Session ZP1: Poster Session IX: Supplementary and Postdeadline

Structure of a magnetized plasma confined between two dielectric walls

The problem is studied with a macroscopic formulation. The small Debye length limit is invoked. The magnetic field is characterized by the incidence angle and its strength. Plasma equations include source terms for ionization and momentum-transfer collisions. The Bohm condition at the edge of the non-neutral sheath determines the strength of the ionization source for a given distance between the walls. The solution of the problem is analyzed for different ranges of the four dimensionless parameters. A three region regime, with similarities with the one found in a related one-wall problem, is found for a doubly distinguished limit of the parameters. The case of grazing incidence merits particular consideration.   

Improved Shell models for screened Coulomb balls

Spherical Coulomb crystals in dusty plasmas [1] are well described by an isotropic Yukawa-type pair interaction and an external parabolic confinement as was shown by extensive molecular dynamics simulations [2]. A much simpler description is possible with analytical shell models which have been derived for Yukawas plasmas in [3,4]. Here we analyze improved Yukawa shell models which include correlations along the lines proposed for Coulomb crystals in [5]. The shell configurations are efficiently evaluated using a Monte Carlo procedure. [1] O. Arp, A. Piel and A. Melzer, Phys. Rev. Lett. 93, 165004 (2004). [2] M. Bonitz, D. Block, O. Arp, V. Golunychiy, H. Baumgartner, P. Ludwig, A. Piel and A. Filinov, Phys. Rev. Lett. 96, 075001 (2006). [3] H. Totsuji, C. Totsuji, T. Ogawa, and K. Tsuruta, Phys. Rev. E 71, 045401 (2005). [4] C. Henning, M. Bonitz, A. Piel, P. Ludwig, H. Baumgartner, V. Golubnichiy, and D. Block, submitted to Phys. Rev. E [5] W.D. Kraeft and M. Bonitz, J. Phys. Conf. Ser. 35, 94 (2006).   

Density profile of strongly correlated spherical Yukawa plasmas

Recently the discovery of 3D-dust crystals [1] excited intensive experimental and theoretical activities [2-4]. Details of the shell structure of these crystals has been very well explained theoretically by a simple model involving an isotropic Yukawa-type pair repulsion and an external harmonic confinement potential [4]. On the other hand, it has remained an open question how the average radial density profile, looks like. We show that screening has a dramatic effect on the density profile, which we derive analytically for the ground state. Interestingly, the result applies not only to a continuous plasma distribution but also to simulation data for the Coulomb crystals exhibiting the above mentioned shell structure. Furthermore, excellent agreement between the continuum model and shell models is found [5]. [1] O. Arp, D. Block, A. Piel, and A. Melzer, Phys. Rev. Lett. 93, 165004 (2004). [2] H. Totsuji, C. Totsuji, T. Ogawa, and K. Tsuruta, Phys. Rev. E 71, 045401 (2005) [3] P. Ludwig, S. Kosse, and M. Bonitz, Phys. Rev. E 71, 046403 (2005) [4] M. Bonitz, D. Block, O. Arp, V. Golubnychiy, H. Baumgartner, P. Ludwig, A. Piel, and A. Filinov, Phys. Rev. Lett. 96, 075001 (2006) [5] C. Henning, M. Bonitz, A. Piel, P. Ludwig, H. Baumgartner, V. Golubnichiy, and D. Block, submitted to Phys. Rev. E   

Coulomb crystallization in two-component quantum plasmas

Coulomb crystallization is a common phenomenon in trapped (non-neutral) plasmas. In a neutral plasma, however, it is hampered by recombination of electrons and ions. Known examples are ion Coulomb crystals in white dwarf and neutron stars. Here, we predict the conditions under which a Coulomb crystal of heavy particles (e.g. ions) can form in the presence of a degenerate delocalized background of light charges (e.g. electrons): the key requirement is the mass ratio has to exceed a critical value of about 80 [1]. This leads to the prediction of novel types of crystals e.g. in hydrogen and helium. Further, we predict that holes in semiconductors can spontaneously order into a regular lattice in materials with sufficiently flat valence bands. A unified phase diagram of Coulomb crystals in two-component systems is derived and verified by first-principe path-integral Monte Carlo simulations [1-3]. [1] M. Bonitz, V.S. Filinov, V.E. Fortov, P. Levashov, H. Fehske, Phys. Rev. Lett. 95, 235006 (2005), Phys. Rev. Focus, Dec 2005 [2] M. Bonitz, V.S. Filinov, V.E. Fortov, P. Levashov, H. Fehske, J. Phys. A: Math. Gen. 39, 4717 (2006) [3] M. Bonitz, V.S. Filinov, V.E. Fortov, P. Levashov, H. Fehske, Phys. Rev. E (2006)   

Gyrokinetic Simulations of ETG and ITG Turbulence

We have previously found that the radial shear in the flux- surface-averaged flow in the late-time quasi-steady phase of ITG turbulence is driven mostly by the Reynolds' stress, and dissipated mostly by the linear (transit-time) damping. Here, the driving and damping are further resolved into contributions to the steady zonal and damped geodesic-acoustic (GAM) eigenmodes. In particular the temporal dependence of the Reynolds stress and its ability to drive the GAMs is examined. Various aspects of ETG turbulence are examined: (1) It is found that the presence of zonal flows in ETG turbulence, which occur at levels small compared with those in analogous ITG turbulence, can either enhance or suppress the turbulence. The mechanisms of enhancement are examined. (2) The effects of spatial resolution, system size, and particle number on delta-f gyrokinetic simulations of ETG turbulence are examined. Our results confirm that in addition to too much particle noise, insufficient spatial resolution can also result in saturated states with artificial steadiness and low levels of thermal transport.   

Ablation of solid materials into discharge plasmas

Ablation of solid materials plays an important role in capillary discharges, current interrupters, plasma thrusters, laser interaction with targets etc. Kinetics of the ablation into discharge plasma is described. The ablation model takes into account the non-free nature of ablation due to the presence of a high-density discharge plasma. Different characteristic sub-regions near the surface namely space-charge sheath, Knudsen layer, presheath and a hydrodynamic layer are considered. The ablation rate is determined by the flow velocity at the edge of the Knudsen layer. The kinetic approaches namely bi-modal distribution function and direct simulation Monte-Carlo are used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling solution of the non-equilibrium, Knudsen layer, with hydrodynamic layer and presheath provides self-consistent solution for the ablation rate. Ablation of the compound materials is considered by taking into account chemical reactions at the surface. Several examples with successful implementation of this model are presented.   

FLR effects in nonlinear tearing mode reconnection

The influence of ion Finite Larmor Radius (FLR) effects in the evolution of the tearing mode is studied analytically and numerically. We use a gyrofluid extension of the usual two-field, reduced MHD equations, where closure is provided by the Gyrokinetic Poisson's law. Two-dimensional slab geometry is adopted. In the linear regime it is shown that significative enhancement of the growth rate of the mode occurs when the ion Larmor radius ($\rho_{i,s}$) exceeds the width of the dissipation layer. Nonlinearly, detailed comparison studies between the classic, no FLR case, and the finite $\rho_{i,s}$ case are presented. In particular, we show how several nonlinear transitional criteria established for the classic case are changed due to the presence of these terms.   

The solar coronal electron heating by short wavelength electromagnetic modes

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

Spatial distribution of toroidal flow velocity in a field-reversed configuration palsma

Rotational instability with toroidal mode number n = 2 is the only destructive instability in a field-reversed configuration (FRC) plasma. Therefore, investigation of source of toroidal spin-up and its spatial property are longstanding problems in the FRC research to improve configuration lifetime. In this work, radial velocity profile of toroidal rotation has been measured with a newly built polychrometer. From the ion Doppler shift measurement of impurity ions, radial profile of toroidal flow was observed. The toroidal flow inside the separtrix start to increase just after the formation and the flow velocity is gradually increased. The velocity is comparable with the ion diamagnetic velocity at 25 $\mu$s. But the flow velocity out side the separatrix keeps small value or settled. Therefore, there is shear of toroidal flow in the vicinity of the separatrix. The effect of this observed shear on higher toroidal mode number of the interchange instability has been investigated. This could be a reason why the higher mode of toroidal deformation has never been observed in the FRC experiments contrary to theoretical expectations.   

Investigation of Resistive Wall Mode Internal Struc\- ture,

Soft x-ray (SXR) signals have great potential to provide the internal structure of resistive wall modes (RWMs), which are typically diagnosed by integrated magnetic signals located well outside the plasma. In particular, recent studies show that the SXR signals are very sensitive to an RWM in its early stage of onset, even before it was detected by magnetic sensors. Furthermore, the RWM internal structure evolution measured by SXR was found to be correlated with plasma rotation, perturbed magnetic fields, and electron temperature. In addition, internal RWM displacements detected by SXR in the main plasma are accompanied by variations in the divertor poloidal magnetic field and radiation power in the divertor. Studies of the correlation between the internal RWM structure and divertor observations will be reported.   

Improved analytical fits of collisionnal cross sections

Local Thermodynamical Equilibrium (LTE) is a powerful assumption to solve Atomic Physics problems. When LTE is not valid, one need to solve the ``rate equations'' governing the population kinetics of a large set of atomic states. A very large number of transition rates, radiation and collision induced, is required. However, computing collision cross sections S(E), where E is the energy of the incident electron, is costly and furthermore has to be integrated over the distribution function of electrons. One generally use a fit of S(E) from 5-20 energy samples before analytical or numerical integration. The classical Sampson {\&} Golden's fit is generally used : S(E) = A +D ln(u) + c1/(a+u) + c2/(a+u)$^2$ where u is the electron energy divided by the transition energy. However in multi-charged, multi-electron high Z ions, it leads to poor fits, with often negative rates,for about 20{\%} of the total number of excitation rates, even using the Born limit at high energy as a constraint. From some examples, we shall expose the requirments for an adequate fit and propose a tractable and efficient fit to replace the S{\&}G formula. The fit will be distributed with the HULLAC.v9 suite of codes in a near future.   

