Session NP1: Poster Session V: General Tokamak; Turb. and Transport; Beams and Rad: Ion Beams, Accelerators, and Lasers; Theory and Sim II; HEDP, ICF, and Diag.

Validity of the Objectives and Solutions of the Ignitor Program*

The validity of the objectives of the Ignitor Program\footnote{B. Coppi, A. Airoldi, et al. \textit{Nucl. Fusion} \textbf{41} (9), 1253 (2001)} and its design solutions have been reaffirmed recently\footnote{P.H. Rebut, \textit{EPS Conference on Plasma Physics, Rome, 19 June 2006}}: i) in order to prove the scientific feasibility of relevant fusion reactors, burning plasmas with $Q \ge 50$ should be produced and studied, ii) copper magnets are the most convenient solution for machines capable of reaching this objective, iii) experiments that do not include a divertor are the most efficient, at producing the highest plasma currents with the best confinement parameters. Ignitor is in fact designed to operate with either an ``extended-limiter'' configuration or with a double X-point configuration (X-points on the first wall). The experiment can reach the conditions where the thermonuclear instability is excited $(Q\rightarrow\infty)$ or where the plasma can be kept under quasi-stationary conditions with large values of $Q$ and the input of modest amounts of ICRH power. The maximum plasma currents with reasonable safety factors are up to 11 MA, corresponding to average poloidal fields $B_p\approx 3.4$ T. The latest physics and technology developments are presented.\\ $^*$Sponsored in part by ENEA of Italy and by the U.S. DOE.   

Ignitor Plasma Performance in the H-mode with New Scalings$^*$

Ignitor can operate with a double-null configuration with the relevant X-points laying close to the first wall, {$B_{T} \simeq 13$ T, $I_{p} \simeq 9$ MA}, {$R_{0} \simeq 1.32$} m, {$a \simeq 0.44$} m. The power threshold to access the H-regime has been found to be considerably lower on the basis of recent scalings\footnote {D.~C.\textsc{} McDonald et al., \textit{Plasma Phys. Control. Fusion} \textbf{48}, A439 (2006);} than originally assessed. The expected plasma parameters in this regime are estimated by using a global O-D model. The operating space corresponding to $Q\simeq10$ is verified to be relatively broad, even considering the pessimistic case of rather flat density profiles, and far from density and $\beta$ operational limits. Moreover, the analysis of JET experimental data\footnote{H.~Weisen et al., \textit{Plasma Phys. Control. Fusion} \textbf{48}, A457 (2006);} indicates that relatively peaked density profiles (e.g. $n_0/\langle n \rangle \simeq 1.5$) can be obtained in the H-regime. With these profiles, the attainable plasma parameters are found to improve considerably and values of $Q$ much larger than 10 can be attained. The adoption of scalings\footnote{J.~W.~Cordey et al. \textit {Nucl. Fusion} \textbf{45}, 1078 (2005).} for the energy confinement time with a weak dependence on $\beta$ does not change the operating space significantly in the case of Ignitor.\\ $^*$Work supported in part by ENEA of Italy and by the US DOE.   

Importance of the Ideal Ignition Conditions and Intermediate Objectives of Ignitor

At the ideal ignition temperature, in D-T plasmas where the produced $\alpha$-particles can be confined by the necessary current, the energy loss by bremsstrahlung emission is compensated for by the $\alpha$-particles heating. Once this condition is reached, the plasma density can be raised during the plasma heating phase without encountering a radiation barrier. This is a meaningful intermediate objective for Ignitor operating with $B_T \simeq 9$ T, a double X-point (on the first wall) configuration, and ${I_p} \simeq 6$ MA, as well as in the `extended limiter' configuration with $B_T \simeq 9$ T and $I_p \simeq 7$ MA. Numerical simulations have been performed considering volume average $ n_e \simeq 2 \times 10^ {20}$ m$^{-3}$, average $Z_{eff} \simeq 1.5$, and 5 MW of ICRH power absorbed by the plasma. Even without accessing the H- regime and with pessimistic assumptions about the energy confinement time (such as that corresponding to the ITER97L scaling) the peak temperatures are 5.5 to 6.5 keV and the $\alpha$ heating power can be as high as 2 MW. The available ICRH power, combined with the Ohmic and $\alpha$-particle heating, makes the access to the H-regime possible in this case as well as in that for which full ignition can be approached ($B_T \simeq 13$ T, $I_p \simeq 9$ MA).   

ICRH Physics and IGNITOR Experiments with Reduced Parameters*

In Ignitor, preparatory experiments with reduced machine parameters are planned before full performance operation. A transport analysis has been carried out to verify that the ideal ignition conditions in D-T plasmas are determined, a significant physics objective. The relevant Ion Cyclotron Heating applied for these regimes is studied in order to identify the power deposition profiles to be used in the transport analysis. The Ignitor ICRH system can operate with a large frequency band (80-120 MHz) in a sufficiently broad range (4-12 MW) of delivered power. This frequency band, is consistent with the use of magnetic fields in the range 9-13 T. In the considered reduced parameter scenarios the magnetic field is 9T with a plasma current of 7 MA in the extended limiter configuration and 6 MA in the double X-point configuration. A parametric study of the power deposition profiles is presented as function of the minority concentration, minority species, frequency band for both configurations, by using a full wave code in plane and toroidal geometry. An optimum frequency band is found in the range 85-95 Mhz with a delivered power of 8 MW (limiter configuration) and 5 MW (X-point). The power is essentially absorbed by the minority and redistributed collisionally to the ion species of the bulk plasma. \newline*Sponsored in part by C.N.R. and E.N.E.A. of Italy and by the US DOE.   

Performance of the High Speed Ignitor Pellet Injector$^*$

The construction of the four barrel, two-stage pellet injector for the Ignitor experiment, a collaboration between the ENEA Laboratory at Frascati and ORNL, is nearly completed. Initial testing of the ORNL subsystems (cryostat, pellet diagnostics and control system) were carried out with D$_2$ pellets. New light gate and microwave cavity mass detector diagnostics were developed specifically for this application. The ENEA pneumatic propelling system, which includes innovative pulse shaping valves and uses fast valves in the independent gas removal lines to prevent the propulsion gas from reaching the plasma chamber, was extensively tested in Italy and is ready for shipping to ORNL. The injector will deliver pellets of different sizes with velocities up to 4 km/s, capable of penetrating near the center of the plasma column when injected from the low field side in Ignitor. The new injector could be tested on existing experiments, such as JET. Our simulations show that a pellet of 5 mm in diameter could reach the inner plasma region in an actual 9 keV discharge that had an internal transport barrier.\\ $^*$Sponsored in part by ENEA of Italy and by the U.S. DOE.   

Fabrication Techniques for the Magnetic Diagnostics of Ignitor$^*$

The design of the full set of electromagnetic diagnostics for the Ignitor experiment and their integration with the plasma chamber has been completed. The estimated neutron flux at the first wall during an ignition discharge is expected to cause a sensible, although reversible, degradation of the inorganic insulators surrounding the conductors that are positioned in the shade of the Mo first wall tiles. The measurement of fundamental plasma parameters such as current and position by means of electromagnetic diagnostics can thus be problematic. This ongoing R\&D program is aimed at the selection of insulator materials with higher damage threshold and to the development of effective and affordable fabrication procedures. Two prototype coils suitable for testing in existing experiments have been manufactured. The first prototype is made of a pre-insulated nickel wire immersed in a magnesium oxide weakly bonded powder. The wire is contained in a fully sintered alumina case sealed with a glass ceramic powder. In the second prototype the nickel wire is immersed in a MgO powder and is wrapped in an oxide ceramic composite layer infiltrated with a glass ceramic matrix. \\ $^*$Sponsored in part by ENEA of Italy and by the U.S. D.O.E.   

The ICRH System for the Ignitor Experiment*

The ICRH system is an integral part of the Ignitor experiment as it provides the flexibility to reach ignition regimes following different paths in parameter space and, in particular, by shortening the time needed for this. Another important use of the ICRH is to maintain the plasma in a slightly sub-ignited state, avoiding the excitation of the thermonuclear instability, under quasi-stationary conditions, for the entire duration of the plasma current flat-top. The ICRH system is structured with a modular configuration and launches the power into the plasma through RF strap-antennas based on 4 straps, grouped in two poloidal pairs, per port. The system is designed to operate in the frequency band 80-120 MHz delivering a total power up to 12 MW at the lower frequencies. Each module consists of 4 high power generators whose power is split over two ports (8 straps) in order to keep the maximum electric field (especially in the vacuum region of the straps and transmission line) below 5kV/cm. A 30$\Omega$ vacuum transmission line, including the feedthrough, tranfers the power of 0.4 MW to each strap with a total power of 1.6 MW per port. The RF configuration of the modules allows a full phase controls (toroidal and poloidal) of the straps though a PLL phase control. Two modules, distributed over 4 ports, can produce about 6 MW at 120 MHz in order to attain ignition with a limited RF pulse during the plasma heating phase. \newline*Sponsored in part by ENEA of Italy and the U.S. DOE.   

X-ray Imaging for Plasma Position Control in the Ignitor Experiment$^*$

In a burning plasma environment, traditional magnetic measurements may be expected to fail because of the high neutron and gamma radiation background. Light extraction and detection will also be more difficult than in present day tokamaks. In general, it will not be possible to keep detectors in the proximity and in direct view of the plasma. In this work we propose a diagnostic system for plasma position control using a multilayer mirror (MLM) as the dispersing element for the soft X-ray radiation emitted from the plasma outer region, and a Gas Electron Multiplier (GEM) detector. In the proposed layout, the radiation of the lower and upper region of the plasma is diffracted by cylindrical MLMs at shallow Bragg angles, and is collected by 2D detectors placed outside the machine horizontal port. GEM detectors are suitable for radiation in the 0.2-8 KeV range, and they are characterized by a very high counting rate. This system should measure the plasma position and detect any plasma movement with sufficient time resolution to be used for real-time feedback control of the vertical plasma position.\\ $^*$Sponsored in part by ENEA and Universita' di Bari of Italy, and by the US DOE.   

Control Optimization for the Position and Shape of the Ignitor Plasma Column*

The performance of the control system for the position and shape of the elongated, tight aspect ratio plasma column of Ignitor has been analyzed using the CREATE\_L linearized MHD deformable plasma response model\footnote{R. Albanese, F. Villone\textit{ Nucl. Fusion} \textbf {38} 723 (1998)}. The possible failure of the relevant electromagnetic diagnostics has been taken into account by considering the feasibility of vertical control by other means, employing X-ray emission and thermography to evaluate displacements of the center of the plasma column and deformations of its outer surface interacting with the first wall. A realistic description of the power supplies has been introduced in the simulation scheme, thus allowing the optimization of the PID (Proportional-Integral- Derivative) controller. Both a voltage and a current loop control scheme have been analyzed: the first has been found to be only marginally better than the second one. The problem of controlling the shape of the plasma cross section has been dealt with by considering shape deformations induced by varying one of the plasma macroscopic parameters (eg., $I_p$, $\beta_ {pol}$, $l_i$) by a few percent.\\ $^*$Sponsored in part by ENEA of Italy and by the U.S. DOE.   

Plasma-wall Interaction Analysis for the Ignitor Experiment$^*$

The thermal wall load on the first wall has been analysed for the set of plasma parameters that correspond to ignition. The ``extended limiter'' configuration of the Ignitor First Wall and the need to analyse the effect of possible off-nominal 3D configurations, does not allow standard edge plasma analysis techniques to be used, such as the B2 code. Thus, the development of a new 2D fluid edge plasma model\footnote{F. Subba, R. Zanino, {\it et~al.}, Bull. Am. Phys. Soc., \textbf{50} (8), 201 (2005).} has been adopted to carry out an analysis\footnote{F. Subba, {\it et~al.}, 17th Inter. Conf. on Plasma Surface Interactions in Cont. Fus. Devices, Hefei Anhui, China, May 22 - 26, 2006} that has verified the low level of the peak heat flux (for the nominal configuration) finding it slightly larger than previous predicted analyses. The presence of a significant deposition localized at the inboard mid-plane plasma-wall tangency point, due to cross field diffusion, is also consistent with previous analyses, where the radial contributions to the heat load deposited onto the wall was introduced as an \textit{ad hoc} hypotesis. A 3D analysis of the thermal loads during the start-up phase of the discharge is being undertaken together with a sensitivity study of the thermal loads obtained under different transport assumptions. \\ $^*$Sponsored in part by ENEA of Italy and by the US DOE.   

Structural Analysis of the Ignitor Load Assembly*

The structural analysis of the IGNITOR machine Load Assembly has been completed taking into account the friction coefficients at the interfaces between its main components. A Finite Element ANSYS model was used to analyze the non-linear mechanical behavior of the structure. The calculation shows stresses within the allowable limits at the operating temperature. Interlaminar shear stresses values on the insulators of the toroidal field coils have been validated by the results of tests performed by Ansaldo. The non-linear analysis takes into account both the in-plane and the out-of-plane loads. Under normal operating conditions the assumed friction coefficient on the wedging surfaces is adequate to assure the structural stability of the Load Assembly. Furthermore, once unloaded, the structure comes back without any permanent deformation. The safety factors of the average shear stresses against the insulation shear rupture strength at the beginning of Ignitor life is always greater than 3, while at the end of life this is reduced to about 2 because of the degradation of mechanical properties due to the neutron dose. Keys of proper dimensions between the 30$^{\circ}$ extension of the C-clamps modules have been adopted to assure structural stability. \newline*Sponsored in part by ENEA of Italy and by the U.S. DOE.   

First Wall Design for the IGNITOR Machine*

A detailed 3D finite element model has been developed in order to evaluate the electromagnetic loads on the (mechanical) carriers of the tiles that constitute the First Wall of Ignitor during a reference Vertical Disruption Event. A thermo- structural analisys of the most stressed tile carrier with a cycled load has been completed. The study employed a non-linear ANSYS Code. The results show a temperature increase up to 341$^ {\circ}$C for a single step of 4 sec. The stresses and deformations on the component which has undergone a cycled load are within the limits of the allowable values. The design layout of the First Wall has been finalized, taking into account all requirements of the IGNITOR Machine. The electrical diagnostics placed inside the plasma chamber have been included in the tile carrier design. The First Wall has been tailored with special consideration for the Faraday Shield facing the ports through which ICRH is injected. \newline*Sponsored in part by ENEA of Italy and by the U.S. DOE.   

Plasma Chamber Design and Fabrication Activities

A fabrication procedure for a typical Plasma Chamber (PC) sector has been developed to cover all the manufacturing phases, from the raw materials specification (including metallurgical processes) to the machining operations, acceptance procedures and vacuum tests. Basically, the sector is made of shaped elements (forged or rolled) welded together using special fixtures and then machined to achieve the final dimensional accuracy. An upgraded design of the plasma chamber's vertical support that can withstand the estimated electromagnetic loads (Eddy and Halo current plus horizontal net force resulting from the worst plasma disruption scenario VDE, Vertical Displacement Event) has been completed. The maintenance of the radial support can take place hands-on with a direct access from outside the cryostat. With the present design, vacuum tightness is achieved by welding conducted with automatic welding heads. On the outer surface of the PC a dedicated duct system, filled by helium gas, is included to cool down the PC to room temperature when needed.   

The Columbus Concept*

The Columbus experiment\footnote{B. Coppi and M. Salvetti, MIT- RLE report PTP(2003)} is proposed as a parallel US project to the Ignitor program carried out in Italy. A spectrum of complementary experiments is in fact required for a ``Science First'' approach to fusion research\footnote{B. Coppi, MIT-RLE report PTP 02/04 (2002)}. The possible discovery of new phenomena and the understanding of known ones, i.e. sawtooth oscillations, under fusion burning conditions will drive the design of future fusion reactors. Columbus is designed to reach ignition conditions in D-T plasmas where the $\alpha$-particle heating compensates for all energy losses. It takes advantage of the Ignitor R\&D effort and the technology acquired during the construction of the full-size prototypes of its main components (the second generation construction of the toroidal field plates has been completed). Columbus is geometrically self-similar to Ignitor, the linear dimensions being multiplied by 25/22 ($R_{0} \cong 1.5$ m) and the volume increased by about 50\%. The toroidal magnetic field is decreased by the factor 12.6/13 and the average poloidal field produced by the plasma current is about equal to that of Ignitor for comparable values of the magnetic safety factor $q_{a}$. The reference plasma current is $I_{p} \cong 12.2$ MA, the value that ITER would produce for the same $q_{a}$ but without reaching ignition. The machine is based on cryogenic resistive magnet technologies. *Sponsored in part by the U.S. DOE.   

The IGNITOR ICRF system

A flexible auxiliary Ion Cyclotron Resonance Heating (ICRH) system (f = 80 -- 120 MHz) has been included in the IGNITOR machine design. ICRH systems have been successfully tested on a number of existing devices especially at high density. Ignition can be accelerated significantly by relatively low levels of ICRH (about 5 MW, a fraction of the final fusion heating) when applied during the current ramp-up. In addition, ICRH provides a useful tool to control the evolution of the current density profile. Four antennas, each composed by 2 straps, 4 tuning stubs, and 2 generators each, can deliver a minimum RF power of about 12 MW for the entire adopted frequency range. The possibility of adding two more antennas has been considered. The antenna design has been based on performance evaluation obtained with the TOPICA{\copyright} simulation suite (Torino Polytechnic Ion Cyclotron Antenna code).   

HBT-EP Active Mode Control Research: Progress and Plans*

HBT-EP MHD mode control research is studying advanced digital feedback control algorithms, ITER relevant internal modular feedback control coil configurations and their impact on kink mode rigidity, and the effects of edge neutral damping as a dissipation mechanism on RWM rotational stabilization. HBT-EP incorporates a segmented adjustable conducting wall, internal modular feedback control coils driven by a high-speed (10 microsecond delay) MIMO digital control system for resistive wall modes (RWM) and a biased electrode for edge rotation control. Primary research thrusts are to: (1) study required feedback gain as a function of control coil modularity and toroidal angle coverage testing possible breakdown in `rigid mode' kink model; (2) test advanced feedback control techniques of adaptive filtering and state estimation, (3) study physics of RWM rotation stabilization by controlled variation of critical parameters (rotation, dissipation, and growth rate). Recent results including measurement of the radial eigenmode structure of the external kink and its dependence on plasma dissipation, enhancements of the VALEN modeling code, development of reduced state space models, and initial kink rigidity studies will be discussed. *Supported by U.S. DOE Grant DE-FG02-86ER53222.   

