] J.J. Martinell, P.N. Guzdar, A.B. Hassam, Phys.\ Plasmas 5, 1273 (1998) [2] P.N. Guzdar et al., Phys.\ Rev.\ Lett. 87, 15001 (2001)

[BP1.004] Theory of the Enhanced Reverse Shear Transition in a Tokamak

A model for transition to the enhanced reverse shear (ERS) or negative central shear (NCS) mode triggered in tokamaks is proposed. This model takes into account the linear and quasilinear behaviour of the ion temperature gradient (ITG) drived perturbation, considered nowadays as the dominant source of anomalous energy losses in the low confinement (L) mode, in the presence of a radially varying parallel velocity. Analytic and numerical studies show that when the magnetic shear has the same sign as the second derivative of the parallel velocity with respect to the radial coordinate, the linear mode may become more unstable and turbulent momentum transport increases. On the other hand, when the magnetic shear has the opposite sign to the second derivative of the parallel velocity, the linear mode may be completely stabilized and turbulent momentum transport reduces.

[BP1.005] Profile Characteristics of H-mode and ITB Tokamak Plasmas

Profile characteristics of tokamak plasmas with transport barriers have been studied under the constraint of the conservation of the total angular momentum. The first results were reported at the 18th IAEA Conference and the 42nd DDP meeting [1]. In those studies, profiles corresponding to the internal transport barriers were well described, but theoretically predicted profiles had a tendency to stay high near the edge region compared to the actual experimental data. This created some difficulty to fit H-mode profiles. This situation has been improved by examining a more generalized constraint of the conservation of the total angular momentum. In this paper, we show the generalized constraint and the improved comparison between theoretical profiles and experimental profiles including H-mode. [1] Paper CN-77 TH4/3 presented at the 18th IAEA Fusion Energy Conference (Sorrento, Italy, October 2000). To be published in Nuclear Fusion. Bull. Am. Phys. Soc. 42, 337 (2000). * Former member of the Plasma Research Center, University of Tsukuba

[BP1.006] H-mode power threshold, grad-B drift direction and ion collisionality

An explanation on the dependence of the H-mode power threshold on the direction of the grad-B drift in diverted tokamaks is presented in the context of the H-mode theory based on the orbit loss and the subsequent turbulence suppression. Here, B is the magnetic field strength. It is shown using the results of a numerical calculation [ A. V. Chankin and G. M. McCracken, Nucl. Fusion \bf10, 1459(1993)] that ion collisionality that defines the onset of the orbit loss depends on the direction of the grad-B drift. The connection length is shorter when grad-B drift is toward the X-point than away from it. Judging from the sensitivity of the power threshold on the grad-B drift direction, we conclude that power threshold must be a simple function of ion collisionality among other dimensionless parameters.

[BP1.007] Potato transport flux in cylindrical coordinates

It is known that the flux surface and radial averaged potato heat flux is finite in the flux coordinates in the near-axis region in tokamaks. When it is converted to the cylindrical coordinates, an incorrect (1/r) dependence is usually obtained. This mistake is resulted from taking the |grad-Psi| out of the radial average unaltered, where Psi is the poloidal flux function. Indeed, when the radial average is properly handled, the potato heat flux is finite. A 'local' potato heat flux is presented for the radius less than the potato width.

[BP1.008] Transport process in the vicinity of magnetic islands

It is shown that in the vicinity of magnetic islands, the toroidal symmetry of the equilibrium magnetic field strength B is broken in tokamaks due to the finite width of the islands. The magnitude of the broken symmetry is of the order of sqrt(delta-B/B) with delta-B the perturbed magnetic field strength. This leads to enhanced plasma transport. Symmetry breaking induced transport flux in the collisionless regime in tokamaks with islands is calculated.

[BP1.009] Impurity Transport in Low Collisionality Tokamaks

For a plasma in which the principal ion species may be in a low collisionality regime, moderately high Z impurities are likely to be in a neoclassical regime. With modest electric fields present, the impurities may also have relatively large mean flow velocities. Since the low collisionality and neoclassical expansions are different, the analysis of a multispecies plasma with such impurities involves a new set of issues. The system will be examined to determine the extent to which impurities affect the energy balance of the system and to obtain the equations that characterize the impurity density distribution. The effect of the impurities on the electrostatic potential will also be considered.

[BP1.010] Transient transport analysis based on transport-MHD model

The transient response of heat pulse propagation is used to examine the characteristic of anomalous transport in high temperature plasmas. To understand the non-local nature of transport observed in such experiments is a key issue to clarify the mechanism of Bohm transport. Using the reduced MHD model in the cylindrical geometry with 1/R correction of the toroidal magnetic field, the heat pulse propagation is examined. The heat pulse is applied in the central region of quasi steady state plasma and the subsequent response is analyzed. It is found that the heat energy applied in the central region is converted into the electric field energy which produces E \times B rotation in the poloidal direction. The combined effect of plasma rotation and local diffusion gives rise to the non-local transport in this model. The effect of toroidal coupling on non-local transport is also investigated and will be reported in detail in this meeting.

[BP1.011] Self-sustained turbulence of current-diffusive ballooning mode and drift instabilities^1

It is important to analyze the turbulent transport phenomena and evaluate the transport coefficients including the current-diffusive ballooning mode (CDBM) and the ion temperature gradient (ITG) mode. We start from two-fluid equations to describe a plasma immersed in the sheared magnetic field, keeping the electron response and including a coupling between the ITG mode and the CDBM. Turbulent transport coefficients derived by renormalizing non-linear terms are included in the fluid equations. We numerically solve the two-fluid equations and Maxwell's equations and obtain the frequency and growth-rate of the eigen mode. The magnitude of transport coefficients in a saturated state are evaluated from the marginal stability condition. The mode structure of CDBM including the finite Larmor radius effect is extensively studied. The contribution of ion and electron temperature gradient will be reported in this meeting. *

^1Supported by Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science and Technology, Japan

[BP1.012] Anomalous Diffusion and Exit Time Distribution of Particle Tracers in Plasma Turbulence Model

We have explored the character of transport in two plasma turbulence models near marginal stability. One is the resistive pressure-gradient-driven turbulence model and the other a ion-temperature-gradient-driven turbulence model. We work under subcritical conditions with added noise. Under these conditions, there is evidence of avalanche-like transport. To determine the character of the transport, we have followed the motion of tracer particles. Both the time evolution of the moments of the distribution function of the tracer particle radial positions, \langle \vert r (t) - r (0) \vert^n \rangle, and their finite-size Lyapunov number are used to determine the anomalous diffusion exponent. The numerical results show that the transport mechanism is superdiffusive with an exponent \nu (n) close to 0.88 \pm 0.07. The distribution of the exit times of particles trapped into stochastic jets is also determined. These particles have the lowest separation rate at the low resonant surfaces.

[BP1.013] Small Sample Effects on Information-Theoretic Estimate

Symbolic time-series methods have received some significant attention recently due to their robustness to noise, numerical efficiency, and ability to use low-resolution sensor data. Given a symbolic time-series, one often proceeds to estimate information-theoretic quantities as measures of information content (Shannon Entropy), correlation between two symbolic processes (Mutual Information), and information transfer (transfer entropy[1]). If the dynamical system under study is weakly non-stationary, or the real-time monitoring of the system requires rapid decision making (e.g. early detection of a plasma instability for control purposes), then the amount of symbolic data in the observation window will be severely restricted. In this poster, we examine the problem of estimating these information-theoretic quantities using limited samples of data. \beginthebibliography9 \bibitems T. Schreiber, Phys. Rev. Lett. \textbf85, 461 (2000) \endthebibliography

[BP1.014] Symbolic Cycle Analysis of Turbulent Plasma Fluctuations

The method for computing symbolic cycles distribution function (SCD) is introduced.(M. Lehrman and A.B. Rechester, Phys. Rev. Lett. manuscript accepted for publications.) This method has been applied for the analysis: 1) Langmuir probes fluctuation data (Texas), 2) Mirnov probes magnetic fluctuation data (MIT), 3) Microwave reflectometry fluctuation data (Princeton). Our results demonstrate that approximately the same complex structure of cycles can be computed using time records of different variables. SCD contains information about nonlinear stability of cycles and is much more informative than Fourier spectra.

[BP1.015] Extracting Symbolic Cycles from Turbulent Fluctuation Data

The method for extracting symbolic cycles from the fluctuation data is presented.(M. Lehrman and A.B. Rechester, Phys. Rev. Lett. manuscript accepted for publications.) For the example of the Lorenz model we demonstrate that approximately the same complex structure of cycles can be computed using time records of different variables. Our method has been applied for the analysis of turbulent fluctuations measured in water flow in a pipe. Even though the fluctuations in the bulk of the water and near the wall of the pipe appears to be very different, the majority of the most stable cycles extracted from the data are identical.

[BP1.016] Advantages of Structure Function Analysis to Investigate the Complex Dynamics of Plasma Turbulence

Both SOC-based and standard turbulence-based models have predicted the existence of complex dynamical behavior, such as long-range correlations, that may have a significant impact on cross-field transport in magnetically confined plasmas. Structure Functions (SF's), which have been used previously to investigate the complex dynamics of fluid turbulence and geophysical data, are applied to plasma turbulence data measured using reflectometry techniques. SF's are used to investigate self-similar scalings, long-time correlations (via the Hurst parameter), intermittency (via the singularity spectrum), and multifractality in the plasma fluctuations. The SF method is shown to have advantages in comparison with other methods, such as rescaled range (R/S) analysis, for investigating complex dynamical behavior. In addition, spectral and correlation analysis are applied. Turbulence data are found to exhibit self-affinity, long-time correlations and intermittency, which change character from the plasma core to the edge sheared flow region.