Undervoltage Breakdown Threshold Criteria

Undervoltage breakdown, the process by which a pulse of electrons induces a discharge gap to break down when it is near but has not achieved its self-breakdown conditions, is discussed. Specifically, threshold criteria that determine the number of electrons required to induce breakdown both to glow and arc discharges are presented. Numerical and theoretical predictions of these criteria are compared with experimental results. Undervoltage breakdown is the phenomenon that governs discharge initiation in gas-fed pulsed plasma thrusters, the device of primary interest to the authors. The phenomenon is also relevant to several other applications including psuedospark switches and other command-triggering devices as well as gas avalanche particle detectors.   

The theory of self-magnetic cusps in bunched annular electron beams

We show the existence of a self-magnetic cusp which can form within a fluid equilibrium model for bunched annular electron beams. The model self-consistently includes the effects of the electric and magnetic fields generated by the azimuthally symmetric beam, the external uniform magnetic focusing field, and the boundary conditions for a cylindrical conducting pipe. The formation of the self-magnetic cusp strongly depends upon the properties of the fast and slow rotation solutions of the beam, which in turn, depends upon the characteristic system parameters, such as the external magnetic focusing strength and the beam current. The formation of self-magnetic cusps may play an important role in high-current annular electron beam experiments.   

Guiding of an intense, femtosecond laser pulse in a discharge-produced capillary plasma

Guiding of an intense laser pulse is supported today's advanced technology such as laser wakefield acceleration, x-ray lasers, high-order-harmonic generation, and inverse Compton scattering. The laser-matter interaction length of a focused laser pulse is fundamentally limited by diffraction to the order of the Rayleigh length, and is further restricted by ionization-induced refraction. We developed a plasma waveguide for propagating intense laser pulse by use of a capillary discharge plasma. The alumina capillary had a diameter of 300 $\mu$m and a length of 10 mm. For present work, the discharge peak voltage and current were 30 kV and 500 A with a pulse width of 100 ns (FWHM), respectively. An electron density and a time-integrated electron temperature were evaluated to be of the order of $10^{18}$ cm$^{-3}$ and a few eV, respectively. The guiding experiments used the laser pulse of the central wavelength of 800 nm from a CPA Ti:sapphire laser with a pulse width of 130 fs (FWHM). A peak intensity of the laser pulse was $1 \times 10^{16}$ W/cm$^2$ with a spot diameter of 30 $\mu$m (FWHM) in vacuum. We demonstrated guiding of a laser pulse over length of up to 10 mm, which corresponded to 10 times the measured Rayleigh length.   

Collisional Relaxation of Super Thermal Electrons Generated by Relativistic Laser Pulses in Dense Plasma

Energy relaxation of the hot electron population generated by relativistic laser pulses in overdense plasma is analyzed for densities ranging from below- to one thousand times solid density. It is predicted that longitudinal beam-plasma instabilities, which dominate energy transfer between hot electrons and plasma at lower densities, are suppressed by collisions beyond solid density. The respective roles of collisional energy transfer modes, i.e. direct collisions, diffusion and resistive return current heating, are identified with respect to plasma density.   

Transport cross sections for proton-noble gases and proton-carbon scattering in the energy range from 0.1 eV to 10 keV

Using the fully quantum mechanical treatment, elastic differential and integral elastic cross sections have been calculated over a wide range of center-of-mass collision energies, 0.1--10 000 eV, for protons scattered by noble gas atoms He, Ne, Ar, Kr, and Xe as well as carbon atoms. In addition, the momentum transfer and viscosity cross sections, relevant to transport modeling, have been computed from the quantal differential cross sections along with results of the classical trajectory Monte Carlo method. The two complementary sets of results (classical and quantal) for the transport cross sections, enriched with the CTMC charge transfer data, provided deeper insight into the accuracy of the data over the broad energy range. Isotopic scaling relations, derived form the calculations, enable application of the results to the deuterium/tritium rich fusion plasma environment. All data are available through the worldwide website of the Controlled Fusion Atomic Data Center (www-cfadc.phy.ornl.gov)[1]. [1] P. S. Krstic and D. R. Schultz, Physics of Plasmas \textbf{13}, 053501 (2006).   

Sputtering by Carbon Impact at Deuterated Carbon Surfaces

We study chemical and physical sputtering by carbon impact at deuterated amorphous carbon and graphite surfaces, surrounded by the divertor deuterium plasma at various temperatures. The energy of C was varied from eV to keV range, while the interacting potentials used in molecular dynamics modeling are bond-order REBO and AIREBO [S. J. Stuart et al, \textit{J. Chem. Phys.} 112, 6472-6486 (2000)] potentials. The consequences of the obtained large total yields of the sputtered deuterium and carbon, as well as the yields of various hydrocarbons are discussed with respect to the erosion of the carbon surfaces and to the divertor plasma chemistry.   

Study on the Flow Z-Pinch Fusion Concept

The Flow Z-Pinch fusion concept is simulated with a model that includes fusion and radiation power. The MHD physics model employed includes bremsstrahlung and synchrotron radiation losses, and fusion source and sink terms. The nondimensionalized form of these equations is simulated with the MacCormack algorithm in 1-D. The results show significant fusion output power, on the order of GW/m. Fuel ion particle loss caused by fusion burn results in significant temperature increases to maintain equilibrium. Separate simulations investigate radiative collapse phenomenon. Synchrotron radiation appears to drive the collapse. Simulations are conducted at conditions of the ZaP Flow Z-Pinch Experiment at the University of Washington. Model and simulation results will be presented.   

Electron kinetic simulations of the interaction a picket-fence laser pulse with a solid target

Recent experiments with the OMEGA laser at LLE [1], with picket fence pulses , have indicated higher absorption than expected (on the basis of hydrodynamic simulations performed with the fluid code LILAC) during the first picket. As this raises the issue of heat transport, we have performed a series of electron kinetic simulations with our electron kinetic code ``FPI'' [2,3], which includes advection, an ambipolar electric field to ensure quasi-neutrality, electron-ion and electron-electron collisions represented with a Fokker-Planck collision term, atomic physics, and fluid ion hydrodynamics. It appears that the very steep density gradients that exist in these conditions enhance the electron heat flow. \newline [1] W. Seka , V. N. Goncharov, J. A. Delettrez, R. W. Short, and R. S. Craxton, Paper F-O5, 36$^{th}$ Annual Anomalous Absorption Conference (June 4-9, 2006). \newline [2] J.P. Matte, T.W. Johnston, J. Delettrez and R.L. McCrory, Phys. Rev. Lett. 53, 1461 (1984). \newline [3] S. \'{E}thier and J.P. Matte, Phys. Plasmas \textbf{8}, 1650 (2001).   

3D PIC Simulations of Particle Acceleration in Electromagnetic Cylinder and Torus

Particle acceleration via Poynting vector with toroidal magnetic field is studied in 3D PIC simulation of electron-positron plasma. We choose two different initial magnetic field configurations to compare how the particle acceleration is affected by the expansion of electromagnetic wave. In the cylindrical case, the electromagnetic field strength decays as $(ct)^{-2}$, and particles are accelerated in the radial direction as well as the axial direction. Rayleigh-Taylor instability is also observed at the center of the cylinder. In the torus case, the field strength decays as $(ct)^{-3}$, making the acceleration less efficient. Particles accelerated in the axial direction by $E\times B$ force creates strong charge separation. We will discuss the relation between the model and the acceleration of particles in the magnetic tower jet from accretion disks, and the radiation profile from particles.   

Extension of adaptive mesh refinement to simulations of high-power plasma experiments

Numerical simulations play a crucial role in the modeling of modern high-power pulsed particle, microwave and laser sources. Inadequate spatial resolution of realistic features (wall boundaries, injectors, targets, pulse shapes etc.) may give rise to unacceptable errors in simulation results. Structured adaptive mesh refinement (AMR) has been successfully applied to increase numerical resolution of fluid dynamics and MHD simulations. Unfortunately, extension of AMR to problems involving electromagnetic and particle-in-cell (PIC) descriptions proves to be nontrivial due to a number of severe numerical difficulties arising due to the presence of fine-coarse mesh interfaces: (i) spurious wave reflection, (ii) macro-particle self-force, and (iii) violation of charge conservation (Gauss' law). The approximation errors due to these numerical effects typically result in loss of simulation accuracy, energy/momentum non-conservation and long-time instabilities. We review our progress in developing specialized techniques that resolve these issues by way of introducing buffer zones and absorbing (PML) boundaries around the fine-coarse interfaces. We demonstrate the efficiency and accuracy of these techniques on realistic examples related to simulations of the generation and propagation of high-power microwave (HPM) pulses, lasers and energetic particle beams.   

Single-crystal X-ray spectropolarimeter

Anisotropy in plasmas, e.g., related to a magnetic field or a directional velocity distribution of the electrons, is sometimes reflected in the polarization of the emitted X-ray spectrum. The usual way to do X-ray polarization spectroscopy is by Bragg reflection off two separate crystals, one for each direction of polarization. Since the two crystals see different parts of the plasma, it is possible that differences between the two polarized X-ray spectra are not caused by plasma anisotropy but come from the different scenes. The single-crystal X-ray spectropolarimeter suggested by Baronova and Stepanenko avoids this so-called scene problem, at the expense of using asymmetric reflections that are rarely considered in X-ray spectroscopy. In last year's presentation we analysed the geometry of the single-crystal X-ray spectropolarimeter in some detail. In this presentation we consider the instrument's crystallographic aspects in more detail.   

