Session CP1 - Poster Session II.
POSTER session, Monday afternoon, November 15
Room Exhibit Hall A, SCC

[CP1.001] C-Mod and JET

[CP1.002] Overview of the ICRF Program on C-Mod

Recent ICRF experiments have focused upon mode conversion, antenna performance and coupling, and wave particle interactions. Fast wave mode conversion into the ion Bernstein (IBW) and/or ion cyclotron (ICW) waves in multi-ion species plasmas should be important for plasma heating, current drive and flow drive. The recently upgraded Phase Contrast Imaging diagnostic (PCI) has allowed simultaneous observation of both the IBW and ICW in a D(^3He) plasma and prove unambiguously the existence of both modes. These results provide a means to verify predictions of full wave codes and to optimize such processes for plasma control. Recent improvements in the antenna designs have allowed 1 sec, 5 MW pulses. ICRF loading studies have shown that loading variations are related to changes in the density pedestal height rather than the evanescent distance. With increased ICRF power, the first monster sawteeth and fundamental and second harmonic Alfven cascades were observed. The sawtooth period was found to be dependent on antenna phasing for minority absorption.

[CP1.003] ICRF Heating, Mode Conversion, and Flow Drive Experiments in D(^3He) Plasmas

In the spring 2004 experimental campaign, ICRF heating, mode conversion and flow drive experiments in D(^3He) plasmas were performed in Alcator C-Mod. The single-pass absorption in D(^3He) minority heating, due to an unfavorable wave polarization factor, is smaller than that in D(H). H-mode plasmas were obtained in 8 T D(^3He) minority heating. At higher ^3He concentration levels, mode converted ion Bernstein wave (IBW) and ion cyclotron wave (ICW) were simultaneously observed by phase contrast imaging (PCI). The MC waves were studied in 8 T and 5 T, and also different plasma currents and ^3He concentrations. The spatial locations, damping distances and relative amplitudes of the two waves were estimated from the PCI measurements and also compared with TORIC modeling. We also ran experiments to study the poloidal flow driven by the MC waves using spectroscopic diagnostics. For the plasmas we studied, the experimental data indicated that the flow velocity near the MC layer is smaller than the diagnostic sensitivity (\sim10 km/sec).

[CP1.004] Search for TEM and ETG Modes with the Upgraded PCI Diagnostic in Alcator C-Mod

Phase Contrast Imaging (PCI) diagnostic has been used in the past to study turbulent density fluctuations up to 500 kHz(A. Mazurenko et al, Phys. Rev. Letts. 89), 225004 (2002). and coherent RF waves(E. Nelson-Melby et al, Phys. Rev. Letts. 90), 155004 (2003).. Recently, the PCI diagnostic has been upgraded from 12 to 32 channels with frequency response up to 10 MHz, which makes the direct study of microscale turbulence possible. Detailed microstability analysis of typical C-Mod plasmas with the gyrokinetic code GS2 yields candidate discharges in which ETG and/or TEM modes are unstable. C-Mod EDA H-Mode discharges, likely candidates for unstable ETG modes, are first surveyed using a parameterization of the ETG critical gradient(F. Jenko et al, Phys. Plasmas 8), 4096 (2001).. Possible regimes for TEM include the ITB(D. R. Ernst et al, Phys. Plasmas 11), 2637 (2004). and L-Mode discharges. Radial ETG streamers predicted in gyrokinetic simulations(W. Dorland et al, Phys. Rev. Letts. 85), 5579 (2000). will also be explored.

[CP1.005] Measurement and Modeling of Alfven Cascades on Alcator C-Mod

Recent current ramping experiments on Alcator C-Mod with early RF heating have produced a flat or slightly hollow q-profile before a steady state current is reached(Porkolab et al, EPS meeting, Berchtesgaden, Germany (1997).)^,(Snipes et al, Plasma Phys. Control. Fusion \textbf42), 381 (2000).. Magnetic pick-up coils and the Phase Contrast Imaging (PCI) diagnostic are being used to study Alfvén wave phenomena including frequency chirping modes identified as Alfvén cascades(Sharapov et al, Physics Letters A \textbf289), 127 (2001).. These modes are believed to be driven unstable by the ICRH hydrogen minority tail (n_H/n_D \quad \sim 5%) as the current is ramped and the q profile evolves. According to theory, the frequency of these modes is proportional to the toroidal mode number n and increases with decreasing q_min, the minimum of the safety factor^4. The MHD-kinetic code NOVA-K has been used to model the frequency chirping behavior of the Alfvén cascade modes, in agreement with the observations.

[CP1.006] Active MHD Spectroscopy of Alfvén Eigenmodes on Alcator C-Mod

Alfvén eigenmode resonances are excited in a variety of plasma conditions in C-Mod with two moderate-n antennas positioned above and below the outboard midplane. Power amplifiers (\approx 3 kW) sweep the driving frequency over the audio range (< 30 kHz) or over a selected \pm 50 kHz range from 100 kHz to 1 MHz. Logic circuitry that calculates the center frequency of the Toroidal Alfven Eigenmode gap, f_TAE=v_A/4\pi qR, in real-time from B_T and \=n_e measurements is being developed to enable the antennas to track f_TAE. Simultaneous in-vessel phase calibration of the pick-up coils will be used to better identify toroidal mode numbers. Shot-to-shot elongation scans do not show the dependence of damping on edge shear that was seen in results at JET. Inner wall limited plasmas with moderate outer gaps show higher damping rates than diverted plasmas with low outer gaps. Low frequency experiments below 20kHz will also be presented.

[CP1.007] Radial Correlations of Edge/SOL Turbulence in Alcator C-Mod

The high levels of cross-field particle transport observed in the outboard SOL are associated with the radial propagation of turbulent structures (blobs) that are aligned with the local field and have small k_\parallel. A 13-channel radial array of views covering edge and SOL with \sim4 mm spatial resolution has been used to measure the fluctuations in local D_\alpha emission. Typically the radial correlation among the measured fluctuations is found to change sign for views on either side of the separatrix and indicates that the radial propagation direction is outward on average, an observation confirmed by 300 frame/250kHz 2D movies of the edge/SOL emission. The radial correlation length depends on the radial location. It is smallest (\sim8 mm) near and just inside the separatrix, increasing to \sim2 cm in the far SOL. Recently the viewing array has been upgraded to include 12 poloidally resolving views and to improve the spatial resolution on 4 of the radial views to 1.8 mm. The design of this upgrade will also be presented.

[CP1.008] Temperature and Density Fluctuations during Peaked Density Plasmas in Alcator C-Mod

We used a heterodyne ECE system to make observations of fluctuations during discharges with peaked density profiles in the Alcator C-Mod tokamak. The peaked density profiles were generated by off-axis ICRF heating and pellet injection. These peaked density profiles are associated with the formation of internal transport barriers. Low-level coherent fluctuations were observed in some cases to extend across a large region of the plasma and had similarities to a quasi-coherent (QC) mode present in the EDA H-mode edge. In other cases, broadband density fluctuations were observed. ECE systems typically measure electron temperature only; this ECE system was also able to detect density fluctuations in the high-density plasma core in some cases due to refractive effects. Implications of these fluctuations for understanding transport in discharges with peaked density profiles are discussed.

[CP1.009] Ion Temperature and Plasma Rotation in EDA H-Mode and ITB Discharges in Alcator C-Mod

In the course of the 2004 campaign on Alcator C-Mod, extensive ion temperature and plasma rotation measurements were made in the outer half of the plasma via CXRS and spectroscopy of ambient species. The most significant of these results are for the unique C-Mod modes: the EDA H-Mode and the RF induced internal transport barrier. The CXRS data was taken with a 50 ms beam pulse which occurs just once during the typical 1.5 s C-Mod discharge. Ion temperature and rotation are inferred from measurements of ambient spectra to fill out the time series for a discharge. Due regard is given to spatial averaging in using this data. Consistency of the data is checked where possible via the momentum balance equation. Thermal transport analysis (TRANSP) is included as well. A long pulse beam is planned for installation in fall 2004. Expected improvements in CXRS will be discussed.

[CP1.010] Measurement of Neutral Beam Attenuation from Beam Emission

CXRS measurements of impurities in fusion plasmas are dependent upon local neutral beam densities. These local values can be found from complex penetration codes that depend upon plasma parameters, but they can also be derived directly from beam emission data from the multi-channel MSE diagnostic. Deriving beam densities in this fashion also provides the opportunity to benchmark the penetration codes. Before beam density can be derived from MSE data a channel-to-channel calibration of the MSE system is needed. This can be achieved by analysis of MSE data taken from beam-into-gas shots at a variety of pressures. The pressure variation allows in-situ measurement of the cross-section for beam attenuation, which is then used to acquire the channel-to-channel calibration constants. We will compare these empirical cross-sections with previous measurements. In some cases the atomic beam stopping cross-sections derived with these calibration constants show good agreement with predictions.( Janev, Boley, Post, D.E. (1989) NUCLEAR FUSION, \textbf29 )12, 2125-39

[CP1.011] Invessel Calibration of the Alcator C-Mod Diagnostic

A comprehensive in-vessel calibration of the Alcator C-Mod Motional Stark Effect (\sc mse) diagnostic has characterized the diagnostic's response to linearly polarized, circularly polarized, and unpolarized light. The polarization angle measured by \sc mse varies nearly linearly with the angle of linearly polarized light, with a deviation from pure linear of order 1^o as the incident light is rotated through 360^o. The error term has a dominant \cos 4 \theta component caused by a \sim 10^o phase shift imposed by three mirrors in the \sc mse optical system. The intrinsic diagnostic accuracy is 0.02^o once these errors are compensated. Ratios of the \sc fft amplitudes at the fundamental and second-harmonic frequency of the photoelastic modulator indicate a conversion efficiency between linearly polarized and circularly polarized light of \sim1% at the optical axis and \sim10% at the edge. Implications for understanding beam-into-gas calibration data and q-profile measurements in plasmas will be discussed.

[CP1.012] Interferometer-polarimeter diagnostic for Alcator C-Mod

An interferometer-polarimeter system is being developed to measure density and poloidal field profiles and fluctuations in C-Mod. During the coming run period, prototype tokamak measurements are planned using a small number of CO_2 and He-Ne chords to test effects of vibration compensation and noise in the experimental environment; scrape-off layer plasma effects will also be evaluated. Ultimately, a \sim30 chord system, using an FIR laser (119 \mum) is planned. The proposed geometry uses retro-reflectors installed between inner wall limiter tiles. The laser beams will propagate in a poloidal fan, launched from the outboard midplane. The wavelength is chosen to be long enough to yield Faraday rotation in the few tens of degrees for typical chords, while being short enough to avoid strong refraction or cutoff in the high density plasmas typical of C-Mod operation. Design considerations, including data inversion techniques, and expected measurement precision for density and q profiles will be described.

[CP1.013] A Multi-Electrode Inner Wall Scanning Probe for Alcator C-Mod

The success of a recently installed magnetically-driven swing probe on the high-field side scrape-off layer in Alcator C-Mod( N. Smick et al., Presented at PSI Conference, Portland 2004) has prompted us proceed with a second, more capable version. The original probe provided electron temperature and density profiles as well as parallel Mach number using a single electrode that sweeps an arc through the plasma. We found strong plasma flows towards the x-point in all single null configurations and reduced density e-folding lengths in balanced double null. This suggests a ballooning-like cross-field transport characteristic that we would like to investigate more thoroughly. The new probe will plunge linearly into the SOL and employ four electrodes to provide more accurate measurements of plasma flows as well as simultaneous information on plasma density and potential fluctuations. In addition, we will investigate the use of a probe geometry that may allow us to infer both parallel and perpendicular components of velocity.

