Session CI2: Accelerators, Beam Dynamics and Radiation

Beam dynamics of NDCX-II, a novel pulse-compressing ion accelerator

The near-term mission of the Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL, a collaboration of LBNL, LLNL, and PPPL) is to study Warm Dense Matter (WDM) at $\sim $1 eV in thin foils heated volumetrically by ion beams. An emerging mission is ion-direct-drive target physics for inertial fusion energy. These goals (especially the WDM mission) require rapid target heating. Beam bunch compression factors exceeding 50 are routinely achieved on the Neutralized Drift Compression Experiment (NDCX) at LBNL. The next facility for this research program, NDCX-II, will employ a unique approach to ion beam acceleration and pulse compression. Using modified induction cells from the decommissioned Advanced Test Accelerator at LLNL, NDCX-II will compress pulses of singly-charged Lithium ions from $\sim $500 ns to $\sim $1 ns as they are accelerated to 3-4 MeV. The required $\sim $sixfold speed-up and $\sim $hundredfold spatial compression are to be accomplished in $\sim $15 m. The beam dynamics employs the strong longitudinal space charge field to halt, and then reverse, an initially imposed pulse compression. This initial compression enables efficient use of the Volt-seconds in the downstream induction cells. Those cells impose further acceleration and the head-to-tail velocity gradient that enables a final neutralized drift compression and focus onto the target. Discrete-particle simulations (1-D, 2-D, and 3-D) have been used to develop the ``physics design'' for NDCX-II. We present the elements of the design, and our progress toward building this machine at LBNL.   

Physics of neutralization of intense charged particle beam pulses by a background plasma

Neutralization and focusing of intense charged particle beam pulses by a background plasma forms the basis for a wide range of applications to high energy accelerators and colliders, heavy ion fusion, and astrophysics. From the practical perspective of designing advanced plasma sources for beam neutralization, a robust theory should be able to predict the self-electric and self-magnetic fields during beam propagation through the background plasma. The major scaling relations for the self-electric and self-magnetic fields of intense ion charge bunches propagating through background plasma have been determined taking into account the effects of transients during beam entry into the plasma, the excitation of collective plasma waves, the effects of gas ionization, finite electron temperature, and applied solenoidal and dipole magnetic fields. Accounting for plasma production by gas ionization yields a larger self-magnetic field of the ion beam compared to the case without ionization, and a wake of current density and self-magnetic field perturbations is generated behind the beam pulse. A solenoidal magnetic field can be applied for controlling beam propagation. Making use of theoretical models and advanced numerical simulations, it is shown that even a small applied magnetic field of about 100G can strongly affect beam neutralization. It has also been demonstrated that in the presence of an applied magnetic field the ion beam pulse can excite large-amplitude whistler waves, thereby producing a complex wake structure of plasma density perturbations in the region of the ion beam pulse. The presence of an applied solenoidal magnetic field may also cause a strong enhancement of the radial self-electric field of the beam pulse propagating through the background plasma. If controlled, this physical effect can be used for optimized beam transport over long distances.   

Studies of Emittance Growth and Halo Particle Production in Intense Charged Particle Beams Using the Paul Trap Simulator Experiment

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory experiment that places the physicist in the frame-of-reference of a long, charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system. The transverse dynamics of particles in both systems are described by the same set of equations, including nonlinear space-charge effects. The time-dependent voltages applied to the PTSX quadrupole electrodes are equivalent to the spatially-periodic magnetic fields applied in the AG system. The transverse emittance of the charge bunch, which is the area in the transverse phase space that the beam distribution occupies, is an important metric of beam quality. Maintaining low emittance is an important goal when defining AG system tolerances and when designing AG systems to perform beam manipulations such as transverse beam compression. Results will be presented from experiments in which white noise and colored noise of various amplitudes and durations has been applied to the PTSX electrodes. This noise is observed to drive continuous emittance growth over hundreds of lattice periods. Additional results will be presented from experiments that determine the conditions necessary to adiabatically reduce the charge bunch's transverse size. During adiabatic transitions, there is no change in the transverse emittance. The transverse compression can be achieved either by a gradual change in the PTSX voltage waveform amplitude or frequency.   

Generalized Phase-Space Tomography for Intense Beams

Many applications of accelerators, such as free electron lasers, pulsed neutron sources, and heavy ion drivers for warm dense matter experiments require good quality beams with high intensity, i.e., cold, high-current beams. At the low-energy end of such machines, collective interactions from space charge dominate the beam dynamics and the beam can be viewed as a nonneutral plasma capable of carrying waves. Consequently, the initial beam distribution significantly affects its downstream behavior and beam characterization at the source is an important requirement to understand its evolution. This work reports on a novel diagnostic for time-dependent beam phase space characterization by using tomographic techniques. Tomography here is the reconstruction of phase space from a number of projections onto configuration space.~Application of tomography to beams with space charge is non-trivial since it involves assumptions about the beam distribution one is trying to measure.This talk will address this issue, as well as the implementation of this diagnostic to both solenoidal and quadrupole focusing lattices. Also discussed will be a series of proof-of-principle experiments conducted at the University of Maryland to test the diagnostic. The tomography is benchmarked both against self-consistent simulation using a particle-in-cell code and against a pinhole-scan direct experimental sampling of phase-space.   

Advances in Modeling of Beam-Wave Interaction in Multi-Megawatt Gyrotrons

High-power gyrotrons, capable to produce several megawatts of CW radiation in millimeter wave range, are used in many magnetic fusion facilities, and planned to be used in ITER. The gyrotrons employ an interaction between a gyrating electron beam and very high order modes of open cylindrical or co-axial cavities to keep Ohmic losses on cavity walls on acceptable level. Since the gyrotron cavity supports a large number of eigenmodes with different azimuthal and radial indexes many of which are capable of interaction with electron beam at different frequencies. The code MAGY [1,2] has been developed to address the mode competition issue in gyro-devices. MAGY model is based on multi time-scale approach and uses electromagnetic fields expansion into series of eigenfunctions of local transverse cross-section. This approach leads to computationally efficient solution of the Maxwell's Equations. MAGY has been used for design and modeling of gyro-devices in CPI, MIT, UMD, NRL for last decade and demonstrated excellent agreement with experimental data. Modeling of Multi-Megawatt gyrotrons operating at high frequencies (170 GHz and above) presents a new challenge due to the unprecedented level of spectral mode density and higher level of beam current. A co-axial cavity gyrotron has been introduced to reduce this spectral density. To address these computational physics challenges a new MAGY model for mode interaction in gyrotrons with co-axial cavities has been implemented. MAGY has been used to model the FZK (Germany) 170 GHz co-axial gyrotron [3,4]. The results of this modeling will be presented. Further advances in the theoretical models for comparison with the existing experimental data will be discussed. \\[4pt] [1] S.C. Cai, et al, \textit{Int. J. Elect.}, 72, p. 759, 1992.\\[0pt] [2] M. Botton, et al, \textit{IEEE Trans on P S, }26, p. 882, 1998.\\[0pt] [3] B. Piosczyk, et al, \textit{IEEE Trans. on P S}., 32, 413, 2004.\\[0pt] [4] A.N. Vlasov, et al, \textit{IEEE Trans. on P S}., 36, p. 606, 2008.   

Wakefields in Photonic Crystal Accelerator Cavities

The RF properties of photonic crystals (PhCs) can be exploited to avoid the parasitic higher order modes (HOMs) that degrade beam quality in accelerator cavities and reduce efficiency and power in RF generators. For example, an accelerator cavity can be designed using a PhC structure that traps only modes within a narrow frequency range, so that the cavity has only a single mode. Although the lack of HOMs is perhaps the most drastic difference between PhC cavities and traditional metal cavities, PhC cavities should allow a much wider range of materials and shapes, which could potentially lead to cavities that operate at higher electric fields and at higher frequencies (with lower losses). However, this greater flexibility introduces many challenges for building actual structures. A hybrid cavity that uses a dielectric 2D PhC along with metal plates to trap fields in the third dimension may offer the advantages of a PhC cavity while being relatively easy to construct. Although the 2D photonic structure may allow only a single mode, the 3D structure can in principle trap HOMs, such as guided modes in the dielectric rods that form the PhC; however, computer simulations show that long-range wake fields can be significantly reduced in such hybrid structures. For a 3D cavity based on a triangular lattice of dielectric rods, the rod positions can be optimized (breaking the lattice symmetry) to reduce radiation leakage using a fixed number of rods; moreover, the optimized structure can further reduce the wake fields.   

Session CT3: Tutorial: Flow driven MHD Instabilities in Weakly Magnetized Laboratory Experiments: Dynamos and MRI

Flow Driven MHD instabilities in Weakly Magnetized Laboratory Experiments: Dynamos and MRI

Astrophysical plasmas are often characterized by high magnetic Reynolds number, turbulent, flowing plasma in which the flow energy is much larger than that of magnetic field. Examples include planetary interiors, accretion disks and the solar wind. Creating such conditions in laboratory plasma experiments is challenging since confinement is required to keep the plasma hot and conducting and requiring strong magnetic fields. For this reason, laboratory experiments using liquid metals have been addressing fundamental plasma processes in this unique parameter regime. This talk will begin by giving a elementary tutorial of two related processes: the dynamo in which magnetic energy is spontaneously generated from flow energy; and the magneto-rotational instability in which a weak magnetic field can act as a catalyst for transporting momentum. Then, I will then show how liquid metal experiments have been contributing the the understanding of such processes. Liquid metal experiments have (1) demonstrated self-excitation of magnetic fields, (2) two scale dynamos where a small scale flow drives a large scale magnetic field, (3) intermittent self-excitation and a variety of time dynamics including field reversals, (4) showed the existence of a turbulent electromotive force (mean-field current generation), and (5) MRI-like instabilities have been observed in Couette flow geometries. Liquid metals are, however, not plasmas: dynamos and MRI may differ in plasmas where the relative importance of viscosity, and resistivity can be interchanged, and new instability mechanisms, outside the scope of MHD may be critical in collisionless plasmas. This suggests that the next generation of experiments in this important astrophysics regime should be based upon plasmas.   

Session CO4: DIII-D Tokamak

Overview of Recent DIII-D Experimental Results

DIII-D experiments in 2009 addressed critical ITER issues and physics understanding needed for extrapolation to future devices. Multiple schemes for rapid plasma shutdown were demonstrated including massive gas injection, large shattered D$_2$ pellets and impurity filled shell pellets. Detailed particle balance experiments show dramatically reduced wall uptake in ITER relevant H-mode compared with L-mode. Joint DIII-D/JET experiments showed no dependence of pedestal pressure width on $\rho^*$, indicating a favorable scaling to ITER. Torque from non-resonant magnetic perturbations improved access to QH-mode at low rotation. DIII-D demonstrated low voltage startup with ECH assist and low $\ell_i$ plasma \mbox{rampdown}, as well as solenoidless startup. Progress on qualifying Hybrid scenario plasmas for $Q=10$ in ITER included $\beta_N = 2.5$ with ELM suppression by RMPs. Advances in physics understanding included: 1) systematic $q_{min}$, $q_{95}$ scans showing the dependence of $n_e$ and $T_e$ profiles on $q(r)$, 2)~plasma response to non-axisymmetric fields, 3)~validation of core turbulence and thermal transport models and 4)~intrinsic rotation studies.   

Particle Control and Carbon Transport Experiments on DIII-D

As part of the 2009 Joint Research Target, DIII-D, along with MIT and NSTX have completed a series of experiments on particle control and transport. On DIII-D, both dynamic (calculated particle balance) and static (pumps closed or regenerated) particle balance experiments were carried out in both L- and H-mode with cryopumping. We find that the exhaust obtained from both techniques is comparable. We find that the uptake can be large in ohmic and L-mode, but in H-mode, the wall retention flux is very small, which is promising for long pulse burning plasma experiments. Also, in support of tritium control research for ITER, we have started a process to qualify the DIII-D internal components for an anticipated air bake (350$^{\circ}$, 10~Torr) in 2010. We find issues with some copper components, but most components are compatible. Air baking removes the co-deposited carbon that can be rich in tritium in ITER with carbon walls.   

Observations of Thermal Transport Enhancement in Stochastic Boundary Experiments at DIII-D and TEXTOR

Comparison of stochastic boundary experiments in TEXTOR L-modes to DIII-D H-modes shows on both experiments a $q_{95}$ resonance in the pedestal pressure $p_e$ which is driven by a resonant decrease of the pedestal electron temperature $T_e$ as $q_{95}$ is varied. This decrease in $T_e$ is correlated to an increase in the modeled stochastic layer width while the electron density does not show a strong $q_{95}$ resonance. The $T_e$ decrease is only seen for DIII-D in an ITER similar shape at high triangularity as opposed to an increase in $T_e$ and a small effect only on the thermal transport for low triangularity plasmas. This indicates significant shape dependence for the $q_{95}$ resonant thermal transport features in stochastic boundary experiments for suppression of type-I edge localized modes by RMP at DIII-D.   

Correlation Between Density Pump-out and Free Streaming Particle Transport in Low Collisionality Resonant Magnetic Perturbation H-modes

Experimental pedestal density data shows a decrease in the gradient within the transport barrier during RMP H-mode, as compared to an ELMing H-mode. Recent modeling, with SOLPS5 and TRIP3D, indicates that this change is the result of an increase in particle transport. This increase in transport is the consequence of the creation of open field lines inside the traditional separatrix. The magnitude ($\sim0.1\,$m$^2$/s) and radial extent of this free-streaming transport are well correlated with experimental changes. In this paper, we present a more systematic study, where we compare the increase in particle transport calculated with TRIP3D, directly with the changes in pedestal density. We notice that the experimental density pump-out during RMP H-mode is linearly correlated with the increase in free streaming transport for low collisionality plasmas.   

Dependence of Bootstrap Current, Stability, and Transport on the Safety Factor Profile in DIII-D Steady-state Scenario Discharges

A high beta, high gain steady state tokamak scenario with large bootstrap current fraction will have strong coupling between the current density and the pressure gradient through turbulent transport and the bootstrap current. To address this coupling experimentally, a scan of the safety factor minimum ($q_{min}$, from 1.1 to over 2) and edge value ($q_{95}$, from 4.5 to 6.5) was performed. The bootstrap current fraction increases with $q_{min}$ and $q_{95}$ by virtue of increasing density gradients. Compared to lower $q_{min}$, $q_{min}>2$ has lower $n=1$ stability limits, enhanced drift wave growth rates, higher low-$k$ density fluctuations, and lower confinement. At $q_{min}>2$ and $q_{95}=4.5$ the unsustainable condition $J_{BS} > J_{Total}$ occurs near the axis. These considerations suggest intermediate $q$ is the optimal operating point.   

Global Structure of a Stable, Driven Kink Mode: DIII-D Measurements and Model Validation

Recent DIII-D measurements of the global structure of the non-axisymmetric plasma perturbation driven by applied $n=1$ magnetic fields enable the quantitative test of ideal MHD theory. Extensive magnetic measurements show that the ideal MHD code MARS-F predicts the plasma response within 20\% for values of beta up to 75\% of the beta limit calculated without a conducting wall, but overestimates the perturbed field at higher pressures. Experiments varying the pitch angle of the applied field at different values of plasma current demonstrate the plasma response depends primarily on the match of the applied field to the kink mode structure. Toroidally distributed soft x-ray measurements indicate the kink-like internal perturbation structure depends on the plasma pressure. The measurements are used to test kinetic stabilization models in the MARS-K code.   

Synergy in Two-Frequency Fast Wave Cyclotron Harmonic Absorption in DIII-D

Fast waves (FWs) at 60 MHz and at 90 MHz are coupled to DIII-D discharges for central heating and current drive at net FW power levels up to 3.5 MW. In 2~T discharges with fast deuteron populations from neutral beam injection, 4th and 6th deuterium cyclotron harmonic absorption on the fast ions competes with direct electron damping and with edge losses. If the fast deuterons are accelerated by absorption of 60 MHz (4th harmonic) FWs, adding 90 MHz power (6th harmonic) increases the fusion neutron rate by a increment larger than the sum of the increments observed with separate 90 MHz and 60 MHz pulses (synergy). Synergy in the global confinement is also observed. The regions of velocity space that are affected with the two-frequency FW heating are studied with fast-ion D$_{\alpha}$ spectroscopy and by detailed characterization of the dynamics of the neutron rate with modulated neutral beams.   

Measurements of the Spatial Structure of Geodesic Acoustic Modes in DIII-D

Geodesic acoustic modes (GAMs) are linearly stable, turbulence driven modes exhibiting oscillating axisymmetric ($m=0$, $n=0$) $E\times B$ flows. They potentially play an important role in establishing the saturated level of turbulence in fusion plasmas. Two Doppler backscattering (DBS) systems at locations separated toroidally by 180$^{\circ}$ are aligned to make simultaneous measurements at the same radial location ($\rho\approx 0.8$) and wavenumber ($k_\perp\sim 4\,$cm$^{-1}$, $k_\perp\rho_s\sim 1$) in a beam-heated L-mode DIII-D plasma. Flow oscillations, which agree with the predicted GAM frequency scaling, correlate toroidally between the two DBS systems with an ensemble averaged cross-coherency of $\gamma\approx 0.6$ over 600 ms. The cross-phase between pairs of the DBS signals is consistent with the expected GAM structure. The radial variation in cross-phase agrees with descriptions of the GAM eigenmode as having an Airy function character with outward radial propagation; the measured radial wavelength is $\lambda_r\approx 2.8\,$cm and the calculated GAM characteristic length scale is $L_{GAM}=\rho_i^{2/3}L_T^{1/3}\approx 1.2\,$cm.   

Heat Transport in Off-axis EC-Heated Discharges in DIII-D

In low-density H-mode discharges in DIII-D, ECH applied off-axis produces electron temperature profiles with strong peaking at the heating location and very slow penetration of heat into the core. This type of discharge is a counter example to the heat-pinch effect normally seen in tokamaks where off-axis heating propagates rapidly to the center. In a recent experiment on DIII-D, the conditions for producing these ``bat-eared" $T_e$ profiles were studied. It was observed that H-mode is a necessary condition; L-mode discharges exhibit the classic heat pinch. A region of low transport corresponds to the $q=1$ surface as verified by the sawtooth inversion radius. Results of transport analysis are presented as well as measurements of $n_e$ and $T_e$ fluctuations.   

Studies of Runaway Electron Confinement in MHD Disruption Simulations

Formation of a runaway electron beam during an ITER disruption is a major concern for machine survival, particularly because the avalanche growth of a seed population will be many orders of magnitude larger than in present devices. Enhanced fast-electron losses due to stochastic fields produced during the disruption, or from applied non-symmetric fields, can combat avalanche growth. The confinement of fast electrons is studied in the context of MHD simulations using a newly developed capability in the NIMROD code to track single particle orbits as the magnetic fields evolve. Macroscopic drift-orbit displacements associated with highly relativistic electrons play an important role in confinement by averaging over perturbing fields during a poloidal transit, thus allowing good confinement in the presence of stochasticity. Verification of the model for a small number of electrons compares the orbits with and without drift terms directly. Confinement of fast electrons during a gas-jet-induced disruption on Alcator C-Mod, and during a controlled error field ramp on DIII-D are presented.   

Solenoid-free Startup of DIII-D

Inductive plasma current startup to 170 kA was achieved in the DIII-D tokamak without the use of inboard poloidal field coils (solenoidless startup). This was achieved with strong preionization/heating using electron cyclotron (EC) power. For outside breakdown and moderated field null quality, flux conversion efficiency to plasma current using only diverter and vertical field coils is similar to DIII-D's ohmic startup. At higher flux states null quality degrades and flux/current efficiency is reduced, possibly from a reduced in EC/breakdown region coupling. EC current drive was minimal for the plasma regime studied. Preliminary solenoidless handoff experiments to neutral beam current drive were also explored. This research is expected to reduce central solenoid requirements for next generation devices and provide a basis for solenoidless startup of toroidal devices with integration of appropriate current drive techniques.   

Identity Experiments in the Hybrid Regime on \mbox{DIII-D} and JET

Hybrid plasmas have the potential for high fusion yield and long pulse tokamak operation. However, performance extrapolation to future devices depends on an understanding of the transport scaling with machine size, which may not be adequately described by existing ELMy H-mode scalings. An identity match and $\rho*$ scan has been performed in the hybrid regime on DIII-D and JET to investigate the core confinement. A similar plasma shape and NBI heating were used and $\nu^*$, $\rho^*$, $\beta$ and Mach number profiles were all matched within about 20\% at the plasma mid-radius. A $\rho^*$ range of roughly 2.5 was covered across the two devices for plasmas with $q_0\sim 1$ and normalized beta in the range $\sim$2.5-3.0. These experiments allow a comparison of transport in this domain on the two devices and an assessment of the $\rho^*$ dependence of core confinement.   

