Session NP9: Poster Session V: ITER and Magnetic Fusion Development; Laboratory Astrophysics; Space and Astrophysical Plasmas; ICF, Laser-Plasma Instabilities, High-Energy Density Physics, and Diagnostics

Modeling of ITER scenarios with improved Multi-Mode model

The Multi-Mode transport model, including a new drift resistive inertial ballooning mode model, is used in PTRANSP simulations. Validation studies have been carried out using L-mode discharges in existing tokamaks. The time evolution of temperature, toroidal angular frequency and current density profiles is predicted in ITER hybrid and steady state discharges. External heating and current drive sources including NBI, LH, ECRH and ICRH, are computed using NUBEAM, LSC, TORAY and TORIC modules, respectively. The NCLASS module is used to compute neoclassical resistivity and bootstrap current. The sensitivity studies include the variation of the pedestal height around the value predicted by EPED1. The fusion power production and fusion $ Q $ computed with the Multi-Mode model are compared with those obtained using the GLF23 model. The dependence of heat deposition is studied with varying ICRF frequency, beam orientation and ECRH launch angles. The discharge scenarios simulated aid in understanding the conditions for optimizing fusion power production and in examining other measures of plasma performance.   

ITER Vertical Stability and Shape Control Studies

A tokamak plasma's vertical stability and shape control system is a critical component of experimental operation. The recent ITER Design Review and subsequent STAC tasks have produced significant modifications to the original ITER vertical stability control system, which used only the outboard coils, PF2-5 (``VS1'' circuit). The addition of a new in-vessel coil set (``VS3'') for vertical control is predicted to augment the control robustness sufficiently to match performance typical of operating devices for similar levels of noise and disturbance amplitude (scaled to minor radius). In this paper we present results of our recent studies of this new system. Linear control-level models are used to analyze controllability and to design controllers, using the GA TokSys toolbox. These controllers are then implemented in more detailed simulations to evaluate their performance under nonlinear conditions. We present Corsica simulations of ITER Baseline 2008 design using these contollers, including controlled and uncontrolled vertical stability events, and flattop and rampdown phases, providing an assessment of the ITER Baseline coil system.   

ITER ECH Transmission System Test Stand and Prototype Component Development

The US ITER Project Office is responsible for providing the ECH transmission lines for ITER. A conceptual design of the system uses a total of 24 transmission lines. Each line is designed to handle 170 GHz power at 2 MW operating in the HE11 mode. A number of prototype components have been procured, primarily from industrial suppliers, and testing of vacuum performance and mechanical alignment has been performed. A 140\r{ } miter bend was developed and tested at low power as an alternative to two adjacent 90 degree miter bends. A waveguide pumpout prototype and a compact waveguide switch have also been built. Components will be testing at high power (up to 2 MW) using a resonant ring configuration. Low power testing of a grating coupler for the resonant ring is underway. Work on installing a power supply and interim 400 kW 140 GHz gyrotron has progressed and procurement of a 170 GHz 0.5-1 MW gyrotron has begun. Low power testing and analysis of waveguide components is underway at MIT [1].\\[4pt] [1] M.A Shapiro, et al, Bulletin of the American Physical Society Vol. 54 No. 15 P 108.   

Low-power Loss Measurements for ITER Gyrotron ECH Transmission Line Components

The ITER transmission line system will transport 20 MW of power from 24 1-MW gyrotrons at 170GHz using overmoded metallic cylindrical waveguides that are 63.5 mm in diameter with quarter wavelength corrugations. Each line must have less than 83{\%} loss, requiring precise loss measurements of waveguide components. An accurate measurement of the loss in these waveguide components was obtained using a low-power S-Parameter analysis technique which reduces the error and increases the accuracy of the loss measurement. The loss in a miter bend was measured to be 0.022 +/- 0.008 dB, in good agreement with theory. In addition, the loss due to a gap in the waveguide was measured for various gap lengths and found to be in good agreement with theory. This measurement shows the accuracy of the technique. To characterize the modes present in corrugated waveguide, a linearly polarized (LP) basis set of modes was derived which accounts for the polarization of the modes present since most high-power applications have linearly polarized Gaussian beam inputs.   

ITER ECH and LFS Reflectometer waveguide testing

The ITER project requires overmoded millimeter waveguide for electron cyclotron heating (ECH) and also the low-field side (LFS) reflectometer diagnostic. The ITER systems will use circular corrugated waveguide due its low loss and good polarization purity and launch beam qualities. The ECH application is narrow band and the reflectometer system requires broadband capability. A number of prototype components such as miter bends, straight sections, and vacuum pumpouts have been procured from industrial suppliers. The ECH system requires water cooling and good vacuum for reliable operation. Both systems will have similar straightness requirements to minimize unintentional mode conversion. The reflectometer system vacuum windows will be supplied by the US and must operate over a wide bandwidth with minimum reflection. Low power tests of mode purity, loss, and reflections are being performed on all components and high power tests are planned for the ECH components. Mode purity tests are performed by antenna pattern analysis with a high mode purity feed using both tapers or a horn/lens combination.   

ITER low-field-side density profile reflectometer: design challenges and optimization

Ensuring the availability, reliability and accuracy of profile, MHD and turbulence measurements in ITER represents a significant challenge. In contrast to optically-based diagnostics, millimeter-wave systems are well-suited to the harsh burning plasma environment. However, a number of design issues remain including cutoff layer modifications due to relativistic effects at high temperatures, diagnostic availability/accessibility for a range of operating conditions/plasma positions, and minimization of phase errors introduced through antenna coupling/mode conversion in overmoded corrugated waveguide. Design issues such as this have been addressed through analysis coupled with laboratory measurements. An optimized conceptual design of the front-end antenna configuration has been generated together with an assessment of the expected accuracy of the density profile measurement.   

Design and Status of the Motional Stark Effect Diagnostic for ITER

The United States has been tasked with the development and implementation of a Motional Stark Effect (MSE) system on ITER. In the harsh ITER environment, in order to transmit light to a detector, a shielded labyrinth is required to mitigate the effect of neutrons and radiation. This necessitates the use of several mirrors to relay the light to the vacuum interface outside the shielded region. However, the plasma facing mirror is susceptible to coating and erosion. This is problematic for any optical diagnostic and particularly polarimetry measurements such as MSE. Even thin coatings can change the phase and reflectivity of $s$ and $p$ polarized light when reflected from a mirror. This makes maintaining and tracking the MSE calibration very challenging. Our proposed approach to the MSE diagnostic is to implement a combination of conventional MSE polarimetry and a new approach to measure the magnitude of the magnetic field from the line shift of the Stark spectrum. The advantage of the latter approach is that the line shifts are independent of polarization. Results of this and conceptual designs of the proposed MSE system for ITER will be discussed.   

ITER ECE in Situ Prototype Calibration Source and its Integration into the ITER ECE Diagnostic

A critical component in the ITER ECE diagnostic is an in situ calibration source. The US and India are developing the diagnostic with the US leading in development of the calibration source. The source is a large area (200mm diameter) emitter. It will generate blackbody emission (emissivity $>$ 0.7) for frequencies greater than 120 GHz in the ITER primary vacuum (VQC 1B). The source will operate at temperatures up to 800 \r{ }C for calibration runs during maintenance periods. A prototype source has been designed, constructed and tested in vacuum conditions. Results of these tests will be presented, along with a progress report on its integration into the ITER ECE system. Additional challenges of real-world application to J-TEXT and EAST will be presented.   

Progress in the Development of a C$_{60}$ Plasma Gun for Disruption Mitigation

We present the status of a C$_{60}$-fullerene plasma gun prototype proposed to be used for disruption mitigation with high-density, hyper-velocity plasma jets on ITER. The key element is the TiH$_{2}$/C$_{60}$ pulsed power, solid state cartridge source. We performed modeling and simulations of the processes critical to the cartridge design. Transient heating of TiH$_{2}$ packed grains, explosive sublimation of C$_{60}$ micron size powder, high pressure buildup, ejection of the molecular gas mixture through nozzles, adiabatic expansion of the plasma jet upon ejection from a plasma gun muzzle, and plasma jet penetration through transverse magnetic field were investigated. We show how we incorporated the results into the design of the TiH$_{2}$/C$_{60}$ cartridge source. Measurements characterizing the molecular gas jet produced by the cartridge source will be presented.   

Fusion Nuclear Science Facility (FNSF) before Upgrade to Component Test Facility (CTF)

The Fusion Nuclear Science Facility (FNSF) aims to address Fusion Energy Sciences research needs in ``Materials in Fusion Environment''. Such an environment can be provided initially in an ST device with the JET-level plasma conditions (Q=0.86 in Hot-Ion H-Mode) providing 0.25 MW/m**2 in outboard fusion neutron wall loading, and subsequently at twice the JET conditions (Q=1.7) to provide 1 MW/m**2. Conservative high-q and moderate-beta plasma conditions are calculated for the FNSF to minimize plasma-induced disruptions and allow the delivery of the required neutron fluence of 1 MW-yr/m**2 and duty factor of 10{\%}. Fully modular designs for all the chamber components, including the single-turn toroidal field coil center-post, allow component installation and replacement via remote handling, which is required for the research operations of FNSF. Since the device support structures are hidden behind the chamber components, the FNSF provides a ready upgrade path to the Component Test Facility (CTF), which will require more stringent fusion nuclear and operational capabilities. Details of the physics, engineering, and research prerequisites assessments for the FNSF will be reported.   

An Advanced Tokamak Fusion Nuclear Science Facility (FNSF-AT)

A Fusion Development Facility (FDF) is a candidate for FNSF-AT. It is a compact steady-state machine of moderate gain that uses AT physics to provide the neutron fluence required for fusion nuclear science development. FDF is conceived as a double-null plasma with high elongation and triangularity, predicted to allow good confinement of high plasma pressure. Steady-state is achieved with high bootstrap current and radio frequency current drive. Neutral beam injection and 3D non-resonant magnetic field can provide edge plasma rotation for stabilization of MHD and access to Quiescent H-mode. The estimated power exhaust is somewhat lower than that of ITER because of higher core radiation and stronger tilting of the divertor plates. FDF is capable of further developing all elements of AT physics, qualifying them for an advanced performance DEMO. The latest concept has accounted for realistic neutron shielding and divertor implementation. Self-consistent evolution of the transport profiles and equilibrium will quantify the stability and confinement required to meet the FNS mission.   

Evaluation of Synchrotron Radiation in a Reactor-Grade Tokamak Plasma

Recent research on synchrotron radiation from a magnetically confined plasma has pointed out that the synchrotron radiation makes a significant contribution to the local electron power balance of a high temperature fusion plasma such as ITER's. In this study, synchrotron radiation in a reactor-grade tokamak plasma has been evaluated taking account of relativistic treatment, magnetic structure, propagation direction and torus shape. An extended Trubnikov's equation for the spherically symmetric relativistic Maxwellian velocity distribution [1] is used for the emissivity in the oblique propagation. It is found that synchrotron radiation of extraordinary mode increases with the angle ($\phi$) between the propagation direction and the magnetic field monotonically, and that the synchrotron radiation of ordinary mode has peaks around $\phi$=60--75$^{\circ}$, because the emissivity decreases and the temperature in passing plasma region increases with the $\phi$. Calculation also shows that the total synchrotron radiation is proportional to the 0.5th power of electron density.\\[4pt] [1] M. Sato and A. Isayama, Fusion Sci. Technol. 52 (2007) 169.   

Burning plasma regime for Fussion-Fission Research Facility

The basic aspects of burning plasma regimes of Fusion-Fission Research Facility (FFRF, $R/a=4/1$ m/m, $I_{pl}=5$ MA, $B_{tor}=4-6$ T, $P^{DT}=50-100$ MW, $P^{fission}=80-4000$ MW, 1 m thick blanket), which is suggested as the next step device for Chinese fusion program, are presented. {\em The mission of FFRF is to advance magnetic fusion to the level of a stationary neutron source and to create a technical, scientific, and technology basis for the utilization of high-energy fusion neutrons for the needs of nuclear energy and technology.} FFRF will rely as much as possible on ITER design. Thus, the magnetic system, especially TFC, will take advantage of ITER experience. TFC will use the same superconductor as ITER. The plasma regimes will represent an extension of the stationary plasma regimes on HT-7 and EAST tokamaks at ASIPP. Both inductive discharges and stationary non-inductive Lower Hybrid Current Drive (LHCD) will be possible. FFRF strongly relies on new, Lithium Wall Fusion (LiWF) plasma regimes, the development of which will be done on NSTX, HT-7, EAST in parallel with the design work. This regime will eliminate a number of uncertainties, still remaining unresolved in the ITER project. Well controlled, hours long inductive current drive operation at $P^{DT}=50-100$ MW is predicted.   

Transformer recharging with alpha channeling in tokamaks

Transformer recharging with lower hybrid waves in tokamaks can give low average auxiliary power if the resistivity is kept high enough during the radio frequency recharging stage. At the same time, operation in the hot ion mode via alpha channeling increases the effective fusion reactivity. It appears that these two speculative, but large cost-saving steps, are compatible.   

Joint Program Centered on the Ignitor Experiment

A Memorandum of Understanding was signed in April between the Governments of Italy and the Republic of Russia concerning the contruction and operation of the Ignitor machine at its the Triniti site (Troitsk, near Moscow). Given that the machine core design has been completed and full size prototypes have been constructed, construction can take place on a relatively short time scale. In parallel to a joint effort on the Ignitor machine there will be a complementary one concerning high magnetic field technologies, basic physics of fusion burning plasmas, plasma heating systems, advanced diagnostics, etc. Univerisities will be involved on both the Russian and the Italian sides. A plan for U.S. participation is proposed. This event opens new scenarios in the road map for nuclear fusion, which will be discussed.   

Ignitor and the High Density Approach for Fusion*

The high plasma density regimes discovered by high magnetic field toroidal experiments have both outstanding confinement characteristics and degree of purity, and are at the basis of the Ignitor design. The main purpose of the Ignitor experiment is, in fact, that of establishing the reactor physics in regimes close to ignition, where the thermonuclear instability can set in with all its associated non linear effects. ``Extended limiter'' and double X-point configurations have been analyzed and relevant transport simulations show that similar burning plasma conditions can be attained with both, by Ohmic heating only or with modest amounts of ICRH auxiliary heating. The driving factor for the machine design ($R_0\cong 1.32 \textnormal{ m}, a \times b\cong 0.47\times 0.83 \textnormal{ m}^2, B_T \leq 13 \textnormal{ T}, I_p\leq 11 \textnormal{ MA}$) is the poloidal field pressure that can contain, under macroscopically stable conditions, the peak plasma pressures corresponding to ignition. Objectives other than ignition can be envisioned for the relatively near term, for example that of high flux neutron sources for material testing involving compact, high density fusion machines. This has been one of the incentives that have led the Ignitor Project to adopt magnesium diboride (MgB$_2$) superconducting cables in the machine design, a first in fusion research. Accordingly, the largest coils (about 5 m diameter) of the machine will be made entirely of MgB$_2$ cables. *Sponsored in part by ENEA of Italy and by the U.S. D.O.E.   

Plasma Regimes for the Ignitor Experiment*

The Poloidal Field System in Ignitor is capable of producing a variety of equilibrium configurations (i.e., ``extended limiter'' or Double X-point) over a wide range of magnetic fields and plasma currents. The most relevant operational conditions have been extensively analyzed, starting from the reference ignition scenario at 13 T and 11 MA. The scenarios with 6MA/9T, 7MA/9T and 10MA/13T had been analyzed earlier\footnote{F. Bombarda, A. Airoldi, G. Cenacchi, B. Coppi and D. Farina, \itshape Proceed. EPS Conf., \normalfont paper PI-196, 2006.} without considering the access to an enhanced confinement regime. The simulation for the 6MA/9T in the H regime have $\left\langle n_e\right\rangle = 1.8 \times 10^{20} \textnormal{ m}^{-3}$; with 5 MW of ICRF power the peak electron temperatures range from 6.5 to 8.5 keV for Deuterium plasmas, and from 7 to 9.5 in D-T plasmas, where the $\alpha$-power is around 2 MW. For the 7MA/9T scenario, by considering $\left\langle n_e\right\rangle = 1.9 \times 10^{20} \textnormal{ m}^{-3}$ and 5 MW of additional heating, the central electron temperatures are in the ranges 7.5 to 10 keV and 8.5 to 11 keV for D-D and D-T plasmas respectively. The third scenario (10 MA/13 T, DN configuration) is analyzed for $\left\langle n_e\right\rangle = 3.1 \times 10^{20} \textnormal{ m}^{-3}$, with the same ICRF heating pulse. The peak temperature reaches 7.5 keV in D plasmas , and it oscillates around 15 keV in D-T . The $\alpha$-power exceeds 25 MW and then decreases to 20 MW at the end of current flattop. *Sponsored in part by ENEA of Italy and by the U.S. D.O.E.   

Ignitor Plasma Physics Performance in the H-Regime at Various Parameters

The plasma physics performance of Ignitor at full ($B_T$ = 13 T, $I_p$ = 10 MA) as well as at reduced parameters ($B_T$ = 8 T, $I_p$ = 5 MA) in the high confinement mode (H-regime) is assessed using global 0-D modelling. At full parameters, high-$Q$ operation is possible if the heating power (a combination of Ohmic, $\alpha$ and limited ICRF power) is above the threshold value $P_{\mathrm{thr}}$ for H-regime confinement. Different scaling expressions for $P_{\mathrm{thr}}$ yield significantly different results when used with Ignitor parameters. Even with the most pessimistic among the proposed scalings\footnote{Y. R. Martin et al., \textit{Journal of Physics: Conference Series}, \textbf{123}, 012033 (2008).} the access to H-regime confinement is possible for Ignitor at full field when the ICRH system is operated at the highest frequency and the generated power is less than at lower frequencies. At reduced parameters, the lower $P_{\mathrm{thr}}$ and the augmented ICRF power available (about 10 MW) facilitate access to H-regime confinement, while the plasma performance remains respectable.   

Analysis of the Ignitor Scrape-Off Layer*

Ignitor has adopted an ``extended limiter'' configuration to fill all the available volume with the plasma, and to keep the peak power on the wall to less than 2 MW/m$^2$ for the reference ignition scenario. To achieve this challenging result, the FW shape follows closely the plasma column and needs to be built with strict tolerances. Accurate predictions of the plasma conditions near the edge were important for the design process, but the FWL geometry presents unique and partially unexplored features that have prompted the development of new modeling tools[1] for the SOL of Ignitor. The new analysis now includes the effect of neutral atoms, obtained by coupling the plasma fluid code ASPOEL with the neutral solver EIRENE. Preliminary results confirm that a large fraction of the recycling neutrals is ionized in the SOL itself, before entering the main plasma. As a consequence, the plasma temperature in the SOL is reduced, limiting wall sputtering. Another configuration with $B_T \cong 13 \textnormal{ T, } I_p \cong 10 \textnormal{ MA}$ and double X-points just outside the FW is analyzed, to facilitate access to the H-regime. In this configuration, the incidence angle of the magnetic field onto the wall grows rapidly near the tangency point, which challenges the need to keep the peak power at a low level. [1]F. Subba, et al., \textit{J. Nucl. Mater.} \textbf{363-365}, 693 (2007). *Sponsored by ENEA.   