[CP1.014] Initial Experimental Results from the Alcator C-Mod Compact Neutral Particle Analyzer

Recent experimental results from the new Compact Neutral Particle Analyzer (CNPA) and a completed multi-detector upgrade of the diagnostic are presented. The CNPA uses Si diodes to detect charge-exchanged (CX) induced energetic (>20keV) neutral particles for ICRF hydrogen minority tail temperature diagnosis. A diagnostic neutral beam (DNB) provides the neutrals for the CX process. The discussed data involve measurements of the on-axis Hydrogen-minority perpendicular energy spectrum during low density (n_eo\sim 10^20/m^3) ICRF D(H) plasmas with 0.5 to 1.5MW of ICRF. During these discharges, tail temperatures reached \sim 200keV. The energy spectrum is compared with TRANSP and Stix-distribution based calculations, and central ICRF power deposition densities are inferred. The upgrade consists of the installation of three additional detectors which provides the diagnostic with multiple sightlines. Using a new long-pulse DNB, the improved CNPA will give spatial and temporal tail temperature measurements for moderate (n_eo\sim 2x10^20/m^3) densities C-Mod D(H) plasmas.

[CP1.015] Results from the new core Thomson scattering diagnostic on Alcator C-Mod*

The core Thomson scattering (TS) diagnostic is used to study profiles of the electron temperature and density in the core plasma region on the Alcator C-Mod tokamak. Results of the profile measurements will be presented as well as comparison with T_e, n_e measurements from other diagnostics. Systematic analysis of Z_eff behavior in different plasma regimes as well as quantitative analysis of impurity accumulation inside the ITB foot will be discussed. Time dependent Z_eff profiles from different regimes will be presented. TS measurements are used to analyze ITB formation and evolution in C-Mod plasmas using the TRANSP code. This requires fitting TS profiles with a smooth function and the results of the fit will be presented. TRANSP analysis shows an increase of bootstrap current at times corresponding to the formation of the H-mode barrier and the ITB. J_BS(r) peaks at the location of the ITB, while I_BS do not exceed 10% of the total plasma current. The analysis of the diffusion coefficients is being undertaken and preliminary results will be presented.

[CP1.016] Visible Spectroscopy measurements from a Transmission Grating Spectrometer to be used at the Alcator C-Mod Tokamak

We present a high throughput (f/3) Doppler spectrometer for toroidal rotation velocity measurements in the Alcator C-Mod plasma. The plasma rotation will be determined from the visible Doppler shifted wavelengths of D_\alpha and magnetic and electric dipole transitions of highly ionized impurities in the plasma. This diagnostic will have a tangential view and measure the plasma rotation at several locations along the outer half of the minor radius (r/a > 0.5). Calibration spectra show a temporal response of \sim 1 ms and a rotation velocity sensitivity of \sim 10^5 cm/s. The fast time resolution and high spectral resolving power (\lambda /\Delta \lambda \quad \sim 15500 at 3800 Åwith a 50 \mu m slit) are possible due to a special LLNL 6" diameter circular transmission grating. The instrument was tested at the Compact Torus Injection Experiment (CTIX) at UC Davis/LLNL. We present those spectra and possibly initial spectra from C-Mod. Performed under the auspices of the DoE by UC LLNL under contract W-7405-ENG-48.

[CP1.017] Gyrokinetic Simulations of Zonal Flows in Alcator C-Mod

Using the global gyrokinetic code, GYRO(J. Candy and R.E. Waltz, \textitJournal of Computational Physics), \textbf186, 2, 10 April 2003, 545-81 \par , we present the results of linear and nonlinear simulations relevant to plasma conditions in Alcator C-Mod. The study focuses on zonal flow formation, structure and evolution, including spatial and temporal fluctuations. Zonal flows are known to be the primary saturation mechanism for ITG driven turbulence in the absence of equilibrium \textbfEx\textbfB sheared flows. We are attempting to identify aspects of these phenomena that may be experimentally observable in the ablation cloud dynamics of injected lithium pellets. Comparisons are made for conditions characteristic of L-Mode, Ohmic H-Mode and EDA H-Mode discharges.

[CP1.018] Digital Plasma Control System for Alcator C-Mod

A digital plasma control system (DPCS) has been designed to replace the present C-Mod system, which is based on hybrid analog-digital computer. The initial implementation of DPCS comprises two 64 channel, 16 bit, low-latency cPCI digitizers, each with 16 analog outputs, controlled by a rack-mounted single-processor Linux server, which also serves as the compute engine. A prototype system employing three older 32 channel digitizers was tested during the 2003-04 campaign. The hybrid's linear PID feedback system was emulated by IDL code executing a synchronous loop, using the same target waveforms and control parameters. Reliable real-time operation was accomplished under a standard Linux OS (RH9) by locking memory and disabling interrupts during the plasma pulse. The DPCS-computed outputs agreed to within a few percent with those produced by the hybrid system, except for discrepancies due to offsets and non-ideal behavior of the hybrid circuitry. The system operated reliably, with no sample loss, at more than twice the 10kHz design specification, providing extra time for implementing more advanced control algorithms. The code is fault-tolerant and produces consistent output waveforms even with 10% sample loss.

[CP1.019] Experimental Results of the Coaxial Multipactor Experiment (CoMET)

Electron multipactoring can occur in vacuum coaxial transmission lines found in ion cyclotron heating systems. Because of the non-linear electric field of coaxial lines, the multipactor can appear at many different electron energies and trajectories. Simple particle tracking codes show that the coaxial multipactor can occur at different harmonic modes on one or two surfaces. The Coaxial Multipactor Experiment (CoMET) is a high Q resonator with a 6 inch vacuum coaxial transmission line section which supports the multipactor discharge. CoMET specifically studies coaxial multipactoring with an array of retarding potential analyzers and directional couplers to determine the limiting voltage, electron energy distribution, spatial location, and current density as a function of frequency and pressure. Results from a single probe suggest the multipactor occurs in a small localized area, while some electrons move throughout the vacuum region, thermalizing on the chamber walls. These low temperature electrons could possibly move into a high voltage region, seeding an arc in that area. Current experimental results and future experiments are presented.

[CP1.020] Machine size scaling of error field induced locked mode thresholds

Error field induced mode locking is a concern for ITER, particularly during the low density start-up phase. One of the principle uncertainties in extrapolating the error field locked mode threshold from current machines to ITER lies in the scaling with machine size. To determine the size scaling law, a set of experiments was designed and carried out on three machines of widely differing size; Alcator C-mod, DIII-D and JET.

The main aim of the experiments was to perform a set of discharges matched in \rho*, \nu* and \beta on the three machines. The discharges were additionally tuned to have the same plasma boundary shape and applied error field harmonic spectrum. Verification that the error field threshold is the same for these dimensionally matched plasmas, together with known density and toroidal field scalings, allows the size scaling to be unambiguously inferred.

Initial results look promising, and a full analysis of the experimental results from the three machines will be presented at the meeting.

[CP1.021] MHD-Calibrated ELM Model in Simulations of ITER

Simulations of ITER have been carried out using the JETTO integrated modeling code in which theory motivated models are used for the H-mode pedestal and for the stability criteria that lead to the ELM crashes. In the simulations, ELM crashes are triggered either by ballooning or peeling modes. The equilibrium and MHD stability analyses codes, HELENA and MISHKA, are used to evaluate the edge stability of the plasma just prior to an ELM crash in order to calibrate and confirm the validity of the stability criteria used to trigger ELMs in the JETTO simulations. In the simulations, core transport is calculated using an anomalous transport model such as the Mixed Bohm/gyro-Bohm model, while ion thermal neoclassical transport is used for the pedestal region. Studies are carried out varying the auxiliary heating power and the width of the pedestal in order to examine sensitivity of fusion Q to these parameters.

[CP1.022] Model of n=0 Energetic Particle Induced Oscillations in JET

Pronounced n=0 frequency sweeping phenomena has been observed in the JET tokamak experiment during ICRF heating. The observed frequency is below the TAE frequency, typically reduced by the inverse aspect ratio. The mechanism for instabiities leading to frequency sweeping is usually attributed to the universal instability drive from energetic particles coupling with Alfvenic excitations as in the case for TAE instabilities and fishbone oscillations. However, for an n=0 mode, the universal instability mode does not apply and the instability mechanism needs to arise from another source. A theoretical model to explain this observation attributes the basic mode to a radial 'breathing" oscillation and instability drive to the energetic ion anisotropy produced by ICRF heating. Analysis and modelling will be presented. This new model produces mode frequencies that scale properly with changing experimental parameters and the anisotropy drive is comparable with the method of heating where ICRF resonance is on the high field side of the magnetic axis.

[CP1.023] Shear and collisionality dependences of particle and impurity pinches in JET and TCV

Results from a wide range of experiments in JET and TCV are reported. Experiments with LHCD in source-free, MHD-quiescent JET L-modes, show for the first time, that the curvature pinch is the dominant convective process resulting in an empirical scaling n_e/\sim1.6\cdot l_i. The same behaviour is obtained in TCV, both in steady state and in current modulation experiments. The latter also show that the Ware pinch cannot account for these observations. Only H-modes at low collisionality exhibit an l_i dependence; at high collisionality H-modes become increasingly flatter. No evidence for parameter dependences other than those on shear and collisionality have been found on JET. On TCV, particle transport is also influenced by the ECH power and deposition radius. In JET, the peaking factor of the intrinsic carbon impurity density profile, is smaller than that of n_e. Carbon density profiles are almost flat in H-modes, irrespective of plasma parameters.

[CP1.024] Modeling divertor radiation in JET ELMy discharges with seeded impurities

ITER design assumes the steady-state fraction of radiation in the divertor is 0.5 Ar and N impurities have been injected in high triangularity high density ELMy H-mode plasmas to demonstrate the feasibility of such a scenario. The degree to which extrinsic impurity radiation either replaces or adds to radiation from intrinsic C remains a question. Multi-species solps5 code simulations for Ar and N, using a semi-analytic ELM model based on features of linear ballooning-peeling modes, are used to evaluate the degree to which injected Ar may increase C chemical erosion, due to D-induced bond passivation and, in contrast, the possibility that injected N may suppress chemical erosion, also due to C bond passivation. Further complications are due to co-deposited films and dust particles. We describe and compare a 1-D analysis of the thermal response of structured layers to ELM energy bursts, and a model for possible ELM-to-ELM variation in surface temperature due to small dust particles, similar to that developed for DIII-D type I ELMs.

[CP1.025] Simultaneous evaluation of Ni, D and electron heat transport in L and H mode JET plasmas

Transient perturbations of electron heat, deuterium density and Ni density have been all applied in the same JET L and H mode discharges to probe the transport properties of heat and particles. Electron heat, deuterium and Ni transport are sensitive to the same threshold in\nabla (Te)/Te that excites electrostatic turbulence (ITG+TEM). Ni diffusion has been found to be similar to the electron thermal diffusivity as well to the main gas diffusivity in both magnitude and radial shape. According to a linear stability analysis code (KINEZERO) the ITG/TEM instabilities are well correlated in space with the regions of high Ni and heat diffusivity.