Scaling of H-mode Pedestal and ELM Characteristics With Gyroradius

The dependence of the H-mode pedestal structure and ELMs on gyroradius ($\rho^* = \rho/a$) was examined in experiments combining data from the JET and DIII-D to produce a factor of 4 variation in $\rho^*$, while keeping the plasma shape, $q$, normalized pressure ($\beta$), collisionality, Mach number, and $T_i/T_e$ at the pedestal top constant. In this scan, the width of the steep gradient region of $T_e$ and $n_e$, $\Delta$, was independent of $\rho^*$ within uncertainties, $\Delta/a\sim (\rho^*)^{0.0\pm 0.15}$. The pedestal pressures and widths were in quantitative agreement with the EPED1 model in which the pedestal structure is set by combining the peeling-ballooning and kinetic ballooning stability thresholds. The ELM energy loss normalized to the pedestal energy decreased from 40\% to 10\% as $\rho^*$ decreased by a factor of 2 in DIII-D, but the trend did not continue in smaller $\rho^*$ on JET.   

Pedestal Density Fluctuations During Quiescent and ELMing H-mode Plasmas

Spatially resolved density fluctuation characteristics have been measured in the pedestal region of quasi-steady-state Type~I ELMing plasmas and ELM-free quiescent H-mode (QH) plasmas using 2D beam emission spectroscopy measurements. During Type~I ELMing plasmas, these fluctuations are modulated with the ELM cycles. Two distinct frequency bands (20-200~kHz and 250-450~kHz) are observed propagating in opposite directions. In QH-mode plasmas, discrete and coherent modes are observed in the pedestal region of particular discharges at relatively high-pedestal pressure. These modes appear from 50-250~kHz, peaking in amplitude around 150~kHz, with a uniform frequency separation of about 10~kHz. Observed characteristics of these modes will be compared with those from ELITE calculations of theoretically predicted pressure-gradient limiting instabilities, such as kinetic ballooning modes.   

Quiescent H-Mode Plasmas with Rotation Driven by Static Non-axisymmetric Fields

A quiescent H-mode (QH-mode) edge allows ELM-free operation of a plasma with good confinement and good particle exhaust. Until recently, QH-mode operation required rather strong plasma toroidal rotation in order for the edge velocity shear to exceed a minimum value [1]. However, rapid rotation may not be feasible in a self-heated burning plasma with little or no momentum injection from neutral beams. New DIII-D experiments in ITER-similar plasmas show that the neoclassical torque from static, nonresonant magnetic fields (NRMFs) provides a useful knob to change the edge rotation profile shear. NRMF application resulted in QH-mode operation with less than half the rotation (evaluated on top of the pedestal) of previous QH-mode without the NRMFs. At this low rotation, the NRMF torque may be amplified by entering the theoretically predicted $1/\nu$ collisionality regime.\par \vskip8pt \noindent [1] K.H.\ Burrell, {\em et al.}, Phys.\ Rev.\ Lett.\ {\bf 102}, 155003 (2009).   

Session CO5: Equation of State, Strength, and Hydrodynamics

Laser-Shock Compression and Hugoniot Measurements of Liquid Hydrogen

Hugoniot data for liquid hydrogen were obtained up to 55 GPa under laser-driven shock loading using impedance matching to a quartz standard. The pressure range we achieved is about 5 times higher than the earlier experiments done by a two-stage gas gun. The experiment was performed on the Gekko/HIPER laser facility at the Institute of Laser Engineering, Osaka University. A significant improvement in the precision of velocity measurements because transparent standard allows direct measurement of the shock velocities for both the standard and hydrogen. The shocked temperature of hydrogen is determined concurrently from the brightness temperature. The temperature is $\sim$ 9000 K at 40 GPa, which is about twice as high as that of shocked deuterium at the same pressure. Compression and temperature along the primary Hugoniot are consistent with theoretical models of equation-of-state.   

Inferring Electron Temperature of Shocked Liquid Deuterium Using Inelastic X-Ray Scattering

A laser-ablation--driven shock wave (12 Mbar) was launched in a planar liquid-deuterium target on OMEGA, and the shocked conditions were diagnosed using inelastic x-ray scattering. The electron temperature ($T_{e})$ is inferred from the Doppler-broadened, Compton-downshifted peak of the noncollective x-ray scattering for $T_{e} \quad > \quad T_{Fermi}$. For this purpose, a saran backlighter foil was irradiated with a group of tightly focused beams having an overlapped intensity of $\sim $10$^{16}$ W/cm$^{2}$. The spectrally resolved x-ray scattering of the Cl Ly$_{\alpha }$ emission (\textit{h$\nu $} = 2.96 keV) was recorded at 90\r{ }. The inferred $T_{e}$ = 20$\pm $5 eV is close to the predicted $T_{e}$ = 22 eV. The experimental design and initial results will be reported. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. The work of G. Gregori and K. Falk was supported in part by EPSRC grant No. EP/G007187/1 and by the HiPER collaboration.   

Measurements of electron density and temperature in shock-compressed Be from x-ray Thomson scattering

X-ray Thomson scattering measurements have provided an insight into characterization of dense plasmas by determining electron temperature, density, and ionization state [1,2]. We have measured spectrally resolved 6 keV x-ray scattering spectra of shock-compressed matter created by counter-propagating shocks at the Omega laser facility. The spectra in non-collective scattering regime show Compton features that give evidence of Fermi-degenerate dense plasmas with a Fermi energy above 30 eV and temperatures of 10-15 eV. Detailed analysis in comparison with radiation-hydrodynamic modeling will be presented. [1] S. H. Glenzer \textit{et al}., Phys. Rev. Lett. 90, 175002 (2003); Phys. Rev. Lett. 98, 065002 (2007). [2] H. J. Lee \textit{et al}., Phys. Rev. Lett. 102, 115001 (2009). This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 and supported by the National Laboratory User Facility program.   

Measurements of Strain-Induced Refractive Index Changes in Shocked and Ramp-Compressed Lithium Fluoride

Lithium fluoride is frequently used as a window in equation-of-state experiments because it remains transparent for multishocks up to 5 Mbar. When compressed, its refractive index changes, affecting the sensitivity of velocity interferometry measurements. For shocked LiF, the refractive index has been measured for pressures up to 1.15 Mbar using gas gun flyer-plate experiments. It has become commonplace to extrapolate the linear dependence for higher-pressure experiments, i.e., those above 1.15 Mb. We report on experiments at the Omega/Omega EP Laser Facilities that use laser-driven shocks and ramp compression to compress diamond targets with LiF windows up to 5 Mbar. Diamond-free surface velocity and diamond/LiF interface velocities are measured. By comparing these velocities, the refractive index of compressed LiF is deduced. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.   

Theoretical Investigation of Strong Coupling and Degeneracy Effects in ICF Implosions

Accurate knowledge of the equation of state (EOS) and opacity is essential to inertial confinement fusion (ICF). Low-adiabat ICF implosion designs reach strongly coupled, degenerate plasma conditions. Using the first-principles, path-integral Monte Carlo method, we have established an EOS table of deuterium, spanning typical ICF shell conditions (densities of 0.001 to 100 g/cc and temperatures of 1 eV to 1 keV). Noticeable differences in energy/pressure at moderately coupled, degenerate regimes have been found in comparison to the \textit{SESAME} and Thomas-Fermi EOS. Hydrodynamic simulations using these EOS's and opacities for OMEGA implosions will be presented. This work was supported by U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.   

Mixed equation of state: dynamical materials experiments on Z and multi-scale simulations

Significant progress in understanding properties of pure materials under extreme conditions has been made recently, with experiments and first-principles theoretical work providing detailed insights for many pure materials. Mixing poses additional fundamental questions regarding the fidelity of first-principles calculations, the reliability of mixing rules for equations of state, as well as the accuracy of experimental approaches. We will present experimental and theoretical results for mixed equation of state. By shock impact of magnetically launched flyer plates on doped poly(4-methyl-1-pentene) foams, we create multi-Mbar pressures in a dense plasma mixture of hydrogen, carbon, and dopant at temperatures of several eV. We analyze the system by multi-scale simulations, from density functional theory to continuum magneto-hydrodynamics simulations.   

Transport properties of Hydrogen and CH under ICF conditions

We present ab initio evaluations of the thermal and of the electrical conductivity of hydrogen at a density of 80 g/cc [1] and 160 g/cc corresponding to the Inertial Confinement Fusion regime. Results are compared with different theories (Hubbard, Lee-More, Ichimaru) and with an average atom (AA) model coupled with a Kubo-Greenwood evaluation of transport coefficients. The Lorentz number, which is the ratio between the thermal to the electrical conductivity, given by the Wiedemann-Frantz law is checked in different regimes ranging from the highly degenerate to the kinetic one. We have also used ab initio calculations to compute the CH thermal conductivity and compared it to the AA approach using mixing rules.\\[4pt] [1] V. Recoules, F. Lambert, A. Decoster, B. Canaud and J. Clerouin, ``Ab initio determination of thermal conductivity of dense hydrogen plasmas,'' Phys. Rev. Letters 102, 075002 (2009).   

Shock-Clump Interaction Studies in the Laboratory

Large-scale directional outflows of supersonic plasma are driven by a wide variety of objects in the universe. Typical models of the outflows assume simplistic geometries; however, images of most outflows show a much more complex structure that consists of multiple clumps and shocks. To bridge the gap between the complex system in space and the simplified models, controlled scaled experiments were performed to elucidate the physics of a shock progressing through a clumpy medium. This talk will present experiments on the Omega Laser in which a shock impacts density discontinuities in order to understand the perturbed shock structure. Two types of discontinuities that had the same average density were tested: one with a uniformly distributed dopant and another with $\sim$47 randomly distributed high-density clumps. We have obtained high-resolution radiographs that detail the temporal evolution of the shock and density discontinuity.   

Ramp loading by shock release of foam reservoirs for the NIF

Previous work has shown that a ramped pressure wave created by the stagnation of an unloading, shocked reservoir can drive a quasi-isentropic compression experiment (ICE) [Edwards et al., \textbf{92} PRL 2004; Lorenz et al., \textbf{2} HEDP 2006]. The size of the shock at the back of the reservoir, the reservoir materials, the size of the gap between the reservoir and the sample, and the sample's sound speed places limits on (1) the thickness of the sample that can be studied before the ramp wave steepens into a shock that would impart significant shock heating into the sample, and (2) the size of the planar drive region. We present simulation and experimental data from a series of CRF foam laser shots done on the Omega Laser Facility to show that the presence of lower density materials in an ICE reservoir reduces the needed gap size between the reservoir and the sample, tailors the ramp drive, and can be simulated using the radiation-hydrodynamics code LASNEX. The combination of these factors have allowed for a compact design suitable for a laser-driven hohlraum that can reach 5 Mbar pressures and beyond on the National Ignition Facility.   

Rayleigh-Taylor stabilization by material strength at Mbar pressures

We present experiments on the Rayleigh-Taylor (RT) instability in the plastic flow regime of solid-state vanadium (V) foils at ~1 Mbar pressures and strain rates of 1.e6-1.e8 1/s, using a laser based, ramped-pressure acceleration technique. High pressure material strength causes strong stabilization of the RT instability at short wavelengths. Comparisons with 2D simulations utilizing models of high pressure strength show that the V strength increases by factors of 3-4 at peak pressure, compared to its ambient strength. An effective lattice viscosity of ~400 poise would have a similar effect. [1] Constitutive models, and theoretical implications of these experiments will be discussed. [1] H.S. Park, B.A. Remington et al., submitted for publication (July, 2009).   

Designs for Solid-State Rayleigh-Taylor Experiments in Tantalum at Omega

We have designed an experiment for the Omega - EP laser facility to measure the Rayleigh-Taylor (RT) growth rate of solid-state Ta samples at $\sim $1 Mbar pressures and very high strain rates, 10$^{7}$-10$^{8}$ s$^{-1}$. A thin walled, hohlraum based, ramp-wave, quasi-isentropic drive has been developed for this experiment. Thick samples ($\sim$50 $\mu$m) of Ta, with a preimposed sinusoidal rippled on the driven side, will be accelerated. The ripple growth due to the RT instability is greatly reduced due to the dynamic material strength. We will show detailed designs, and a thorough error analysis used to optimize the experiment, minimize uncertainty, and predict strength model sensitivity.   

Rayleigh--Taylor Measurements in Planar CH and SiO$_{2}$ Foils on OMEGA

Understanding how areal-density modulations grow at unstable ablative Rayleigh--Taylor (RT) interfaces is crucial to achieving inertial confinement fusion ignition. Recent planar RT experiments demonstrated increased stabilization in CH targets driven at high intensities (1 $\times $ 10$^{15}$ W/cm$^{2})$ compared to simulations. Planar experiments were preformed on the OMEGA laser using CH, SiO$_{2}$, and CH-SiO$_{2}$ targets with 2-D modulations (imprinted by drive beams or pre-imposed) using shaped drive pulses at high (1 $\times $ 10$^{15}$ W/cm$^{2})$ and low (5 $\times $ 10$^{14}$ W/cm$^{2})$ intensities. The temporal growth of these modulations was measured with face-on x-ray radiography using Pd and Dy x-ray backlighters. Experimental results will be compared with simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-08NA28302.   

Potential of FAIR at Darmstadt and LHC at CERN for High Energy Density Physics Research: the HEDgeHOB Collaboration

Substantial progress in the development of technology of high quality, well focused, strongly bunched intense partile beams have led to development of a novel, very efficient technique of studying High Energy Density Matter (HEDM) in the laboratory. This method involves generation of large samples of HEDM by isochoric and uniform heating of solid targets by these ion beams. Two huge accelerator projects are on the way in Europe. One is the Facility for Antiiprotons and Ion Research (FAIR), at Darmstadt and the other is the Large Hadron Collider (LHC) at CERN. Extensive theoretical work has been carried out over the past years to assess the potential of these accelerators to generate HEDM and several experimental schemes have been proposed [1-4]. A brief overview of this work is presented in this talk. [1] N.A. Tahir et al., PRL 95 (2005) 035001. [2] N.A. Tahir et al., PRL 94 (2005) 135004. [3] N.A. Tahir et al., Nucl. Instr. Meth. A 577 (2007) 238. [4] N.A. tahir et al., PRE 79 (2009) in print.   

Analytical theory for the interaction of a planar shock wave with an isotropic 2D/3D isotropic density field

The response of a shock front to different kinds of perturbations in the fluid upstream is of paramount importance to several fields, in particular to ICF. We present here an analytical linear model that describes the interaction of a shock front with a random pre-shock density perturbation field. Exact expressions for the velocity, density, vorticity and pressure of the compressed fluid particles are obtained. For isotropic pre-shock conditions, the mode averaging can be easily implemented in 2D/3D. Fully closed analytical expressions for the kinetic energy, vorticity generation, density non-uniformity amplification and for the intensity of sound emitted downstream are shown in the whole range of gas compressibilities and shock intensities. A comparison to an existing model [J. G. Wouchuk \textit{et al}., Phys. Rev. E. \textbf{79}, 066315 (2009)] that describes the shock interaction with a turbulent vorticity field is also given.   

Modification of the Hugoniot adiabat due to turbulence generated in shocked deuterium-filled CH foams

Direct-drive laser targets are often designed with DT-filled CH foam ablator. Accurate modeling of these targets requires understanding of shock propagation in such non-uniform media. The interaction of the shock front with the preshock random density non-uniformities generates a random motion (turbulence) in the postshock flow. The energy coupled into the postshock turbulent motion, in turn, modifies the shock adiabat. As first detected in simulations by G. Hazak \textit{et al}., Phys. Plasmas \textbf{5}, 4357 (1998), shock compression and shock velocity in a deuterium-filled foam would be, respectively, less and greater than those predicted for the uniform medium of the same average density. We report an exact analytical theory of this ``shock undercompression'' effect and present explicit formulas for the shock adiabat modification. We discuss the contributions of post-shock Reynolds stresses, acoustic energy flux emitted downstream and correlations between vortical and entropy perturbations and highlight the difference between the cases of 2D and 3D turbulence.   

Session CO6: Magnetic Reconnection and Turbulence

Instability of the Sweet Parker reconnection layer and onset of fast turbulent reconnection

Within purely resistive MHD without any anomolous effects reconnection sets into a steady state knox to center around an elongated current sheet, the Sweet-Parker (SP) layer, where dissipations allow reconnection. However, such layer is known to be possibly unstable to tearing-like modes. A recent discovery [1,2] is that following the destabilisation of the SP layer reconnection can develop into a fast trubulent regime. This new regime requires no anomlous processes and it is purely resistive MHD, progressing as fast as the fastests kinetic or MHD processes. We investigate such transition. \\[4pt] [1] Self-Feeding Turbulent Magnetic Reconnection on Macroscopic Scales Giovanni Lapenta, Phys. Rev. Lett. 100, 235001 (2008), DOI:10.1103/PhysRevLett.100.235001 \\[0pt] [2] Turbulent Magnetic Reconnection in Two Dimensions: Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.; Cowley, S. C.; Yousef, T. A.: eprint arXiv:0904.0823   

Electron scale structure of thin current sheets in collisionless magnetic reconnection

Cluster observations have shown highly structured electron-scale current sheets (CS), viz. bifurcated, filamented and triple peak structures during magnetic reconnection. An electron-magnetohydrodynamic model shows that these structures develop at various stages of time dependent reconnection. The Lorentz force on electrons due to the interaction of electron outflow velocity and normal component of magnetic field bifurcates the CS in the outflow regions, with scale sizes of the individual peak $\sim 3d_e$ ($d_e$ being electron skin depth), similar to those observed by Cluster spacecraft. The bifurcation limits the length of the reconnecting CS which is further reduced by the secondary instabilities growing on the bifurcated CS. The secondary instabilities causes filamentation of the CS in the outflow region. Such filamentary structures have been observed by Cluster spacecraft in magnetopause. In the presence of many reconnection sites, triple peak structure of the CS forms at the secondary sites as a result of reconnection inside the bifurcated CS associated with the main reconnection site.   

Fast magnetic reconnection in fluid models of collisionless pair plasma

The original studies of the GEM magnetic reconnection challenge problem exhibited fast magnetic reconnection in models which included Hall term effects. Subsequent PIC simulations showed that fast reconnection occurs even in pair plasmas, where the Hall term is absent; these studies attributed fast reconnection to nongyrotropic pressure. So we ask, (1) \emph{Can a model of pair plasma with isotropic pressure exhibit fast reconnection?}, and (2) \emph{Can a fluid model replicate patterns of fast magnetic reconnection seen in PIC simulations}? We have simulated the GEM problem for a pair plasma using ten-moment gas-dynamics for each species coupled to Maxwell's equations. Surprisingly, we find that the adiabatic collisionless ten-moment model gives slow reconnection but that isotropization \emph{increases} the rate of reconnection to typical fast rates. We hope to demonstrate fast reconnection in anisotropic pair plasma without direct isotropization by using a nonadiabatic closure for the generalized heat flux; in particular, we expect to report results for David Levermore's 10-moment closure.   

Phase-space signature of electron diffusion in collisionless magnetic reconnection: A standing electron phase-space hole

The structure and dynamics of the electron layer holds the ultimate mystery of how magnetic reconnection can occur in a collisionless plasma. Results from 2D fully kinetic simulations indicate that the electron crossing orbits within the electron layer is the main cause for the electron motion decoupling from the magnetic flux during collisionless magnetic reconnection with zero guide fields. The key evidence is revealed in a hole structure in the electron phase space that stands in the center of the electron layer. The hole structure starts to emerge at the beginning of the explosive growth phase of reconnection, becomes the most prominent when the reconnection rate peaks, and spatially extends, along the outflow direction, through the entire electron diffusion region. Corresponding to the electron hole are a layer of bipolar electric field embedded in the bipolar Hall electric field within the electron layer, and bifurcations of the electron density and the out-of-plane velocity. Flow diversion, energy conversion, as well as regulation of electric currents in the reconnection layer can be understood in terms of electron crossing orbit dynamics.   

Electron holes in PIC Simulations with Physical Mass Ratio

Numerical simulation of reconnection with the kinetic approach is presented. Calculations are performed using the implicit particle-in-cell code PARSEK. The initial configuration is taken to be a conventional Harris current sheet with a guide field and an initial X-point perturbation is superposed to drive the reconnection process. The simulations reproduce such typical features as the Hall structure, the plasma exhaust jets and particle acceleration near X-point. Our attention is focused on the study of kinetic processes near the separatrix. Fast electron flows formed by Hall current system are favourable for development of electrostatic instabilities (namely, electron-ion Buneman instability) [Pritchett, 2005], [Goldman, 2008] as electrons stream much faster than ions there. The distribution functions are investigated for the evidence of electron holes formed by the Buneman instability and the corresponding bipolar spots of electric field. The relation between those reconnection signatures and development of separatrix instability in simulations is discussed.   