Progress with the High Speed Pellet Injector for Ignitor*

The four barrel, two-stage Ignitor Pellet Injector (IPI) has been designed to reach speeds up to 4 km/s, for effective low field side injection into ignited plasmas ($T_e \cong T_i \cong 11$ keV). The IPI has been developed in collaboration between ORNL and ENEA, who have built and tested two indipendent subsystems each. Previous experimental campaigns at ORNL verified that the equipments matched properly, while their respective control systems interfaced correctly. The injector performed outstandingly well, showing very good repeatability. However, the pellet diagnostics expressely developed for this device did not observe intact pellets over 2 km/s. Recently a new arrangement was successfully tested, accommodating both a two-stage gun and a standard propellant valve on each barrel, allowing seamless switching between standard and high speed operation on any or all gun barrels; the cryogenic system was also improved with supplemental cooling by liquid helium. Injection speeds up to 2.6 km/s were obtained, but pellets seldom remained intact above 2 km/s. Optimization of power levels of the upstream and downstream heaters, which up to date have been used sparingly, in the next campaign could help in attaining integral pellets at higher speeds. *Sponsored in part by ENEA and by the D.O.E.   

Tritium Minority Heating by Ion Bernstein Waves in Ignitor

A promising scenario of minority heating of Tritium ions by Ion Bernstein Waves (IBW) coupled by mode conversion of fast waves in D(H) plasmas has been recently proposed.\footnote{C. Castaldo and A. Cardinali, \textit{ Phys. of Plasmas}, in press (2010)} The tritium ions are accelerated at energies high enough to increase significantly the DT fusion reactivity at relatively low temperature. It has been shown that breakeven can be reached considering a specific heating scenario for the JET machine. A similar heating scheme is analyzed for the Ignitor machine at reduced parameters. It is shown that 10 MW of ICRF power at $f = 91.6 \textnormal{ MHz}, N_{||}=3.6$ that are coupled as fast waves to plasmas at $B_T=9 \textnormal{ T}, I_p=6 \textnormal{ MA}, n_{e0}= 2 \times 10^{20} \textnormal{ m}^{-3}, T_{e0}=T_{i0}=8 \textnormal{ keV}$, with 25\% T, 40\% D, 35\% H concentration, are mode converted to IBW near the D-H hybrid resonant layer and are efficiently absorbed by tritium ions via cyclotron damping at $\omega =2\Omega_T$. The tritium ions are accelerated at energies of the order of 100 keV, where the the DT fusion reactivity peaks. As a result about 50 MW/m$^3$ of peak fusion power are obtained, and the expected fusion power is about 30 MW, with $Q =2$. The detailed comparison between equivalent scenarios in 50-50 D-T plasma is underway by means of the JETTO transport code.   

Design of an Integrated Plasma Control System and Extension of XSCTools to Ignitor

The performance of the integrated system for vertical stability, shape and plasma current control for the Ignitor machine has been assessed by means of the CREATE\_L linearized model of plasma response\footnote{R. Albanese, F. Villone, \textit{Nucl. Fusion} \textbf{38}, 723 (1998)} against a set of disturbances for the reference 11 MA limiter configuration and the 9 MA Double Null configuration. A new design, based on the methodology of the eXtreme Shape Controller (XSC) at JET, has been tested : by using all the shape control circuits with the exception of those used to control the vertical stability is possible to control up to four independent linear combinations of the 36 plasma-wall gaps. The results point out a substantial improvement in shape recovery, especially in the presence of a disturbance in $\slshape l_i$. The new shape controller can also automatically generate, via feedback control, new plasma shapes in the proximity of a given equilibrium configuration. The XSC Tools\footnote{G. Ambrosino, R. Albanese et al., \textit{Fus. Eng.\& Des.} \textbf{74}, 521 (2005)} have been adapted and extended to develop linearized Ignitor models including 2D eddy currents and to solve inverse linearized plasma equilibria.   

ICRH System, Physics and Burn Control for the Ignitor Experiment

The ICRH system for the Ignitor experiment is designed to operate over a broad frequency range (80-120 MHz), generating 16 down to 8 MW of power. The frequency band is consistent with the use of magnetic fields in the range 9-13 T. A study of the ICRH physics is presented for the reference maximum performance scenario, ($B_T = 13 \textnormal{ T}, I_p = 11 \textnormal{ MA}$) with particular emphasis on the control of the thermonuclear instability by means of ICRH. In the case where internal plasma modes may not be effective in saturating the thermonuclear instability at acceptable levels without external action, a scenario is considered where Ignitor is led to operate in a slightly sub-critical regime, by adding a small fraction of $^3$He to the nominal 50-50 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, and then increase the global plasma temperature via collision. The power deposition profiles on ions and electrons are obtained by means of a full wave code in toroidal geometry configuration and they are used as input data to solve the temperature evolution equation.   

Overview of the Levitated Dipole Experiment

The Levitated Dipole Experiment (LDX) investigates plasmas confined in the closed field line dipole magnetic geometry where the plasma stability is provided by compressibility and where plasma convection leads to peaked profiles and may allow for $\tau_E > \tau_p$. Recent experiments have demonstrated a substantial density pinch driven by low frequency interchange turbulence leading to a stationary density profile with near equal number of particles per flux tube. Over the past year, transient transport experiments using modulated ECRH and gas puffing have lent corroborating evidence for this result. Analysis of data from multi-channel photodiode arrays indicate that incoherent broadband turbulence is responsible for the turbulent pinch, while observed quasi-coherent turbulence exists with supercritical density gradients and provides insufficient transport to maintain stationary profile. Ongoing upgrades the the LDX diagnostic capability include the addition of a swept heterodyne interferometer to measure the peak density, additional interferometer channels at 90 GHz, and installation of a Thomson scattering diagnostic. In preparation for of the installation of a 1 MW ICRF transmitter, a time-of-flight neutral particle analyzer will be installed to measure ion temperature and initial ICRF antenna coupling experiments will be performed.   

LDX and the Density Pinch

We observe in LDX a strong, turbulence driven density\footnote{A. Boxer et al., Nature-Physics {\bf 6} (2010) 207. } and the resulting stationary density profile. A turbulent pinch is predicted by both MHD and kinetic theory. A turbulent pinch is also observed in tokamaks\footnote{D. Baker, M. Rosenbluth, PoP {\bf 5} (1998) 2936.}, but the effect is particularly strong in a dipole because the magnetic field falls strongly ($B\propto 1/R^3)$, there is no rotational transform (and therefore no ``passing" particles) and the turbulent modes are interchange-like. As a result, whereas for a tokamak the stationary density tends to fall as $\sim 1/q$ (i.e. a factor $\sim$3), in LDX the peak can rise a factor of $\sim$30 above the edge density. The stationary profiles are robust, as seen in experiments with a modulation of the heating power or of the edge fueling. Low frequency fluctuations are observed, both at the outer plasma edge and as core chordal measurements. Quasi-coherent fluctuations are also observed under the condition of low gas feed and in this circumstance the density can diverge from the stationary profile.   

High Power RF Heating in the LDX Experiment

Exploration of higher-density plasmas created with high-power RF heating is key objective of the next phase of the \urllink{LDX research program}{http://www.psfc.mit.edu/ldx/}. This poster describes the use of a 1 MW HF Band (4 to 26 MHz) radio-frequency transmitter in a two-part program. First, we will evaluate axisymmteric ($m = 0$) antenna and match-box designs and make low-power 1~kW measurements. Secondly, we will apply high power ($> 100$~kW) RF heating at a range of frequencies with the objective to create, sustain, and investigate high-density ($n > 10^{19}$~m$^{-3}$), high-beta dipole confined plasma with $T_i \approx T_e$. The RF heating expected in LDX has been modeled using full-wave electromagnetic calculations in realistic geometry and boundaries. Following the method of Jaeger and co-authors \footnote{Jaeger, {\it et al.}, \textit{Computer Physics Communications}, {\bf 40}, 33-64, (1986).}, we calculate the electric fields from both the near-field of the antenna and waves launched in the plasma. The linear antenna loading, reactive power flow, and heating deposition is calculated, and we predict acceptable loading throughout the HF band.   

Warm population measurements on the Levitated Dipole Experiment (LDX)

Magnetic flux measurements of the diamagnetic current in LDX indicate that a significant portion of the ECRH power absorbed by the plasma creates a warm population in addition to energetic hot electrons. We present measurements to characterize this population using a silicon drift detector (SDD) and several cadmium-zinc-telluride detectors (CZTs). The SDD measures the soft X-ray spectrum from 1-20 keV and can pivot to view different tangency radii within the plasma. The three CZT detectors measure the higher energy X-ray spectrum from 10-670 keV and view three different fixed tangency radii. Results show the presence of high-Z impurities as well as the expected non-Maxwellian distribution of ECRH heated electrons. We are also installing a time-of-flight diagnostic that will exploit charge exchange to measure the energy of the ion population. This diagnostic will be of particular interest in future experiments as we begin to heat the ions with a 1 MW HF Band (4 - 26 MHz) transmitter.   

ECRH in LDX with Many Microwave Frequencies

The large magnetic field range from 0.007 to 3.2 Tesla on closed flux surfaces around the LDX floating coil makes LDX uniquely capable of using many frequencies for electron cyclotron resonance heating (ECRH) to breakdown, build up, and sustain a core plasma. There are five sources installed with a combined injected power of 27 kW: two 2.45 GHz magnetrons at 2.5 and 1.9 kW, a 6.4 GHz, 2.5 kW klystron, a 10.5 GHz, 10 kW klystron, and a 28 GHz, 10 kW gyrotron. With all sources operating, D$_{2 }$plasma density has increased to new highs near 10$^{18}$ m$^{-3}$. Modeling with natural profiles shows strong ECRH absorption localized to discreet toroidal rings, each encompassing the plasma profile, that are located more inward with frequency. The relative size of the launched ECRH patterns to the absorption regions requires reflective trapping for complete absorption. Experimental observations show that higher frequencies are more efficient at generating density and lower frequencies are better at generating stored energy and energetic electrons.   

Modifying turbulence by driving interchange flows in a dipole-confined plasma

The Collisionless Terella Experiment (CTX) is a mechanically supported dipole magnet that studies interchange turbulence. Previous study\footnote{B.A. Grierson, M.W. Worstell, M.E. Mauel, {\it Phys. Plasmas} {\bf16} 055902 (2009)} revealed dynamics consistent with two dimensional turbulence. A hallmark of which is the presence of an inverse energy cascade from small to larger spatial scales. We report the results of application of electrostatic bias to experimentally alter the fluctuation spectrum via the inverse energy cascade. The bias is applied with a twelve point equatorial biasing array that can be configured to drive static and rotating interchange flow with azimuthal modes from $m=0$ to 3. We find that application of $m=3$ interchange drive causes a significant amplification of $m=1$ perturbations and an apparent reduction in turbulent dynamics. Feedback phase-controlled and constant frequency open-loop perturbations will be discussed as well.   

Plasma interchange velocimetry in a dipole-confined plasma with electrostatic perturbations

The Collisionless Terella Experiment (CTX) is a mechanically supported dipole confinement experiment aimed to understand the physics of strong interchange transport and flow. We report new observations and analyses using a unique polar imager diagnostic, a 96 point array of gridded energy analyzers spanning the entire plasma which measures flux-tube particle number. Inverting the flux-tube integrated continuity equation allows us to solve for the electrostatic potential of the plasma, which serves as the stream function for plasma flux-tube motion. Observed plasma dynamics in the high density regime are consistent with predicted two-dimensional turbulence and resulting particle convection. Applying electrostatic perturbations we drive specific modes and modify the turbulent spectrum. Additionally we present plans to install a 31 probe array at the plasma edge to measure both local transport and potential boundary conditions. Local transport can be directly compared to those calculated globally while the boundary conditions will improve the continuity inversion.   

Observation of plasma flows through the insertion and imaging of dust

We present plans for a new diagnostic aimed to measure the low-frequency convection fields inside a dipole plasma. Through the application of mono-disperse dust particles and high speed videography we can measure the perturbed velocity of falling dust grains deflected by the plasma electric field and viscous forces. The design is composed of a dust container positioned above the dipole plasma, which allows a controllable amount of micron-scale dust particle to sift through a orifice in the bottom, agitated by a piezoelectric transducer. Due to the low density of our plasma, the dominant forces on these particles are gravity and the electric fields in the chamber. We observe the motion of these dust particles via fast camera, and can calculate the perturbed velocity and acceleration. By observing the trajectories of dust grains of various diameters, we hope to estimate the strength of convection electric fields excited by radial biasing and to directly measure interchange flow.   

Python Graphical User Interface (GUI) for Control of the Levitated Dipole Experiment

The Levitated Dipole Experiment (LDX) is used to study the confinement properties of plasmas in a magnetic dipole field. In LDX a superconducting coil is levitated for up to 3 hours within a large vacuum chamber to produce the confining dipole field. The plasma experiments take place during this time, with $\sim $10 second plasma shots, one shot every $\sim $5 min. MDSplus software is used to run the experiment and store the data. The software is currently controlled by command line operations. Since levitation time is limited, it's important to maximize efficiency and accuracy of experimental operations. Here, we present a Graphical User Interface (GUI) to efficiently control the operation of the experiment. The need for a GUI that integrates the MDSplus data cycle, cell access control, and routine experimental parameter controls is necessary. The GUI program provides a simple method for monitoring and setting experiment parameters. Python is used as the primary language to run the commands. A program called XRCed distributed by wxPython works as a visual tool.   

Overview of the Maryland Centrifugal Experiment

MCX produces supersonically rotating plasmas in a mirror geometry with a radial electric field produced by a coaxial core biased at high voltage. MCX has achieved high density (n $>$ 10$^{20}$ m$^{-3})$ fully ionized plasmas rotating supersonically with velocities of $\sim $100 km/sec for times exceeding 8 ms. Centrifugal confinement of the plasma at higher mirror ratio has been unambiguously demonstrated with two IR interferometers and an axial array of diamagnetic loops. The results are compared with an ideal MHD equilibrium model and the agreement is excellent for a wide range of mirror ratio. MCX has now achieved ~: a) supersonic rotation; b) sheared velocity profiles; c) centrifugal confinement. A high-speed imaging camera has been installed to capture a single image per plasma discharge and reveal the shape of plasma-confining magnetic flux surfaces. A biasable annular limiter is planned to control the radial electric field at the plasma edge. Upgrade plans include more extensive diagnostics, a new core configuration, and an azimuthal B capability, with an emphasis on fluctuation studies.   

MHD Equilibrium and Diamagnetism of Rotating Plasmas in Shaped Magnetic Fields

A combination of diamagnetic and magnetic pick up loops external to the Maryland Centrifugal Experiment's (MCX) vacuum vessel measure changes in the local radial magnetic field and the averaged axial magnetic field. The measurements result in an axial profile of the rotating plasma's diamagnetism on a millisecond timescale, limited by the L/R time of the vacuum vessel. Additionally, two interferometers provide average density measurements and a multi-chord spectrometer estimates radial rotation and ion temperature profiles. Combining these measurements allows for comparison to MHD equilibrium found by numerically solving for a perturbative solution to the Grad-Shafranov equation including supersonic rotation. This comparison constitutes a test for the efficacy of centrifugal confinement, a central goal of the MCX experiment. Preliminary analysis shows remarkable agreement for the magnitudes and axial profiles of plasma diamagnetism across broad parameter variations. The addition of magnetic measurements inside plasma will also be described.   

Plasma Evolution Studies Using High-speed Imaging at the Maryland Centrifugal Experiment

A high-speed imaging camera has been installed at the Maryland Centrifugal Experiment (MCX) [R.F. Ellis, et al., Phys. Plasmas 12, 055704 (2005)], in order to capture a single image per plasma discharge with practical shutter speeds as fast as 200 ns. The camera captures visible light emitted by plasma-neutral interactions, and reveals the shape of plasma-confining magnetic flux surfaces. Changes in brightness profiles at different camera shutter speeds suggest plasma escapes the confining flux surfaces in bursts. Preliminary correlations with magnetic field, density, and discharge voltage measurements suggest that burst timescales are between a few to tens of microseconds. These bursts are conjectured to initiate at the mirror midplane, and then propagate axially towards the insulator ends. Imaging through various ports, stereoscopy techniques, spectroscopy, and correlations with other diagnostics are being used to test this hypothesis.   

Plasma Equilibrium in the Maryland Centrifugal eXperiment with variable axial temperature

Recent observations have shown that the centrifugal confinement in the Maryland Centrifugal eXperiment (MCX), seems to be better than that predicted by conventional MHD theory. For the magnitude of rotations achieved in MCX one expected a density ratio of about six between the central value and that measured at the mirror throat. Observations seem to indicate that this ratio is twelve, double of that predicted by theory. One possible explanation is that the temperature is not constant along a field line and that there may be an axial variation in the temperature. To take this variation into account we have developed a new relaxation code to determine the equilibrium density profile since the non-constant temperature case does not lend itself to an analytical solution of the equilibrium density. With knowledge of this new pressure profile one can then solve the Grad-Shafranov equation with flow to compute the perturbed magnetic field and then compare it with the recent observations obtained from the axially located diamagnetic loops on MCX.   

Plasma Limiter Studies at the Maryland Centrifugal Experiment

An annular limiter experiment is being designed and constructed at the Maryland Centrifugal Experiment (MCX). This experiment has been motivated by the improved performance of the Gas Dynamic Trap using a biased limiter to induce vortex flows [A. A. Ivanov, et al. paper IAEA-CN-94/EX/P5-12 at Conference ``Fusion Energy-2002'']. The limiter may be biased with respect to the MCX vacuum vessel to attempt control over the radial electric field at the plasma edge. Measurements of the radial electric field in the edge region are planned using a Langmuir probe. Early results on the limiter's effects on MCX's performance will be reported.   

Spatial Structures and Temporal Evolutions of High-Beta Plasma in RT-1

The Ring Trap-1 (RT-1) device can sustain an ultra high beta plasma in the artificial magnetosphere which is realized by the superconducting magnet levitated in the vacuum chamber. By optimizing the operation conditions, we have achieved the confinement of the high beta plasma whose diamagnetic signal is 4.0 mWb, which we estimate that the maximum local beta value exceeds 70$\%$. In order to improve the estimate accuracy of the plasma pressure and to evaluate the temporal evolution of the pressure profiles, we have developed a fast Hall probe array in RT-1. In contrast to the existing magnetic measurement located outside the magnetic separatrix on the equatorial plane, the new system is installed from a bottom port of RT-1, close to the plasma boundary, is more sensitive to the pressure of the plasma near the dipole coil. We have observed not only an equilibrium structures of a stably generated plasma but also the time evolution of the pressure profile during the events which involve a change of the confined energy such as the ``afterglow'' or a mode transition.   