[CP1.026] Beam ion distribution function in large tokamaks

The distribution function of beam ions formed by the Neutral Beam Injection (NBI) is studied in order to describe it analyticaly including the collisional velocity drag and pitch angle scattering mechanisms. This distribution function in large tokamaks like JET and planned ITER, is typically strongly anisotropic in the velocity space, which affects the stability of different MHD modes such as Alfvén eigenmodes. In this study we develop a model for the beam ion distribution function in the form of slowing down in velocity and Gaussian-like in pitch angle. We employ image source/sink method for the pitch angle scattering diffusion, which shows good agreement with the Monte-Carlo simulations if the pitch angle width is small as compares with the confinement regions in the velocity space. Surprisingly, we find that for TAE modes the model distribution function increases, rather than decreases, the growth rate that would be obtained from the ømega_* drive if one omitted the energy derivatives of the distribution function.

[CP1.027] A High Throughput Spectrometer System for CER Spectroscopy and Helium Ash Detection for JET

The Charge Exchange Recombination (CER) Spectroscopy system at JET is being upgraded to improve the photon throughput of the diagnostic system and improve its detection efficiency. The system will provide not only routine measurements of ion temperature, toroidal rotation velocities, and impurity densities, but also will be optimized for helium ash detection in future DT operation of JET. This diagnostic uses CER spectroscopy in conjunction with neutral heating beams to measure the carbon and helium densities at 40 radial locations(\approx 4 cm resolution) across the JET plasma via the 5290 ÅC and 4686 ÅHe lines and an array of heated quartz fibers. The diagnostic utilizes a high throughput spectrometer with f/1.8 input optics, two entrance slits, a transmission grating, and refractive optics. The detector is a thinned back-illuminated charge coupled device that has a high quantum efficiency of \approx 90 %, a 10 MHz readout, and a time resolution of 10 ms.

[CP1.028] Poloidal Magnetic Field Measurements Using Emission from Fast Secondary Lithium Atoms

Emission from fast secondary lithium atoms has been observed during the injection of a Li beam (40-50 keV) into JET plasmas. Secondary atoms (SA) are produced due to neutralization of the fast gyrating Li^+ ions created by the Li beam. The intensity of the SA emission is 10-20% of that from the beam atoms, with spectral width up to 1 nm. Since the SA preserve the velocity of the gyrating ions at the moment of neutralization, the Doppler spectrum of the SA emission is determined by the inclination of the gyration plane to the beam and line of sight. Hence, the components of the magnetic field vector can be inferred from an analysis of the SA spectrum. The shape and intensity of the SA-emission spectrum are successfully simulated by assuming the Li ions are locally trapped by the magnetic field near the injection port. Results from SA spectroscopy to determine the edge poloidal magnetic field in JET are presented. This work was performed under EFDA, and was partly funded by the UK Engineering and Physical Sciences Research Council and by EURATOM.

[CP1.029] Burning Plasmas

[CP1.030] High-Beta Steady-State Advanced Tokamak Regimes for ITER and FIRE

An attractive tokamak based fusion power plant will require the development of high-\beta steady-state advanced tokamak regimes to produce a high gain burning plasma with a large fraction of self-driven current and high fusion power density. Both ITER and FIRE are being designed with the objective to address these issues by exploring and understanding burning plasma physics in the conventional H-mode regime, and in the advanced tokamak (\beta _N \sim 3 - 4, f_bs \quad \sim 50 - 80%) regime envisioned for an attractive steady-state high power density fusion power plant. ITER has employed conservative scenarios, as appropriate for their nuclear technology mission, while FIRE has employed more aggressive assumptions aimed at exploring the scenarios envisioned in the ARIES power plant studies. The main characteristics of the advanced scenarios presently under study for ITER and FIRE are compared with advanced tokamak regimes envisioned for the European Power Plant Conceptual Study (PPCS-C) and the US ARIES-RS Power Plant Study. The physics and plasma technology issues of ITER and FIRE are very similar, and technical solutions for one will likely be applicable to the other. The goal of the present work is to develop AT modes that would fully exploit the capability of ITER and FIRE. This paper will summarize the status of the work and indicate critical areas where further Ramp;D is needed. Supported by DOE Contract # DE-AC02-76CHO3073.

[CP1.031] Spectrum of Experiments on Burning Plasmas: The Case for a U.S. Ignition Device

A spectrum of experiments on meaningful fusion burning plasmas is a natural step for fusion research. Within this spectrum, a U.S. experiment (Columbus) designed to reach ignition in a D-T plasma is envisioned. To shorten the design and construction times, the Columbus concept [1] adopts the same design solutions as those developed for the compact high field device Ignitor to be sited near the Italian-French border. The plasma volume is about 50% larger than that of Ignitor but Columbus (R_0 \simeq 1.5m,a\times b\simeq 0.54\times 0.98m^2) retains the ability to reach ignition by Ohmic heating alone by producing the same average poloidal field øverline B _p \simeq 3.4T, as Ignitor, with the same magnetic safety factor q_\psi \simeq 3.6. The corresponding plasma current I_P \simeq 12.6MA is the same as that estimated for the Iter-Feat concept assuming the same safety factor. It is expected that the first wall and the ICRH systems will be designed with complementary criteria to those adopted for Ignitor. The magnitude and number of issues to be resolved in the physics of burning plasmas is the main justification for two parallel ignition experiments at this time. [1] B. Coppi and M. Salvetti, MIT (RLE) Report PTP 02/06, 2002

[CP1.032] The Potential Role of Fusion Energy in China and India

It is projected that both China and India will install many 100's of megawatts electric (MWe) of additional electrical capacity by 2050 with more additions later. All energy resources will be required to meet such a demand. Fortunately, while world energy demand will be increasing, the world is well endowed with a variety of energy resources. However, their distribution does not match well the areas of demand and there are many environmental issues. Such geopolitical issues affect China and India and make it important for them to be able to deploy improved technologies. International collaborations in developing these technologies, such as the International Thermonuclear Experimental Reactor (ITER), may be important in all energy areas. In this regard, Korea is an interesting example of a country that has worked with other countries to develop its own capability to do advanced technologies - such as nuclear fission plants - in a relatively short time. Fusion energy is viewed as interesting potential option in these three countries.

[CP1.033] Tritium recovery in ITER by radiative plasma terminations

Safety considerations will limit the in-vessel inventory of tritium (T) in ITER to 350 g. It is predicted that the T retention rate will be > 3 g / pulse, due to codeposition of T in redeposited carbon layers formed by plasma erosion and deposition. To minimize the operational impact of T retention in ITER, it is necessary to develop routine, effective in-situ T recovery techniques. Planned radiative plasma terminations are examined as a method to recover tritium from plasma-deposited layers in the ITER tokamak. The technique exploits the high energy density of the ITER plasma, which is converted into a quasi-uniform radiation pulse by massive impurity injection that benignly terminates the plasma discharge. The radiation pulse transiently heats all plasma-viewing surfaces in order to desorb the tritium, which is released into the vessel and recovered by pumping. Calculations indicate significant tritium removal at reduced plasma current, \sim 6-10 MA, indicating the possibility of routine T recovery during the current rampdown phase of each discharge or during low current tritium recovery discharges. Supported by the US D.O.E. under Grant No DE-FG02-04ER54762.

[CP1.034] Runaway electron generation in a cooling plasma

Large numbers of runaway electrons are often generated in tokamak disruptions. In the classic calculation of Dreicer runaway generation it is assumed that the plasma is in a quasi-steady state. Although it is generally true that the plasma cools down in a disruption on a time scale longer than the electron collision time, electrons in the high-energy tail of the pre-disruption Maxwellian lose energy relatively slowly. Just after the thermal quench of the disruption an enhanced population of energetic electrons is therefore present in the plasma. These electrons are easily converted into runaways by the rising electric field, and this can lead to much more efficient runaway electron generation than the usual mechanism if the thermal quench is sufficiently rapid. This appears to be the case in present-day experiments, and can be expected to an even higher degree in ITER. Runaway production may thus be more severe than previously thought in ITER.

[CP1.035] DYNAMICS OF IGNITING PLASMAS

A unique feature of the Ignitor experiment is that is designed to reach for the first time the conditions where the thermonuclear instability due to -particle heating can develop. We have investigated the means by which the instability can be controlled, including the injected plasma heating power, the deuterium/tritium concentrations, and the effects of the expected sawtooth oscillations driven by the plasma pressure gradient. An ad hoc version of the JETTO transport code [1] has been used with the deuterium and tritium densities evolving separately under independent inflows. The boundary conditions for the main ion diffusion equation include recycling that assures density conservation in the absence of external inflows. Different combinations of the inflows of the main ions and of the duration and values of the injected RF power are shown lead to a large range of possibilities, from the onset of ignition and of the thermonuclear instability to quasi-stationary burning plasmas with a fusion gain exceeding 10.

[1] A. Airoldi and G. Cenacchi, Nuclear Fusion 41, 687 (1997)

[CP1.036] Optimization of the Ignitor Operating Scenario at 11 MA

A new reference 11 MA operational scenario for Ignitor has been developed in order to reduce electromagnetic loads and power supply requests, and to avoid the use of Dispersion Strengthened Copper in some of the PF coils. The analysis and a relevant simulation of a typical fast vertical disruption have been carried out with the MAXFEA code, obtaining values within the engineering constraints during the whole operating scenario. A new approach for mitigating the EM loads on the plasma chamber has also been investigated, based on the use of copper toroidal layers added to the plasma chamber in order to simulate the effects of a plasma chamber of varying thickness in the outer regions of its vertical cross section. This appears to be quite effective not only in increasing the time constant of the plasma displacement but also in reducing the vertical force and its combined effect with hoop force on the vessel.

[CP1.037] Ignitor Performance in Plasmas Without Tritium

Ignitor is a high-field (B_T = 13 T), high plasma current (I_p = 11 MA), compact (R_0 = 1.32 m, a= 0.47 m) experiment whose main objective is to attain ignition conditions in deuterium-tritium plasmas with Ohmic heating and the possible aid of modest amounts of ICRF heating. It is expected, however, that most experiments during the life time of the machine will be carried out with hydrogen, deuterium, helium and mixtures of them, without the benefit of alpha particle heating. Therefore we have analyzed the plasma regimes that can be obtained in the absence of tritium and found that, when compared with the results of present day experiments, they are of definite relevance to the physics of burning plasmas. In particular, we have considered cases where the Ignitor machine is operated with lower parameters than those indicated earlier and longer plasma current pulse durations. An example is B_T = 9 T, I_p=7 MA, with a 12 s current pulse flat-top.

[CP1.038] Optimisation of the Current Distribution in the Ignitor Poloidal Field Coils During the Reference Operating Scenario

A 2D axisymmetric integral code developed in ENEA has been used to calculate the temperatures and resistances in the poloidal field coils during the whole Ignitor reference operating scenario at 11 MA and its results compared with those obtained with the code MAXWELL FEM. Our code calculates both the electromagnetic forces and resistivity for every turn of the coils during the expected current scenario. The temperature increase due to the Joule effect is then computed and the maximum temperature value for each coil is obtained. Due to the short duration of an Ignitor discharge, the heat transfer mechanism is approximated as being completely adiabatic (that is conservative). It is seen that acceptable temperature values are reached in the inner central coils when an optimal current density redistribution is adopted and an appropriate grading technique for their design is employed.