Dynamo action with flow shear and magnetic shear

Dynamo action is a fundamental mechanism that explains ubiquitous magnetic fields in a variety of systems, including astrophysical, geophysical and laboratory plasmas. In this contribution, we provide an analytical theory of dynamo ($\alpha$ and $\beta$ effects) in 3D forced helical MHD turbulence [1]. By non-perturbatively incorporating the effect of shear, we show that the $\alpha$ and $\beta$ effects are enhanced by a weak shear while strongly suppressed by strong shear. In particular, for strong shear, the $\beta$ effect is shown to be much more strongly suppressed than the $\alpha$ effect with the scalings $\alpha \propto A^{-5/3}$ and $\beta \propto A^{-7/3}$, respectively ($A$ is the strength of the shear). The quenching of the $\alpha$ and $\beta$ effect by shear has recently been confirmed in a numerical experiment [2]. One of the interesting implications of these results is that the dynamo efficiency, conventionally measured by the dynamo number $D$, depends more strongly on the shear than conventionally assumed. Specifically, $D$ scales as $A^{4}$ rather than $A$. Incorporating a shear in the magnetic field, we then discuss its effect on the stability. Magnetic shear is shown to destabilize when it is stronger than flow shear. On the other hand, a weak magnetic shear compared to flow shear weakens the stabilizing effect of flow shear, thereby leading to a stronger turbulence than in the case without magnetic shear. \\[0pt] [1] N. Leprovost and E. Kim, Astrophys J Lett. v696, L125 (2009); Phys. Rev. Lett., v100, 144502 (2008) \\[0pt] [2] D. Mitra et al, Astron \& Astrophys, v495, 1 (2009)   

The effect of two-dimensional turbulence on resistive-MHD reconnection

Two-dimensional numerical simulations of the effect of background turbulence on 2D resistive magnetic reconnection are presented. For sufficiently small values of the resistivity ($\eta$) and moderate values of the turbulent power ($\epsilon$), the reconnection rate is found to have a much weaker dependence on~$\eta$ than the Sweet-Parker scaling of~$\eta^{1/2}$ and is even consistent with an $\eta-$independent value. For a given value of $\eta$, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in $\epsilon$ above which the reconnection rate is significantly enhanced.   

Fast 3D Reconnection of Weakly Stochastic Magnetic Field: Prospects of the Research

If the necessary requirement for the fast reconnection is the fluid being collisionless, then most of MHD simulations, including those of interstellar medium, do not represent astrophysical reality, as high numerical diffusivity makes reconnection fast for present-day simulations. Fortunately, the model of fast reconnection proposed in Lazarian \& Vishniac (1999) does not have these restrictive constraints as it allows for fast reconnection in MHD limit provided that magnetic field is weakly stochastic. As turbulence is ubiquitous in astrophysical environments, weak stochasticity of magnetic field lines is a default state for most of astrophysical magnetic fields. This still leaves a question of what is happening when the magnetic fields are rather laminar. Our research shows that the reconnection itself may increase the level of turbulence resulting in reconnection instability or bursts of reconnection. The most evident application of the model is related to explaining of Solar flares. The predictions of the model above include First Order Fermi acceleration of energetic particles within the extended reconnection layers predicted in the model as well as the removal of magnetic flux during star formation. More astrophysical applications of the process are to follow.   

Spectrum of weak MHD turbulence

Turbulence of magnetohydrodynamic waves in nature and in the laboratory is generally cross-helical or non-balanced, in that the energies of Afv\'en waves moving in opposite directions along the guide magnetic field are unequal. We propose that such turbulence spontaneously generates a condensate of the residual energy $E_v-E_b$ at small field-parallel wave numbers. As a result, the energy spectra of counter-propagating Alfv\'en waves are generally not scale-invariant. In the limit of infinite Reynolds number, the universality is asymptotically restored at large wave numbers, and both spectra attain the scaling $E(k)\propto k_{\perp}^{-2}$.   

Numerical studies of weak MHD turbulence

Results from numerical simulations of weak magnetohydrodynamic (MHD) turbulence in steady-state are presented, with resolutions as high as $1024^2\times256$ grid points. Weak turbulence refers to the limit of MHD turbulence in which the energy transfer toward smaller scales results from the weak interaction between Alfv\'en waves moving along of against a strong guide magnetic field. The energies of the Alfven waves moving in the opposite directions can be either equal, in which case the turbulence is called balanced, or unequal, in which case it is unbalanced. The numerical set up is optimized as to drive either balanced or unbalanced turbulent cascades. We obtain the spectra of Alfv\'en waves for various degrees of imbalance and Reynolds numbers. We discuss our results and compare with recent theories of weak MHD turbulence.   

Theory of incompressible MHD turbulence with scale dependent alignment and cross-helicity

Boldyrev's theory of incompressible MHD turbulence is different from that of Goldreich \& Sridhar (1995) and others in that it contains a scale dependent alignment of velocity and magnetic field fluctuations in the inertial range. Evidence for this alignment comes from direct numerical simulations and from solar wind data. An extension of Boldyrev's theory to imbalanced turbulence has been proposed by Perez \& Boldyrev. We propose a different theoretical approach which generalizes the results of Perez \& Boldyrev and is based on two new solar wind observations. The first is the observation that the normalized cross-helicity is approximately constant in the inertial range. The second is the observation that the probabilities $p$ and $q$ are approximately constant in the inertial range, where $p$ and $q$ are the probabilities that the velocity and magnetic field fluctuations at a randomly chosen point $(x,t)$ are either aligned or anti-aligned, respectively. Aligned means that the angle between the velocity and magnetic field fluctuations is between 0 and $\pi/2$; anti-aligned means that the angle is between $\pi/2$ and $\pi$. Using these two observational constraints, a generalization of Boldyrev's theory is constructed in which the cascades of the two Elsasser species are each in a state of critical balance and the eddy geometries are required to be scale-invariant. In the new theory, $E(k_{\perp})\propto k_{\perp}^{-3/2}$, $k_{\parallel} \propto k_{\perp}^{ 1/2}$, and the normalized cross-helicity is scale-invariant (a constant).   

Scaling criteria for high Reynolds number MHD turbulence

Magnetohydrodynamic (MHD) turbulence has been employed as a physical model for a wide range of applications in astrophysical and space plasma physics. This paper addresses the following questions. At what MHD flow condition can investigators be sure that their numerical simulations have reproduced all of the most influential physics of the flows and fields of practical interest? Another question, perhaps more specific, is can one define a metric to indicate whether the necessary physics of the flows of interest have been captured and suitably resolved using the tools available to the researcher? This issue was previously addressed in the context of high energy density physics where the Reynolds number of the minimum state was determined to be 1.6$\times $10$^{5}$ [Zhou, Phys. Plasma, 14, 082701 (2007)]. The current paper focuses on extending the threshold minimum state criteria to include the correspondingly high Magnetic Reynolds number influences in MHD applications.   

Thermodynamics, Vertical Structure, and Coronal Power of Optically-Thick MRI-Turbulent Accretion Disks

Determining the thermal structure of an accretion disk heated by the dissipation of MRI turbulence, and the fraction of accretion power released in the disk corona are two critical problems in plasma astrophysics. In this contribution, these two intertwined problems are considered in the case of a disk threaded by a weak vertical magnetic field. The vertical disk structure is calculated by balancing the local turbulent heating due to the disruption of MRI channel flows by parasitic instabilities, and the cooling by radiative diffusion. It is argued that, neglecting the effects of large-scale MHD disk dynamo, the MRI dissipation rate should be uniform across the disk, almost up to its photosphere. This enables one to obtain a self-consistent solution for the disk's thermal structure. Next, the efficiency of Parker instability, viewed as a secondary parasitic instability feeding off MRI channel flows, is assessed by comparing its growth rate with that of other parasitic instabilities. It is shown that Parker instability becomes important near the disk surface, leading to a certain minimal coronal power fraction.   

Magnetosphere-Ionosphere Coupling through Plasma Turbulence in Electrojet

Field-aligned currents enter the high latitude E-region ionosphere from the magnetosphere causing cross-field electric fields and currents. During periods of intense geomagnetic activity, these fields induce the formation of strong electrojets, plasma instabilities, and turbulence. This turbulence gives rise to intense anomalous electron heating and nonlinear transport which significantly affects the E-region conductivity. Electrojet conductivities play an important role in the Magnetosphere-Ionosphere system. These conductivities determine the polar-cap potential saturation level and the evolution of field-aligned currents. Quantitative understanding of turbulent conductivities and energy conversion issues is important to accurately model magnetic storms and substorms essential for Space Weather predictions. We will present results of recent theoretical efforts of global energy flow, along with results of 2D and 3D fully kinetic, particle-in-cell, simulations. These simulations reproduce many of the observational characteristics of radar signals and provide information useful in accurately modeling plasma turbulence. They demonstrate the significant progress we have made simulating physical processes in E-region electrojets.   

Session CO7: Low Temperature Plasmas I

The Electrodeless Lorentz Force Thruster

The Electrodeless Lorentz Force (ELF) thruster is a novel plasma thruster under development at MSNW and the University of Washington which utilizes Rotating Magnetic Field (RMF) current drive technology to ionize a neutral gas and drive an azimuthal current to form a Field Reversed Configuration (FRC) plasmoid in a diverging magnetic field. The magnetic gradient imparts a net force to the FRC which is ejected from the thruster at high velocity. ELF has been shown to operate from 10 - 100 kW, with an exhaust velocity of 15 - 40 km/s. The ELF thruster is expected to have an extremely large range of efficient power levels, high thrust density, high specific power, long lifetime, and the ability to utilize virtually any type of propellant. Thruster design and operation, novel diagnostics, and a discussion of experimental results detailing the key physical phenomena within the thruster and exhaust plume will be presented.   

Self consistent kinetic simulations of SPT and HEMP thrusters including the near-field plume region

SPT (Stationary Plasma Thruster) and HEMP (High Efficiency Multistage Plasma) thrusters are both relying on the creation of propulsive ion beams by ionization of propellant atoms. The specific shape of the magnetic fields in both concepts is used to optimize efficiency and ion acceleration. 2d3v-PIC-MCC calculations are used to compare the two different thruster concepts. They result in quite different plasma-wall interaction characteristics. The SPT thruster relies on the strong secondary electron emission from the dielectric walls of the thruster channel, which causes a large ion flux over the whole channel surface and consequently high erosion rate. In contrast, in the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion flux to the thruster channel surface as compared to SPT. Consequently, experimental studies of HEMP gave no evidence of erosion. In order to study the wall erosion for both thrusters, the binary collision approximation (BCA) based Monte-Carlo code SDTrimSP is applied.   

Initial Results of Time-Resolved VUV Spectroscopy of Pulsed Dielectric Surface Flashover in Atmosphere

This paper describes some initial results from an experimental setup designed for studying the optical emission during pulsed surface flashover for the wavelength range from 115 nm to 180 nm at atmospheric pressures. A VM 505 from Acton Research Corporation was used as the spectrograph, with an Andor DH740 series ICCD camera mounted at the exit flange. Spectra were measured in nitrogen and air at atmospheric pressure with a flashover spark length of 8 mm under pulsed 35 kV excitation. Emission intensities were measured during gated 50 ns intervals, and it was concluded that most VUV emission occurs during the first stage of the flashover event. This is important because it is believed only radiation below 180 nm is energetic enough to cause photoionization leading to streamer discharge, and very little is known about VUV emission during this initial stage. Utilizing the NIST Atomic Spectra Database, a library of temperature dependent emission spectra was generated with SpectraPlot, a spectral software suite developed at TTU. The measured spectra will be discussed in relation to the physics of surface flashover at atmospheric pressure.   

Determination of OH radicals in the far downstream of an atmospheric pressure microwave helium plasma jet

A recent study has reported observation of OH radicals in the far downstream of an atmospheric argon microwave plasma jet. The far downstream is referred to as the location where the ratio of the distance from the jet orifice to the length of the jet column is $>$ 3. In this work we report that this phenomenon also exists in a similar plasma jet of 2.5 mm long, operating by helium gas. A detailed characterization of the helium microwave plasma jet was carried out by using UV pulsed cavity ringdown spectroscopy and optical emission spectroscopy. The nonthermal plasma temperatures were determined from stimulations of the emission spectra of several vibronic bands of the 2$^{nd}$ positive system of N$_{2}$, the 1$^{st}$ negative system of N$_{2}^{+}$, the (0,1,2,3-0) bands of NO (A-X), and the (0-0) band of OH (A-X). Absolute number densities of OH were measured along the plasma jet column. Dependence of OH concentration on plasma power and gas flow rate at different locations along the jet axis was characterized. The electron densities were also measured by recording Stark broadening of the hydrogen Balmer beta line (H$_{\beta })$ at 486.1 nm.   

Studies of the vacuum breakdown behavior using refractory-metal thin film coated electrodes

A reliable operation of ICRF antennas in fusion devices is often limited by its breakdown threshold. Surface conditions of electrodes during high voltage operations have played a key role in affecting breakdowns. In this work, the effects of coating electrodes with refractory-metal thin films to improve on the reliability and power delivered by ICRF antennas have been investigated. Using the Surface Plasma Arcs by Radiofrequency - Control Study (SPARCS) facility at the Center for Plasma-Material Interactions which is designed as a DC system, the current and voltage breakdown patterns and the measured energy in the arc at an electric field of up to 150 MW/m were studied. Experiments with electrodes coated with W, Mo and Ta operated at high temperature of 600 $^{o}$C and above were explored. Surface studies were also conducted on the electrodes to determine the electrode conditions and other surface reactions after the breakdown.   

Design of experiments on a DC Steady State Atmospheric Pressure Plasma Sterilizer

Our Resistive Barrier Discharge has been demonstrated to be successful on E. coli, Pseudomonas fluorescens (5RL), spores and bacteriophages. It has been tested successfully in sterilizing pagers at the St. Jude Research Hospital in Memphis, TN. In this recent work, we evaluate three primary factors in the atmospheric pressure resistive barrier discharge, hydrogen peroxide, charged ions and air (oxygen). The experiment used was Analysis of Variance (ANOVA) and regression analysis. The tests used 144 Petri Dishes and the bacteria used were E. coli. The hydrogen peroxide was used as a replacement for the water conductor on the resistive barrier discharge electrode. The charged ions were removed by a double charged wire mesh between the discharge and the Petri Dish. The air was displaced by a slow flow of nitrogen into the experimental area. The basic conclusions are that air, and charged ions are both extremely effective in killing bacteria. In addition, air and charged ions together strongly enhance each other. Hydrogen peroxide in our experiments did not enhance the kill rate.   

Session CP8: Poster Session II: Diagnostics, Heating, Current Drive; Diagnostics, Laser Plasma Interactions, and Fast Ignition

Enhancements to the Edge CXRS System on JET

Enhancements have been made to 2 of the 4 instruments comprising the edge (r/a $\sim$0.5 to $\sim$1.0) charge-exchange recombination spectroscopy (CXRS) suite of diagnostics on the Joint European Torus (JET). Both enhanced instruments now consist of short focal length spectrometers coupled to fast-framing CCD cameras at ``high dispersion.'' Between these two instruments the number of plasma viewing channels increases from 24 to 34. The time resolution is improved to 10 ms. The neutral-beam induced emission of C VI at 529.1 nm, of Ne X at 524.8 nm, and of Ar XVIII at 522.4 nm is observed simultaneously, complementing the existing edge CXRS instruments, which can be tuned to observe any visible wavelength of interest. These enhancements enable the simultaneous observation of the temperature, rotation, and concentration of multiple plasma impurity ions at improved temporal and spatial resolution. Preliminary data will be shown from the recent JET campaign.   

Measurement of Type-I ELM Pulse Propagation in Scrape-Off Layer Using Optical System of Motional Stark Effect Diagnostics in JT-60U

Propagation of plasma ejected by type-I ELM has been measured in scrape-off layer (SOL), using optical system of motional Stark effect (MSE) diagnostics in JT-60U as beam emission spectroscopy (BES) diagnostics. This MSE/BES system measures Dalpha emission from heating neutral beam excited by collisions with the ejected plasma, as well as background light (e.g. bremsstrahlung). In order to separate the beam emission and the background light, a two-wavelength detector is introduced into the MSE/BES system The detector observes simultaneously at the same spatial point in two distinct wavelengths using two photomultiplier tubes through two interference filters. One of the filters is adjusted to the central wavelength of the beam emission and the other is outside the beam emission spectrum Subtracting the background light, temporal change in the net beam emission in SOL has been evaluated Comparing conditionally-averaged beam emission with respect to 594 ELMs at 5 spatial channels (0.02-0.3 m outside the main plasma near equatorial plane), radial velocity of the ELM pulse propagation in SOL is about 0.8-1.8 km/s. Work supported by Grand-in-Aid for Young Scientists (B) No. 20760586   

Progress on a 200kW Diagnostic Neutral Beam

The interaction of neutral beam atoms with a magnetized plasma provides diagnostic access to the interiors of fusion experiments. Parameters which can be measured using neutral beams include ion temperature and velocity, density fluctuations and also local magnetic field direction. Nova Photonics, Inc and Lawrence Berkeley National Laboratory are developing a diagnostic neutral beam for use in fusion experiments which lack neutral heating beams, or on which the heating beam is not suitable for diagnostics. Our apparatus is designed to produce a 1 s duration, 5~x~8~cm elliptical cross section hydrogen beam at energies up to 40 kV and up to 5~A current. Hydrogen ions are produced in a multicusp 13~kW, 13~MHz RF source. The extracted ions have current densities of 100 - 150~$\mathrm{mA/cm}^2$. The proton fraction of the hydrogen ions is 85\%. Beams are extracted from the source with a rectangular, multi-aperature grids. Details of the source performance will be presented as well as initial operation of the extraction optics and neutralizer region. This work is supported by the U.S. DOE under grant DE-FG02-05ER86256.   

Relativistic Depolarization Effects in Thomson Scattering

Relativistic depolarization effects have been well studied for several cases of Thomson scattering - particularly the simplifying case of 180 $^{\circ}$ backscattering utilized in LIDAR Thomson scattering systems [K. V. Beausang and S. L. Prunty, Plasma Phys. Control. Fusion 50, 095001 (2008)], as well as the more general case where the detector is assumed to collect only scattered radiation with the component of the scattered electric field parallel to the incident wave electric field [O. Naito, H. Yoshida, and T. Matoba, Phys. Fluids B 5, 4256 (1993)]. These results are not valid for the Thomson scattering diagnostic on the MST reversed-field pinch, which collects all polarizations of the scattered radiation and measures radiation scattered at many different angles. We derive a compact form for the scattering spectrum for this case and present an analytic approximation. The accuracy of this approximation is determined for temperatures up to 40 keV. This derivation improves the accuracy of Thomson scattering measurements made on the MST without sacrificing calculation speed; even at temperatures of a few keV, the onset of relativistic depolarization can significantly alter the scattering spectrum. Furthermore, this approximation provides an accurate spectrum of interest in the study of higher-temperature fusion plasmas. *This work was supported by the U.S. Department of Energy.   

Dual-Array Electron Cyclotron Emission Imaging (ECEI): a New Millimeter Wave Imaging System for Electron Temperature Fluctuation on the DIII-D Tokamak

A new diagnostic tool has been developed for simultaneous real-time imaging of electron temperature fluctuations at both the high and low field sides. Separate imaging arrays spanning 75 to 110 and 90 to 140 GHz, respectively consist of 160 channels (20 vertical by 8 radial) with $\sim $1 cm$^{2}$ resolution, providing up to 55 cm of vertical plasma coverage. Fluctuations of 1{\%} are measurable on $\mu $s time-scales. The technical capabilities of this diagnostic, as well as potential physics issues to be investigated, are discussed. The details of the constituent technologies, including advanced antennas and substrate lenses, quasi-optical planar filter components, and double down-conversion heterodyne signal detection will be addressed.   

Advances in Velocimetry Techniques for Plasma Turbulence

The HOP-V (Hybrid OPtical-flow Velocimetry) code has been developed for extracting time-resolved 2-D velocity maps from turbulence imaging diagnostics. The HOP-V code combines optical-flow and local pattern-matching techniques to derive ``dense'' velocity fields at the full temporal resolution and a fraction of the spatial resolution of the underlying image frames, often tens of pixels per side and thousands of timepoints in duration, with temporal and spatial resolution sufficient to resolve the relevant coherence decay quantities. Recent work has resulted in a new module to the HOP-V code, using a ``next generation'' optical flow approach capable of obtaining accurate flow-fields from highly nonrigid motion, as is commonly the case in turbulent scalar measurements. This approach not only derives flow fields containing local curl, but also simultaneously provides a decomposition of the flow field into a coherent pattern with separable small-scale patterns. This can be particularly important in separating the local ``swirling'' motion from flows having a more global impact on transport.   

Validation of Velocimetry Techniques using Synthetic Diagnostics in Edge Turbulence Simulations

The HOP-V (Hybrid OPtical-flow Velocimetry) code, developed for extracting time-resolved 2-D velocity maps from turbulence imaging diagnostics, combines optical-flow and local pattern-matching techniques to derive ``dense'' velocity fields at the full temporal resolution and a fraction of the spatial resolution of the underlying image frames, often tens of pixels per side and thousands of timepoints in duration, with temporal and spatial resolution sufficient to resolve the relevant turbulent structures. The code has been validated for a variety of artificial test patterns of convective flow, including highly sheared cases. Beyond verifying the validity of the velocimetry algorithms for extracting the true motion of the visible structures lies the physical interpretation of the derived velocity fields. To approach this question, we have implemented a synthetic diagnostic (similar to the Gas Puff Imaging instrument) to analyze the output of the BOUT edge turbulence simulation. Here we present the results of a study directly comparing the derived velocity fields to the known plasma quantities from the simulation, in an attempt to define the connection between the observed velocities and underlying plasma behavior.   