Imaging X-Ray Crystal Spectrometers (XCS) for Measurement of Ti and Flow-Velocity (v) Profiles in ITER

A US-ITER team is designing a spatially resolving XCS for Doppler measurement of ion temperature (Ti) and flow-velocity profiles of impurities (W, Fe) in ITER with $\sim $7 cm (a/30) spatial and 10-100 ms temporal resolution. The imaging XCS uses a spherically bent crystal and 2d pixel array x-ray detectors to achieve high spectral resolving power ($>$6000) in the horizontal dimension and spatial imaging vertically. Two XCS arrays will measure Ti and both poloidal and toroidal rotation velocity profiles. Simultaneous measurement of many spatial views permits tomographic inversion for determination of local parameters. The design of the ITER instrument and predictions of its performance, as well as measurements and data analysis techniques for prototype instruments on the Alcator C-Mod and Chinese EAST tokamaks will be presented.   

Collaborative Investigations on the Gas Dynamic Trap

The Gas Dynamic Trap (GDT) may represent a practical compact fusion neutron source for materials testing. To explore this possibility we have proposed U.S. participation in experimental, theoretical, and computational studies of stability and energy transport on the Gas Dynamic Trap (GDT) experiment at the Budker Institute in Novosibirsk, Russia. Electron temperature is a critical parameter in the gas dynamic trap (GDT) for high beta operation but, in addition, 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. Electron temperature profiles will be measured by fielding an expanded Thomson scattering diagnostic. Beta limit and stability studies will be facilitated primarily with internal magnetic field measurements via a Motional Stark Effect diagnostic. Computational studies will utilize the ICEPIC code, which contains an extensive set of physics capabilities. This work performed under the auspices of the U.S. DoE by LLNL under Contract DE-AC52-07NA27344.   

Recent Experiments on the Gas Dynamic Trap Device

The Gas Dynamic Trap (GDT) is an axially symmetric mirror device. The solenoid has a mid-plane magnetic field of 0.3 T and a mirror ratio 25-30. Two ion components are confined in the GDT with electron temperature up to 250 eV.. The first ion component is the warm collisional plasma confined in the gas-dynamic collisional regime. The second component is fast ions produced by 20 keV neutral beam injection with an anisotropic distribution in velocity space. The fast ion density peaks near their turning points. The ratio between plasma pressure and the vacuum magnetic field pressure reaches 0.55 at these regions. One of the key issues of linear machines is longitudinal losses. Suppression of thermal conductivity along the magnetic field-lines to the end walls was demonstrated in GDT. Experiments with one ambipolar end-plug were carried out. Longitudinal losses decreased 5-fold with an ion density in the end-plug only 1.5 times higher than in central cell. Another key issue is MHD-stability. Convective losses were suppressed by the ``vortex confinement'' method. Shear flow produced by applying a voltage to the plasma edge lead to the nonlinear dissipative saturation of flute-type oscillations   

A Fusion Neutron Source for Materials and Subcomponent Development and Qualification

The magnetic-mirror based Gas Dynamic Trap (GDT) device in Novosibirsk Russia is developing the physics basis for a compact DT Neutron Source (DTNS) for fusion materials and subcomponent development as well as a driver for a fusion-fission driver for nuclear waste burn-up. The efficiency of this concept depends on electron temperature. This paper describes past experimental results as well as methods and prospects to further increase the electron temperature.   

Highly Radiative Shock Experiments driven by GEKKO XII

In this paper, recent experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Using the GEKKO XII laser, highly radiative shocks generated with intensity on target up to 10$^{15}$ W/cm$^{2}$ were produced. Our original gas cell design sustains a 0.1 bar pressure, lower than previously. The radiative shocks generated are high-Mach number shocks with a strong coupling between radiation and hydrodynamics. Several visible diagnostics were implemented in order to determine shock velocity, temperature and ``precursor'' electron density. It is the first time that velocities up to 250 km/s are observed in a low-density gaz. Preliminary comparison with 2D radiative hydrodynamic simulations will be discussed.   

Investigation of radiative-shock structure in x-ray-driven shock-tube simulations

The Center for Radiative Shock Hydrodynamics (CRASH) seeks to improve the predictive capability of models for shock waves produced in xenon when a laser is used to shock, ionize, and accelerate a beryllium plate into a xenon-filled shock tube. These shocks, when driven above a threshold velocity of about 100 km/s, become strongly radiative and convert most of the incoming energy flux into radiation. Among the interesting features observed in CRASH experiments is the formation of wall shocks, which result from ablation of the polyimide walls of the shock tube. This ablation is due to heating caused by a radiative precursor that propagates ahead of the primary shock. We show here the results of simulations studying the formation and evolution of radiative shocks and associated features. We find that wall ablation plays an important role in shaping the evolution of wall shocks and, as a consequence, directly influences the evolution of the primary shock and the system as a whole.   

Early-Time Radiation-Hydrodynamic Modeling of Radiative Shock Experiments

The Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan is developing an AMR radiation-hydrodynamics code that currently requires input from another code, Hyades, in order to model laser driven experiments. Hyades is a Lagrangian radiation-hydrodynamics code with the capability of modeling laser deposition, whose results are passed to CRASH as initial conditions. The physics models in Hyades have a large number of tunable parameters, which need to be calibrated to a particular problem. Results from shock breakout experiments performed on the OMEGA Laser at LLE can be used to improve this calibration, which then leads to an improvement in the predictive capability of the CRASH code. The results of a series of Hyades simulations of the radiative shock problem in both 1D and 2D are presented. This research was supported by the DOE NNSA under the Predictive Science Academic Alliance Program by grant DEFC52- 08NA28616.   

Characterization of initial state of radiative shock experiments on Omega

Radiative shocks, which are in a regime where most of the incoming energy flux is converted into radiation, can be created in a laboratory using a high-powered laser. We have performed experiments on the Omega Laser that irradiate a 20 $\mu $m thick Be disk with $\sim $4 kJ of laser energy. This shocks and accelerates the disk into a Xe or Ar gas at 1.1 atm. These radiative shocks can reach up to 130 km/s. Diagnostics for this experiment have included x-ray radiography, x-ray Thomson scattering, optical pyrometry, and UV Thomson scattering. A 3D, MHD code with a radiation solver is being developed at the Center for Radiative Shock Hydrodynamics (CRASH) that will model this experiment. The laser deposition is modeled using the Hyades code. The results from the Hyades simulation are used to initiate the CRASH code. It is important for this modeling effort that the initial pressure deposited by the laser and the initial state of the Be plasma be well characterized. A recent experiment used VISAR and optical pyrometry for early time diagnosis of this initial state of the Be. These results will be presented. Supported by the US DOE NNSA under the PSAAP by grant DE-FC52-08NA28616.   

Reverse Radiative Shock Experiments Relevant to Accreting Stream-Disk Impact in Interacting Binaries

In many Cataclysmic Binary systems, mass onto an accretion disk produces a ``hot spot'' where the infalling flow obliquely strikes the rotating accretion disk. It has been argued (Armitage {\&} Livio, ApJ 493, 898) that the shocked region may be optically thin, thick, or intermediate, which has the potential to significantly alter its structure and emissions. We report the first experimental attempt to produce colliding flows that create a radiative reverse shock. The experiment will have occurred at the Omega-60 laser facility in August 2010. Obtaining a radiative reverse shock in the laboratory requires producing a sufficiently fast flow ($>$100 km/s) within a material whose opacity is large enough to produce energetically significant emission from experimentally achievable layers. We will discuss the experimental design, the available data, and our astrophysical context. Funded by the NNSA-DS and SC-OFES Joint Prog. in High-Energy-Density Lab. Plasmas, by the Nat. Laser User Facility Prog. in NNSA-DS and by the Predictive Sci. Acad. Alliances Prog. in NNSA-ASC, under grant numbers are DE-FG52-09NA29548, DE-FG52-09NA29034, and DE-FC52-08NA28616.   

Quantifying Uncertainties in Modeling of Radiative Shocks Using Coupling of HYADES and CRASH

The Center for Radiative Shock Hydrodynamics (CRASH) is a computational center at the University of Michigan focused on modeling radiation-hydrodynamics and developing a quantified assessment of predictive capability of the CRASH code. Critical to the later goal is the utilization of statistical tools for uncertainty quantification (UQ) of both the models and the experiment. In order to model laser experiments, the CRASH code must be coupled with HYADES, a 1D and 2D Lagrangian radiation-hydrodynamics code with a laser energy deposition model. Results from a batch of 1D simulations, initialized in CRASH using output from HYADES, to model a radiative shock experiment carried out on the Omega laser facility in October 2008, will be presented. The batch is designed to investigate experimental and modeling uncertainties and do a sensitivity analysis of diagnosable features to the system parameters. 2D simulations of radiative shock experiments utilizing 2D HYADES (h2d) to initialize CRASH will also be reported.   

Design of a spherically symmetric standing accretion shock experiment in high-energy density plasmas

Standing accretion shocks (SAS) arise when the expansion of a shock front stalls and can no longer sustain its development. The aim of our study is to identify feasible conditions and parameters for an experimental system that is able to capture the essential physics processes required for SAS development. Analytic methods and high-resolution hydrodynamic simulations in multidimensions are used to investigate the design. Our framework reproduces the results of Blondin \& Mezzacappa obtained in the supernova SAS context, and has characterized system values that are required to produce realistic laboratory scenarios. Our results highlight key differences between the experimental setup and astrophysical environment, and provide design parameters for future experiments aimed at probing core-collapse supernova explosions.   

Development of a Pre-Ionization Method and X-Ray Imaging System for the Caltech Laboratory Plasma Experiments

The Taylor relaxation of plasmas at the Caltech spheromak experiment is qualitatively similar to the evolution of plasma jets emitted from protostars and active galaxies. However, the parameter regimes which can be accessed by the laboratory experiment are limited by the Paschen criterion for the breakdown of hydrogen in a DC electric field, which sets a lower bound on the initial neutral gas density that is required to achieve plasma formation. Pre-ionizing hydrogen in the gas nozzles before discharging the experiment's high voltage capacitors would allow for the formation of lower density, faster jets. We are investigating pre-ionization schemes using a battery-powered 13.56 MHz RF source capable of producing over 3.5 kW pulsed output. RF power may be efficiently coupled to the plasma through the excitation and subsequent damping of helicon waves. We also report on the development of a UV/x-ray imaging system for the solar coronal loop experiment at Caltech. The imaging system is sensitive to photons with energies 5 eV and above and is gated for exposure times as short as 10 ns.   

Behavior of irradiated low-Z walls and adjacent plasma

In many laboratory astrophysics and high-energy-density experiments, a source of soft x-rays irradiates a low-Z surface. This happens in ICF capsules, in hohlraum- driven experiments, and in radiative shock experiments. There is often a background gas, as for example in ongoing experiments at the National Ignition Facility in which a gas-filled hohlraum is used to drive an equatorial package. In such systems, the soft x- rays penetrate and heat the gas and sustain the temperature of the material ablated from the surface, forming the isothermal rarefaction, before being absorbed at the heat front. The resulting high pressure drives a shock into the dense wall or package material. We discuss the overall structure of such a system and the errors introduced when it is under-resolved as may be necessary in simulations of complex laser targets.   

Time-dependent atomic kinetics modeling of a neon photoionized plasma experiment at Z

We present a modeling study of time-dependent atomic kinetics for a neon photoionized plasma. The neon atomic model considers several ionization stages of highly-charged neon ions as well as a detailed structure of non-autoionizing and autoionizing energy levels in each ion. Atomic processes populating and de-populating the energy levels consider photoexcitation and photoionization due to the external radiation flux, and spontaneous, stimulated and collisional atomic processes including plasma radiation trapping. Relevant atomic cross sections and rates were computed with the FAC code. The calculations are performed at constant particle number density and driven by the time-histories of temperature and external radiation flux. These conditions were selected in order to resemble those achieved in current photoionized plasma experiments at the Z facility. We also calculate transmission spectra in an effort to identify time-dependent effects in observed spectral features.   

Improving Target Characterization for Laboratory Astrophysics Experiments

We have fabricated and characterized targets for laboratory astrophysics since 2003, and have made improvements focusing on characterizing particular target features and their variances. Examples of measurements include machined features, material thickness and uniformity, location and thickness of glue, and mating conditions between adjacent materials. Measurements involve new technology and characterization methods, such as pre-shot radiography. More accurate characterization also leads to improvements in fabrication techniques, and helps integrate new technology into our build process. Quantifying variances more precisely also helps us better evaluate each fabrication method for both accuracy and consistency. We present these characterization methods and their impact on fabrication. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number DE-FG52-09NA29034.   

Plasma Astrophysics in the Laboratory with Accelerator Beams

An ultra-relativistic electron/positron or ``fireball'' beam interacting with a laboratory plasma is subject to the current filamentation instability (CFI). In the near future, ultra-short ($<$100fs), ultra-relativistic (25GeV) electron and positron bunches will become available at the SLAC FACET facility. These bunches are accelerated one half period apart and overlapped in space and time near the final focal point. With an equal number of particles, these two bunches form a neutral, field- and charge-free beam that we call a relativistic fireball beam. The interaction of this beam with laboratory plasma is rather different from that of either the electron or positron bunch alone. No large wakefields are generated. Instead the beam is subject to the CFI, which results in transverse filamentation, accompanied by strong plasma density modulation, generation of large magnetic fields, and generation of radiation that can be detected. This situation is similar to that of space relativistic plasmas, e.g. from supernovae, interacting with the interstellar medium. The CFI generates the magnetic field, and the charged particles emit radiation as in gamma ray bursts afterglow. Detecting the CFI and measuring it characteristics will validate astrophysical models. CFI may also play an important role in the propagation of hot electrons in plasmas for example in the fast igniter concept of ICF. We describe the CFI and the experiment to detect it.   

Studies of laser-driven isentropic compression of iron in the context of geophysics

The study of iron using dynamic compression paths yielding parameters different from that achieved on the principal Hugoniot might allow to access parameters relevant for the understanding of the solid-liquid phase transition in the Earth core (330 GPa, $\approx $ 5000 K). Beside the geophysical interest, dynamic compression allows to study the dynamics of the alpha-epsilon phase transition, as compression characteristic times are comparable with reaction kinetics. We have performed laser-driven ramp compression experiments on iron samples using the LULI laser facility. Different pressure ramp shapes and target samples will be presented. These results are also important to design future experiments using very large-scale facilities, which would allow to explore pressure-temperature conditions relevant to terrestrial-type exoplanets, which were recently discovered.   

Implementation of Laser Energy Deposition in FLASH

FLASH is a highly capable, fully modular, extensible, and professionally managed code widely used for the simulations in astrophysics and other communities. Over the past year we have been adding capabilities to FLASH for use by the academic HEDP community. Laser energy deposition is one of key capabilities to be added in the process. In this work we present the algorithmic development for laser energy deposition and the results of verification tests. The path of lasers through matter is approximated as rays using the principles of geometric optics. We exploit the infrastructure for Lagrangian tracer particles already available in FLASH, treating rays logically as trajectories of independent particles. The required data structures are very similar and the nature of motion through the domain can be treated using the same infrastructure. We take the laser energy to be deposited via the inverse-bremsstrahlung process.   

Implementation of 3T Plasma With Electron Energy Advection in \texttt{FLASH}

FLASH is a highly capable, fully modular, extensible, professionally managed Eulerian hydrodynamic code with a wide user base. Recently we have begun adding capabilities to FLASH, to make it a highly capable code for simulations in the academic HEDP community. One of the capabilities we are adding is the ability to simulate a 3-temperature, single-fluid plasma consisting of electrons, ions, and radiation (in the diffusion approximation) that can exchange, evolve, and conduct heat. Here we describe the development of this capability and the results of verification tests to which we subject it. A key question about this approximation is how to close the dynamical system in such a way as to deal consistently with shock discontinuities. In addition to conservation of mass, momentum, and energy, and advection of radiation, one must choose an additional condition to determine the evolution. One possible choice is the conservative advection of electron entropy (up to LTE processes of heat exchange, evolution, and convection), which reproduces the classical plasma shock approximation of Shaframov (1957) under shock conditions. We describe the implementation and testing of this closure choice.   

Implementation of An Implicit Unsplit Staggered Mesh MHD Solver in FLASH

FLASH is a publicly available community code designed to solve highly compressible multi-physics reactive flows. We have been adding capabilities to FLASH to make it an open science code for the academic HEDP community. A key need is to provide a computationally efficient time-stepping integration method that overcomes the stiffness that arises in the equations describing a physical problem when there are disparate time scales. To address this problem, we are developing a fully implicit solver based on a Jacobian-Free Newton-Krylov implicit formulation. The method has been integrated into a robust, efficient, and high-order accurate Unsplit Staggered Mesh MHD (USM) solver. We are also integrating this solver into an anisotropic Spitzer-Braginskii conductivity model to treat thermal heat conduction along magnetic field lines, and into a treatment of the Biermann Battery effect that accounts for spontaneous generation of magnetic fields in the presence of non-parallel temperature and density gradients.   

Hydrodynamic Instability Test Problems in CRASH

We present the results of hydrodynamic instability simulations using the current version of the CRASH code. In particular, we concentrate on the early-time behavior of Rayleigh-Taylor and Richtmyer-Meshkov instabilities as a necessary validation and verification step before exploring the behavior of Rayleigh-Taylor instabilities in laser experiments relevant to supernovae. We compare the quantitative growth rates calculated based on the extracted features of the test runs with the analytical and semi-analytical solutions, as well as with previous results with other hydrodynamic simulation packages. In addition to test runs replicating the parameters used in previous studies, we also conducted systematic surveys of slices of the parameter space where analytical solutions are available using different simulation resolutions where computational resources permitted. We will discuss any systematic errors discovered in the CRASH test runs and their plausible causes.   

Laboratory experiments of supersonic flows through clumpy environments

Supersonic flows through heterogeneous environments are common in astrophysics as evidenced by high resolution Hubble Space Telescope images of a variety of astrophysical objects, including supernova remnants and stellar jets. In many instances, the imaged flows exhibit a complex morphology consisting of multiple clumps, bow shocks, and filamentary structure extending over a range of spatial scales. To gain a better understanding of the dynamics occurring in such multi-clump flows, scaled laboratory experiments are being carried out at the Omega Laser Facility. In these experiments, a laser pulse is used to heat a halfraum to indirectly drive a near planar shock through a target that typically consists of many small dense spheres embedded in lower density foam. The evolution of the target is then imaged using x-ray radiography. Targets have been designed to span the parameter space of clump number and clump size distribution, as well as investigate the quantitative differences in shock propagation through a clumpy target with that of a uniform target of the same average density. An overview of the experiments and comparison with simulations will be presented.   

Laboratory studies of active space experiments

Laboratory experiments have been conducted on the formation of diamagnetic and plasma cavities in collisionless flowing plasma streams interacting with stationary plasma structures. Previous laboratory experiments using a purely magnetized target successfully created a cavity much smaller than the ion Larmor radius. Similar sub-ion Larmor orbit radii cavities are observed on the Moon and on asteroids like Ida and Gaspra. Active space experiments such as AMPTE (Active Magnetospheric Particle Tracer Explorer) conducted in space also resulted in the formation of a small scale diamagnetic cavity. We have conducted laboratory experiments that provide a more controlled environment to investigate interacting plasmas. Results are presented of investigations of cavities in a laboratory supersonic flowing plasma.   