[CP1.039] Effects of Density Profile Peaking on Confinement

The suggestion that peaked density profiles produced by the injection of pellets in order to unlock the confinement from its “saturated” state in Ohmic regimes was made by one of us on the basis of the theory of both “plane” [1] and “toroidal” [2] ion temperature gradient (ITG) driven modes. A series of experiments started with the Alcator C machine and continuing with current experiments with repeated pellet injections on the FTU machine have confirmed that confinement is improved systematically. The same kind of profiles is optimal for the conditions under which ignition can be achieved in burning plasmas. A comparison of relevant dimensionless parameters obtained in different experiments, including the Alcator C Mod machine, with those of ignition regimes, to be produced by Ignitor for instance, is made and related to the results of numerical simulations of the plasma heating process toward ignition process. [1] B. Coppi, M. N. Rosenbluth and R.Z. Sagdeev, Phys. Fluids 10, 582 (1967) [2] B. Coppi and E. Pegoraro, Nucl. Fus. 17, 969 (1977)

[CP1.040] Edge Modelling for Ignitor

The Ignitor design is characterized by the absence of a separate divertor volume. The plasma chamber is covered by a first wall of molybdenum tiles acting as an extended limiter that follows very closely the plasma shape. The available 2D simulation codes are not able to treat this configuration because of the singularity at the tangencypoint between LCFS and first wall. Therefore more flexible numerical schemes are being explored for a proper treatment of the Ignitor configuration. Simpler analyses show that a large fraction of the power available during a high performance discharge in Ignitor can be radiated. The remaining fraction is assumed to be deposited on the first wall by convective/conductive mechanisms, and the resulting thermal loads on the tiles are estimated. Moreover the thermal wall loadings resulting from possible 3D asymmetries have been analyzed by simple geometrical modelling of relevant configurations.

[CP1.041] Ignitor Vacuum Vessel Structural Design with Dynamic Loads Due to Plasma Disruption Event

The new reference plasma disruption for IGNITOR produces a significant increase of electromagnetic (EM) loads and requires a dynamic elastic-plastic structural analysis of the vacuum vessel (VV). The EM loads due to the worst disruption event (VDE) have been calculated using the MAXFEA 2D code and it is found that the stresses and deformation that would be produced on a relatively thin chamber could be excessive. A varying thickness configuration for the VV has been adopted on the basis of a step by step optimization with the aim of minimizing the vertical displacement while complying with the allowable plastic strains. A non-linear analysis is required with a modelling of the entire (360°) VV structure. With the new thickness distribution, the VV is capable to withstand several hundred of cycles under plasma disruption conditions in compliance with the ASME III code rules.

[CP1.042] The Ignitor Fast Pellet Injector

A collaboration between the ENEA Laboratory at Frascati and the Fusion Technology Group of Oak Ridge for the development of a fast pellet injector for the Ignitor ignition experiment has been established. The program aims at the construction of a 4 barrel, double stage gun able to reach speeds up to 4 km/s and thus penetrate to the core of the plasma column. The compact size of the Ignitor machine favors the injection from the low field side, for which very positive results have been obtained on the FTU machine [1], in terms of density profile peaking and good energy confinement. The ongoing activities include the procurement of all the hardware for the criocooler, diagnostics and control electronics, from the ORNL side, and the design and construction of the gun by ENEA. A new fast valve has been developed that considerably reduces the requirements on the expansion volumes necessary to prevent the propulsion gas to reach the plasma chamber.

[1] D. Frigione, et al., Nuclear Fusion 41, 1613 (2001).

[CP1.043] Ignitor Electrical Power Supply System

An iterative optimization process to reduce the total installed electrical power required for Ignitor has been performed, bringing its value down to about 70% of that estimated originally. Ignitor is planned to be installed within the 400 kV Station of Rondissone (near Turin). The required electrical power (1000 MVA / 320 MVAr, including 480 MVAr locally compensated through static system, SVC) has been demonstrated by the technical authority GRTN to be compatible with the Grid capability. The magnet systems of Ignitor are supplied by means of a set of 14, 12 pulse, current regulated, sequentially or internal freewheeling controlled, fully static power amplifier units which are installed inside standard, outdoor-kind containers, located near to the related step-down transformers. Each container can house up to 100 MW, 2x12 pulse power amplifier units. The connection between the power amplifiers and the machine is performed by means of coaxial, outdoor-kind, segregated bus-bars. These choices make the whole power supply system as flexible as possible in terms of the overall layout of the Ignitor plant.

[CP1.044] First Wall System and Plasma Chamber of Ignitor

The designs of the Plasma Chamber of Ignitor and of the First Wall system have been integrated and carried out considering the most updated scenarios for disruption as well as the estimates for the maximum thermal wall loadings at ignition. The first wall system consists of a set of Molybdenum tiles that cover the entire plasma chamber and are attached to a smaller set of tile carriers that can be replaced by an appropriate remote handling system. The design of the system is based on the experience gained on the JET and the FTU machines. The peak wall loading on the tiles at ignition is valued at \simeq1.8\ MW/m^2 when extended limiter equilibrium configurations (with no X-points within the plasma chamber) are considered. The same tile system is compatible with the thermal wall loading estimated for double-X point equilibrium configurations and operation in the H-regime up to ignition. A detailed structural analysis of the most loaded set of tiles has been carried out and has confirmed the validity of adopted design and fabrication criteria.

[CP1.045] Transport and Turbulence

[CP1.046] Sources and Sinks in the Zonal Flow Energy Balance in Tokamak Microturbulence

The relative contributions of various terms to the driving and damping of the zonal flows in toroidal ion temperature gradient turbulence are investigated using nonlinear gyrokinetic simulations. An in-code calculation of the contributions to the zonal-flow shear (A.M. Dimits et al. APS-DPP02 meeting) is used. Our investigation addresses zonal flows in the late-time turbulent steady-state, in addition to their early-time generation. It is found that zonal flow energy is generated primarily through the Reynolds'-stress term and dissipated by the transit-time damping terms. The source/sink rates of other terms, such as the diamagnetic Reynolds stress, are finite but lower. We also examine whether a spatially local determination of the flow shear contributions, which is more analagous to what could be probed with esperimental diagnostics, can provide similar or useful information on the zonal-flow balances.

[CP1.047] Global Gyrokinetic Particle Simulation of Shaped Plasmas

A general geometry capability has been developed for the gyrokinetic toroidal code GTC with enhanced and extended features including a systematic treatment of plasma rotation and equilibrium E\timesB flow, realistic plasma profiles and corresponding MHD equilibria and electron dynamics, etc. A symmetry coordinate system is used to construct a relatively regular mesh in real space for strongly shaped plasmas, which also facilitates straightforward visualization. By rescaling the radial coordinate with a factor of 1/ \sqrtT_i, grid size is correlated with the local gyroradius which may vary substantially from the core to the edge. Gyrokinetic transformation of potential and charge density between particle and guiding center positions in general geometry is carefully treated, taking into account finite B_\theta/B. The applied equilibrium E\times B flow, which is believed to play an important role in determining the turbulence level, is calculated from our global neoclassical particle code GTC-Neo. In the large aspect ratio circular geometry limit, cross benchmarks with the original GTC code and the eigenvalue code, FULL, show good agreement in both real frequency and growth rate for ion temperature gradient modes. Nonlinear electrostatic simulations of shaped plasmas are conducted with focus on turbulence and transport properties in rotating plasmas and in reversed shear plasmas with consideration of possible radially-localized structure.

[CP1.048] Alfven wave propagation in gyrokinetic tokamak plasmas

A new finite element Poisson solver is developed and successfully implemented into the GTC code which enabled us to simulate non-adiabatic kinetic electrons.(With an assistance of algebraic multigrid; acts-tool, PETSc and hypre). Further, Pade approximation to the Poisson equation is applied. Employing the fluid-kinetic hybrid electron model,(Z.~Lin and L.~Chen Phys. Plasmas 8), 1447 (2001). the magnetic perturbation is obtained by inverting the induction equation E = - \nabla \Phi - \partial_t A instead of solving the Ampere's law, which has facilitated the computation. We focus on the electromagnetic and finite beta effects on drift wave turbulence. At a critical \beta value, we expect excitations of new electromagnetic modes, that are the Alfvenic ion temperature gradient mode (AITG)(G.~Zhao and L.~Chen, Phys. Plasmas 9), 861 (2002). and the kinetic ballooning mode (KBM). The linear growth rate and the onset (the threshold \beta value) of the modes are investigated. As one of the test problem, we perturb a magnetic field line and visualize three dimensional structure of the shear Alfven wave propagation. Work supported by DOE Cooperative Agreement DE-FC02-03ER54695 (UCI), DE-AC02-76CH03073 (PPPL).

[CP1.049] Evaluation of the Neoclassical Radial Electric Field in a Collisional Tokamak

The neoclassical electric field in a tokamak is determined by conservation of toroidal angular momentum. In the steady state and in the absence of momentum sources and sinks it is explicitly evaluated by the condition that the radial flux of toroidal angular momentum vanish. Of course, for isothermal ions the viscosity must simplify to an expression that vanishes for a radial Maxwell-Boltzmann ion response. In the presence of ion temperature variation obtaining the electric field in terms of density and temperature gradients is far more complicated. For a collisional or Pfirsch-Schlüter short mean free path ordering in which the plasma flow is allowed to be sub-sonic we find that there are two limiting cases of interest. The first is the simpler case of a strongly up-down asymmetric tokamak (for example, just inside the separatrix of a single null configuration) for which the lowest order gyroviscosity does not vanish and must be balanced by the leading order collisional viscosity in order to determine the radial electric field. The up-down asymmetric contribution to the viscosity is formally larger than customary estimates for the viscosity and so may be responsible for a portion of the experimentally observed enhancement of angular momentum diffusivity. The second case is the more complicated case of an up-down symmetric tokamak for which the gyroviscosity must be evaluated to higher order and balanced by the lowest order collisional viscosity to determine the radial electric field. Work supported by U.S. DoE

[CP1.050] MHD and Electrostatic Turbulence in the Helimak Device

MHD and electrostatic drift wave simulations are carried out for the Helimak experiment and compared with experimental data. The Helimak is a cylindrical device with inner radius r_1=0.6~m, outer radius r_2=1.6~m. A toroidal field is produced by 16 field coils. Biased end plates produce a variable radial electric field that drives sheared axial \mathbfE\times\mathbfB flow. Three poloidal field coils produce a weak vertical field that creates very long (up to 1~km) helical magnetic field lines from the botton to the top of the chamber. The objective is to classify the various types of turbulence in the ECH driven hot electron plasma and control the turbulent transport with the imposed radial electric field. Viscous-resistive MHD simulations as well as 2D and 3D drift wave simulations are being carried out to predict the fluctuation spectrum. The viscous-resistive MHD code has sheared flows and sheared magnetic fields and uses a radial Chebyshev-tau expansion that resolves steep radial gradients. The code was benchmarked against the linear eigenmodes from magnetized Couette and Poiseuille plane flow solutions. Work supported by DOE grant DE-FG02-04ER5474.

[CP1.051] Drift-wave Turbulence in the Helimak

The Helimak realizes a simplified cylindrical slab geometry to study drift-wave plasma turbulence in argon and hydrogen. Low density allows arrays of hundreds of Langmuir probes. The Helimak remains stable at values of vertical magnetic field below that expected from the Suydam criterion. At the smallest value of the vertical field, the system exhibits an MHD instability of global character with a fluctuating magnetic field. Otherwise, only typical drift-wave turbulence occurs. The density fluctuations have correlation lengths of 0.1m, characteristic timescale of 0.1ms and poloidal (vertical) wave phase velocity \sim 1000 m/s consistent with the diamagnetic drift velocity. New electric field (potential) measurements are also consistent with drift waves and allow for computation of turbulent particle fluxes.