Quantifying Kink Mode Dissipation Using Radial Eigenmode Measurements*

Understanding the magnitude and source of plasma dissipation that governs resistive wall mode rotational stabilization is crucial for the extrapolation of current experimental results to future burning plasma regimes of operation. To date, methods to determine the magnitude of dissipation affecting kink mode dynamics has been through the measurement of the complex damping rate of the mode using MHD spectroscopic techniques [1,2], or by detailed profile measurements of momentum loss as the kink mode evolves in time [3]. Here we present an alternate method to quantify the magnitude of dissipation using measurements of the polodial magnetic field fluctuations associated with the kink's radial eigenfunction. A twenty element, high spatial resolution Hall sensor array was used to measure the kink mode perturbed poloidal fields. Comparison of the relative phase shift of these fluctuations as a function of minor radius with calculations of the expected structure of the kink-RWM eigensystem show a sensitive dependence upon the magnitude of dissipation allowing its quantitative characterization. Estimates of the magnitude of dissipation using these phase shift measurements are in good agreement with previous MHD spectroscopy measurements [1]. *Supported by U.S. DOE Grant DE-FG02-86ER53222 1. M.E.Mauel, \textit{et al}., Nuc. Fusion, 45, 285 (2005) 2. H. Reimerdes, \textit{et al}., PRL, 93, 135002 (2004) 3. W. Zhu, \textit{et al}., PRL, 96, 225002 (2006)   

Using a Kalman Filter during Active Feedback of External Kink Modes in HBT-EP

Active feedback stabilization has been shown to stabilize the $(m,n) = (3,1)$ external kink mode in tokamak discharges, but noise may limit system performance. In numerical simulations, Kalman filtering has been shown to enhance external kink feedback by mitigating the effects of sensor noise.\footnote{M.~E.~Mauel, \textit{et al.}, Bull. Amer. Phys. Soc. Paper BP1.00007 (2005).} The HBT-EP tokamak is equipped with a versatile, high-speed, digital mode control system that enables rapid development and testing of new feedback schemes. Kink mode suppression in plasmas near the ideal wall limit has been achieved using a Discrete Fourier Transform (DFT) decomposition of sensor coil signals in conjunction with a static lead-lag compensator.\footnote{A.~Klein, \textit{et al.}, Phys.~Plasmas, {\bf 12}, 040703 (2005).} The Kalman filter makes dynamic estimates for the state of a system based on sensor inputs and an internal model. Experimental studies of Kalman filter implementations using HBT-EP's digital mode control system are presented.   

Observer Design for Resistive Wall Mode Detection*

Design of a linear observer to detect only the unstable resistive wall mode (RWM) contribution to a realistic set of sensor coil signals is described. Accurate low order computational models of the plasma, wall, feedback, and sensor coil system are essential for reliable observer design. We use two methods to derive a reduced, state space model of the RWM constructed using the VALEN code. (1) A simple method has been developed for calculating quantitative ordinary differential equation models of the resistive wall mode using contracted matrix equations calculated by the VALEN code. Using eigenvectors of the unstable RWM system as determined by VALEN, dimensionless coupling numbers that characterize the mutual inductances of the plasma-wall-feedback coil system are calculated. These dimensionless coupling numbers are then incorporated into a scalar ordinary differential equation that can be used for data analysis, estimation of system eigenvalues, and design of complex feedback control algorithms such as observers. (2) Low order state space models have also been constructed from VALEN frequency response transfer function data. The observer performance using these two reduced model types is illustrated and compared by applying it to RWM feedback on the HBT-EP and D-IIID tokamaks. *Supported by U.S. DOE Grant DE-FG02-86ER53222.   

The Effects of Neutral Damping on Resistive Wall Mode Physics

The physics of the dissipation mechanism responsible for rotational stabilization of the resistive wall mode (RWM) is an object of intense current research. On HBT-EP, there is experimental evidence that edge neutral damping is a significant dissipation mechanism that affects tearing mode behavior [1]. To quantify the possible effect of neutral damping on RWM physics, we are constructing a 16-channel linear photo-detector array to measure D$_{\alpha }$ emission and its fluctuations. These measurements will be used in conjunction with a 1D space, 2D velocity kinetic transport model of the atomic and molecular deuterium penetration to quantify neutral profiles within the plasma [2]. Ongoing efforts to measure the neutral damping contribution to RWM rotational stabilization utilizing the measured D$_{\alpha }{\rm g}$ profiles to estimate the edge neutral density will be presented. *Supported by U.S. DOE Grant DE-FG02-86ER53222 1 E. D. Taylor, \textit{et al}., \textit{Phys. Plasmas} \textbf{9}, 3938 (2002) 2 B. LaBombard, MIT PSFC RR-00-9, (2000).   

Experimental Study of Biased Probe Induced \textit{ExB} Rotation on MHD Modes*

The effect of plasma rotation on the behavior of MHD modes is a topic of importance for both resistive wall and tearing mode stability and their effect on the performance of present and future magnetic fusion devices. On HBT-EP, a biased molybdenum electrode inserted into the edge plasma is used to change the intrinsic \textit{ExB} rotation of MHD activity of both kink and tearing mode fluctuations in a controllable systematic way. It has been possible to brake MHD mode rotation to zero rotation frequency using this technique. For large applied bias voltage, MHD activity is observed to accelerate in the direction opposite to the naturally occurring mode rotation with frequencies up to two or three times the natural rotation rate. Measurements will be presented using a triple probe array to quantify changes in the edge profiles of the fluctuating electron temperature, plasma density, and potential near the rotating magnetic islands under electrode bias. A Hall magnetic field sensor array and external pickup coils are also used to characterize the plasma and MHD fluctuations during bias probe induced mode rotation changes. Initial calculations of the effect of magnetic islands on perpendicular plasma conductivity will be discussed. *Supported by U.S. DOE Grant DE-FG02-86ER53222   

VALEN RWM Control Modeling: Kalman Filtering for Noise Reduction and Reduced State Space Descriptions*

Resistive wall kink modes (RWM) are an important performance-limiting instability for magnetic confinement fusion systems. The growth rate of the ideal kink mode is slowed as it electromagnetically interacts with nearby conducting walls. The result is a RWM grows on the resistive time scale of the wall. A feedback control system can be designed to further reduce the growth rate of the RWM and stabilize the instability. The VALEN computer code was designed to accurately model and study different RWM feedback control scenarios [1]. Kalman filtering techniques are being investigated to obtain improvements in control system performance and reduction in power requirements for feedback suppression of the RWM. Significant reduction in the required control system voltage was demonstrated for a simple wall, control, and sensor coil model. Recent work on Kalman filter implementation in both full and reduced state space models of DIII-D and the proposed International Thermonuclear Energy Reactor (ITER) will be presented using a realistic noise model based on actual experimental DIII-D data. \newline 1. J. Bialek, et al., Phys. of Plasmas, 8, 5, 2170, (2001)   

VALEN Enhancements: Transfer Functions and Progress in Including Multiple Plasma Modes*

The capabilities of the VALEN RWM active control modeling code have been enhanced. VALEN now has the capability to compute transfer functions based on a single unstable plasma mode. This allows the standard techniques of frequency response analysis and design, such as Nyquist analysis and feedback compensation design to be applied to VALEN RWM problems. VALEN Nyquist analyses for ITER benchmark problems without plasma effects are in excellent agreement with MARS code results. With plasma included in the model good agreement between MARS and VALEN was obtained up to mid-way between the no-wall and ideal wall pressure limit. At higher values of plasma pressure near the ideal limit the two codes differ with VALEN observing more complexity in Nyquist plots resulting in saturation in maximum stable pressure with proportional gain feedback. We also report on progress in including the effects of multiple plasma modes in the VALEN model. The new version of VALEN will include the effects of additional stable plasma modes in the calculation. The method assumes a linear plasma response to an applied external magnetic perturbation and uses the DCON ideal-MHD stability code to obtain the total normal magnetic field distribution on the plasma surface and the eigen-energies of the modes. Results are presented for HBT-EP and ITER. *Supported by U.S. DOE Grant DE-FG02-86ER53222.   

Investigation of the influence of different auxiliary heating methods on the Density Limit in TEXTOR

The dependence of plasma rotation and heating power on the density limit for MARFE onset has been studied on TEXTOR using different mixtures of auxiliary heating methods (ICRH, co-, and ctr- NBI). The edge density limit in the plasma heated by NBI is two times larger than that observed in the plasma heated by ICRH ( P$_{NBI }$= P$_{ICRH }$= 1.3 MW). The dependence of the density limit with regard to NBI direction is not noticeable, which could be because variation of plasma edge rotation by NBI is one or two orders of magnitude lower than the ion sound speed. The experimental data indicates that the different heating methods changes the distribution of the neutral particle flux, which plays an important role in determining the threshold for the MARFE onset.   

Control simulation of neoclassical tearing modes in KSTAR

Control of neoclassical tearing modes (NTMs) is one of the key issues to achieve stable high performance discharges for future advanced tokamaks. In KSTAR, active suppression of m/n = 3/2 and 2/1 NTMs will be pursued by using a 3MW electron cyclotron current drive (ECCD) system. To develop a NTM control system in KSTAR, a prototype NTM control simulator is developed. A NTM stability model is constructed by the modified Rutherford equation (MRE) with KSTAR equilibrium parameters. In the NTM controller, the plasma radial position is controlled to align the ECCD to the resonant flux surface where the tearing mode resides by utilizing the fast in-vessel control coils (IVCCs) of KSTAR. To model radial plasma responses during the control sequence, a linear, non-rigid plasma model is constructed by following perturbed equilibrium formulation. Performance of the prototype simulator is assessed in terms of suppressing the NTM modes in KSTAR and utilized to provide controller design criteria for the complete suppression of the modes. The prototype simulator will be used to develop a new NTM control algorithm for the model-based advanced controller with high control efficiency.   

Equilibrium reconstruction using EFIT code for KSTAR

For application to the KSTAR (Korea Superconducting Tokamak Advanced Research) device, we have made some modification to the EFIT code and installed it on our computing system. The main function of EFIT is reconstruction of plasma equilibrium using discharge data. After every discharge, the code will be run for a chosen time array and the results will be stored in the same way as experimental data will be. An MDSplus system will be used as the data storage for KSTAR; therefore, the EFIT reads experimental data from the MDSplus server and writes the results to it. We have added some subroutines to EFIT for direct link with the MDSplus server and also converted it to Fortran 95 form. Test runs of the code will be made by using the KSTAR plasma control system. This paper will also present results of equilibrium data obtained with the equilibrium mode of EFIT.   

Introduction of EAST Project --- Mission and Progress

\textbf{EAST} is an \textbf{E}xperimental \textbf{A}dvanced\textbf{ S}uperconducting \textbf{T}okamak approved in 1997. \textbf{Main parameters}: B$_{t}$=3.5 T, R$_{0}$= 1.75 m, I$_{p}$= 1MA, a= 0.4m, (b/a)= 1$\sim $2 with the flexibility of double and single null divertor, P$_{LHCD}$= 3.5 $\sim $ 4 MW, P$_{ICRH}$= 3 $\sim $ 4 MW, P$_{ECRH}$= 0.5MW and pulse long will be 1000 s. For the second phase T$_{c}$ on SC magnet will decrease from 4.2 K to 3.8 K and then B$_{t }$= 4.0 T, I$_{p }$= 1.5MA, the power for heating and CD will increase further. \textbf{Characteristics:} ``D'' shape TF and both TF and PF are SC; PF coil each has own PS to be able to produce double or single null diverter; The vacuum chamber has double-layer and can be cooling, heating and shielding of neutron; Changeable interior components included in: first wall;diverter; internal feeadback control coils and all magnetic measuring systems; CW LHCD, ICRH and NBI in second phase. \textbf{Mission:} Investigate 1) both physics and technology bases of SSO advanced tokamak included in: full ST and un-transformer start-up operation; the control technology included avoiding or mitigation of disruption for SSO; CW heating included simulated $\alpha $ particle heating and CW CD; 2) the power and particle handle with diverters under SSO;3) advanced (higher $\beta$ and $\tau$) model under SSO. \textbf{Progress:}1) Final assembly completed at end of 2005. 2) The engineering commissioning has been done successfully at early of 2006. Both TF and PF were cooling down to 4.5-5 K and then charged successfully. 3) The first plasma will be obtained around August--September of 2006. The results will be given.   

Modeling of ICRF Heating Scenarios for the EAST Tokamak

Experimental Advanced Superconducting Tokamak (EAST) is a fully superconducting tokamak (R = 1.7 m, a = 0.4m, Bt = 3.5T, pulse length $<$= 1000 sec) being commissioned at ASIPP. Radio frequency (RF) power in the ion cyclotron range of frequencies (ICRF) will be one of the primary auxiliary heating techniques for EAST. The ICRF system will provide more than 6 MW power coupled to the plasma in the frequency range of 30 - 110 MHz. Two actively cooled 2-strap antennas are being developed. In this modeling study, three physics scenarios are considered: (a) Fast Wave (FW) minority heating; (b) FW mode conversion electron heating; (c) FW mode conversion current drive. The simulations are carried out using a parallel version of TORIC, a finite Larmor radius ICRF code, on the Marshall cluster at MIT.   

Plasma Rotation in JET Discharges with Low Momentum Input

Studies of plasma rotation in ohmic and ICRF heating were recently performed at JET. Hollow rotation profiles with the core either co or counter rotating had been previously observed with ICRF heating. In the new experiments the conditions for counter-rotation were investigated in L-mode plasmas (P$_{ICRF}$=3-6MW, B$_{T}$=2-2.75T, I$_{p}$=1.2-2.6MA). NBI bleeps were used for rotation measurements with charge exchange recombination (CER) spectroscopy. In the absence of NBI, MHD mode analysis is used as a rotation diagnostic in the plasma core. Plasma acceleration with ICRF power is seen from sawtooth precursor frequencies as well as from CER measurements. The effect of different plasma currents (I$_{p})$ and ICRF heating details (antenna phasing, H minority concentration and cyclotron resonance position) were considered. Clear profile differences were observed with plasma current. With off-axis ICRF heating, peaked co-rotating profiles were observed at high I$_{p}$, while hollow counter-rotating profiles were obtained at low I$_{p}$.   

Alfv\'{e}n Cascade Quasi-modes

Alfv\'{e}n Cascades are shear Alfv\'{e}n type perturbations in tokamak plasmas with non-monotonic safety factor profiles. They typically exhibit an upward (rather than downward) frequency sweeping as the minimum value of the safety factor decreases in time during the discharge. The preferred direction of sweeping indicates existence of a radial potential well for the upward sweeping eigenmodes, as opposed to a potential hill for the downward sweeping perturbations. The hill-to-well transition appears as frequency rollover in Alfv\'{e}n Cascade observations in JET plasmas, in which the ``hill'' modes occupy a broad frequency band, which shrinks occasionally to a narrow spectral line. In this work, we interpret recent JET data on such a rollover in low-frequency Alfv\'{e}n Cascades in terms of Alfv\'{e}n Cascade Quasi-modes that arise on the potential hill and stay there transiently prior to damping at the Alfv\'{e}n continuum resonance. We calculate the lifetime of Quasi-modes and compare relative roles of three factors that determine their minimum frequency: geodesic acoustic coupling, pressure gradient effect, and energetic ion effect. Discharges with high power ICRH and NBI show that energetic ions with large orbits can alter the minimum frequency significantly.   

Enhanced Charge Exchange Recombination Spectroscopy Measurements on the Joint European Torus.

During the shutdown of 2004/5 the Joint European Torus (JET) charge exchange recombination spectroscopy (CXRS) system underwent a major upgrade. As part of the upgrade two new spectrometers were added to the suite of CXRS diagnostics. The new spectrometers complement and enhance the existing CXRS measurement capabilities on JET. These high-throughput, transmission grating instruments allow measurements down to 5 ms resolution. One instrument is optimized for the 529.1 nm C VI line, while the other instrument is optimized for the 468.5 Be IV and 468.6 He II lines. This allows for the assessment of CXRS measurements in a carbon-free machine (Be IV) and for alpha particle (helium ash) CXRS in future D-T experiments. Results from the new instruments will be compared to measurements from the existing, upgraded systems, and will include analysis using the new CXSfit routine, developed to supplement KS4fit.   

Prospects of the Minimum Fisher Regularisation in the Experimental Analyses of Plasma Particle Transport at JET

Minimum Fisher Regularisation (MFR) proved to be a rapid and robust method in solving ill-conditioned inverse problems. This approach has been recently applied at JET for tomographic analysis of neutron emissivity based on data acquired by the JET neutron cameras. The reconstructed time evolution of 2D emissivity after tritium puff clearly shows the influx of fuel to the plasma core. Under certain assumptions, the observed emissivity evolution can be used to estimate fuel transport coefficients (i.e. diffusion coefficient and pinch velocity) near plasma core, including a possibility to trace down spatial behaviour of the two coefficients. In the procedure, Fuel Ratio method and Singular Value Decomposition analysis provide powerful tools. Preliminary results will be presented in comparison with recently published trends in tritium confinement. Further possible optimisation of the existing regularisation constraints, in particular the properties of the emissivity smoothness, will be discussed.   

Predictive Simulations of Toroidal Momentum Transport in JET

Predictive simulations of temperature and toroidal momentum profiles were made using the new version of the Weiland model. Here the toroidal momentum transport due to ITG/TE modes is calculated self-consistently and the momentum flux contains a diagonal outward term ($\Gamma_{\rm tor}\sim dV_{\rm tor}/dr$) and non-diagonal pinch terms (Weiland, Nordman, EPS 2006, P2.186). The model predicts that the Prandtl number $\chi_{\rm tor}/\chi_{\rm i}$ is about 1/3 for typical tokamak parameters, in rough agreement with recent results from JET. Predictive JETTO simulations have been performed for JET L-mode, H-mode and hybrid discharges at low and high density. Temperature profiles were well reproduced. Simulations performed with only the diagonal part of the momentum transport under-predicted the toroidal momentum. With the non-diagonal terms included a slight over-prediction of the toroidal momentum was obtained. This may be reduced by including effects of collisions on ITG/TE mode driven momentum transport.   

Carbon Migration during JET $^{13}$C Injection Experiments.

JET performed two dedicated migration experiments using $^{13}$C labeled methane injected into repeated discharges. The $^{13}$C migration was measured by IBA and SIMS techniques on removed vessel components. One experiment used toroidally localized injection into L-Mode plasmas from the vessel top. In the second, methane was introduced toroidally uniformly at the outer strike point vicinity into in Type I ELMy H-Mode plasmas. The EDGE2D/NIMBUS code has been used to model carbon migration in both experiments. Three migration pathways were important: 1. Re-deposition near the injection location, 2. Migration through the main chamber SOL, and 3. Migration through the private flux region. In H-Mode, the migration is influenced by the ELM cycle. Most of the long-range migration occurred in the inter-ELM periods when the SOL and divertor were cooler and carbon was ionized closer to the separatrix.   