Instability of obliquely propagating dust waves in a collisional highly magnetized dusty plasma

In laboratory dusty plasmas immersed in large magnetic fields of the order of a tesla, the ions and electrons can be magnetized while micron-sized charged dust grains are generally unmagnetized because their collision frequency is much larger than their gyrofrequency. In this case, very low frequency dust wave instabilities may be excited by ion or electron cross-field drifts. We consider theoretically the excitation of obliquely propagating dust waves due to a dissipative modified two-stream instability driven by ion cross-field drift$^{1}$. The growth rate is compared with those of other dust wave instabilities that may occur in such collisional, highly magnetized dusty plasmas; these include a streaming instability driven by ions flowing along the magnetic field$^{2}$, and a drift instability driven by electron diamagnetic drift$^{3}$. We determine which instability dominates in various parameter regimes. $^{1}$Rosenberg, M. and Shukla$, $P. K.,\textit{ J. Plasma Phys}., to appear, 2006. $^{2}$Rosenberg, M. and Shukla, P. K., \textit{J. Plasma Phys}. \textbf{70}, 317 (2004). $^{3}$Rosenberg, M. and Shukla, P. K., \textit{Plasma Phys}. \textit{Control. Fusion} \textbf{46}, 1807 (2004). Work partially supported by DOE Grant No. DE-FG02-04ER54804.   

Sensitivity Study of 29 1D Parameters for a Beryllium NIF Ignition Capsule

We report the results of performing 10,000 1D simulations of a National Ignition Facility capsule, each varying 29 design parameters. Starting with a baseline graded doped Beryllium ignition capsule, we vary all of the 29 parameters randomly. Each parameter is varied according to its design specification and some are assumed to vary normally while parameters that can be measured and rejected if outside specifications are modeled as a top hat distribution. We run 10K capsule simulations and then analyze robustness statistics of this dataset. As a whole, the design specifications for these 29 parameters ensure 98 percent of NIF capsules will ignite in 1D. A rather surprising discovery from the analysis of this data is that, for all the modes of variability included in this data set, the capsule yield is well represented as a two variable function of DT fuel entropy and fuel velocity. We outline our efforts to understand and fit this relationship. 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.   

Measurement of Dynamic Atomic Dipole Polarizability for Tungsten and Molybdenum using Integrated Phase Technique and Electrical Exploding Wires in Vacuum

The Integrated Phase Technique [1] was applied to measure dynamic atomic dipole polarizability for two refractory metals. A fast-rising current pulse $\sim $1000A/ns vaporized 16$\mu $m diameter wires of either W or Mo in vacuum. To avoid the generation of dense plasma we used wire coated with polyimide. Under these conditions the deposited energy totally converts the wire to metallic vapor. In this case the radial integration of the interference phase shift allows the reconstruction of atomic polarizability for the probing wavelength [1]. Partial vaporization of the metal or its ionization gives a lower value of the reconstructed atomic polarizability. In this case the correct atomic polarizability can be reconstructed as the maximum value vs. deposited energy. \newline \newline [1]. G.S. Sarkisov, et al., Phys. Rev. A, 73, 042501 (2006).   

Azimuthal Clumping Instability in Wire Array Z-pinches

UM and Sandia have analyzed an azimuthal clumping instability that bunches discrete wires in z-pinches. Highest instability growth rate is pi-mode: wires clumped in pairs. An efficient discrete wire code agrees with analytic theory, showing bunching in sub-100 ns, close to MA z-pinch risetimes. Using Sandia ALEGRA code, wire arrays are simulated utilizing a wedge-shaped sector with reflective boundary conditions. By choosing the wedge sector angle, pi-mode growth of the clumping instability is studied for a given wire number by simulating only a single wire within that wedge. A non-linear analytic theory shows excellent agreement with both ALEGRA and discrete wire codes for high ($\sim $600) and low (8) wire-number arrays. Results are presented of azimuthal clumping experiments on Cornell COBRA.   

Status of a Miniature W-Band Dielectric Traveling-Wave Tube Development

We will report on the status of the development of a compact W-band dielectric traveling-wave tube (DTWT) amplifier. The DTWT amplifier is based on the interaction between a magnetized electron beam and the fields of a traveling wave inside a very compact dielectric waveguide. A high permittivity dielectric waveguide is used to slow down the wave and replaces helix structures used in conventional traveling-wave tubes. A novel approach in this development is the use of micromachining techniques for the fabrication of the various components of this amplifier. We will present results of RF and beam transport experiments along the W-band DTWT circuit. The DTWT should be capable of producing millimeter-wave radiation for future military battlespace applications.   

Proton acceleration with high intensity lasers interacting on underdense targets

In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications [1]. Proton beams accelerated from solid planar targets have exceptional properties that open new opportunities for ion beam generation and control. Recently, experiments have shown that a gaseous target can produce proton beams with similar characteristics [2]. New experiments have been conducted on the 10 TW laser at LBNL to obtain the dependence of the proton beam characteristics on laser and target parameters. The experimental results are well reproduced by 2D PIC simulations and new simulations were performed to determine the optimum parameters for various applications. The proton acceleration efficiency was compared with proton acceleration from a solid target and the influence of electron laser-wakefield acceleration has been investigated. [1] J. Fuchs et al., Nature Physics 2, 48 (2006). [2] L. Willingale et al., Phys. Rev. Lett. 96, 245002 (2006).   

Prediction and Control of Locked Modes at DIII-D

Control of rotating neoclassical tearing modes (NTMs) by localized electron cyclotron current drive (ECCD) has proved successful on various tokamaks. However, slowly rotating NTMs like those expected in ITER or those obtained at DIII-D for balanced neutral beam injection are more prone to locking. Because they can lock in a toroidal position where they are not accessible to the gyrotron beams, it is proposed to force them to rotate or to lock them with a programmed toroidal phase, by applying a rotating or static, respectively, resonant magnetic perturbation. In both cases, intervention requires a timely knowledge of when and where the mode is going to lock. Here the results of simple locking predictors based on real-time analysis of magnetic diagnostics will be presented and their performances and reliability statistically assessed over a number of locking events. Preliminary control results will also be presented.   

A Spinning Mirror for Fast Angular Scan of EBW Emission

Angular scans of electron Bernstein wave (EBW) emission were performed at the Mega Ampere Spherical Tokamak (MAST) by radiometry along a steerable line of sight in a number of reproducible discharges. They led to identifying the conditions for strongest emission and, by reciprocity, for most efficient EBW heating by ordinary-extraordinary- Bernstein (OXB) mode conversion. Measurements confirmed that the conversion efficiency contours are elongated functions of the view angles. The contour minor axis is parallel to the magnetic field at the O-mode cutoff layer for a frequency $f$. Thus, measurements at various $f$ offer the potential for inferring the pitch angle profile. For this, and in order to quickly assess the best conditions for heating within a single shot, a tilted spinning mirror capable of a full angular scan every 2.5-10 ms was prototyped and installed in front of the MAST radiometer. The materials adopted avoid magnetic braking and other eddy currents effects and withstand the high mechanical stresses involved. Vibrations were minimized by a special design and a balancing machine. Preliminary measurements will be presented.   

Broadening of Calculated EC-Driven Currents in NTM Stabilization Experiments at DIII-D

The agreement between the measured and calculated width of EC driven currents in earlier NTM stabilization experiments at DIII-D [1] was improved by simultaneously taking into account several broadening mechanisms. Doppler and relativistic broadening were evaluated by means of a new semi-relativistic formulation of the dielectric tensor recently incorporated in the GENRAY ray tracing code. Smearing of the driven currents within the magnetic island and along the deformed flux surfaces external to the island was taken into account. The radial diffusion of current across the flux surfaces was incorporated in a Fokker-Planck calculation of driven current, assuming a radial diffusion coefficient consistent with confinement. Finally, the mutual misalignment of gyrotron beams was estimated and included in the evaluation of the total current driven by multiple beams. Implications for ITER will be discussed.\par \vskip6pt \noindent [1] C.C. Petty, et al., Proc. 20th IAEA Fusion Energy Conf., Vilamoura, Portugal, 2004, paper EX/7-3.   

Blobs localized in the divertor region

X-point shear may effectively decouple toroidally-asymmetric plasma perturbations in the divertor region and main SOL. In Ref. 1, we found that in such a situation there may exist blobs localized entirely in the divertor region. Here we extend this analysis to include effects of the finite plasma pressure, in combination with the radial tilt of the divertor plate. We provide an analysis of “strange” blobs localized in the private flux region. We discuss also the situations where plasma is detached from the divertor plates, and resistive effect in a cold transitional plasma become important. These divertor blobs may lead to damage to those parts of the divertor which are normally thought of as inaccessible for the plasma flux. Work performed for DoE by UC LLNL under contract No. W-7405-Eng-48. \newline [1] R.H. Cohen, D.D. Ryutov. Contrib. Plasma Phys., 46, \# 7-9, 2006.   

Modeling of lower-hybrid coupling in the Madison Symmetric Torus

In Reversed-Field Pinches (RFPs) the magnetic- field configuration is sustained by the MHD dynamo whose magnetic fluctuations degrade the energy confinement. Inductive Pulsed Poloidal Current Drive (PPCD) has been shown to relax the MHD dynamo, reduce the magnetic fluctuation level and significantly increase the energy confinement time. To provide steady-state poloidal current drive, two different RF schemes are being evaluated in the Madison Symmetric Torus (MST) RFP: Electron Bernstein Wave (EBW) and Lower Hybrid (LH). The Oak Ridge RF codes RANT3D and AORSA1D-H have been adapted for LH waves in the RFP configuration. RFPs require a tightly fitting conducting shell for MHD stability. A waveguide grill would create unacceptable field errors and a launch structure entirely inside the conducting shell must be flat enough to fit in the approximately 2 cm vacuum layer between the shell and the plasma edge. The Inter-Digital Line (IDL) traveling-wave antenna meets these strict requirements. We will present preliminary simulation results of LH coupling with the IDL antenna in MST.   