Work supported by the Department of Energy Office of Fusion Energy Sciences DE-FG03-00ER54609.

[CP1.052] Helimak -- Drift-Wave Turbulence in the Cylindrical Slab

The Helimak is a good approximation to the infinite cylindrical slab. Conducting end plates and a helical magnetic field provide an MHD equilibrium unstable to drift waves. The equilibrium profiles result from a balance among source, convective flow along field lines to the ends, and radial turbulent transport. Measurements of the plasma profiles, particle confinement times, turbulent fluxes, and Reynolds stresses will be presented.

Work supported by the Department of Energy Office of Fusion Energy Sciences DE-FG03-00ER54609.

[CP1.053] Gyrokinetic simulation of ITG modes in a three-mode coupling model

A three-mode coupling model of ITG modes with adiabatic electrons is studied both analytically and numerically in 2-dimensional slab geometry using the gyrokinetic formalism. It can be shown analytically that the (quasilinear) saturation amplitude of the waves in the system should be enhanced by the inclusion of the parallel velocity nonlinearity in the governing gyrokinetic equation. The effect of this (frequently neglected) nonlinearity on the steady-state transport properties of the plasma is studied numerically using standard gyrokinetic particle simulation techniques. The balance [1] between various steady-state transport properties of the model (particle and heat flux, entropy production, and collisional dissipation) is examined. Effects resulting from the inclusion of nonadiabatic electrons in the model are also considered numerically, making use of the gyrokinetic split-weight scheme [2] in the simulations.

[1] W.\ W.\ Lee and W.\ M.\ Tang, Phys.\ Fluids 31, 612 (1988).

[2] I.\ Manuilskiy and W.\ W.\ Lee, Phys.\ Plasmas 7, 1381 (2000).

[CP1.054] Multispecies density and temperature gradient dependence of quasilinear particle and energy fluxes

The variations of the normalised quasilinear particle and energy fluxes with artificial changes in the density and temperature gradients, as well as the variations of the linear growth rates and real frequencies, for ion temperature gradient and trapped-electron modes, are calculated. The quasilinear fluxes are normalised to the total energy flux, summed over all species. Here, realistic cases for tokamaks and spherical torii are considered which have two impurity species. For situations where there are substantial changes in the normalised fluxes, the ``diffusive approximation,'' in which the normalised fluxes are taken to be linear in the gradients, is seen to be inaccurate.

[CP1.055] Nonlinear Saturation of Zonal Modes in Ion Temperature Gradient Driven Turbulence

The nonlinear excitation of damped eigenmodes provides a new mechanism for the saturation of collisonless trapped electron mode (CTEM) turbulence^1,2. The damped eigenmodes also provide a finite-amplitude-dependent damping of the zonal modes (k_y =0), and hence saturation. Ion temperature gradient (ITG) turbulence simulation has shown the similar behavior to that of CTEM turbulence. Here, we will present numerical results of the excitation and saturation of zonal modes(k_y = 0) in ITG turbulence. A local three-field model, with fixed wavenumber in the direction of homogeneous magnetic field, is used to investigate the role of nonlinearly excited damped and neutrally stable eigenmode branches on the zonal modes. The effect of nonlinear zonal mode damping on saturation of ITG instability will also be studied.

(1) P. W. Terry, et.al., Phys. Rev. Letts. \textbf89 (2002) 205001. (2) D. A. Baver, et.al., Phys. Plasmas \textbf9 (2002) 3318.

[CP1.056] Inward Particle Flux in Collisionless Trapped Electron Mode Turbulence

In collisionless trapped electron mode (CTEM) turbulence, saturation occurs by energy transfer to a damped eigenmode excited by nonlinear advection of electron density. The damped eigenmode produces an inward particle flux component. We examine the overall flux produced by the nonlinear eigenmode, which combines unstable and damped contributions, including the cross correlation of the non-orthogo-nal eigenmodes. The inward flux components are nearly as large as the outward components, making the net flux positive but significantly reduced relative to the quasilinear flux. The inward flux has diffusive and convective components. The latter is a pinch that is fundamentally different from the collisionless thermodiffusive pinch,^1 but is much smaller than the negative diffusion. We also examine the role of near-zonal modes, which contribute to the inward flux and whose amplitude is elevated by proximity to the zonal modes, where the spectrum peaks. ^1P.W. Terry, Phys. Fluids B \bf1, 1932 (1989). Work supported by USDOE.

[CP1.057] Ion transport from collisions and finite guiding centre drift excursions

A study is made of the effects on ion transport of collisions and of finite drift excursions for a variety of guiding centre drift orbit shapes. The drift excursions are calculated from the guiding centre drift equation for individual orbits. Collisions are described by a Fokker-Planck operator valid in all collisionality regimes which describes the interaction between a test particle and a thermal plasma. The test particles represent the thermal ions of the plasma such that the collision operator is made to conserve particle number, momentum and energy. The momentum conservation leads to a new formulation of the ion heat flux from test particle calculations. General Monte Carlo type equations are derived from moments of the collision operator. A plasma equilibrium based on a JET configuration is used in computations which scan a phase space of three dimensionless variables that characterise the guiding centre orbits. The time-space dependent contributions from the drifts across flux surfaces are accumulated to yield the ion heat flux profile. This profile differs from those predicted by conventional neoclassical theories in the axial region, but is in rough agreement in the outer region. The edge value is approximately a third of the experimental value.

[CP1.058] Electron Internal Transport Barrier Triggered by Nonlocal Transport Phenomenon in the Large Helical Device

An electron internal transport barrier (ITB) appears when a Tracer-Encapsulated Solid Pellet (TESPEL) is injected to induce a rapid cooling of the edge plasma in the Large Helical Device (LHD). The formation mechanism of the TESPEL induced electron ITB accompanied by an increase in plasma collisionality due to the TESPEL injection is quite different from that of the electron ITB associated with the transition from ion root to electron root under the condition that the plasma is well into the collisionless regime by decreasing electron density. The TESPEL induced electron ITB is triggered by a nonlocal temperature rise in response to the edge cooling, which is observed for the first time in toroidal helical plasmas. The nonlocal electron temperature rise in response to the edge cooling has been observed even in net-current free plasmas obtained by electron cyclotron resonance heating (ECH) as well as in plasmas heated by neutral beam injection (NBI) and NBI + ECH. The detail analysis results of the nonlocal electron temperature rise in response to the edge cooling will be shown and discussed in the presentation.

[CP1.059] Role of magnetic shear in dynamics of large-scale structures in electron temperature gradient turbulence

We investigate how the magnetic shear governs the dynamics of large-scale structures, such as zonal flows and streamers, in electron temperature gradient (ETG) driven turbulence. Based on the well-known 2D Hasegawa-Mima turbulence modeling, which is the inviscid version of fluid (or gyrofluid) ETG turbulence [1], we derive a general dispersion relation of secondary fluctuations through modulation instability analysis. The results show that the formation of different large-scale structures including zonal flow, streamer and so-called generalized Kelvin-Helmholtz (GKH) mode in ETG turbulence depends on the spectral anisotropy of turbulent fluctuation. In a slab geometry, the magnetic shear closely relates to the ETG mode structures so that it may determine the pattern selection in the quasi-steady ETG turbulence. 3D gyrofluid slab ETG simulations show that turbulent ETG fluctuation energy condenses to the zonal flows in the weak shear plasmas and to the streamer component for the high shears. 2D ETG simulations with rather high resolution not only exhibits the global spectral distribution of zonal flows, but also further confirm a mechanism: enhanced zonal flow in weak shear ETG turbulence is limited by exciting a KH mode [1]. Furthermore, in toroidal ETG simulations, streamer structures are observed at around good curvature region along the flux tube in the quasisteady state in some medium shear regime. Related streamer dynamics are also investigated.

[1] Jiquan Li and Y. Kishimoto, Phys. Plasmas 11, 1493(2004)

[CP1.060] Wave-particle interaction and the nonlinear saturation of the electron temperature gradient mode

It has been proposed that the electron temperature gradient (ETG) driven turbulence is responsible for experimentally relevant electron thermal transport in tokamak plasmas. Significant transport levels are possible by the creation of radially elongated vortices or ``streamers" [1,2], which are sustained by the nonlinear saturation of the instability and are not susceptible to shear flow destruction, as is the case with the ion temperature gradient (ITG) mode. We present a dynamical system to explore the dependence of saturation level due to \mathbfE \times \mathbfB and E_\| motion, as well as the effect of radial elongation. With this model, we can predict the nonlinear saturation level of the ETG streamers. We compare our theoretical predictions with a 2D shear-less slab gyrokinetic electron code that includes the E_\| nonlinearity. [1]F. Jenko, W. Dorland, M Kotschenreuther, and B.N. Rogers, Phys. Plasmas 7, 1904 (2000). [2]C. Holland, and P.H. Diamond, Phys. Plasmas 9, 3857 (2002). [3]W. M. Manheimer, Phys. Fluids 14, 579 (1971). [4]R. A. Smith, John A. Krommes, and W. W. Lee, Phys. Fluids 28, 1069 (1985).

[CP1.061] Analytic theory of L\rightarrowH transport bifurcation for a simple model of coupled heat and particle fluxes

The origin and structure of edge and internal transport barriers is one of the central problems in magnetic fusion research. A simplified model proposed in [1] includes coupling between the nonlinear fluxes of particles and heat in a form of two diffusion equations. Earlier, we solved this model analytically in a steady state assuming that regularization (taken in a form of hyperdiffusion) is applied to only one field (density or pressure). In this simple case the transition is shown to obey the Maxwell equal area rule. However, different regularization schemes result in different transition rules. We have shown that inclusion of the curvature of radial pressure profile, for example, leads to a criterion that the transition occurs at lower heat and particle fluxes. This dependence of transition criteria on the regularization clearly demonstrates the necessity of dynamical modelling. In this paper, we therefore also explore a time dependent approach. In particular we discuss the front propagation solutions describing the penetration of the H-mode state into L-mode state and vice versa.

[1] Hinton, F. L. and Staebler, G.M. Phys. Fluids, v,5, 1281 (1993)

[CP1.062] Optical and electrical measurements of edge turbulence in TPE-RX

Electrostatic turbulence in the edge region of RFPs has shown coherent structures emerging from the background. A new diagnostic system has been developed, aimed at identifying these structures by non-intrusive methods, at high plasma currents and thermal loads. The system consists of a gas-puffing nozzle, 32 optical chords measuring the Dalpha radiation emitted from the puffed gas and a removable array of Langmuir probes. The signals can be sampled at 10 MHz with 2 MHz band-width. The first extensive measurement campaign has been carried out in the TPE-RX RFP device in the AIST, in low and high current discharges, exploring different plasma conditions. High quality signals with large signal-to-noise ratio and effective band-width up to 400 kHz are obtained. Preliminary analyses show a distinct difference in the power spectrum of the optical signals between those from the puffed gas and those from the background radiation. The frequency spectrum obtained with gas puffing is consistent with the expected features of the turbulence in RFP edge region. Moreover the presence of coherent structures, propagating with a velocity of the order of 10 km/s, has been identified.