Giant sawtooth stability and core-localized fluctuations in JET plasmas

In ICRF heated plasmas giant sawteeth (ST) can develop with periods larger than one second. At low ICRH power ($<$3 MW) a well defined ST period that increases with power is observed. At higher powers a large variation in ST periods is observed with a long ST-free period followed by a phase of shorter ST periods. At higher ICRH powers Alfven eigenmodes (AEs) are also observed. ST are stabilized by the fast-ion pressure inside the q=1 surface but the pressure gradients drive AEs which can lead to fast ion losses and triggering of ST. Other ST trigger candidates are low-frequency MHD activity and broadband turbulence induced transport. Due to the improvement of core diagnostics, especially the X-mode reflectometer, details of the AE activity and of the turbulent fluctuations can be studied in great detail inside the q=1 surface. Experimental results will be shown and compared with modelling results. Evidence will be presented for possible causes of giant ST crashes.   

First operation of the multi-channel Fourier Transform spectrometer for perpendicular and oblique ECE measurements at JET

The upgraded 6 channels Martin Puplett interferometer for Electron Cyclotron Emission measurements has entered operation during 2006 experimental campaign at JET. The instrument provides the ECE spectra for three lines of sight at different toroidal angles (0, 10 and 22 degrees with respect to the perpendicular to the toroidal field) and two linear polarizations over an extended bandwidth to avoid aliasing (75-800 GHz), with 11 ms/profile time resolution and 7.5 GHz single line equivalent spectral resolution. While the absolute in-vessel calibration of the whole system is foreseen for the next shutdown, at present the data of the perpendicular channel are relatively calibrated on the Michelson interferometer. As preliminary step of the oblique channels validation the measured data are compared with the calculated emission and cross-checked with the local characterization measurements. The process of data validation and the first physics results obtained will be discussed.   

Fast Ion Loss Measurements from JET Plasmas

Two fast ion loss diagnostics for JET have been commissioned recently. These are a poloidal array of thin foil Faraday cups and a scintillator-based probe. The former measures the loss at multiple locations, with crude energy resolution. The scintillator probe gives the loss flux versus energy and pitch angle, typically sampled at 20 Hz. Initial observations from the Faraday cup array show a loss of what are thought to be MeV ICH tail ions across a wide variety of conditions. Bursts of this loss are seen at sawtooth crashes, and Alfv\'{e}n mode activity is observed to enhance the loss substantially. Initial data from the scintillator probe show the loss of DD charged fusion products (3 MeV p {\&} 1 MeV T) plus the apparent ICH tail ions over a much wider range of energies. The loss during ICH is localized in pitch angle.   

Active MHD spectroscopy at JET

Active MHD spectroscopy on the JET tokamak is accomplished using an array of active antennas which excite stable toroidal Alfven eigenmodes (TAE's), and with synchronous detection circuitry for measuring plasma response. Recently, new antennas were installed which extend the regime for studies to medium toroidal mode numbers (5 $<$ n $<$ 25). This system will be used to measure damping rates of TAE's in a range of discharges to validate theories that predict stability thresholds and damping rates for ITER. TAE and similar MHD activity can lead to fast ion and alpha particle losses and potentially pose problems for ignition scenarios in a burning plasma. The upgraded TAE diagnostic is described, and preliminary results will be discussed. The possibility of intentionally driving TAE's to cause fast ion transport as a mechanism for burn control in a burning plasma is also elucidated.   

MHD induced fast ion losses in ASDEX Upgrade

We present the first results obtained with the new Fast Ion Loss Detector (FILD) installed recently in ASDEX Upgrade. An overview of the measurements and their preliminary conclusions is presented. FILD provides energy and pitch-angle (arcos (v$_{\vert \vert }$/v)) resolved FIL measurements with a bandwidth of 1 MHz, which comfortably covers all the dynamics up to Alfv\'{e}n modes. The energy range covers from 60 keV up to 700 keV for deuterium ions at a central magnetic field of 2T while the pitch-angle ranges from 20$^{\circ}$ up to 87$^{\circ}$. Lost particles have been observed in the presence of a rich variety of MHD phenomena, from low frequency MHD modes like NTMs to high frequency modes i.e. TAEs. A strong correlation between mode amplitude and amount of particle losses is observed. The loss mechanisms involved in the ejection of fast ions due to ELMs, NTMs and TAEs are discussed. In addition, a new MHD mode has been identified for the first time. A strong and deleterious influence on the energetic deuterium ion population was established.   

Isomak

An isothermal tokamak, Isomak, is investigated to demonstrate that nearly exact, rigidly toroidally rotating Maxwellian solutions exist for both the ions and the electrons. For the ions this Maxwellian solution is valid in the limit in which unlike collisions of the ions with the electrons are weak and the induced electric field unimportant, while for Maxwellian electrons unlike collisions can be retained as long as the friction with the ions is small (electron-ion collision frequency times the electron gyroradius much smaller than the electron transit frequency times the characteristic scale length). In such cases magnetically confined, exponentially decaying density profiles are allowed, minimizing contact with the wall or limiter. Indeed, the near Maxwellian behavior assures that radial particle and heat fluxes are small. In fact, for specially tailored ion and electron current drives it is possible to maintain the Maxwellians as exact steady state solutions of the full ion and electron kinetic equations. The three reasons to consider an Isomak are its usefulness as an ideal tokamak reference, its possible relevance to Lithium-walled tokamaks, and its value in checking codes in the isothermal limit.   

Pinch Mitigation in the UCLA tokamak

The UCLA tokamak (R = 5 m, B = 0.25 T, A = 5 m, a = 1 m, $\kappa $ = 1.5, I$_{p}$ = 50 kA, $\tau _{pulse} \quad <$ 5 s) is running excellent and clean plasmas since 2000. Ohmic discharges show poloidal rotation, without any use of auxiliary heating. This natural spin generates a strongly peaked density profile. This particle pinch is due to a negative radial electric field, which increases considerably inward ion mobility. The density build-up usually terminates on strong MHD activity. A disruption brings the core density back down to lower values as the poloidal rotation suddenly reverses. A series of experiments aiming at controlling the pinch are presented. A direct mitigation of the pinch can be done using low power ICRF. Another method involves stochastic fields. By applying a local radial magnetic field, increased diffusivity also mitigates directly the pinch. Scaling these results to ITER, we explore the possibility of using this technique to exhaust ashes from the plasma.   

Two-dimensional simulation of magnetorotational instability with a large Reynolds number

Magnetorotational instability (MRI) is a likely mechanism for enhanced angular momentum transport in accretion disks, whose test has been recently proposed or started in laboratory experiments [1,2]. However, the magnetic Prandtl number (ratio of kinematic viscosity to resistivity) is tiny in those liquid-metal experiments ($10^{-5} - 10^{-6}$) while it is supposed of order unity in accretion disks. It is desired to understand the consequence of the disparate magnetic Prandtl number for the interpretation of experimental results. Small Prandtl number, however, leads to extremely high Reynolds number, which has been inhibited the access of direct numerical simulation of the experimental devices. Here we approach realistic values of the Reynolds number by making a two-dimensional spectral simulation in cylindrical geometry with automatic resolution adjustment. By a proper adjustment of the magnetic Reynolds number, we may access the wide range of magnetic Prandtl number from order unity to $10^{-4}$. We explore the relation of small Prandtl number and profile relaxation effect to the low saturation level observed in the experiment. Comparison to parasitic instability theory [3] will be also made in the presentation. *This work supported in part by the CMPD, DOE grant DEFC0204ER54784. [1] H.T. Ji et al., Mon. Not. Roy. Astron. Soc. 325, L1 (2001). [2] D.R. Sisan et al., Phys. Rev. Lett. 93, 114502 (2004). [3] J. Goodman and G. Xu, Astrophys. J. 432, 213 (1994).   

Turbulent Resistivity in 2D Wave Turbulence

In their seminal paper, Cattaneo {\&} Vainshtein [1] demonstrated that small-scale magnetic fields can significantly alter mean-field evolution in high-Rm MHD turbulence, even for very weak large-scale fields. Consequently, diffusion of the mean flux in 2D is strongy suppressed, or ``quenched.'' Self-consistent mean-field electrodynamics suggests that this quench depends critically upon the magnetic Reynolds number, as well as the self-correlation time of the fluid and the field. To elucidate the theory, we consider wave turbulence in a model of 2D MHD in the presence of stable stratification. In this model, there arises an unambiguous time-scale associated with three-wave resonance of ``magneto-internal waves.'' We show that such triad interactions can act as an alternate source of irreversibility, and that the Rm-dependent quench can be circumvented at the cost of moving to higher order in wave-slope. An explicit calculation of the flux of magnetic potential in the presence of stratification is presented. Finally, we examine certain classes of triad interaction and examine which make the dominant contribution to the turbulent resistivity. \\newline [1] Cattaneo, F. and Vainshtein, S.I., Astrophys. J. 376, L21-24 (1991)   

Determination of fractional transport exponents in drift-wave turbulence: the Lagrangian method vs the Propagator method

Recently, a nonlocal (quasilinear) renormalization scheme for turbulent transport of passive scalars has been formulated that allows one to derive renormalized transport equations for passive scalars in terms of fractional differential operators [1]. This resulted in a new method for obtaining fractional transport exponents for these problems by characterizing the statistics and correlations of the Lagrangian velocities along the characteristics trajectories of the flow. In this contribution, we use this new method to determine the fractional exponents in simulations of drift-wave turbulence in slab geometry [2] and discuss the advantages and disadvantages of the method. Several driven and non-driven situations will be explored, in which the relative dominance of the polarization and ${\rm\bf E}\times{\rm\bf B}$ nonlinearities will be tuned artificially. In this way, we can test the robustness of the fractional transport models to changes in the basic dynamics, which helps assess the general potential of these methods. \newline \newline [1] R. S\'anchez, et al, Phys.Rev. E (in press, 2006); \newline [2] D.E. Newman, et al, Phys. Fluids B \textbf{5}, 1140 (1993)   

Fokker-Planck diffusive law: its interpretation in the context of plasma transport modeling

It was recently proposed that, when building phenomenological transport models for particle transport in tokamaks, use of the Fokker-Planck diffusive law might be preferable to Fick's law to express particle fluxes [1]. In particular, it might offer a possible explanation for the excessive pinch velocites observed in some experimental situations with respect to the values expected from the forces and asymmetries existent in the system. In spite of the fact that Fokker-Planck's law was first proposed many years ago, it produces a series of counterintuitive results that at first sight seem in contradiction with the second law of thermodynamics. In this contribution we will review the basic concepts behind its formulation and show that, through the use of simple examples relevant to plasma physics, the second law of thermodynamics is not violated in any manner if properly used. The benefits of its use within the modelling of transport in tokamaks will also be clarified.\\ \noindent REFERENCES: [1] R. Sanchez et al, Phys. Plasmas {\bf 12}, 056105 (2005); B.Ph. van Milligen et al, Plasma Phys.Contr.Fusion {\bf 47}, B743 (2005)   

The impact of non-Fickian diffusion on entropy production in a simple model

Recent theoretical work has suggested that the standard model of Fickian diffusion is not appropriate for inhomogeneous systems [B. Ph. van Milligen, {\it et al.}, Eur. J. Phys. {\bf 26}, 913 (2005)]. As an alternative, van Milligen {\it et al.} suggested a Fokker-Planck diffusivity law. The flux from Fick's law is given by $\Gamma \left( x,t \right) = - D\left( x,t \right) \partial n\left( x,t \right) /\partial x$ while the flux from the Fokker-Planck diffusivity law is $\Gamma \left( x,t \right) = - \partial \left[ D\left( x,t \right) n \left( x ,t\right)\right]/\partial x$. In this work, a simple model is used to analyze the effect of the two different diffusivity laws on the production of entropy. Three cases are considered: (1) the spatial dependence of the diffusivity is due solely to a density-dependent diffusivity, $D = D_0 n^\alpha$; (2) an arbitrary spatial dependence in the diffusivity, $D=D\left( x \right)$; and (3) a coupled density and temperature model with both the diffusivity and the conductivity as functions of the density and temperature, $D = D_0 n^{\alpha 1} T^{\alpha 2}$ and $\chi = \chi_0 n^{\alpha 3} T^{\alpha 4}$. Analytic and numerical results for each of these cases will be presented with a focus on the transport and production of entropy.   

Vlasov-Fokker-Planck simulation of transport in magnetically turbulent plasmas

The author presents kinetic simulations of the effect of multi-mode magnetic turbulence on cross-field transport. We have developed and fully benchmarked a finite-difference code that solves the Vlasov-Fokker-Planck equation in three spatial dimensions. It utilises the spherical harmonic expansion of the distribution function in velocity space, a technique previously used successfully in codes to study Laser-Plasma interactions [1]. In contrast to previous work using particle tracking codes, our code allows the arbitrary control of collisionality and does not suffer from statistical noise. We are currently investigating the nature of the cross-field transport in a regime relevant to magnetically confined plasmas, and in particular, the effect of magnetic turbulence. The code allows us to study regimes where Quasi-Linear theories are no longer valid, for example, when the turbulence length scales are comparable to the Larmor radius and have a large mode amplitude.\\ \newline [1] A R Bell et al 2006 Plasma Phys. Control. Fusion 48 R37-R57   

Generation of streamers due to the four wave modulational instability

It is well known that Charney-Hasegawa-Mima equation is unstable to a four-wave modulational instability that results in the strong growth of zonal (poloidal) flows, which are the k$_y$ = 0 component of the electrostatic potential. Similarly, this nonlinear system is also unstable to the generation of streamers which are the radial analog of zonal flows. Analytically, the dispersion relation for streamers is considerably more complicated because the governing equation is cubic in teh growth rate for streamers, as opposed to quadratic for zonal flows. Previously, work has been done that describes the stability of streamers in the limit of q $<<$ k$_y$ where q is the poloidal wave vector of the streamer, and k$_y$ is the radial wave vector of the background turbulence. In this work, we develop general analytical expressions for the growth rate of the streamer instability that is general for all q. These are compared to the growth rates for the zonal flow and a comparison of the realtive strengths for these instabilities is presented. It is found that the zonal flow is generally much stronger, except for the case where the background turbulence is inhomogeneous and elongated poloidally.   

Scaling characteristics of convective blob transport in the SOLT model of edge and scrape-off layer turbulence

Following the observation that enhanced blob transport is correlated with electrical disconnection from the sheath in 3D BOUT simulations, [1] the SOLT (Scrape-Off Layer Turbulence)\textit{ 2-region model} code was developed to study the interaction between curvature-driven turbulent transport in the outboard midplane and resistive current loops in the X-point region. In this \textit{reduced }model, evolution equations of vorticity and density are solved in the plane perpendicular to the local B-field in the two regions, and are coupled in the parallel direction by a \textit{jump condition} on Ohm's law that involves the parallel resistivity. Enhanced cross-field conductivity, by X-point induced field-line fanning and shear, [2] is achieved via the coordinate transformation between the two regions. Vorticity loss to the sheath is included in the X-point region. Results of simulations that explore the \textit{regime-dependent}, predicted radial velocity scaling with blob size [3] are presented, including progress on extracting scaling laws for self-consistent blob creation and propagation in different turbulent regimes [3] of collisionality and scale size. 1. D.A. Russell, D.A. D'Ippolito, J.R. Myra, W.M. Nevins, X.Q. Xu, Phys. Rev. Lett. \textbf{93}, 265001 (2004). 2. D. Farina, R. Pozzoli, and D.D. Ryutov, Nucl. Fusion \textbf{33}, 1315 (1993). 3. J.R. Myra and D.A. D'Ippolito, Phys Plasmas \textbf{12}, 092511 (2005).   

On 2D modeling of 3D meso-scale structures

Meso-scale structures, driven by curvature and gradB effects, like blobs and ELMs play a very important role in edge and SOL plasma transport in tokamaks. However, modeling of the dynamics of such structures with 3D codes is a very challenging computational problem. Therefore, in recent years different 2D models of such structures have been developed and used intensively (see Ref. 1 and the references therein). Although these 2D models describe many essential features observed in experiments, so far they did not account for the effects related to the inter-connection of ``bad'' and ``good'' curvature regions in tokamak. For the case of ballooning modes this effect sets the threshold of ballooning instability. Here we try to mimic the inter-connection of ``bad'' and ``good'' curvature regions (which is intrinsically 3D effect) in 2D model by introducing the threshold for the polarization of meso-scale structures based on the gradient of plasma pressure. We study the dynamics of edge plasma density by introducing density source and describing density transport with our modified 2D turbulence model. The results will be presented. [1] S. I. Krasheninnikov, A. I. Smolyakov, G. Yu, and T. K. Soboleva, Czechoslovak Journal of Physics, \textbf{55} (2005) 307   

Potential Vorticity Homogenization and the Transition From Hydrodynamic to MHD Turbulent in 2D

Potential vorticity (PV) homogenization is a useful concept in understanding the overall trends in 2D hydrodynamic mixing and turbulence. It provides a natural way to understand the forward cascade of enstrophy in 2D hydro \textit{without} invoking the apparatus of statistical turbulence theory. Also, it is well known that the inverse cascade of energy in 2D hydro is a consequence of the dual conservation laws of that system, along with the fact that PV is mixed. Here, we investigate the effects of a weak magnetic field on PV homogenization, with the aim of determining the strength of the field required to convert the direction of energy transfer from inverse to forward. Analytical calculations suggest a Hartmann number criterion for this alteration of the dynamics. Numerical calculations are consistent with the analysis, but suggest that some transfer of energy to small scales begins during the nearly kinematic stage of flux expulsion. Sensitivity of the results to vortex asymmetry and alignment of streamlines and field lines will be discussed.   

Theory and Simulation of Toroidal Momentum Transport

By constructing a radial flux of toroidal angular momentum from the ``energy conserving'' nonlinear gyrokinetic equation in toroidal geometry [1], we can readily identify a diffusive flux and a non-diffusive flux. For the diffusive flux from ITG turbulence, it has been shown that $\chi_{\phi} \sim \chi_{i}$ [2] in rough agreement with observations from NBI-heated plasmas. We've investigated possible physical mechanisms behind the nondiffusive flux, and found that: Mean ${\bf E \times B}$ shear can induce a net momentum flux by breaking the quasi- translational invariance of the ballooning eigenfunctions. Results from the FULL code demonstrate such modifications of eigenmodes. However, ${\bf E \times B}$ shear suppression makes resulting parallel flow weak. New nonlinear simulation results from GTC code including plasma shaping will be reported [3]. \newline \newline [1] T.S. Hahm, Phys. Fluids {\bf 31}, 2670 (1988). \newline [2] N. Mattor and P.H. Diamond, Phys. Fluids {\bf 31}, 1180 (1988). \newline [3] W.X. Wang {\it et al.,} Submitted to Phys. Plasmas (2006).   

Modelling of turbulence driven momentum tranport

We suggest a simple model of turbulence driven transport of parallel momentum. The model incorporates the commonly invoked effects of diffusion, so-called momentum ``pinch'' term (i.e. a supposedly inward advection of mean momentum) and an additional off-diagonal term driven by and proportional to the radial $\mathbf{E\times B}$ shear. It is observed that in a cylinder the a part of this ``pinch'' term comes from the fact that particles can carry momentum, and that there is a pinch in particle transport. On the other hand, the off-diagonal term comes purely from the Reynolds stress between the parallel momentum fluctuations and the perpendicular $\mathbf{E\times B}$ fluctuations, and it requires symmetry breaking. The form of the model presented here is based on the assumption that the dominant mechanism for symmetry breaking in the core of a periodic cylinder is a shift of the eigenmode from the rational surface induced by the radially sheared poloidal $\mathbf{E\times B}$ flow.   