Experimental studies of radiatively cooled supersonic plasma jets produced in wire array z-pinches

We will present results of recent experiments with radiatively cooled supersonic plasma jets performed on the pulsed power MAGPIE facility (1.5MA, 250ns) at Imperial College. The jets are produced by the plasma ablated from the wires arranged in conical or radial configurations. Convergence of the flow on the axis of symmetry of the system produces plasma jets with dimensionless parameters (Mach number $\sim $20, cooling parameter $\sim $1) similar to those in proto-stellar jets, and the flow has high Reynolds number ($>$10$^5$). We will present measurements of the jet parameters obtained with laser and XUV diagnostics providing high spatial resolution, and will discuss how this set-up can be scaled to 20MA Z facility.   

Spike morphology in supernova-relevant hydrodynamics experiments

This presentation describes experiments performed on the Omega and Omega EP lasers exploring the 3D Rayleigh-Taylor instability at a blast-wave-driven interface. The laser irradiates a plastic disk and creates a planar blast wave, which then crosses the interface between the disk and a lower-density foam, inducing the Rayleigh-Taylor instability. The plastic disk has an intentional pattern machined at the plastic/foam interface. This seed perturbation is three-dimensional with a basic structure of two orthogonal sine waves with a wavelength of 71 $\mu $m and amplitude of 2.5 $\mu $m. Interface structure has been detected under these conditions using x-ray radiography, and some of the resulting data will be shown. Current experiments are further examining the features of the unstable interface using proton radiography.   

Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes

The Plasma Bubble Expansion Experiment (PBEX) is conducting laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun ($\sim $10 kV, $\sim $100 kA, $\sim $2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. Experimental data from plasma bubble injection into a background plasma, particularly magnetic probe measurements, will be discussed. \\[4pt] [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).   

Radiation from sub-Larmor scale magnetic fields

Spontaneous rapid growth of strong magnetic fields is ubiquitous in high-energy density environments ranging from astrophysical sources and relativistic shocks, to reconnection, to laser-plasma interaction laboratory experiments, where they are produced by kinetic streaming instabilities of the Weibel type. Relativistic electrons propagating through these sub-Larmor-scale magnetic fields radiate in the jitter regime, in which the anisotropy of the magnetic fields and the particle distribution have a strong effect on the produced radiation. We present the general theory of jitter radiation, which includes (i) anisotropic magnetic fields and electron velocity distributions, (ii) the effects of trapped electrons and (iii) extends the description to large deflection angles of radiating particles thus establishing a cross-over between the classical jitter and synchrotron regimes. Our results are in remarkable agreement with dedicated particle-in-cell simulations of the classical Weibel instability. Particularly interesting is the onset of the field growth, when the transient hard synchrotron-violating spectra are common, which can serve as a distinct observational signature of the violent field growth in astro sources and lab experiments. It is also interesting that a system with small-scale magnetic turbulence fields tends to evolve toward the small-angle jitter regime. (This work is supported by DE-FG02-07ER54940, AST-0708213, NNX-08AL39G.)   

Flow Generation in the Plasma Couette Experiment

One goal of the Plasma Couette Experiment (PCX) is to study the magnetorotational instability (MRI), a fundamental mechanism in astrophysical accretion disks. Local linear stability analysis suggests that densities of 10$^{12}$ cm$^{-3}$ and velocities of 10 km/s are sufficient for onset of MRI. In PCX, plasma is produced either by a LaB$_6$ cathode, or by electron cyclotron resonance heating and is confined by a cylindrical, axisymmetric, highly localized ring cusp magnetic field at the boundary. Preliminary LaB$_6$ plasmas have already achieved Te=10 eV and n=5x10$^{10}$ cm$^{-3}$ with only 400 W discharge power. To create the differential rotation necessary to study MRI, electrode rings between the magnets are biased to induce ExB rotation. Mach probe measurements indicate that the azimuthal plasma flow velocity reaches 2 km/s with 50{\%} modulations, depending on distance from the electrodes. This suggests the presence of diamagnetic flows due to the density gradient in the multicusp field. Controlling the plasma rotation profile with the electrodes depends critically on electrode location and the efficiency of velocity transfer through viscous effects.   

Prototype Plasma Dynamo Experiments

The Madison Plasma Dynamo Experiment (MPDX) is under construction to explore the self-excitation processes of a range of astrophysical dynamos. NIMROD simulations of von K\'arm\'an flow, in which the upper and lower hemispheres of the plasma are spun in opposite directions, have shown that the resulting two vortex flow can produce a dynamo when the magnetic Reynolds number is sufficiently high. This poster discusses prototype experiments on the Plasma Couette Experiment (PCX) to create von K\'arm\'an flow. The PCX (like the MPDX) uses an axisymmetric multicusp plasma confinement scheme that works in tandem with electrodes of alternating bias to create flow at the plasma boundary via ExB drift. This poster will review the theory with an emphasis on requirements on the plasma parameters and then show that the measured plasma parameters ($n_e \approx 10^{17}$ m$^{-3}$, $T_e \sim $ 10 eV) and flow speeds of 10 km/sec are high enough to self-excite, but are in a regime in which Hall MHD will likely be important. Higher densities (possible with higher power LaB6 cathodes) will be required to operate in the MHD regime. Work supported by NSF.   

Laser Induced Fluorescence Diagnostic for the Plasma Couette Experiment

The Plasma Couette Experiment (PCX) at U. Wisconsin-Madison consists of a rotating high-beta plasma and is well-suited to the study of flow-driven, astrophysically-relevant plasma phenomena.~ PCX confinement relies on alternating rings of 1kG permanent magnets and the rotation is driven by electrode rings, interspersed between the magnets, which provide an azimuthal ExB. I will discuss the development of a laser-induced fluorescence diagnostic (LIF) to characterize the ion distribution function of argon plasmas in PCX.~ The LIF system--which will be scanned radially--will be used to calibrate internal Mach probes, as well as to measure the time-resolved velocity profile, ion temperature and density non-perturbatively.~ These diagnostics will be applied to study the magneto-rotational instability in a plasma, as well as the buoyancy instability thought to be involved in producing the solar magnetic field. This work is supported by NSF and DOE.   

Strategies for Observing Self-excitation in the Madison Dynamo Experiment

In the Madison Dynamo Experiment(MDE) two counter-rotating impellers drive a turbulent flow of liquid sodium in a one meter-diameter sphere. One of the goals of the experiment is to observe the spontaneous generation of magnetic field. Initial runs of the MDE saw intermittent bursts of a transverse dipole field similar to the induced field predicted by laminar kinematics, but no sustained self-excited field was observed. This poster will present recent results from the MDE after an equatorial baffle was installed to stabilize the position of the shear layer between the two counterrotating hemispheres and to help in the reduction of of large-scale turbulence and the motors were run up to maximum power. Required motor power indicates that the baffle has decreased the amount of turbulence in the flow. When run up to full power still no self-excited dynamo was observed, but there was significant amplification of the transverse dipole field with extended decay rates indicating we may be approaching the dynamo threshold. Future modifications to the experiment will also be presented exploring a subcritical dynamo transition by supplying a sufficiently strong magnetic field and the addition of poloidal baffles to optimize the helicity of the mean flow. This work is supported by the NSF/DOE partnership in plasma physics.   

Reduction of Turbulent Diamagnetism in the Madison Dynamo Experiment

The dynamo effect is a magnetic instability whereby a flowing conductor generates a magnetic field such as those seen in the Earth and Sun. The Madison Dynamo Experiment (MDE) is a 1 m diameter sphere filled with liquid sodium that aims to produce this effect in a flow driven by two counter rotating impellers. Previous experiments on the MDE demonstrated an induced axisymmetric magnetic dipole counter to the applied axisymmetric dipole. An antidynamo theorem exists that shows the observed diamagnetism is impossible in a two vortex flow, and is thus associated with a turbulent $\mathcal{EMF}$. This poster shows results from a new campaign with an equatorial baffle installed that drasically diminishes the turbulent diamagnetism. Spherical harmonic decomposition of the induced field also shows a reduction of higher order magnetic modes associated with three mode coupling between the applied field and large scale velocity fluctuations. Numerical simulations of the sodium flow with and without baffles also indicate the possibility of reduced hydrodynamic turbulence while maintaining a two vortex flow.   

The role of system-scale turbulence on MHD activity in the Madison Dynamo Experiment

The Madison Dynamo Experiment studies the onset conditions for magnetic field growth in a turbulent flow of liquid sodium and is investigating the turbulent electromotive force (EMF) $\varepsilon=\left \langle \widetilde{v} \times \widetilde{b} \right \rangle$. This work analysis the influence of a recently installed equatorial baffle to reduce the largest scale turbulent eddies in the flow. The averaged magnetic fluctuations drop about 20\%. A spherical harmonic decomposition of the magnetic field indicates a reduction of the largest scale magnetic fluctuations, consistent with an unmeasured reduction of the large-scale velocity fluctuations. Amplification of a transverse seed magnetic field (the expected dynamo eigenmode) show a gain of about 50\%, in contrast to experiments without the baffle which had negligible gain. These observations may also indicate a reduction of the beta-effect. A two-axial velocity probe will provide velocity fluctuations by measuring potential differences in a uniform field of a small permanent magnet. In combination with Hall sensors detailed investigations of the local EMF are possible. This work is supported by the NSF/DOE partnership in plasma physics.   

Status of the Madison Plasma Dynamo Experiment

Construction is underway to build a new experimental facility for investigating self-generation of magnetic fields in plasma and a broader range of flow driven MHD instabilities. The Madison Plasma Dynamo Experiment (MPDX) consists of a 3 meter diameter spherical vacuum chamber lined with a series of high strength neodymium permanent magnet rings in a cusp confinement geometry which provides for a large, unmagnetized and hot plasma. Plasma will be produced by a combination of lanthanum hexaboride cathodes and electron cyclotron heating. The plasma will be stirred from the magnetized edge via electrode and ExB flows. This poster will (1) give an overview of the physics goals and required plasma parameters, (2) describe the engineering design of the facility including laboratory infrastructure, vacuum chamber, diagnostics, and heating systems, and (3) give a status report on the construction schedule. The construction is being funded by the NSF Major Research Instrumentation program.   

Observation of large-scale velocity fluctuations in the Princeton MRI experimen

The Princeton MRI Experiment is a modified Taylor-Couette device with a GaInSn working fluid used for the study of rotating MHD flows. A recently-installed Ultrasound Doppler Velocimetry (UDV) system allows the measurement of internal fluid velocities. Starting from both hydrodynamically stable and hydrodynamically unstable background flow states, large-scale, large-amplitude, coherent, nonaxisymmetric velocity fluctuations have been observed when a sufficiently strong magnetic field is applied. The presence and saturated amplitude of these fluctuations is dependent on both rotation speed and magnetic field strength. The fluctuations are absent in regimes where the magnetorotational instability is expected to be observed. Theoretical investigations of these fluctuations using linear stability analysis and nonlinear 3-D simulations are ongoing. Measurements from the UDV diagnostic and from external magnetic diagnostics will be presented.   

Overview of recent results from the Princeton MRI experiment

The Princeton MRI experiment has been constructed to study the magnetorotational instability (MRI), the mechanism believed to be responsible for the transport of angular momentum in accretion disks. The MRI can be excited when a vertical magnetic field is applied to an electrically conducting fluid with a radially-decreasing azimuthal velocity profile. For this experiment, such a velocity field is generated in a Taylor-Couette apparatus with independently-rotating split endcaps. The working fluid is the gallium eutectic GaInSn. When an axial magnetic field is applied to the experiment, the hydrodynamic azimuthal velocity profile, as measured using an ultrasonic velocimetry system, is modified. The ability to fine-tune the resulting azimuthal profile, by modifying the end-cap ring speeds, and consequently achieve an ideal Couette azimuthal profile, is presented. Results from a global-mode MRI instability analysis, based on an ideal Couette azimuthal profile, is presented, indicating our operational proximity to instability. Magnetic perturbations are measured using an array of Mirnov Coils, from which the large-scale structure of the induced magnetic field is reconstructed. The latest results from the search for the MRI will be presented.   

A method for minimizing secondary flows in Taylor-Couette experiments

The Princeton MRI Experiment is a Taylor-Couette device with differentially rotatable endcaps which enable significant reduction of secondary (poloidal) flows. The experimental goal of this project is the observation of the magnetorotational instability (MRI) in a rotating liquid metal with an applied axial field. It is expected that the MRI will be most clearly observed in cases where the the secondary flow is minimized. When the system is optimally tuned, hydrodynamic experiments show remarkable agreement between the azimuthal rotation profile and the ideal Couette profile, a state where the rotation profile is determined solely by the viscous force. This presentation examines how the boundary conditions modify the bulk flow. We present a model of secondary flow generation due to small axial pressure gradients; minimization of large scale secondary flow (Ekman circulation) occurs when the fluid pressure from the ideal Couette rotation balances the fluid pressure near the axial boundaries. Model predictions generally agree with experiments and will be compared with calculations from the finite element engineering code ANSYS and the compressible MHD code MINERVA. We will present design parameters of a new experiment for the study of purely hydrodynamic turbulence with an optimized geometry based on these principles.   

Study of the equilibrium, stability and magnetic self-organization of line-tied toroidal plasma discharges

A set of electrodes are inserted into MRX (1) to generate line-tied toroidal plasmas which can be regarded as flux ropes. The 3-D structure of these plasmas is monitored by a fast framing camera and magnetic probes (2). Time resolved measurements of discharges with peak currents of 10--30 kA reveal that both stable and unstable flux ropes can be formed with their ends line-tied to the electrodes. It is found that the magnetic tension force of the toroidal field lines plays an important role in these equilibria. Using the $q$ value, which describes the rotational transform of field lines, the stability condition for external kink modes is found to be consistent with the Kruskal-Shafranov limit with modified line-tied boundary conditions. Additionally, internal relaxation events are observed even after the flux rope stabilizes against the external kink mode. The basic features of the self-organization events will also be discussed. (1) M. Yamada et al, Phys. Plasmas, v4,1936 (1997), (2) E. Oz et al: This conference.   

Study of Disruptive Current Layers in the Magnetic Reconnection Experiment (MRX)

One of the key open questions in magnetic reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. Comparisons between fully kinetic 2-D simulations of the Magnetic Reconnection Experiment (MRX) and experimental data indicate that three-dimensional dynamics, such as current layer disruptions recently observed in MRX, may play a key role in resolving an important discrepancy in the reconnection rate and layer width [1,2,3]. These disruptions are often associated with fluctuations in the lower hybrid frequency range and a rapid local reconnection rate. Some discharges also display ``O-point'' signatures consistent with magnetic island like structures. The present research explores the relationship between the disruptions and fluctuations in the context of the reconnection rate problem. Comparisons with 3-D simulations are ongoing in order to determine what key physics is responsible for the broader current layers observed in the experiment. [1] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [2] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [3] V. Roytershteyn, et al., Phys. Plasmas 17, 055706 (2010). Supported by NDSEG, DOE, NASA, and NSF.   

Study of ion heating mechanisms during magnetic reconnection in MRX

The mechanisms of energy dissipation during magnetic reconnection have been studied intensively. Previous research [1] indicates that ions are heated non-classically during magnetic reconnection in MRX [2]. However, it is not yet known which non-classical ion heating mechanisms are present. As a candidate for the mechanism, ion heating and acceleration by the in-plane electric field is investigated. A 4 channel Ion Doppler Spectroscopy Probe (IDSP) is used to measure radial profiles of ion temperature and radial ion flow velocity in a single plasma discharge. The radial in-plane electric field is calculated from floating potential measurements. Potential wells on the order of 10V, on top of the inductive electric field generated by the time varying toroidal field (TF) coil current, are observed. Since ions are unmagnetized around the diffusion region, they are expected to gain energy from the potential well as they approach the X point. To estimate the effect of the electron temperature on the floating potential, radial profiles of the electron temperature and floating potential are measured at the same time.\\[4pt] [1] S. C. Hsu \textit{et al}., \textit{Phy. Rev. Lett}., 84(17), 3859 (2000).\\[0pt] [2] M. Yamada \textit{et al}., \textit{Phys. Plasmas}, \textbf{4}, 1936 (1997).   

An Experiment to Investigate the Role of Neutrals in Magnetic Reconnection

Magnetic reconnection in the solar chromosphere has become a topic of recent interest as it may be a source of energy transfer into the corona [1], and observations show evidence of fast reconnection [2]. Unlike the corona, the plasma in the chromosphere is relatively cool (T $\sim 10^4$ K) and is weakly to partially ionized ($n_n/n \sim 10^0-10^4$). Furthermore, simulations have shown that the reconnection rate can depend on the ionization fraction and neutral collisionality [3]. Damping due to ion-neutral viscosity may also play a role. In the Magnetic Reconnection Experiment (MRX), we plan to study the effects of neutrals on reconnection in a controlled laboratory setting. A optical probe diagnostic is used to measure neutral density, and we plan to develop a UV diagnostic to facilitate comparisons with solar observations. Initial pressure scans have shown that we can access a parameter space relevant to the chromosphere. \\[4pt] [1] P. A. Sturrock, ApJ \textbf{521}, 451 (1999).\\[0pt] [2] J. Chae, et al., J. Korean Astron. Soc., \textbf{36}, 13 (2003).\\[0pt] [3] P. D. Smith, et al., A\&A \textbf{486}, 569 (2008).   

A Next Generation Magnetic Reconnection Experiment: Accessing ``Reconnection Phase Diagrams'' for Space and Astrophysical Relevances

Ongoing dedicated laboratory experiments, such as Magnetic Reconnection Experiment (MRX), have been productive in providing original and valuable data in achieving much needed understanding of fast reconnection and associated processes. However, further critical contributions to astrophysical plasmas are limited by the achievable parameters. In this paper, we discuss results from our ongoing efforts\footnote{H. Ji et al., APS 51st DPP Annual Meeting (November, 2009), http://meetings.aps.org/link/BAPS.2009.DPP.TP8.111} to develop plans for a next-generation reconnection experiment based on MRX. Most recent results from two-dimentional, large-scale numerical simulations suggest the existence of a \lq\lq reconnection phase diagram", which illustrates \lq\lq phase transitions" between different \lq\lq states" or regimes. They include \lq\lq collisional MHD without plasmoids regime", \lq\lq collisional MHD with plasmoids regime", \lq\lq kinetic and MHD hybrid regime", and \lq\lq collisionless regime". The latter three regimes are considered to be relevant to reconnection in solar tachocline, solar corona, and Earth's magnetosphere. A natural goal for the next generation of reconnection experiments is the ability to access all of these regimes so that phase transitions can be studied in a controlled environment and the results are potentially applicable to astrophysical plasmas. Experimental requirements, aided by numerical simulations, will be discussed in detail.   