Fullwave Simulation of Doppler Reflectometry in Turbulent Plasmas

Doppler reflectometry is a microwave diagnostic for plasma density fluctuations and flow velocities. A meaningful interpretation of Doppler reflectometry measurements necessitates the analysis of the wave propagation in the plasma using simulations methods. While the beam path can usually be reconstructed with beam tracing methods, the modeling of the scattering process demands the use of wave simulation codes. Furthermore, in the presence of strong density fluctuations, the response from the plasma is dominated by dispersion and multiple scattering, and hence becomes non-linear. IPF-FD3D [1] is the finite difference time domain code used to investigate the dependence of the scattering efficiency on the various plasma conditions. It uses the full set of Maxwell equations and the electron equation of motion. First results in slab geometry indicate a strong dependence of the scattering efficiency on the density gradient, the turbulent fluctuation strength, and the wave polarisation. In addition, the actual plasma conditions in ASDEX-Upgrade are recreated in the simulation in order to interpret experimental measurements.\\[4pt] [1] C. Lechte, IEEE Trans. Plasma Sci. 37 (6), 2009   

Transmitter Upgrade for JET Alfv\'{e}n Eigenmode Fast Particle Interaction Studies

One of the main missions of the worldwide fusion R{\&}D effort is to develop predictive and control capability of burning plasmas in support of ITER. A unique 8-coil antenna system has been implemented on JET to study fast-ion interactions with Alfv\'{e}n eigenmodes in the 50 -- 500 kHz range that could potentially increase losses of $\alpha $ particles and reduce fusion gain. The single 4 kW transmitter will be replaced with eight 1 kW transmitters that will independently power each antenna to more uniformly distribute the power among the antennas. This will improve the coupling to higher order modes (n = 5 - 30) for damping studies. Independent drivers will also be used to make possible multi frequency and arbitrary phase studies of multiple modes and traveling modes. Various analog and digital driver approaches are being considered to provide the needed flexibility. A systems design will be presented.   

X-ray GEM Detectors for Burning Plasma Experiments

The harsh environment and higher values of plasma parameters to be expected in future burning plasma experiments (and even more so in future power producing fusion reactors) is prompting the development of new, advanced diagnostic systems. The detection of radiation emitted by the plasma in the X-ray spectral region is likely to play the role that visible or UV radiation have in present day experiments. GEM gas detectors, developed at CERN, are the natural evolution of Multiwire Proportional Chambers, with a number of advantages: higher counting rates, lower noise, good energy resolution, low sensitivity to background radiation. GEM's can be used in several different ways, but two specific applications are being explored in the framework of the Ignitor program, one for plasma position control and the other for high resolution spectroscopy. The diagnostic layout on the Ignitor machine is such that the detectors will not be in direct view of the plasma, at locations where they can be efficiently screened by the background radiation. Prototype detectors 10 $\times$ 10 cm$^2$ in area have been assembled and will be tested to assess the optimal geometrical parameters and operating conditions, regarding in particular the choice between Single and Triple GEM configurations, the gas mixture, and the problem of fan-out associated with the high number of output channels required for high resolution crystal spectrometers.   

SSPX discharges with tungsten hexacarbonyl prefill

The ITER tokamak will have a tungsten divertor and, consequently, the plasmas are expected to contain tungsten ions. The spectral emission from these ions can serve to diagnose the divertor for plasma parameters such as tungsten concentrations, densities, ion and electron temperatures, and flow velocities. The ITER divertor plasmas will have densities around 10$^{14 - 15}$ cm$^{-3}$ and temperatures below 100 eV. These conditions are similar to the plasmas at the Sustained Spheromak Physics Experiment (SSPX) in Livermore. To simulate ITER divertor plasmas, a tungsten impurity was introduced into the SSPX spheromak by prefilling it with tungsten hexacarbonyl at injection pressures up to 1 Torr prior to the usual hydrogen gas injection and initiation of the plasma discharge. These discharges lasted a few milliseconds and achieved plasma currents up to 1 MA. The possibility of using the emission from low charge state tungsten ions to diagnose tokamak plasmas was investigated using a high-resolution EUV spectrometer in the 50 to 450 {\AA} range. Work performed under the auspices of the US DOE by LLNL under contract DE-AC52-07NA-27344.   

Determination of Experimental Mutual Inductances in Magnetic Diagnostics Through Linear Modeling

When using magnetic diagnostics for equilibrium reconstruction of a plasma, it is necessary to know the mutual inductances between the diagnostics and known sources of current, such as field generating coils. The mutual inductance is a purely geometric factor and, as such, can be found computationally given the locations of the target coils. Even so, direct calculation may not be the most accurate method of determination. This method does not, for example, take into account the error inherent in the placing of the coils (which can have a large effect when a perfectly placed coil should have an extremely low inductance). A method for experimentally determining the mutual inductances, explored here, is possible through a linear model. The flux in each diagnostic is measured during a plasma-free (vacuum) shot. Under the assumption that any flux in the magnetic diagnostics during such a shot is the product of measured coil currents and their mutual inductances with the diagnostic, a chi-squared minimization is done on the difference between the measured flux data and the product of the model. This method also has the advantage of offering some insight into the modeling of induced currents in the vacuum vessel.   

Miniature magnetic field probes for use in high temperature plasmas

An ideal internal magnetic probe would provide high temporal and spatial resolution, without perturbing the plasma. Optimizing the following moves towards this ideal: Size - as small as possible; Plasma facing material - insulating, difficult to ablate, low Z; Shielding - electrostatic, short field penetration time; Electronics - high gain integration, long term stability. Over the years, significant improvements in these areas have been made. The latest probe, built for TCSU, is 3 axis with 96 windings. It is BN clad with a 6 mm outside diameter, is UHV compatible, and can be baked to 200 C. The integrators used are gated, with a 10 usec RC time, and have less then a 10 mV drift per second. Plasmas with widely varying parameters have been probed. A few hundred eV, 1e20 m-3 density plasma with a 1 msec duration represents a reasonable upper limit for probe usability. Plasma duration, density, and temperature can be traded for each other. Design criterion and construction details will be presented, with a focus on the ``how to'' of actually building one.   

A Baffled-Probe Technique for Real-Time Edge Diagnostics

A baffled probe offers the advantages of direct measurements of the plasma fluid observables, while being non-emitting and electrically floating [1]. The principle of operation of the probe is based on the dependence of the voltage drop in the plasma-probe sheath on the direction of the local magnetic field. When the magnetic field is parallel to the probe surface, the electron-repelling sheath can be significantly reduced as the magnetic field also impedes the cross-field electron flow and therefore, a smaller sheath voltage is needed to maintain the zero current balance to the floating probe. As a result, the accuracy of direct measurement of the plasma potential is greatly increased by eliminating the contribution of electron temperature to the floating-potential measurement. The baffled-probe designs proposed for edge diagnostics will increase the capability to characterize separately plasma properties in real-time for understanding of underlying physics in the edge plasma of tokamaks.\\[4pt] [1] V. I. Demidov et al., Rev. Sci. Instrum. 73, 3409 (2002).   

Self-consistent simulations of rf heating in the ion cyclotron range of frequencies

The rf-SciDAC collaboration is developing computer simulations to predict the damping of radio frequency (rf) waves in fusion plasmas. The recent iterative coupling of the all-orders spectral wave solver AORSA to the Monte-Carlo particle codes ORBIT-rf and sMC+rf allows finite width ion orbits and rf induced spatial transport to be studied in the ion cyclotron range of frequencies [Green et al., \textit{Proc. of 18th Topical Conference on Radio Frequency Power in Plasmas, Gent, Belgium}]. Here we investigate the effects of including finite ion orbits and the importance of using the full $\vec{k}$ spectrum when constructing the quasi-linear (QL) rf heating operator. Power absorption and deposition results for simulations with and without finite ion orbits and for various QL heating operators are compared for heating scenarios including minority H on Alcator C-Mod, beam heating on DIII-D and high harmonic fast wave heating on NSTX. Additionally we present the preliminary results of extending AORSA to calculate the linear wave solution in the open field line region outside the last close flux surface on NSTX.   

ICRF Heating Scenarios for the Reduced Magnetic Field, Non-nuclear Phase of ITER

Radio frequency power in the ion cyclotron range of frequencies (ICRF) is one of three external heating sources planned for ITER. Previous full-wave simulations of high-power electromagnetic wave heating in ITER using the AORSA code [1] have concentrated on the burning plasma regime at full magnetic field and plasma current. Here, we consider instead the startup, non-nuclear phase of ITER. ASTRA modeled plasma profiles are assumed for hydrogen plasmas at 7.5 MA and 2.65 T with 3{\%} minority He$^{3}$ ions. The 2$^{nd}$ harmonic He$^{3}$ resonance occurs near the magnetic axis, while the fundamental H resonance occurs on the inboard edge. Three cases represent a good range of conditions to study the application of ICRF: 1) L-mode conditions before ICRF is applied and well away from the H-mode threshold, 2) L-mode conditions with ICRF approaching the H-mode threshold, and 3) fully developed H-mode with all power available.   

Modeling of an ITER Antenna Module, in Vacuum, and with Facing Plasma

We report on the process of modeling the electromagnetic properties of a single ITER module, including Faraday screen, with the finite-difference time-domain software, VORPAL. CAD drawings and other descriptive materials are used to create an input file and geometry description suitable for EM modeling. Though finite-difference based, this software provides finite-element-like accuracy in the geometry representation, due to its cut-cell boundary capability. Parametric descriptions and enhancements are also used to resolve issues, add drive terms, and diagnostic features, and to insure reusability, e.g., for simulation of an entire antenna assembly in the future, and for installation into a larger toroidal-geometry simulation. Vacuum electromagnetic properties, such as peak fields and radiation impedance are measured, and compared with existing data, where possible. In addition, this software contains a time-domain plasma model that allows seamless integration with edge and possibly even internal plasma. An investigation of the electrical properties is then repeated for sensible edge plasma parameters.   

RF propagation in the turbulent edge plasma

Most present day codes treat the propagation of rf through the edge plasma in relatively simple models in which the background plasma is steady state, laminar, and one dimensional (varying only in the flux coordinate). In reality, the edge plasma is strongly turbulent and intermittent in both space and time. As a first approximation, we consider the SOL to consist of a tenuous background plasma upon which denser filamentary field-aligned blobs of plasma are superimposed. Thus the (time and poloidally averaged) mean and local densities are very different. The blobs are regarded as stationary on the rf time-scale. Questions include phenomenology near resonances and cutoffs in intermittent plasmas, wave propagation and evanescence (e.g. when the blob and background are on opposite sides of a cutoff), and scattered power. We begin to address these questions by reporting on the scattering of a fast or slow plane-wave from a field-aligned cylinder of higher density plasma, in the cold plasma model.   

A numerical analysis of the RF wave propagation under the sheath boundary condition in the ion cyclotron range of frequencies

Applying radio-frequency (RF) waves to heat plasmas and drive current is an important technique for magnetic fusion, and much research effort has been spent on improving the methods, particularly in the ion cyclotron range of frequencies. In this study, a numerical analysis is carried out in order to observe the RF wave propagation and its interaction with the sheath in the scrape-off layer. A two-dimensional finite element code is developed to test the effect of sheaths on waves in cold plasma with the equilibrium magnetic field having a small component into the wall. Here the C-Mod like parameters are used to construct the calculation domain, on which the sheath boundary condition proposed by D'Ippolito and Myra, and the absorbing boundary condition are imposed. Various mechanisms for antenna coupling to the slow wave (SW) and fast-wave coupling to the SW by the sheath boundary condition are qualitatively investigated.   

Reconstructing lower hybrid wave fields from ray tracing data

Full wave simulations of lower-hybrid waves in plasmas can now be performed, and some of the results display features that look like rays or beams [1]. While some features of the full wave results can be reproduced using ray tracing methods, other features cannot be. In this work, we use the higher order terms in the ray tracing approximation to construct an approximate wave field from ray tracing data. In order to correctly deal with caustics - such as the reflection of the lower hybrid wave from the cutoff at the plasma boundary - we implemented a field reconstruction algorithm based on wave packet dynamics [2]. We then applied this algorithm to the case of a lower hybrid wave reflecting from the cutoff in a cold plasma slab model, and the preliminary results show good agreement with the analytical solution.\\[4pt] [1] J. Wright, et al. Full wave simulations of lower hybrid wave propagation in tokamaks. Proceedings of the 18th Topical Conference on Radio Frequency Power in Plasmas, 2009.\\[0pt] [2] R. Littlejohn. The semiclassical evolution of wave packets. Physics Reports, 138(4-5):193-291, May 1986.   

Towards the modeling of ICRH using the delta-f particle-in-cell method in RZ geometry

The delta-f particle-in-cell (DFPIC) method is a PIC method with a high signal-to-noise ratio which has been used for modeling electron Bernstein waves and ion cyclotron fast waves. It offers the capacity to model particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. It presents an alternative to linear wave codes like AORSA and TORIC which include only first-order parallel and perpendicular gradient variations of cyclotron frequency. Here we explore the use of the DFPIC method in the VORPAL computational framework for ion cyclotron resonance heating in RZ geometries based on eqdisk fusion data. We also consider the coupling to the bounce-averaged nonlinear Fokker-Planck code, CQL3D, through the generation of quasi-linear diffusion coefficients using a novel approach based on the DFPIC method. A benchmarking of the quasi-linear diffusion coefficients generated with the DFPIC method will be presented in 1D.   

AORSA-1D simulation of parametric decay instability (PDI) in tokamak plasmas

Theory and experiment have suggested that PDI is a possible nonlinear edge loss mechanism. This study simulates the PDI in ICRF heating for the C-MOD and NSTX tokamaks, using an extended 1D full wave spectral code, AORSA [1], where a non-uniform plasma is taken into account. PDI is described by a set of coupled equations for a long-wavelength ``dipole'' pump and short-wavelength daughter waves. Fixing the pump wave, so that a direct method can be used to find the solution, eliminates possible numerical instability associated with iterative methods. We successfully excite the decay instability into an ion Bernstein wave and an ion cyclotron quasi-mode. Simulation shows the PDI threshold of C-MOD is consistent with the estimate from experiment, and the linear damping is so weak that non-linearly excited waves can propagate into the bulk plasma. NSTX has a much lower PDI threshold, and the narrow distance between harmonics prevents the daughter wave energy from getting into the bulk plasma. Comparison with local dispersion relation calculations shows strong effects of damping and poloidal wave number $k_y$ on the PDI.\\[4pt] [1] E.F. Jaeger, et al., Phys. Plasmas 7, 3319, 2000.   

JET ITER-Like Antenna Simulation Using the TOPICA Code

In this work, we carried out the analysis of the recently installed JET ITER-Like antenna with TOPICA code. Comparisons between TOPICA simulations and measurements taken during the actual experiment are presented. As routinely done for all simulated antennas, TOPICA inputs are the technical drawings of the launcher and the accurate density and temperature profiles, which, in this case, have been provided by the JET team. The standard outputs are the input parameters of the antenna, namely the impedance matrix, the electric current distribution and the electric field pattern at the interface between the antenna region and the plasma column. This work provides an additional proof that the code can be adopted to predict the behavior of the ITER antenna, and to confidently use TOPICA for the challenging task of optimizing the complex design of the actual ITER antenna. More generally viewed, the possibility to reliably simulate the detailed geometry of an ICRF antenna, given a realistic plasma description, and to obtain the actual antenna input parameters, is of paramount importance to evaluate and predict the system performances, and to assist in system operation.   

Simulations of lower-hybrid coupling in the Madison Symmetric Torus

An ana\-lysis will be presented of radio-frequency (RF) coupling with the inter-digital line slow-wave antenna used for lower-hybrid (LH) heating and current drive at 800~MHz in the Madison Symmetric Torus (MST) reversed-field pinch (RFP). The primary simulation tool was the VORPAL code, but MicroWave Studio and RANT3D/AORSA1D-H were also used. Due to the special requirements of the RFP configuration (tight-fitting conducting shell in which only minimal portholes are acceptable to maintain MHD stability), the unusual inter-digital line antenna was chosen. Accessibility in MST requires a very large parallel wave number $k_\parallel$, with $N_\parallel = c k_\parallel / \omega > 7.5$. A blind V\&V exercise done in vacuum showed excellent agreement for the phase difference between the antenna rods, with VORPAL and measurement differing by only $1.0^\circ$, but with MWS deviating more. Unfortunately the phasing excites a wave with $N_\parallel$ approximately 10\% too small. With plasma, VORPAL gives $N_\parallel$ around 15\% below the accessibility limit. VORPAL simulations performed on ANL Intrepid to investigate antenna modifications to increase $N_\parallel$ will also be presented.   

Examination of Up-Down Asymmetry Effects on CQL3D Calculation of ECCD and Multi-Species FW Heating in the DIII-D Tokamak

The CQL3D Fokker-Planck code [1] which calculates the 3D (r, v$_{\bot}$, v$_{//})$, time-dependent electron and ion distributions has been recently upgraded to include effects of non-up-down symmetry, and also to simulate simultaneous quasilinear diffusion of multiple ion species. We make applications to two types of previous modeling of the DIII-D experiment: (1) ECCD, now particularly as regards effects on up-down asymmetric equilibria; and (2) D/minority-H modeling of a canonical DIII-D fast wave shot. Code modification issues, and results for ECCD and the effects of minority-H on the higher harmonic ion absorption of the FW, are presented. \\[4pt] [1] R.W. Harvey and M. McCoy, The CQL3D Fokker Planck Code, Proceedings of the IAEA Technical Committee Meeting on Simulation and Modeling of Thermonuclear Plasmas, Montreal, Canada, 1992; also, http://www.compxco.com/cql3d.html.   

Kinetic evolution of electron distribution function in presence of RF waves

Radio frequency (RF) waves are routinely used to modify the current profile in tokamaks. In ITER, electron cyclotron waves will be used for such a purpose. We have formulated a kinetic description for the evolution of the electron distribution function $f_e$ in the presence of RF waves in a tokamak magnetic geometry [1]. The evolution of $f_e$ and the electron orbits is treated simultaneously, so that the evolution equation for $f_e$ is a functional mapping. This is useful as the electron phase space is inhomogeneous and bounded. All possible electron orbits, correlated and uncorrelated, are properly included. We use action-angle variables of an axisymmetric toroidal plasma. If we assume that $f_e$ is randomly distributed in one or all of the angles, a diffusion-like equation for the evolution of $f_e$ is obtained. The diffusion coefficient is time dependent and non-singular. In the limit of infinite time, we obtain the usual, singular, quasilinear diffusion coefficient. However, this description is incorrect as the time scale for the evolution of $f_e$ is inconsistent with the infinite time scale for determining the diffusion coefficient. The consequences of our description on the evolution of $f_e$ will be discussed.\newline [1] Y. Kominis et al., Phys. Plasmas {\bf 15}, 122501 (2008).   

Nonlinear heating of ions by electron cyclotron frequency waves in tokamaks

Previously it has been shown that small amplitude waves in the lower hybrid frequency range can nonlinearly heat ions in plasmas [1]. We study the possibility of heating ions by two electron cyclotron (EC) waves with slightly different frequencies in tokamak plasmas. The EC beams can be either the X or O waves and propagate at two different angles with respect to the local magnetic field. The ion motion in the interaction region, where the beams overlap spatially, is determined by canonical perturbation theory applied to the Hamiltonian of the ion motion. An analysis of the EC beam parameters for the two waves that are required to energize ions is presented. We consider the possibility of using such a scheme to heat ions in ITER-type plasmas.\\[4pt] [1] D. B\'enisti, A. K. Ram, and A. Bers, Phys. Plasmas {\bf 5}, 3224 (1998); A. K. Ram, A.\ Bers, and D. B\'enisti, J. Geophys. Res. {\bf 103}, 9431 (1998).   

Scattering of radio frequency waves by edge density fluctuations

The coupling of externally launched radio frequency (RF) waves to a plasma is through an edge region with fluctuating density. The fluctuations can lead to scattering of the waves and hinder their coupling into the core plasma. Consequently, the efficiency for heating and/or current drive by RF waves is lowered. We study the effect of density fluctuations on RF waves in the ion cyclotron, lower hybrid, and electron cyclotron range of frequencies. We compare the full wave effects with a model where the waves are represented by rays. Then the Hamilton-Jacobi equations are applicable. A statistical model for the refraction of rays due to the fluctuating part of the plasma permittivity is developed. We will present results from this model showing the effect of fluctuations on the coupling of various RF waves.   

Drift of circulating orbits due to toroidal electrical field

The drift orbit of circulating particles in a tokamak geometry with a toroidal electric field is studied. Unlike trapped particles, which move significantly due to the Ware-pinch effect, circulating particles deviate far less across flux surfaces. The orbits of circulating particles drift away from the center of tokamak with a velocity smaller than the ware pinch velocity, but larger than the ${\rm {\bf E\times B}}$ drift velocity. For trapped particles, the Ware pinch effect is accompanied by acceleration in the parallel direction. Thus, trapped particles first are pinched inward, then untrapped and then the resulting untrapped particles drift outwards. Thus, trapped particles first are pinched inward, are then untrapped, and then the resulting untrapped particles drift outwards. This effect may be relevant to toroidal rotation observed in the presence of lower hybrid (LH) waves, where resonant trapped particles may be pinched inward, whereas resonant circulating particles may drift away from the center of tokamak. Both transport mechanisms could affect the radial electric field, which generates the rotation in the toroidal direction.   