[CP1.063] Coupled simulations of edge plasma turbulence and transport with evolving temperature profiles

Predictive simulation of tokamak edge plasmas requires coupling of profile evolution and turbulence because each strongly affects the other. A systematic effort is underway to develop a full coupling between the UEDGE 2D fluid transport code and the BOUT 3D fluid turbulence code. Initially, the density and parallel velocity profiles were evolved in response to the radial turbulent particle flux obtained from BOUT.(T.D. Rognlien et al.), Contrib. Plasma Phys. 44 (2004) 188. Here those results are extended to include evolving ion and electron temperature profiles together with radial turbulent energy fluxes. The turbulent fluxes are represented in the transport equations as a combination of diffusion and convection to maintain numerical stability. Progress on time dependent evolution(X.Q. Xu et al.), Contrib. Plasma Phys. 44 (2004) 105. and including the evolving radial electric field will also be discussed.

[CP1.064] Density Threshold for Edge Poloidal Flow Generation

A numerical transport model is used to examine a density threshold for the onset of an edge poloidal velocity shear layer in toroidal devices. This work is motivated by recent experimental results from the TJ-II stellarator which indicate a critical density threshold for the development of an edge poloidal velocity shear layer [1]. Edge shear-flow layers are commonly observed in toroidal confinement devices, even in L-mode discharges. The numerical transport model has been used to examine internal transport barriers and front propagation of internal transport barriers [2]. The transport model couples together density, ion temperature, electron temperature, poloidal flow, toroidal flow, radial electric field, and a fluctuation envelope equation which includes a shear-suppression factor. In this work, we present results from a series of cases using parameters that are typical of TJ-II discharges. The dependence of the critical density threshold on flow damping and Reynolds stress drive is investigated.

[1] C. Hidalgo, M. A. Pedrosa, L. Garcia, and A. Ware, “Direct experimental evidence of coupling between sheared flows development and increasing in level of turbulence in the TJ-II stellarator”, submitted to Phys. Rev. E.

[2] D. E. Newman, B. A. Carreras, D. Lopez-Bruna, P. H. Diamond, and V. B. Lebedev, Phys. Plasmas 5, 938 (1998).

[CP1.065] Analytic theory of resistive modes in divertor geometry, and application to edge plasma quasi-coherent oscillations

Unstable resistive modes in the edge plasma are believed to be responsible for both intermittent and coherent transport across the separatrix. In divertor geometry, edge turbulence is markedly influenced by X-points and standard analytical techniques such as the two-scale approximation for resistive ballooning modes usually fail. Here we explore an alternative approach, based on treating the X-point region as a parallel boundary condition, dominated by strong local shear. Both WKB and asymptotically matched Born limits are considered. The resistive X-point (RX) modes seen in previous numerical studies are recovered analytically, and we show their relationship to the usual ideal strong ballooning and resistive ballooning regimes. Both electromagnetic and electrostatic RX modes are identified. The RX mode appears to share some properties with the quasi-coherent (QC) mode (associated with EDA operation) and previously reported simulations thereof. Progress in understanding and modeling QC oscillations will be discussed.

[CP1.066] Reduced-model simulations of turbulence and rf-driven convection in the edge and scrape-off layer plasma

Convective cells, ballistic (e.g. blob) transport and highly nonlinear fluctuations, associated with edge plasma turbulence, can be generated by, and/or interact with, strong ``dc'' sheath-generated electric fields from rf-launching structures.(D. A. D’Ippolito, et al., Phys. Fluids \bfB 5), 3603 (1993). We solve the coupled fluid equations of continuity and vorticity evolution numerically in the tokamak edge region and scrape-off layer (SOL), including the relevant rf source terms through radial boundary conditions and modification of the sheath terms. Though the simulations are restricted to the poloidal plane, we model parallel density and vorticity (charge) transport with terms intended to mimic different current loop closures, for example, in sheaths or by enhanced cross-field conductivity in the X-point region. These models will be studied and compared for their effects on the local plasma profiles to assess the implications for rf physics (e.g. antenna/plasma interaction) and in an attempt to identify a control knob for edge turbulence (e.g. through rf-antenna-driven sheared E).

[CP1.067] Measurements of Classical Transport of Fast Ions in the LAPD

To study fast ion transport in a well controlled background plasma, a 3cm diameter RF ion gun launches a pulsed, ~400 eV ribbon shape argon ion beam in the LArge Plasma Device (LAPD) at UCLA. The beam velocity distribution is calibrated by Laser Induced Fluorescence (LIF) on the Mirror of UCI and the beam energy is also measured by a two-grid energy analyzer at different axial locations (z=0.3-6.0 m) from the source on LAPD. Slowing down of the ion beam is observed when the beam is launched parallel or at 15 degrees to the 0.85 kG magnetic field. Using Langmuir probe measurements of the plasma parameters, the observed energy deceleration rate is consistent with classical Coulomb scattering theory. The radial beam profile is also measured by the energy analyzer when the beam is launched at 15 degrees to the magnetic field. The beam follows the expected helical trajectory and its contour has the shape predicted by Monte Carlo simulations. The diffusion measurements are performed at different axial locations where the ion beam has the same gyro-phase to eliminate the peristaltic effect. The spatial spreading of the beam is compared with classical scattering and neutral scattering theory.

[CP1.068] Measurements of Turbulent Transport of Fast Ions in the LAPD

Understanding the spatial transport induced by fluctuations is important to the confinement of magnetized plasmas. The paradox of fast ions being much better confined than thermal ions, i.e. the effective diffusion coefficient of fast ions being much smaller than that of thermal ions, has been observed experimentally [1], explained theoretically [2], and analyzed by simulations [3]. Gyroradius averaging and drift averaging are two predicted effects that are responsible for reduced fast-ion transport. Our goal is to quantitatively confirm these effects and make further exploration by measuring fast-ion transport as a function of gyroradius in the LArge Plasma Device (LAPD) plasma with well-characterized background fluctuations. A 3D gridded analyzer is used to measure the spatial profile of the beam produced by an ion gun launching ~500 eV Argon ions [4]. Strong drift wave fluctuations are generated by inserting a disk into the center of the plasma. First results will be presented.

[1] W. Heidbrink, G. Sadler, Nucl. Fusion, Vol. 34, p. 535 (1994); [2] P. C. Efthimion et al., Plasma Phys. and Cont. Nucl. Fusion Res., Vol. 1, p. 307 (1988); [3] G. Manfredi, R. Dendy, Phys. Rev. Lett. 76, p. 4360 (1996); [4] H. Boehmer et al. , Rev. Sci. Instrum. , Vol. 75, p. 1013 (2002)

[CP1.069] Dynamics of fluctuation driven flows in a toroidal system

Plasma polarization governed by plasma quasineutrality constraint is a critical element in the excitation of the plasma flow in response to the non-ambipolar radial electric current induced by drift wave fluctuations. In toroidal geometry, the neoclassical parallel viscosity provides a dominant contribution to the quasineutrality equation. This contribution is responsible for coupling of poloidal and toroidal flows and eventually manifests itself in the so called enhanced neoclassical polarization. As a result, the amplitude of the driven flow becomes controlled by the neoclassical polarization. We formulate a full system of the evolution equations describing the generation of flows in toroidal geometry. Various regimes of the neoclassical polarization are identified depending on plasma collisionality. We derive a fluid model where collisional (q^2/\epsilon ^2 factor enhancement), collisionless (q^2/\sqrt \epsilon factor enhancement), and intermediate regimes of the neoclassical polarization are investigated.

[CP1.070] Toroidal Plasma Rotation in TCV Ohmic L-mode Discharges

In the Tokamak à Configuration Variable (TCV) the toroidal velocity profile of fully stripped carbon is measured by active Charge eXchange Recombination Spectroscopy with a temporal resolution of typically 50ms and a spatial resolution of 2-3cm [1]. Recently steady state measurements of plasma rotation were performed on ohmic L-mode TCV plasmas with different values of the edge safety factor. The helicity of the magnetic field was also changed by inverting the direction of the plasma current. A fine scan in density was performed keeping constant all major plasma parameters. Carbon usually rotates in the counter-current direction with a velocity of few tens of km/s in the plasma centre. The toroidal velocity profile is typically hollow or flat in the presence of sawtooth activity and becomes peaked when q(0)>1, where q is the safety factor. The dependence of the toroidal rotation profile on plasma current and density will be described in details and compared with neoclassical theory predictions [2]. The correlation of MHD mode with toroidal plasma rotation will be assessed, as well as the effect of large modes on plasma rotation. [1] P.Bosshard, B.P.Duval, J. Mlynar, H. Weisen, Proc. 28th EPS Conf. on Plasma Phys. Control. Fusion, Madeira, 2001, Proc. 29th EPS Conf. on Plasma Phys.Control. Fusion, Montreux, 2002. [2] Y. B. Kim et al., Phys. Fluids B, 3 (8), August 1991, pp. 2050-2059.

[CP1.071] Confinement Bifurcations by Poloidal Magnetic Flux Perturbations in the TUMAN-3M

In experiments performed in TUMAN-3M, the possibility of switching on/off the H-mode by poloidal magnetic flux perturbations has been observed. The flux perturbations were created by fast current ramp up/down or by magnetic compression/decompression produced by fast increase/decrease in the toroidal magnetic field. It was found that the current ramp up and magnetic compression are robust means of H-mode triggering. The current ramp down and magnetic decompression allow termination of the H-mode. The transitions between the confinement modes in these experiments might be understood in terms of a unified mechanism in which E\times B sheared flow variation is induced by strong change in the toroidal electric field E_\varphi connected with poloidal magnetic flux perturbations. Possible roles of variations of the current density profile j(r) and power input in the L-H and H-L transitions in the above experiments are discussed as well.

[CP1.072] Short Pulse Laser-Plasma Interactions and Fast Ignition

[CP1.073] PLASMA PREHEATING BY ELECTRON CYCLOTRON WAVES PRODUCED BY A LASER PULSE PROPAGATING ALONG THE EXTERNAL MAGNETIC FIELD

We investigate analytically and via PIC simulations the possible mechanism of transverse electron heating associated with the turbulence of fast magnetosonic waves parametrically excited by a laser pulse. These waves can play an important role as an additional channel for plasma preheating during the experiments on interaction of the laser pulse with magnetized plasma. In the case when the spectrum of phase velocities is broad enough the heating can be described using the framework of quasi-linear theory. Numerical simulation of the interaction of the laser pulse propagating along the external magnetic field shows that along with the electrostatic upper hybrid wave laser pulse can parametrically excite a broad spectrum of fast magnetosonic waves with the frequencies below the electron cyclotron frequency. In simulations heating of electrons predominantly in the perpendicular to the direction of the laser pulse propagation direction was observed as well.

Work supported by the US Department of Energy under Grant No. DE-FC52-01NV14050 at UNR

[CP1.074] Laser-matter interaction including ionization and relaxation process

Ionization and relaxation processes play an important role in the interaction between high power laser and various material states such as gas, sold, clusters[1], etc. In order to study such a complex interaction, we have developed a Particle-In Cell (PIC) based extended 3-dimensional relativistic simulation code (EPIC), which includes both field and electron impact ionization, and collision among plasma particles. By using the EPIC, we investigate the interaction between carbon target and high power laser in the range of 10**17-19W/cm^2. Contrary to the usual laser-plasma interaction, the absorption of laser power and associated heat conduction inside the solid takes place accompanied by the complex ionization process. An avalanche of the ionization and associated propagation of the ionization wave dominated by the ambi-polar electrostatic field near the front is observed. The ionization front is found to be unstable against the ionization and show a complex spiky structure similar to that observed in a lightning event. Characteristics of nonlinear heat transport accompanied by the ionization will be also discussed. [1] Y. Kishimoto et al., Phys. Plasmas 9, 589 (2002)

[CP1.075] PIC modeling of the absorption region in short-pulse high intensity laser plasma interactions

In multi-dimensional PIC simulations, a rippled depression develops in the plasma density at the relativistic critical surface when a high intensity short pulse laser interacts with an overdense plasma. Electrons are ejected in a frequency of ømega_0, indicating a form of resonance absorption. We study the competition between resonance absorption and the J \times B effect in both 2D and 3D PIC Z3 simulations. Our modeling shows significant differences in the electron spectra in and out of the laser polarization plane. We study the development and evolution of the absorption mechanisms, the relativistic critical surface, and the generated hot electrons. We model cases with and without a pre-formed underdense plasma, and both normal and oblique angles of incidence. In this report, we present both the methods used to diagnose these multi-dimensional effects and the physics results obtained.