Multidimensional Radiation Emission and Absorption Processes in a Large Diameter Krypton Gas Puff Z-Pinch Plasma on the ZR Simulator

In a hot and dense plasma environment, such as that expected to be produced in a large diameter krypton gas puff load implosion on the ZR simulator, the radiation plays a significant and influential role on the time and space evolution of the plasma. An investigation of the multidimensional radiation emission, absorption, and transfer processes as well as their effects on the energetics {\&} dynamics of the krypton Z-pinch plasma on the simulator, is made using the mach2 2D radiation MHD code. The incorporation of the dynamical domain tabular collisional radiative equilibrium (DDTCRE) radiation transport model [Y. K. Chong, et. al., ICOPS 2005, Monterey, CA.] into mach2 affords a realistic description of the self-consistent non-local non-LTE ionization dynamics {\&} radiation transport physics in a computationally efficient manner. An extensive krypton atomic structure model including the M-, L-, and K-shells forms the basis for the transport model. In addition, the K- and L-shell radiation yield and power signatures, as well as their spectral {\&} spatial characteristics are highlighted through a detailed postprocess analysis of the plasma during various stages of the implosion process using the AXSTRAN 2D non-LTE radiation ionization dynamics code {\&} the SPECAM 3D multifrequency non-LTE spectra/image synthesizer code. *Work supported by DTRA.   

Plasma jet accelerator optimization with supple membrane model

High density ($\ge 3\times 10^{17}cm^{-3})$ and high Mach number (M$>$10) plasma jets have important applications such as plasma rotation, refueling and disruption mitigation in tokamaks. The most deleterious blow-by instability occurs in coaxial plasma accelerators; hence electrode shape optimization is required to accelerate plasmas to $\sim $200 km/s [1]. A full 3D particle simulation takes a huge computational time. We have developed a membrane model to provide a good starting point and further physical insight for a full 3D optimization. Our model approximates the axisymmetrical plasma by a thin supple conducting membrane with a distributed mass, located between the electrodes, and connects them to model dynamics of the blow-by instability and to conduct the optimization. The supple membrane is allowed to slip along the conductors freely or with some friction as affected by Lorenz force, generated by magnetic field inside the chamber and current on membrane. The total mass and the density distribution represent the initial plasma. The density is redistributed adiabatically during the acceleration. An external electrical circuit with capacitance, inductance and resistivity is a part of the model. The membrane model simulation results will be compared to the 2D fluid MACH2 results and then will be used to guide a full 3D optimization by the LSP code. 1. http://hyperv.com/projects/pic/   

Three-dimensional theory of Compton scattering

Compton scattering is studied theoretically both in the time and frequency-domain, using the Lorentz-boosted Klein-Nishina cross-section for unpolarized electrons. Both spatially and temporally Fourier transform-limited and chirped laser pulses are considered, as well as higher-order Hermite-Gaussian modes. Laser propagation is realistically modeled by Fresnel integrals, and recoil is included as well. Such a highly detailed model is required for the design of next-generation, narrow-band, tunable x-ray and $\gamma $-ray sources based on TW-class lasers and high-brightness electron linacs, where a number of spectral broadening mechanisms play a significant role, including laser bandwidth, laser diffraction (effective bandwidth), electron beam energy spread, electron beam emittance, three-dimensional nonlinear effects, radiation reaction (soft recoil), and hard recoil. 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.   

Kinetic stability of internal kink mode in ITER

ITER's standard operation baseline scenario is susceptible to the $m/n=1/1$ internal kink instability. Kinetic effects modify the inertia and the perturbed potential energy of the mode, which are the two key elements to determine the mode stability. Numerical results are obtained for different $q$-profiles and plasma betas for ITER-like realistic equilibria using the QSOLVER and PEST1 codes and a kinetic postprocessor. In particular, for the fishbone branch, the trapped suprathermal bulk electrons contribute a significant portion of Kruskal-Oberman type to the perturbed potential energy; the trapped bulk ion contribution is reduced by the effects of the bounce frequency and is comparable to the circulating bulk ion one; the trapped $\alpha$ contribution can be stabilizing or destabilizing depending on the radius of $q=1$ surface. For the fishbone mode, the kinetic ion resonant contribution is always opposite to the $\alpha$'s one and is stabilizing. The kinetic modifications of the inertia are mainly from the trapped and circulating bulk ions, and they are always stabilizing for the fishbones. The fishbone branch is destabilized at high $\beta$ or large radii of the $q=1$ surface, almost regardless of the fluid instability drive. For moderate magnetic shear within the $q=1$ surface, the MHD branch is fully suppressed by the kinetic effects over a large range of parameters, and for $q$-profiles with low magnetic shear within the $q=1$ surface, the MHD branch can be destabilized at high $\beta$ or larger radii of the $q=1$ surface.   

Guiding of laser beams in plasmas by electromagnetic cascade compression

The near-resonant beatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few- femtosecond electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red- and blue-shifted by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser phase, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids {\bf B} 2, 2196 (1990)]. After self-focusing, the laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. Thus, a train of high intensity radiation spikes with continually evolving longitudinal profile can be self- guided over several Rayleigh lengths in homogeneous plasma. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW show that achieving GeV energy is possible under realistic experimental conditions.   

Fast Electron Heating in Cone-wire Targets

We present results of fast electron heating of 10$\mu $m diameter, 1mm Cu wires. In the experiments, an 80J, 1ps, 1053nm pulse is focused into a Au cone, generating energetic electrons which heat the wire. 68eV XUV images obtained with a multilayer spherical mirror are compared with simulations to indicate peak wire heating of $\sim $350eV near the cone tip falling with a scalelength of $\sim $100$\mu $m. K$\alpha $ linewidth measurements were compared to simulations of K$\alpha $ broadening to estimate average wire temperatures of $\sim $160eV. LSP simulations predict a cone tip temperature of $\sim $350eV and a 120$\mu $m scalelength of heating along the wire. This work is consistent with an ohmic limiting of the electron penetration to the observed 100$\mu $m scalelength.   

The Krook Collision Model as a template for calculating Electron Thermal Flux in Laser Produced Plasmas

This paper explores what appears to be a new and promising model for electron energy transport in laser produced plasmas, a Krook model for electron electron collisions. This model treats the collison operator as $-\nu(f-f_{max})$. It is particularly simple in that it involves no velocity derivatives and can be treated as a steady-state problem on the ion fluid time scale. In fact in some cases, one can calculate analytically steady-state solutions in the nonlocal limit. However this formulation is also inherently problematical in that if $\nu$ depends on particle velocity, it is not necessarily particle or energy conserving. However, using it to compute only energy flux does maintain the overall conservative nature of the fluid simulation. In some ways, a Krook model may even be more accurate than a Fokker-Planck simulation because of the rather small values of the Coulomb logarithm over large regions of the plasma. This paper will present analytic and numerical aspects of our recent investigation of the Krook model.   

Accurate Modeling of Laser-Plasma Accelerators with Particle-In-Cell Codes

Recent experiments have demonstrated the production of high quality electron bunches at 1 GeV by a laser plasma accelerator.\footnote{W.P. Leemans et al., submitted.} Here the bunch electrons are self-trapped and accelerated from the background plasma. The degree of self-trapping can be a strong function of plasma temperature. We investigate numerical heating and macro-particles push errors due to the grid in 2D PIC simulations. The effects of grid resolution, laser polarization and particle shape on the plasma momentum spread are studied. We find that particle smoothness improves the particle push description and reduces numerical heating. Reducing the phase-space errors associated with numerical heating is essential for a detailed modeling of self-trapping in laser-plasma accelerators. Simulations of high quality bunch production for self-trapping and for laser injection methods will be presented.   

Cutoff wave number for shear waves in a 2D dusty plasma

The cutoff wave number for shear waves in a liquid-state strongly-coupled dusty plasma was measured experimentally. The phonon spectra of random particle motion were measured at various temperatures in a monolayer dusty plasma. In a liquid state of this particle suspension, shear waves were detected only for wavelengths smaller than 20 to 40 Wigner-Seitz radii, depending on the Coulomb coupling parameter. In the experiment, a monolayer suspension of polymer microspheres was levitated in the sheath above a horizontal electrode in a radio-frequency plasma. The particles interacted with a Yukawa potential, and formed a triangular lattice. To melt this lattice and form a liquid, we used a laser-heating method. Two focused laser beams were moved rapidly around drawing Lissajous figures in the monolayer and applying random kicks to the particles. The kinetic temperature of the particles increased with the laser power applied, and above a threshold a melting transition was observed. This laser-heated dusty plasma has some characteristics of a thermal equilibrium.   

The Role of Electron Transport in Generating Ion Shocks in Dense Targets Irradiated by Intense, Short Laser Pulses

Ion shocks may be generated after the interaction of an intense, short laser pulse with a dense target (e.g. pre-compressed DT fuel capsules). The source for ion acceleration is the electric field determined by the distribution of electrons. We study the role played by the transport of fast electrons through the target during the laser pulse and their subsequent relaxation to some thermal distribution on the field generation and ion dynamics. We make use of a 1 D2P Vlasov-Fokker-Planck model, coupled to Maxwell's equations, to describe the electron transport with an assumed hot electron generation mechanism. The electric field is determined by the balancing of the collisionless forward and collisional return currents through the target. The ions may be described either by a simple hydrodynamic model or an ion particle model which allows for relaxation of the shock via ion-ion collisions.   