* Supported by the National Science Foundation under grant No. 0078372

[BP1.017] Characterization of self similarity properties of turbulence in

The understanding of turbulence in magnetized plasmas and its role in the cross field transport is still greatly uncomplete. Some previous works relying on high values of the Hurst (H) exponent obtained with the Rescaled Range Statistics (R/S) applied on experimental data in tokamaks concluded to the existence of long range correlations compatible with an avalanche type of radial transport. In this paper we show the limitations of this R/S method when used to compute the H parameter and we put in light the interest of the wavelets decomposition as a tool to characterize the self similarity properties of the experimental signals. The study of modified fractional Brownian motion series allow us to show that the high values of the Hurst exponent measured for long time scales can simply reflect the self similarity properties at small time scales and do not necessarily imply the existence of long range correlations. The results of analysis of turbulence signals measured by Langmuir probes at the edge of different tokamaks will be presented.

[BP1.018] Non-linear Phenomena I

[BP1.019] Supression of coherent interchange modes in a magnetic dipole with

Interchange instabilities excited by energetic electrons trapped by a magnetic dipole nonlinearly saturate with complex spectral characteristics. Since low-frequency interchange instabilities preserve the electron's first and second adiabatic invariant, the wave-particle interaction is described with a two-dimensional phase-space that is directly observable. Electron flux modulations together with numerical simulation illustrate rotating "phase-space holes" that move inward as the mode rotation frequency rises. When monochromatic electric fields are applied near the bounce-frequency of the resonant energetic electrons, the saturation behaviors of the interchange instability change dramatically. For applied fields of sufficient intensity and pulse-length, we observe (1) the suppression of coherent interchange fluctuations, (2) a reduction of radial transport of energetic electrons, and (3) a steepening of the density gradient of confined plasma. Possible explanations include breaking the second adiabatic invariant so as to fill "phase-space holes" and enhancing the plasma density so as to increase the stabilizing polarization current.

[BP1.020] Planned Observation of Rotationally-Driven Interchange Instabilities in a Laboratory Dipole Plasma

Installations to the Collisionless Terrella Experiment designed to cause bulk rotation in the dipole-confined plasma are presented. These installations include a hot-filament bias control system as well as a diagnostic imaging system. The former is designed to alter the plasma’s electrostatic potential, causing azimuthal ExB flows which should excite centrifugally-driven Rayleigh Taylor instabilities. The latter is a 96-point gridded energy analyzer that will diagnose polar currents and particle flux and will be able to reconstruct ‘movies’ of the plasma flows. The equatorial tungsten filament array will enable axisymmetric and nonaxisymmetric radial electric fields and plasma convection. The system will also allow study of instabilities caused by a combination of B field curvature and centrifugal drives simultaneously. In addition, multi-point correlations of floating potential probes will assist in reconstruction of the global mode structure of the flows. Finally, a fully self-consistent numerical simulation will offer comparison with experimental observations of mode structure, plasma flows and instability growth and saturation.

[BP1.021] Electron and Ion Phase Space Holes From Buneman Instabilities in a Current-Driven Plasma

Recent 1-D simulations of a current-driven plasma(D.~L.~Newman, Invited Paper, this meeting) show that a strong local double-layer electric field accelerates electrons into a beam. The resulting two-stream instability produces electron phase-space holes traveling in the direction of the electron beam. In a later stage, after ions have been accelerated in the opposite direction by the same double-layer field, the simulation reveals a train of spatially-alternating electron and ion phase-space holes moving slowly in the direction of the ion beam. We postulate that this alternation results from the trapping of ions and electrons in successive potential minima and maxima of a wave train. The origin of this wave train is likely to be a modified Buneman instability, which can occur only in the presence of cold accelerated ions. This instability is slow because of kinetic effects in the hot electron distribution. By contrast, the initial current is stable to Buneman growth because both the initial ion and electron distributions are hot. Other aspects of Buneman instabilities and effects of higher dimensions are also discussed.

[BP1.022] An accurate structure of Alfven soliton formed by modulational interaction of the Lower hybrid waves with a Kinetic Alfven mode

Auroral observations show strong correlation between localized lower hybrid waves (LHW) and the kinetic Alfven waves (KAW). We propose a model in which the observed localization of LHW is produced by their modulational interaction with KAW. The small density variations associated with KAW act as the potential well for LHW leading to the modulation of their intensity. With the intensity modulation of LHW, the Reynolds stresses are exerted on plasma, leading to formation of dipolar vortex structures in plasma density. In nonlinear evolution of the modulational interaction the two dimensional soliton is formed, in which LHW are trapped. The soliton travels along magnetic field with Alfven speed and has a cross field localized structure with a typical size of the order of electron skin depth (~ 100 m in the auroral conditions). The exact form of the solitary structure is found by numerical solution of the fourth order differential equation for LH potential. Results of calculations are compared with observations.

[BP1.023] Ion Heating and Transport due to Kinetic Alfvén Waves

Compressional waves can mode convert to kinetic Alfvén waves in the presence of gradients in the Alfvén resonance frequency. The resulting kinetic Alfvén wave is amplified and has wavelength the order of the ion gyroradius. We examine particle motion in the presence of a kinetic Alfvén wave and show that above a modest threshold amplitude the particle motion becomes stochastic leading to significant ion heating and plasma transport. Thesholds, heating rates, and diffusion rates are presented and their dependence on wave amplitude, frequency, and background magnetic field profile (rotation and gradient) is examined. Such stochastic heating and transport can be important at the Earth's magnetopause where large amplitude kinetic Alfvén waves (with frequency below the ion cyclotron frequency) are readily excited by compressions in the solar wind/magnetosheath. Particle distributions in the magnetosheath and magnetopause have been observed with energization of the low energy core consistent with stochastic kinetic Alfvén wave heating. Stochastic particle transport can also contribute to the formation of the plasma boundary layer found near the magnetopause.

[BP1.024] Modeling of Landau damping of nonlinear Alfven waves

The envelope evolution of quasi-parallel nonlinear Alfven waves in a small-beta plasma is governed by the Derivative Nonlinear Schroedinger (DNLS) equation that describes their parametric coupling to ion-acoustic-like oscillations. In finite-beta isothermal plasma resonant interaction of the plasma protons with ion-acoustic quasi-modes changes drastically the wave dynamics. Trapping of resonant protons by ponderomotive potential and their bounce oscillations significantly modify their distribution function as well as Alfven wave dynamics. Nonlinear evolution of Alfven wave packet in finite beta plasma is investigated numerically. Two types of nonlinearity are taken into account (i) the weakly nonlinear motion of plasma bulk particles that leads to mode coupling and ion-acoustic quasi-mode formation and (ii) strong nonlinearity of resonant particles that are responsible for the Landau dissipation. The dynamics of nonlinear Alfven wave packet as well as the particle distribution function is studied.

[BP1.025] Viscous MHD Detonation

It has been found previously^1,2 that in ideal MHD plasmas marginally unstable ballooning modes inevitably become ``explosive'' evolving towards a finite time singularity. The effects of finite gyroradius have been shown^3 to effectively block access of the mode from linear to nonlinear instability in certain regions of parameter space, however other regions of parameter space that allow unbounded growth still exist. Like finite Larmor radius effects, finite viscosity may be sufficient to inhibit a nonlinear ballooning mode's tendency to progress to finer spatial scales as nonlinear drives and dissipation compete. In this paper, we use a set of Euler-Lagrange equations, derived from the nonlinear ``detonation'' PDE via a variational technique, to consider the nonlinear stability and dynamics of the viscous MHD ballooning mode. [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.] ^1 S.C. Cowley and M. Artun, Phys. Rep., 283, 185, (1997). ^2 O.A. Hurricane, B.H. Fong, and S.C. Cowley, Phys. Plasmas, 4, 3565, (1997). ^3 B.H. Fong, S.C. Cowley, and O.A. Hurricane, Phys. Rev. Lett., 82, 4651, (19 99).

[BP1.026] Bifurcation Properties of an ITG Instability in Slab Geometry

Using a simple kinetic model, first the onset of the \eta_i-instability is investigated by linear theory. Also a non-local analysis is performed. It turns out that the local approximation is only a very rough approximation which may drastically overestimate the instability conditions. A numerical solution of the full model allows to follow the nonlinear development of the instability. Using a numerical scheme based on the Lagrange structure of the equations of motion, the saturation values are obtained. A constriction of the density profile is accompanied by a broadening of the ion-temperature profile. The normal form of the bifurcation is obtained together with the scaling of the anomalous transport (in terms of the deviation from the marginal condition).

[BP1.027] Plasma Hole as a Localized Structure of Vorticity in a Rotating Magnetized Plasma

Spontaneous formation of a cylindrical density-cavity, or ''plasma hole,'' has been observed in a rotating magnetized plasma. Density of the plasma hole is one tenth of that of ambient plasma, and is bounded by a steep transition layer of the order of several ion Larmor radii. Using a directional Langmuir probe, 2-dimansional flow field on a plane perpendicular to the magnetic field has been experimentally determined, showing a monopole vortical structure with a sink. It is found that the vorticity distribution is localized near the center of the hole, and is identified as a Burgers vortex, which is formed by the balance between convective concentration and viscous diffusion of vorticity. The dissipation of vortical motion due to internal friction has been also determined by evaluating the rate-of-stress tensor. It is found that a dissipation layer presents in the peripheral region surrounding the plasma hole.

[BP1.028] Ducting of high power microwaves in preformed plasma waveguide

The optical guiding of an intense electromagnetic wave is demonstrated with use of high power microwaves in a preformed plasma density channel. The preformed density channel is made by inserting a thin glass strip in plasma acting as a physical boundary, lowering the plasma density near the strip. This will make a favorable density configuration to trap the electromagnetic wave within the channel. The radial width of the channel, which is the width between two spatial locations where plasma density goes to cutoff density for the microwaves, is kept to be the cutoff for the microwaves to enter the plasma waveguide. The high power microwave makes a density duct into overdense area by the ponderomotive force in preformed density channel and is guided along the duct. The parameter dependencies of the plasma channel are demonstrated. The radial distribution of the electric field in the plasma channel is also investigated. The numerical calculations are carried out and the results are in fairly good agreement with the results observed in the present experiment.