Emission Structures and Bursty Events in WIRX

We report on observations and analysis of ICCD images taken in the Wheaton Impulsive Reconnection Experiment (WIRX). The experiment is composed of two parallel electrodes, linked by a magnetic arcade generated by a coil surrounding the electrodes. Images reveal a plasma ball which expands from the arcade and an elongated emission feature connected to one end of the arcade. These are interpreted using magnetic field line tracing and an ad hoc model of the plasma current. Under some driving conditions, bursty events appear which are similar in some ways to reconnection events in other plasmas. Work is ongoing to determine if these events involve reconnection. ICCD camera images suggest a bursty emission of plasma from the arcade during these events. Photodiode cameras and magnetic probes are under development to better characterize the evolution of the arcade in time and space and to look for signatures of reconnection. Work supported by U.S.D.O.E. grant DE-FG02-08ER55002.   

Plans for a 3D reconnection experiment

Plasma-filled, current-carrying magnetic flux tubes are the essence of tokamaks, RFP's, spheromaks, solar coronal loops, and astrophysical jets. Relevant behaviors/issues are magnetic helicity content and injection, motion of the tube axis (hoop force, kinking), plasma confinement (balance between hydrodynamic pressure and pinch force), axial jet flows (acceleration and stagnation), waves, particle orbits, reconnection, and open v. closed field lines. These behaviors/issues and their mutual interaction are being investigated via Alfven time-scale imaging and conventional diagnostics in highly reproducible experiments having the simplest relevant geometry. High-speed movies clearly show flux tube kinking, motion of the flux tube axis due to hoop force, axial jet flows, an unusual particle orbit associated with flows counter to the electrical current, and reconnection between adjacent co- or counter-helicity flux tubes. A new experiment now under construction will have two slightly offset plasma-filled, current carrying flux tubes locally reconnect in 3D to form a single long flux tube. The setup requires two floating power supplies to drive the pre-reconnection currents as post-reconnection the power supplies become series-connected. A means for overcoming the topologically unavoidable mutual repulsion between the pre-reconnection currents is also required. It is anticipated that Alfven waves will radiate from the 3D localized reconnection region.   

Experiment to Study Alfven Wave Propagation in Plasma Loops

Arched plasma-filled twisted magnetic flux tubes are generated in the laboratory using pulsed power techniques (J.F. Hansen, S.K.P. Tripathi, P.M. Bellan, 2004). Their structure and time evolution exhibit similarities with both solar coronal loops and spheromaks. We are now developing a method to excite propagating torsional Alfven wave modes in such plasma loops by superposing a $\sim $10kA, $\sim $100ns current pulse upon the $\sim $50kA, 10$\mu $s main discharge current that flows along the $\sim $20cm long, 2cm diameter arched flux tube. To achieve this high power 100ns pulse, a magnetic pulse compression technique based on saturable reactors is employed. A low power prototype has been successfully tested, and design and construction of a full-power device is nearing completion. The full-power device will compress an initial 2$\mu $s pulse by a factor of nearly 20; the final stage utilizes a water-filled transmission line with ultra-low inductance to attain the final timescale. This new pulse device will subsequently be used to investigate interactions between Alfven waves and the larger-scale loop evolution; one goal will be to directly image the wave using high-speed photography. Attention will be paid to wave propagation including dispersion and reflection, as well as dissipation mechanisms and possible energetic particle generation.   

New dynamics of magnetically driven plasma jets in response to changes in applied current

The Caltech spheromak formation experiment produces a T$\sim$5 eV, n$\sim$10$^{21}$ m$^{-3}$ plasma using one of three possible power supply configurations: a capacitor bank with a FWHM $\sim$10 $\mu$s current, a recently incorporated pulse forming network (PFN) with a FWHM $\sim$55 $\mu$s current, or the two supplies in concert. Past experiments using only the capacitor bank showed that the current-carrying plasma jet kinks consistent with the ideal MHD kink limit[1]. In recent experiments, plasmas produced using only the PFN or using both power supplies follow this trend, with the varying shape and increased time of the current giving rise to additional new behavior. The radius of unkinked jets expands and contracts in time following the changing current. Now not only can kink-unstable plasmas exhibit two visible twists but they can also evolve in two distinct ways post kink onset, with kink amplitude growing either slowly or quickly. In the latter case there is often a distinct fine-scale structure in the kinked jet as well as signs of plasma twists piling up and of the plasma jet detaching and reconnecting.\\[4pt] [1] Hsu and Bellan, Phys. Plasmas 12, 032103 (2005)   

Experimental and Numerical investigations into AKR generation processes

Energetic electron streams descending through the auroral magnetosphere are subject to magnetic compression, increasing their gyrational energy which in turn relaxes through cyclotron maser emission in the kilometer band, the Auroral Kilometric Radiation (AKR). A scaled experimental and numerical program has been undertaken to demonstrate the mechanism of this process at microwave frequencies in the laboratory. Recent progress has included the introduction of a low temperature, low density background plasma into the experiment to replicate the residual low energy particles in the auroral magnetosphere and the investigation of the response of the instability to the cyclotron detuning in 3D PiC codes. These tests are important to determine the potential absorption of the radiation at the upper hybrid resonance.   

Bright Spots: UV Measurements Using a Vacuum Photodiode Array

Solar coronal loops typically erupt abruptly after long quiescent periods. Such eruptions might be initiated by interactions between adjacent loops; this possibility was explored in a laboratory experiment where two plasma-filled flux tubes merge in either a co-or counter-helicity arrangement (J.F. Hansen, S.K.P. Tripathi, and P.M. Bellan, Phys. Plasma 2, 3177(2004)). The latter arrangement produces a bright region with enhanced soft x-ray emission. We investigate such mergings with a new array of EUV photo-detectors (based on S.J. Zweben, R.J. Taylor, Plasma Physics, Vol. 23, No. 4(1981)) that provides spatially and temporally resolved measurements of radiation between 10 and 120 nm. The detector boasts a sub-microsecond rise-time and provides a large signal without amplification. The detector is shielded from the charged particle background by permanent magnets. A novel two-step scheme diverts RF ground loop currents and greatly improves the signal-to-noise ratio.   

Low Energy Nuclear Fusion Possible w/o Artifice of Tunneling

Low energy nuclear reactions such as deuterium-deuterium fusiomn on the sun can occur w/o tunneling if nuclear vibration is taken into account. The temperature needed for such fusion is $4.0x10^7K$. The nuclear barrier height to be overcome is $8.286 x 10^{-15}j$ using the equipartition of energy formula $1/2mv^2 = 3/2kT$. Using a formula stated in an earlier paper in which the both nuclei are assumed to be oscillating which is KE needed = $kq_1q_2/[3A(3cos^2X]^{1/2}]$, where A is the average amplitude of oscillation equal in all directions, RMS value for the barrier height is $kq_1q_2/3A(6)^{1/2}$ with a maximum barrier height of infinity for no nuclear oscillation. Solving for A, the average ampltude of vibration needed for two deuterium nuclei to fuse is approximately 3.79 fermis.   

Neutrino plasma interactions and supernovae shock revival

One of the outstanding problems with supernovae is how to reverse the implosion due to gravity to create an explosion. This is sometimes referred to as reviving the stalled shock wave by neutrino heating. During the supernovae collapse an intense flux of neutrinos is emitted. These neutrinos drive a novel class of plasma instabilities: the electroweak versions of the standard electron or photon driven streaming or forward scattering instabilities. Using the relativistic kinetic equations for neutrinos interacting with plasmas via the weak interaction, we explore the different collective plasma instabilities driven by intense neutrino fluxes. We examine the anomalous energy transfer between the neutrinos and the shocked plasma via electron plasma waves and the generation of quasi-static magnetic fields, the electroweak Weibel instability. A quasi linear model of the streaming instability results in plasma heating with about 1{\%} of the neutrino energy being absorbed by the plasma this is sufficient to revive the shock wave and create the explosion.   

Plasma Regimes, and High Frequency QPOs Near Black Holes

The observed twin peak non-thermal spectra of High Frequency QPOs are associated with the excitations of spiral modes, with the 3:2 ratio of their frequency. The modulation of the observed radiation associated with general relativistic effects is analyzed, considering different emission processes. These are connected to strong variations of the plasma density corresponding to local rarefaction and compression, associated with the excited spirals. These modes [1] can grow under the combined effects of the differential rotation and the vertical gradients of the plasma density and temperature. The spirals are localized over radial widths that defines one of the regions surrounding a black hole and have frequencies that are multiples of the plasma rotation frequency. The high toroidal number $m_{\phi}$ modes are considered to decay into $m_{\phi}=2$ and $m_{\phi}=3$ modes.\\[4pt] [1] B. Coppi, \textit{A\&A} {\bf504}, 321-329 (2009).   

Active Black Holes: Relevant Plasma Structures, Regimes and Processes Involving All Phase Space$*$

The presented theory is motivated by the growing body of experimental information on the characteristics, connected with relevant spectral, time and space resolutions, of the radiation emission from objects considered as rotating black holes. In the immediate surroundings of these objects three plasma regions [1] are identified: an innermost Buffer Region, an intermediate Three-regime Region and a Structured Peripheral Region. In the last region a Composite Disk Structure that is a sequence of plasma rings corresponding to closed magnetic surfaces is considered to be present and to allow intermittent accretion flows along the relevant separatrices. The non-linear ``Master Equation'' describing this structure is derived and solved in appropriate asymptotic limits. The rings structure, depending on microscopic plasma characteristics: i) can be excluded from forming in the intermediate region allowing the onset of a spiral structure with which High Frequency Quasi Periodic Oscillations are associated; ii) may be allowed to propagate to the outer edge of the Buffer Region where successive rings with opposite currents are ejected vertically (in opposite directions) and originate the observed jets; iii) is dissipated well before the Buffer Region. *Sponsored in part by the U.S. D.O.E. [1] B. Coppi, \textit{Plasmas in the Laboratory and in the Universe}, Eds. G. Bertin \textit{et al}. (Publ. \textit{American Institute of Physics}, New York, 2010).   

Do boundary conditions affect the global behavior of magnetorotational instability?

Flow-driven magnetorotational instability (MRI) is believed to contribute to turbulence and momentum transport in astrophysical disks. We investigate the effect of boundary conditions in axisymmetric MRI computations using two configurations, namely a thick disk and a toroidal Cartesian geometry. Linear and nonlinear computations are performed using the extended MHD code NIMROD. First, we investigate the stability and saturation of MRI in an astrophysically relevant disk configuration. The effect of boundaries on MRI is studied for a hydrodynamically stable flow in which a large shear is localized far from the conducting wall boundaries. We find that the MRI mode structure is localized around the flow shear region and boundaries do not affect its stability. Second, we perform MHD computations with boundary conditions corresponding to the Madison Plasma Couette Flow Experiment (MPCX). As proof of principle we numerically obtain an experimentally relevant flow, a Taylor-Couette flow generated by a tangential $E\times B$ drift set at the boundaries. The MRI in this configuration will be discussed.   

The solar coronal electron heating by short wavelength electromagnetic modes

The electron heating of the solar coronal plasma has remained as one of the most important problems in solar physics. An explanation of the electron heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the electrons. Our objective here is to present an estimate for the electron heat in grate in the presence of finite amplitude short wavelength in comparison with the ion gyroradius dispersive electromagnetic (SWDEM) waves that propagate obliquely to the magnetic field in the solar corona, Specifically, it is demonstrated that the SWDEM waves can significantly contribute to the solar coronal electron heating via Joule heating involving electron-SWEDEM wave interactions. .   

A thermally stable heating mechanism for the intracluster medium: turbulence, magnetic fields and plasma instabilities

We consider the problem of self-regulated heating and cooling in galaxy clusters and the implications for cluster magnetic fields and turbulence. Viscous heating of a weakly collisional magnetized plasma is regulated by the pressure anisotropy with respect to the local direction of the magnetic field. The intracluster medium is a high-beta plasma, where pressure anisotropies caused by the turbulent stresses and the consequent local changes in the magnetic field will trigger very fast microscale instabilities. We argue that the net effect of these instabilities will be to pin the pressure anisotropies at a marginal level, controlled by the plasma beta parameter. This gives rise to local heating rates that turn out to be comparable to the radiative cooling rates. Furthermore, we show that a balance between this heating and Bremsstrahlung cooling is thermally stable. Given a sufficient (and probably self- regulating) supply of turbulent power, this provides a physical mechanism for mitigating cooling flows and preventing cluster core collapse. A balance between parallel viscous heating and radiative cooling gives predictions for magnetic field strengths, turbulent velocities and turbulent scales. If confirmed, these predictions would constitute strong evidence that microphysical processes play an important role in the large-scale structure and evolution of galaxy clusters.   

Damping of Whistler Waves through Mode Conversion to Lower Hybrid Wave in the Ionosphere

The VLF waves excited by powerful ground-based transmitter propagate in the Earth-ionosphere waveguide and leaks through the ionosphere to the magnetosphere. Recent studies [Starks et al. 2008] using combined Earth-ionosphere waveguide model and ray-tracing model found that the model systematically overestimates the VLF wave field strength in the plasmasphere owing to VLF transmitter by $\sim$20 dB at night and $\sim$10dB during the day. We present a numerical model to simulate linear mode conversion between whistler wave and lower hybrid wave due to the interaction with short scale density striations such as field-aligned irregularities in the Earth's ionosphere. It is found that at the altitudes between 90 to 120 km in the ionosphere, the energy of whistler wave energy can be converted to the lower hybrid wave and the lower hybrid wave can be subsequently damped by ion-neutral collisions. The mode conversion of whistler wave to lower hybrid wave in the E region ionosphere may play an important role in the whistler wave damping. This work is supported by ONR MURI grant.   

Gyrokinetic Particle Simulation Of Drift Compressional Modes In Magnetic Dipole Geometry

The Pc5 magnetic pulsations dominated by compressional modes have been regularly observed in the Earth's magnetosphere. The objective of this project is to study the linear excitation and nonlinear evolution of these ultra low frequency pulsations, focusing on unstable drift compressional modes, with kinetic effects due to wave-particle resonance and finite Larmor radius. The method is to develop a three dimensional gyrokinetic particle simulation, with the dipole equilibrium field modelling the Earth's magnetosphere. Results of linear drift-kinetic and linear gyrokinetic simulations will be presented. The current code development is focused on resolving the radial mode structure due to finite Larmor radius effects.   

Ion Temperature Maps of the Magnetosphere

Measurements of ion temperatures throughout the magnetosphere provide an important description of magnetospheric dynamics because ion heating has been correlated with magnetic reconnection, instabilities, convection of plasma, and other phenomena. We present ion temperature maps of the magnetosphere created using energetic neutral atom (ENA) data from the TWINS spacecraft. These data have been sorted according to solar wind and magnetospheric conditions and the resulting ion temperature maps will be compared. For example, during fast solar wind and quiet magnetospheric conditions, a dawn-dusk ion temperature asymmetry is observed. There is also evidence of braking and heating of the ions at the boundary between the tail-like open magnetic field lines and the inner dipole closed field lines. The remotely-obtained ENA measurements will also be compared with ion temperature measurements from \textit{in situ} satellites.   

Strapping field profile to reproduce transition from slow rise to fast eruptions

The hoop force causes arched, current-carrying plasma loops to expand unless additional forces are applied. This expansion was slowed and even inhibited by a magnetic field of proper polarity in previous solar coronal loop experiments [1] but there was no attempt to reproduce the slow expansion to fast eruption behavior often exhibited by solar loops. Kleim and Torok [2] predicted that a transition from a slow expansion to a fast eruption occurs if the magnetic field's rate of decay with increasing altitude meets an instability criterion. We have calculated the magnetic profiles which attain the instability criterion within the length scale of the Caltech experiment and are constructing an auxiliary coil designed to provide the required magnetic profile. We plan to image the plasma loop behavior under the influence of these coils. \\[4pt] [1] J. F. Hansen and P. M. Bellan, Astrophys. J. Lett. \textbf{563}, L183 (2001)\\[0pt] [2] B. Kleim and T. Torok, Phys. Rev. Lett. \textbf{96}, 255002 (2006)   

Characterization of plasma-filled flux tubes and other open flux systems

The Caltech ``solar'' gun not only accesses the physical regime found in the solar corona, but also provides a powerful experimental platform for studying fundamental forces in dynamic open flux plasma structures. The magnetized plasma gun comprises two semicircular electrodes in front of four electromagnetic coils. Each coil can be independently reversed or disconnected, making a host of different magnetic configurations available. Among these are single plasma loops and pairs of adjacent loops that can have the same or opposite helicities. B-dot probes are used to take time-resolved measurements of the plasma magnetic field. Different neutral gases can be supplied to the gun, with the option of using one or two species per plasma. Using two species makes it possible to image different sections of the plasma with optical filters. When making two loops, each loop can be formed from a different gas and hence imaged separately. In a single loop, the dual gas technique is used to measure the speed of plasma flowing into the magnetic flux tube from each end. Flow speeds are found to be directly proportional to the azimuthal magnetic field generated by current flowing along the loop and inversely proportional to the plasma mass density.   

Suppression of energetic electron transport by double layers in flares

Recent observations from RHESSI revealed coronal hard X-ray emissions came from an above-the-loop-top source. It is not clear how the flare-accelerated electrons stayed above the loop top for a prolonged period of time. Using particle-in-cell simulations, we set up an initial system of very hot electrons in contact with cold electrons parallel to the local magnetic field, and let it evolve over time. After a short phase of diffusion, a large-amplitude, localized electrostatic electric field (in the form of a classic double layer) spontaneously forms at the boundary between the hot and cold electrons. The double layer then suppresses the hot electron transport into the cold region. The barrier supports a significant temperature drop between the two regions that is sustained for the duration of the simulation. The dynamics of the double layer and the associated transport suppression are being explored.   

Hybrid Simulations of the Termination Shock: Ion Velocity Distributions in the Heliosheath

TheLos Alamos hybrid simulation code has been used to examine kinetic properties of pickup ions at the heliospheric termination shock and in the downstream heliosheath. The simulations represent the electrons as a zero-mass fluid, and address only perpendicular shocks. Three topics are studied. First, one-dimensional shock simulations show that, contrary to a widely held opinion, specular reflection does not play a role in the energy gain of pickup ions at the termination shock. Rather, pickup ions which gain the most energy at the shock are those with gyrophase which enables them to return upstream and interact with the motional electric field. Second, simulations are carried out for three different upstream Mach numbers; the results show that faster solar wind flows lead to an increased flux of ions in the tails of the suprathermal component, consistent with energetic neutral atom observations by the IBEX spacecraft. Third, two-dimensional simulations of the shock show that anisotropies in the proton velocity distribution caused by the termination shock give rise to both Alfv\'en-cyclotron and proton mirror instabilities in the heliosheath. In these simulations, the cyclotron instability dominates and, via pitch-angle scattering, reduces the proton anisotropies in the heliosheath.   