Gradient Scalings of Nonlinear Inward Flux Component in Trapped Electron Turbulence

Inward particle transport is desirable for ITER. Trapped electron mode turbulence has inward flux components because the nonlinearity of electron density advection strongly excites a damped eigenmode at low collisionality. We derive the scaling of inward components with density and temperature gradient to determine whether they are diffusive, convective, or of some other form. This requires a detailed solution of the saturated state, including the fluctuation levels and gradient scalings of the growing and damped eigenmodes, and their complex-valued cross correlation. We obtain such a solution in an expansion for low collisionality, proximity to threshold, and long wavelength, by checking asymptotic energy saturation balances for consistency under all possible scalings in a weak turbulence regime. The procedure yields a flux that is highly nondiffusive and has inwardly directed components that scale as $L_{n}/L_{T}^{2}$ and $L_{n}^{2}/L_{T}^{3}$. These components are nearly as large as the outward flux. We speculate on the effect of this mechanism in ITG, where the quasilinear flux is inward, but nonlinear effects such as this have not been explored.   

Nonlinear Trapped Electron Mode Pinch in Strong Turbulence Regime

Recent work has shown that there is an inward flux component in collisionless trapped electron mode turbulence produced by a nonlinear cross phase$^{2}$. The result was obtained for a weak turbulence regime, consistent with near threshold conditions. We extend this work to the strong turbulence regime, applying asymptotic analysis to the nonlinear frequency expressions generated from self-consistent statistical closure theory. We first check to see if there is a consistent strong turbulence regime for the previously considered threshold ordering$^{2}$, and examine the properties and scalings of the inward flux components. We then examine other orderings that are further above the instability threshold. The orderings will be compared with experimental profiles to determine likely regimes and nonlinear pinch properties. $^{2}$P.W. Terry and R. Gatto, Phys. Plasmas \textbf{13}, 062309 (2006).   

Nonlinear MHD Simulations of Sheared Flows and Turbulence in the Helimak

We report results of three-dimensional nonlinear numerical simulations and theory for a magnetohydrodynamic slab model of the Helimak, using magnetic and flow profiles based on experimental data. The Helimak experiment was designed to study the interaction between sheared mass flows and ambient turbulence in a confined plasma. The experiment is well modeled as a bounded magnetized jet in a slab geometry, with no slip boundary conditions in the cross-stream direction, and periodic boundary conditions in the other two directions. In the new nonlinear codewe have developed, space is discretized using a Chebyshev-collocation--Fourier-pseudospectral algorithm. Time is discretized with a third-order Runge-Kutta--Crank-Nicolson scheme. Important features of the code include three spatial dimensions, the presence of walls, and the inclusion of resistivity and viscosity. The nonlinear development of unstable eigenmodes, computed with a Chebyshev-$\tau$ algorithm, will be discussed. We analyze the linear results by examining the stresses and perturbed dissipation. Preliminary results show that as the linear modes attain finite amplitude, there is a development of multiscale plasma excitation.   

Interaction between magnetic island and electrostatic turbulence

The interaction between electrostatic turbulence and a magnetic island is investigated numerically. The physical model used is a 2-D version of the Hasegawa-Wakatani equations extended to include a curvature term and to account for the presence of a magnetic island.~ This is the simplest model of electrostatic turbulence that takes into account the effect of magnetic shear. The magnetic curvature makes the model linearly unstable to interchange instability. As a first approximation, it is assumed that the island growth is not affected by the surrounding turbulence since the latter evolves on a much faster time scale. Thus, the model is electrostatic and the island can be treated as a fixed object. The equations are solved numerically in a slab box by using a finite difference, fully implicit code that uses PETSc libraries. The interchange turbulence with and without the magnetic island is compared. In particular, the response of the turbulence to different magnetic island widths and collisionality values is examined.   

On the generation of poloidal flow as result of an increased edge particle source

A transport model is used to study the impact of ramping an edge particle source on the generation of poloidal flow. The motivation for this work is gas puffing experiments conducted on the TJ-II stellarator [C. Hidalgo, {\it et al.}, Phys. Rev. E {\bf 70}, 067402 (2004)] that demonstrated the development of an edge poloidal velocity shear layer. In this work, a numerical transport model is used to examine for hysteresis in the development of an edge poloidal velocity shear layer due to a modeled gas puff. The transport model couples together density, ion and electron temperatures, poloidal flow, toroidal flow, radial electric field, and a fluctuation envelope equation which includes a shear-suppression factor and now implements a modified Runge-Kutta with adaptive time-stepping. With the inclusion of diamagnetic flows, both critical and subcritical flows are possible. For subcritical flows (i.e., flows that do not trigger transition to a higher confinement regime), there is no true hysteresis in the flow. An apparent lag may be observed if the rate of ramping the particle source is rapid relative to transport time scales. For critical flows, a local transition model that does not include diamagnetic effects also shows the lack of a true hysteresis.   

Progress towards measurement of the slow wave in the WVU Helicon Plasma Source

We report the updated status of the 300 GHz collective scattering system on the Hot hELIcon eXperiment (HELIX) at WVU. Vacuum chamber extensions for the injection beam and scattered beam collection apparatus have been installed on HELIX and optical component alignment was accomplished using a simple laser pointer. System calibration, before installation, was done using an acoustic cell scattering technique. The acoustic cell, using a 1 MHz piezoelectric transducer on HDPE and Teflon, is used to create scattered waves with angles of 39\r{ } and 60\r{ }, corresponding to scattered wave vectors of 42 1/cm and 63 1/cm respectively. With the limitation of measurable wave vectors, due to chamber geometry, ranging from approximately 53 to 89 1/cm, only the Teflon acoustic cell could be used for the full system calibration.   

A Preliminary Basic Experiment on the Production and Identification of ETG Modes

The Electron Temperature Gradient (ETG) mode is believed to be a possible candidate for anomalous electron energy transport. The high frequency (few MHz) and short wave length $(k_\perp \rho_e <1)$ make the direct observation of ETG modes difficult in experiments. We have fairly succeeded in producing the parameter regime appropriate for ETG modes in the Columbia Linear Machine (CLM). The requisite electron temperature gradient is obtained via dc acceleration (via a biased screen) and subsequent thermalization in the core of the plasma. The resulting electron temperature of $\sim 20 eV$ in the center and $\sim 1 eV$ in the edge are obtained. This allows us to vary $\eta_e = d ln T_e / d ln N$ from 1 to 6. Fluctuations at $\sim 2 MHz$ correlated with high $\eta_e$ are seen. Much wider and deeper parametric study of these fluctuations is necessary for its identification as ETG modes.   

Thermal and Fast Ions transport in RFP Quasi Single Helicity regimes

The hamiltonian code ORBIT has been used to investigate the effect of helical structures on particles transport in Reversed Field Pinch plasmas. Thermal particles averaged diffusion coefficients computed in Single Helicity (SH) states are of the order of 0.5 m$^{2}$/s, quite lower than the experimental values in standard chaotic plasmas (about 20-30 m$^{2}$/s). The motion of fast ions in high-performance RFP plasmas has been studied too: the presence of helical surfaces in the fast ions orbits space due to new resonances between the orbital motion of the fast ions and the structure of the field is found to dramatically improve the confinement of fast ions (much longer than for thermal ions), consistent with experimental observations in MST (G.Fiksel et al, Phys.Rev.Lett \textbf{95},125001 (2005) ).   

Investigation of Active Feedback Control of Turbulent Transport in a Magnetized Laboratory Plasma

Toroidal fusion devices now generate transport barriers where heat and particle transport are reduced below Bohm diffusion levels. However, minimal particle transport may lead to such negative effects as core impurity accumulation or alpha particle buildup in a reactor. To reduce this kind of effect, active feedback control over cross-field transport is investigated in the new HELCAT (HELicon-CAThode) linear device at UNM. Sheared ExB flows, generated via biased concentric rings, are utilized to modify the transport. Fluctuations and flux are monitored with probe arrays. Open loop experiments have demonstrated that drift fluctuations can be fully suppressed by simple biasing, though the physical mechanism remains unclear, since no azimuthal flow shear appears to be present. Additionally, a 1D transport code is being used to model the system and investigate possible control methods numerically. Initial experimental and modeling results will be presented.   

Modeling control of turbulent transport in a linear device

A transport code is used to model active control experiments on the HELCAT (HELicon-CAThode) experiment (for more details on the HELCAT experiment see S. Xie, {\it et al.}, this meeting). The 1D transport code includes evolution of the density, ion and electron temperatures, poloidal flow, radial electric field, and rms fluctuation amplitude. The helicon/cathode source is modeled as a power input with a flat-top radial profile and the majority of the power going into the electrons. The control elements, biased concentric rings in the experiment, are modeled as localized momentum sources in the transport code. The effect will be identical to a source of polidal {\bf E}$\times${\bf B} flow in the limit of zero $\beta$ (i.e., when diamagnetic flows are negligible). By varying the momentum sources a sheared radial electric field can be generated that can suppress turbulent particle and heat transport. The results of modeling a typical experimental equilibrium will be presented along with initial results from varying the amplitudes of the momentum sources.   

Flows and Transport Driven by Electron Temperature Gradients

An experimental study is made of the plasma flows and heat transport associated with controlled electron temperature gradients established in a large magnetized plasma. The phenomena investigated illustrates processes encountered in magnetic and inertial fusion, and in space observations. Axial and transverse electron temperature gradients are established in the LAPD-U device by injecting a narrow electron beam into a cold afterglow plasma. The beam energy is less than the ionization energy of the background neutral gas and the conditions approximate a localized heat source embedded in an infinite, strongly magnetized plasma. For low heating powers and/or short times, classical heat transport prevails and temperature gradients are formed both parallel and perpendicular to the applied magnetic field. As the heating power is increased, flows develop and drift-Alfven waves become unstable. Late in time these features evolve into broadband turbulence and result in anomalous transport that exhibits various spatio-temporal patterns. This study focuses on the properties of the flows and the spectral features that trigger the transition from coherent fluctuations to broadband turbulence.   

Heat Flux Driven Instabilities in Magnetized Temperature Filaments-UCLA

An analytical and computational study is made of low-frequency instabilities driven by parallel electron heat flux in a temperature filament whose length along the magnetic field is much larger than its transverse dimension. This is a situation encountered in magnetic and inertial fusion, ionospheric HF heating and at the surface of the sun. A linearized eigenvalue problem is formulated for magnetized ion acoustic modes that are evanescent outside the filament. Specific numerical results are obtained by coupling the stability analysis to a two-dimensional classical transport code. The code is used to deduce the spatial dependence of the perturbed electron distribution function associated with the heat flux. Certain criteria for the existence of the instability are found to interpret measurements of low-frequency fluctuations that develop spontaneously in controlled electron temperature filaments generated in the LAPD-U device.   

Heavy ion beam driven warm dense matter experiments

We describe near term heavy-ion beam-driven warm dense matter (WDM) experiments. Initial experiments are at low beam velocity, below the Bragg peak, increasing toward the Bragg peak in subsequent versions of the accelerator. The WDM conditions are envisioned to be achieved by combined longitudinal and transverse neutralized drift compression to provide a hot spot on the target with a beam spot size of about 1 mm, and pulse length about 1-2 ns. The range of the beams in solid matter targets is about 1 micron, which can be lengthened by using porous targets at reduced density. Initial candidate experiments include an experiment to study transient darkening in the WDM regime; and a thin target dE/dx experiment to study beam energy and charge state distribution in a heated target. Further experiments will explore target temperature and other properties such as electrical conductivity to investigate phase transitions and the critical point.   

Laser Plasma Interaction with Multi-Layer Targets: Ion Acceleration and Ion Heating

In the present analysis, we explored the physics of the interaction of high intensity (I $>$ 10$^{21})$, short laser pulses with multi-layer targets of various densities and composition by means of particle in cell (PIC) simulations with Osiris 2.0 in 1 (1D) and 2 (2D) dimensions. The results have shown that, when the layer thicknesses are appropriate and the layer densities decrease along the laser propagation direction, multiple shock structures are formed in the transition regions between the layers. The shocks accelerate the ions inside the target creating a series of mono-energetic ion beams. Since the velocity of the shocks decreases with distance from the interaction region, the first shock rapidly reaches the next creating a new structure that accelerate the ions previously picked up from both shocks. As a result, the interaction of a short laser pulse with multi-layer targets give rise to a quasi-monoenergetic ion beams. The results have also shown that, when the layer densities increase along the laser propagation direction, the multiple shock structures move in opposite directions: the shock detaching from the front surface moves forward while the shocks formed at the boundaries between the layers move backward. The collisions of different shocks give rise to two stream vortexes that effectively channel their energies to high wave-number structures eventually leading to very localized regions of hot ions ($>$ 100 keV).   

Modeling Electron Clouds in High-Current Ion Accelerators with Solenoid Focusing

Contamination from electrons is a concern for solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons, produced directly by beam ions hitting lattice elements or indirectly by ionization of desorbed neutral gas, can potentially alter the beam dynamics, leading to beam deflection, increased emittance, halo, and possibly electron-ion instabilities. The electrostatic particle-in-cell code WARP is used to simulate electron-cloud studies on the solenoid-transport experiment (STX) at Lawrence Berkeley National Laboratory. We present self-consistent simulations of several STX configurations to show the evolution of the electron and ion-beam distributions first in idealized 2-D solenoid fields and then in the 3-D field values obtained from probes. Comparisons are made with experimental data, and several techniques to mitigate electron effects are demonstrated numerically.   

Development of a low inductance metal vapor vacuum arc (LIZ-MEVVA) ion source

We are continuing development of a Low Impedance Z-Discharge Metal Vapor Vacuum Arc (LIZ-MEVVA) to produce high charge state metallic ions. The plasma arc occurs in a diode connected to a 1.4$\mu $F capacitor by a low impedance transmission line. The capacitor is charged to between 6 and 12kV and stores up to 100J of energy. Currently the electrode material is aluminum and the system has been run in two regimes: an LC dominated ``ringing'' arc of period 4.1$\mu $s and a 1-3$\mu $s wide ``pulsed'' arc, where a small series resistance has been added to critically damp ringing. The current in the plasma arc can be up to 30 kA. A 1$\mu $s pulsed extraction voltage of up to 10kV, which has a variable delay with respect to the start of the arc current, is used to accelerate the ions. Ions are analyzed using time-of-flight and, more recently, a Thomson parabola. To date we have detected Al$^{+}$, Al$^{++ }$and Al$^{+++}$.   

A Helicon Ion Source for the SNS Power Upgrade

The SNS Power Upgrade will require an ion source capable of producing negative hydrogen ion (H--) beams of 70-95 mA, depending on source emittance, with a duty factor of 7.4{\%}. Presently no sources in operation at existing accelerator facilities can simultaneously meet these requirements of beam current, emittance, duty factor with a reasonable lifetime. The possibility of meeting these requirements by combining a helicon hydrogen plasma generator previously developed in the Fusion Energy Division (FED) at ORNL with the existing SNS-LBNL H-- ion source will be discussed. Both these systems have been highly optimized and reflect the current state-of-the-art in high-density hydrogen plasma production and high-brightness H-- generation. The helicon plasma generator has demonstrated the capability of producing hydrogen plasma densities up to an order of magnitude greater than in the current SNS-LBNL source.   

High Current Density Compression of Intense Ion Beam Pulses

Space-charge-dominated ion beam pulses for warm dense matter and heavy ion fusion applications must undergo simultaneous transverse and longitudinal bunch compression in order to reach high beam intensities. Longitudinal focusing is achieved by imposing an axial velocity tilt on the beam and subsequently neutralizing its space-charge and current in a drift region filled with high-density plasma. A strong solenoid is modeled near the end of the drift region in order to transversely focus the beam to a sub-$mm$ spot size coincident with the longitudinal focal plane. The neutralization provided by the background plasma is critical in determining the total achievable compression of the beam pulse. Simulations predict that the ion beam current density can be compressed over a few $m$ by factors greater than $10^5$ with peak $n_{beam}$ in excess of $10^{14}$ cm$^{-3}$. The peak $n_{beam}$ sets a lower bound on the $n_{plasma}$ required near the focal plane for optimal beam compression, since simulations show stagnation when $n_{beam} > n_{plasma}$ and the generation of strong collective excitations in the plasma by the beam-plasma interaction. Simulations of simultaneous focusing are presented, as well as beam energy deposition dependence on background plasma and final-focus solenoid parameters.   

Ferroelectric Plasma Source for Heavy Ion Beam Charge Neutralization

Plasmas are a source of electrons for charge neutralizing intense heavy ion beams to allow them to focus to a small spot size and compress their pulse length. To produce one-meter-long plasma, sources based upon ferroelectric ceramic (BaTiO$_{3})$ with large dielectric coefficients are being developed. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic, and $\sim $ 7 kV is applied between the drift tube and the front surface of the ceramic. A prototype 20 cm ferroelectric source was characterized, integrated into the Neutralized Transport Experiment (NTX), and successfully charge neutralized a K$^{+}$ ion beam. A one-meter-long source comprised of five 20-cm-long sources has been built and tested. Two capacitor banks and networks provide power to two groups of plasma sources. Resistors were added to sources to optimize the applied voltages to achieve a uniform density of mid 10$^{10}$ cm$^{-3}_{.}$ Preliminary data from pulse compression experiments will be presented.   

Transverse Beam Compression by Adiabatic Waveform Changes in the Paul Trap Simulator Experiment (PTSX)

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory Paul trap that simulates a long, thin charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient transport system by putting the physicist in the frame-of-reference of the beam. The transverse dynamics of particles in both systems are described by the same sets of equations -- including all nonlinear space-charge effects. Results are presented from experiments in which the amplitude and frequency of the applied confining voltage are adiabatically changed over time in order to transversely compress a beam with an initial depressed-tune $\nu/\nu_0 \sim 0.9$. Emphasis is placed on determining the conditions that minimize emittance growth and the number of particles that are found at large radius (so-called halo particles) after the beam compression. It is found that increases of up to a factor of two in the lattice strength can be implemented in only four lattice periods. The results of PIC simulations performed with the WARP code agree well with the experimental data.   