[BP1.029] CHARMing Zonal Flows

The Charney-Hasegawa-Mima equation (CHME) is generalized to include zonal flows and used to investigate the nonlinear dynamics of drift waves interacting with zonal flows. Positive definite energy and enstrophy integral invariants of the generalized system are derived. The modulational instability of an initial, small (but finite) amplitude monochromatic pump wave and a zonal flow perturbation, interacting with each other and their two side-bands in a four-wave system is investigated and shown to have a readily satisfied pump threshold depending on the zonal flow wave number. The fully nonlinear CHME is solved numerically, demonstrating the conservation of the two exact invariants. The simulations show the validity of the four-wave model over three instability growth times. Zonal flows can be `jet-like' or `highly corrugated' depending upon the ratio of the system size to the density scale-length. They can also be dramatically reduced when the most unstable wave does not fit into the system.This research was supported by EURATOM, UK DTI, US DOE Grant No. DE-FG02-96ER54370 and the Southeastern Louisiana Univ.

[BP1.030] Self-stabilizing effects in the nonlinear regime of the parallel velocity/tearing instability

Recently, a new parallel velocity instability has been found.(J. M. Finn, Phys. Plasmas), \bf2, 12 (1995) This mode is a tearing mode driven unstable by curvature effects and sound wave coupling in the presence of parallel velocity shear. Under such conditions, linear theory predicts that tearing instabilities will grow even in situations in which the classical tearing mode is stable. The nonlinear regime has been explored using a 2D implicit Newton-Krylov resistive MHD code. Nonlinear results indicate that, for large total plasma beta and large parallel velocity shear, the instability results in the generation of large poloidal shear flows and large magnetic islands even in regimes when the classical tearing mode is stable. The self-generated poloidal shear flow is a stabilizing effect. In the tearing-unstable regime (electromagnetic regime), such poloidal shear flow is found to have little influence on the instability growth rate. However, in the tearing-stable regime (electrostatic regime) the shear flow is in fact able to stabilize the mode. In some scenarios, a sawtooth pattern is observed in which the instability is completely stabilized by the shear flow, decays, and resumes growth once the shear flow weakens.

[BP1.031] Equilibrium and Stability of Self-Organized Electron Spiral Toroids

A cold-fluid model for a self-organized electron spiral toroid (EST) is presented (C. Chen, R. Pakter and D.C. Seward, Phys. Plasmas 8, in press (2001).). In the present model, the electrons are assumed to undergo energetic spiral motion along a hollow torus with a fixed ion background, the electron mean free path is assumed to be long compared with the torus size, and the minor radius of the EST is assumed to be small compared with the major radius. Using this model, the equilibrium and stability properties of the electron flow in the self-organized EST are analyzed. It is found that a class of self-organized EST equilibria exists with or without an externally applied toroidal magnetic field. It is shown that in the absence of any applied toroidal magnetic field, the EST equilibria are stable at high electron densities (i.e., at high toroidal self-magnetic fields), although they are unstable at low electron densities (i.e., at low toroidal self-magnetic fields).

[BP1.032] Autoresonant Pulse Excitation and the Nonlinear Schrödinger Equation

It has been previosuly demonstrated [1] how to excite high amplitude nonlinear phase locked states of the Nonlinear Schrödinger Equation (NLS) using autoresonance (i.e. a spatially non-uniform drive with a frequency chirp). In the present work, we explore the use of a special class of exact solutions [2] of the NLS as "targets" for autoresonant pulse excitation. These solutions have narrow pulse shapes and envelopes which are periodic in time. Potential experimental applications will also be discussed.

[1] L. Friedland and A.G. Shagalov, Phys. Rev. Letters \textbf81,4357 (1998). [2] E.R. Tracy and A.R. Osborne, to be published

[BP1.033] Pulse Formation via Passive Mode-Locking

Pulse formation can arise via passive mode-locking as a consequence of the combined effects of: 1] A spatially localized gain region that can both generate waves via spontaneous emission, and amplify waves which re-enter the region via stimulated emission; 2] cavity resonance effects which select certain wave modes; 3] saturable absorption; 4] dispersive effects. We conjecture that the general concepts concerning pulse formation via passive mode-locking and their stability have application in plasma physics--for example ion cyclotron emissions (ICE) observed in DT plasmas under fusion burn conditions[1]. In previous work, we presented the bifurcation analysis of a simple 1-dimensional, discrete time map that incorporated effects 1-3 listed above. In this poster, we extend the analysis to include the slow background response to the passage of a pulse, and pulse-to-pulse memory effects.

[1] B.Coppi, G. Penn, and C. Riconda, Annals of Physics 261 (1997) 117.

[BP1.034] Nonlinear propagation of two-dimensional gravity wavetrains in MHD

Nonlinear evolution of modulated two-dimensional gravity wavetrains in a conducting fluid subject to a tangential applied magnetic field are considered (D.Rollins and B. Shivamoggi, Phys.Plasmas 8, 2930 (2001)). The effect of the applied magnetic field on the stability of the modulation and on the saturation amplitude in the long-time evolution are examined.

[BP1.035] Perturbed drift solitary-wave propagation

Drift solitary-wave propagation in a slowly-varying configuration is considered. A perturbed regularized long-wave equation is used to model this problem (B. Shivamoggi and D. Rollins: Chaos, Solitons and Fractals, in press (2001)). The perturbed solitary wave does not conserve `mass' so, a tail is introduced of which the near tail portion remedies this `mass' defect, while the far tail portion exhibits a plateau structure.

[BP1.036] Short laser pulses amplification and compression in process of Raman backscattering in plasma inside a capillary

Probably the most prospective way for petawatt and exawatt short laser pulses amplification and compression consists of using the advantages of plasma technology [Malkin, Shvets and Fisch, PRL 82, 4448 (1999)]. Replacing all the major elements of amplification-compression scheme by one element containing fully ionized plasma capable of acting simultaneously as the stretcher, the nonlinear amplification medium and the compressor, is cheaper and more adequate comparing with the extensive development of traditional solid-state devices.

The present report includes the results of numerical and analytical studying of one of the possible amplifier schemes based on the process of Raman backscattering in plasma inside a dielectric (quartz) capillary. It is supposed that the short pulse being amplified and the long pumping pulse, which power is assumed to be less than the critical power of relativistic self-focusing, interact with each other inside plasma of a wide (quasi-optical) capillary. During the process of interaction, preferentially excited is the lowest quasi-optical mode of the short pulse due to the higher level of radiation energy losses through the capillary walls for higher modes. For practical applications, important is the fact that due to the high effective transverse "elasticity" of the mode being amplified, the amplification can be efficient in nonuniform plasmas, too, despite the transverse gradients of plasma density.

Analytical study is based on the variational approach under the assumption that the amplification is taken place in axially symmetric plasma layers in the capillary, and the energy redistribution along the whole mode is carried out by linear and nonlinear dispersion.

[BP1.037] Nonlinear oscillations in radiative plasmas

It shown that nonlinear uniform temperature oscillations may exist in optically thin radiative plasmas. Plasmas consisting of hydrogen and light element ions have been investigated. Because of the finite relaxation time of the charge state distribution, the phase shift of the electron temperature and charge state distribution occures. It leads to the uniform (in space) instability. The mode is stabilised by nonlinear effects. Carbon plasma has been investugated for the temperature range 3-4 eV. Only CII and CIII ions exist in this temperature range. Thus, the set of equations has been reduced to the ordinary differential equation of the second order. The equation is equivalent to the equation describing the Newtonian particle under the external force and nonlinear friction force. The qualitative analysis of the equation is easy. The conditions for the nonlinear steady-state oscillations have been found. The frequency of oscillations is proportional to the plasma density and may be changed from 1 to 1000 000 (1/c). The oscillations may be used for plasma laser excitations.

[BP1.038] On the Radiation of Ion-Sound by a Langmuir solitary wave in inhomogeneous media

When the coupling between Langmuir and ion-sound waves is studied from the point of view of the two-fluid model, it is found that they are described by the Zakharov equations [1]. These are essentially a time dependent Shrödinger equation for the electric field, where the pontential is the deviation of the ion density from the unperturbed value. The latter evolves according to a wave equation forced by the ponderomotive force of the electric field. In the approximation of negligible inertia for the ions, the Zakharov equations reduce to the non-linear Schrödinger equation that is well known to have soliton solutions. In contrast, Zakharov equations have solitary wave solutions, but it has been numerically found that their interaction differs from that of real solitons. Kaw et al. [2] showed that they radiate ion-sound when accelerated in an inhomogeneous ion density. The purpose of this work is to revisit this problem using modern techniques[3].

[1]. V.E. Zakharov, Sov. Phys. JETP, Vol. 35, 908 (1972). [2]. P.K. Kaw, N.L.Tsintsadze and D.D. Tsakhakaya, Proc. 1982. International Conference on Plasma Physics, Göteborg, Sweden, 1982, p. 225. [3]. N.F. Smyth and W.L. Kath, Phys. Rev. E, Vol. 63, 36614

[BP1.039] Electromagnetic solitons in a high temperature electron-positron plasma.

The set of the relativistic hydrodynamic equations for a hot two-species plasma are specialized with the aim of studying the existence of one-dimensional soliton-like spatial distributions of the electromagnetic energy in an electron-positron plasma. The investigation shows that (i) non-drifting bright solitons can exist in a hot plasma, within well defined ranges of plasma temperature; (ii) extremely high electromagnetic energy concentrations are possible in an ultrarelativistic plasma; (iii) the consistent plasma temperature develops strong spatial nonuniformities.

[BP1.040] Bright and dark relativistic solitons in electron-ion plasmas

A set of nonlinear differential equations, which describes the moving relativistic solitons with the ion response taken into account, is investigated analytically and solved numerically. The modifications induced by the ion motion on the soliton structure are analyzed, and it is shown that that depending on the propagation velocity there are bright solitons, dark solitons, and electromagnetic collisionless shock waves. Dark soliton and shock waves solutions occur at low velocities (less or approximately (m_e/m_i)^1/2). In the case of multi-node bright solitons, the effects of the ion dynamics result in the limiting of its amplitude. The constraint on the maximum amplitude corresponds to either the ion motion breaking in low node number case or to the electron trajectory intersection in the case of high node number solitons. The soliton breaking provides a novel mechanism for the ion and electron acceleration in the high intensity laser pulse interaction with plasmas [D. Farina and S. V. Bulanov, Phys. Rev. Lett. 86, 5289 (2001)].