Novel visualization and computational methods for iterated conversions in tokamak RF heating

Mode conversion is of great interest as a tool for RF heating and control of flow and current in fusion devices. In a closed system, waves convert many times, leading to a complex interference pattern. To aid in visualization, we introduce the concept of a `room' associated with each of two uncoupled modes, and illustrate the idea with a tokamak model for its two- dimensional poloidal cross-section (hence the ray phase space is four-dimensional). Each of the two dispersion surfaces, $D_ {j }(x,y,k_{x},k_{y})$ = 0 for $j=$1,2, is three-dimensional, hence they can be visualized as two separate 3-spaces. The set of points where conversion can occur is a two-dimensional surface in each room. When a ray of type 1 in room 1 punctures the conversion surface, it continues in room 1 as a transmitted ray, but it also spawns a daughter ray of type 2 in room 2. Starting from a point on the conversion surface, we can follow a ray of either type in the relevant room to construct two maps, which take the conversion surface to itself. All possible sequences of conversions can be summarized by all possible combinations of the maps.   

Mitigation of the Thermonuclear Instability by Low-Power ICRH Minority Heating in Ignitor

The expected ability of Ignitor to achieve ignition with high peak densities ($n_0 \cong 10^{21} \rm m^{-3}$) and relatively low temperatures makes it possible to investigate the thermonuclear instability that can develop in these regimes. As a consequence of the instability, self-heating of the plasma by the fusion produced $\alpha$-particles can lead to a significant rise of the plasma temperature and, with this, to an increase of its pressure. Then, internal plasma modes may be excited and saturate the thermonuclear instability at acceptable levels without external intervention. In the case where an internal process may not be effective, a scenario is considered whereby Ignitor is led to operate in a slightly subcritical regime, i.e. the plasma parameters are so chosen that the thermonuclear heating power is slightly less than the power lost, and a small fraction of $^3$He is added to the optimal Deuterium-Tritium mixture. The difference between power lost and $\alpha$-heating is compensated by additional ICRH heating, which should be able to energize the minority species (minority heating) directly, which can transfer the power to the main plasma species by collisions. Other options to control the thermonuclear instability are discussed.   

RF Power to Plasma Increase Using EBG Surfaces in IC and LH Antennas

High impedance surfaces or electromagnetic band gap (EBG) surfaces have proved themselves to be useful in wireless communications applications due to their unique characteristics such as no propagating surface wave support, no conduction of RF current for a given bandwidth, in-phase electromagnetic reflection and non-inverted image of the electric charge in front of them [1]. These characteristics make possible to design compact antennas achieving better performance in terms of radiation and input impedance. ICRF and LH antennas in plasma experiments can take advantage of using EBG surfaces. One of the main issues in ICRF plasma heating is the high mismatch between the feeding lines and the antenna inputs. The adoption of EBG surfaces in the ICRF antenna structure and the advantages offered by a predictive designing tool as TOPICA [2] offer the possibility to improve significantly the coupled power to plasma. The adoption of EBG surfaces in the LH waveguides permits to reduce the major dimension of waveguides not affecting the propagation. It is then possible to manufacture compact LH arrays of waveguides. \\[4pt] [1] IEEE Trans. Microwave Theory Tech., vol. \textbf{47}, pp. 2059--2074, Nov. 1999. \\[0pt] [2] Nucl. Fusion, \textbf{46} (2006) S476.   

Toroidal plasma start-up, refluxing and sustainment by repetitive plasma injection

A critical problem for most toroidal plasma configurations is to demonstrate solenoid-free start-up and sustainment: one solution might be to repetitively inject helicity-bearing plasmoids. We are exploring this concept in the Pulsed Build-up Experiment (PBX) [1] and with 3D MHD simulations [2]. PBX is designed to produce three spheromaks by energizing magnetized planar coaxial electrodes, and inject each subsequent spheromak into a copper flux-conserver. Three 32uF, 8kV banks produce 100kA currents in 10us pulses to form the plasmas, and six 16uF banks are used to energize compression coils. Magnetic energy in the flux conserver is monitored by use of magnetic field coils. We report first results from the experiment and summarize theoretical and computational understanding that points to favorable start-up, refluxing and sustainment scenarios that are not deleterious to confinement. Applications to other closely related toroidal plasma configurations is discussed. [1] S. Woodruff et al J. Fusion Energy v28, p229-234 (2009) [2] A. I. D. Macnab et al J. Fusion Energy v28, p183-186 (2009).   

Absolute X-Ray Yields from Laser-Irradiated Metal-Doped Low-Density Aerogels

The X-ray yields from laser-irradiated, high-Z-doped, ultra-low-density aerogel plasmas have been measured in the energy range from sub-keV to 13 keV at the 20~kJ OMEGA laser. The targets' X-ray yields have been studied for variation in target size, aerogel density, laser pulse length and intensity. For Ti-doped targets that result in plasmas with electron densities in the range of $\sim $10{\%} of the laser's critical density, one can expect $\sim $2{\%} laser-to-X-ray conversion efficiency (CE) in the 4 - 6 keV energy band; for Zn-doped aerogels, $\sim $1{\%} CE has been measured for 9 keV X rays. For Ge-doped aerogels, one can expect $\sim $0.7{\%} laser-to-X-ray CE for X-rays above 9 keV, and $\sim $40{\%} CE for energies below 3.5 keV. These results for doped-aerogel targets are consistent with other CE measurements made recently at the GEKKO laser for metallic Ti nano-fiber materials, and are also consistent with recent measurements of CEs for Ge-lined cavities, but are below the CEs measured for Ti-lined cavities and below the CEs measured for pre-exploded Ti foils.   

X-ray conversion efficiency measurements for CsI and Sn

We measured the absolute conversion efficiency of Sn and CsI in the energy range of 3900 to 5600 eV using the Omega laser at the Laboratory for Laser Energetics. The laser intensity was varied from 2x10$^{15}$ W/cm$^{2}$ to 2x10$^{16}$ W/cm$^{2}$. The efficiency measurements were for 1 ns laser pulse widths and were determined based on previous calibration measurements for several x-ray films. To obtain the efficiencies, we measured absolute film exposures in several energy bands by employing different x-ray filters. The overall efficiency was then determined by calibrating these individual band measurements to the overall spectrum. One band was used as a high energy background measurement. Our results indicate the overall conversion efficiency was relatively insensitive to intensity in this regime and in general was of order 0.1-1{\%}. We conclude with a discussion of the usefulness of such broadband backlighters for HED experiments.   

Development of Laser-Produced High-Energy X-ray Sources for Phase Contrast Imaging

Experiments performed on the TRIDENT-200TW facility show phase contrast effects from K-alpha x-ray sources produced from 2-ps laser pulses using 17-keV Mo backlighters. These low magnification images show high-spatial resolution and enhanced contrast on these 3-mm undriven CH disks. We will compare these results to some predictions and discuss plans to measure dynamic properties of shocked material on the OMEGA-EP facility. Results from pulse duration scaling on OMEGA-EP will also be presented.   

Reflectometer Measurement for LDX

A flexible and general purpose microwave reflectometer system is being developed for density measurement in the Levitated Dipole Experiment. LDX is uniquely suited for reflectometry due to its observed high density gradients and shear-free magnetic field. Various diagnostics exist in LDX to make chordal measurements of the plasma, including an interferometer and visible light diagnostics; the reflectometer will be able to make non-perturbative local measurements in the core of the plasma. In its initial configuration, the reflectometer will be used to determine the peak plasma density. It will sweep the frequency of launched waves through the peak density O-mode cutoff frequency. Once it passes above that frequency, a sharp jump in time of flight will be observed due to waves passing through the entire radius of the plasma and reflecting off the floating coil at the center of the vessel. The reflectometer will be reconfigured to measure density fluctuations by using a fixed frequency and observing the time of flight as the location of the density-dependent cutoff layer fluctuates. First results will be presented.   

Rotational temperature measurements of the Princeton FRC using non-optical electron-impact excitation selection rules

Spectroscopic rotational temperature measurement techniques are often used in molecular gas dynamics and generally can be related to the gas translational temperature. Many authors assume a low-mass electron cannot significantly disturb the molecular rotational level distribution, enforcing a rotational selection rule $\Delta K =0$. Others believe optical selection rules apply $(\Delta K =0, \pm 1)$. In either case, these selection rules allow for the use of simple Boltzmann plots to estimate the rotational temperature. However, rotational transitions for $\Delta K >1$ are in fact allowed by molecular symmetries and dipole selection rules. It has been found through this study that these larger transitions $(\Delta K = \pm2)$ for the hydrogen Fulcher- $\alpha$ emission $(H_2 \ d ^3 \Pi_u \rightarrow a ^3 \Sigma_g^+)$ can affect the rotational distributions by up to $40\%$ for $K=5$ upper rotational states and also results in inferred rotational temperatures about $30\%$ lower than would be obtained with Boltzmann plots and optical selection rules. This broader use of non-optical selection rules is applied to measuring rotational temperatures radially across the plasma column of the Princeton Field-Reversed Configuration device at a variety of pressures.   

Development of diffractive XUV-VUV light extractors for fusion plasma diagnostic

The diagnostic and control of next generation MFE and ICF fusion experiments will require optical light extractors capable of withstanding intense plasma and radiation exposure. A solution applicable from the XUV to the infrared is to use free-standing diffractive optics such as transmission gratings or zone plates. Here we present results on XUV-VUV diffractive extractors for the diagnostic of boundary MFE plasmas. For the VUV range we developed Si transmission gratings having 1 $\mu $m period, 5 $\mu $m thickness, 40{\%} open fraction, 1x2 mm active area, and coated with Ni, while for the XUV range we use SiN gratings having 0.2 $\mu $m period, 0.3 $\mu $m thickness, 1x1 mm area, and coated with Ta. The grating extractors are spectrally and spatially calibrated in the laboratory using a newly developed extended XUV-VUV source and will be employed for imaging spectrometry on the NSTX experiment. The operational characteristics of the extended source and first space resolved XUV-VUV spectra will be presented. Work supported by DoE Grant DE-FG02-99ER54523 at JHU and Contract DE-AC02-09CH11466 at PU.   

Coherent population trapping to measure magnetic fi elds in hydrogen plasma

A laser-based diagnostic to measure weak magnetic fields in hydrogen plasmas using the quantum optics phenomenon of coherent population trapping (CPT) is described. In CPT, a bichromatic laser beam causes non-linear optical-pumping of a 3-state ($\Lambda$) atomic system whose lower states' separation is set by the externally applied magnetic field (Zeeman effect). At CPT resonance, fluorescence from the upper state decreases significantly. The frequency difference of the bichromatic laser beam can be adjusted in search of the Zeeman splitting corresponding to magnetic field strengths present. Magnetic field direction can be obtained from polarization information. Critical physics issues, studied with Bloch equations, include the effects of all possible n=3$\rightarrow$2 transitions, Doppler broadening, hyperfine structure, and Stark shift. For sub-keV H$^0$ temperatures, CPT resonance does not depend on Doppler shift, but Doppler broadening of multiple transitions of the n=3$\rightarrow$2 manifold will decrease CPT contrast.   

Plasma signatures on radially resolved line emission

In the last few years, various intriguing emission profiles have been observed in time-gated, radially resolved measurements of K-shell line emission from imploding and stagnating Z-pinch plasmas. The radially resolved lines have appeared as hollow or closed ovals whose extents in the spatial and (Doppler-shifted) wavelength dimensions record the plasma radius and velocity, respectively. Optically thick lines can lead to asymmetries in both spatial and wavelength dimensions, such as limb darkening and preferential absorption of velocity-matched wavelengths. We present the results of a comprehensive investigation of density, temperature, and velocity gradients and their effects on radially resolved emission lines, listing the combinations of plasma conditions that can give rise to signature emission features. Sandia is a multi-program 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.   

Magnetooptical Faraday and Light-Scattering Diagnostics of Laser Plasma in Leopard Laser Facility at UNR/NTF

Laser plasma of the solid target on Leopard Laser Facility at University of Nevada Reno was investigated using polarimetry, interferometry and laser-scattering diagnostics. 50 TW Nd:glass Leopard laser operates on 1056 nm wavelength, 10 J energy and 1ns/400 fs pulse width. Power flux on a target surface varied from 10$^{14}$ to 10$^{19}$W/cm$^{2}$ with 20 $\mu$m focus spot from off-axis parabola. The diagnostic of spontaneous magnetic fields in laser plasma was carried out using three-channel polarinterferometer with Faraday, shadow and interferogram channels. Ultrafast two-frame shadowgrams/interferograms with two probing beams with orthogonal polarizations were used for investigation of fast moving plasma phenomena (jets, ionization front propagation). Continuous 1W green DPSS-laser with external modulation was used for light scattering experiments for investigation of the late-time micro-particles generation in laser plasma with expected large charge number of the grain Z $\sim $ 100-1000.   

Thomson-Scattering from electron plasma waves in a magnetized laser-produced plasma

We present temporally resolved Thomson-scattering measurements of the electron temperature and density of a magnetized laser-produced plasma. Our experiment demonstrates that by applying a 25T external magnetic field parallel to a laser beam in the plasma the electron temperature increases by nearly a factor of 2. Comparison with hydrodynamic modeling indicates the formation of a plasma channel suitable for guiding ultra-short pulse laser beams at conditions for GeV laser wakefield acceleration. This experiment was performed at the Jupiter Laser Facility, Lawrence Livermore National Laboratory, using a 527 nm, 5-ns long, 420 J laser beam focused with a random phase plate to an intensity of 1x 10$^{15}$ W/cm$^{2}$. He gas from a 1.5 mm gas jet is ionized to produce a plasma with an initial electron density of 3x10$^{18}$ cm$^{-3}$. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was partially funded by the Laboratory Directed Research and Development Program under project tracking code 06-ERD-056.   

Imaging X-ray Thomson Scattering Development at Trident

X-ray Thomson scattering is a powerful technique to accurately measure conditions such as density, temperature, and ionization state in near-solid density plasmas. Such measurements are required to assess equation of state variables, for example, in the warm dense matter regime. Experiments using x-ray Thomson scattering reported by other research groups utilized high-collection-efficiency x-ray spectrometers with high spectral resolution, but very poor spatial resolution. Thus, those experiments required fairly uniform conditions within the volume of dense plasma being probed. In this present research, we report the development of a high-collection-efficiency toroidally curved imaging spectrometer, with high spectral and spatial resolution (2 eV, 20 $\mu$m) for x-ray photon energies in the 4 to 5 keV region. In principle, it can be used as part of an imaging x-ray Thomson scattering experiment whereby spatial gradients in dense plasma conditions can be measured. The spectrometer was fielded on Trident to demonstrate its resolution characteristics, and to demonstrate a proof-of-principle use of imaging x-ray Thomson scattering by nonuniformly heating a solid-density target. We report preliminary results from these experiments, and future prospects for this diagnostic capability.   

Localized Density Measurement by Scattered X-Ray Imaging

Transmission x-ray radiography has been used successfully as a diagnostic for high energy density experiments for many years. This method is limited, though, as radiographs provide only integrated density measurements along the x-ray path and require a collinear source-detector configuration. These constraints do not exist for the imaging of x-rays, which may provide localized, point-wise interrogation of density structure inside an experimental package and allows much greater flexibility in source-detector experimental geometry. Here we describe the method of scattered x-ray imaging by defining the forward problem, applying it to model systems, and exploring methods of solving the related inverse problem. Also presented are initial experimental results from scattered x-ray imaging experiments on the Omega Laser at the Lab for Laser Energetics.   

Core spatial structure and areal-density modulation in OMEGA direct-drive implosions cores

We discuss the observation of spectrally resolved image data from argon-doped, deuterium-filled OMEGA direct-drive implosions. A titanium-doped tracer layer is also embedded in the plastic shell. The image data were recorded simultaneously along three quasi-orthogonal lines of sight (LOS) using three identical, gated Direct-Drive Multi-Monochromatic x-ray Imagers (DDMMI). For each LOS, a set of space-resolved argon emission and titanium absorption line spectra can be extracted from the spectrally resolved core image data recorded with the DDMMI instruments. The argon x-ray emission emitted at the collapse of the implosion provides a spectroscopic signature for the spatial structure of the imploded core, while the titanium line absorption of continuum radiation has information about the areal-density modulations in the compressed shell. We discuss the connection between the areal-density modulations observed along the three LOS and the spatial-structure of the core.   

X-Ray Spectroscopy of Shock-Ignition Implosions

We discuss the observation and spectroscopic analysis of argon K-shell x-ray line spectra from argon-doped deuterium-filled OMEGA direct-drive shock-ignition implosions based on data recorded with streaked crystal spectrometers. The argon line spectrum is primarily emitted at the collapse of the implosion thus providing a spectroscopic signature of the state of the imploded core. The observed spectra includes parent and satellite line transitions in H-, He- and Li-like Ar ions thus covering a broad photon energy range from 3200 eV to 4200 eV with a spectral resolution power of approximately 500. Both optically thick and thin lines are simultaneously modeled, including line overlapping and Stark-broadening effects. The spectroscopic analysis results show core temperature and density time-histories associated with the collapse implosions. A comparison is also made with LILAC hydrodynamic simulations.   

Absolute Calibration of X-ray Filters Employed By Laser-Produced Plasma Diagnostics

The electron beam ion trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of X-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete mono-energetic lines at appropriately chosen X-ray energies. X rays are detected using the high-resolution EBIT calorimeter spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the X-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification of filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. An overview of these activities will be discussed. Prepared by LLNL under Contract DE-AC52-07NA27344.   

Kirkpatrick-Baez Microscope for Hot-electron Transport Imaging in Fast Ignition Experiments

H. TIEDJE, A. ALI, N. VAFAEI-NAJAFABADI, Univ Alberta, T. MA, L. JARROT, D. MARISCAL, C.W. MURPHY, B. WESTOVER, B.S. PARADKAR, T. YABUUCHI, UCSD - K-alpha emission from tracer layers is a powerful diagnostic for quantitatively measuring the generation and transport of MeV electrons in studies of Fast Ignition Fusion. We are developing a Kirkpatrick-Baez microscope for such experiments at the Titan Laser Facility using grazing incidence platinum coated mirrors together with metal filters to detect copper K-alpha emission from tracer layers in planar and cone-wire targets. The instrument performance has been modeled using ray tracing and characterized by a cw x-ray source. Broadband multilayer grazing incidence mirrors are also being designed for both copper K-alpha and silver K-alpha imaging. The characteristics of the KB microscope and initial experimental results on electron transport will be presented.   

The NIF wedge-range-filter proton spectrometer

A new wedge-range-filter (WRF) proton spectrometer has been designed for implementation at the National Ignition Facility. Based on the existing WRF spectrometers currently in use at the OMEGA laser facility, this model will be modified to optimize performance in the NIF environment. The WRFs will measure proton spectra from 4 to 25 MeV, and a primary application will be diagnosis of ablator $\rho $R and $\rho $R asymmetry in DT implosions (through measurements of knock-on ablator protons). Calibration of these WRFs will be performed using 15-MeV D$^{3}$He protons produced in the MIT Nuclear Products Generator. The WRFs will be ready for installation at the NIF for the Ignition Campaign. This work was supported in part by US DoE, LLNL, and LLE.   

Reconstruction of proton paths in CR-39 for radiography experiments

Recent mono-energetic proton backlighter experiments on the dynamics of laser-plasma interaction and inertial fusion implosions have revealed high-intensity magnetic and electric fields in high-energy-density regime plasmas. Current radiographic methods measure particle fluence and energy at the detector surface. By reconstructing incident proton trajectory on the detector, radiography techniques may strongly constrain the strength and location of fields in ICF capsule implosions, hohlraum implosions, and other complex high-energy-density plasmas of interest. A new diagnostic method developed on the MIT Nuclear Products Generator, utilizing CR-39 as a multiple-stage particle detector, is presented and the applications of this method to experiments at LLE and NIF are discussed. This work was supported in part by US DoE, LLNL, and LLE.   

Using proton radiography to measure Rayleigh-Taylor-induced magnetic fields

The Rayleigh-Taylor (RT) hydrodynamic instability has been a concern for shell integrity during the acceleration phase of Inertial Confinement Fusion (ICF) implosions. RT-induced magnetic fields on the order of a mega-Gauss have been theoretically predicted and simulated, but never measured. If present, these self-generated fields will reduce heat flux and affect implosion dynamics. An experimental method for measuring these elusive fields using a combination of mono-energetic proton radiography, X-ray radiography, and Monte-Carlo simulations is described, and experimental measurements of RT-induced magnetic fields are presented. This work was performed at the LLE NLUF, and was supported in part by the FSC at U. of R., US DoE, LLNL, and LLE.   