Initial Operation of Laser-Induced Fluorescence Diagnostic System with Barium Ion Source in the Paul Trap Simulator Experiment

Installation of a laser-induced fluorescence (LIF) diagnostic system has been completed and initial operation of the system has begun on the Paul Trap Simulator Experiment (PTSX). The PTSX device is a linear Paul trap that simulates the collective processes and nonlinear transverse dynamics of an intense charged particle beam propagating through a periodic focusing quadrupole magnetic configuration. A barium ion source has also been installed on PTSX and tested with the existing charge collector. Although there are several transition lines for the laser excitation of barium ions, the transition from the metastable state $\rm 5 ^2D_{3/2}$ to the excited state $\rm 6 ^2P_{1/2}$ is considered mainly because there exists a commercially available, stable, broadband, high-power laser system in this region of the red spectrum. The LIF system is composed of a dye laser, fiber optic transmission lines, a line generator which uses a Powell lens, collection optics, and a CCD camera system. Streaming operation of the PTSX device is considered for the initial tests of the LIF system to make optimum use of the metastable ions. With the long integration time ($\sim$10 sec) of the CCD camera and image intensifier, it is expected that the fluorescence image of the initial beam mismatch between the focusing channel and ion the source can be captured.   

Hollow anode plasma source for high-current electron beam generation.

We report on results of a large cross-sectional area ($\sim$ 170 cm$^{2}$), high-current ($\sim 1000$A), uniform electron beam generation using a hollow anode plasma source at pressure of $^{5} \quad 8\times 10^{-5}$ Torr, in a diode supplied with an accelerating pulse of 300 kV and 300 ns duration. The hollow anode discharge was sustained for $\sim$ 10 $\mu$s by seven BaTi based ferroelectric plasma sources. The resistive decoupling of each plasma source produces a uniform plasma density distribution at the hollow anode output grid at a discharge current $\le 1000$A. It was found that the hollow anode plasma is characterized by a density of $\sim 10^{12}$ cm$^{-3}$, an electron temperature of $\sim 8$ eV and a group of fast electrons with energy of $\sim 50$ eV. It was shown that an increase in the hollow anode output grid potential allows one to significantly reduce the plasma pre-filling of the accelerating gap.   

Three-dimensional theory of nonlinear Thomson scattering

A fully relativistic, three-dimensional code, tracking multiple electrons interacting with the electromagnetic field distribution of an intense laser pulse propagating paraxially in vacuum, has been developed to predict their radiation characteristics, within the context of classical Thomson scattering (no recoil). A 4$^{th}$-order Runge-Kutta algorithm tracks the electron dynamics over 2$^{n}$ steps, and is coupled to an FFT to provide fast, efficient simulations, with highly enhanced spectral dynamic range. It is found that, in addition to the well-known radiation pressure downshift and transient harmonics characterizing nonlinear Thomson scattering, the spectral lines are broadened inhomogeneously by the nonlinear ponderomotive pressure acting on the electrons during the interaction. These effects can significantly degrade the spectral purity of laser-linac-based light sources; a scheme devised to alleviate this problem will be presented. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.   

The effects of the pre-pulse on capillary discharge XUV laser

In the past few years collisionally pumped XUV lasers utilizing a capillary discharge were demonstrated [1-4]. An intense current pulse is applied to a gas-filled capillary, inducing magnetic collapse ($Z$ pinch) and formation of a highly ionized plasma column. Usually, a small current pulse (pre-pulse) is applied to the gas in order to pre-ionize it. In this paper we investigate the effects of the pre-pulse on a capillary discharge Ne-like Ar XUV laser (46.9~nm). The importance of the pre-pulse in achieving suitable initial conditions of the gas column and preventing instabilities during the collapse is demonstrated. Furthermore, measurements of the amplified spontaneous emission (ASE) properties (intensity and duration) in different pre-pulse currents revealed unexpected sensitivity. Increasing the pre-pulse current by a factor of 2 caused the ASE intensity to decrease by an order of magnitude and to nearly disappear. This effect is accompanied by a slight increase in the lasing duration. We attribute this effect to axial flow in the gas during the pre-pulse. \newline \newline [1] J. J. Rocca et al., PRL, \textbf{\textit{73}}\textit{, 2192 (1994)} \newline [2] A. Ben-Kish et al., PRL, \textbf{\textit{87}}\textit{, 015002 (2001)} \newline [3] G. Niimi et al., J. Phys. D \textbf{\textit{34}}\textit{, 2123 (2001)} \newline [4] G. Tomassetti, et al., Eur. Phys. J. D \textbf{\textit{19}}\textit{, 73 (2002)}   

Nitrogen Recombination X-Ray Laser Scheme in a Capillary Discharge Z-Pinch

A recombination based X-Ray laser has a preferred energy scaling compared to collisional ionization scheme [1-3]. The difficulty in realizing this scheme lies in the required plasma cooling rate [4,5]. Implementing a nitrogen recombination laser at $\lambda \sim $13.4 nm, requires initially T$_{e}\sim $140eV and N$_{e}\sim $10$^{20}$cm$^{-3}$, and than cooling to T$_{e}<$60eV, at a time scale shorter than the 3-body recombination time scale of 3-6ns. An experimental setup has been built to achieve these conditions in a capillary discharge. A 90mm long capillary with 3-6mm inner diameter was filled with 0.5-3 Torr N$_{2}$ and coupled to a generator supplying a peak current of 60-70 KA at 70 ns. The radiation from N$^{5+}$ and N$^{6+}$ was measured with XRD and appropriate filters. The results show that the cooling time of the plasma is shorter than 5 ns, indicationg that the recombination scheme may be feasible. The experimental measurements will be used in search for the optimal initial conditions for lasing. \newline [1] Elton R. C.: \textit{X-Ray Lasers}, Academic Press, New York, 1990. \newline [2] Rocca J.J. \textit{et. al}., \textbf{PRL 73}, 2192, (1994). \newline [3] Ben-Kish A. \textit{et. al.}, \textbf{PRL} \textbf{87}, 015002, (2001) \newline [4] Lee K., Kim J. H., Kim D., \textbf{Phys. of plasmas} \textbf{9}, 4749, (2002). \newline [5] Vrba P., \textit{et. al.}\textbf{, 6th Intl. Conf. on Dense Z-Pinches}, 2005   

Nonlinear Perturbative Simulation Studies of Collective Processes in 3D Finite-Length Charge Bunches at High Space-Charge Intensities

The collective processes in 3D finite-length charge bunches at high space-charge intensities are described self-consistently by the nonlinear Vlasov-Maxwell equations. The nonlinear delta- f method, a particle simulation method for solving the nonlinear Vlasov-Maxwell equations, is being used to study collective effects in high-intensity bunched beams. For bunched beams, the equilibrium and collective excitation properties are qualitatively different from those for coasting beams. Due to the coupling between the transverse and longitudinal dynamics induced by the 2D nonlinear space-charge field, there exists no exact kinetic equilibrium which has anisotropic temperature in the transverse and longitudinal directions. Even in a thermal equilibrium with isotropic temperature, the particles' trajectories on constant energy surfaces are non-integrable, which implies that it is not possible to perform an integration along unperturbed orbits to analytically calculate the linear eigenmodes. An approximate self-consistent kinetic equilibrium is first established for bunched beams with anisotropic temperature. Then, the collective excitations about the equilibrium are systematically investigated using the delta-f method implemented in the Beam Equilibrium Stability and Transport (BEST) code.   

Effects of finite pulse length, magnetic field, and gas ionization on ion beam pulse neutralization by background plasma

We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of a solenoidal magnetic field, gas ionization and the transition regions during beam pulse entry and exit from the plasma. Analytical studies show that a sufficiently large solenoidal magnetic field can increase the degree of current neutralization of the ion beam pulse. However, simulations also show that the self-magnetic field structure of the ion beam pulse propagating through background plasma can be complex and non-stationary. Plasma waves generated by the beam head are greatly modified, and whistler waves propagating ahead of the beam pulse are excited during beam entry into the plasma. Accounting for plasma production by gas ionization yields a larger self-magnetic field of the ion beam compared to the case without ionization, and a wake of the current density and self-magnetic field are generated behind the beam pulse. Beam propagation in a dipole magnetic field configuration and background plasma has also been studied.   

Collective Interaction Processes in Intense Heavy Ion Beam-Plasma Systems*

This paper presents a survey of the present theoretical understanding of collective interactions in intense heavy ion beams for high energy density physics and fusion applications. Emphasis is placed on identifying operating regimes that minimize the deleterious effects of collective instabilities on beam transport and focusing. In the beam transport region, the topics covered include: the electrostatic Harris instability and the transverse electromagnetic Weibel instability driven by strong temperature anisotropy in a nonneutral ion beam; and the electron-ion two-stream (electron cloud) instability driven by an unwanted component of background electrons. In the neutralized drift compression and target chamber regions, the collective interaction processes associated with beam propagating through a dense, charge-neutralizing background plasma are discussed, including the multispecies electromagnetic Weibel instability, and the electrostatic two-stream instability with and without longitudinal velocity tilt in the beam ions. Finally, a class of exact, kinetic, dynamically-compressing (both transversely and longitudinally) beam equilibria are presented for the case of an intense, stable ion beam propagating through a background plasma. * Research supported by the U.S. Department of Energy.   

The effect of ion motion in an adiabatic plasma ion- focusing channel.

We study numerically the effect of ion motion in an adiabatic plasma ion- focusing channel, motivated by a recent suggestion that ion motion in an adiabatic focuser might be significant and even preclude operation of the focuser as previously envisioned. It is shown that despite ion motion the adiabatic focuser should work as well as originally envisioned.   

Warm fluid theory of a thermal rigid-rotor equilibrium for a charged particle beam in a periodic solenoidal focusing magnetic field

A warm fluid theory of a thermal rigid-rotor equilibrium for a charged particle beam in a periodic solenoidal focusing magnetic field is presented. Warm fluid equilibrium equations are solved in the paraxial approximation. The equation of state is obtained. The numerical algorithm for solving the self-consistent Poisson's equation is discussed. Density profiles are calculated numerically for low-intensity and high-intensity beams. Temperature effects in such beams are investigated.   

Perturbative Particle Simulation Studies of Periodically Focused Intense Charged Particle Beams.

High intensity charged particle beam propagation in a periodic focusing lattice is numerically studied. The beam equilibrium and dynamic behavior are described self-consistently by the nonlinear Vlasov-Maxwell equations. For a beam equilibrium which is inhomogeneous in the transverse direction, the solution to the Vlasov-Maxwell equations for periodic focusing configurations can only be determined numerically. To carry out this investigation, the Beam Equilibrium Stability and Transport (BEST) code which uses a 3D low-noise perturbative particle simulation method, has been extended. The scheme begins with a smooth-focusing lattice which is the smooth-focusing approximation for the periodic lattice, and adiabatically replaces the smooth-focusing lattice by the periodic lattice. With this approach, periodic solenoidal configurations are first investigated, and then periodic quadrupole configurations are studied.   

Self-guiding of a high-power laser

The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances greatly exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. Furthermore, if a single 100+ GeV LWFA stage is to be generated then the high-power laser (P/Pc$>>$1) will need to propagate through meters of plasma. We use the PIC codes OSIRIS and QuickPIC to study guiding of such pulses. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion (blowout) of the plasma electrons. For sufficiently high powers and intensities, the index of refraction at the leading edge of the laser changes in a distance much shorter than the pulse length. This combined with the local pump depletion can lead to a larger degree of self-guiding than had been previously thought. We investigate the parameter space in which such guiding can be effective enough that external guiding may not be required.   

Exact analytic solutions for the electromagnetic fields of few-cycle, focused laser pulses

With few cycle light pulses available and development progressing at a high rate, detailed vector models of the fields are required to describe experiments. To meet this need, the analytic solution for the fields of a focused laser beam is derived for any spot size saving a factor of $>\!\!\!100$ in computation time compared to the integral solution [1]. Using this monochromatic model, the pulsed fields are then derived without approximation saving an additional factor of $>\!\!\!100$ in computer time. This analytic model forms a complete vector description of each of the electromagnetic field components of a laser pulse focused to any spot size and pulse length. As the pulse duration decreases below ten cycles, significant changes arise. Specifically, the fraction of the laser energy in the focus is reduced from the monochromatic value of 86.5\% to 83.5\% for a 5 fs Ti:Sapphire laser and to 72.7\% in a single cycle pulse. \newline \newline [1] S. Sepke and D. Umstadter, Opt. Lett. \textbf{31}, 1447 (2006)   

Laser Snow Plough of Electrons in the Blow-Off Regime of Relativistic Laser Plasma Interaction

A relativistic short pulse laser, propagating through an underdense plasma, exerts a pondermotive force on electrons, piling up their density at the laser front and evacuating them from the rear, forming an ion bubble. As the self-focused laser amplitude approaches a critical value, the velocity of axial electrons at the laser front approaches the laser group velocity and large electron density buildup at the front occurs. The radial pondermotive force and space charge field accelerate these electrons radically outward, moving them along the boundary of the bubble. Eventually these electrons reconverge at the stagnation point of the bubble and re-enter the bubble axially. This in fact appears to be the injection mechanism for monoenergetic electrons, which are subsequently accelerated by the ion field as trapped electrons to energy $\varepsilon \simeq $ mc$^{2}$ $\gamma_{g}^{2}$(R$\omega_{p}$/c)$^{2}$/3, where $\gamma_{g} = (1-v_{g}^{2}/c^{2})^{-1/2}$, v$_{g}$ is the laser group velocity and R is the bubble radius that scales as half power of laser amplitude. As the laser loses energy to the electrons it suffers nonlinear absorption over a scalelength $2(\omega^{2}/\omega_{p}^{2})\tau_{L}c$, for normalized laser amplitude a$_{0}$ \underline {$>$} 1, $\tau _{L}$ is the laser pulse length.   

Hamiltonian Formulation of Direct Laser Acceleration in Vacuum

We present a new formulation for the direct laser acceleration of electrons in vacuum based on the Hamiltonian theory. Two different regimes for the snow-plowed accelerated electrons are identified and characterized, the first pertaining to high intensity and the second to low-intensity pulses, both leading to efficient electron acceleration. Particle energy yields are shown to be independent on the exact shape of the laser pulse and energy gains are estimated. The radiation signature due to electrons being reflected from the photon pulse is also permitted.   

Optimization Studies of a Multi-GeV Single Stage Laser-Plasma Accelerator

Using a self-consistent Hamiltonian model of beam transport in a background plasma\footnote{\frenchspacing B. A. Shadwick, G. M. Tarkenton and C. B. Schroeder, Bull. Am. Phys. Soc., \textbf{50}, 283 (2005).}, we consider the design of a single stage, multi-GeV plasma accelerator. In this model the beam is described by phase-space moments and the bulk plasma is taken to be a cold fluid. We present a detailed study of beam propagation in a resonant laser-wakefield accelerator with final energy gain between 5 and 10 GeV. We discuss optimization of the system with regard to energy gain and beam quality.   

Phase velocity evolution in plasma waves driven by relativistically-intense short-pulse lasers

The phase velocity of a plasma wave driven by an intense short-pulse laser is determined by the transport velocity of the laser in the plasma (which is dependent on the laser group velocity). In this work, we investigate the nonlinear transport velocity of a relativistically-intense short-pulse laser propagating in a cold underdense plasma. Expressions for the plasma wave phase velocity dependence on the relativistic laser intensity are derived in the adiabatic and quasi-static regimes. The relativistic laser evolution (energy depletion, frequency shifting, and intensity steepening) is also considered. In a laser-plasma-based accelerator, the plasma wave phase velocity excited by the laser pulse determines the dephasing length of the accelerating structure, and therefore the upper bound on the energy gain of the accelerated charged particle beam.   

Reduced Phase-Space Models of Intense Laser-Plasma Interactions

We undertake a detailed comparison of a variety of reduced models --- moment based descriptions: warm\footnote{\frenchspacing B. A. Shadwick, G. M. Tarkenton and E. H. Esarey, Phys.\ Rev.\ Lett.\ \textbf{93}, 175002 (2004).} and cold fluids as well as fixed-shape distributions: water bag, \textit{etc.} --- to direct solutions of 1-D Vlasov equation\footnote{\frenchspacing B.~A. Shadwick, G.~M. Tarkenton, E. Esarey, and C.~B. Schroeder, ``Fluid and Vlasov Models of Low-Temperature, Collisionless, Relativistic Plasma Interactions,'' Physics of Plasmas {\bf 12}, 056710 (2005).}. We examine the quality of the agreement between the various models as a function of both initial plasma temperature and plasma wave amplitude. We determine parameter regimes of validity for the various reduced models and comment on applicability of these models to studying laser-driven plasma accelerators.   

Nonlinear Theory for Relativistic Plasma Wakefields in the Blowout Regime

We present a theory for nonlinear, multidimensional plasma waves with phase velocities near the speed of light. It is appropriate for describing plasma waves excited when all electrons are expelled out from a finite region by either the space charge of a short electron beam or the radiation pressure of a short intense laser. It works very well for the first bucket before phase mixing occurs. We separate the plasma response into a cavity or blowout region void of all electrons and a sheath of electrons just beyond the cavity. This simple model permits the derivation of a single equation for the boundary of the cavity. It works particularly well for narrow electron bunches and for short lasers with spot sizes matched to the radius of the cavity. It is also used to describe the structure of both the accelerating and focusing fields in the wake. Beam loading is also considered with this model.   

Analysis of mobile ions in extreme regime of high intensity beams in plasma wake-field accelerators

We investigate the effect on ion motion by high intensity beams in future beam driven plasma wake-field accelerators. We show that the witness beam is indeed the main concern since we can design the drive beam to reduce the undesirable effects. We compare Hydrogen, Lithium and Xenon as plasma gases and show that Argon is perhaps the best choice. We, then analyze the problems of using Argon such as trapped electrons, multiple ionization and beam loading.   

Laser-produced plasma EUV source using a colloidal microjet target containing tin dioxide nanoparticles

We realized a low-debris laser-produced plasma extreme ultraviolet (EUV) source by use of a colloidal microjet target, which contained low-concentration (6 wt\%) tin-dioxide nanoparticles. An Nd:YAG laser was used to produce a plasma at the intensity on the order of $10^{11}$ W/cm$^2$. The use of low concentration nanoparticles in a microjet target with a diameter of 50 $\mu$m regulated the neutral debris emission from a target, which was monitored by a silicon witness plate placed 30 cm apart from the source in a vacuum chamber. No XPS signals of tin and/or oxygen atoms were observed on the plate after ten thousand laser exposures. The low concentration nature of the target was compensated and the conversion efficiency (CE) was improved by introducing double pulses of two Nd:YAG lasers operated at 532 and 1064 nm as a result of controlling the micro-plasma characteristics. The EUV CE reached its maximum of 1.2\% at the delay time of approximately 100 ns with the main laser intensiy of $2 \times 10^{11}$ W/cm$^2$. The CE value was comparable to that of a tin bulk target, which, however, produced a significant amount of neutral debris.   