[BP1.041] Is there Hamiltonian Chaos in a Tokamak's Magnetic field?

A vacuum magnetic field in a tokamak can (typically) be expressed as a near-integrable Hamiltonian system. Many have modeled this system using simple area preserving maps of the plane,(R.~Balescu, M.~Vlad, and F.~Spineanu, Phys.\ Rev.\ E 58) 951 (1998). which have exhibited the classical signatures of Hamiltonian chaos. Instead, we study an existing model for an intrinsically nonaxisymmetric tokamak using a field line tracing code that make no assumption about the symmetry of the perturbation spectrum.(T.E.\ Evans, Proc.\ 18th EPS Conf.\ on Controlled Fusion and Plasma Physics, Berlin, Germany, 1991, Vol.\ 15C (European Physical Society, Petit-Lancy, 1992) p.~65.) Using this code, we calculate the ``actual" Poincar\acutee map of the system. We investigate the existence of homo(hetero)-clinic tangles and the transport derived from the map and compare these features to previous models.\par \vskip6pt ^2001 National Undergraduate Fusion Fellow.

[BP1.042] Waves and Shocks

[BP1.043] Propagation of whistler waves in homogeneous and inhomogeneous plasmas

Even after a century of investigation, whistler waves are still a subject of intense research. Laboratory experiments are of particular value to clarify satellite data which is often ambiguous or difficult to interpret. The linear magnetised plasma device VINETA is designed to establish a large (4m long, 40cm diameter) and dense (n_e\le10^19m^-3) plasma with flexible magnetic configuration (max. field B_0=100mT). The experiment is ideally suited to study whistler wave propagation. Two 2D probe positioning systems and 70 flanges provide access to detailed measurements at all important regions within the chamber. This paper reports experiments on the propagation of electron whistler waves under various different conditions: in homogeneous plasmas, in the presence of ambient density gradients, and in plasma with strongly inhomogeneous magnetic field. First experiments on the characteristics of ion whistler waves in single and multicomponent plasmas are also discussed.

[BP1.044] Mode Conversion of Shear Alfven Waves in a Helicon Plasma

Mode conversion of shear Alfvén waves is being investigated in the Auburn Linear Experiment for Space Plasma Investigations (ALESPI). The helicon discharge provides the high-density plasmas necessary to propagate Alfvén waves. The helicon wave used to produce this discharge is launched by a helical twist antennae with 900 W of radio frequency power at 10 MHz into a fill pressure of 9 mTorr of Helium and a background magnetic field of 0.1 T. A chord average density of 6x1018 m-3 across the plasma and a core electron temperature of 5 eV are measured. Shear Alfvén waves are produced in this discharge by means of a 1x10-4 H inductive coil with a resistance of 0.7 W positioned to oscillate the magnetic field perpendicular to the background field lines. The waves are detected by means of a 1x10-3 H inductive coil with a resistance of 30.5 W and through the use of a floating double probe for compressional waves. Mode conversion is initiated through a perpendicular density gradient and a parallel magnetic field gradient relative to the average background magnetic field. Initial investigations have shown shear Alfvén wave propagation along the background magnetic field lines, with a small perpendicular wave vector, causing some spreading of the wave across field lines. We will present investigations of mode conversion of these shear waves to surface compressional waves and attenuation of the waves within the plasma.

[BP1.045] Excitation of Ion-Acoustic-Like Waves by Sub-Critical Currents in a Plasma Having Equal Electron and Ion Temperatures

The effect of a magnetic field aligned plasma flow with a transverse velocity gradient (parallel velocity shear) on the excitation of current-driven ion-acoustic-like waves in a plasma having equal electron and ion temperatures was investigated experimentally in a double-ended Q machine. In agreement with theoretical predictions [V. V. Gavrishchaka, S.B. Ganguli, and G. I. Ganguli, Phys. Rev. Lett. 80, 728 (1998)] the presence of sheared plasma flow substantially reduces the critical electron drift velocity needed to produce the ion-acoustic instability. Preliminary results of experiments investigating the effect of parallel velocity shear on the excitation of the electrostatic ion cyclotron instability will also be presented.

[BP1.046] Study of MHD Effects on Surface Waves in Liquid Gallium

The liquid metal experiment (LMX) at the Princeton Plasma Physics Laboratory has been constructed to study magnetohydrodynamic (MHD) effects on the propagation of surface waves in liquid metals in an imposed horizontal magnetic field. The physics of liquid metal is of interest generally as a regime of small magnetic Reynolds number MHD and more specifically contributes basic knowledge to the applications of liquid lithium walls in a fusion reactor. Surface waves are driven by a wave driver controlled by a PC-based Labview system. A non-invasive diagnostic measures surface fluctuations at multiple locations accurately by reflecting an array of lasers off the surface and onto a screen recorded by an ICCD camera. The real part of the dispersion relation has been measured precisely and agrees well with a linear theory, revealing the role of surface oxidation. Experiments have also confirmed that a transverse magnetic field does not affect wave propagation, and have qualitatively observed MHD damping (a non-zero imaginary component of the dispersion relation) of waves propagating in a parallel magnetic field. Planned upgrades to LMX will enable quantitative measurement of this MHD damping rate as well as experiments on two-dimensional waves and nonlinear waves. Implications to the liquid metal wall concept in fusion reactors will be discussed.

[BP1.047] Ion-ion Instability with Biased Mesh Grid as Boundary Condition

We studied chaotic behavior of ion-ion instability experimentally. It was reported[1] that the system with a certain boundary condition became chaotic. This is interpreted as follows: the boundary condition decreases the degrees of the system's freedom and as a result the turbulent state becomes chaos. However, it is not understood exactly that the boundary condition influences the system. We also reported[2] that the ion-ion instability saturated due to a particle trapping effect. The dynamics of the trapped particles is affected by the amplitude of waves. Therefore it is expected that controlling the bias potential to the mesh grid affect the unstable wave system. Time-series and power spectra were measured for various configurations of bias potentials. It was found that the system with a positively biased mesh grid became more periodic than other case. In the system with a strongly negative biased separation grid, the chaotic oscillation excited in a sheath region was observed. Reference [1] M. Matsukuma et.al.: J. Phys. Soc. Jpn. 69 (2000) 303. [2] M. Matsukuma et.al.: Proc. ICPP2000 1 300.

[BP1.048] Observation of Density Transitions by Voltage Biasing in Cylindrical Magnetized Plasma

Plasma generation and sustainment in the stable conditions in time and space are one of the critical issues in the various fields of plasmas. Bifurcations have been major concerns, in addition to hystereses and mode changes. However, there have been few experiments [1] from a basic viewpoint to study this topic as well as to control the density and rotation profiles (electric field), connected with the transport and structure formation. Here, we report global transition phenomena with reductions of the electron density (bistable system). This was done by the voltage biasing to an inserted electrode of the ten concentric rings in a RF produced, magnetized plasma. Transitions were accompanied by changes such as the floating potential and the bias current, and characteristic-staying time depended on argon fill pressure. Control of the staying time probability was tried and hysteresis loops were found, changing the bias voltage. [1] S. Shinohara et al., Surf. Coat. Technol. 112 (1999) 20; Jpn. J. Appl. Phys. 38 (1999) 4321; Trans. Fusion Technol. 39 (2001) 362; Phys. Plasmas 8 (2001) 1154.

[BP1.049] 3D Wave Collapse in Nonlinear Medium with a Normal Dispersion

New features of 3D wave packets nonlinear dynamics are studied for a medium with normal group velocity dispersion that is described by nonlinear evolution type equation with a hyperbolic spatial operator. It is shown analytically and by computer simulations that wave packets with initial hyperbolic symmetry (of the type of hollow axialy symmetric distributions) are collapsing in the processes of self-contraction and fall to the axis of the packet with a singularity formation (infinite intensity growth) at the wave packet centre. Collapse stabilization due to nonlinear (multiphoton) absorption or refractive index nonlinearity saturation are studied.

[BP1.050] Possibility of Relativistic Electromagnetic Ion Cyclotron Instabilities Driven by MeV Ions

A general relativistic dielectric tensor has been derived by employing kinetic theory. It is shown that the inclusion of relativity gives an extra term in everyone of the nine tensor components. This relativistic term due to gyro-phase bunching is in the same order as that due to conventional real-phase bunching. In fact, the relativistic term and the conventional term are proportional to ( ømega / k_z)^2 and c^2, respectively, in the nine tensor components.

While the relativistic electrostatic ion cyclotron instabilities driven by MeV ions have been studied and proven to be important, the possibility of the relativistic electromagnetic instabilities will be studied through the analysis of the general relativistic dielectric tensor.

[BP1.051] Exact Relativistic Dispersion Functions

Exact relativistic dispersion functions are compared with weak relativistic plasma dispersion functions for n_\parallel=0 (Dnestrovskii functions) for plasmas of fusion interest. Comparisons are made for T_e=10 keV (\mu=m_ec^2/kT_e=51.1) and T_e=25.5 keV (\mu=20). Using hypergeometric functions, K_xx and K_zz are calculated by evaluating a single integral over momentum that includes all harmonics (no sum). Although the integrand is singular, displacing the integration path off the real axis yields an accurate and reliable result. The other dielectric tensor components require either two or three integrals. Comparisons between the exact and approximate results show substantial deviations for modest values of \lambda=k_\perp^2\rho_e^2/2, limiting the weak relativistic results to \lambda\ll1. Similar integral expressions for each individual harmonic are compared with the corresponding weak relativistic result and show the deviations term by term.

[BP1.052] Ion acoustic waves in two-negative ion species plasmas

Ion acoustic waves in multi-ion plasmas including two negative ion species are investigated both numerically and experimentally. Numerically, the kinetic dispersion relation in two-negative ion plasmas is investigated. There are three modes of the ion acoustic waves in two-negative ion plasmas. In an Ar^+-F^--SF_6^- plasma, only one of the three modes is dominant, regardless of the values of the electron and the ion temperatures. In a Xe^+-F^--SF_6^- plasma, on the other hand, two modes can be important for a certain range of the electron-ion temperature ratio. The results also imply the possibility of the coexistence of the fast mode and the slow mode in one-negative ion plasmas. Experimentally, ion acoustic waves are observed in those plasmas using a double plasma device and the results are compared with the theoretical prediction [R. Ichiki et al. J. Phys. Soc. Jpn. 69, 1925 (2000)].