Numerical investigation of new regimes in laser-plasma and laser-solid interactions

The steady increase in the capabilities of the world's strongest lasers opens up parameter regimes for laser-plasma and laser- solid interaction experiments that were inaccessible before. This is even more true if one considers projected upgrades, such as the Vulcan 10 PW upgrade or the Astra Gemini system (two 50 fs pulses of 500 TW each). In order to become familiar with the physical processes that dominate laser-matter interactions in these regimes, extensive numerical investigations are needed. In this paper, we present the results of particle-in-cell simulations of laser-plasma interactions for electron acceleration in the blowout regime, using Astra Gemini-style pulses, as well as laser-solid interactions for fast ignition fusion research, using Vulcan Petawatt-style pulses. The simulations have been performed using the Osiris framework. New features of the interaction processes that are a direct consequence of the elevated pulse capabilities will be highlighted, and consequences for future experiments will be discussed.   

Laser-driven, picosecond ion beams as probes for warm dense matter

Laser-accelerated ion beams have the great advantage over conventional ion beams of retaining the sub-ps pulse duration of the drive-laser. Together with the high beam current of kA-MA this makes them unique probes that enable new classes of experiments. One example of this is ion transport and stopping in hot, dense plasmas, where several competing models predict different effects. We performed a first proof-of-principle experiment, using two short pulse lasers: the first to accelerate the ion beam and the second to generate a hot, dense plasma. The first beam accelerates ions up to $\sim $5 MeV/amu. Half of that beam is than passed through an interaction target that is isochorically heated by the second shortpulse, while the other half remains unperturbed. Two Thomsonparabola particle spectrometers record the ion energy and charge state distributions enabling a direct comparison of perturbed and unperturbed spectra. First results and simulations as well as comparison to ion stopping models will be presented. * Work performed under the auspices of the U. S. DOE by the LANS, LLC, Los Alamos National Laboratory.   

Curtailment of stimulated Brillouin scattering by localized magnetic field generation

A new mechanism is proposed which will lead to the curtailment of stimulated Brillouin scattering (SBS). When SBS is excited in a laser speckle in an underdense plasma, the localized photon momentum deposition arising from both absorption and back-scatter will cause the generation of a secular magnetic field in the azimuthal direction. This converts the electrostatic ion acoustic waves associated with SBS into dominantly electromagnetic, fast magnetosonic waves. These will have a strong spatially varying phase and group velocity, because the azimuthal magnetic field varies strongly in space, being proportional to distance from the axis of each speckle. In turn this destroys the coherent planar density variations associated with the ion acoustic wave and so curtails the coherent back-scattered light. The higher frequency plasma waves of SRS are in contrast negligibly affected by magnetic fields, and these can now grow, having been previously inhibited by the density gradients associated with the ion acoustic wave. This mechanism is consistent with much experimental data.   

High Power Electrical Explosion of Single and Multi Wire Arrays in Water

Electrical explosions of wires in water medium is a promising method for generation of strong shock waves and non-ideal plasma. Here we report on underwater electrical wire explosions (UEWE) that were investigated experimentally and using computer modeling. Micro- and nano-second time scale generators for UEWE of Al, Cu and W wires were employed. A $\mu $s (6 kJ stored energy, current of 80 kA, rise time of 2.5 $\mu $s) and ns (400 J stored energy, current of 100 kA, rise time of 50 ns) generators were used in $\mu $s and ns time scale experiments, respectively. Obtained scaling laws for explosion parameters suggest that the increase in the discharge power rate leads to an increase in the generated pressure amplitudes. Furthermore, increasing the power rate allows for an extremely high energy deposition, namely up to 200 eV/atom was registered in ns Cu UEWE. The high value of the energy deposition is due to the absence of shunting plasma shell which presents in vacuum electrical wire explosions. In order to amplify the pressures generated by the exploding wires, a cumulation effect in imploding cylindrical wire arrays was implied. High pressures of converging shock waves up to 0.2 Mbar were registered near the axis of the array.   

On non existence of tokamak equilibria with purely poloidal flow

It is proved that irrespective of compressibility tokamak steady states with purely poloidal mass flow can not exist in the framework of either magnetohydrodynamics (MHD) or Hall MHD models. Non-existence persists within single fluid plasma models with pressure anisotropy and incompressible flows.   

Controlled Filament Non-Local Discharge (CFND) .

Recently there has been increased interest in methods to achieve non-local electron effects to tailor the electron energy distribution (EED) for special applications like singlet delta oxygen (SDO) generation. However, a way to favor SDO production ( requires an E/N $\sim $ 10 Td = 10$^{-16}$ Vcm$^{2})$ while still having a high pressure and large volume has not been achieved. Here we present an innovative new concept -- the controlled filament non-local discharge (CFND) in an effort to overcome these shortcomings. The CFND uses micro protrusions on the cathode surface to produce a multi-filament breakdown. The filaments create highly non-equilibrium beam-like electrons embedded in the background plasma discharge, providing control over the volume E/N. The micro-projection cathode design will be discussed and is the key to achieving the CFND. The high electric fields at the projection tips imitate micro arc discharges, enabling discharge breakdown with a relatively low applied voltage despite a high pressure. Once initiated, the discharge voltage drops as a non-local discharge develops over the volume. It is estimated that after initial breakdown at 600 V, an E/N of 10$^{-16}$ Vcm$^{2}$ is obtained at roughly atmospheric pressure in oxygen with an applied voltage of 100 V in planar electrode geometry at a spacing of 10 cm.   

Proton configuration and mass variations are observed in each of the 3036 isotopes studied.

The fission and decay transitions of unstable isotopes are studied with particular detailed analysis of nuclei masses, proton - neutron substructure, and the change in mass experienced by individual nucleons of parent, daughter and product isotopes. The data shows the 3036 isotopes studied contain nucleons of a mass unique to each isotope, and further, indicating 3036 proton variations, each differentiated by a distinct mass. Of these, 283 proton variations are further distinguished by belonging to stable benchmark isotopes. The same variations were found with bound neutrons. A direct correlation is observed between the nearest stable benchmark mass and the mass of the nucleon returning to ground state during the transition, indicating a mass dependence to nuclear stability. These findings indicate that a nucleus in an excited state cannot stabilize or return to the ground state until it adjusts mass to match the nearest $Z - N$ and mass per nucleon benchmark. These conclusions were further tested with the analysis of nucleon mass adjustments occurring within the natural and artificial alpha emitter nuclei. The developed system of analysis provided good results when tested against the incident and product particles of high and low energy interactions and events of nuclear transmutation. Every transition to a stable product demonstrates a strong correlation with a specific mass per nucleon benchmark as a third condition of nuclear stability.   

Laser pincette for high-density attosecond electron bunch generation

An attosecond high-density electron bunch is produced by an intense short-pulse TEM10+TEM01-mode laser. The transverse ponderomotive force of the TEM10+TEM01-mode laser confines pre-accelerated electrons in the transverse direction, just like a laser pincette, and at the same time the laser longitudinal electric field accelerates the electrons [1]. Our three-dimensional particle simulations show that the pre-accelerated electrons are accelerated to a few hundreds MeV and are compressed to $\sim $499 attoseconds with a low energy spread ($\sim $±3.5 {\%}). The electron density of the attosecond bunch reaches $\sim $43 times as high as the initial number density. Such the attosecond electron beam is now available to attophysics. [1] Q. Kong, S. Miyazaki, S. Kawata, et al., Phys. Rev. E, 69, 056502(2004)   

Laser-produced proton-beam quality control by a robust structured foil target

A quality of a laser-produced ion beam is one of the critical factors in ion beam generation in laser-foil interaction. A purpose of this study is suppression of transverse proton divergence by a controlled electron cloud in laser-foil interactions. In this study, the foil target has a hole at the opposite side of the laser illumination. The electrons accelerated by an intense laser are limited in transverse by a neutral plasma at a protuberant part. Therefore the protons are accelerated and also controlled transversely by the electron cloud structure: The laser-generated electron cloud edge induces the proton beam divergence in transverse, and the protuberant part of the rear hole eliminates the electron cloud edge effect. In this work we propose a new realistic robust structure of the foil target in order to relax the laser alignment precision to produce the high quality proton beam. Our simulation results demonstrate that the structured foil target is rather robust against the laser mis-alignment and also against the proton layer mis-placement. [1]~R. Sonobe, et al., Phys. Plasmas, 12 (2005) 073104.   

Dust particle spin-up caused by cross-field plasma flow and turbulence.

Spinning of dust particles adds new interesting features to dust particle dynamics and to the dusty plasma physics. Several reasons for dust particle spin-up have been suggested (e.g. Ref. 1): i) sheared flow of plasmas around charge dust particles, ii) dust particle surface irregularities, and iii) sheath effects resulting from the interactions of a charge dipole of a dust particle (caused by plasma flows into the sheath) with the sheath electric field. Here we present a novel mechanism for charged dust particle spin-up. The physics of the present mechanism is simple and robust, and is associated with the interaction of a charge dipole of a dust particle, \textbf{D}, induced by the \textbf{E}x\textbf{B} cross-field flow of a magnetized plasma (\textbf{D} $\propto $ \textbf{E}x\textbf{B}), where \textbf{E }and \textbf{B }are the electric and ambient magnetic fields. Since the resulting torque is proportional to $\vert $\textbf{ E} $\vert ^{2}$, the presented mechanism of charged dust particle spin-up works for both stationary and non-stationary (turbulent in particular) electric fields. In many cases the turbulent electric field stremgth is much larger than the laminar one so that the impact of turbulence can be dominant. We present theoretical analyses for charged dust particle spin-up and estimate the maximum value for the angular velocity charged dust particle can acquire due to our new spin-up mechanism. [1] N. Sato ``Spinning Motion of Fine Particles in Plasmas'', AIP Conference Proceedings No. 799, p. 97; AIP, New York, 2005.   