Characteristics of THz emission from a femtosecond-laser produced dense plasma

Recently, the THz radiation from a femtosecond-laser-produced dense plasma have been studied. The short electromagnetic pulse in THz spectral region emits by the interaction between a laser wakefield in a static magnetic field. The magnetized wakefield has both electrostatic and electromagnetic components, and has nonzero group velocity. This enables the wake to propagate through the plasma and couples radiation into the vacuum. This phenomenon is called the Cherenkov wake radiation, and the emitted frequency is expected to be close to the plasma frequency. The theory predicts the production of GHz to THz radiation at a power approaching GW level by using the wakefield excited by current laser systems and the appropriate magnetic field. We demonstrated a proof-of-principle experiment of a Cherenkov wake radiation from the femtosecond-laser-produced magnetized wakefield. A maximum frequency up to 0.3 THz with a pulse width of 200 ps (FWHM) was observed. In addition, we also observed an angular distribution of the radiation, which has an annular cone profile at far-field attributed TM$_{01}$ mode in a plasma. In addition, we also show the development of an electro-optic (EO) sampling system for detecting coherent THz emission from a laser-produced dense plasma.   

Enhancing plasma wakefield and e-cloud simulation performance using a pipelining algorithm

Modeling long timescale propagation of beams in plasma wakefield accelerators at the energy frontier and in electron clouds in circular accelerators such as CERN-LHC require a faster and more efficient simulation code. Simply increasing the number of processors does not scale beyond one-fifth of the number of cells in the decomposition direction. A pipelining algorithm applied on fully parallel code QUICKPIC is suggested to overcome this limit. The pipelining algorithm uses many groups of processors and optimizes the job allocation on the processors in parallel computing. With the new algorithm, it is possible to use on the order of 100 groups of processors, expanding the scale and speed of simulations with QuickPIC by a similar factor.   

DRACO development for 3D simulations

The DRACO (r-z) lagrangian radiation-hydrodynamics laser fusion simulation code is being extended to model 3D hydrodynamics in (x-y-z) coordinates with hexahedral cells on a structured grid. The equation of motion is solved with a lagrangian update with optional rezoning. The fluid equations are solved using an explicit scheme based on (Schulz, 1964) while the SALE-3D algorithm (Amsden, 1981) is used as a template for computing cell volumes and other quantities. A second order rezoner has been added which uses linear interpolation of the underlying continuous functions to preserve accuracy (Van Leer, 1976). Artificial restoring force terms and smoothing algorithms are used to avoid grid distortion in high aspect ratio cells. These include alternate node couplers along with a rotational restoring force based on the Tensor Code (Maenchen, 1964). Electron and ion thermal conduction is modeled using an extension of Kershaw's method (Kershaw, 1981) to 3D geometry. Test problem simulations will be presented to demonstrate the applicability of this new version of DRACO to the study of fluid instabilities in three dimensions.   

Three-dimensional Low Mode ICF Target Simulations

This paper describes the application of a three-dimensional radiation hydrodynamics code to problems typical of ICF pellet design. The compressible hydrodynamics code, FastRad3D, contains most of the physical effects relevant for the simulation of high-temperature plasmas including inertial confinement fusion (ICF)-regime Rayleigh-Taylor unstable direct drive laser targets The calculations show the effects of low mode surface non-uniformities and laser intensity non-uniformities on gain for a typical ICF pellet designs. The 3D results are compared to previous results from 2D and 1D calculations.   

On the Role of Numerical Differentiability in the Modeling of Fluid Instabilities in Inertial Confinement Fusion Hydrodynamics Codes

The problem we wish to address is that of accurately modeling the evolution of small-amplitude perturbations to a time- dependent flow, where the unperturbed flow itself exhibits large-amplitude temporal and spatial variations. In particular, we wish to accurately model the evolution of small- amplitude perturbations to an imploding ICF pellet, which is subject to both Richtmyer-Meshkov and Rayleigh-Taylor instabilities. Any errors that we make in numerically modeling the flow, if they have a projection onto the space of the perturbations of interest, can easily compromise the accuracy of those perturbations, even if the errors are small relative to the unperturbed solution. As we have reported recently, most of the progress we have made toward our goal of accurately modeling the evolution of such small-amplitude perturbations has been achieved by imposing a ``differentiability condition'' on the individual numerical components of our radiation hydrodynamics codes. Here we give an update on that work, and modify our previous numerical design criteria to include the notion of ``effective nondifferentiabiliy.''   

Perturbation Growth Resulting from Shock Interaction with Density Gradients and Density Non-Uniformities in Shocked Materials

Theoretical work has shown that a short sub-ns laser pulse (spike) and a rarefaction wave behind it shape a density/adiabat gradient in the target that suppresses laser imprint, reduces the RT seeding due to the surface roughness, delays the onset [1] and reduces the rate [2] of the RT perturbation growth in the target. At the same time, the decaying shock from the spike produces strong areal mass oscillations in the target [3], which the subsequent shock from the foot of the main laser pulse can amplify, thus increasing the contribution of the early-time RM-like growth to the overall perturbation growth in the target. We present the results of analytical and numerical studies of perturbation growth resulting from shock interaction with density gradients and density non-uniformities in previously shocked targets. Although the density/adiabat tailoring with a spike adds some new sources of perturbation growth, its net stabilizing effect is large and robust. [1] N. Metzler \textit{et al}., Phys. Plasmas \textbf{8}; 3283 (1999); \textbf{9}, 5050 (2002); \textbf{10}, 1897 (2003). [2] V. N. Goncharov \textit{et al}., Phys. Plasmas \textbf{10}, 1906 (2003); R. Betti\textit{ et al}., Phys. Plasmas \textbf{12}, 042703 (2005). [3] A. L. Velikovich \textit{et al}., Phys. Plasmas \textbf{10}, 3270 (2003).   

Laser Spike Prepulses and the Ablative Richtmyer-Meshkov Instability

Recent work by various authors has suggested that there are hydrodynamic advantages to using ``spikes'' or ``pickets'' prior to the driving laser pulse in ICF target interactions. These spikes can suppress laser imprint [1] and reduce the growth rate of the Rayleigh-Taylor instability of targets by tailoring the target's adiabat (increasing the ablation velocity) [2,3]. We look at the development of hydrodynamic instability during the compression (early time) phase of the target interaction, prior to target acceleration, when the Richtmyer-Meshkov instability is typically active. We find that under certain conditions, simulations show that hydrodynamic growth of target perturbations can be enhanced by these spikes. We show the results of these simulations, and discuss the causes and conditions during which this enhanced growth can occur. \newline 1. N. Metzler \textit{et al.}, Phys. Plasmas \textbf{6}, 3283 (1999) \newline 2. V. Goncharov \textit{et al.}, Phys. Plasmas \textbf{10}, 1906 (2003) \newline 3. K. Anderson and R. Betti, Phys. Plasmas \textbf{10}, 4448 (2003).   

New experimental platform for turbulence and turbulent mixing in rotating and accelerating fluids at high Reynolds numbers

A new high-performance experimental platform for studies of turbulent flows and turbulent mixing in accelerating and rotating fluids is presented. This novel experimental approach is based on ultra-high performance optical holographic data storage technology. The state-of-the-art electro-mechanical, electronic, and laser components allow one to realize and study flows with extremely high Reynolds numbers ($>10^7$) in a relatively small form-factor, with extremely high spatio-temporal resolutions and bandwidth. The technology can be applied for investigation of a large variety of hydrodynamic problems including fundamental properties of non-Kolmogorov turbulence and turbulent mixing in rotating and accelerating fluids, pre-mixed combustion, and MHD. Unique metrological capabilities of the technology have excellent provisions for the studies of the transports of momentum, angular momentum and energy, as well as scalings, invariants and statistics of complex turbulent flows.   

Simulation, Theory, and Observations of the Spectrum of the Rayleigh-Taylor Instability due to Laser Imprint of Planar Targets

A limitation on the efficiency of high gain direct drive inertial confinement fusion is the extent of pellet disruption caused by the Rayleigh-Taylor (RT) instability. The RT instability can be seeded by pellet surface irregularities and/or laser imprint nonuniformities. It is important to characterize the evolution of the RT instability, e.g., the k-spectrum of areal mass. In this paper we study the time-dependent evolution of the spectrum of the Rayleigh-Taylor instability due to laser imprint in planar targets. This is achieved using the NRL FAST hydrodynamic simulation code together with analytical models. It is found that the optically smoothed laser imprint-driven RT spectrum develops into an inverse power law in k-space after several linear growth times. FAST simulation code results are compared with recent NRL Nike KrF laser experimental data. An analytical model, which is a function of Froude and Atwood numbers, is derived for the RT spectrum and favorably compared with both FAST simulation and Nike observations.   

Flexible Large Batch Production of High Energy Density Physics Targets

Currently, experimental High Energy Density Physics (HEDP) targets are fabricated one at a time. Individual production limits target quantities due to time and cost. Demand for statistically relevant HEDP data has led to development of higher repetition rate lasers and targeting systems. To meet increased target demand, larger batches of 100 to 1000 targets will be needed. Routes to batch production of a wide variety of targets with essentially identical or slightly modified characteristics are examined. Target attributes considered include complex geometry, different materials (i.e. metals, plastics, foams of variable density), material layering, and variable thickness. The compatibility of the machining, deposition and other processes required to produce these targets is discussed. Potentially desirable HEDP targets are identified and batch fabrication steps specific to these targets are outlined.   

Fabrication and Characterization of Tantalum Oxide Aerogel for Radiation Transport Experiments

Tantalum aerogel was fabricated and machined for use as a radiation transport target. The aerogel material was synthesized as small billets from an acid catalyzed tantalum ethoxide solution. After gelation the material was supercritically dried in alcohol, providing dry aerogels with densities between 200-300~mg/cc. Slots were milled in the material as small as 100~$\mu$m wide and the piece was ultimately cut down to a 100~$\mu$m thick disk with slots. The material has been characterized for pore size/void content and surface finish. Thermogravimetric analysis of the material indicates a very rapid uptake of water in ambient conditions, consistent with its high surface area.   

Fabrication of Fill Tube Targets to Study Shadowing and Compositional Effects on Inertial Confinement Fusion Implosion Characteristics

Target design for the National Ignition Facility requires either a SiO2 or CH fill tube to fill the confinement capsule with DT fuel. To study the effects of diameter and composition of the fill tube on the implosion of the capsule, surrogate fill tube targets were fabricated. Multiple fill tubes were placed on one capsule to maximize data during NIF relevant experiments at the Z-Pinch Facility at Sandia National Laboratory. Targets were fabricated with three or four fill tubes on the equator of the capsule. SiO2 and CH (as well as capsules with just SiO2) fill tubes were placed on the same capsule with diameters ranging from 10-45 µm. In order to attach the tubes, blind holes were first drilled in the capsules using an excimer laser system. All targets were characterized using an x-ray tomography system.   

Evaluation of effects of bonding joint in machined capsules on ignition at the National Ignition Facility (NIF)

The current point design for ignition capsules to be fielded at NIF is a beryillium capsule with a graded copper dopant made by a sputtering process. Although this fabrication process has been and continues to improve there is still a desire to provide an alternative capsule, should the sputtering process fail to meet all specified requirements. To this end, capsules made with uniform copper dopant and by a machining process are still a viable alternative to those made with sputtering. These capsules are made as two hemispheres and then bonded together with a small weld joint. However, one major risk for the viability of these machined capsules is the effect of this joint on the ignition performance of these capsules. To mitigate the expected effect of these joints on ignition the National Ignition Campaign (NIC), last year, specified that these joints would be 0.1 mm wide and only penetrate 1/3 of the ablator shell. These specifications were chosen for two reasons, the target fabrication was feasible, although at the very limit of expected capabilities, and the limited calculations we had performed to date indicated that with this specification we should not effect ignition. In this paper, we present further simulations using the code HYDRA, which help bound the requirements for the fabrication of this joint. These calculations further enhance our confidence that a machined capsule with a joint as specified is a viable alternative to the sputtered capsule, should an alternative design be required.   

Improving Laser/Plasma Coupling with Rough Surfaces

In the Fast Ignition scenario the photons from a petawatt laser are converted into electrons at a solid surface typically with 30{\%} efficiency. Recent experiments have shown this can be doubled with the use of a rough surface. For Fast Ignition targets, we wish to produce rough surfaces on the inside tip of a narrow cone. We can produce the needed structure in that confined space by making the cone on a plastic mandrel and roughening its surface with particle track etching. To achieve a surface of desired roughness requires exposure to 10$^{10}$ ions/cm$^{2}$ with ion energies in the range of 0.5 to 2MeV/nucleon and weights ranging from Si to Zn. Conical pits are then etched into the plastic with a height to diameter ration of 3 to 1 and the resulting surfaces replicated by sputter coating the plastic with metal and then etching the plastic away.   

Development of a thermal x-radiation source using ``hot'' hohlraums

High temperature (``hot'') hohlraums have been fielded at the NIF and OMEGA lasers. They reach high radiation temperatures by coupling a maximum amount of laser energy (10 kJ) into a small gold hohlraum (400-800 $\mu $m diameter) in a short time (1 nsec). They fill rapidly with plasma. Radiation temperatures of 370 eV have been measured in the laser entrance hole (LEH) region of these targets. However, since this LEH radiation is not thermal it cannot be used as a radiation drive for opacity or atomic physics packages. In addition, a physics package inside the hohlraum cannot be shielded from this radiation or protected from being crushed by the plasma filling. The radiation source we are developing uses the x-ray burnthrough of a thin wall of the hohlraum to heat a physics package. We report on the measured radiation drive of this source and the use of this source to heat a surrogate physics package (a ``witness plate''). We characterize the radiative heating of the witness plate by measuring its thermal expansion and soft x-ray spectrum. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48 and grant number DE-FG52-2005NA26017 (NLUF).   

Optimization of NIF scale backlighters for radiographing thin shell capsule surrogates in indirect drive*

To produce sufficiently symmetric implosions for indirect drive ignition with the NIF laser, we will require laser illuminated foils as x-ray backlighters for radiographing distortions on surrogate thin shells. The back lit x-ray images will be used as a basis for tuning beam pulse shape, timing, and other aspects of target design, to achieve optimum symmetry of implosion. The accuracy of the symmetry measurement is limited by the backlighter x-ray flux, photon statistics, and other noise sources, as well as the resolution of the camera, and the uniformity of the source.. We have performed experiments on the Omega laser to test the backlighter configuration and imaging system with NIF relevant beam intensites, x-ray energies, and beam incidence and detector viewing geometry. The x-ray source is imaged with gated x-ray pin hole cameras and optics similar to those planned for the NIF ignition experiments to determine uniformity and x-ray flux is detected with absolutely calibrated diodes to determine conversion efficiency. Results of these experiments will be discussed in the context of the measurement accuracy under ignition conditions.\newline *This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.   

2D low energy LMJ target design

Achieving ignition is one of the objective of the ``Laser MegaJoule'' (LMJ). Several indirect drive were designed to reach ignition with this laser. In an indirect drive configuration, laser light is converted to X-rays in a high-Z, typically gold, hohlraum. The resulting radiative energy drives the implosion of the central cryogenic DT capsule. Inside the hohlraum, a low density gas, for example H-He mix, retains the gold blowoff. The LMJ will deliver up to 2 MJ and 550 TW. A 1.4 MJ ignition target has already been designed. We present here the 2D design of a smaller target which requires 1 MJ and 300 TW of laser energy and power. This target could be shot during pre-ignition campaigns. Then, we compare both targets. In the smaller one, optimizing the beam passage through the laser entrance holes and tuning the radiation symmetry have become a real issue. Especially, we study the influence on radiation symmetry of H-He gas density.   

Interpretation of symmetry experiments on Omega

The interpretation of the symmetry experiments performed on Omega in 2005 with 3 cone LMJ-like irradiation is presented here. The goal of this campaign was the characterization of the irradiation symmetry by X-ray imaging of the D2Ar capsule. Images of backlit implosion (as done in earlier campaigns with foam balls) and core emission were obtained on the same shot, and can be compared to FCI2 simulations. This set of shots comfirms former results with foam balls of a good symmetry control with 3 cones in empty hohlraums. The influence of the hohlraum shape on symmetry is also studied by comparison of cylindrical hohlraums vs rugby ones.   

Hohlraum Simulations for Symergy Capsules

The use of a single capsule implosion within a hohlraum to provide information on both the asymmetry of the radiation drive impinging on the capsule and the total energy absorbed by it has led to the concept of experiments with ``symergy'' capsules.\footnote{ N. M. Hoffman, D. C. Wilson, and G. A. Kyrala, 2006 High-Temperature Diagnostics Conference, May 2006, Williamsburg, VA USA, to appear in \textit{Rev Sci Inst.} \textbf{77} (2006)} We present simulations for planned shots at Omega with hohlraum drive approximating the first 6 ns of the actual NIF ignition drive and surrogate capsules for the NIF ignition capsule. The hohlraum modeling can assess the effects of hohlraum gas fill, laser timing variations and beam pointings. In addition to its immediate design use, it should be useful in validating both the predictive capability for observed symergy capsule responses and the modeling of the initial stage of the NIF ignition process.   

Reemission Ball and Symmetry-Capsule diagnostics for symmetry measurements

The most recent Livermore NIF design is a gas filled hohlraum without shine shields [1]. Two symmetry diagnostics, reemission ball and symmetry-capsule, are examined using the new ignition design. Both reemission ball and symmetry-capsules have been used in the past to measure capsule symmetry on NOVA experiments. [2-5] Livermore and Los Alamos scientists are now pursuing both concepts to study symmetry on NIF. [6] Here we compare the predicted symmetry for the two techniques. Issues related to the three-dimensional nature of the reemit diagnostic will be discussed. Issues such as the viewing holes in the hohlraum wall will be addressed by applying a three-dimensional view-factor code. \newline [1] Steve Haan et al., private communication \newline [2] Magelssen et al., Phy. Rev. E 57, 4663 (1998). \newline [3] Delamater et al., Phy. Rev. E 53, 5240 (1996). \newline [4] Hauer et al., Phys. Plasmas 2 (6), 2488 (1995). \newline [5] Harris et al., Bull. Am. Phys. Soc. 38, 1885 (1993). \newline [6] Don Meeker private, communication and Nels Hoffman, private communication   

Accuracy of the shock timing obtained for a National Ignition Facility ignition target

The indirectly-driven ignition target for the National Ignition Facility features a cryogenic capsule driven by a series of four shocks which must be precisely timed. The timing of the first three shocks will be measured and tuned experimentally using a surrogate target which features a line of sight pipe attached to a mock capsule. The interior of the line of sight pipe and the ablator shell are filled with liquid deuterium in the surrogate target. The view through the pipe enables precise, direct measurement of the timing of shocks transiting the shell. We present simulations which assess how closely the timing information obtained from this surrogate target matches the ignition target. The plasma conditions in the surrogate target are a near match to the ignition target. These simulations make use of new capabilities in the Arbitrary Lagrange Eulerian ICF code HYDRA. They resolve the ablation physics using a multiblock mesh that conforms to the target geometry. Techniques employed in these HYDRA simulations also enable modeling of other ICF targets having complex, asymmetric geometries, such as a diagnostic patch or a slot.   