[BP1.053] Multidimensional wave conversion: a ray-based algorithm

We consider the propagation of a linear wave electric field in the tokamak poloidal plane. (Our methods can be generalized to any magnetic field configuration.) When the wave propagates to a conversion region, standard WKB methods must be modified. We have developed a technique for dealing with the conversion process. For each ray incident on the coversion region we monitor (in the 4-dimensional ray phase space) its ray velocity and acceleration. These two vectors define a local plane in which conversion takes place. We match the ray locally to a hyperbola, and monitor the ray hamiltonian in its vicinity. The appearance of a saddle structure in the local hamiltonian is the signature of linear conversion. The optimum hyperbola yields the conversion point and the transmitted ray, while the local hamiltonian provides enough information to construct the local S-matrix (except for the phase of the converted ray). That phase is obtained by projecting the dispersion matrix onto the local polarization vectors.

[BP1.054] Ion Drifts and Density Perturbations Associated With Large Amplitude Shear Alfvén Waves

In the Large Plasma Device at UCLA, the ion drifts and density perturbations associated with large amplitude (B_wave/B_0 \sim 10^-3) shear Alfvén waves have been studied in detail using a diverse set of diagnostics. These include laser-induced fluorescence (LIF), \partial\mathbfB/\partial\mathitt, Langmuir probe measurements of n_e and T_e, and ion saturation current. The waves propagate down the axis of a cylindrical Ar plasma, and great care was taken to record all of the above measurements at the same spatial positions on four cross-sectional planes along the length of the plasma. Two-dimensional LIF was used to make direct time-resolved measurements of T_i and the \mathbfE \times B and polarization drifts. The two drifts are distinguished by their phase relation to \mathbfB \mathit_wave and allow us to compute \mathbfE_\perp (the transverse component of \mathbfE \mathit_wave). E_\parallel is estimated using the appropriate dispersion relation. LIF was also used to measure low frequency drifts associated with density perturbations in comparison with the measured n_e and ion saturation current. Taken all together, the four planes of measurements reveal the comprehensive structure and propagation of the wave as well as a detailed description of the ion motion.

[BP1.055] Possibility of Plasma Heating in Reversed Field Pinches at the Fundamental Ion Cyclotron Resonance.

The method of plasma heating by rf waves at the fundamental ion cyclotron resonance is considered to be ineffective for fusion applications. This method does not work in tokamaks, while it performs better in stellarators and mirror machines. For the later, the better performance is due to a particular magnetic field inhomogeneity. Magnetic field structure in an RFP is significantly different from that in a tokamak. The field is nearly poloidal near plasma surface and it is toroidal on axis. This rapid radial change of the magnetic field direction occurs on the length comparable with the wave length of the launched fast wave. This situation may lead to changes in the wave polarization near the resonance and to plasma heating. We perform full wave calculations in cylindrical geometry to study the applicability of this plasma heating method for an RFP.

[BP1.056] Full wave analysis of ICRF waves and Alfvén eigenmodes in toroidal plasmas

In order to investigate the behavior of ICRF waves and Alfvén eigenmodes in toroidal plasmas, such as tokamaks and toroidal helical devices, we have revised the full wave code TASK/WM to deal with the plasma with three-dimensional inhomogeneity. We solved Maxwell's equation as a boundary-value problem in the flux coordinates and the response of the plasma is described by a dielectric tensor including kinetic effects. First we analyze propagation and absorption of the ICRF waves in LHD plasmas. Parameter dependence of the deposition profile and the power partition rate is studied. The results are compared with experimental observations. Next we analyze the Alfvén eigenmodes both within and below the toroidicity-induced frequency gap in tokamaks. Mode-structure of EPM/RTAE and excitation by energetic ions are studied. The analysis in reversed magnetic shear configuration will be also presented.

[BP1.057] Growth and Staturation of Alfven Cascades

Alfven Cascade Modes arise in magnetic shear reversed tokamaks in the presence of energetic particles. They represent a new energetic particle mode localized around the zero shear point. Here we extend previously developed theory to calculate the growth rate and the damping rate of the mode, due to continuum damping, and we use a near-threshold nonlinear theory to estimate the mode saturation level.

[BP1.058] Krook Collisional Models of the Kinetic Susceptibility

An assessment is made of Krook collisional models used to describe the kinetic behaviour of collective oscillations, i.e., when Landau damping and collisions must be considered, as is the case for Alfven waves. An energy-conserving model [1] developed in 1966 is shown to be identical to a more recent version used in drift-wave stability studies [2]. The inadequacy of the simpler, and more popular, non-conserving model is illustrated. Comparisons are established with recent studies of ion acoustic waves [3] and electron plasma waves [4]. A useful empirical fit is found that corrects the Braginskii susceptibility to incorporate kinetic effects.

1. B. D. Fried, A. N. Kaufman, and D. L. Sachs, Phys. Fluids 9, 292 (1966).

2. G. Rewoldt, W. M. Tang, and R. J. Hastie, Phys. Fluids 29, 2893 (1986).

3. V. Yu. Bychenkov, J. Myatt, W. Rozmus, and V. T. Tikhonchuk, Phys. Plasmas 1, 2419 (1994).

4. C. S. Ng, A. Bhattacharjee, and F. Skiff, Phys. Rev. Lett. 83, 1974 (1999).

[BP1.059] Rayleigh-Taylor instability in plasmas with shear flow

The temporal evolution of the Rayleigh-Taylor instability in plasma with homogeneous shear flow is studied. It is found that shear flow leads to the suppression of the nonlinearly excited perturbations of the electrostatic potential for the value of the velocity shear parameter, which is larger than the ones obtained earlier(N.Chakrabarti, K.H. Spatchek, J.Plasma Physics,59,pt.4,737 (1998)) for the stabilization of the linearly unstable solution. However, even in this case the stabilization of the electrostatic potential is a real physical process not a mathematical artifact. At the same time perturbation of the electron density does not suppressed by flow shear. After the stage of the temporal algebraic growth, oscillations of the electron density perturbations with permanent amplitudes are settled.

[BP1.060] Three dimensional relativistic fluid simulations of the Weibel instability

The Weibel instability is an electromagnetic instability driven by plasma anisotropies, such as electron momentum or temperature anisotropy. It plays a key role in the magnetic field generation in the wake of an ultra-intense, ultra-short laser pulse propagating in an underdense plasma. Recently, much attention has been paied to this instability also in the overdense plasma regime where filaments of currents are observed in large scale 3D PIC numerical simulations. Here we study the evolution of the Weibel instability in the 3D fluid (relativistic) limit in the case of two initially counterstreaming electron beams in order to understand the typical magnetic structures (and the characteristic time and lengthscales) to be expected as a consequence of the development of the Weibel instability. Applicability to the overdense laser-plasma regime is discussed.

[BP1.061] Modification of Plasma Current by a Large-Gradient Radial Electric Field.

The effect of the large-gradient electric field on plasma current is analyzed by means of the Guiding Field Line (GFL) model(T. S. Huang, J. Geophys. Res. 105, 5541 (2000).)(Yu. Petrov, T. S. Huang, Phys. Plasmas 7, 4095 (2000).), that has been improved to describe the particles trapped above or below the midplane in a spherical torus. The variation of the current is caused by the change of the orbits' shape - of both trapped and passing particles - that explicitly enters the representation of current in the model. Not only is change in radial width of the orbits essential, but in the side width as well. The modification of the current, if given in percentage value, is shown to have a weak dependence on a particular guiding-field-line distribution function. The calculations were performed for parameters of the NSTX. For the spike-like profile of E_r the modification of parallel current is significant, but perpendicular current remains almost unchanged. For the case of a gradual profile, E_r \sim (1/e)dT/dr, the GFL model predicts the toroidal rotation of ions with velocity \sim 40 km/s in plasma core, directed opposite to the Ohmic current. At the edge, the toroidal velocity is reversed and reaches 5 km/s.

[BP1.062] Physical Mechanism of the Electron Acceleration to Ultrarelativistic Energies in an Oblique Shock Wave

Production of ultrarelativistic electrons by an oblique magnetosonic shock wave is studied by means of a one-dimensional, relativistic, electromagnetic, particle simulation code with full ion and electron dynamics. Simulations show that high-energy electrons with their Lorentz factors exceeding 100 are produced promptly. We discuss the physical mechanism of the electron acceleration and theoretically obtain the maximum electron energy in a new simple manner. Electrons reflected near the end of the main pulse region of a shock wave are then trapped and accelerated. These electrons gain energy from the electric potential and the constant electric field appearing in the wave frame. At certain propagation angles, the reflected electrons can travel a long distance in the direction perpendicular to the external magnetic field. The acceleration is particularly strong in this case.

[BP1.063] Experimental study of the interaction of a strong shock with a spherical density inhomogeneity

Laser-driven experiments conducted on the Omega Laser are described which probe the interaction of a very strong shock with a spherical density inhomogeneity. The interaction is viewed simultaneously from two orthogonal directions. This enables visualization of both the initial distortion of the sphere into a double vortex ring structure as well as the onset of an azimuthal instability that ultimately results in the three-dimensional breakup of the ring. The experimental results are compared with three-dimensional numerical simulations using an adaptive mesh refinement technique. The agreement between experiment and simulation is shown to be quite good. The experimental results completely define the three-dimensional topology of the flow, and the three-dimensional breakup is shown to be in remarkable agreement with the incompressible theory of Widnall et al.

Work performed for the US DOE by UC LLNL under contract W-7405-Eng-48.