Perpendicular Ion Heating by Low-Frequency Alfvenic Turbulence in the Solar Wind

A critical unsolved problem in the study of solar wind turbulence is to determine whether low-frequency Alfven-wave (AW) and kinetic-Alfven-wave (KAW) turbulence can explain the perpendicular ion heating that is observed in coronal holes and low-beta fast-wind streams. In linear wave theory, low-frequency AWs and KAWs are incapable of causing perpendicular ion heating. On the other hand, a number of observations suggest that low-frequency AW/KAW turbulence is the primary heating mechanism in the solar wind. This poster describes recent work that offers a possible solution to this long-standing problem, and which extends previous studies of ``stochastic heating.'' An analytic expression for the stochastic heating rate in low-beta plasmas is derived and tested against simulations of test particles interacting with a spectrum of randomly phased AWs and KAWs. This expression is then used in conjunction with an observationally constrained model of solar-wind turbulence to obtain ion temperature profiles, which agree well with observations from the Ultraviolet Coronagraph Spectrometer.   

Understanding Compressive Fluctuations in Solar Wind Turbulence using Artificially Generated Data

At large scales the turbulent fluctuations in the solar wind are approximately 90\% incompressible and 10\% compressible. The composition of the compressible component is an open question, specifically if it behaves like MHD fast or slow modes. The nature of the mode can be determined by investigating the correlation between the pressure and parallel magnetic field fluctuations. We have generated artificial data of fast and slow turbulent fluctuations in order to determine the observational signature from single point satellite measurements. However, given the low collisionality of solar wind plasma, MHD theory is not strictly valid. Therefore, we also compare artificial data generated from MHD and fully kinetic Vlasov-Maxwell eigenfunctions of fast and slow modes.   

Kinetic Simulations of the Dissipation Range of Solar Wind Turbulence from Ion to Electron Scales

The first nonlinear kinetic simulation of the dissipation range of plasma turbulence resolving both the characteristic ion and electron scales with a realistic mass ratio is presented. The resulting energy spectra are qualitatively consistent with nearly power-law spectra observed in recent satellite measurements of the solar wind dissipation range. This result demonstrates that a kinetic Alfven wave cascade can reach the electron scales and disproves a recent claim to the contrary. A weakened cascade model for the kinetic turbulent cascade is presented that explains the spectra by accounting for nonlocal contributions to the energy cascade rate.   

Turbulent Heating of Heliospheric Plasmas

Heliospheric plasmas undergo a turbulent cascade of energy which transforms large-scale spatial energy into small-scale fluctuations, which are ultimately dissipated via kinetic mechanisms as heat. Recent high sampling rate solar wind data has extended our observational knowledge of the solar wind well into the dissipation range of the turbulence, and theoretical studies have demonstrated the dissipation range to be well modeled by a cascade of kinetic Alfv\'{e}n waves. Milestone nonlinear kinetic simulations employing a realistic mass ratio and plasma $\beta = 0.01$, $0.1$, $1$, $10$, and $100$ spanning from MHD scales to the electron gyroradius are analyzed. The large dynamic range of the simulations and their kinetic nature capture both the splitting of the turbulent energy at the proton gyroradius scale into a kinetic Alfv\'{e}n wave cascade and ion entropy cascade and the physical dissipation of the turbulence below the proton gyroradius. Preliminary results demonstrating scale-by-scale heating of the electron and proton populations relevant to the solar wind and corona are presented.   

Turbulence Diagnostics in Local Interstellar Clouds from High Resolution Astronomical Spectroscopy

There are 15 diffuse clouds known within about 50 light years of the Sun. These clouds consist of partially ionized plasmas, with an ionization fraction of $\simeq$ 50 \%, an electron density of about 0.1 cm$^{-3}$, and ion temperatures from 4000 - 8000 K. High resolution spectroscopic measurements of absorption lines against nearby stars have been made for lines of several atoms and ions. From these data, the temperature can be determined, as well as a non-thermal Doppler motion which is interpreted as turbulent motions within the clouds. The rms turbulent velocity amplitude is typically about 2.2 km/sec. Using published data on spectral line widths for 32 lines of sight possessing 53 absorption components, we have examined the extent to which this turbulence possesses properties of turbulence in the solar wind, such as velocity fluctuations perpendicular to the large scale magnetic field, enhanced perpendicular-to-parallel temperature ratios, and preferential heating of ions with large Larmor radii. The data for the local interstellar clouds show no evidence of these features. We will discuss possible reasons for the differences between solar wind and local interstellar turbulence.   

Electron Density Fluctuations in Kinetic Alfven Wave Turbulence

Electron density fluctuations become dynamically active in Kinetic Alfv\'en wave turbulence at small length scales --- around ten times the ion-sound gyroradius and smaller. The density gradient is shown to have non-Gaussian statistics with large kurtosis, and turbulent fields within this regime have long-lived sheet and filamentary structures that may be responsible for the enhanced statistical tails. We present global statistics and local characterizations of these long-lived structures. The gradient field remains non-Gaussian even when varying the damping parameters over a large range of values. The primary structure morphology changes from filaments to sheets as the dominant damping is in either diffusivity or resistivity, respectively. We investigate the implications of the non-Gaussian statistics of the density fluctuations for interstellar pulsar scintillation, observations of which have provided evidence of non-Gaussian fluctuations in electron density.   

Two-fluid relativistic waves and free electron lasers in pulsar plasmas

A relativistic two-fluid approach for a streaming magnetized pair plasma is developed. Such a scenario corresponds to secondary plasmas created at the polar caps of pulsar magnetospheres. Recent studies show that the temperature of such plasmas is very close to the rest mass energy of the particles. It is therefore critical to determine the exact properties of waves at such temperatures. For parallel propagation, four transverse modes are found. Two are electromagnetic plasma modes, which at high temperature become light waves. The remaining two are Alfv\'{e}nic modes, split into a fast and slow mode. The slow mode is cyclotron two-stream unstable at large wavelengths and is always sub-luminous. We find that temperature effects cannot suppress the instability in the limit of large (finite) magnetic field. We discuss the implications of the unstable mode for radio emission theories. For example, for typical values, the instability is quite fast, and the waves can grow to sizable levels, such that, the magnetic modulation could act as a wiggler. The pulsar primary beam could interact with this wiggler and simulate a free electron laser like effect, yielding coherent radiation.   

Spectroscopics database for warm Xenon and Iron in Astrophysics and Laboratory Astrophysics conditions

The main contribution to spectral properties of astrophysics mixtures come often from Iron. On the other hand, in the so-called domain of ``Laboratory Astrophysics,'' where astrophysics phenomena are scaled down to the laboratory, Xenon (and Argon) are commonly used gases. At so called ``warm'' temperatures (T=5-50eV), L-shell Iron and M-shell Xenon present a very large number of spectral lines, originating from billions of levels. More often than not, Local Thermodynamical Equilibrium is assumed, leading to noticeable simplification of the computation. Nevertheless, complex and powerful atomic structure codes are required. We take benefit of powerful statistics and numerics, included in our atomic structure codes, STA[1] and HULLAC[2], to generate the required spectra. Recent improvements in both fields (statistics, numerics and convergence control) allow obtaining large databases (ro x T grid of $>$ 200x200 points, and $>$ 10000 frequencies) for temperature down to a few eV. We plan to port these improvements in the NLTE code SCROLL[3]. [1] A.Bar-Shalom, et al, Phys. Rev. A 40, 3183 (1989) [2] M.Busquet,et al, J.Phys. IV France 133, 973-975 (2006); A.Bar-Shalom, M.Klapisch, J.Oreg, J.Oreg, JQSRT 71, 169, (2001) [3] A.Bar-Shalom, et al, Phys. Rev. E 56, R70 (1997)   

Influence of external radiation on non-LTE opacities of Xe

In Laboratory Astrophysics, where astrophysics phenomena are scaled down to the laboratory, Xenon is commonly used. In most cases, astrophysical plasmas are not dense enough to warrant LTE. However, they are surrounded by radiation fields. Extensive detailed level computations of non-LTE Xe around Te = 100eV were performed with HULLAC [1], with different radiation temperatures and/or dilution factors. Generally, the effects are very important, even with small dilution factors. \\[4pt] [1] M. Klapisch and M. Busquet, High Ener. Dens. Phys.\textbf{5}, (2009) 105-9; Bull. Am. Phys. Soc.\textbf{54}, (2009) 210.   

A statistical model of magnetic islands in a large current layer: validation from Hall MHD simulations and Cluster FTE observations

Magnetic islands have been observed in large current layers for various space plasmas, including the magnetopause and solar corona. Since the direct simulation of very large systems is not possible, we have developed a statistical model which describes the formation, growth, convection and coalescence of these magnetic islands. An integral- differential equation is derived for the island distribution function, which characterizes islands by the flux they contain $\psi$ and the area they enclose $A$. We use Hall MHD simulations to validate the model and to benchmark its parameters. The steady- state solution of the evolution equation predicts a distribution of islands. A database of 1,098 flux transfer events observed by Cluster between 2001 and 2003 is shown to be consistent with the model's predictions.   

Full particle-in-cell simulation study on solar wind interaction with a small scale magnetosphere

Solar wind interaction with a small magnetosphere comparable to or less than the ion inertial length is investigated by using full particle-in-cell simulation. Such micro-scale magnetospheres would be used for the next-generation interplanetary flight system called Magneto Plasma Sail. In the preliminary two dimensional simulations, magnetic reconnection takes place at the night side of the magnetosphere even in the northward IMF case and a typical signature of quadruple magnetic field is observed over the entire magnetosphere. A current density peak is formed inside the magnetosphere due to the electron backflow from the reconnection region, in addition to the induced current density at the front boundary layer where the solar wind momentum is primarily diverted. Based on the results of three dimensional simulations using nested grid system, detailed structure of the inner electron flow, its impacts on the solar wind interaction, and the resulting propulsion will be discussed.   

Simulations of plasma dynamo in cylindrical and spherical geometries

We have performed the numerical investigation of plasma flow and possibility of dynamo effect in Madison Plasma Couette Experiment (MPCX) and Madison Plasma Dynamo Experiment (MPDX), which are being installed at the University of Wisconsin- Madison. Using the extended MHD code, NIMROD, we have studied several types of plasma flows appropriate for dynamo excitation. Calculations are done for isothermal compressible plasma model including two-fluid effects (Hall term), which is beyond the standard incompressible MHD picture. It is found that for magnetic Reynolds numbers exceeding the critical one the counter-rotating Von Karman flow (in cylinder) and Dudley- James flow (in sphere) result in self-generation of magnetic field. Depending on geometry and plasma parameters this field can either saturate at certain amplitude corresponding to a new stable equilibrium (laminar dynamo) or lead to turbulent dynamo. It is shown that plasma compressibility results in increase of the critical magnetic Reynolds number while two- fluid effects change the level of saturated dynamo field. The work is supported by NSF.   

Radiation from electrons in magnetic field turbulence astrophysical scenarios

Radiation emission from gamma-ray bursts is a hot topic in astrophysics. Both the Weibel and the Kelvin-Helmoltz instabilities have been proposed as mechanisms involved in the generation of magnetic fields in turbulent scenarios relevant to this context. In this work we explore scenarios of Weibel and Kelvin-Helmoltz generated turbulence through 3D particle-in-cell (PIC) simulations performed with OSIRIS 2.0. We analyze the evolution of the magnetic field and the electron dynamics and determine the spectrum of radiation emitted by these using a post-processing diagnostic. The temporal evolution of the radiation spectrum from these scenarios will be presented and compared. Initial results indicate that though the spectra are similar (increasing up to a maximum and then decreasing at higher frequencies), the detailed features are not the same. Results suggest that the decrease at high frequencies obeys a broken power law in the case of the Weibel with a steeper descending slope than in the Kelvin-Helmoltz scenario.   

Effect of Energetic Electrons on Quiet Auroral Arc Formation

The theory of feedback instability between the magnetosphere and ionosphere is believed as one of the candidate to explain the formation of quiet auroral arc. Then, some magneto-hydro- dynamics simulations showed the arc formation by this macroscopic instability, while the effect of auroral energetic electrons on the arc formation was neglected or given as a macroscopic parameter in these simulations. On the other hand, because of the recent development of particle simulations, auroral energetic electrons are thought to be produced by the super ion-acoustic double layer that should be created by microscopic instability. To make close investigation of auroral arc formation, it is necessary to consider the interaction with microscopic instability. In this paper, we numerically study the effect of energetic electrons on quiet auroral arc formation by means of the Macro-Micro Interlocked simulation.   

Tracking spectral evolution of high-energy astrophysical plasmas through wavelet analysis

High-energy astrophysical phenomena frequently produce transient, rapidly-evolving spectral features that reflect the underlying dynamics of plasma systems in which field configuration and energy distribution can vary quickly. Wavelet analysis has several advantages over standard Fourier analysis for analyzing and modeling such systems, in being able to track both time and frequency information over a range of scales. Through wavelet analysis performed on observations of several transient and explosive astrophysical phenomena such as supernovae, GRBs, and solar flares, we demonstrate the advantages of such an approach in tracking the evolving behavior of these systems. We present the extension of this approach to modeling radiation from such systems using wavelet analysis of related plasma simulations.   

High-Lundquist Number Numerical Simulations of Coronal Heating: Reduced MHD via GPGPUs

In the last few years, we have performed a number of numerical simulations of a coronal heating model based on three-dimensional (3D) reduced magnetohydrodynamics (RMHD), which is generalized from our 2D model [C. S. Ng and A. Bhattacharjee, Astrophys. J., 675, 899 (2008)]. In this model, random photospheric footpoint motion is applied to obtain converged average coronal heating rates. In the high-Lundquist number limit, we find that the heating rate is independent of the Lundquist number, with average magnetic energy saturating at a constant level due to the formation of strong current layers and subsequent disruptions. The computational loads required for adequately resolving such current layers renders any extension of our analysis towards even higher Lundquist numbers exceedingly difficult on conventional parallel architectures. We present here initial results from a port of our RMHD code to Nvidia CUDA (Compute Unified Device Architecture) for hardware acceleration using general purpose graphics processing units (GPGPUs). We report code performance on a dedicated research workstation and well as larger scale distributed memory GPU equipped machines. This work is supported by NASA NNX08BA71G, NNX06AC19G, NSF AGS-0962477, and DOE DE-FG02-07ER54832.   

Energy Stable Space-Time Discontinuous Galerkin Approximations of the 2-Fluid Plasma Equations

Energy stable variants of the space-time discontinuous Galerkin (DG) finite element method are developed that approximate the ideal two-fluid plasma equations. Using standard symmetrization techniques, the two-fluid plasma equations are symmeterized via convex entropy function and the introduction of entropy variables. Using these entropy variables, the source term coupling in the two-fluid plasma equations is shown to have iso-energetic properties so that the source term neither creates nor removes energy from the system. Finite-dimensional approximation spaces utilizing entropy variables are utilized in the DG discretization yielding provable nonlinear stability and exact preservation of this iso-energetic source term property. Numerical results for the two-fluid approximation of magnetic reconnection are presented verifying and assessing properties of the present method.   

Nike Experiment to Observe Strong Areal Mass Oscillations in a Rippled Target Hit by a Short Laser Pulse

When a short (sub-ns) laser pulse deposits finite energy in a target, the shock wave launched into it is immediately followed by a rarefaction wave. If the irradiated surface is rippled, theory and simulations predict strong oscillations of the areal mass perturbation amplitude in the target [A. L. Velikovich \textit{et al}., Phys. Plasmas \textbf{10}, 3270 (2003).] The first experiment designed to observe this effect has become possible by adding short-driving-pulse capability to the Nike laser, and has been scheduled for the fall of 2010. Simulations show that while the driving pulse of 0.3 ns is on, the areal mass perturbation amplitude grows by a factor $\sim $2 due to ablative Richtmyer-Meshkov instability. It then decreases, reverses phase, and reaches another maximum, also about twice its initial value, shortly after the shock breakout at the rear target surface. This signature behavior is observable with the monochromatic x-ray imaging diagnostics fielded on Nike.   

Optimizing pulse shaping and zooming for acceleration to high velocities and fusion neutron production on the Nike laser

We will present results from follow-on experiments to the record-high velocities of 1000~km/s achieved on Nike [Karasik et al., Phys.\ Plasmas 17, 056317 (2010) ], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce extreme shock pressures and result in heating of matter to thermonuclear temperatures. Still higher velocities and higher target densities are required for impact fast ignition. The aim of these experiments is shaping the driving pulse to minimize shock heating of the accelerated target and using the focal zoom capability of Nike to achieve higher densities and velocities. Spectroscopic measurements of electron temperature achieved upon impact will complement the neutron time-of-flight ion temperature measurement. Work is supported by US DOE and Office of Naval Research.   

Numerical study of the irradiation uniformity of a directly driven inertial confinement fusion target

In the Inertial Confinement Fusion the uniformity of the irradiation still represents a crucial issue. In this context a spherical capsule directly driven by laser beams have been assessed numerically [1]. Two schemes characterized by 32 and 48 directions of irradiation [2] with associated a single laser beam or a bundle of laser beams [3] characterized by a super-Gaussian intensity profile are considered. Beam imperfections as power imbalance and pointing errors have been taken into account. It is found that the focal spot that minimizes the rms deviation depends on the beam imperfections [4]. The numerical calculations show that the uniformity of the irradiation evolves in time. The results calculated considering the illumination of a spherical target will be compared with those obtained when the irradiation is taken into account. [1] M. Temporal, B. Canaud. Eur. Phys. J. D 55 139 (2009). [2] M. Murakami, N. Sarukura, H. Azechi, M. Temporal, A.J. Schmitt, in press to Phys. Plasmas (July issue, 2010). [3] M. Temporal, B. Canaud, B. J. Le Garrec, Phys. Plasmas 17 022701 (2010). [4] M. Temporal, B. Canaud, S. Laffite, B.J. Le Garrec, M. Murakami. Phys. Plasmas 17 064504 (2010).   

Optimizing Direct-Drive Performance for Thin-Shell ICF Implosions on NIF

The Applications of Ignition (AoI) project at LANL is designing direct-drive NIF experiments for analyzing the evolution of feature-driven shocks in the presence of TN burn. Because the NIF beam geometry is optimized for hohlraum targets, care must be taken to achieve the most symmetric drive possible, to ensure that irregularities imposed by the drive do not overwhelm the intended experimental features. NIF Polar Direct Drive (PDD) configurations have been proposed in the past [Cok et al., Phys. Plasmas, 15, 082705 (2008)], but for the purpose of maximizing neutron yield. We present results from an extension of the Cok et al. work aimed at minimizing the Legendre mode content imposed by the PDD configuration. This required multiparameter modeling of the empirical NIF phase-plate data within our Lagrangian radiation-hydrodynamic calculations. We conducted multidimensional parameter scans of our calculations to identify the optimal drive configuration for thin-shell NIF capsules.   

Analysis of Structured ICF Implosions Using Multiresolution Analysis Techniques: From Radiation Symmetry to Turbulent Mix

We will show, using a series of images taken at the Z facility at Sandia, and in anticipation of NIF implosion images to come, that structured implosion X ray radiographs can be decomposed into logically distinct pieces which contain quantitative information on radiation drive asymmetry, on mesoscale correlated structures, sometimes radial, sometimes azimuthal and sometimes, mixed, as well as fine scale multifractal, texture like features which can all be quantified. Thus different time snap shots of a given implosion as well as different targets can be compared to each other as well as to any code predictions as there may exist which have sufficient resolution to tackle the hundreds or thousands of Legendre modes necessary to resolve surface bumps, their collusion, their amplification and eventual fuel-ablator surface tangled and possibly turbulent mix. Three independent and complimentary multiresolution analysis techniques will be shown which can isolate and track the most interesting features and compare them to theory.   