An improved algorithm for solving Collisional Radiative Equilibrium (CRE) equations

Elements used in ICF target designs can have many charge states in the same plasma conditions, each charge state having numerous energy levels. When LTE conditions are not met, one has to solve CRE equations for the populations of energy levels, which are necessary for opacities/emissivities, Z* etc. Although successful statistical methods have been devised[1], these are insufficient in case of sparse spectra, or when configuration interaction is important (open d or f shells). For these cases the HULLAC code[2] can be used to generate transition rates. The equations to be solved may involve tens of thousands of levels. Moreover, the system is by nature ill conditioned. In this poster, we present a powerful, quick and robust CRE equation solver. We factor the level populations in ion population times level reduced population. The algorithm consists of double Newton --Raphson iterations. Results will be shown on Carbon and Xenon. \newline \newline [1] A Bar-Shalom, J Oreg, and M Klapisch, J. Q. S. R. T.,65, 43 (2000). \newline [2] A Bar-Shalom, J Oreg, and M Klapisch, J. Q. S. R. T.,71, 169 (2001).   

Advances in Vlasov-Fokker-Planck Simulation of Nanosecond Laser-Plasma Interactions

We have developed the first computational tool which is ideally suited to modelling the effects of non-local transport (i.e. departures from Braginskii's transport theory) and self-generated magnetic fields over nanosecond timescales in two spatial dimensions. The current code is a significant development of an existing VFP code (IMPACT$^{1})$ that has been modified to allow hydrodynamic motion of the ions; this allows for more realistic plasma simulation over the timescales of interest. We briefly outline the procedure by which one includes the effect of moving ions in the Vlasov-Fokker-Planck (VFP) equation. We investigate the suppression of non-local heat flow, by externally applied magnetic fields, in long-pulse laser produced plasmas$^{2,3}$. The effects of resistive diffusion, `frozen-in' flow and Nernst advection determine the evolution of the spatial structure of the magnetic field -- under the action of laser heating -- and are included in our model. The exact profile of the magnetic field affects the degree of importance of non-local heat flow and so is part of our discussion. [1] R.J. Kingham {\&} A. Bell, Journal of Computational Physics, Vol. 194, p1, 2004. [2] G. Gregori \textit{et al}, Physical Review Letters, Vol. 92, No. 20, p205006-1, 2004. [3] D.H. Froula \textit{et al}, submitted to Physical Review Letters, Spring 2006.   

Design of an Omega Experiment to Diagnose Ablator Burn-through with d-3He Proton Yield and Spectra

Design calculations are presented for proposed Omega experiments to diagnose ablator burn-through using d-3He proton spectra. These experiments use ``symergy'' capsules which are sensitive to both drive asymmetry and strength. These experiments will help develop the ``symergy'' capsule for use as a burn-through diagnostic for future application to NIF experiments. We are considering scanning through a range of shell thicknesses of 20-50 micron using Ge-doped GDP plastic shells in capsules of outside diameter 560 micron and filled with up to 60 atm D2-3He. Expected neutron yields are up to 1e9 and proton yields up to 1e7, using a 1 ns laser pulse in an Omega scale hohlraum. This should give measurable proton spectra and ion temperature measurements. We are also planning on using these experiments to measure drive asymmetry from pole-hot to equator-hot by varying the laser pointing and observing the response in both x-ray imaging and d-3He protons and DD neutrons. Preliminary 2-D computational results will be presented.   

Effect of Laser Pointing on NIF Neutron Diagnostics and Burn Symmetry

We have been working on 2-D capsule-hohlraum implosion calculations for the NIF that utilize a laser drive pulse that peaks at 300 eV and uses less than 1 MJ of energy. We have carried out a systematic study of how changing the laser pointing changes the symmetry of the ignition capsule implosion. We performed energy-gated neutron image simulations to better understand which neutron energy bins will provide the most symmetry information for capsules that ignite or fail to ignite. We are especially interested in the symmetry of capsules that ignite, since we would like to correlate distortions in the density contours with neutron intensity contours in neutron images. This appears to be difficult, as ignition appears to remove the distinction between the hot spot and the fuel in simulated neutron images.   

Update on Los Alamos 1 MJ National Ignition Facility Capsule-Hohlraum Calculations

Recent plans for ignition on the National Ignition Facility (NIF) call for the first ignition attempt to utilize about 1 megajoule (MJ) of laser energy. Our 2-D capsule-hohlraum calculations has capsule with a 0.3 atom{\%} uniformly Cu doped beryllium ablator capsule that has an inner ice radius of 753 $\mu $m, and inner ablator radius of 825 $\mu $m, and an outer ablator radius of 1000 $\mu $m. We use post-processing to simulate results expected from neutron imaging, high-energy X-ray images, and neutron reaction history diagnostics. We are especially interested in how we can use these diagnostics to determine the difference between laser pointing errors and problems with the time dependent shape of the laser pulse and examine this in detail here.   

Update on specifications for NIF ignition targets, and their rollup into an error budget

Targets intended to produce ignition on NIF are simulated to set specifications for fabrication, the laser, and experimental campaigns prior to ignition. Recent work has focused on refining designs that use 1.0 MJ of laser energy. Ablators are Be(Cu), CH(Ge), and high-density CVD C. The main-line hohlraum design has a He gas fill, a wall of U-Au layers, and no shields as were formerly proposed between capsule and laser entrance holes. Complete requirements tables have been prepared for all the targets. The specifications are combined into an error budget indicating adequate margin for ignition with all of the designs. The emphasis in this presentation will be on changes in requirements in the last year, and on the overall rollup of the errors quantifying margins and uncertainties.   

Ignition Capsule with High Density Carbon Ablator for NIF

An ignition capsule with nano-crystalline high density CVD carbon ablator is emerging as one of the principal configurations for NIF because it offers several advantages. (1) With the same outer radius, the higher density ablator absorbs more energy than the beryllium ablator. (2) The carbon ablator formed by vapor deposition can have smaller and more uniform grains than beryllium. Rapid progress is being made in target fab in reaching ignition specs. (3) The higher density reduces coupling of the DT ice surface and the ablator/ice interface from the unstable ablation front, reducing growth of perturbations seeded by ice roughness and inner shell roughness. Possible disadvantages are: (1) The ice surface might in fact be rougher because of differences in the beta-layering in C vs Be. (2) The outer surface needs to be smoother because of slightly lower ablation rates, and because a given surface roughness corresponds to a larger mass perturbation. Overall the carbon ablator has good stability behavior, especially at the ablator-fuel interface. We will present 1-D design for capsules operating at 270 and 300 eV peak hohlraum temperatures, 2-D stability calculations, and melt behavior after the passage of the 2$^{nd}$ shock.   

Update on Ignition Studies at CEA

In the frame of the ICF Program at CEA with the Laser Megajoule (LMJ) we sum up our main results regarding experimental results obtained with the Omega laser (DOE collaboration): they concern some implosions of capsules filled with D2+Ar, the diagnostics are the core images with temporal resolution and the radiograph (symmetry study). On the other hand, the hydro-instability experiments are devoted to the study of the interplay of 2 perturbation modes and 3D perturbations. As far as the target design is concerned, we are extending the LMJ domain of operations to low laser energy.   

Surface effects and droplet evolution in a liquid/vapor flow of aluminum heated by a heavy ion beam for Warm Dense Matter studies.

We have made estimates of surface effects and droplet evolution in the two-phase flow that should be observed in the upcoming foil heating experiments planned for the NDCXII machine at LBNL. An aluminum foil of order micron thickness will be heated by a heavy ion beam to the 1 eV range. The expansion will take place in the two-phase regime, so the heated metal will first melt, then fragment into droplets, and then the droplets will undergo some evaporation. We propose hydrodynamic criteria to estimate the maximum size of the droplets ($\sim $100 nm), considering a balance between hydrodynamic disruptive forces and restoring surface tension. We estimate the relevant thermodynamic functions (surface tension, latent heat, viscosity) for temperatures up to the critical temperature, and we use them to make a simple model for the partial or total evaporation of a droplet in the expanding flow.   

Recent Developments in the EOSTA model

The EOSTA model that combines the STA and Inferno models, was extended to calculate EOS and Opacities on the same footing. The Inferno section was improved and includes efficient algorithm for tracing all the shape resonances and to follow their detailed shapes. In addition higher partial waves improves the accuracy. Optimized Effective Potential (OEP) and Parametric Potential are used for transition energies. In the calculation of internal energy we apply exact exchange with appropriate reduction of the self-energy. A new method for calculating EOS that was presented recently is further developed. The lower component representation of the relativistic virial theorem yields a differential equation that is a basis for very good approximations. Excellent agreement is achieved in comparison with experiments and other calculations.   

A Mie-Gruneisen Equation of State for ICF Applications

We develop and test a relatively simple Mie-Grunesen equation of state (EOS) that incorporates a condensed matter -- vapor change of phase for possible application in inertial confinement fusion (ICF) calculations. The pressure and energy equations are polynomial functions of temperature and volume that self-consistently model molecular repulsion and attraction. These EOS are uniquely characterized by only four parameters (e.g., critical point, and coherence energy); additional data provides self-consistency tests. Characterizing parameters and self-consistency tests are collected for a variety of materials with special attention to the metal Beryllium and the molten salt Flibe (LiF-BeF$_{2})$.   

Computer Simulations of Radiatively-Driven Shocks Using Mei-Gruneisen Equations of State

Mei-Gruneisen Equations of State (EoS) have been developed for Flibe (BeF$_{2}$ and LiF) and Beryllium for Inertial Confinement Fusion (ICF) target applications. Layers or jets of Flibe has been suggested as a means of protecting ICF target chamber walls from the target-generated x-rays. Beryllium (doped with Copper) has been suggested as the ablator material for radiatively-driven capsules for NIF. We will show calculations, performed with the BUCKY computer code, of the response of slabs of Beryllium and Flibe to x-ray irradiation. The calculations are performed with different equations of state, including Mei-Gruneisen. Both situations (ablators and chamber protection) the manner of vaporization is important. The Mei-Gruneisen EoS has a particular treatment of the vapor dome, whose details are important to the details of vaporization.   

Measurements of physical parameters on laser-irradiated iron and hydrogen targets relevant to earth and planetary interior conditions

We have been developing an experiment for the measurement of the sound velocity of high-temperature, high-density iron relevant to earth core by side-on x-ray radiography. When a foil target is irradiated by laser, shock wave propagates in the foil. After the shock front reaches the rear surface, reflected rarefaction wave moves back to the laser-irradiated surface. When the rarefaction wave (sound wave) reaches the laser-irradiated surface, the laser-irradiated surface starts to accelerate. From the measurement of the shock breakout timing and the rarefaction breakout timing with x-ray radiograph, it is possible to obtain the sound velocity. The experiments were done on the HIPER laser facility at ILE, Osaka Univ. In order to avoid the preheating, we employed three-layered target (CH - Au - Fe). The pulse shape of the irradiated laser was foot pulse (2$\omega $, 4 ns, 2x10$^{12}$ W/cm$^{2})$ followed by main pulse (3$\omega $, 7.5 ns, 2x10$^{13}$ W/cm$^{2})$. We measured the shock velocity and the shocked temperature from the rear-surface emission spectrum to characterize pressure and temperature of the laser-compressed iron in addition to the sound velocity. We also started an experiment for liquid hydrogen targets relevant to Jupiter condition. Preliminary experimental results on the shock measurements on hydrogen are presented.   

Characterization of Dense Plasma Targets for Equation of State Experiments.

The measurement of the Equation of State (EOS) of materials in the dense-plasma state is difficult. The standard method for measuring EOS relies on the shock driven Hugoniot technique, where the material is initially at standard temperature and pressure and is shocked using a flyer plate. The locus of states produced using this technique is called the standard Hugoniot. However, the states produced do not fall into the regime of dense plasmas, where the EOS of the material is quite uncertain. We are developing a technique for measuring the EOS in a dense plasma, conditions far away from the standard Hugoniot. This technique requires that the initial condition of the material be at densities well below and temperatures well above standard. We have completed initial experiments producing and characterizing the plasma targets using visible spectroscopy and imaging. We have also begun development of a dynamic phase contrast imaging system required for measuring the shock velocity in the plasma. Simulations of these initial measurements and of the laser drive necessary to produce a uniform shock in the material are also shown. The conditions that we calculate to be produced by this shock are then compared to models for the EOS of this material.   

Measuring material structure of samples dynamically compressed to high pressure

Dynamic quasi-isentropic compression will be used on the National Ignition Facility to generate pressures approaching 3000 GPa. This will enter a materials regime impossible to reach in the solid state by static and shock compression techniques. There is sparse data on materials at these pressures to validate the models and quantum molecular dynamics simulations that are now possible. Our goal is to develop diagnostic techniques that can be used dynamically to measure key properties of these materials at these extreme conditions. We will discuss the development of dynamic x-ray diffraction from quasi-isentropically compressed samples on laser-based platforms as a means of determining the crystallographic structure. This work performed for the US DOE by UC LLNL under contract W-7405-ENG-48. The project (06-ERD-017 and 06-SI-004) was funded by the Laboratory Directed Research and Development Program at LLNL.   

Experiments on material dynamics at extreme pressures and strain rates

Solid state, materials dynamics experiments at extreme pressures, 10-100 GPa (0.1-1 Mbar) and strain rates (1.e6 - 1.e8 1/s) are being developed on high-energy laser facilities. A quasi-isentropic, ramped-pressure (shockless) drive is being developed to reach the highest pressures in the solid state. Constitutive models for material strength of aluminum and vanadium under these conditions are tested with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS), and from dynamic x-ray diffraction measurements. Large-scale MD simulations elucidate the microscopic dynamics of the lattice response to the high pressure, high strain rate compression. Deformation mechanisms, such as the slip-twinning transition in shocked single-crystal Cu are examined using recovery techniques. Designs are being developed to reach much higher pressures, greater than 1000 GPa (10 Mbar), in the solid state on the NIF laser. Highlights from this work will be presented.   

Absolute equation-of-state measurements for an important metal

Aluminum is one of the most important metals in many scientific scenes. In the research fields of high-pressure physics, the metal plays a crucial role as the standard material of equation-of-state (EOS). Since Al EOS is known well up to GPa regime, the impedance matching method is fairly useful. However, above TPa pressures, the Al EOS even the principle Hugoniot is uncertain. As it is impossible for the conventional drivers to achieve the pressure conditions, theoretical models have not been experimentally validated. This limits the use of Al for the impedance matching method in TPa pressure regions. In this paper, aluminum EOS experiments at the GEKKO/HIPER laser facility of the Institute of Laser Engineering are presented. The Hugoniot were absolutely measured using a side-on x-ray backlighting diagnostic. From the shock and pusher (particle) velocities, the Hugoniot EOS points were determined up to multi-TPa pressures. This laser-driven EOS experimental scheme can provide new absolute EOS data of any opaque materials previously inaccessible in the conventional pressure drivers, helping to establish EOS standard materials at higher pressures.   

Simulations of Gd opacity experiments at the Omega laser

We have performed experiments at the Omega laser to validate opacity codes and associated opacity tables. These experiments used dual-axis imaging spectroscopy of tamped Gd:Al co-mixed samples. The samples were heated inside large (4mm dia.) shielded 3-chamber hohlraums to 35-45eV. The sample expansion was measured radiographically and the sample transmission was measured spectroscopically in several spectral bands. We modeled the laser drive, radiation transport, and hydrodynamics of the expanding sample inside the hohlraum using LASNEX. To generate synthetic spectra that correspond to the experimental spectroscopic detector orientation we post-process LASNEX simulations using CRETIN, a non-local thermodynamic equilibrium and radiation transport code, with varying levels of detail in the atomic data. Comparisons between simulated drive conditions, simulated spectra, and experimental data are conducted.   

Using Krypton K-shell Emission as a Diagnostic of Fuel Conditions in Implosions of SIO2 Shells

To study how hi-Z impurities in imploding capsules affect the equilibration of ion, electron, and radiation temperatures, the D3He fill gas of SIO2 shells have been doped with various amounts of krypton and xenon. If xenon is used as the main adjustable impurity affecting this equilibration, the amount of krypton placed in the D3He fill gas can be kept at a level that minimizes the optical depth of the krypton K-shell emission lines. With the small optical depths, these emission lines can provide important time-resolved information on the electron temperature in the imploding fuel through the analysis of the relative intensities of the lines. With sufficient spectral resolution, these lines can even provide time-resolved information on the electron density of the imploding fuel by analyzing the widths of the emission lines. Used in conjunction with the emitted proton spectrum from which time-resolved ion temperature and rhoR can be inferred, we can directly study the effect of hi-Z impurities on temperature equilibration and yield.   

Determination of the Charge State Distributions from X-ray Spectra in Au Plasmas at the OMEGA Laser

The determination of the charge state distributions (CSD) of highly ionized Au in Non-LTE high-density plasmas ($\sim$ 10$^{21}$ cm$^{-3}$) is critical for benchmarking radiation-hydrodynamic physics codes. Predictive calculations of the CSD have produced widely varying results. We present Au CSD’s inferred from spectroscopic measurements of reduced-scale hohlraum target experiments at the OMEGA Laser having high electron temperatures (5 - 10 keV). Time integrated spectra were recorded with the Henway crystal spectrometer. Time and spatially resolved spectral measurements were done with a new spectrometer, the MSPEC. The MSPEC can accommodate a variety of crystal configurations, connects to a standard X-ray framing camera, and has a better spectral range and resolution than previous instruments. Measurements of the 5f$\rightarrow$3d transitions in Ni- to Na-like Au and the 3d$\rightarrow$2p transitions in Co- to Ne-like Au were compared to atomic modeling from the Hebrew University Lawrence Livermore Atomic Code and the Flexible Atomic Code to infer the CSD and average ionization state (Z=58.5$\pm$1.3). The experimentally inferred CSDs will be compared with predictions from several available codes. This work was performed by the University of California LLNL under the auspices of the DOE under contract W-7405-ENG-48.   

Parallel Implementation of the Multi-Dimensional Spectral Code SPECT3D on large 3D grids.

The multi-dimensional collisional-radiative, spectral analysis code SPECT3D can be used to study radiation from complex plasmas. SPECT3D can generate instantaneous and time-gated images and spectra, space-resolved and streaked spectra, which makes it a valuable tool for post-processing hydrodynamics calculations and direct comparison between simulations and experimental data. On large three dimensional grids, transporting radiation along lines of sight (LOS) requires substantial memory and CPU resources. Currently, the parallel option in SPECT3D is based on parallelization over photon frequencies and allows for a nearly linear speed-up for a variety of problems. In addition, we are introducing a new parallel mechanism that will greatly reduce memory requirements. In the new implementation, spatial domain decomposition will be utilized allowing transport along a LOS to be performed only on the mesh cells the LOS crosses. The ability to operate on a fraction of the grid is crucial for post-processing the results of large-scale three-dimensional hydrodynamics simulations. We will present a parallel implementation of the code and provide a scalability study performed on a Linux cluster.   