[CP1.076] Enhanced Implicit Modeling of Intense Laser-Matter Interactions

The 2-D ANTHEM simulation model has been enhanced to study a variety of short-pulse laser matter interaction problems. These improvements include: 1) Relativistic PIC hot electron transport, which now models detailed distribution dependent dynamics, while a hot electron fluid option provides a smooth economical alternative treatment. 2) Particle/fluid options for the background ions that accommodate detailed studies of either collisionless ion blow-off or collisional plasma shocks. 3) A new limiter on the ponderomotive force (PMF) near the critical density that limits the momentum exchanged to its content in the driving light. Also, the fluid/PIC background ions and cold electrons continue to allow for a density range from far below critical to 1000-times solid density. Implicit Moment fields avoid finite grid heating for cells much larger than a Debye length. Hot electron collisional loss and cold electron resistivity are modeled via electron scattering and drag. With the PMF limiter and finer, sub-skin depth zoning, ANTHEM now shows Weibel instability near the critical surface, in agreement with earlier explicit full PIC simulations, and related fast ion features on the back sides of thin foils.

[CP1.078] The role of space charge on the Weibel instability

We use analytical theory and PIC simulations using the code OSIRIS to examine the role of space charge on instabilities related to the electron distribution function anisotropy. Space charge effects become important, when the electron distribution function exhibits large relative temperature variations. We can therefore trace them back to the details of the distribution function.

These results will be important in understanding the development and evolution of unstable electromagnetic modes in regimes with such highly non-Gaussian distribution functions. An overdense laser-irradiated plasma, where a hot electron population propagates in the direction of the laser and a cold current-neutralizing background moves slowly in the other direction is such a regime. The fast ignition scenario is therefore amenable to application of this theory and we will discuss how our results affect the current filamentation instability in this case.

[CP1.079] Study of electron beam propagation in dense plasmas

The generation and transport of relativistic electron beams is a field of topical interest, in particular for the fast ignitor scheme relevant for inertial confinement fusion. We have studied the propagation of laser accelerated electrons in dense plasmas. Aluminium- and foam targets with various thicknesses were irradiated with the Petawatt laser beam at the Rutherford Appleton Laboratory (U.K.). The electron beam is investigated by observing the coherent transition radiation (CTR) generated at the target rear side. A decrease of CTR intensity for the thicker targets is observed and explained by dephasing of the electron bunches as they propagate through the plasma. For the foam targets, a break-up of the electron beam into filamentary structures is evident, showing that the relativistic electron beam is sensitive to Weibel type instabilities due to the counter propagating current of cold electrons. The experimental results are consistent with 3D PIC simulations.

[CP1.080] Relativistic Electron Transport in Ultra-Short Pulse Laser Cone-Fiber Target Interactions

We report the first experiments on cone-fiber targets from 100 TW to 1 PW class lasers. This is one method to confine or guide electron energy to small volumes. Targets consist of thin Gold cones with 10 mm wall thickness with 10 mm diameter Copper fibers from 100 to 200 mm long attached at the cone tip. We illuminated these targets on the interior surface at laser intensities of 10^18 - to 10^20 W/cm^2 in 1-10 ps pulse durations. Coupling of the electron energy to the Cu fiber is measured via imaging of x-ray fluorescence, fluorescent x-ray yields, HOPG spectra of x-ray line-shifts, and heating via XUV x-ray imaging. This approach may lead to higher energy density experiments and bright micron-scale x-ray radiography sources in the future.

[CP1.081] Laser Ablative Cleaning of Short-Pulse Fast-Ion Targets

Fast-ion beams are generated when sub-picosecond high-intensity laser pulses strike thin solid targets. The purity of the ion pulse can be improved by minimizing contamination (including oxidation) at the surface. We are developing a laser ablation technique to remove a thin surface layer (where acceleration gradients are highest) moments before the fast ions are generated. A 100 ps pulse is used to ablate the surface. We have performed planar simulations of the ablation process using the Lasnex 2-D radiation-hydrodynamics code. Simulations for several different metal foils have been performed. Thin layers of water and carbon were placed on the surface of the substrate to simulate measured amounts of H, O and C contaminants. Simulation results indicate the threshold for foil substrate removal is 10^10-10^11 W/cm^2 (substrate dependent). How the ablation depth changes with laser intensity will be shown. Techniques to measure ablation depth in the 10 nm range and comparisons with our experimental data to date will be described.

[CP1.082] Simulation of the generation and long distance transport of proton beams at LULI

High current, energetic protons are produced by irradiating thin metal foils with intense lasers[1]. At LULI[2], the current and energy of these protons as well as that of their accompanying electron cloud have been measured using magnetized and filtered Faraday cups. Here, the laser plasma interaction produced relativistic electrons at the critical surface. These electrons were transported through a 10-\mum Au foil and created a space charge cloud that accelerates protons contaminants on the back side. The energetic protons and electrons drift several centimeters before reaching the Faraday cup. Self-consistent electromagnetic simulations of this process using a hybrid code are presented with comparisons to data. The neutralization of the high quality proton beam by the electron cloud is then studied. 1. R. Snavely et al., Phys. Rev. Lett. 85, 2945 (2000). 2. M. Hegelich et al., Phys. Rev. Lett. 89, 085002 (2002).

[CP1.083] Neutral Particles in Thomson Parabola Spectra

A Thomson parabola diagnostic is commonly used to distinguish separate charge-to-mass ratio ion species accelerated from a thin foil irradiated by a ps laser. A CR-39 plastic nuclear particle track detector is used to record the data. Undeflected neutral particles appear in Thomson parabola spectra (the so-called zeroth order) and carry information about total ion flux born in the laser target. We examine charge exchange and recombination as sources of the neutral flux. The ion energy distribution of unique charge states is known from the parabolic record. The zeroth order signal in principle allows an alternate validation of the absolute ion flux from the source, especially for protons. This analysis will aid in assessing the role of charge exchange and recombination for the population of multiple charge states for a given element. Microscopic images of zero order signals are presented.

[CP1.084] Optimization of K\alpha Emission Yields for Short-Pulse High Intensity

X-ray radiography will be an important diagnostic on the National Ignition Facility (NIF). Unlike the low-mass targets previously used for laser-driven experiments for which thermal backlighters of a few keV were sufficient, radiography on the NIF will require bright sources of 20-100 keV x rays. Such x rays cannot be produced with high efficiency using conventional long-pulse laser driven thermal backlighters. Experiments suggest that K\alpha emission driven by short-pulse, high-intensity lasers will provide suitable backlighter sources. This has motivated this design study of K\alpha fluorescence optimization. We will report on LSP [1] calculations of these experiments. We will present new K\alpha conversion efficiency data for these experiments and will show examples of different geometries, such as cones attached to wires.

[CP1.085] High Energy K-alpha Radiography Using High-Intensity-Short-Pulse Laser

We are developing high-energy, high-brightness K-alpha backlighters (20-100 keV) for NIF High-Energy-Density (HED) experiments using high-intensity-short-pulse petawatt lasers. The HED projects require probing mid- to high-Z implosion capsules and high areal density planar samples. Hard K-alpha x-ray photons are created through high-energy electron plasma interactions in the target material after irradiation by high-intensity lasers with >10^17 W/cm^2. In order to understand the characteristics of such high energy K-alpha sources, we have utilized the Vulcan laser at RAL and the JanUSP laser at LLNL to create >20 keV x-rays to radiograph high-Z samples. We employed thin Sm foils (100x100x14 \mu m) to create 1-D line sources and imaged Ta and Au ripple targets using a CsI/CCD camera and image plates. In this experiment we clearly resolved features having a 20-\mu m period of thicknesses varying between 45 and 33 \mu m with moderate MTF. We also characterized the background spectrum using step-wedge targets and compared it with simulation. This paper will present initial results.

[CP1.086] Creating uniform plasmas with short-pulse lasers by field and collisional ionization.

Laser plasma interactions depend on the uniformity of the plasma density, temperature, or flow velocity. Gas jets and gas-filled balloons may not have sufficiently uniform gas profiles for optimum performance of backward Raman amplification.(V. M. Malkin, G. Shvets, and N. J. Fisch, Phys. Rev. Lett., 82), 4448 (1999). In addition, the process of plasma production usually involves ionization and heating with non-uniform laser beams over hundreds to thousands of picoseconds. During this time the plasma has sufficient time to develop undesirable nonuniformity. Here we present new methods for producing a uniform gas and, with a short laser pulse, creating a low electron density plasma ``channel.'' The short pulse peak intensity is a few times the ionization potential. The optimum beam focus and pulse duration scale with the plasma length. For such short times, the plasma ions cannot respond fast enough to alter the initial uniformity.

[CP1.087] Effect of random inhomogeneities in plasma concentration on parasitic pump scattering in powerful backward Raman amplifiers

Pump laser pulses can be scattered by thermal plasma noise even before meeting the counter-propagating seed pulses in backward Raman amplifiers (BRA). The premature pump scattering can be prevented by an appropriate detuning of the Raman resonance through a plasma density gradient or/and pump frequency chirp. This work addresses a potentially dangerous effect of random inhomogeneities in plasma concentration on the above method of the pump stabilization. The danger consists in that even small short-scale random density inhomogeneities may produce noticeable random gradients in plasma frequency capable of compensating the regular detuning gradient in some random spots. At such spots, the pump propagation might become vulnerable again to premature scattering by thermal plasma noise. We analyzed this local instability and derived criteria for its suppression to a benign level by Langmuir wave damping (Landau and collisional) or/and nonlinear pump frequency chirp.

This work was supported under the U.S. Department of Energy contract No. DE-FG03-00ER54606/A000, DOE DEFG030-98DP00210, DOE DEAC02CH03073 and DARPA.

[CP1.088] Manipulating ultra-intense laser pulses in plasmas

We propose an efficient way for manipulating ultra-intense laser pulses in plasmas using resonant 3-wave interactions. Poor quality ultra-intense laser pulses can be efficiently transformed into high quality focused laser pulses, while the entropy is taken by resonant plasma waves. This can be accomplished within such thin plasma layers that parasitic scatterings and instabilities of laser pulses do not have enough time to develop there. Combined with laser pulse compression in plasmas, this scheme might be usefully employed in the National Ignition Facility (NIF). The plasma-based compression block can be pumped directly by NIF lasers, without intermediary Chirped Pulse Amplification (CPA) blocks, thus avoiding usage of expensive and fragile big gratings. The scheme has a broad operative parameter range; in particular, it might be also used to produce output pulses for Fast Igniter (FI) scenario of inertial fusion, including higher power variations on the FI concept, as well as to produce extremely high-intensity pulses for fundamental high-energy studies at NIF.

This work was supported under the U.S. Department of Energy contract No.~DE-FG03-00ER54606/A000, DOE DEFG030-98DP00210, DOE DEAC02CH03073 and DARPA.