Diagnostics for heavy ion beam driven Warm dense matter experiments

A set of diagnostic has been developed for the WDM experiments at Berkeley. The diagnostics are aimed at the in-situ measurement of temperature, expansion velocity and pressure of a WDM sample.A specially developed two-channel pyrometer probes color temperatures at 750 nm,1000 nm and 1400 nm, with 75 ps temporal resolution. The system has a broad dynamic range with a lower limit $\sim $2000 K and upper limit $\sim $100000 K. The pyrometer design is based on custom spectrally selective beam splitters and can be upgraded up to seven channels. Continuous target emission from 450 nm to 850 nm is recorder by a custom spectrometer, consisting of a high dynamic range Hamamatsu streak camera and a holographic grating. The system is calibrated absolutely with a tungsten ribbon lamp (NIST traceable). The various sweeping times of the streak unit allows for temporal resolution varying from 1 ps to 1 us. The spectrometer has a lower sensitivity than the pyrometer and applied in experiments with higher temperatures. Hydrodynamic expansion velocity of a target's free surface is measured by a commercially available all- fiber Doppler shift laser interferometer (VISAR). The installed delay etalon allows for velocity detection with 2 m/s precision and 0.5 ns resolution.   

Thomson Parabola Ion Energy Analyzer

A new, versatile Thomson parabola ion energy (TPIE) analyzer has been designed and constructed for use at the OMEGA-EP facility. Multi-MeV ions from EP targets are transmitted through a W pinhole into a (5- or 8-kG) magnetic field and subsequently through a parallel electric field of up to 24 kV/cm. The ion drift region may have a user-selected length of 10, 50, or 80 cm. With the highest fields, 500-MeV C$^{6+}$ and C$^{5+}$ may be resolved. TPIE is TIM-mounted at OMEGA-EP and can be used opposite either of the EP ps beams. The instrument runs on pressure-interlocked 15-VDC power available in EP TIM carts. It may be inserted to within several inches of the target to attain sufficient flux for a measurement. For additional flux control, the user may select a square-aperture W pinhole of 100 $\mu $m or 250 $\mu $m. The detector consists of CR-39 backed by an image plate. The fully relativistic design code and design features will be discussed. Ion spectral results from first use at OMEGA-EP are expected.   

Measurements of down-scattered and TT neutrons at OMEGA using the Magnetic Recoil Spectrometer

A Magnetic Recoil Spectrometer (MRS) was built and is currently being used on the OMEGA laser for absolute measurements of down-scattered and primary neutrons. The areal densities of CH and cryogenic DT implosions have been inferred from the down-scattered neutron spectrum. TT neutrons have also been observed in the down-scattered continuum. To correctly interpret these measurements, the MRS response function was characterized using the Monte Carlo code GEANT4 and diagnostic activation experiments. Measurements of the absolute neutron spectrum at OMEGA, inferred using the MRS response function, will be presented. This work was supported in part by the U.S. DoE, LLE, and LLNL.   

Processing of the HXR and neutron signals registered with the time resolved scintillation detectors

The DD fusion reaction was studied experimentally on the PF-1000 plasma focus (IPPLM, Warsaw, 1-2 MA current and 1011 neutrons per shot). The neutron measurements were carried out with the set of detectors in the downstream, upstream and radial directions, which make possible to estimate the time dependence of neutron energy distribution. The signals from the detectors consist of a few of the hard X-ray and neutron pulses. The signals are distorted by the dimensions and characteristics of the detectors and photomultipliers. Hard X-rays are influenced by the transit time of the electrons before collisions with the walls of the chamber. Neutron signals are influenced by the moderated and scattered neutrons. In order to remove these distortions from the signals, the supposition of the linear dependence of delayed particles on the time and intensity is used. The processing includes the filtration of the signals and further the adjustment of the neutron signals with the supposition of the 10\%, 30\% and 50\% delayed particles.   

Determination of average kinetic energy of reacting deuterons on the basis of neutron time-of-flight diagnostics

The kinetic energy of reacting deuterons is one of the important parameter of the fusion plasma where deuterium is presented in a load. The energy of deuterons is determined from the reconstructed neutron energy spectra which are obtained by extended time-of-flight (TOF) method where time-resolved neutron detectors are placed at several distances on two opposite directions from the neutron source. Provided that the deuteron energy is much smaller than the fusion Q-value, it is possible to show that the neutron energy is only a function of the component of the deuteron kinetic energy (and vice versa) in the direction of neutron detection. Consequently, the side- on and end-on energy components of deuterons can be found on the basis of TOF measurement of neutrons in the radial and axial directions. Finally, the average kinetic energy of reacting deuterons can be evaluated on an assumption of radial symmetry of neutron production from Z-pinch plasma.   

Nuclear diagnostics utilizing robust CR-39 for OMEGA, OMEGA-EP, and the NIF

Harsh EMP/x-ray/gamma-ray environments such as those found at OMEGA and OMEGA-EP (and soon the NIF) hinder electronic detection schemes for sensitive measurements of charged particles and neutrons. This has made passive particle detectors such as CR-39 attractive, especially since they measure the position, energy, and species of individual charged particles. To enhance the accuracy of CR-39-based measurements, and to lay the groundwork for new applications, new measurements of CR-39 response to accelerator-generated protons (from 0.35 MeV to 11.7 MeV) and 2.5-MeV neutrons have been made using a variety of CR-39 types and CR-39 processing techniques. Results include determination of energy-measurement accuracy and the sensitivity of energy measurements to CR-39 thickness, vacuum exposure, heat exposure, and various processing parameters. Application to a new and sensitive neutron detector for OMEGA, OMEGA-EP, and the NIF will be presented. This work was supported in part by US DoE, LLNL, and LLE.   

Interaction of ultra-intense ultra-short laser light with a magnetized target

An ultra-intense short-pulse laser is an important tool capable of isochorically heating a thin solid target to beyond 100eV in a picosecond before hydrodynamic effects force it to expand. The temperature we could achieve depends on the dynamics of hot electron transport inside the target. We have simulated in 2D the hot electron transport in solid density plasmas using a collisional particle-in-cell code, PICLS. Because of rapid lateral motion of hot electrons the target heating is less efficient especially in low Z targets, such as a CH target. We have proposed uniformly magnetized isochoric heating by using a 1MA Z-pinch machine as a MG field generator and have studied the hot electron diffusion across the imposed magnetic field. We found that the external magnetic field was partially expelled from the heated region due to the circular motion of the hot electrons, and was compressed at the edge of the region. That is why the presence of an external MG field is able to slow down the hot electrons' lateral diffusion, and improve the bulk heating efficiency significantly. We will also show the effects of scaling the external magnetic field on the confinement of hot electrons.   

Algorithm Development for Simulation of the Interaction of Intense Laser Light with a Multiscale Plasma

The kinetic simulation of the interaction of intense laser light with plasma in a multiscale limit presents severe challenges. Conventional, explicit-integration, particle-in-cell (PIC) methods require resolving the light waves and electron plasma waves with appropriately small time steps and mesh sizes in order that the simulation be both numerically stable and accurate. In the simulation of laser light interacting with a fast-ignition target plasma, the domain spans a range of electron densities going from vacuum to thousands of times the critical density. For the electron temperatures in the target plasmas, the underdense plasma is collisionless and the overdense plasma becomes highly collisional. We have introduced a new two-region algorithm that is well suited to the simulation of fast ignition, employing explicit PIC with complete Maxwell's equations at low densities through densities above critical and a reduced set based on Ohm's law for higher densities. Collisions in the high-density region set limits on time steps, and we examine subcycling the collisions to improve efficiency. Analysis and demonstrations of the algorithm are presented.   

ePLAS code improvements for short pulse laser-matter interaction studies

We detail new features for ePLAS, a 2D implicit/hybrid simulation model in use for Fast Ignition. The hybrid/PIC code tracks laser light with ponderomotive force, depositing at critical into relativistic hot particle electrons, while pulling cold collisional, return-current Van Leer fluid electrons through fluid ions by means of self-consistent Implicit Moment\footnote{R. J. Mason, J. Comp. Phys. \textbf{71,} 429 (1987).} $\quad E-$ and $B-$fields. The new features include: a 1D formulation for light absorption studies with generalized \textit{E- and B-} fields, multiple laser beams, real EOS data from analytic models or the Sesame tables, K{\_}$\alpha $ imaging, generalized cold electron elevation to hots, particle ions for fast ion fusion, improved graphical options, and new Linux and Mac OS X implementations. The focus of the talk is code enhancements.   

ePLAS examination of short-pulse laser- wire and foil interactions

An enhanced 2D implicit hybrid simulation code ePLAS has been used to examine short-pulse laser interactions with cone-wire and foil targets. The code deposits picosecond pulses of 1 $\mu $m, $\sim $3x10$^{20}$ W/cm$^{2}$ laser light near critical, and tracks resultant megavolt ``hot'' particle-in-cell (PIC) electrons through an ionized copper or carbon background plasma. The background is modeled as collisional Van Leer ``cold electron'' and ion fluids. The code now elevates the returning fluid colds to hot particles, when their energy exceeds a specified threshold (e.g. 20 keV). It also uses real equations of state from analytic models or the Sesame Tables. Cylindrical and Cartesian results are compared. The emphasis will be on recent cone/nail-wire experiments\footnote{T. Ma et al., ``Transport of energy by ultra-intense laser-generated electrons in nail-wire targets,'' submitted to Physics of Plasmas} with target heads of varying mass, and revisited foil studies.\footnote{R. J. Mason, et al. Phys. Rev. E \textbf{72}, 01540 (R) (2005).}   

Ultrashort laser pulse absorption in dense targets

A theory of ultrashort laser pulse absorption in dense targets is important for modeling of basic physics and applications of short laser pulse plasma interactions. Recent absorption measurements and large number of indirect observations point to complex scenarios of short laser pulse absorption where the laser prepulse, ionization physics, density profile modifications, collisional processes and collisionless mechanisms occur all within short pulse duration and contribute to the absorbed fraction of the incident laser energy. A model of ultrashort laser pulse absorption, which includes linear absorption and thermal transport into dense plasma will be described. Plasma dielectric function in our model describes collisional and collisionless absorption mechanisms including the effect of electron-electron collisions. Thermal transport is modeled using nonlocal expressions that are valid in the weakly collisional regime. The inhibited and nonlocal thermal transport can contribute to the increase of the electron temperature in the skin layer. Theoretical predictions will be compared with the results of Vlasov-Fokker-Planck simulations for moderate laser intensities. Also numerical simulations will illustrate transition into relativistic regime of laser intensities.   

Laser acceleration of monoenergetic protons via a double layer emerging from an ultra-thin foil

Theoretical and numerical studies are presented of the acceleration of monoenergetic protons in a double layer formed by the laser irradiation of an ultra-thin film. The ponderomotive force of the laser light pushes the electrons forward, and the induced space charge electric field pulls the ions and makes the thin foil accelerate as a whole. A stable double layer is formed, in which the ions are trapped by the combined electric field and inertial force in the accelerated frame, together with the electrons that are trapped in the well of the ponderomotive and ion electric field. The trapped ions reach monoenergetic energies up to 100 MeV and beyond, making them suitable for cancer treatment. We present an analytic theory for the laser-accelerated ion energy as a function of the laser intensity, foil thickness and the plasma number density. The underlying physics of the trapped and untrapped ions and of the stabilization of the Rayleigh-Taylor instability are discussed.   

Abundant generation of quasimonoenergetic ions by Coulomb explosions of optimized nanostructure

In Coulomb explosions of spherical clusters composed of two ion species (light and heavy), the initial density profile of light ions is optimized to have iso-Coulomb potentials. This results in the generation of many quasimonoenergetic ions with the highest possible energy coupling. The overall coupling efficiency (equal to the summed kinetic energy of the light ions in the highest 1-percent energy band divided by total kinetic energy of both ions) is estimated to be as high as 30-40 percent in a one-dimensional simulation. The monoenergeticity and efficiency can be further improved by using even more ion species or by exploiting different ionization levels of the heavy ions. The present scheme has high potential to provide a reasonably efficient method for generating quasimonoenergetic ions for practical applications.   

Ionization dynamics of high-intensity laser-target interactions

The ionization dynamics of thin foils irradiated by an ultrashort pulse laser is investigated with a fully relativistic 2D particle-in-cell model. The PIC model is integrated with a ionization dynamics model, which includes optical field and collisional ionizations. The spatio-temporal evolution of the ion charge and electron density of a 5 micron aluminum foil are studied for peak laser intensities 10$^{18}$-10$^{20}$ W/cm$^{2}$ and laser pulse duration of 80 fs. The optical field ionization dominates in the pre-plasma region, creating a dense plasma of highly charged ions, while the collisional ionization is most effective in the bulk of the target. A series of ionization waves launched at the front surface of the foil propagate with high velocity ($\sim $0.2$c)$ through the target.   

Comparison of radiaton cooling models for particle-in-cell simulations

Under extreme acceleration, charged particles can radiate strongly and the corresponding radiation damping/cooling can become important in the plasma energetics and dynamics. This occurs when radiated energy in the interaction time is comparable to \textit{mc}$^{2}$. In particular, under the presence of ultra high intensity lasers or other intense electro/magnetic fields the motion of particles in the ultrarelativistic regime can be severely limited by radiation damping. The standard Particle-in-Cell (PIC) algorithms do not include radiation damping/cooling effects. Even though this is a well known mechanism, there is not yet a definite algorithm nor a standard technique to include radiation cooling in PIC codes. We have compared several models for the calculation of radiation damping force, with the goal of developing an algorithm for radiation damping in Osiris [1]. The results of the different models are compared with analytical models and standard results, and the relevance/advantages of each model are discussed.   

Non-Equilibrium Plasma Dynamics Modeling of Xenon Clusters Irradiated by an Intense Laser Pulse

Population inversions have been experimentally observed when small xenon clusters of 5-20 atoms are irradiated by $\sim $230 fs high intensity laser of 10$^{19}$ W/cm$^{2}$ and wavelength of 248 nm [1]. Consequently, a plasma channel $\sim$1.5-2 cm in length and $\sim$1.5--2 $\mu$m in diameter is formed which produces amplified x-ray emissions with gains $\sim$20-60 for wavelengths in the range 2.71-3 {\AA}. It has been conjectured [2], that population inversions in laser generated xenon plasmas may be efficiently created within M-shell ionization stages by photo- or collisional-ionization of 2s and 2p inner shell electrons. In this study we focus our attention on the influence of non-Maxwellian electron energy distributions on the collisional dynamics by which hollow atoms are generated in different ionization stages of xenon. These distributions are calculated from a relativistic molecular dynamics model. \\[4pt] [1] A. B. Borisov, \textit{et al.}, J. Phys. B \textbf{40}, F307 (2007). \\[0pt] [2] W. A. Schroeder, \textit{et al}., J. Phys. B \textbf{34}, 297 (2001).   

Cluster mass fraction and size distribution determined by fs-time-resolved measurements

Characterization of supersonic gas jets is important for accurate interpretation and control of laser-cluster experiments. While average size and total atomic density can be found by standard Rayleigh scatter and interferometry, cluster mass fraction and size distribution are usually difficult to measure. Here we determine the cluster fraction and the size distribution with fs-time-resolved refractive index and absorption measurements in cluster gas jets after ionization and heating by an intense pump pulse. The fs-time-resolved refractive index measured with frequency domain interferometer (FDI) shows different contributions from monomer plasma and cluster plasma in the time domain, enabling us to determine the cluster fraction. The fs-time-resolved absorption measured by a delayed probe shows the contribution from clusters of various sizes, allowing us to find the size distribution.   

Size distribution of microclusters in laser-irradiated plasmas

Laser interactions with a mixture of a gaseous plasma and microclusters depend strongly on the cluster-size distribution, which is usually difficult to measure directly. We present a new approach for recovering the cluster-size distribution from time-resolved measurements of the absorbed energy in a pump-probe experiment. The pump pulse ionizes microclusters to a peak density that exceeds the critical plasma density for the probe pulse. The existence of plasma resonances enhances the energy absorption for individual clusters. As a cluster expands, its peak density decreases and the resonance eventually disappears. The expansion time is shorter for smaller clusters than for larger ones, which makes the absorbed energy dependent on the cluster-size distribution. We can then find the cluster-size distribution by matching a convolution of the distribution with a single cluster absorption curve to the measured absorption. We demonstrate feasibility of this technique by analyzing the data from recent pump-probe experiments at the University of Texas.   

High temperature deuterium plasmas produced by laser irradiation of clusters in a confining magnetic field

Experiments have shown that interactions of intense ultrafast lasers with targets of small atomic clusters with thousands of atoms can create plasmas with high density and high average ion energies ($>>$ 1keV). DD fusion neutrons can be produced with laser pulses of a few joules to kilojoules. The fusion yield is limited by the fast expansion time ($<$100 ps)of the plasma. The expansion could be affected by a large magnetic field ($>$ 100 T) to limit transport in the radial direction that would lead to an increase of fusion neutron yield. We present preliminary design of the magnetic field generator for fields as large as 200 T. This includes a 100 kV capacitor bank that can deliver 2.2 MA through coaxial cables that feed into a conical transmission line. This line is connected to two destructible concentric millimeter coils in a mirror configuration to generate the high magnetic field for a microsecond. We will use a cryogenically cooled gas jet to produce 10 nm deuterium clusters as the laser target. The jet will be irradiated by a femtosecond laser beam propagating on the axis of a 100 T magnetic field.   

Effect of micro-structure growth on x-ray production

High intensity short pulse laser interactions with solid targets have been shown to produce an x-ray burst. The effect of micro-structures on laser coupling efficiency to x-rays was investigated. Metallic targets with and without micro-structure growth were shot at the Scarlet Laser Facility with an intensity near than 3 x 10$^{19}$ W/cm$^{2}$ and energy near 1J. Results will be presented on the enhancement of x-rays.   

An interaction between strong laser field and carbon nantubes

An interaction between strong laser field and carbon nanotubes has been investigated using a particle-in-cell code, which includes a collisional and ionization effect. Carbon nanotubes are considered as a nano-scale solid cylinder. According to a series of our works about laser-cluster interaction using the PIC code[1--2], electrons in a nano-cylinder absorb large amount of laser energy through a resonant absorption. Such a strong excitation of electron oscillation can cause a nonlinear excitation of a low frequency radiation such as terahertz waves. We will present about the simulation results of the interaction between carbon nanotubes and a strong laser field. We will also show a possibility of a coherent radiation from a periodically arrayed carbon nanotubes.\\[4pt] [1] T. Taguchi, et al., Phys. Rev. Lett., 92, 20, 2004, 205003.\\[0pt] [2] T. M. Antonsen, Jr., et al., Phys. Plasmas 12, 5, (2005), 056703.   

Calculations of fast electron transport through different materials at solid density using a robust hybrid code

Development of a robust hybrid code is useful for efficient calculation of fast electron transport, in conjunction with a radiation hydrodynamics code. The code THOR has been developed for coupling to a fluid code in this fashion for modelling this fast electron population generated during short-pulse laser experiments. It is built on the hybrid philosophy of work by J.R. Davies, which provides an intuitive and relatively straightforward computational framework, and makes it easier to take advantage of parallelism for reducing noise in the solution. The basic algorithms of the code are described along with the approximations and limitations of the current implementation. Recent experiments by D. Hoarty at AWE have demonstrated a method of heating solid density Aluminium layers to hundreds of eV, buried at various depths in a plastic target. Application of the THOR code in reproducing these measurements is shown with encouraging results. The quality of the match to the data is discussed with layers placed at various depths as in the experiments, and with different laser sources. The problems of comparing the code outputs with the measurement technique used in the experiment are also described.   

Relativistic Electrons from Slab Targets Interacting Strongly with Intense Light in Vacuum from High-Contrast Laser Pulses

When light of electron-relativistic intensity in several-cycle laser pulses are obliquely incident on slab targets with extremely low pre-pulse energy, copious amounts of high laser harmonic light emerge [1] (See also ongoing work at the ALLS 200 TW Ti-Saph laser at INRS EMT. (Pulses are 24 fs at 10 Hz with 10$^{-10}$ contrast, even without plasma mirrors).) 2-D PIC (OSIRIS code at INRS) simulations [2] (and earlier work by Naumova et al. [3] have shown that intense beams of electrons are not only injected into the target [2] but that significant relativistic electrons are also emitted more or less along with the emitted light. These frontally-emitted relativistic electrons emerge from the narrow regions of intense current responsible for the harmonics [2] and interact strongly with the incident and emitted light. [1] B. Dromey et al Nature Phys. Lett., 2, 456-459 (2006). [2] T. Johnston et al. Poster YP8 48, Bull. Amer. Phys. Soc 52, 16 November (2007). [3] N. Naumova, et al., Phys. Rev. Lett. 93, 195003 (2004). Note: This is work meant to be reported in 2008, but was not for medical reasons. This is likely to be the last Bulletin Abstract submitted by the lead author.   

Magnetic Field Measurement in Laser-Plasma Interaction via Relativistic Electron Deflectometry

In laser matter interactions, whether it is with a short pulse laser or a long pulse laser, magnetic fields are produced which can affect the energy transport in the target. So characterization of these fields is important. Recently, protons are used for magnetic field measurements. We report a theoretical study to assess use of relativistic electrons for the detection of magnetic field. Electrons are produced in short pulse laser matter interactions. In this modeling rad-hydro code h2d was used to produce magnetic field by a long laser pulse ($\sim $10$^{14}$W/cm$^{2})$ due to the thermoelectric effect. The probe electron beam was produced using a hybrid particle-in-cell code LSP. Results show that the field and their shape can be characterized by the deflection of the electron beam. Results will be discussed at the meeting. Work supported by Research Fellowship of the JSPS, and by the Dept. of Energy under contract DE-FG-02-05ER54834.   