Using Proton Radiography to Measure Rayleigh-Taylor-Induced Magnetic Fields

The Rayleigh-Taylor (RT) hydrodynamic instability can compromise the 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 the heat flux and affect the implosion dynamics. A method for measuring these fields using a combination of mono-energetic proton radiography, X-ray radiography, and Monte-Carlo simulations is described. Scaled length estimates based on mono-energetic proton radiographs, suggest RT-induced magnetic fields of order $\sim $0.3 MG. This work was performed at the LLE NLUF, and was supported in part by the US DOE, LLNL, LLE and FSC.   

The Use of Tritium in D, H, and 3He Gas Filled Plastic Capsules at NIF

The addition of tritium gas to the plastic symmetry capsules designed for the National Ignition Facility offers the opportunity for enhanced nuclear diagnostics of capsule performance. Without mix between shell and fuel, Rev 5 symmetry capsules calculate to give as much as 1.2e+16 D+T neutrons for 50:50 D:T. If such yields can be reached, alpha particle heating increases the ion temperature by $\sim$0.5 keV. Based on 2009 experiments we expect only 0.1-0.3 of clean yields. Actual yields less than 1e+14 allow neutron imaging, while gamma rays show the burn history and measure shell rho-r. A deuterated layer in the plastic shell with nearly pure tritium gas might also produce D+T yields above 1e14 and could test mix models. A 99:1 DT capsule calculates to produce 1e15 D+T and 1e14 D+D neutrons which could simultaneously measure D+D and D+T neutron Doppler broadening. Calculations show a 0.2 keV ion temperature difference. This work was funded by the USDOE at Los Alamos and Lawrence Livermore National Laboratories.   

Measurements of down-scattered and TT-neutron spectra using the Magnetic Recoil Spectrometer (MRS) on OMEGA

The down-scattered and TT-neutron spectra from an ICF implosion have been measured for the first time using the Magnetic Recoil Spectrometer (MRS) at OMEGA. From the measurements of the down-scattered neutron spectrum, an areal density was inferred for both CH and low-adiabat cryogenic DT implosions. From the TT-neutron measurements, the astrophysical S-factor (``cross section'') and the branching ratio for the different TT-reaction channels were determined at energies inaccessible by conventional accelerator techniques. These measurements are unique because the ICF implosions produce weakly coupled, low-density plasmas in which electron screening has no impact on the S-factor. In this poster, the results from these measurements will be presented. This work was supported in part by the U.S. DOE, LLE and LLNL.   

Dynamic Phase Imaging using Ultrafast High-Energy X-rays

High-energy x-ray images of laser-shocked polystyrene produced through phase contrast imaging performed on the Trident 200-TW laser facility are presented. The plastic targets are nominally transparent to traditional x-ray absorption but show detailed features in regions of high density gradients due to refractive effects often called phase contrast imaging. The 200-TW Trident laser is used both to produce the x-ray source and to shock the polystyrene target. X-rays at 17-keV produced from 2-ps, 100-J laser interactions with a 12-micron molybdenum wire are used to produce a small source size, required for optimizing refractive effects. Shocks are driven in the 1-mm thick polystyrene target using 2-ns, 200-J, 532-nm laser drive with phase plates. X-ray source characteristics, x-ray images and shock comparisons to 1-D hydro calculations, HELIOS-CR, will be presented.   

Investigation of the LMJ ignition target sensitivity to the laser pulse shape with 2D integrated calculations

The A943 cryogenic target in a Rugby hohlraum is our current nominal design for ignition with 160 beams on the Laser MegaJoule (Laffite et al 2007, 49th Annual Meeting of the Division of Plasma Physics, Loiseau et al 2010, 40th Annual Anomalous Absorption Conference). In this study we redesign the laser pulse of the target under the form of a sum of six supergaussians, which is more amenable to a sensitivity study : four supergaussians are used to launch the four main shocks in the capsule, and two additional supergaussians are used first to remove the LEH windows and then to control the acceleration of the first shock, respectively. We use our 2D FCI2 code to compare the radiation hydro of the capsule, obtained with this new pulse, to what was previously obtained. We investigate the sensitivity of the yield on some parameters, which are the maximum powers and respective timings of the different components of the laser pulse.   

First Feasibility Shots For Radiography Experiments at LIL Facility

The Laser Integration Line (LIL), based at CESTA (The Aquitaine Research Center of the French Atomic and Alternative Energies), has been designed as a prototype to validate the concepts and the laser architecture of the Laser Mega Joule (LMJ). The LIL facility is a 4-beams laser representing a quad structure of the LMJ. The LIL facility launched in November 2009 its first campaign of side radiography feasibility (2 shots). The experiment was aimed at focusing 3 beams onto an aluminum target whose back-side induced plasma was X-rayed by an X source positioned at 10 mm and radiated by the 4$^{th}$ beam of the chain. The facility proved to be capable of shifting one beam regardless of the 3 others. During the 2$^{nd}$ shot, the shifted beam was desynchronized by 500 ps. Plasma observation was performed using an analyzer coupled to a streak camera with 200 $\mu $m aperture slot (40 $\mu $m on target) and a 10 ns time aperture. The LIL facility hence proved to be able to perform side X-ray shots and image plasma expansion using a streak camera on CCD or film.   

Recent progress of inertial confinement fusion experiments in China

The experimental progresses for inertial confinement fusion (ICF) on Shenguang laser facilities in China since 2000 are reviewed in this paper. Many experiments were made on Shenguang II (SG-II) and Shenguang III prototype (SG-III YX). Eight beams of 0.35$\mu$ m laser with pulse duration of 1 ns and total energy of 2 kJ enter into a hohlraum to create intense X-ray radiation of 180 eV on the SG-${\rm I}{\rm I}$ laser facility. The experiments on SG-II included much physics research, which consisted with hohlraum physics, implosion physics, fluid dynamical instability, opacity and shock wave driven by radiation. A lot of experimental data were obtained on SG-II. The DT neutron yield driven by radiation achieved 10$^{8}$ on SG-II. After SG-III YX was completed in 2006, the ICF experiments were mainly be made on SG-III YX that was a 8-beam, 351-nm, Nd:glass laser with an on-target energy capability in excess of 8 kJ. The radiation temperature was about 220 eV and the DT neutron yield driven by radiation was over 10$^{10}$ on SG-III YX.   

Robust Direct-Indirect Hybrid Target Implosion in Heavy Ion Fusion

In inertial fusion target implosion, beam illumination non-uniformity must be reduced to less than a few percent. In this study a direct-indirect hybrid implosion mode is discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement dz from the center of a fusion reactor chamber. In a direct-driven implosion mode, dz of about 20 micron m was tolerable, and in an indirect-implosion mode, dz of about 100 micron m was allowable. In the direct-indirect hybrid mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer the radiation transport is expected to smooth the HIB illumination non-uniformity. Two-dimensional implosion simulations are performed, and show that the HIB illumination non-uniformity is well smoothed in the direct-indirect mixture target. The results also present that dz of a few hundred micron m is allowed in HIF.   

Modeling Integrated High-Yield IFE Target Explosions in Xenon Filled Chambers

We will present the results of several radiation-hydrodynamics simulations which model the aftermath of an exploding high yield (200~MJ) indirect drive target in a xenon filled reactor chamber. The goal is to determine the radial extent to which debris from the target and hohlraum expands into the target chamber. The 1D radiation-hydrodynamics code BUCKY is used to perform integrated simulations of the target explosion beginning from ignition and includes interactions between the chamber gas and tungsten first wall. The 3D radiation-hydrodynamics code Cooper will be used to model the growth of fluid instabilities as the target material expands into the xenon gas. Cooper will also be used to investigate the early-time interaction between the burning target and hohlraum shortly after ignition.   

Low-Isentrope, High-Efficiency Heavy Ion Direct Drive Capsule Simulations

We build upon recent work [1] that presented simulations of heavy ion beams' passive range lengthening in directly-driven DT targets by now raising the ion energy over the course of the drive to follow the ablation front inward. We have scaled the target from ref. [1] to reactor grade and have chosen a higher-energy driving ion species to reduce beam perveances. While an arbitrarily strong shock cannot compress the fuel by more than a finite factor (4X in a perfect monatomic gas), there is no bound on the entropy it can add. We present 1-D implosion calculations that demonstrate the approach to adiabatic compression with an increasing number of shocks tailored to keep the fuel nearly Fermi degenerate. We have studied capsule performance using either two discrete ion beam energies or a steadily ramped main pulse energy. These simulations show that a linear energy ramp reduces heating of the fuel early in the main pulse and improves coupling as ablated plasma accumulates.\\[4pt] [1] B. G. Logan, L. J. Perkins, and J. J. Barnard, \emph{Phys. Plasmas} \textbf{15}, 072701 (2008).   

Application of nonlocal transport model to experiment

Our Krook model for nonlocal electron energy transport [1-5] has been developed on solid theoretical grounds. The model is characterized by both some flux limitation and some preheat as was shown for example in the calculation of a spherical implosion [3]. In the present work, we compare results of our model with an experiment performed at the U. of Rochester [6]. Preliminary results indicate that our Krook model does not exhibit any flux limitation for this case. The reduction in pressure -as indicated by the use of an average flux limiter of .07 to reproduce the experimental result at 1015 W/cm2- can be achieved by a combination of several classical effects, namely a reduction in the absorption fraction and taking into account 2D effects. Numerical diagnostics will be presented to support this interpretation.\\[4pt] [1] W.Manheimer (WM), D.Colombant (DC) and V.Goncharov (VG), Phys. Plasmas (PP), 15, 083103, 2008\\[0pt] [2] DC {\&} WM, PP, 15, 083104, 2008\\[0pt] [3] DC {\&} WM, PP, 16, 0627051, 2009\\[0pt] [4] DC {\&} WM, J. Comp. Phys (2010)\\[0pt] [5] DC {\&} WM, submitted to PP\\[0pt] [6] S.X.Hu, V.A.Smalyuk, VG et al, Phys. Rev. Lett., 101, 055002, 2008   

Particle Monte Carlo Transport in HYDRA

Accurate simulation of diagnostics for thermonuclear burn requires detailed modeling of the spatial and energy distributions of particle sources, in-flight reaction kinematics, and Doppler effects. In the ALE multiphysics code HYDRA, this is now achieved using a new Monte Carlo particle transport package based on LLNL's Arrakis library. It tracks neutrons, gammas, and light ions on 2D quadrilateral and 3D hexahedral meshes. Neutrons and gammas track using the latest LLNL nuclear data; light ions undergo continuous slowing down with corrections for Fermi degeneracy, small angle Coulomb deflections at track end points, nuclear collisions, and direct Coulomb collisions with plasma ions. The package agrees well with idealized analytical problems as well as high resolution diffusion burn ICF capsule and hohlraum simulations as shown and achieves run times commensurate with production requirements. An overview of the charged particle physics models used is given.   

A Vlasov-Fokker-Planck Code for Shock Ignition

A 2D3P parallel object-oriented Vlasov-Fokker-Planck code that relies on the expansion of the electron distribution function to spherical harmonics [1] has been developed and it is used to study non-local electron transport for Shock Ignition [2]. The code makes use of a rigorous formalism for the collisions between electrons, which derives from the Rosenbluth potentials and conserves energy and number. This code makes it possible to accurately model the kinetic as well as the hydrodynamic behavior of the plasma and is particularly efficient for collisional plasmas. The features of the code are showcased using standard plasma physics problems. For Shock Ignition the electron temperatures can reach up to 100keV while densities range from less than critical to greater than solid. Shock Ignition is therefore an excellent candidate for this VFP code, because the target is sufficiently collisional to allow for extremely efficient modeling.\\[4pt] [1] A. R. Bell et al, Plasma Phys. Control. Fusion 48, R37-R57 (2006).\\[0pt] [2] R. Betti et al, Phys. Rev. Lett. 98, 155001 (2007).   

Addition and Validation of a 2-D Nonlocal Electron Flux Module in DRACO

A nonlocal thermal heat flux module is being implemented in 2-D in the DRACO radiation hydrodynamics code to provide a more accurate representation of the effects of hot electron transport on Inertial Confinement Fusion target implosions. The basic theory, developed in 1-D by Manheimer, Colombant, and Goncharov,\footnote{W. Manheimer, D. Colombant, and V. Goncharov, \emph{Phys. Plasmas} \textbf{15}, 083103 (2008).} has been extended for use in $x-y$ and $r-z$ geometries. A Krook model is used for the collision operator, and a perturbative approach is followed to compute the anisotropic component of the distribution function for each electron energy. Taking the $v^3$ moment of the distribution function allows the electron thermal heat flux to be computed. The code is being validated through comparison with results obtained using traditional Spitzer-Harm heat conduction.   

New regimes and challenges for laser plasma coupling in ignition-scale hohlraums

In NIF experiments new regimes of laser plasma coupling have been accessed. Much larger plasmas have been irradiated with many large spot overlapping laser beams in a highly shaped pulse. The new features include cooler underdense plasmas, sizeable stimulated Raman scattering from densities less than 10{\%} of the critical density and even on the rising part of the laser pulse, hot electron temperatures significantly less than 30keV, and important overlapped beam effects, such as cross beam energy transfer and cooperative scattering. A simple discussion of these new effects will be given. Finally, it is clearly prudent to strongly reduce stimulated Raman scattering and use cross beam energy transfer to simply ``fine tune'' the symmetry. Then the beam balance and time-dependent symmetry would not be so dependent on the detailed nonlinear competition between two laser plasma instabilities. Some potential ways to mitigate SRS are discussed, including the use of narrower laser beams.   

Continuum Vlasov Simulation in Four Phase-space Dimensions

In the VALHALLA project, we are developing scalable algorithms for the continuum solution of the Vlasov-Maxwell equations in two spatial and two velocity dimensions. We use fourth-order temporal and spatial discretizations of the conservative form of the equations and a finite-volume representation to enable adaptive mesh refinement and nonlinear oscillation control [1]. The code has been implemented with and without adaptive mesh refinement, and with electromagnetic and electrostatic field solvers. A goal is to study the efficacy of continuum Vlasov simulations in four phase-space dimensions for laser-plasma interactions. We have verified the code in examples such as the two-stream instability, the weak beam-plasma instability, Landau damping, electron plasma waves with electron trapping and nonlinear frequency shifts [2]$^{ }$extended from 1D to 2D propagation, and light wave propagation.$^{ }$ We will report progress on code development, computational methods, and physics applications. This work was performed under the auspices of the U.S. DOE by LLNL under contract no. DE-AC52-07NA27344. This work was funded by the Lab. Dir. Res. and Dev. Prog. at LLNL under project tracking code 08-ERD-031. [1] J.W. Banks and J.A.F. Hittinger, to appear in IEEE Trans. Plas. Sci. (Sept., 2010). [2] G.J. Morales and T.M. O'Neil, Phys. Rev. Lett. \textbf{28},417 (1972); R. L. Dewar, Phys. Fluids \textbf{15},712 (1972).   

Spatially autoresonant stimulated Raman scattering in inhomogenous plasmas in the kinetic regime

The impact of spatial autoresonance on backward stimulated Raman scattering in inhomogenous plasmas in the kinetic regime is investigated. Starting from the system of three coupled wave equations, the inclusion of a nonlinear frequency shift due to kinetic effects in the equation of the electron plasma wave is found to lead to a cancellation of the frequency shift due to the density gradient. Through the amplitude of the electron plasma wave, the kinetic nonlinear frequency shift is observed to self-adjust to maintain this cancellation over a region in space, giving rise to phase-locked solutions to the electron plasma wave equation. A reduced model is employed to provide analytic insight to the autoresonant wave coupling solutions and comparisons with 1D PIC simulations are made.   

An investigation of the time dependence of crossed beam energy transfer at the National Ignition Facility (NIF)

The recent energetics campaign [1] conducted at the NIF in Fall, 2009 successfully employed crossed beam energy transfer [2] to achieve symmetry of the imploding capsule. In this laser-plasma interaction, two crossing light waves share an ion acoustic wave, and energy is transferred to the wave with the lower frequency in the frame of the plasma. In addition, plasma flows Doppler shift each beam's frequency. The amount of energy transferred from one set of beams to another is not directly measured, but rather is inferred from x-ray images of the target [3]. Radiation-hydrodynamics simulations of targets are then performed [4] that infer the amount of energy transfer required to match the measured symmetry. Here we investigate the time dependence of the crossed beam energy transfer and assess mechanisms such as saturation by kinetic effects and momentum deposition for plasma conditions expected in NIF experiments. [1] N. B. Meezan \textit{et al.,} Phys. Plasmas \textbf{17}, 056304 (2010). [2] P. Michel \textit{et al.,} Phys. Plasmas \textbf{17}, 056305 (2010). [3] G. Kyrala, invited talk, this conference. [4] R. P. J. Town, invited talk, this conference.   

Theory of superhot electron spectra generated by Raman scatter

In laser-plasma interaction (LPI) stimulated Raman scatter, electrons are accelerated by the electric field of the Langmuir decay wave, modifying the electron distribution function in the neighborhood of the phase velocity. Particle-in-cell (PIC) simulations of SRS in one or so laser speckles produce a shoulder in the distribution function that falls off rapidly at higher energy. However experimentally the energy distribution is fitted to Maxwellians extending far beyond $\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}m_e (\omega /k)^2$. Nature makes Maxwellian distributions by a succession of accelerations. Passing an electron again through a similarly-oriented plasma wave seems unlikely to kick it above the trapping width unless the fast electron's direction is oblique to the plasma wave, so that $\mbox{k}\cdot \mbox{v}/k$ is brought within the trapping width. This deflection might be by electron-ion scattering or B fields. We consider such reheating mechanisms in plasma conditions motivated by NIF ignition targets, using multidimensional (PIC) simulations and simpler models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. DE-AC52-07NA27344.   

The Parameter Dependence of Reflectivity Levels in Particle-in-Cell Simulations of Stimulated Raman Scattering

Stimulated Raman scattering (SRS) can reflect the incident laser energy of the National Ignition Facility, but modeling SRS reflectivity in this regime is difficult due to kinetic effects. Within this context, we show the parameter dependence of SRS reflectivity over a range of electron temperatures and densities, laser intensities, and speckle lengths through 1D and 2D particle-in-cell simulations with k*lambda{\_}D = 0.26-0.34 for the backscatter plasma wave. For constant k*lambda{\_}D, lower electron densities have substantially lower reflectivities since SRS saturates at amplitudes for which the detuning rate due to the nonlinear frequency shift is on the order of the growth rate. Lower reflectivities are also shown for shorter speckles due to the evolution of plasma wave packets and an inflationary onset when the ratio of the speckle length to the convective gain length is $\sim $ O(1). 2D reflectivity is lower than 1D due to transverse localization of the plasma wave, but similar dependences are shown.   