Structural Assessment of the Central Solenoid of IGNITOR

A thermo-mechanical analysis of the Central Solenoid of Ignitor has been carried out using the ANSYS code based on a linear 3D Finite Element model. The adopted model takes into account the insulation layers and the epoxy resin fillings required by the coil design. The structural assessment considers, in particular, the transient conditions at both the beginning of the plasma current pulse (heating) and during the cooling phase of the solenoid that follows the end of the plasma current pulse. This transient which causes high shear stresses on the insulation material has led to the design of an optimized feeder connection. The stresses under the most critical conditions (start-up) are within the allowable values found by tests carried out by Ansaldo.   

Advances in the Fabrication of Toroidal Field Coil Prototypes*

The Bitter-type Toroidal Field Coils (TFC) adopted for Ignitor consist of plates that are cooled down to 30 K by Helium gas. Copper OFHC has been selected for these plates, allowing for an Electron Beam (EB) welding solution of the cooling channels. Kabel Metal set up the welding parameters and qualified the process to achieve full joint penetration with acceptable metallurgical structure. The qualification covers both the welding of the cooling channels and the inlet/outlet tube made on two full size samples. A metallographic examination and vacuum and pressure tests have been preformed to validate the basic suitability of the EB welding process. \newline*Sponsored in part by ENEA of Italy and by the U.S. DOE.   

IGNITOR Remote Handling System

The detailed design of the in-vessel Remote Handling System, based on the ``two port concept'' with two operating booms, has been completed. A 3D mock-up of the plasma chamber (PC) has made it possible to simulate the boom. This validates the ability of the boom, equipped with the attached end-effectors, to reach any in-vessel zone by 180$^{\circ}$on each side without interferences. Thus, the operating procedures applicable to several interventions have been established. Furthermore, a failure analysis of the boom components has been carried out in order to identify a recovery proceedure. The design of the ex-vessel cabin with the function of holding the boom apparatus and managing the removal and installation of in- vessel components has been completed. The material removed from the PC is treated as radioactive waste material. The boom is made up by a sliding straight arm and articulated links. A structural analysis of both components under a maximum payload of 25 kg has evaluated an acceptable deflection of about 7 mm.   

Optimized Operation and Electrical Power Supply System of Ignitor*

The performance of the control system for the position and shape of the elongated, tight aspect ratio plasma column of Two reference sets of parameters for the operation of Ignitor have been identified. One, the main set, involves plasma currents up to 11MA and toroidal fields up to 13T. The reduced parameter set corresponds to 7MA with fields of 9T and considerably longer pulse flat-tops. The evolution of the relevant currents in the toroidal and the poloidal field magnet systems has been optimized in order to minimize the requirements on the electrical power supply and cryogenic cooling systems. Thyristor amplifiers are adapted to drive both the toroidal and poloidal field magnet systems. The total installed power for these systems is 2400 MVA. The connection of this to the terminals, involving two nodes of the 400 kV grid, at the Caorso site, which houses a dismantled nuclear power station, has been analyzed and authorized by the TERNA- GRTN Agency. A particular consideration has been given to the problems involving the control of both the position and the shaping of the plasma column.\newline*Sponsored in part by ENEA of Italy and by the U.S. DOE.   

Laser Plasma Acceleration Experiment at the Naval Research Laboratory.

The traditional long term strategy for producing high quality electron beams in a single stage LWFA involves three elements: operation in the resonant or standard regime, the use of optical guiding to extend the acceleration region, and external injection of a precisely-phased, high quality injection electron bunch. The standard regime and optical guiding has been studied by many research groups and promise good results for the acceleration. The creation of the electron beam for external injection is still a very problematic issue. Most experiments to date have operated in the self modulated (SM) regime, which produces very large accelerating gradients but poor quality electron beams with large energy spread. More recently, quasi-monoenergetic acceleration of particles from the background plasma has been observed in simulations and experiments operating in a shorter pulse regime. Such quasi-monoenergetic electrons could be a candidate for injection into a following stage of standard LWFA if not for the relatively poor shot to shot reproducibility. We are in the initial stage of experiments to generate injection electrons using the HD-LIPA schemes with a 10 TW 50 fs laser system. The second stage accelerator will be a capillary discharge plasma channel for extended acceleration distance. Preliminary results, including statistics on the stability of quasi-monoenergetic acceleration, will be presented. Supported by DOE and ONR.   

BGK-type waves in slowly evolving plasmas

We introduce a specific class of BGK-type waves that arise naturally in slowly-evolving Vlasov plasmas, characterized by a distribution function in terms of the canonical particle action. Using some naturally motivated assumptions and the constraints of self-consistency, we determine the wave's nonlinear properties and compare these to driven Vlasov systems. We then show how this may lead to reduced models of driven plasmas relevant, for example, to simulated Raman scatter.   

Tilt instability at formation phase of field-reversed configuration plasma

A field-reversed configuration (FRC) plasma is produced by a negative-biased theta-pinch. It is known that the FRC attains to an equilibrium phase after an axial contraction of the plasma at the formation phase. However, when high bias field is applied to the plasma, the FRC is disrupted due to the strong axial contraction. The present report is aimed to investigate the disruption mechanism of the FRC in detail. For this purpose, two kinds of diagnostic systems are constructed, which are a magnetic probe array with sine-cosine windings and an optical fibers array without any lens at the front facets of the fibers. A fluctuating component in the confinement field and the radiation of the plasma with n=1 and 2 toroidal modes can be analyzed using the diagnostic systems. It is found that the toroidal modes appear associating with the axial contraction. Their amplitudes increase when the FRC is disrupted. The experimental evidence is compared with a result of a computer simulation using a plasma model with a tilting configuration inside a separatrix.   

Electron Impact Ionization of Heavier Ions

The electron impact ionization (EII) is a dominant ion creation process in various kinds of plasmas. Hydrogenic atoms occurs not only in plasmas but may also be formed due to radiation effects in many organic and inorganic materials. Apart from its fundamental importance in collisional physics the knowledge of the EII cross sections finds its wide applications in modeling astrophysical and fusion plasmas. So the demand of the EIICS is enormous. It is hard to fulfill such a demand either by experimental or a\textit{b initio }calculations. Thus various analytical and semi-classical models are employed to generate accurate EII cross sections. We report here a modified version [1] of the Bell et. al. equations [2] including both the ionic and relativistic corrections (MBELL). We generalize the MBELL parameters for treating the dependency of the orbital quantum numbers \textit{nl}; evaluating cross sections for various species at different energies tests the accuracy of the procedure. Detail will be presented at the meeting. \newline [1] A. K. F. Haque, M. A. Uddin, A. K. Basak, K. R. Karim and B. C. Saha, Phys. Rev. A73, 052703 (2006). \newline [2] K. L. Bell, H. B. Gilbody, J. G. Hughes, A. E. Kingston, and F. J. Smith, J. Phys. Chem. Ref. Data 12, 891 (1983).   

Experimental Realization of an Exactly Solvable Plasma Expansion

~We study the expansion of ultracold neutral plasmas into a surrounding vacuum from the early acceleration phase until the approach to a terminal velocity. Ultracold neutral plasma is created by photoionizing laser-cooled and trapped neutral Sr$^{88}$ atoms. A fraction of the electrons, which have been heated and perhaps accelerated by the photoionizing laser, leave the plasma and enter the surrounding vacuum, creating a strong ambipolar electric field that accelerates the ions outward. The initial density distribution of the plasma is Gaussian and it remains Gaussian as it expands. Using absorption imaging techniques, we can observe the evolution of the ion and electron kinetic energy in the plasma. Measurements of the ion kinetic energy show that the expansion is described well by an analytical solution of the Vlasov equations. ~The behavior is closely related to the dynamics of plasmas produced by laser irradiation of solids, clusters, and gases with fast-pulse lasers.   

Calculation of the gyroviscosity using a gyrokinetic formalism

Gyrokinetic variables for parallel velocity, magnetic moment, gyroangle and gyrocenter are obtained for arbitrary perpendicular wavelength electrostatic fluctuations to second order in the expansion for small Larmor radius of the background magnetic field by demanding the gyrokinetic equation contain no gyrophase dependent terms order by order. The resulting nonlinear gyrokinetic equation is valid for arbitrary collisionalities and perpendicular wavelengths for electrostatic turbulence. The distribution function in these gyrokinetic variables when Taylor expanded for large perpendicular wavelengths recovers the correct gyroviscosity and Reynold's stress tensor found by drift kinetic [1] and moment [2] approaches. The full gyrokinetic generalization of the gyroviscosity and Reynold's stress tensor is expected to be required to evaluate the coupling of the axisymmetric portion of the radial electric field associated with zonal flow and neoclassical toroidal angular momentum transport. \newline \newline [1] A. N. Simakov and P. J. Catto, Phys. Plasmas 12, 012105 (2005). \newline [2] J. J. Ramos, Phys. Plasmas 12, 052102 (2005).   

Measuring Magnetic Field Evolution in SSPX

A magnetic probe with two linear arrays of chip inductors is being designed and fabricated to investigate magnetic field evolution at SSPX in LLNL. The design is based on a previous design already implemented at SSPX. The same entry port on the side of the flux conserver, including vacuum hardware to insert or retract the probe, will be reused from the previous design. The new design consists of two probe arms each fitted with a linear array of three-axis chip inductor clusters. The probe arms are designed to be opened and closed at various angles, and to be rotated 180 degrees about the tubular axis. Due to the harsh plasma environment inside the flux conserver, precautions are being taken to eliminate metal-to-metal contact, taking into account durability issues as well. Moveable mechanisms include formed and welded bellows, and custom-made bearing systems fabricated out of metal and macor.   