Suppression of parasitic noise by strong Langmuir wave damping in quasitransient regimes of backward Raman amplification of intense laser pulses in plasmas.

Currently built powerful soft x-ray sources may be able to access intensities needed for backward Raman amplification (BRA) of x-ray pulses in plasmas. However, high plasma densities, needed to provide enough coupling between the pump and seed x-ray pulsed, cause strong damping of the Langmuir wave that mediates energy transfer from the pump to the seed pulse. Such damping could reduce the coupling, thus making efficient BRA impossible. This work shows that efficient BRA can survive despite the Langmuir wave damping significantly exceeding the linear BRA growth rate. Moreover, the strong Langmuir wave damping can suppress deleterious instabilities of BRA seeded by the thermal noise. This shows that it may be feasible to observe x-ray BRA for the first time soon.   

A Simple Model for the Performance of the First Empty Hohlraum Experiments on NIF

We present a simple energy balance model for predicting the performance of the first hohlraums to be irradiated on the National Ignition Facility (NIF) as the input energy and power is varied. Key ingredients include the scaling of x-ray conversion efficiency with irradiance (as well as with pulse length), as well as some assumptions about the absorption fraction. Wall loss formulae follow the results of Hammer {\&} Rosen (PoP 10, 1829 (2003)). Other fine points are also considered. Specifically they involve the difference between the Au wall material temperature and a ``virtual'' drive temperature; the latter differs from the former due to Milne conditions. Also analyzed is the predicted ``observed via Dante'' temperature which differs yet again from the two former quantities due to albedo / Marshak limb brightening angle-of-view effects.   

Simulation of Asymmetrically Driven Hohlraum Experiments on OMEGA

A campaign of experiments is being undertaken on the OMEGA laser to asymmetrically drive an imploding capsule within a hohlraum. This acts as a stringent test of the modeling of both the conditions inside the hohlraum and the evolution of complex hydrodynamic systems. These experiments are being modeled using two methodologies. Simulating the laser deposition and early- time evolution in a Lagrangian code, before linking to an Eulerian code for the late-time evolution, is a well established route. Simulation of the entire evolution using an ALE (Arbitrary Lagrangian Eulerian) code is also being attempted. A number of techniques have been identified which potentially offer significant control of both the spatial and temporal asymmetry of the drive on the capsule. These are being tested systematically in two ways. Uniform density aerogel spheres are used to resolve the temporal variation in drive and thin glass shells with a GDP ablator are used to resolve the spatial variation in drive. In both cases the evolution of the configuration is being determined using titanium area backlighting at 4.7 keV combined with a gated x-ray imaging system.   

Multi-Variable Sensitivity Studies of the Beryllium NIF Ignition Target

We report the results of our continuing effort to optimize and control sensitivities for the Beryllium (Be) NIF ignition capsule. We will compare the two candidate scales for the latest (Revision 4) Be capsule: maximum hohlraum radiation temperature of 285 eV (capsule radius 1.18 mm) and 270 eV (1.3 mm). The performance of these capsules is assessed by performing a sensitivity analysis which integrates 35 1D capsule design parameters with 2D surface roughness specifications for each of the seven distinct capsule layer interfaces as well as laser drive asymmetry specifications. We will highlight efforts to understand and control the sensitivities deriving from inhomogeneities within the sputtered Be ablator material including the diffusion of Copper across the internal graded doped layers as well a clumping of impurities such as Argon associated with the Be crystal microstructure.   

Sensitivity of Thermonuclear Burn to Charged Particle Stopping Power Models in NIF-like Targets

Accurate treatment of fusion product charged particle transport (in particular the 3.5 MeV alpha particles) is very important for the accurate simulation of ICF ignition, bootstrap heating and burn. Models have been proposed by many authors to account for collisional scattering, dielectric scattering, degeneracy effect, and combined collisional-dielectric behavior. We present 1D calculations comparing the behavior of NIF ignition-like targets for a series of different stopping power models. As each of these models has complicated validity constraints, we keep track of validity violations in terms of the amount of energy deposited while using a theoretically invalid stopping power. For our calculations we use the radiation-hydrodynamics code BUCKY and have developed a stopping power library: Deeks. Deeks implements the stopping power models of Landau; Spitzer; Li and Petrasso; Brown, Preston and Singleton; Kihara and Aono; May and Cramer; Brysk; Skupsky; and a degenerate extension of Li and Petrasso's model in the library Deeks. Additionally, Deeks can mix electron and ion components of different models while retaining validity checks for the hybrid model.   

Automated parameter space searches for calibrating mix models in NIF ignition implosions

Turbulent transport (``mix'') models typically have many adjustable coefficents, which must be calibrated against experimental or numerical simulation data. We calibrate mix models against high-resolution 2D simulations of NIF ignition capsules [Hammel \textit{et al.}, \textit{J. Phys.: Conf. Ser.} \textbf{112}, 022007 (2008)]. The time-varying radial profiles of species composition in the imploding capsule serve as the calibration reference. We perform one-dimensional implosion simulations using two mix models: one from Zhou, Zimmerman, and Burke [\textit{Phys. Rev. E}\textbf{ 65, }056303 (2002)] and a $k-\varepsilon $ model by one of us (OS). We can calibrate so that one-dimensional composition profiles roughly match the simulation profiles for a Rev3 CH(Ge) ignition capsule at several times, although non-monotonic features of the profiles cannot be represented by the mix models. For fitting, we use automated scripts and fitting metrics, which allow parameter spaces of up to five dimensions to be searched rapidly. Besides identifying optimal coefficient sets, such searches reveal the sensitivity of model results to variations in inputs.   

Shock interaction with an isotropic field of sound waves

Interaction of shock waves with vortical, entropic and acoustic preshock fluid perturbations must be well understood to study and model shock interaction with more general turbulent flows, which is important for ICF and many other areas. We focus here on the interaction of a shock front with a random isotropic field of acoustic waves. The dynamics of the shock interaction with a single-mode pre-shock acoustic perturbation field is analyzed in detail and mode averaging is performed to study the turbulence generated downstream. Analytical results are shown for the postshock turbulent kinetic energy, vorticity, acoustic energy flux, internal energy, and noise level as a function of the fluid compressibility and shock strength. Good agreement with previous theoretical results is demonstrated. Comparison to the shock interaction with vortical [J. G. Wouchuk \textit{et al}., Phys. Rev. E 79, 066315 (2009)] and entropic perturbations is also presented.   

Influence of binary particle collisions on trapped particle nonlinearities and the onset of stimulated Raman backscatter in the kinetic regime

The onset of stimulated Raman backscatter (SRBS) in a single laser speckle is examined in the kinetic regime using 1D and 2D VPIC [K. J. Bowers et \textit{al}., Phys. Plasmas \textbf{15}, 055702] simulations. A binary particle collision model [T. Takizuka and H. Abe, J. Comput. Phys. \textbf{25}, 205] is used to isolate and independently study the effects of like-particle (e-e) and pair-particle (e-i) collisions on trapped particle nonlinearities (e.g., frequency shift) in relation to SRBS onset, under conditions relevant to short-pulse ($\sim$3 ps at FWHM), single-speckle experiments at Trident [J. L. Kline et \textit{al}., J. Phys.: Conf. Series \textbf{112}, 022042]. Regimes of weak and strong collisionality are identified and collisional results are compared with those obtained in the collisionless limit [L. Yin et \textit{al}., J. Phys.: Conf. Ser. \textbf{112}, 022033].   

Initiation and Saturation of Backward Stimulated Raman and Brillouin Scatter in Single Speckles: Influence of Scattered-Light Seeds and Collisional Heating

A suite of 2D and 3D PIC simulations of backward stimulated Raman and Brillouin scattering (SRS and SBS) in ICF hohlraum and Trident plasma have been performed on the heterogeneous multi-core supercomputer, Roadrunner. These calculations reveal that the physics governing the nonlinear saturation of SRS in 3D is consistent with that of prior 2D studies [L. Yin, et al. Phys. Rev. Lett., 99, 265004, 2007], but with important differences arising from enhanced diffraction and side loss in 3D compared with 2D. In addition to wavefront bowing of electron plasma waves (EPW), we find that EPW self-focusing also exhibits loss of angular coherence by formation of a filament necklace, a process not available in 2D. These processes in higher dimensions increase the side-loss rate of trapped electrons, increase wave damping, decrease source coherence for backscattered light, and fundamentally limit how much backscatter can occur from a laser speckle. The SRS onset threshold is lower if initiated by SRS seeds compared with the onset threshold if SRS is initiated by thermal electron density fluctuations alone. Furthermore, we show that the presence or absence of SBS may be sensitively determined by collisional heating and transverse electron temperature variations.   

Role of kinetic nonlinearities in Raman scatter in NIF ignition targets

Raman scattered light generated over the capsule in an ignition target propagates back towards the laser entrance hole (LEH). Along this path, several millimeters in length, the light may undergo a further Raman decay; the resulting rescattered light will not likely be observable outside the hohlraum. In the LEH region, where many incoming beams overlap, the Raman scattered light may also undergo further amplification, driven by the intensity of the overlapped beams. We analyze kinetic simulations along the lengthy beam path, between LEH and capsule, for the role of nonlinearities, including ``inflation'' and hot electron production.   

Considerations of stimulated sideward scattering in NIF ignition-scale hohlraums

It's prudent to consider the possibility of stimulated Raman and Brillouin sideward scattering in NIF ignition-scale hohlraums. NIF beam spots are quite large (with diameter $>$1mm), and the gradient threshold intensities for these instabilities are rather low. Some simple calculations are given for the convective gain of sideward scattering assuming heavily-damped electrostatic waves. A possible enhancement of sideward scattering in the azimuthal direction is examined. Various ways to detect sideward scattering and its effects are discussed. For seeded angular scattering in the region where the laser beams overlap, see recent calculations by P. Michel \textit{et. al}.\footnote{P. Michel \textit{et. al}., 39$^{th}$ Anomalous Absorption Conference, Bodega Bay, CA (June 14-19, 2009)}   

Suppression of stimulated Raman scattering due to localization of electron plasma wave in laser beam filaments

The filamentation of the high power laser beam by taking off-axial contribution is investigated when ponderomotive nonlinearity is taken into account. The splitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays. It is observed that the weak electron plasma wave (EPW) propagating in the z direction is nonlinearly coupled in the modified filamentary regions of the laser beam. The semi-analytical solution of the nonlinear coupled EPW equation in the presence of laser beam filaments has been found and it is observed that the nonlinear coupling between these two waves leads to localization of the EPW. Stimulated Raman scattering (SRS) of this EPW is studied and back reflectivity has been calculated. Further, the localization of EPW affects the eigen frequency and damping of plasma wave. As a result of this, mismatch and modified enhanced Landau damping lead to the disruption of SRS process and a substantial reduction in the back reflectivity. For the typical laser beam and plasma parameters with wavelength ($\lambda $=1064nm), power flux ($\approx $10$^{16 }$W cm$^{-2})$, and plasma density (n/n$_{cr})$ = 0.2; the back reflectivity was found to be suppressed by a factor of around 20{\%}.   

The growth and saturation of the two-plasmon decay instability in inertial confinement fusion

We present particle-in-cell (PIC) and fluid simulations on the two-plasmon-decay (TPD) instability under conditions relevant to direct-drive inertial confinement fusion experiments. The PIC simulations show a wide TPD spectrum, with modes whose perpendicular mode number $k_{\perp}$ larger than the cutoff predicted by the linear theory for absolute modes. The fluid simulations, solving the full set of the linear equations of TPD, show that large-$k_{\perp}$ modes are convective and have linear growth rates comparable to the absolute modes. The convective modes grow at the lower density region and can cause pump depletion, reducing the growth of the absolute modes. The convective modes, saturating before reaching the convective limit, are energetically dominant in the nonlinear stage. The PIC simulations show that both the absolute and convective modes saturate due to ion density fluctuations. The results show that the convective modes of TPD are important to the performance of current and future direct-drive experiments.   

The Effects of Plasma Packets and Local Pump Depletion in Stimulated Raman Scattering

Stimulated Raman scattering (SRS) for NIF-relevant parameters involves nonlinear, kinetic physics. Previous simulations have focused on the nonlinear physics involved in SRS saturation (such as nonlinear frequency shifts and trapped-particle sideband instabilities) in isolation from and without regard to finite spatial effects. However, SRS is bursty in both space and time, generating plasma wave packets that locally generate bursts of reflected light, deplete incident laser light, and interact with each other through scattered light. The recurrence rate of SRS reflectivity is shown to depend on the nonlinear packet speed and the nonlinear frequency shift of plasma waves in packets. Packets are shown to locally deplete the incident laser energy, but as the packets are etched away and new laser energy propagates past the packet edge without being depleted, packets undergo renewed growth, resulting in new bursts of reflectivity. For interaction lengths that allow several packets to grow and convect simultaneousl, backscattered light from one packet provides an enhanced seed for a nearby packet. This causes the reflectivity to increase as a function of time. We present results for both 1D and 2D simulations.   

Nonlinear, Local Kinetic Damping of Finite-Size Plasma Waves Relevant to Stimulated Raman Scattering

Computer simulations of stimulated Raman scattering (SRS) indicate that the instability is bursty in time and space, leading to finite-size plasma waves in both the longitudinal and transverse directions. Using particle-in-cell (PIC) simulations with an external, ponderomotive impulse driver, we present the results of detailed study of the nonlinear behavior of finite-sized plasma waves in order to better understand the long-time behavior of SRS reflectivities. In one dimension, we present recently published results (Fahlen \textit{et al.}, PRL \textbf{102}, 245002 (2009)) showing that finite-length plasma waves erode from the rear edge as new resonant particles enter and locally damp the packet. In multiple dimensions, recent results show that finite-width plasma waves localize about their axis due primarily to local, kinetic damping at the edges. The simulations are performed using a 1D and 2D electrostatic PIC code, and also using a 2D Darwin PIC code. This work was supported by DOE under Grant Nos. DE-FG52-03-NA00065, DE-FG52-06NA26195, and DE-FG02-03ER54721.   

A PIC simulation study on the evolution of the real and imaginary frequencies of 1D plasma waves

We use electrostatic PIC simulations to study the evolution of both the real and complex frequency of 1D plasma waves. We are considering especially the linear regime where the asymptotic damping rate is much bigger than the bounce frequency. In this regime the waves are typically very small and below the thermal noise. These waves can be studied using a subtraction technique where two simulations where identical random number generation seeds are carried out. In the first, a small amplitude wave is excited. In the second simulation no wave is excited. The results from each simulation are subtracted providing a clean linear wave that can be studied. As previously predicted, the damping is divided in two stages, an initial transient and an asymptotic decay (Landau's formula). The time-dependent resonant width measured in the simulations is compared with the theoretical prediction. In typical ICF plasmas nl$_{d}^{3} \quad <\sim $10$^{3}$. Therefore, the number of resonant electrons can be small for linear waves. We will consider the effects of small numbers of resonant particles and their consequences of the observed damping.   

Simulations for plasma heating of the core plasma in fast ignition

Heating of core plasma by fast electrons is a backmost and utmost issue in fast ignition. Although several efforts in simulation to understand the heating mechanism and consequently the deposit energy in the core, it has been unknown due to complicated physical processes and insufficient computer resource for a full-scale simulation. For this situation, we separate collisional and collective processes by using different type of simulations. In order to simulate collisional energy deposition, we performed a Monte-Carlo code, EGS5, to estimate the core temperature by using the previous integrated experiment as the calculation condition [1]. In the results, the temperature increases from the low dense to the core where the maximum temperature is obtained up to several tens eV, which is near the half of the temperature in the experiment In addition, we found the electrons around 1 MeV mostly contribute to the heating. On the other hand, we observe the significant reduction of electrons up to 10 MeV possibly by depositing their energies on the core in the above experiment and indicate a new collective energy deposition mechanism in EMHD framework [2]. We're developing a new code to verify the EMHD approach. [1] R. Kodama et al., Nature 412, 23 (2001). [2] T. Yabuuchi et al., submitted to New J. Phys. (2009).   

Hybrid simulations of strong filamentation of relativistic electron beam propagating through collisionless plasma.

Development of the Weibel instability during propagation of relativistic beam through ambient plasma leads to formation of low-current filaments, which continue to merge with each other and eventually form filaments with large currents. Analytical theory and computationally efficient simulations of this nonlinear stage of Weibel instability are presented. In our hybrid approach [1] beam electrons are modeled using numerical macroparticles while plasma electrons are modeled as a passive fluid responding to the beam evolution. But in contrast to [1], present analysis captures effects of violation of the charge quasi-neutrality near the boundaries of high-current filaments and reproduces in details the structure of the electron plasma-void regions. This approach is especially effective in the cases when beam electrons have a large relativistic factor. Results of hybrid simulations are compared with those obtained from direct fully electromagnetic PIC simulations and applicability limits of the developed model are established. [1] Oleg Polomarov et al., Phys. Plasmas 14,043103 (2007).   

Progress in indirect drive fast ignition capsule design for the National Ignition Facility

We describe our ongoing work in developing indirect drive Fast Ignition (FI) target designs to be fielded on the National Ignition Facility. Previous efforts [Bull. Am. Phys. Soc. 53, 52 (2008)] focused on capsule designs using deuterium-tritium fuel and doped beryllium ablators. In keeping with the need to diagnose electron beam heating of the assembled fuel at low beam energies, these target designs have evolved into non-cryogenic surrogate targets using silver-doped, deuterated plastic ``fuel'' layers and plastic ablators. Two designs are described in detail, one using a single shock pulse shape followed by a quasi-isentropic compression and a second using a more conventional four-shock pulse shape. The control of pre-heating of the reentrant gold cone in FI targets is particularly problematic in the hard x-ray environment of indirect drive, and a variety of shell dopant materials are investigated in these designs to mitigate the pre-heat. Finally, the reliability of these target designs in assembling the required fuel areal density is assessed in the face of expected target and radiation drive uncertainties using a series of statistical scans including all expected 1-D sources of error.   

On the role of relativistic shocks in fast ignition

One of the critical issues for fast ignition of fusion targets is to understand/optimize the coupling of the ignition laser to the fast particles, and their transport in the mildly to high dense region of the target. We have performed a series of 2D PIC simulations in order to examine laser absorption and electron transport using ignition lasers with ultra-high intensities, up to 5x10$^{21 }$W/cm$^{2}$, and density gradients up to 1000 nc. Our results indicate that the dynamics of the Weibel/streaming instabilities leads to an isotropization of inward heat flux. This causes energy to be bottled up near the laser interaction point causing a shock to be launched. In uniform plasmas, this process and the emission of plasmons by the inward flowing electrons leads to a softening of the electron energy spectrum to the 1-3 MeV range for ultra-high laser intensities. In fast ignition (both channel and cone guided) this shock and the associated heat flux need to propagate up a density gradient to the core. The inclusion of the density gradient is observed to be crucial, leading to a stronger energy release by the shock structure and therefore to potentially higher efficiencies.   

Dependence of core heating properties on heating pulse duration and intensity

In the cone-guiding fast ignition, an imploded core is heated by the energy transport of fast electrons generated by the ultra-intense short-pulse laser at the cone inner surface. The fast core heating ($\sim $800eV) has been demonstrated at integrated experiments with GEKKO-XII+ PW laser systems. As the next step, experiments using more powerful heating laser, FIREX, have been started at ILE, Osaka university. In FIREX-I (phase-I of FIREX), our goal is the demonstration of efficient core heating ($T_{i} \quad \sim $ 5keV) using a newly developed 10kJ LFEX laser. In the first integrated experiments, the LFEX laser is operated with low energy mode ($\sim $0.5kJ/4ps) to validate the previous GEKKO+PW experiments. Between the two experiments, though the laser energy is similar ($\sim $0.5kJ), the duration is different; $\sim $0.5ps in the PW laser and $\sim $ 4ps in the LFEX laser. In this paper, we evaluate the dependence of core heating properties on the heating pulse duration on the basis of integrated simulations with FI$^{3}$ (Fast Ignition Integrated Interconnecting) code system.   

Study of fast electron transport in warm dense plasma targets

Recent experiments [Le Pape et al., RSI 79, 106104, 2008] successfully demonstrated creation of a warm dense plasma using ns laser driven shock compression in a low-density foam target. Fast electron transport in such shock heated targets relevant to fast ignition is investigated using the Titan laser at LLNL. K-shell x-ray emission from the Cu fluorescent layer in the foam package targets is measured using Bragg crystal imagers and HOPG spectrometers. Electron transport through cold, conductor and shocked compressed foam targets is compared. The experiment is modeled using a 2D radiation hydro code and the hybrid PIC code LSP.   

Creation of warm dense matter with a proton beam generated by the OMEGA EP laser beam

The creation of warm dense states of matter has important implications in astrophysics and the fast ignition scheme for inertial confinement fusion. We report on an experiment performed using OMEGA EP laser (1 kJ, 10 ps), which was focused on a hollow Cu hemisphere to produce an intense, focused proton beam. This proton beam was used to heat a 25 um thick, 2 mm diameter Be disk placed 375 um from the apex of the hemisphere. Variable spaced grating spectrometers were used to diagnose the continuum spectrum emitted from the rear side of the disk. The results were then compared to LASNEX simulations to infer a bulk temperature. A detailed analysis will be presented. Work performed under the auspices of the U.S. DOE by LLNL under contracts DE-AC52-07NA27344 and DE-FG-02-05ER54834. The authors acknowledge the support of OMEGA EP and LLNL technical staff.   