Analysis of the spatial structure of ICF implosion cores using a multi-objective method for fitting pinhole image intensity profiles

We apply a method for the simultaneous and self-consistent fitting of a set of intensity spatial profiles from several narrow-band x-ray pinhole images from argon-doped ICF implosion cores, and the space-integrated line spectrum. The data was recorded in a series of argon-doped, deuterium-filled plastic shell implosion experiments performed at OMEGA. This method is independent of geometry inversions and takes advantage of both optically thin and thick image data. Results are shown for four-objectives based on argon Ly$\alpha $, He$\beta $, and Ly$\beta $ image data, and the space-integrated line spectrum. This work is supported by DOE-NLUF Grant DE-FG52-05NA26012, and LLNL under Contract W-7405-Eng-48.   

Spectroscopic Determination of Temperature and Density Spatial Profiles and Mix in Inertial Confinement Fusion Implosion Cores

This work is focused on extracting temperature and density gradients from data obtained in indirect drive ICF implosions. Imaging was provided by the Multi-Monochromatic X-ray Imager (MMI). Two new spectroscopic techniques have been developed to characterize the core gradients. The emissivity ratio of Ly$\beta $/He$\beta $ is analyzed first to extract temperature, and either emissivity or intensity equations are then solved to infer density. The idea of solving intensity equations permits consideration of the opacity effect. In order to extract the mixing spatial profile, the optically-thick Ly$\alpha $ line is brought into the analysis. Two mix models have been used to independently estimate the level of mixing, and the results show reasonable agreement with the experimental data analysis.   

Benefits of high spectral resolution and complementary target materials for spectroscopic diagnostics

Spectra of H- and He-like ions and their satellites are rich in information about the emitting plasma and have long been used as plasma diagnostics. However, since line intensities can have a complex interdependence on density, temperature, non-thermal electrons, and plasma size, it can be difficult to infer a unique set of plasma conditions from line intensities alone. This challenge can be overcome by supplementing intensity data with density- and opacity-sensitive line widths (requiring high spectral resolution) and by measuring emission from elements which respond in distinctive ways to changes in the electron energy distribution. We illustrate these diagnostic benefits through an analysis of K-shell emission spectra with E/$\Delta $E=5000 from Al and F plasmas created at the ULTRAS 2TW laser facility. Robust diagnostics derived from multifaceted measurements are used to investigate changes in plasma conditions under variations in laser intensities, energies, and prepulses.   

Quantitative extraction of spectral line intensities and widths from spectra recorded with gated MCP detectors

Plasma spectroscopy requires determination of spectral line intensities and widths. At Sandia's Z facility we use elliptical crystal spectrometers equipped with gated MCP detectors to record time and space resolved spectra. We collect a large volume of data typically consisting of 5-6 snapshots in time, and 5-10 spectral lines with 30 spatial elements per frame, totaling to more than 900 measurements per experiment. The sheer volume of data requires efficiency in processing. Each line is approximated by a line profile in a line fitting routine, taking into account the photo-electron statistics to determine the uncertainties. Analysis of the MCP photo-electron statistical distribution will be discussed. Effects of the assumptions made in the line fitting routine will be addressed.   

Improved Microchannel Plate Modeling and Experimental Comparisons in an X-ray Framing Camera Setup

We have developed an improved 3D microchannel plate (MCP) model that includes detailed end-spoiling effects and statistical gain variations. Our aim is to model the pulse height distribution and detection quantum efficiency of an MCP based x-ray framing camera operated in DC mode. We attempt to validate our model with experimental results from MCPs with two different photocathode coating schemes: a layering of Nb, Cu, and Au and CsI. Once validated the model is used to investigate possible MCP based imaging performance improvements by adjusting the pore geometry and coating schemes. In particular, modeling results and experimental data from MCPs with square pores (10x10$\mu $m) are presented.   

Determination of the Electron Temperature of a Hot Gold Plasma Utilizing High-Resolution X-Ray Spectroscopy of the L-Band Emission

The x-ray emission of high--temperature plasmas contains a wealth of information about the plasma conditions. A plasma parameters of interest is the electron temperature, which can be determined from the distribution of the ionic species in the plasma. Each ion charge distribution emits a characteristic x-- ray spectrum and, thus, high-resolution x--ray spectroscopy provides a tool to observe this characteristic ``fingerprint''. The ``L--band'' spectrometer was designed to determine the electron temperatures in laser--heated gold hohlraums by measuring the 3d --- 2p transitions in highly charged gold ions. Recent L--band measurements at the OMEGA laser facility on high--temperature hohlraums will be presented and compared to LASNEX calculations.   

1- and 2-frame monochromatic x-ray imaging of NIF-like capsules on Z, and future higher-energy, higher-resolution, 2- {\&} 4-frame x-radiography plans for ZR

The Z accelerator - presently undergoing the ZR upgrade - has recently been used to study ultrasmooth, NIF-like capsules that have glass and polyimide fill-tubes placed around a great circle. The 2-mm CH shells were driven by the uniform, 70-eV Planckian field of a z-pinch-driven double-ended hohlraum. High-brightness, high-spatial-resolution, x-radiography was key to these tests. As such the TW-class, multi-kJ, 526.57 nm Z-Beamlet Laser (ZBL) [Appl. Opt. \textbf{44,} 2421 (2005)] was used to produce the x-ray source for the 6.151-keV curved-crystal imaging system [Rev. Sci. Instrum. \textbf{75,} 3672 (2004)]. Previous enhancements to the latter [G. R. Bennett \textit{et al}., Rev. Sci. Instrum., in press.] have led to brighter images, allowing subtle capsule implosions details to be observed for the first time. Recent enhancements to the former, have led to the ZBL capability of acquiring two temporally separated images per Z shot, and brighter 1-frame images. 1- {\&} 2-frame unperturbed-shell {\&} fill-tube hydro data, as well as higher-energy, higher-resolution 2- {\&} 4-frame x-radiography plans for ZR, will be discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under DE-AC04-94AL85000.   

Imaging of High-Z doped, Imploded Capsule Cores

The ability to correctly ascertain the shape of imploded fusion capsules is critical to be able to achieve the spherical symmetry needed to maximize the energy yield of proposed fusion experiments for the National Ignition Facility. Implosion of the capsule creates a hot, dense core. The introduction of a high-Z dopant into the gas-filled core of the capsule increases the amount of bremsstrahlung radiation produced in the core and should make the imaging of the imploded core easier. Images of the imploded core can then be analyzed to ascertain the symmetry of the implosion. We calculate that the addition of Ne gas into a deuterium gas core will increase the amount of radiation emission while preserving the surrogacy of the radiation and hydrodynamics in the indirect drive NIF hohlraum in the proposed cryogenic hohlraums. The increased emission will more easily enable measurement of asymmetries and tuning of the implosion.   

Performance Evaluation of a Microchannel Plate based X-ray Camera with a Reflecting Grid

Microchannel Plates (MCPs) are used in a variety of imaging systems as a means of amplifying the incident radiation. Using a microchannel plate mount recently developed at the University of Michigan, the effects of a metal reflecting grid are explored. Employing the reflecting grid, we create a potential difference above the MCP input surface that forces ejected electrons back into the pores, which may prove to increase the quantum efficiency of the camera. We investigate the changes in the pulse height distribution, modular transfer function, and Quantum efficiency of MCPs caused by the introduction of the reflecting grid. Work supported by the Naval Research Laboratory, National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant DE-FG52-03NA00064, and through DE FG53 2005 NA26014, and Livermore National Laboratory.   

Development of the High Sensitivity Multi Channel Bulk Absorption Laser Calorimeter

The ICF experiments performed at Shenguang II facility need to measure the total energy of stimulated Raman scattering(SRS) and stimulated Brillouin scattering(SBS) as well as the weak backscattered SRS and SBS. Generally used laser calorimeter whose sensitivities are rather low, cannot meet the needs of such measurements. Because of long signal cable and AC power disturbance, simply boosting the amplifier gain will lead to the weak signal submerged by noise. Equipped with third order low pass active filters and software smooth filter, the multi channel bulk absorption laser calorimeter introduced in this paper, can significantly restrain the noise. Thus, the sensitivity of laser calorimeter can be greatly improved about two orders higher by means of boosting the amplifier gain than that of the normal type laser calorimeter. Using the new type laser calorimeter in the ICF experiments performed at Shenguang II facility, we obtained results different from that before. The experimental arrangement and the results are presented.   

New Aluminum Backlighter Characterization at the OMEGA Laser

We have characterized keV emission from Al plasmas for various laser illuminations at the OMEGA laser with the goal of optimizing the ability to backlight low-atomic-number (low-Z) materials such as beryllium for fusion ignition studies. The conversion efficiency to Lyman $\alpha $ at 1.73 keV has been determined for 1 to 7 laser beams as a function of laser energy/power. The plasma is diagnosed by line ratios and the slope of the continuum to determine the temperature and density. Results are compared to detailed theoretical atomic physics models. For these experiments, half or more of the x-ray photons observed arise from the bremsstrahlung continuum rather than from Al line radiation, which reduces the importance of the line radiation for backlighting.   

Simulation of monoenergetic proton radiography images of ICF hohlraums and capsules

A Monte-Carlo program is being developed for simulating radiographic images that could be obtained of objects of importance to the ICF program by using 14.7-MeV fusion protons from imploded ICF capsules with thin glass shells and D$^{3}$He fuel. Experiments we've performed at the OMEGA laser facility have already proven that such imaging is very good for studying the spatial distribution of $B$ fields generated by laser-plasma interactions when the protons pass through small amounts of low-Z material (e.g. $\sim $ 1 mg/cm$^{2}$ of Al or CH). Other objects we would like to image, including high-Z hohlraums with laser-generated B fields, imploded ICF capsules, and various foils used for planar Rayleigh-Taylor experiments, will subject the protons to more scattering that will degrade image spatial resolution. We will present simulations of images of some of these objects and discuss the practical limits of this type of imaging technology. The work described here was performed in part at the LLE National Laser User's Facility (NLUF), and was supported in part by US DOE (Grant No. DE-FG03-03SF22691), LLNL (subcontract Grant No. B504974), and LLE (subcontract Grant No. 412160-001G).   

A Neutron Streak Camera Designed For ICF Fuel Ion Temperature

A neutron streak camera was designed for inertial confinement fusion (ICF) fuel ion temperature diagnostic. It is made of a 1 cm thick $\times $ 8 cm diam piece of 3{\%} benzophenone quenched plastic scintillator with about a 190 ps FWHM and a streak tube (55ps time resolution) with large-area photocathode ($\phi $30 mm) showed no slit. The electron beam from the photocathode is focused into a little spot ($\phi $1mm). Then the spot is scanned directly and multiplied by an internal microchannel plate. This greatly improves the sensitivity of the tube. The neutron streak camera combines the advangtages of scintillation detector (with high neutron detection efficiency) and of streak camera (with fast time response). The whole detection system time resolution is 300ps and can record neutron time of flight signals from ICF implosion target with yields of 10$^{7}$ DT neutron per shot.   

Image Characterization Study for ICF Neutron Imaging

Performance requirements for the National Ignition Facility Neutron Imaging System (NIS) call for a spatial resolution of 10 microns and a signal-to-noise ratio (SNR) of 22 at the 20{\%} contour for both the hot-spot (14 MeV) and the downscattered (6 -- 12 MeV) images. An MCNPX-based model is being used to conduct a systematic study of the capabilities of different imaging system designs to satisfy these requirements, as well as to establish the most useful and accurate definitions of resolution and SNR. The NIS design parameter space includes: neutron yield, aperture geometry, magnification and source size and position with respect to the system's axis. The model includes accurate source distributions of a failed implosion, three aperture geometries (ring, square pinhole and triangular wedge), their associated point spread functions, and a pixelated plastic scintillator detector array. The simulated recorded images are deconvolved using a modified regularization algorithm, producing overall simulations of the expected source images. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.   

Lead Activation Neutron Yield Measurement System Used In ICF Experiment

Lead activation measurement system is used to measure very low yield neutron of DT or DD reaction, activation sample is Pb sheath that surrounds a NaI(Tl) detector or Pb disks in front of it. Using this system, we can measure the $\gamma $ rays from the activated sample(207$^{m}$Pb) with 0.8s half-life decay and calculated the yield. Because half-life decay is too short to move activated sample to measure room manually or mechanic, we place the detector as close as 32cm from the laser target. To minimize this effect of the X-rays burst from the laser irradiated target, we use a gate circuit to remove the detector high voltage about 200ms to 1s adjustable, and restores it less than 100ms after the shot. The drift of the peak address of the pulse-height spectrum is unavoidable because of the NaI(Tl) detectors and the electronic system. We used an embedded multi-channel pulse height analyzer in this system to adjust the peak address of the in time. This system is used successfully in ICF experiment on SG-II facility in 2005.   

CR39 based Neutron Yield Measurements on the Z-Accelerator

Implosion dynamics of both Z-pinch driven Deuterium gas puffs producing $\sim $3x10$^{13}$ DD neutrons as well as ignition-size 2-mm-diameter capsules driven by Dynamic hohlraums producing $\sim $1x10$^{11}$ neutrons have been studied at the Z-accelerator. CR39 based neutron yield measurements are being explored to compliment existing yield measurements based on Indium activation. One possible advantage to the CR39 based diagnostic is it's relative insensitivity to the significant high-energy Bremsstrahlung radiation produced in these z-pinch experiments. The diagnostic configuration and initial results for a set of measurements comparing the two diagnostic techniques for both of these neutron sources will be presented. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Dept. of Energy under contract No. DE-AC04-94AL85000.   

Improved Gamma Bang Time Measurements on Omega

The time of peak fusion reactivity with respect to the impingement of laser light on an ICF capsule is known as Bang Time (BT). This is an essential parameter in the understanding of ICF implosions. Traditionally, BT has been determined through temporal measurements of 14 MeV fusion neutrons. Unlike neutrons, gammas are not subject to temporal spreading, making proximity of the detector to the source a lesser concern. However, the unfavorable branching ratio for the DT fusion gamma-ray branch ($\sim $5e-5) presents detector sensitivity challenges. A Gas Cherenkov Detector (GCD) has been developed to overcome these challenges. Initial gamma bang time (GBT) measurements on Omega were recently made using a GCD. Recent improvements have significantly enhanced the ability to accurately measure GBT, and the first measurements of GBT on 50/50 DT Cryo shots have now been made.   

Cross-Calibration of Neutron Detectors for the Dense Plasma Focus FN-II Time of Flight Analysis

The \textit{Fuego Nuevo II} (FN-II) dense plasma focus machine is a small device ($\sim $5kJ @ 37 kV). In order to have an adequate picture of the neutron pulse with temporal resolution, a set of five similar scintillation-photomultiplier detectors have been assembled, using BC-400 scintillators, 50 mm high and 120mm radius, coupled to photomultipliers. These detectors are shielded by a lead wall, 50 mm thick. This work shows some preliminary results, in which a response of the five systems is shown, when they are placed 7.5 m away from the neutron source. A comparison between the time integrated neutron pulses and the neutron yield, measured with silver activation counters, is made.   

Laser probing diagnostics of z-pinches at the Zebra generator

Laser probing diagnostics were developed for the investigation of implosion dynamics and magnetic fields in cylindrical, linear, and nested wire arrays at the Nevada Terawatt Facility. Plasma diagnostics includes a five-frame optical probing of the z-pinch in 3 directions with a long 34-ns or short 9-ns pulse train. Four frames of the shadowgraphy cover two probing directions. The third probing direction includes: shadowgraphy, Faraday rotation diagnostics, interferometry, and schlieren diagnostics all at one temporal location. In every z-pinch shot this high-resolution multi-frame imaging diagnostics produces eight instant images of fast moving plasma objects on CCD cameras. Implosions with speeds 250-500 km/s were recorded in the wire arrays and the dynamics of the implosion plasma bubbles, current reconnection, as well as a shock in the precursor were observed. The issues of z-pinch imaging and Faraday rotation diagnostics with 1-MA wire arrays were analyzed.   

Imploded core structure of shell target with a cone for fast ignition observed with SIXS: Sampling-Image X-ray Streak camera

2D-SIXS: two-dimensional sampling image x-ray streak camera is a technique to obtain ultra-fast two-dimensional x-ray images by using an x-ray streak camera [1]. We have developed a 2D-SIXS system with 40x39 sampling pinholes coupled to a Hamamatsu C-7700-31 x-ray streak camera. 2D-SIXS was used to observe time-resolved structure of the imploded core plasma of a spherical shell target with a cone for fast ignition. Spatial and temporal resolutions were 20 microns and 24 ps, respectively. 50 sequential frames were successfully reconstructed. It was found that the x-ray emitting region of the core moves towards the tip of the cone. [1] H. Shiraga, et. al., Rev. Sci. Instrum., 70, 620 (1999).   

The LIL facility: A testbed for LMJ and an experimental tool for laser-matter interaction

The Laser MegaJoule (LMJ) under construction at CEA-CESTA in Fance is designed to produce 240 beams, 1.8 MJ - 500 TW of ultraviolet light for high energy density physics experiments and thermonuclear burn of DT targets. The first step of LMJ program consisted in the construction of a full scale prototype the ``Ligne d'Int\'{e}gration Laser'' (LIL) which was developed to demonstrate LMJ performances and qualify its components as well as maintenance procedures. Commissioned in 2002 , LIL facility mainly includes a laser bay which houses a bundle of 8 laser beams similar to the LMJ ones and a target bay where are located the 1$\omega -$3$\omega $ conversion system, the focusing gratings and the 4.5-meter diameter target chamber equipped with plasma diagnostics. From June 2002 to December 2005 about 300 high energy shots were performed on LIL most of them with a quad. Performances obtained at 1$\omega $ (1.053 $\mu $m) and 3$\omega $ (0.35 $\mu $m) showed that LIL meets the LMJ requirements in terms of energy, power and focal spot. The first plasma experiments started in december 2004.This paper describes the LIL facility, the results obtained during laser qualification phase and presents recent results obtained on focal spot characterisation. A brief status of the LMJ construction progress is also presented.   

Simulations of Foils Irradiated by Finite Laser Spots

Recent proposed designs (Obenchain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities with lower laser energies combined with higher irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) that may lead, for example, to the generation of fast electrons. The proposed use of a 248 nm KrF laser is expected to minimize LPI, and this is being studied by experiments on NRL's NIKE laser. Here we report on simulations aimed at designing and interpreting these experiments. The 2d simulations employ a modification of the FAST code to ablate plasma from CH and DT foils using laser pulses with arbitrary spatial and temporal profiles. These include the customary hypergaussian NIKE profile, gaussian profiles, and combinations of these. The simulations model the structure of the ablating plasma and the absorption of the laser light, providing parameters for design of the experiment and indicating where the relevant LPI (two-plasmon, Raman) may be observed.