[BP1.064] ICF Physics and HEDP

[BP1.065] Emission and Velocity Profile Measurements of High Pressure (50-150 Gpa) Deuterium Shocks

In recent experiments,* the EOS of liquid deuterium has been evaluated by reflected shock techniques at the NRL NIKE facility. New experiments are in process to measure the evolution of the shock front in response to the temporal and spatial pressure profiles in the shock. Velocity sensing interferometry (VISAR) and streak camera imaging are used to measure the simultaneous velocity and emission intensity of the shock under conditions of controlled pressure variations. These experiments will address several simple theoretical models which predict that the emission intensity should scale as a very strong power of shock velocity. * A. N. Mostovych et al., Phys. Plasmas 8, 2281 (2001).

[BP1.066] Design Studies for Multiple-Reflected-Shock Experiments on Deuterium

Experiments on the Nike Laser Facility at the U.S. Naval Research Laboratory are being planned for probing the equation-of-state (EOS) properties of highly-compressed liquid deuterium using multiple, reflected, shock waves. An impedance matching technique [1] is proposed that may permit the extreme compression of deuterium to several g/cc at about 10 Mbar. In this approach, a moderate-intensity pulse from the Nike laser would impinge on a plastic-coated, aluminum, pusher plate, which would then launch a planar shock into an adjacent cryogenic sample of deuterium. Multiple reflections of the shock between the pusher plate and a rear aluminum anvil would steadily increase the pressure in the deuterium until it matched the value at the ablation surface, at which time the intensity of the laser pulse could be increased for further compression. In this presentation, we will first discuss the role of the impedance matching technique in prior EOS studies using singly-reflected shock waves [2] that reached deuterium pressures of about 6 Mbar. Results of one-dimensional numerical simulations using the FAST2D code [3] will then be presented to illustrate the salient details and important design criteria of the proposed multiple-reflected-shock experiments.

[1] Y.B. Zel'dovich and Y.P. Raizer, ``Shock Waves and High-Temperature Hydrodynamic Phenomena,'' Vol. II (Academic Press, New York, 1967), pp. 726-730.

[2] A.N. Mostovych et al., Phys. Plasmas 8, 2281 (2001).

[3] J.H. Gardner et al., Phys. Plasmas 5, 1935 (1998).

[BP1.067] Emission measurements from laser-driven shocks propagating in planar deuterium targets.

Properties of deuterium at high pressure and density are important in astrophysics, inertial confinement fusion, and condensed matter physics. We will present initial experimental results on time-resolved light emission from shock breakout from an aluminum pusher into liquid deuterium. As the shock begins to propagate into the deuterium, the emission signal evolves from characterizing the hot aluminum to a state that is primarily characteristic of the shocked deuterium. Measurements of this transition time are expected to give us information about the conductivity and optical depth of the shocked deuterium. Measurements are preformed using a streak camera at up to 2ps time resolution on targets driven by the Nike KrF laser. In addition, we will present spatially resolved measurements of shock temperature using the absolute emission data and emissivity values obtained from the reflectivity measurements.

[BP1.068] Isentropic Compression on the 10-MA Saturn Pulsed Power Generator

Over the past few years, a very useful technique has been developed at SNL to obtain accurate, equation-of-state data by means of isentropic loading via magnetic pressure.[1] This isentropic compression experimental (ICE) technique has been pioneered on the 20-MA Z generator[2], with each experiment capable of producing continuous EOS data for several materials simultaneously from zero pressure to a stress which may exceed one megabar. However, much of the demand for experiments are in the 20 to 500 kbar pressure regime. In this paper, we report on the first measurements using ICE on the 10-MA Saturn generator in the long pulse mode[3] with pressures up to 300 kbar. Saturn offers a lower shot cost, higher shot rate capability to meet the demand for lower pressure EOS data. VISAR diagnostics of the 6-mm-diameter, 100- to 1000-µm-thick samples (eight per shot) demonstrates the sample to sample uniformity, as well as the transition from a wave to shock profile. This data will be presented along with a discussion of pulsed power modifications to lengthen and shape the current pulse to ensure shockless loading. (1) C. Hall, et al, Phys. Plasmas 7, 2069, (2000). (2) R.B. Spielman, et al, Phys. Plasmas 5, 2105, (1998). (3) C. Deeney, et al, Phys. Plasmas 6, 3576, (1999).

[BP1.069] Two-Dimensional Simulations of Laser Produced Shock Propagation

One and two dimensional simulations have been performed of laser produced shocks measured in experiments using a variety of materials (Lexan, aluminum, gold, and molybdenum). The shocks were produced by direct drive laser absorption with intensities ranging over an order of magnitude from 5.0e13 to 5.0 e14 W/cm2. The one dimensional simulations consistently over estimate the shock speeds by 10-20dimensional simulations. The experimental and simulation results will be presented, along with an analysis of two dimensional energy transport which quantifies the role of radial energy loss.

*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.

[BP1.070] Laser driven high pressure, high strain rate materials experiments

We have conducted shock experiments in thin Si and Cu crystals at using both an x-ray drive and direct laser irradiation. Transient x-ray diffraction signatures from the (400) and (040) lattice planes in Si and (200) and (020) lattice planes in Cu (parallel and perpendicular to the shock propagation direction) were recorded as a function of time. The diffracted signals from shocked Si show uni-axial compression of up to 10%. The diffraction signatures from shocked Cu show 3-D compression of up to 3%, indicated by a shift of the diffraction signal from the two orthogonal lattice planes on the same shot. We are extending these experiments to use a wider angle coverage to record other lattice planes. In addition, we record VISAR wave profile measurements to correlate with the time-resolved lattice response. Shock compressed crystals have been recovered for post-shock deformation analysis. We will describe the x-ray diffraction and VISAR measurements, and post-shock analysis.

[BP1.071] Laser-Driven Near Isentropic Compression of an Aluminum Flyer Plate

A new design for producing a ramped pressure wave for the study of material response in solid media under nearly isentropic compression conditions will be discussed. A plasma source, initiated from laser heating of a low-density carbon foam, unloads across a vacuum gap onto an Al target to provide a ramped, shockless, pressure load. Experiments using HE to create shockless drives have previously been demonstrated by Barnes, et al. [1] and Levedev, et al. [2,3]. This type pressure drive is coupled to targets having modulated surfaces for the study of material response and strength. The current design configuration of our near isentropic drive will provide peak pressures and strain rates on order of 0.4Mbar and 106 - 107sec-1, respectively. Initial experiments using VISAR, x-ray radiography and thin Al foils will examine both the planarity and the time-dependent nature of the pressure loading in the target. Recent experimental results and as well as experimental simulations scaled to the laser drive conditions will be presented.

This work was performed under the auspices of the US Department of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

[BP1.072] An atomic database computing system for opacity calculations

An atomic database computing system has been developed to integrate the computing of large scale atomic data for ICF applications, spectrum analysis for laser-produced plasmas, and EOS and opacity data visualization into a single platform. The system is based on the distributed commodity architecture. An Oracle database is used to be the atomic data provider as the back-end in the three-tier architecture. Commodity network computing technologies such as CORBA and Enterprise JavaBean are used as glue to connect the back-end services and the front-end graphical user interface. A new model (RSSUTA) based on the relativistic single-configuration single-electron transition approximation has been developed for high Z elements using JJ coupling schema. To calculate enormous numbers of transition lines and other radiative properties for high Z elements, we implement the RSSUTA model in a parallel computing environment using MPI. Trial runs on the NPACI IBM SP show that the speedup is linearly dependent on the number of processors. For general users, we provide graphic user interfaces from data generation to visualization. Using this program, users can easily obtain atomic data for ICF applications.

[BP1.073] Electronic Contributions to the Equation-of-State of Warm Dense Matter*

We describe calculations with the INFERNO[1] atom-in-jellium model to produce single-shock Hugoniot curves for aluminum, copper, and still other elements, from their normal initial density and also from "expanded" states of initial density of about 1/10 normal. These calculations address the regime of "warm-dense-matter", the former in support of experiments toward maximum compression, and the latter in support of experiments toward isentropic compression. INFERNO provides the electronic contributions to the internal energy and pressure, and ideal-gas or QEOS[2] atomic nuclear contributions complete the scheme. We compare INFERNO’s fully quantum-mechanical treatment of electrons with the familiar Thomas-Fermi model. We also investigate the one-component-plasma[3] model for the non-ideal contributions of atomic ions in strongly-coupled plasmas.

[1] D.A. Liberman, Phys Rev B, 20, 4981 (1979) [2] R.M. More, K.H. Warren, D.A. Young, and G.B. Zimmerman, Phys Fluids, 31, 3059 (1988) [3] H. DeWitt, W. Slattery, and Gilles Chabrier, Physica B, 228, 21 (1996)

*This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

[BP1.074] Probabilistic approach to the Laser MégaJoule robustness study

In the Laser MégaJoule (LMJ) configuration, the robustness study aims at specifying the sensitivity of the yield to power imbalance, laser beam pointing and target fabrication errors. In this context, we have computed and validated a Monte-Carlo calculation which provides, from standard deviations of these parameter values, the probability of failing to reach ignition. This computation is based on an empirical model which links the ignition conditions to given errors. In this poster, this probabilistic approach is tested on the bidimensional errors persistent during the laser pulse, only. But it may be easily extended to instantaneous power imbalance and also to tridimensional errors. For this feasibility study, we use a temporary simplified model, partly deduced from SYMCAL calculations(F. Poggi and J. Giorla, Bull. Am. Phys. Soc., \bf44), 35 (1999).. So, the results presented here are more significant from a qualitative point of view than from a quantitative o! ne! ! .

[BP1.075] Inertial Confinement Fusion Capsule Optimization

This poster presents recent work on the search for an optimal inertial confinement fusion (ICF) capsule. We define the optimal ICF capsule for ignition experiments as the capsule which is the most tolerant of fabrication imperfections, subject to driver constraints. A large design space exists for ICF capsules. Important variables include: ablator composition, ablator dopant concentration, capsule outer radius, ablator layer thickness, fuel layer thickness, fuel adiabat, and drive temperature. To scan this capsule design space efficiently we are developing automated tools that determine the capsules’ performance in the absence of imperfections (1-D). Determining the capsule performance when imperfections are present requires 2-D calculations that take significantly longer than 1-D runs, therefore, brute force optimization in 2-D is intractable. Methods of estimating a capsules 2-D performance without time consuming calculations are required. We present ideas on how this may be done. Progress on the optimization for NIF CH capsules and low radiation temperature, high yield capsules for inertial fusion energy will be discussed.