Fast electron transport in shock-wave heated planar Au targets

Hydro modeling shows that in a re-entrant cone-guided Fast Ignition, shell compression launches a shock into the tip of the cone through which the ignition electrons must propagate. The transport of fast electrons through shocked and unshocked Au targets is investigated using the Titan laser at LLNL. A shock wave is launched by the long pulse (300 J, 3ns, 532 nm) interacting with the CH of a CH/Cu/Au target. Fast electrons generated by the short pulse (150J, 0.7 ps, 10$^{20}$ W/cm$^{2})$ interacting with the Au are transported through the gold. Cu K-alpha induced by the electrons is recorded with HOPG spectrometers and spherical Bragg crystal imagers as a function of the delay of two pulses. Detailed analysis of results will be presented. This work was supported by the US DOE under contracts DE-FC02-04ER54789 (Fusion Science Center) and DE-FG-02-05ER54834 (ACE).   

Fast electron generation and transport in cone-attached wire targets irradiated by 800 J, 10 ps OMEGA EP laser pulses

Study of fast electron generation and transport is of a fundamental importance for the success of fast ignition of ICF. OMEGA EP provides an important platform to carry out such a study. We report experiments using copper wires attached to gold cones with 800 J, 10 ps pulses at the OMEGA EP laser facility. The fast electron generation and transport were investigated with the Cu K$\alpha $ x-rays, to show energy coupling into the wire, from the emitted electrons, to show their energy spectrum, and by backlighting with an MeV proton beam to show electrostatic fields around the target. Experimental results are compared with 150 J, 1 ps pulses using the Titan laser at LLNL.   

A Hybrid Ion/Electron Beam Fast Ignition Concept

Fast ignition (FI) inertial confinement fusion is an approach to high-gain inertial fusion, whereby a dense core of deuterium/tritium fuel is assembled via direct or indirect drive and then a hot spot within the core is heated rapidly (over a time scale of order 10 ps) to ignition conditions by beams of fast charged particles. These particle beams are generated outside the capsule by the interaction of ultra-intense laser pulses with solid density targets. Most study of FI to date has focused on the use of electron [Tabak et al., Phys. Plasmas 1, 1696 (1994)] or ion [Fern\'andez et al., Nuclear Fusion 49, 065004 (2009)] beams, however a hybrid approach involving both may have advantages. This paper will describe recent work in this arena. Work performed under the auspices of the U. S. Dept. of Energy by the Los Alamos National Security, Los Alamos National Laboratory. This work was supported by LANL Laboratory Directed Research and Development (LDRD).   

Laser Energy Absorption Scaling and Ion Production in Thick and Thin Targets

A fully relativistic model has been developed for the interaction of an intense laser with an overdense plasma. The model is based on conservation laws in one dimension for momentum flux and energy flux across the vacuum-plasma boundary. The main results are (a) that the maximum hot electron temperature scales as $(1+2^{1/2}a_0 )^{1/2}-1$, in units of the electron rest mass energy and (b) the light absorption can be 80{\%}-90{\%} for intensity $>$10$^{19}$ W cm$^{-2}$ This theory has been extended to the case of a thin target, at the rear boundary of which fast electrons can reflux. Momentum and energy flux conservation leads to surface ion acceleration (typically protons in experiments), while refluxing electrons re-entering the front boundary region lead to greatly reduced laser-light absorption. This is relevant to proton driven fast ignition.   

On the Advantages of Fast Ignition with Ultra-High Intensity Lasers

One of the critical design constraints for fast ignition targets is the need to have a small cross section for the hot spot at the target core while delivering enough power to the hot spot with hot electrons of the proper energy range, $\sim $ 1-3 MeV, to couple to the core. We use two-dimensional Particle-In-Cell simulations of isolated targets to investigate the feasibility of using 1$\mu $m ignition lasers with ultra-high intensities, up to 8x10$^{20}$W/cm$^{2}$, for fast ignition. The self-consistent absorption of energy from an ultra-high intensity laser by overdense plasma and the subsequent energy transport through the collisionless overdense plasma, $\nu _{ei} \quad < \quad \omega _{p}$, of a 50$\mu $m radius isolated target, is explored in detail. At these ultra-high intensities, we find that most of the energy transport is in a hot bulk and not in the super-hot tail of the electron distribution. Electrons in a relatively low energy range, below 3MeV, transport 90{\%} of the heat flux through 50$\mu $m of 100n$_{c}$ plasma to the target core.   

Hosing in Laser Channeling in Fast Ignition

Laser channeling aims to reduce the energy loss of an ignition pulse in the mm-scale underdense plasma of fast ignition targets. Previous full-scale particle-in-cell (PIC) simulations in 2D identified laser and channel hosing as an important instability that causes channel-bifurcation and limits channeling speed [1]. Hosing in 3D has also been observed in recent PIC simulations, which show that hosing grows slower in 3D than in 2D. Laser hosing in this long wavelength regime is through coupling with the ion acoustic waves. A variational analysis of hosing in 2D and 3D will also be presented. This work was supported by the U.S. Department of Energy under Cooperative Agreement Nos. DE-FC52-92SF19460, DE-FC02-04ER54789, and DE-FG02-06ER54879. \\[4pt] [1] G. Li et al., Phys. Rev. Lett. 100, 125002(2008).   

Electron Acceleration by High Intensity Lasers at Sharp Matter Interfaces

A key question in the fast ignition approach to nuclear fusion is how electrons are accelerated at a light-plasma interface by very intense lasers. To investigate this, we use the PIC code OSIRIS to model the interaction of high intensity lasers (I$>$=5x10$^{19}$ W/cm$^{2})$ with a sharp boundary of an over-critical plasma (n$>>$n$_{c})$. We find that, for these experimental parameters, none of the commonly proposed absorption mechanisms -- i.e., inverse Bremsstrahlung, JxB, Brunel heating -- can account for the spectrum of forward accelerated electrons. Instead, we propose a mechanism in which these electrons thermally exit the plasma, resonantly interact with the incoming and reflected laser light within a quarter wavelength of the surface, and then turn back into the plasma - gaining in the process up to twice the quiver velocity. Electrons must leave the plasma at high energies, specific angles, and in phase with the laser wave in order to be accelerated. This mechanism is confirmed by 2D OSIRIS simulations with particle tracking, as well as from the results of a 1D numerical imposed field model.   

Numerical Simulation of Pre-formed Plasma Generated by Low Intensity Pre-Pulse Before Main Heating Laser in Fast-Ignition

We investigated the plasma expansion of the inner surface of the cone used for the fast-ignition scheme of the inertial confinement fusion (ICF). LFEX laser [1] in Osaka University is high intense and short pulse laser system, which has 10$^{19}$W/cm$^{2}$ to 10$^{20}$W/cm$^{2}$, and ps pulse duration. However, it has also low intense pre-pulse with the contrast ranging from 10$^{5}$ to 10$^{8}$. It is high enough to ablate the inner surface of the cone wall used for fast ignition target. We developed the two-dimensional simulation code (Star-2D) [2], and simulate plasma expansion of the inner surface of the cone. We will discuss our simulation results, and also effects of the pre-plasma expansion on fast electron production. On the other hand, our code has been applied to simulate the laser-produced plasmas for Extreme-Ultraviolet research, and its accuracy has been tested with various experiments. We will also discuss the accuracy of our simulations. \\[4pt] [1] H. Azechi et at., in EPS. \\[0pt] [2] A. Sunahara et al., \textit{Journal of Physics: Conference Series }112(2008) 042048-1-4.   

Application of a New Turbulent Transport Model to Double-Shell Inertial Confinement Fusion Capsule Implosions

Recent progress in the modeling of the performance of non- cryogenic double-shell inertial confinement fusion capsules is discussed. A new two-equation eddy viscosity-based $K$- $\epsilon$ turbulent transport and mixing model is briefly described and then applied to a set of double-shell capsules with glass and plastic inner shells. One- and two-dimensional simulations are presented and compared to measurements previously obtained from experiments on the OMEGA laser. It is shown that the model predictions, using coefficients consistent with both high resolution numerical simulation data of Rayleigh- Taylor instability-induced turbulence and with analytical solutions of the model in particular limiting cases, are well within the uncertainties of the experimentally measured capsule yields. Various quantities from the capsule simulations are discussed and interpreted physically within the context of both ICF physics and turbulence.   

Laser-Plasma Interaction Experiments in Gas-Filled Hohlraums at the LIL Facility

The first laser-plasma interaction campaign conducted at the LIL facility, using gas-filled hohlraums, ended in spring 09. Two different gas-filled hohlraums have been designed in order to mimic plasma conditions expected along two particular beam paths in ignition hohlraums. The targets consist of 3- or 4-millimeters long, 1 atm neo-pentane gas-filled gold hohlraums. The LIL quadruplet is aligned with the hohlraum's axis and delivers a 6-ns long pulse with 15 kJ at 3$\omega $. Optical smoothing is achieved by longitudinal dispersion and a phase plate giving a near 10$^{15}$ W/cm$^{2}$ mean intensity on the focal spot at maximum power. Plasma conditions from hydrodynamic calculations allow to calcule SBS and SRS linear gain with the PIRANAH code. The calculated spectra are compared to experimental results. We use the paraxial code HERA to investigate the propagation of the LIL quad. Finally, 1D and 2D PIC simulations based on the plasma conditions of the cavity will be discussed in order to understand experimental SRS spectrum.   

Session CM9: Mini-Conference on Innovative Magnetic Mirror Concepts and Applications II

Vortex Confinement of Plasmas in Axially Symmetric Mirrors

Efforts to optimize operation of the Gas Dynamic Trap with variation of plasma rotation led to discovery of a new way of efficient plasma confinement. Its nature is similar to confinement of material in the dead zone of a vortex flow. It is achieved by applying voltage to the limiters and the endplates of the device, thus creating shear-flow layer, which surrounds the core of the discharge. In this regime the gas-dynamic stabilization is shown to be unnecessary, as the confinement is excellent even with straight field lines in the expanders. While the axisymmetric equilibrium remains unstable, there appears a new dynamic state of confinement with approximate axial symmetry and low convective losses. The needed power consumption is a fraction of parallel ion losses (30kW), while the theoretical scaling predicts the scheme to work even at fusion temperatures. The talk will contain simplified analytic theory of the nonlinear dissipative saturation of the m=1 mode in the presence of the externally-driven vortex flow, and the two-dimensional drift-ordered MHD simulation of the vortex confinement in the GDT.   

The Design of anchor divertor of GAMMA10

The plan that one of the anchor mirror cells, which was installed for the flute interchange mode stability, is replaced by an axisymmetric divertor mirror cell is in progress. The main object of the divertor mirror is to simulate the ITER divertor physics. Then the scenario on the effective evacuation of core plasma in the divertor mirror cell to the magnetic null region is required in order to obtain a high power plasma flow outside the divertor mirror cell region. We are designing the divertor mirror coil system in GAMMA10 and estimating the plasma parameter in the divertor system and radial energy loss flux outside the magnetic null. The MHD stability is determined with help of the kinetic analysis of flute mode by taking into account the ion FLR, magnetic field line curvature and plasma compressibility. The stored energy is calculated by the bounce-averaged Fokker-Planck code. The radial evacuation of hot ions is estimated by the reduced MHD simulation taking into account the flute-like electrostatic potential fluctuations.   

Trapped Particle Instability in Kinetic Stabilized Tandem Mirror

The kinetic stabilizer tandem mirror (KSTM) devised by R. F. Post (J. Fus. Energy 2007) is an innovative concept devised to stabilize a symmetric tandem mirror machines using a concept devised by D. Ryutov (Proc. of Course and Workshop, Varenna, Italy, 1987) and empirically verified in the Gas Dynamic Trap (Ivanov, et. al. Trans. Fusion Technology 39, 127, 2001). The KSTM uses the momentum flux of unconfined particles that only sample the outer end regions of the mirror where there is very favorable field line curvature. Charged ion beams at relatively low energy are externally injected into the ends and reflected out from the ends. MHD stability with a power drain less than the fusion power production can be achieved. We examine the effect of fast growing trapped particle instability (Berk et. al. Sov J. Plasma Phys. 1983) on the overall stability. In this case stability is very sensitive to the electron connection between the stabilizer and end plug.   

The TASKA, TDF, and TASKA-M Fusion Neutron Materials Test Facilities

This talk will summarize key features of three conceptual fusion neutron test facilities designed in the early 1980s: TASKA,$^1$ TDF,$^2$ and TASKA-M.$^3$ Motivated by the accessibility and maintainability of cylindrical geometry, these magnetic-mirror designs possess a simple central cell, as in a fusion neutron test facility based on the gas dynamic trap (GDT).$^4$ The TASKA-M design, like today's GDT designs, included the injection of neutral beams into the central cell to create a sloshing-ion distribution that gives density peaks near the materials test modules. In TASKA and TDF, the minimum-B end-cell designs contained thermal barriers, regions of low electrostatic potential to reduce electron flow between central cell and end cells. Thermal barriers improve performance but require more complicated input power systems, and their physics basis is less well established than that of simple mirrors. For TASKA-M, a more conservative design, minimum-B end cells provided MHD stability, but thermal barriers and an end-plug potential peak were absent. [1] B. Badger, et al., UW FTI Report UWFDM-500 (1982). [2] T.H. Batzer, et al., LLNL Report UCID-19328 (1983). [3] B. Badger, al., UW FTI Report UWFDM-600 (1984). [4]~P.A. Bagryanski, et al., {\it Fus. Eng. Design} {\bf 70}, 13 (2004).   

Minimum B mirror with expander aimed for transmutation and energy production

A comparatively simple fusion driven fission device may be developed for industrial transmutation and energy production from spent nuclear waste [1-2]. This opportunity stems from the large fission to fusion power production ratio, $P_{fis}$/$P_{fus} \quad \approx $150, in a subcritical fusion device surrounded by a fission mantle with the neutron multiplicity $k_{eff }$=0.96. Power production is predicted if the electron temperature exceeds 700 eV. The expanders may improve the electron temperature by a formation of an ambipolar potential. Theoretical studies include RF heating, magnetic coil designs, fission mantle kinetics and some basic plasma investigations. A 20 m long mirror with a 40 cm plasma radius could be sufficient for a electric power production of 500 MW. [1] S. Taczanowski, ``Premises for development of fusion-fission hybrid systems'' in IAEA-RC-870.3, TWG-FR/132, Chennai, India 15 -- 19 January 2007. [2] O. {\AA}gren, V.E. Moiseenko, A. Hagnest{\aa}l, ``The straight field line mirror concept and applications'', Problems of atomic science and technology \textbf{6}. \textit{Series: }Plasma Physics, 8 (2008).   

Gas Dynamic Trap Neutron Source (DTNS) -- applications and development path

The successes in the Gas Dynamic Trap at the Budker Institute of Nuclear Physics -- stable operation to $\beta \sim $60{\%}, T$_{e}$ increasing with neutral beam power to $>$200 eV, and classical behavior of hot ions (Ivanov and Beklemishev, this conf.) -- motivate building a DTNS. The DTNS provides $\sim $2 MW/m$^{2}$neutron flux, and 20 l irradiated volume (in a 2.5 cm thick annulus) to enable aggressive programs in fusion materials development, tritium-breeding blankets (which do not have to breed initially because the DTNS burns less than 200 g/yr of T), and hybrid fission blankets. The major issue is steady-state operation of a configuration that has been demonstrated during 5 ms pulses. The known issues are all engineering: cooling components impinged by beams, pumping the gas and regenerating the pumps. Possible plasma physics issues, such as drift waves, are expected to have slow growth times enabling suppression or saturation at low levels.   

Investigations of axisymmetric mirror boundary conditions using Reconnection Scaling Experiment

Axisymmetric magnetic mirrors such the Gas Dynamic Trap (GDT) concept do not need complex and expensive minimum B magnetic coil structures to enhance MHD stability. GDTs and related mirror designs typically contain a large end loss region region of flared and expanding magnetic field lines between a mirror coil and an end cell with radial and axial end walls. This end loss region can furnish pressure weighted good curvature field line forces that stabilize MHD behavior, and also provide electrostatic sheaths that confine electron heat loss. Investigations of axial boundary conditions will be useful to determine how and why MHD stability can be enhanced, and how to improve confinement of electron heat flux. The Reconnection Scaling Experiment (RSX) has been used to for a wide range of conditions in an MHD relevant experiment. We have demonstrated a continuous range of adjustability between line tied (fixed) and non line tied (free) axial boundary conditions.   

MHD-Stabilization of Axisymmetric Mirror Systems Using Pulsed ECRH

A method of MHD-stabilizing axisymmetric mirror systems, demonstrated in the Gas Dynamic Trap [1] and analyzed by Ryutov [2] employs low pressure plasma on expanding field lines outside the mirrors. Methods of creating such plasmas have been analyzed [3]. This paper studies another technique: Pulsed ECRH in regions of positive curvature. The ansatz: If the repetition time is shorter than the MHD growth time, and if their time-averaged amplitude is exceeds that required by the theory the system will be stable. The calculations confirm the ansatz. Applications include axisymmetric tandem mirror and multiple-mirror systems. In the latter it might perform the functions of MHD-stabilization and of biasing cell-loss probabilities inwardly. Post and Li [4] showed that such biasing leads to confinement times that increase exponentially with the number of cells, rather than linearly, as occurs with symmetric losses. Prepared by LLNL under Contract DE-AC52-07NA27344. [1] P. A. Bagryansky, et. al., Trans. Fusion Tech. \textbf{35}, 79 (1999) [2] D. D. Ryutov, Proc. of Course and Workshop, Varenna, Italy, Vol II, 791 (1987) [3] R. F. Post, Trans. Fusion Tech., \textbf{39}, 25 (2001) [4] R. F. Post and X. Z. Li, Nuc. Fusion, \textbf{21}, 135 (1981).   

Alpha-Channeling in Mirror Machines

Linear magnetic trap is an attractive concept for fusion research and plasma applications due to its relative engineering simplicity and high-beta operation. Application of the alpha-channeling technique to mirror machines can benefit this concept by efficiently redirecting alpha particle energy to fuel ion heating or sustaining plasma confinement, thus increasing the effective fusion reactivity. To identify waves suitable for alpha-channeling a rough optimization of the energy extraction rate with respect to the wave parameters is performed. After the optimal regime is identified, the systematic search for modes with similar parameters in mirror plasmas is performed by assuming quasi-longitudinal, or quasi-transverse wave propagation. As a result, modes suitable for alpha particle energy extraction are identified in several device designs including the LAPD experiment. Under a proper choice of the tandem mirror device parameters, the predicted modes are expected to feed ICRH waves in the device plugs, thus redirecting the extracted energy to sustaining the plasma confinement.   

Alpha channeling using stationary waves in a centrifugal mirro

In a mirror with supersonic rotation, charged fusion products might interact with radio-frequency waves to maintain the rotation against drag forces. Magnetic ripples that are stationary in the lab frame can match the cyclotron frequency in the particle frame, allowing resonant interaction without requiring power input. We examine the feasibility of using these waves in a fusion device with a deuterium-tritium plasma.   

Proposed Thomson scattering measurements on the Gas Dynamic Trap

We describe a proposed short-term collaborative experimental investigation of electron temperature on the Gas Dynamic Trap (GDT) experiment at the Budker Institute in Novosibirsk, Russia using the double-pulse multipoint Thomson scattering diagnostic from the decommissioned SSPX spheromak at Lawrence Livermore National Laboratory. Electron temperature is a critical parameter in the gas dynamic trap (GDT) since fast-ion energy losses are governed by electron drag, which decreases with increased electron temperature. Higher fast-ion densities lead to higher neutron production in fusion neutron sources based on the GDT concept. Expected plasma conditions and measurement capabilities will be compared. Suitable experimental campaigns will be presented. This work performed under the auspices of the U.S. DoE by LLNL under Contract DE-AC52-07NA27344.   

Extension of XGC kinetic simulation codes to magnetic mirror configurations

The XGC codes, developed to simulate the edge regions of tokamak plasmas, are modified to carry out kinetic simulations of axisymmetric magnetic mirror configurations. The XGC codes are particle in cell kinetic codes that include a virtual sheath condition where magnetic field lines run into end plates. The XGC1 code is a fully five dimensional kinetic code that is used to investigate turbulence, while the faster XGC0 code uses the axisymmetric average electrostatic potential in order to simulate charged particle drifts, losses and collisional effects. Kinetic electron computations, neutral beam injection, atomic physics and the effects of thermal neutrals are included in the XGC codes. Changes are being made to allow the XGC codes to accept mirror equilibria and to run without a toroidal magnetic field component. The XGC0 code will be used to compute particle dynamics, electrostatic potentials, and moments of the distribution functions including plasma flows in mirror configurations. \newline [1] C.S. Chang, S. Ku, H. Weitzner, Phys. Plasmas {\bf 11} (2004) 2649