Anomalously Heated Electrons Due to Stimulated Raman Rescattering for Parameters Relevant to the National Ignition Facility

We show via one- and two-dimensional particle-in-cell simulations using the code OSIRIS how stimulated Raman backscattering (SRBS) of stimulated Raman forward scattered (SRFS) light can generate hot electrons for parameters relevant to the National Ignition Facility. The plasma wave from the rescattering process can generate electrons with energies greater than 50 keV by trapping and accelerating electrons from the original backscatter. Furthermore, in some cases electrons that are heated through rescattering can be subsequently trapped and heated by the SRFS plasma wave, even though the phase velocity of the SRFS plasma wave is high enough that SRFS alone would not trap electrons in the background electron distribution. In these cases 0.4-1.0 MeV electrons can be generated.   

Spatially resolved collective Thomson-Scattering from electron plasma waves

We present the first spatially and temporally resolved Thomson-scattering measurements of the electron temperature and density from electron plasma wave scattering in laser-produced plasmas. By fitting the Thomson scattering form factor S(k,$\omega )$ to the experimental data the density is determined primarily by the spectral separation of the peaks in the scattered spectrum, while the temperature affects the Landau damping and consequently the width of the peaks. The experiments are performed at the Jupiter Laser Facility, Lawrence Livermore National Laboratory, using a 1 ns square, 1054 nm, 400 J laser focused onto gas jets or foils to create the plasma and a 200 ps, 527 nm (2$\omega )$, 45 J laser pulse for the Thomson scattering probe. The 2$\omega $ beam probes 2 mm with a spatial resolution of 15 $\mu $m, and density scale lengths of 1 mm have been resolved. This allows a measurement of the electron heat transport in laser-plasma interactions. Comparison with hydrodynamic modeling is also presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.   

Particle-in-Cell Simulations of the High Frequency Hybrid Instability in Inertial Confiment Fusion Plasmas

We present results on the laser-plasma interaction near the quarter critical surface under conditions relevant to inertial fusion. Under these conditions, the high frequency hybrid instability (HFHI) where one of the daughter waves have mixed polarization, is likely to be dominant. In fully nonlinear kinetic simulations with the code OSIRIS we show that the spectrum at early time is consistent with theory and the growth rate predicted by HFHI theory is born out by these simulations. We also investigate the saturated electrostatic (and electromagnetic) spectrum for long timescales for both fixed and mobile ions. For high temperatures where the HFHI is dominant the absorption is dominated by the absolutely unstable modes and absorption levels near 40\% can occur even below the pure 2wp modes. In these cases, it is possible to excite HFHI modes as long as one is above the Raman threshold. We also investigate in detail the evolution of unstable modes. Nonlinear effects, such as the generation of hot electrons, half harmonics and the excitation of low frequency ion fluctuations, will also be discussed.   

Hot electron effects in laser driven shock ignition*

Shock Ignition$^{1 }$(SI) emphasizes a final, hundred-ps scale, shock-driving laser pulse, after the slower adiabatic direct-drive compression of a fueled target over several ns. Hot electrons produced during this final spike can preheat the fuel and diffuse the shock, degrading the final compression. This issue is also relevant to the earliest ``optimal'' direct drive pulses with a final intensity rise$^{2}$. Here, we use the ePLAS$^{3}$ implicit/hybrid code to study the quality of shocks generated at anticipated $\sim $8 x 10$^{15}$ W/cm$^{2}$ peak intensities for SI in compressed hydrogen. The code tracks laser light rays to the critical density, absorbs and emits prescribed 35 keV ``hot'' electrons isotropically as a fluid. These hot electrons then flow under self-consistent \textit{E{\&}B-}fields, while scattering off background ions, and dragging to low energy against the background electrons. After 65 ps we find that they have heated the background ions and electrons to 300 eV near critical, and initiated shock formation beyond it. By 520 ps a strong shock has been launched, showing more than a 2-fold frontal density rise, and corresponding pressure jump. The dependence of shock quality on peak laser intensity and the generated hot electron spectrum will be discussed. 1. R. Betti et al, PRL \textbf{98,} 155001 (2007), 2. R. Mason and R. Morse, PoF \textbf{18,} 814 {\&} 816 (1975), and 3. R. Mason, PRL \textbf{96,} 035001 (2006). *Supported partially by USDOE, DE-FG02-07ER84723.   

Ion beam driven HEDP experiments on NDCX

Intense beams of heavy ions are capable of delivering precise and uniform beam energy deposition, with the capability to heat volumetric samples of any solid-phase target material to high energy density. The WDM conditions are achieved by combined longitudinal and transverse space-charge neutralized drift compression of the ion beam to provide a hot spot on the target with a beam spot size of about 1 mm. Initial experiments use a 0.3 MeV, 30-mA K$^{+}$ beam from the NDCX-I accelerator to heat foil targets such as Au, Pt, W, Al and Si. The NDCX-1 beam contains a low-intensity uncompressed pulse up to $>$10 $\mu $s of intensity $\sim $0.4 MW/cm$^{2}$, and a high-intensity compressed pulse (FWHM 2-3 ns and fluence $\sim $4 mJ). WDM experiments heat targets by both the compressed and uncompressed parts of the NDCX-I beam, and explore measurement of temperature, droplet formation and other target parameters. Future plans include target experiments using the NDCX-II accelerator, which is designed to heat targets at the Bragg peak using a 2-3 MeV lithium ion beam.   

Optical diagnostic of warm dense matter at NDCXI

This work is related to recently warm dense matter experiments at Lawrence Berkeley National Laboratory (LBNL), Neutralized Drift Compression Experiment (NDCX) accelerator, which delivers a 30-mA, 350-keV K$^{+}$ ion beam. Using the recently-developed technique of neutralized drift compression, the beam is simultaneously compressed longitudinally by a factor of 50, and focused transversely down to a 1 mm spot. The beam pulse is used to pulse heat various target materials, including Al, W, C, Pt and Si, above 3000 K driving samples into two-phase, liquid-vapor states. The next generation accelerator, NDCX-II, is being built and scheduled to be accomplished in 2012. This new machine will, utilize 2 MeV Li+ ions, to heat 2 micrometer thick metal targets up to 1,5 eV in 0.5 ns. This will allow us investigate near critical points properties of matter. The talk will focus on diagnostics aspects of WDM at NDCX. The fielded diagnostics include a specially developed three-channel optical pyrometer which probes color temperatures of the target at 750 nm, 1000 nm and 1500 nm, with 75 ps temporal resolution. Continuous target emission from 450 nm to 850 nm is recorded by a custom spectrometer, consisting of a high dynamic range Hamamatsu streak camera and a holographic grating. Free expansion of the sample is measured by a VISAR. Future diagnostics for the NDX-II user facility will be also discussed.   

X-ray Thomson scattering in warm dense matter at low frequencies

The low-frequency portion of the x-ray Thomson scattering spectrum is determined by electrons that follow the slow ion motion. This ion motion is characterized by the ion-ion dynamic structure factor, which contains a wealth of information about the ions, including structure and collective modes. The frequency-integrated (diffraction) contribution is considered first. An effective dressed-particle description of warm dense matter is derived from the quantum Ornstein-Zernike equations, and this is used to identify a Yukawa model for warm dense matter. The efficacy of this approach is validated by comparing a predicted structure factor with data for the extreme case of a liquid metal. A Thomas-Fermi model is then introduced to allow the separation of bound and free states at finite temperatures, and issues with the definition of the ionization state in warm dense matter are discussed. For applications, analytic structure factors are given on either side of the Kirkwood line. Finally, several models are constructed for describing the slow dynamics of warm dense matter. Two classes of models are introduced that both satisfy the basic sum rules. One class of models is the ``plasmon-pole''-like class, which yields the dispersion of ion-acoustic waves. Damping is then included via generalized hydrodynamics models that incorporate viscous contributions. This suggests a method by which viscous transport properties can be measured.   

Creation and characterization of warm dense plasmas with lasers for transport study of fast electrons

In fast ignition (FI), fast electrons propagate through hot dense plasmas before arriving the compressed fuel to ignite it. Study of the fast electron transport in plasmas is important for FI under various conditions of temperature and density, which determine the plasma resistivity. To develop a platform for the transport study, a large volume warm dense plasma was created and its conditions were investigated using Al 1s-2p line absorption spectroscopy. A long pulse laser ($\sim 10^{15}$ W/cm$^2$) was used to shock heat an Al doped CH foam (0.2 g/cm$^3$) target. The target was backlit with a quasi-continuous Sm x rays around 1.5 keV and the absorption spectra were measured with x-ray streak camera. The measured spectra were fitted with an atomic physics code to infer the plasma density and temperature. A comparison of the results with 2D radiation hydrodynamics code DRACO will be presented.   

Development of an 18 keV X-Ray Thomson Scattering Source for the Characterization of Dense States of Matter

The accurate characterization of material properties under extreme conditions is an important issue for the understanding of high energy density states of matter, from planetary interiors to capsule implosions relevant to inertial confinement fusion. High energy x-ray Thomson Scattering at 18 keV will make it possible to characterize very dense states of matter such as 50x compressed beryllium, ICF-like ablator materials, aluminum compressed up to 4x by a single shock, and isochorically heated mid-Z elements (such as Ti). Here we present results from a backscattering experiment carried out at the Omega Laser Facility, performed on aluminum, the highest-Z material probed to this date. We will also demonstrate the viability of molybdenum He-alpha (18 keV) as a suitable backlighter probe source.   

Equation of State Determination from Quasi-Isentropic Compression of Solid Beryllium Liners on Z

We investigate the beryllium equation of state through constraining magneto-hydrodynamic and magneto-solid dynamic simulation with experimentally determined density profiles of a compressed beryllium cylindrical liner. Experiments utilizing pulse shaping techniques on Z have achieved quasi-isentropic compression of cylindrical beryllium liners to approximately 3 Megabars, and simulation results suggest that a large fraction of the liner remains in the solid phase through peak pressure for a 20 MA current pulse on Z. This opens up the possibility of extending the range of pressures we can explore with magnetic drive by utilizing cylindrical convergence. However, the cylindrical geometry limits the usefulness of diagnostics commonly applied to planar equation of state measurements on pulsed power machines and requires the development of new methods to unfold isentropes from the experimental data.   

An improved low-temperature equation of state model for integrated IFE target-chamber response simulations

A new quotidian equation of state model (QEOS) has been developed to perform integrated inertial fusion energy (IFE) target explosion-chamber response simulations. This QEOS model employs a scaled binding energy model for the ion EOS and utilizes both $n$- and \textit{$\ell $}-splitting for determining the ionization state and electron EOS. This QEOS model, named BADGER, can perform both local thermodynamic equilibrium (LTE) and non-LTE EOS calculations. BADGER has been integrated with the 1-D radiation hydrodynamics code BUCKY to simulate the chamber response of an exploding indirect-drive deuterium-tritium (DT) target, xenon gas-filled chamber and tungsten first-wall armor. The simulated system is a prototypical configuration for the LIFE reactor study being conducted by Lawrence Livermore National Laboratory (LLNL).   

Application of Dynamic Logic Algorithm to Inverse Scattering Problems Related to Plasma Diagnostics

In plasma diagnostics scattering of electromagnetic waves is widely used for identification of density and wave field perturbations. In the present work we use a powerful mathematical approach, dynamic logic (DL), to identify the spectra of scattered electromagnetic (EM) waves produced by the interaction of the incident EM wave with a Langmuir soliton in the presence of noise. The problem is especially difficult since the spectral amplitudes of the noise pattern are comparable with the amplitudes of the scattered waves. In the past DL has been applied to a number of complex problems in artificial intelligence, pattern recognition, and signal processing, resulting in revolutionary improvements. Here we demonstrate its application to plasma diagnostic problems. \\[4pt] Perlovsky, L.I., 2001. Neural Networks and Intellect: using model-based concepts. Oxford University Press, New York, NY.   

Measuring the Propagation of a Supersonic Radiation Front in Foam via Spatially Resolved Spectral Imaging of a Tracer Layer

We present results obtained at Omega with a diagnostic designed to characterize the propagation of a supersonic radiation front in low-density foam. Methods used to measure the propagation of a subsonic radiation wave, which rely on imaging the hydrodynamic evolution of objects placed in its path, cannot be used for supersonic waves. Instead, a tracer is embedded in the foam and its charge state diagnosed as it is heated by the radiation. We use a Ti foil, its face perpendicular to the direction of wave propagation. A broad-band x-ray source illuminates the face of the foil, and its absorption of these x-rays is measured using a Bragg spectrometer, with a high-speed detector recording spatial information along the wave propagation direction and spectral information in the orthogonal one. We thus obtain a spatially and temporally resolved measurement of the ionization state of the tracer, and making certain assumptions, of its temperature and that of the foam. We also describe a version of the diagnostic planned for experiments on NIF.   

The Spectral Diagnosis and its radiative transportation

With the evaluated data of atomic process, We found that the ratio of both spectral lines and line to satellite line rapidly change with electronic temperature, and the profile rapidly with electronic density. With the help of the radiative transportation of one-dimensional equation, we analyzed some implosion experiments, done by Chinese Academe of Engineering physics, and obtained their temperature and density.   

Development of novel optics for X-ray phase-contrast imaging applications in ICF research

Differential phase-contrast (DPC) imaging with X-rays from a few keV to a few tens of keV is attractive for ICF diagnostic due to its sensitivity to density gradients in low-Z matter. DPC radiography could help characterize the ICF pellet from its pre-implosion, through its early and late implosion stages. To separate the absorption and refraction contributions to ICF radiography we explore using shearing interferometry with micro-periodic optics. For X-ray energies below 25 keV we investigate using phase and absorption gratings in the Talbot-Lau configuration. Absorption and phase gratings of 10 $\mu $m periods were tested for phase-contrast imaging of ICF pellet-like objects using a small-focus X-ray source and a high resolution X-ray CCD. For DCP measurements at higher X-ray energies we propose a novel type of X-ray optics, consisting of lithographically made grazing incidence micro-periodic mirrors [1]. Prototype mirrors of 5-100 $\mu $m period fabricated with this method showed promising characteristics in laboratory tests. Work supported by DoE Grant DE-FG02-99ER54523. \\[4pt] [1] D. Stutman, M. Finkenthal, and N. Moldovan, to appear in Rev. Sci. Instrum.   

Experimental validation of a novel imaging scheme to eliminate astigmatism

Recent papers by Bitter et al.$^{1-3}$ have proposed novel imaging schemes to eliminate astigmatism by matched pairs of spherically bent crystals or reflectors. These imaging schemes should allow stigmatic (or point-to point) imaging at arbitrarily large angles of incidence and be applicable to a broad spectrum of the electromagnetic radiation, including microwaves, visible light, EUV radiation, and x-rays, if appropriate spherically bent reflectors are used. This paper presents experimental results from tests of one of these imaging schemes with visible light, which validate the concept of this scheme and show that stigmatic imaging of objects with areas of about 5 mm x 5 mm is possible. $^{1}$M. Bitter et al, Rev Sci. Instrum. \textbf{79}, 10E927 (2008); $^{2}$M. Bitter et al., J. Xray Sci. Technol. \textbf{17}, 153 (2009); $^{3}$M. Bitter et al., J. Phys. B: At. Mol. Opt. Phys. \textbf{43}, 144011 (2010)   

Geant4 simulations of the Gamma Reaction History Diagnostic at the NIF, Omega and HIGS calibration facility

This paper discusses the development of a Geant4 model of the Gamma Reaction History (GRH) diagnostic at NIF and Omega, Inertial Confinement Fusion (ICF) laser facilities. The GRH diagnostic has been developed to measure bang-time and burn-width parameters for ICF implosions at both facilities, further investigations have also shown that measurements, such as ablator aerial density and ion temperature, may also be possible. Absolute gamma calibration experiments have been performed at the High Intensity Gamma Source (HIGS) facility at Duke University to increase confidence in parameters supplied by simulation for the use in calculations at both laser facilities. A comparison between HIGS data, Geant4 and the ITS ACCEPT code will be presented along with other important GRH properties, such as temporal unit response function, peak-timing shift and Cherenkov production profile, all as a function of pressure and incident gamma energy.   

Electron Beam Radiography as a Proposed Plasma Diagnostic

Several recent studies have shown that charged particle diagnostics of ICF implosions provide new and useful information on the capsule implosion and the E and/or B fields associated with the finite scale plasma structures. Possible mechanisms for the plasma self-generation of these fields have been discussed but are not fully clear. In the present study, an electron beam (eBeam) radiography system (30MeV) is proposed which may have significant advantages over the existing methods which use 15 MeV nuclear-fusion driven protons as the charged particle diagnostic ``point'' source. The relativistic electron beam has a greater penetration (cm2/g) and is predicted to have improved deflection from E or B relative to the scattering from multiple coulomb collisions. The scattering determines the plasma density image but simultaneously contributes noise to the signal due to E or B deflections. On-going studies focus on the forward calculation of the eBeam through simple plasma and test objects. The self-consistent generation of the E or B fields in the dynamic transient plasma may require new computational tools to explicitly include multi-species plasma in the presence of E or B fields and to resolve the mixing structures at the fuel-capsule interface in ICF implosions.   

Imaging X-ray Thomson Scattering Concept for the Matter in Extreme Conditions Instrument at LCLS

The Linac Coherent Light Source at SLAC, an x-ray free electron laser tunable in the range 800 -- 8000 eV, with 2 x 10$^{12}$ photons in a 200 fsec pulse, is a revolutionary facility that will impact many fields of science, including high energy density (HED) laboratory plasmas. The Matter in Extreme Conditions (MEC) instrument at LCLS will use high-power lasers to create HED plasmas, and will use the XFEL with various diagnostics to probe these conditions. One proposed use of the LCLS-MEC is to perform Thomson scattering in dense plasmas using the x-ray laser as a probe. Recent experiments at LANL's Trident Laser demonstrate the ability to measure spatial profiles of dense plasma conditions using a laser-plasma x-ray source, together with a high-efficiency, high-resolution imaging spectrometer, to perform imaging x-ray Thomson scattering. Here we propose an imaging spectrometer design, with $<$20-$\mu $m resolution, that will provide profiles of density, temperature, and ionization state in near-solid-density plasmas with a 8 keV probe at the LCLS-MEC, and propose an initial experimental design to examine shocks in near-solid-density plasmas.   

Imaging X-ray Thomson Scattering at the Omega Laser Facility

Probing dense plasmas using the technique of x-ray Thomson scattering(XRTS) can yield the temperature, density, and ionization state. Measurements of these parameters are essential to refine models for the equation of state (EOS). We report on the development of a 1D imaging spectrometer which combines high spatial ($<$25 $\mu$m) and spectral (3-4 eV at 9 keV) resolutions with a long (several mm) field of view. Plasma parameters can be extracted along spatial profiles for the study of the EOS for radiative shocks in dense plasmas, the warm dense matter regime, and many more potential applications in high-energy density experiments. We report on initial results from fielding a similar design on an XRTS experiment at the Trident laser at Los Alamos National Laboratory. These results motivate the integration of the diagnostic on the OMEGA laser at the Laboratory for Laser Energetics.