[CP1.089] ATI with ultra-relativistic laser in tightly focused regime

We report on optical field ionization of Ne, Ar and Kr atoms by 10 TW Ti:sapphire laser with duration of 30 fs focused with f/2 parabola to a spot size of 2 microns and to a peak intensity of 10^20 W/cm^2. The comparison between the experiment and the Ammosov-Delone-Krainov model will be presented. The dynamics of electrons ionized from high charge states of argon by laser with intensity of 10^20 W/cm^2 in a tightly focused regime has also been studied theoretically. We found that the dynamics of the ejected electrons is strongly influenced by the longitudinal electric fields of the laser providing smaller electron acceleration than predicted by the paraxial approximation and leading to a significant angular spread.

[CP1.090] THz radiation from overdense laser-plasma interactions

The interaction of a 80 fs laser pulse with thin, overdense plasma targets is investigated via particle-in-cell (PIC) simulations. During the interaction, electrons are accelerated into the foil and are recirculated by the sheath electric field. The impact of the laser pulse creates an electrostatic ion shock that propagates through the foil. At the shock front, ions are accelerated in both longitudinal and transverse directions. Electromagnetic perturbations are observed to propagate away from the shock and through the foil. The dispersion relation for these perturbations is derived and shown to agree with the simulations. The spectrum of the emitted waves is broad with peak frequencies in the THz range. An observed dependency of the emitted peak frequency on the laser intensity is explained

[CP1.091] Application of detuned laser beatwave for generation of few-cycle electromagnetic pulses

An approach to compressing high-power laser beams in plasmas via coherent Raman sideband generation is described. The technique requires two beams: a pump and a probe detuned by a near-resonant frequency Ømega<ømega_p. The two laser beams drive a high-amplitude electron plasma wave (EPW) which modifies the refractive index of plasma so as to produce a periodic phase modulation of the incident laser with the laser beat period 2\pi/Ømega. Thus, a train of chirped laser beatnotes (each of duration 2\pi/Ømega) is formed in plasma. The chirp is positive (the longer-wavelength sidebands are advanced in time) when Ømega<ømega_p and negative otherwise. Finite group velocity dispersion (GVD) of radiation in plasma can compress the positively chirped beatnotes to a few-laser-cycle duration thus creating in plasma a sequence of sharp electromagnetic spikes separated in time by 2\pi/Ømega. Driven EPW locks the phase of laser sidebands and thus reduces the effect of GVD. Compression of the chirped beatnotes can be implemented in a separate plasma of higher density, where the laser sidebands become uncoupled.

[CP1.092] Coherent x-ray emission from hollow Xe atoms

We investigated small Xe clusters subject to intense ultrashort laser radiation. The dynamics and evolution of the cluster plasma is described by a relativistic time-dependent 3-D molecular dynamics model and a detailed atomic physics model describing the formation of hollow Xe atoms. At a peak laser intensity of (1-5)x10^20 W/cm^2 the model predicts inversions in a number of states distributed in several ionization stages in agreement with experimental observations [1,2]. The particle simulation model suggests that at laser intensities below 10^20 W/cm^2 the outer electrons form a low-density uniform plasma, while at higher intensities the electrons may behave collectively in a manner similar to that described by the "collective oscillation model" [1,2]. [1] W. A. Schroeder, F. G. Omenetto, A. B. Borisov, J. W. Longworth, A. McPherson, C. Jordan, K. Boyer, K. Kondo, and C. K. Rhodes, J. Phys. B 31, 5031 (1998) [2] W. A. Schroeder, T. R. Nelson, A. B. Borisov, J. W. Longworth, K. Boyer, and C. K. Rhodes, J. Phys. B 34, 297 (2001)

[CP1.093] Short pulse lasers for the development of broadband x-ray sources

We have performed a set of bench-mark experiments on cans at the Rutherford Appleton Laboratory. Copper cans were heated with a 400~J, 1~ps, pulse focused to a 5\,\mu\,m spot size. The can diameters varied from 250\,\mu\,m to 800\,\mu\,m with a 10\,\mu\,m wall thickness. Several measurements were performed to estimate the plasma scale-length, heating mechanism, and thermal temperature. These data will be discussed along with the analysis.

[CP1.094] Shock Shells in the Coulomb Explosion of Very Large Clusters

When irradiating large (\sim10^6-10^7 atoms) deuterium clusters with ultra-short (tens of fs) and ultra-intense (I>10^16 W/cm^2) laser pulses, highly energetic deuterium ions (E\sim100 KeV), capable of driving nuclear fusion reactions, are produced via Coulomb explosion of the clusters themselves. The laser-cluster interaction brings a huge variety of physical scenarios and leads to very rich and nonlinear phenomena, such as the formation of particular two-knee structures in phase space, referred to as ``shock shells''. We show that small-scale shock shells form naturally during the laser-induced Coulomb explosion of large clusters, and that large-scale shock shells are easily obtained using sequential laser pulses (e.g. a weak pulse followed by an ultra-intense one, with a proper time delay \Delta t). The ability of generating and controlling large-scale shock shells opens the way to intra-cluster nuclear fusion reactions.

In order to provide a self-consistent description of the phenomenon and capture the full physics, we have carried out a set of 3D simulations, resorting to the OSIRIS framework, also including the effects of self-consistent field ionization (ADK ionization model])

[CP1.095] Ultrashort Laser Pulse Interaction with Dielectrics

Propagation of intense, ultra-short laser pulses in dielectrics is accompanied by a broad range of physical processes. These include linear processes such as dispersion and nonlinear processes such as an optical Kerr effect, stimulated Raman scattering, and ionization. As a result numerous phenomena associated with laser pulse propagation have been observed which may have practical applications for remote sensing and electronic countermeasures. These include optical shock formation, backscattering and generation of ultrabroadband radiation. To understand the nature of these phenomena in detail it is necessary to solve a wave equation for the laser field that is driven by the self-consistent current due to the free electrons as well as the polarization arising from the bound electrons. Formulation of a theoretical model for analyzing these processes is discussed. Numerical results are presented to illustrate the diversity of the physical processes and to demonstrate the ability of the model to represent them.

[CP1.096] Z-Pinch-Driven Hemispherical Capsule Implosions for Fast Ignitor Fuel Assembly

Rad-hydro simulations indicate that partial-sphere fusion capsules can be compressed to peak densities of interest for fast ignition experiments with the symmetry control available in a single-ended indirect drive vacuum hohlraum configuration. We are presently investigating this approach to fast ignitor fuel assembly using pulsed-power driver technology. Current from the Sandia Z accelerator implodes a single wire-array z-pinch in the primary hohlraum, efficiently generating thermal x rays to drive the ablative compression of a hemispherical capsule moving on a high density glide surface in the secondary hohlraum. We report on recent work in two areas: (1) x-ray backlighter imaging of 3.0-mm-diam., 110-um-thick GDP hemispherical capsule implosions, complicated at high convergence by gold plasma expansion from the glide surface; and (2) development of a hemispherical liquid cryogenic fusion capsule in which a liquid cryogenic fuel layer is condensed in situ from a low pressure external gas supply and confined between concentric plastic shells mounted on the glide surface. Progress in measurement of shell distortion using high resolution 6.151 keV monochromatic crystal imaging will be discussed. Technology issues for liquid cryogenic fuel capsule development and progress toward demonstration of a working capsule will be presented.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

[CP1.097] Integrated Simulations of Dense Core Heating for Fast Ignition (FI) Scenarios

We study the laser/plasma interaction at the critical surface integrated with hot electron transport and heating through corona and core (5 orders of magnitude in density) for FI using the 3D EM implicit hybrid PIC code, LSP[1], coupled to a rad-hydro code. LSP treats the laser/plasma interaction explicitly, at the proper spatial scale, and follows the hot electrons through the corona and core implicitly. The LSP simulations have been validated with GEKKO/PW data, lending some credence to our approach. Self-consistent fields in the corona and core modify the hot electron distribution and have an important influence core heating efficiency. We plan to present results for: 1) GEKKO/PW, 2) ZR coupled to a vacuum hohlraum, the core heated with Z-Beamlet/PW, and 3) a high \rho r system (about 0.3 g/cm^2) at high average density (300 g/cm^3) and laser intensity (I a few 10^21 W/cm^2) to investigate near ignition conditions. The ignition case may pose a challenge, since the high I implies very energetic electrons difficult to stop in 300 g/cm^3 cores, even considering anomalous processes. [1] D.R. Welch, et.al. Nucl. Instrum. Meth. Phys. Res. A 464, 134 (2001). Sandia is a multi-program Lab operated by Sandia Corp., a Lockheed Martin Co., for the USDOE under Contract # DE-AC04-94AL85000

[CP1.098] Characteristic of the high-density core plasma produced by non-spherical implosion for fast ignition

For the fast ignition scheme, formation of a high-density core plasma is one of the critical issues. Using 2-D integrated implosion code PINOCO, we have simulated the cone-guided implosion and observed the existence of high-density core plasma. The characteristic of the core plasma affects the burning efficiency of DT fuel heated by the ultra-intense laser. Therefore, we have investigated the detail properties of core plasma which is imploded by non-spherical implosion. Those simulations are same scale size as the FIREX-I experiment at ILE Osaka Univ. Especially, a jet formation and hydrodynamic around the tip of the cone is important. We will show the simulated result of implosion of cone-guided target, and discuss the optimized laser pulse and target parameters for fast ignition. This work was supported by MEXT, Grant-in Aid for Creative Scientific Research(15GS0214).

[CP1.099] Electron Beams for Fast Ignition

In the fast ignitor scenario an intense relativistic electron beam is used to deposit energy inside the fuel target and trigger the thermonuclear reaction. This electron beam is produced on the outer plasma layer of the target by the interaction of an ultra-intense laser. The energy transfer from the laser to the electron beam, and the stability of the propagation of the electron beam are crucial for a successful fast ignitor scheme. We have used three-dimensional particle-in-cell simulations using the OSIRIS.framework [1] to explore the self-consistent generation of high current electron beams by ultra intense lasers. Novel laser pulse configurations are explored in order to generate electron beams transporting more energy, and capable of avoiding the deleterious effects of collisionless instabilities in the plasma corona.

[1] R. A. Fonseca et al., LNCS 2331, 342-351, (Springer, Heidelberg, 2002);

[CP1.100] Transport Limitation of Laser Accelerated Electrons in Vacuum

The electric current of hot electrons generated by ultra-intense laser can be larger than the Alfvén current. If the current is larger than the Alfvén current, hot electrons must be influenced by the self-generated magnetic field and the total number of escaping hot electrons is limited. Hot electrons are also affected by the electrostatic field at the backside of a target. The energy spectrum and the angular distribution of hot electrons were measured simultaneously using imaging plates in order to obtain the absolute number of hot electrons at the laser system Gekko Module II. The effects of electric fields were estimated by comparing the results obtained in two cases, which are the case without rear-plasma and the case with rear-plasma generated by a long pulse in advance. If there is rear-plasma, the hot electrons can be emitted into vacuum without affecting by the sheath potential. The relationship between total number and the temperature of electrons is obtained and the influence of each field for the limitation is summarized.

[CP1.101] Current Filament Instability in Fast Ignition

Previous theory for current filament instability in fast ignition assumes a purely transverse mode (k\cdot E =0).

However, for a single current beam, any current filamentation is accompanied by charge filamentation and an electrostatic field would develop along k. Only when this space charge is neutralized by the return electrons and/or ions can the mode be purely transverse. Consideration of the coupling of the transverse and the longitudinal modes reve