Low-frequency instabilities in an ultracold neutral plasma

We report the observation of low-frequency instabilities in an ultracold neutral plasma. By applying a small transverse magnetic field ($\sim $1G) perpendicular to an applied electric field ($\sim $50 mV/cm), we observed large oscillations in the emission of electrons from the expanding ultracold plasma with a frequency range from 50 to 300 KHz. We identify the electron emission as a signature of plasma instabilities due to electrons drifting relative to ions across the magnetic field. Two possible instabilities qualitatively match our observations: density-gradient drift instability due to the coupling of diamagnetic drift wave with the density gradient to the ion plasma oscillations, or a Farley-Buneman instability (two-stream) where the electrons and ions have different drift velocity. These ultracold plasma instabilities may help us understand the dynamics of ultracold neutral plasma in magnetic fields, such as Debye screening, Landau damping and magnetic confinement.   

Microscopic non-ideal effects in collisionless reconnection in the current sheet.

The microscopic violation mechanism of frozen-in condition of magnetic field is investigated by means of 2+1/2 dimensional explicit electromagnetic particle simulation. Microscopic non-ideal terms in two-fluid equation are examined based on particle simulation results. Two instabilities, Lower Hybrid Drift Instability (LHDI) and Drift Kink Instability (DKI) are observed to grow in the current sheet. The wavy coupling components, which appear in electric force term at the periphery and in magnetic force term at neutral sheet, become significant in accordance with the excitation of these instabilities. In the DKI growing phase, DC electric field is generated at the neutral sheet through the wave-particle interaction and it contributes to reduce magnetic flux. Thus, an anomalous resistivity leading to collisionless reconnection is generated by the DKI. The deformation process of current sheet due to the LHDI and the mass ratio dependence of the growth of the DKI will be discussed in the meeting.   

Flow Stability in Closed Magnetic Field Geometry

Simple dipole solutions of the Grad-Shafranov equation are known to exist [1,2]. Reference [1] gives the solution for a stationary magnetic dipole, while [2] presents a solution for a toroidally rotating dipole plasma. The MHD stability of the first solution was investigated in [3]. However, the stability of the second is far more difficult to analyze. This difficulty is a reflection of a fundamental MHD problem - the impossibility of a general Energy Principle formulation for an equilibrium with flows. The current work is aimed at analyzing the stability of the simplest limit case of a rotating dipole solution - a hard core Z-pinch with sheared axial flow. We focus on an axial flow with a particular dependence on radius that results in the simplest possible eigenvalue equation. Stable solutions are found that may be relevant to dipole configurations such as Jupiter and the Levitated Dipole Experiment (LDX). [1] ``A Magnetic Dipole Equilibrium Solution at Finite Plasma Pressure,'' S. I. Krasheninnikov, P. J. Catto and R. D. Hazeltine, Phys. Rev. Lett. 82, 2689 (1999). [2] ``Effects of Rotation on a Finite Plasma Pressure Equilibrium in a Dipolar Magnetic Field'' by P. J. Catto and S. I. Krasheninnikov, Phys. Letts. A 258, 153 (1999). [3] ``Resistive Stability of Magnetic Dipole and Other Axisymmetric Closed Field Line Configurations.'' A. N. Simakov, P. J. Catto, J. J. Ramos and R. J. Hastie, Phys. Plasmas 9, 4985 (2002).   

High power (50MW), pulsed, broadband (50{\%}) microwave amplifier

The first time operation of a coherent, broadband microwave amplifier with an output power of 80 MW and amplification of 36 dB over a frequency range from 2 to 3 GHz has been demonstrated. The amplifier is based on the Cherenkov mechanism of interaction between electrons and plasma and converts the kinetic energy of a relativistic electron beam (500 keV, 2 kA) into microwave energy. The radiation frequency is determined by the plasma density which can be varied over a wide range resulting in the broad frequency tunability of the device. The microwave signal is delivered to the amplifier entrance by a coaxial cable and the amplified radiation exits the device as a TE11 mode of a circular waveguide. Experimental results showed that the phase difference of the signals at the amplifier entrance and exit are fixed, i.e. the waves are coherent between 2 and 3 GHz. Details of the complete system and the experimental results will be presented.   

Kinetic Alfven Waves Driven by Rotating Magnetic Island in Tokamaks

Kinetic Alfven waves (KAWs) result from modification of the Alfven wave through the FLR effect of the ions. In high temperature plasmas, they are weakly damped and can be approximated as natural eigenmodes of the tokamak with a full set of discrete spectrum that depends on the plasma density, safety factor and temperature profiles. These waves may be driven resonantly to large amplitudes by appropriate boundary perturbations at these resonant frequencies such as the case of a natural rotating magnetic island. The resultant amplitude depends on the damping mechanism. The theory of the spectrum of the KAW in tokamaks with general cross-sections is formulated and its spectrum studied numerically. The consequence of these excited KAW includes the possibility of steady state current drive and the scattering of energetic particles. This may provide an explanation for the observation of the clamping of the q0 value in hybrid discharges in the presence of a rotating 3/2 island [1].\par \vskip6pt \noindent [1] P.A. Politzer, et al., 32nd EPS Conf. on Plasma Physics, Tarragona, Spain (2005).   

Echo Effects in the Solar Coronal Loops

EUV coronal loops having well defined filamentary structure, often appear as an arcade of thin magnetic threads resembling winding in a curved solenoid or a funnel. Such arcades are typical to (but not limited by) the post-flare coronal structures formed immediately after a short explosive phase of a major flare. Compared to flare timescales, post-flare arcades are long living, well organized structures. Elemental filaments in arcades are, however, in highly dynamic state, showing not only a subtle oscillations, but harboring frequent microflares. These microflares, having various intensities, often appear simultaneously in different places, i.e. several elemental filaments far removed from each other light up almost simultaneously. Besides, many individual filaments produce "homologous microflares", i.e. strong localized brightenings may occur repetitively in the same filament. Time intervals between the first two brightenings and their successors fallow a pattern typical to temporal plasma echos studied theoretically and observed in laboratory plasma experiments. To study the spatial and temporal regularities in the post-flare coronal arcades we use high cadence uninterrupted time series of data taken by Transition Region and Coronal Explorer (TRACE) in the chromosphere/coronal lines (1600 A, Fe IX/X 171 A, and Fe XII 195 A). We find that these regularities can be understood on basis of a spatial, temporal, or spatio-temporal echoes of plasma waves resulted from nonlinear response of a system to impulsive disturbences. With the upcoming Solar-B mission the observed spatial-temporal echos can be used for diagnostic goals. In particular, one can estimate a local anisotropic electron and ion temperatures across the filaments, the electric current densities, and other characteristics of a system.   

Atmospheric Pressure DC and RF plasmas for materials processing

Atmospheric pressure discharges have been characterized for their applications to low cost materials processing and micro-fabrication. A challenge in using atmospheric pressure plasmas is creating stable, non-thermal, uniform discharges and preventing the transition to an arc. Such discharges can be created; however, as so called microplasmas with dimensions less than 1mm. Using discharge visualization, voltage-current measurements, and optical emissions spectroscopy the characteristics of DC and RF discharges were measured. The discharges operate as pressure and temperature scaled versions of the familiar low pressure normal glow discharge. The DC discharges operate with normal current density and constant electric field in the positive column. The RF discharges are observed to operate in alpha and gamma modes. Discharges were studied in a variety of gases including, Air, Nitrogen, Hydrogen, Helium, and Argon. Analysis of the spectra emitted by the N$_{2}$ 2$^{nd}$ positive system indicates gas temperatures in the range of 300K to 2000K depending on gas composition and discharge power. Vibrational temperatures were measured as high as 5000K indicating non-thermal plasma discharges. Using methane-hydrogen mixtures a:C-H coatings of various qualities have been deposited and characterized using Raman spectroscopy.   

Hybrid Ion Source Development Project at Los Alamos Neutron Science Center

The goal of the of the HYBRid Ion Source (HYBRIS) development project at Los Alamos Neutron Science Center (LANSCE) is to design and test a helicon plasma generator assisted high-current-density H$^{-}$ ion source. The hybrid ion source is a combination of a long-life plasma cathode, sustained by the helicon plasma generator, with a stationary, pulsed main discharge (H$^{-}$ production chamber) directly coupled to each other. The electrons generated in the helicon plasma are transferred to the multi-cusp chamber by ambipolar diffusion igniting the main discharge. The first Langmuir-probe measurement results describing the plasma properties of the helicon discharge will be presented together with the design of the multi-cusp H$^{-}$ production chamber. The strength of the magnetic multi-cusp field confining the plasma in the H$^{-}$ production chamber can be adjusted with the aid of small iron bars. Simulation results illustrating the effect of this special technique on the cusp-field strength will be presented. Also the physical processes affecting the coupling of helicon plasma generator with the primary discharge chamber and the effects of the multi-cusp field strength on plasma confinement will be discussed.   

The influence of additional ballast volume on pulsed ICP discharge plasma parameters.