[BP1.076] Pulse Shaping of ICF Capsules

The performance of an inertial confinement fusion (ICF) capsule depends strongly on the fuel entropy profile. This profile is set by a series of carefully timed shocks (a pulse shape) and the subsequent hydrodynamic evolution of the capsule fuel. The pulse shape is typically found by the capsule designer through an iterative and sometimes time consuming process. General rules of thumb are known: shocks should not be allowed to overtake one another, long rarefactions between shocks should be avoided. However the obvious pulse shape which satisfies these rules (arranging for all shocks to arrive at the inside of the fuel layer at the same time) actually has a poor entropy profile due to shocks which are generated as the capsule relaxes to a uniformly accelerating equilibrium. In this poster we present a systematic investigation into pulse shaping, using a series of 1D hydrodynamics calculations. Analytical and computational models are used to gain insight into the simplified two-shock problem. We analyze a variety of pulse-shaping methods, including the method proposed by Munro^1, to optimize capsule performance.

^1 Munro D., et al, Physics of Plasmas 8, 2245 (2001).

[BP1.077] Simulation of the Radiative Heating of Gold-Backed Thin Foils in Z-pinch Experiments

We report on the simulation of thin foil radiative heating experiments performed at the Sandia Z facility. In these experiments, one side of thin CH-tamped Al foils is exposed to z-pinch radiation. The Al is backed by a thin Au layer, on the side opposite the pinch, with thicknesses ranging up to 3200 ÅThe purpose of the experiments is to study the effect of the Au reemission on the heating of the Al. X-ray measurements of Al K\alpha absorption spectra are used to monitor the heating of the Al. In our analysis, the time- and frequency-dependent radiation field incident on the foil is computed from VISRAD 3D view factor simulations. Results from 1D radiation-hydrodynamics simulations are post-processed using SPECT3D to compute the K\alpha absorption spectra. We will present results from simulations and comparisons with experimental measurements.

[BP1.078] Spectral Analysis of Al/MgF Foils Heated by Z-pinch Radiation

Sandia National Laboratories’ Z machine provides a good test bed for conducting basic plasma research on the interaction of x-rays with matter. In particular, recent experiments have been conducted that irradiate thin Al/MgF metal foils by the radiation pulse from the side-on emission of a fast z-pinch. In these experiments, spatially and temporally resolved spectra of K-shell absorption lines, backlit by the high-energy tail of the z-pinch radiation, are the primary diagnostic of the foil plasma conditions. The experiments are simulated by 1-D radiation-hydrodynamics calculations using a time- and frequency-dependent radiation boundary condition determined by 3-D view factor simulations of the z-pinch diode region. The calculated plasma conditions are then utilized in a collisional radiative equilibrium (CRE) model to determine the relative amplitude of absorption features over the spectral range of interest. These calculations, and their comparison to the experimental data, will be presented and discussed.

[BP1.079] Self-consistent analysis of X-ray line spectra and monochromatic images in imploded cores at OMEGA

We report on a spectroscopic method for the determination of the gradient structure in imploded cores based on the self-consistent analysis of simultaneous X-ray monochromatic images and X-ray line spectra. This technique is applied to a series of stable and spherically symmetric indirect drive experiments where Ar-doped D_2-filled plastic shells were imploded with the OMEGA laser system. Argon K-shell X-ray line spectra were measured with streak crystal spectrometers, and two X-ray monochromatic imagers recorded Ar He\beta and Ly\beta lines and continuum images of the core. The analysis self-consistently determines the temperature and density gradients that yield the best fits to the monochromatic spatial emissivity profiles and spectral line shapes. This measurement is critical for understanding the atomic kinetics, radiation transfer and plasma dynamics associated with the implosion process. In addition, since the results are independent of hydrodynamic simulations they are important for the verification and benchmarking of detailed fluid dynamic models of hot dense plasmas.

[BP1.080] X-ray spectroscopic measurements of temporal variation of ICF core plasma gradients

Direct-drive implosion of fusion pellets has been investigated using time- and space-resolved x-ray spectroscopic measurements. The experiments were designed to explore the influence of the low-modal irradiation non-uniformity on the imploded coreplasma dynamics. The time-resolved Ar K-shell spectra were recorded using an x-ray streak spectrograph (XSS). Time- and space-resolved monochromatic images of He\beta (1s^2-1s3p) and Ly\beta were observed with a monochromatic x-ray framing camera (MXFC). Spatial gradients of the electron temperature and density in the imploded core were investigated by means of a self-consistent analysis of the spectra from the XSS data and emissivities obtained by Abel inversion for the MXFC data for each time frame. The gradients were compared with ones predicted with the hydro-code simulation, in which the heat conduction is treated by Spitzer-Harm model, resulting incomparable density, lower temperature and larger core radius. Comparisons with the Fokker-Plank simulation are now under way. The implosion dynamics will be discussed.

[BP1.081] Studies of soft x-ray emission at the Nike laser facility

To investigate pellet designs for direct drive inertial confinement fusion[1], the Nike group has an ongoing experimental effort to study the soft x-ray emission (\lambda \sim 0.5-7.5 nm) from a variety of target materials over a range of laser irradiances (10^12-10^13 Wcm^-2). Absolutely calibrated, time-resolving transmission grating spectrometers, filtered Si photodiodes, and a time-integrating grazing incidence spectrometer have been fielded. This poster will present data from two experimental series. The angular and spatial dependence of the soft x-ray emission is being studied for comparison with theoretical spectra obtained from non-LTE hydrodynamic simulations[2]. Some results will also be presented from a study of laser imprint[3]. The soft x-ray radiation during the laser prepulse from a thin Au or Pd layer (10-80 nm) on a plastic target was of particular interest in these experiments.[1]Bodner, et al., Phys. of Plasmas, \textbf7, 2298 (2000); [2]Colombant, et al., Phys. of Plasmas, \textbf7, 2046 (2000);[3]Obenschain, et al., this conference.

[BP1.082] Large Scale Simulation on MeV Electron Transport in Dense Plasmas

The relativistic electron transport in dense plasmas has been a critical issue in the fast ignition research. It has been studied by theory , simulation and experiment extensively. In the simulations by Honda and Sentoku etal , it was found that when relativistic electrons penetrate into dense plasmas , magnetic fluctuations grow up by the Weibel instability . The magnetic fields form channels through which relativistic electrons flows into plasmas as filaments . The initial size of the filaments is 6c/wp which corresponds to the wavelength of maximum growing mode of Weibel instability. Since relativistic electrons are scattered by the magnetic fluctuations, the momentum distribution of electron becomes isotropic and the Weibel instability is stabilized. In this situation , the filaments start to merge, become larger scale and longitudinally rippled by secondary instability. During the secondary instability, transverse eddy currents and longitudinal magnetic fields are generated as well as longitudinal electric fields which causes anomalous stopping of relativistic electrons and anomalous resistivities on the return current. The merging continues to reduce number of filament and increases filament size. In this presentation,the merging processes are analyzed by introducing a master equation for filament size distribution function. It is also discussed that this filament merger model is similar to the bubble merger model in nonlinear state of Rayleigh- Taylor instability(Shvart etal.).

[BP1.083] Detailed Modeling of MAGO, FRC, and Other Magnetized Target Fusion Experiments

Magnetized Target Fusion (MTF), in which a preheated and magnetized target plasma is hydrodynamically compressed to fusion conditions, is an approach to controlled fusion which may lead to inexpensive experimental demonstration of fusion ignition. Magnetothermal insulation of a target plasma may make practical such "liner-on-plasma" compressions, magnetically driven using relatively inexpensive electrical pulsed power. Solid liner compressions, without a plasma fill, with suitable liner kinetic energies of several megajoules have been demonstrated at numerous locations. A number of potential target plasmas are under experimental development, including the Russian MAGO scheme, and the Field Reversed Configuration (FRC) at Los Alamos. Because the target and imploded plasmas in MTF are reltively dense, magnetohydrodynamic (MHD) calculations can accurately describe a great deal of the detail of MTF plasma formation and compression. Modeling of target plasmas and proposed liner-on-plasma experiments with available MHD codes including detailed radiation, heat conduction, and resistive field diffusion will be shown.

[BP1.084] Stopping of ultra-relativistic electrons precisely in the core of an inertial fusion target.

In the fast igniter scenario of inertial fusion, it is generally assumed that an energetic electron beam can be produced by laser-plasma interaction near the critical surface and then transported through a plasma with density rising by about four orders of magnitude from the critical layer to the core where the electrons are stopped. This scenario, however, requires scrutiny. Two major effects were considered so far: The deleterious Weibel instability could develop at the initial stage of the transport, at densities somewhat higher than critical. Electrons were modeled as stopped just by collisions, which then gives what may be a too restrictive upper limit of just a few MeV on the energy of an electron that could be stopped in the core. We show that another dangerous instability, namely, the beam instability to plasma waves and turbulence, may develop and affect the beam transport to the core. We specify the parameter range for which this instability in convectively suppressed in plasma layers with a reasonable density gradient, but develops in the core where the density profile is flat. Then, even ultra-relativistic electrons are stopped efficiently by the turbulence precisely in the core.