An analysis of plasmachemical reactor parameters has been performed for the case of a small discharge volume connected to a much larger diffusion chamber (see, for example, V. I. Demidov et al., Phys. Rev. Lett., v.95, 215002, 2005) for both the active and afterglow phase of the discharge. During the active phase, plasma is formed primarily in the smaller volume and the large ballast volume has a comparatively low charged particle density. As a result, the ballast volume has little effect on the plasma parameters in the discharge chamber. However, in the afterglow phase the situation changes markedly. This is a result of the significantly different diffusion-loss times between the two volumes. Due to the rapid decrease in electron density in the smaller discharge volume, the density becomes less than in the ballast volume. Therefore, during the afterglow phase, the axial component of the gradient in the plasma density changes sign as does the axial component of the ambipolar field. The large volume plays a thermostatic role and significantly affects plasma parameters and transport processes in the small volume. This leads to a number of effects, in particular to a much slower degradation of the electron density and temperature in discharge volume, and to the rate of change of charged particles densities.   

Ultracold Plasma Electron Temperature Measurements using Collective Mode Diagnostics

Applying a radio-frequency electric field to an expanding ultracold neutral plasma leads to the observation of Tonks- Dattner resonances, electron sound waves propagating in a finite, inhomogeneous plasma. These TD resonances have strong dependence on the boundary conditions of the plasma; while earlier studies were done using plasmas confined in cylindrical chambers, our freely expanding spherical plasmas have no clear outer turning points for the TD electron waves. Choosing an outer turning point where the local Debye length equals the plasma size, a WKB approximation yields good agreement with the mode frequencies, extracting a temperature consistent with other measurements. We note that the outer turning point used is similar to the location of an ion shock wave predicted in simulations, which may play a role in establishing the boundary conditions for the TD resonances. The determination of a well- defined turning point for the sound waves will allow accurate temperature measurements using TD resonance frequencies.   

Using wavelet transforms for improving the conditional sampling results

We combine two innovative techniques namely the wavelet transform and the conditional sampling in order to identify coherent moving structures existing in low frequency density fluctuations. The experiments are conducted for continuous, ArII plasma column immersed in 1KG magnetic field. The fluctuation measurements are obtained using laser induced fluorescence. Induced fluorescence signals are collected through two optical periscopes having mobility along the field lines inside the plasma chamber. The wavelet transform is initiated for filtering purposes, since the induced fluorescence signal is obscured by fluctuations due to photon statistics. Using the wavelet transform on the reference probe signal ease our search for conditions. We mark the indices for the samples satisfying the forced condition, and return to raw signal collected from the moving periscope in order to apply the conditional sampling technique.   

A US Based Ultrafast Interdisciplinary Research Facility

The US scientific competitiveness on the world arena has substantially decreased due to the lack of funding and training of qualified personnel. Most of the potential workforce found in higher education is composed of foreign students and post-docs. In the specific field of low- and high-field science, the European and Asian communities are rapidly catching-up with the US, even leading in some areas. To remain the leader in ultrafast science and technology, new visions and commitment must be embraced. For that reason, an international effort of more than 70 countries for a US-based interdisciplinary research facility using ultrafast laser technology is under development. It will provide research and educational training, as well as new venues for a strong collaboration between the fields of astrophysics, nuclear/high energy physics, plasma physics, optical sciences, biological and medical physics. This facility will consist of a uniquely designed high contrast multi-lines concept housing twenty experimental rooms shared between four beams:[0.1 TW, 1 kHz], [10 TW, 9 kHz], [100-200 TW, 10 Hz] and [500 TW, 10 Hz]. The detail schematic of this multi-laser system, foreseen research and educational programs, and organizational structure of this facility will be presented.   

Development of a radiation monitoring program for a multidisciplinary ultrafast research facility in collaboration with the Advanced Laser Light Source

Monitoring radiation exposure and radiation safety trainings of users in ultrafast high power lasers science is not as stringent as other fields. Most national laboratories and centers, because of the insufficient in-house expertise of the scientists involved in this research, that usually originate from the plasma or optical sciences communities, rely on collaborators such as those from nuclear/high energy physics. With the international effort to build a US based multidisciplinary ultrafast research facility (presented in another poster), a dedicated program that will address and implement the appropriate procedures, including acquiring exhaustive sets of data, developing dedicated tracking training tools, etc., is being developed. This program is using the newly operational international facility, the Advanced Laser Light Source (ALLS), located in Varennes, Canada. Dedicated monitoring devices were recently installed for that purpose. Description of the concept and plans for this program will be presented along with very preliminary data newly acquired at this facility.   

On the role of mean flow in zonal flow generation in drift wave turbulence

The coherent mean flow is an important ingredient to regulate turbulent transport in magnetic fusion plasmas. A minimal modeling for zonal flow instability with mean flow effects on 4-wave modulation process[1] was developed based on Hasegawa-Mima(HM) turbulence, in which direct interaction between the mean flow and pump waves was ignored for the simplicity, similar to the approximation in[2]. As an example, ETG turbulence was sampled as the pump waves and ITG driven zonal flow was assumed as the mean flow like a stationary standing wave. The minimal modeling analysis showed that the zonal flow generation is reduced by the mean flow through increasing the real frequency of zonal flow [3]. To justify the validity of the minimal modeling and evaluate the role of the mean flow, a spectral code to solve 2D HM equation with the mean flow effect is advanced to calculate the whole contribution of all possible nonlinear interaction to the zonal flow generation in the system with mean flow, zonal flows and pump waves as well as sidebands. It is found that the mean flow can only slightly reduce the zonal flow generation. The mean flow scatters the pump energy to a wider spectrum, which may in turn enhance the modulation response for the zonal flow excitation. [1] Li {\&} Kishimoto, PoP 9, 1241(2002) [2] Kim {\&} Diamond, PoP 10, 1698 (2003) [3] Uzawa et al. APS 2005, PFR 1, 024(2006)   

X-ray emissions by inner-shell ionization in laser-cluster interaction

The dynamics of clusters irradiated by high intensity laser pulse has been interested due to its unique nature of the interaction different from other conventional targets and various applications have been proposed [1]. Specifically, an enhanced electric field that is more than one order of magnitude greater than the applied laser field is found to be produced due to the polarization effect near cluster surface. Generation of anomalously high charge state ions and associated short pulse X-rays were observed [2]. Based on simulation studies utilizing our particle code including atomic and relaxation processes [3] incorporated with a perturbation analyses of inner-shell ionization, we have investigated the properties of X-rays from F,O,N,C,B,Be,Li-like argon ions. With an increase of laser intensity, the X-ray pulse length becomes short, comparable to the order of incident laser pulse. [1] Y. Kishimoto et al., Phys. Plasmas 9, 589 (2002) [2] Y. Fukuda et al., Laer and Particle Beams 22, 215 (2004) [3] Y. Fukuda et al., Phys. Rev. A 73, 031201(R) (2006)   

Implementation of an SRS-SBS interaction model

Previous work in experiment and theory has shown an anti-correlation of SRS and SBS reflectivities. A dependence of SRS reflectivity on ion-acoustic wave (IAW) damping has also been demonstrated experimentally. In this poster we will show recent work implementing a physical model for this effect into LLNL's pF3D code. PIC simulation results demonstrating the SRS-SBS anti-correlation were compared with theory based on the frequency detuning of the SRS-driven Langmuir wave (LW) due to the density modulation resulting from the SBS-driven IAW. The calculated modified-LW dispersion agreed well with LW modes measured in the PIC results. A new frequency calculation, based on the SRS-SBS interaction, will be added to the code. The purpose of pF3D is to predict the level of laser-plasma interactions present in fusion ignition targets at the NIF, and thus all relevant physics must be included. The IAW-damping dependence of SRS has also been attributed to pump-depletion and Langmuir decay of the SRS LW, in addition to the mode-coupling. The dependence of SRS on IAW-damping could be used as a strategy to reduce reflectivities, if the dominant mechanism is identified.   

The Magnetothermal Instability in Dilute Accreting Plasmas

In dilute accreting astrophysical plasmas, such as around Sagittarius A*, even an extremely weak magnetic field can lead to large heat fluxes and viscous stresses along field lines that can destabilize a differentially rotating or thermally stratified plasma. These are referred to as the magnetoviscous instability (MVI) (Balbus, ApJ 616, 857 (2004)) and the magnetothermal instability (MTI) (Balbus, ApJ 616, 857 (2001)), respectively. In addition, the lack of radiation in these dilute flows requires that energy generated from gravitational infall of matter must be transported or dissipated (Balbus \& Hawley, Reviews of Modern Physics 70, 1 (1998)). This motivates our analysis of the kinetic MTI for a plasma with Keplerian rotation profile and outwardly decreasing temperature in the kinetic and fluid regimes. We demonstrate that the instability can transport angular momentum and thermal energy outwards. We also demonstrate that the kinetic MTI reduces to the fluid MTI (Islam \& Balbus, in preparation) at collision frequencies faster than the sound crossing time of the fastest growing modes, where collisionless damping is suppressed (Sharma et. al., ApJ 596, 1121 (2003)).   

Laser Laboratory for Energetic

Silk from the spider Steatoda Triangulosa is used to mechanically support direct-drive laser fusion targets at the Lab for Laser Energetics (LLE) in Rochester, NY. Using superglue, each target is suspended from 4 dragline samples, each of which consists of a pair of cylindrical lines. Empty targets are first attached to the silk, and then filled with fuel (deuterium, tritium, or a mixture of the two) over a long time period. During the filling process for cryo-DT targets, the silk is subjected to doses of beta radiation of approximately 100 Mrad. To examine the impact of radiation on silk strength, samples of silk were exposed to doses of beta radiation (ranging from several Mrad through several Grad). The strength of the irradiated samples was compared to the strength of unirradiated samples. It was found that there is no measurable impact on strength for doses less than 10Mrad, and that silk strength decreases logrhythmically for doses larger than that. For the dose of interest (100 Mrad), the strength of the silk is found to be reduced by about 25{\%}, indicating that the use of spider silk for cryo-DT targets is still a viable option.