[BP1.085] Solid state physics at ultrahigh pressure and strain rate on NIF*

Over the past decade, work at a number of laser facilities around the world has shown that solid state experiments at high pressure are possible, albeit over brief time intervals and small spatial scales. The ability to diagnose lattice response to strong shocks, P > 100 kbar, on sub-nanosecond time scales in single crystal samples has been demonstrated. [1] The ability to access strain rates of 10^7 - 10^8 s^-1 has also been shown. [2] A method for inferring solid-state strength in metal samples at pressures P > 1 Mbar has recently been presented. [3] We propose to carry this class of solid-state physics research to much higher pressures, P >> 1Mbar, on the NIF laser facility. [4] We will show a series of experimental designs that will access ultrahigh pressures in the solid state over a range of strain rates spanning10^6 - 10^8 s^-1. *This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48. [1] A. Loveridge-Smith et al., Phys. Rev. Lett. 86, 2349 (2001) [2] E. Moshe et al., Appl. Phys. Lett. 76, 1555 (2000) [3] D.H. Kalantar et al., Phys. Plasmas 7, 1999 (2000) [4] B.A. Remington et al., LLNL Report, UCRL-ID-142676 (2001)

[BP1.086] New Developments in Cone-Focussed Fast Ignition

In the "cone-focussed" concept for FI, the spherical capsule has a conical shell of dense material penetrating through one side to near capsule center. The implosion proceeds as usual, the cone holding open a clear path for the high intensity laser so that its energy can be deposited within \sim100 \mu m or less of the high density core. 2-D simulations, by us, of implosion, ignition, and burn exploring this concept and direct-drive experiments at ILE-Osaka [Kodama et al, Bull.Am.Phys.Soc., 45, 160, 2000] have shown considerable promise. We report our continuing efforts to develop the concept. Asymmetrically driven implosions can produce a more compact high-density core that is easier to ignite. Fast-ignited cores with a fuel <\rho \Delta r> less than about 1.5 g cm^-2 disassemble too rapidly to achieve the burn-up fraction of <\rho \Delta r>/(<\rho \Delta r>+6~g~cm^-2) associated with conventional hot-spot ignition. Ignition may proceed in two steps - the igniter beam energy and early burn can drive additional convergence, actually increasing the core <\rho \Delta r> and generating a new hot spot at very high density. This effect is enhanced if the igniter beam is protons (rather than electrons) [Roth et al, Phys. Rev. Lett. 86, 436, 2001]. We explore whether enhanced mix can produce a higher average density core and whether the initial presence of a layer of DT ice on the cone will degrade the implosion performance. We show the results of indirectly driven, cone-focussed implosion experiments on Omega - testing how the cone "perturbs" the implosion.

[BP1.087] Direct Drive Beryllium Ablator Capsules for the Omega Laser

We are designing direct drive beryllium ablator capsules for the Omega laser as part of our effort to develop beryllium ablator ignition capsules for the National Ignition Facility (NIF). The main goals for this experimental campaign is to develop the fabrication expertise for roughly NIF size capsules and obtain experimental data on how the copper- brazed joint between the beryllium hemispheres affects the implosion. Our proposed design calls for an 1180 micron outisde diameter capsule with 40 micron thick beryllium walls containing 50 atm of deuterium gas. Some of the capsules will also have 0.05 atm of argon. We plan to image the joints with argon fluorescence from inside the capsule. Our plan is to use a 1 ns square pulse with 30 kJ of laser energy. With this drive, we expect the convergence ratio to be about 6.5 to 7. Depending on the capsule design details, we expect that the peak temperature will be 490 \pm 40 eV, and the neutron yield will be anywhere from 1\times 10^8 to 8\times 10^8 neutrons. Some of the uncertainty comes from whether or not we use argon and questions about how much mix the copper-brazed joint will cause. The yield also depends strongly on which beryllium alloy we use. We calculate better implosions in direct drive with pure beryllium, but requirements on allowable grain size may force us to use copper-doped beryllium, which would reduce the yield by about 50%.

[BP1.088] Direct drive pellet designs for high gain and NIF

We are designing and analyzing direct drive icf pellets for application to both high-gain ICF and the 1.6 MJ glass laser National Ignition Facility (NIF). The primary tool for this analysis is the NRL FAST MPI radiation-hydrocode; it runs in one to three dimensions, includes LTE amp; nonLTE multigroup radiation transport with an STA opacity database, and has fusion burn with multigroup alpha particle transport. The pellets under consideration for direct drive are composed of a variety of ablator materials (plastic, plastic foams wicked with DT, DT, and with and without thin high-Z layers) [S.E. Bodner, D.G. Colombant, A.J. Schmitt, and M. Klapisch, Phys. Plasmas 7, 2298 (2000); D.G. Colombant, et al., Proc. 26th ECLIM 2000, SPIE 4424 224 (2001)]. We present the resulting pellet designs, discuss them in the context of hydrodynamic instability theory, and summarize the simulations of the effects of nonuniformities on gain. Nonuniformity sources that are examined include laser imprint, surface finish imperfections, and low-mode power imbalance due to beam misalignment and pulse jitter.

[BP1.089] Real material effects in laser fusion direct-drive targets

In our previous direct-drive target designs1 we use all-CH ablator, all-CH wicked foam and all-DT fuel. In practice, all these various components of a direct-drive target will most likely contain impurities and/or contaminants. We look at the effects of various impurities in these components. We start from a high-yield design (G>100) and introduce in succession impurities in the various components of the target. The effects of impurities will be shown on the gain and 1D stability analysis. Pulse shape modifications are required to make the target burn in the presence of some impurities and limits on impurity levels for acceptable performance of the targets will be shown and discussed. Work supported by USDOE under a contract with NRL.

1. D.Colombant et al, Proc. 26th ECLIM,2000 SPIE Vol. 4424, 224 (2001)

[BP1.090] Properties of SiO_2 Aerogels Suitable for Astrophysical Experiments

We are studying inhomogenieties in SiO_2 aerogel. The aerogel has been treated in our hydrodynamic simulations as a material with uniform density but is modeled to grow by diffusion-limited cluster-cluster aggregation (DLCA) during the sol-gel process. We have modified DLCA FORTRAN code to grow a SiO_2 aerogel model to be used as input in established hydrodynamic code in order to calculate the propagation of a converging conical shock wave through the foam. The foam has an average density of 100 mg/cm^3 and consists of roughly spherical globules of SiO_2 molecules with an average radius of 100 nm\pm5 nm. This foam is being tested for plasma jet experiments relevant to astrophysics in which a conical shock wave propagating through the foam is driven by one to six OMEGA laser beams. Fluid downstream of the shock wave is forced through an aperture to create a plasma jet imaged by self-emission and silicon x-ray absorption. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

[BP1.091] A Parallel Scheme for Multi-Group Radiation Diffusion in DRACO

A flexible parallel scheme for the solution of multi-group radiation diffusion on logically rectangular meshes is presented and its performance is assessed. This scheme combines two types of parallelism: (a) the radiation groups are distributed to different processors for independent simultaneous solution and (b) the matrix equation for each radiation group is solved in parallel using the PETSc library. It is therefore possible to realize parallel speedup for problems with a range of geometry sizes/resolutions and a variation in the number of radiation groups. This scheme is implemented in the DRACO multi-physics radiation hydrodynamics code for two differencing approximations of the diffusion operator and tested over such a range of problems. Runtime, speedup and accuracy of the results are discussed.

[BP1.092] Three-dimensional ICF Target Simulations on a LINUX Cluster

This paper describes the application of a three-dimensional radiation hydrodynamics code on a workstation cluster to problems typical of ICF pellet design. The compressible hydrodynamics code, FastRad3D, contains most of the physical effects relevant for the simulation of high-temperature plasmas including inertial confinement fusion (ICF)-regime Rayleigh-Taylor unstable direct drive laser targets. These effects include inverse bremmstrahlung laser energy absorption, classical flux-limited Spitzer thermal conduction, real (table look-up) equation-of-state with either separate or identical electron and ion temperatures, multi-group variable Eddington radiation transport, and multi-group alpha particle transport and thermonuclear burn. FastRad3D uses an MPI message-passing model to obtain parallelism on workstation clusters and supercomputers. The calculations show the effects of surface non-uniformities and laser intensity non-uniformities on gain for a typical DT pellet. The 3D results are compared to previous results from 2D and 1D calculations.

[BP1.093] First wall survival studies for dry wall IFE chambers

Every implosion of an IFE target produces a threat spectrum of x-rays and ions. For the multiple-Hz rate at which targets would be imploded in current proposed reactor designs, the first wall of a dry wall reactor must survive each shot with no evaporation. We explore several criteria for first wall survivability for several proposed IFE targets. These criteria include buffer gas composition and opacity modeling; first wall material, operating temperature, and radius; and target output, including output from a 160MJ directly driven radiatively pre-heated target proposed by NRL and a 400 MJ indirectly driven HIB target proposed by LLNL. The authors are grateful for support from the Department of Energy and the Naval Research Laboratory.

[BP1.094] Implosion modeling and output calculations for high yield direct drive targets.

We present details of implosion and energy output calculations for fusion power plant scale cryogenic targets. Along with fusion neutrons, x-rays and energetic debris ions produced during and immediately after the burn account for most of the energy released by the target. Depending upon their energies, these x-rays and ions may be very damaging to the target chamber first wall. We have used BUCKY 1-D radiation-hydrodynamics code to study implosion burn and energy distribution in the target output. We will discuss different mechanisms that may affect x-ray and ion output calculations and subsequently Inertial Fusion Energy target chamber designs.

[BP1.095] Initial Results from IFE Chamber Materials Response to Ions and X-Rays from RHEPP-1 and Z*

Future Inertial Fusion Energy (IFE) reactor operation is expected to deposit 1-1000 J/cm^2 of either x-ray or ion energy, or both, per shot on chamber walls. Because of the energy characteristics of the expected spectrum, x-ray and ion energy is likely to be deposited in a thin surface layer. The mechanical response of proposed chamber wall materials to one-sided, high-flux heating needs to be studied. Both dry walls (such as carbon fibers, carbon composites and refractory metals) and thick-liquid walls (PbLi and FLIBE) have been proposed. The Z machine at Sandia National Laboratories provides a variety of x-ray fluences (up to several 1000 J/cm^2)to test the feasibility of these wall materials and measure the materials response. The first tests are planned to expose a wide range of dry materials up to 200 J/cm^2. A variety of accelerated ions is possible on the RHEPP-1 ion beam facility, with deposited fluences as high as 10 J/cm^2. Measurements of materials response will be presented (including cross-sectioned SEM/TEM to verify ablated material thickness and microstructural changes caused by ion/x-ray doses), and compared with BUCKY computer simulations.

*Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., under US DOE Contract DE-AC04-94AL85000.

Part B of program listing