Session YP9: Poster Session IX: Beams and Coherent Radiation; Supplemental Posters; Post-Deadline Posters

Recent progress in developing a 170 GHz, 500 kW gyrotron for testing ITER transmission line components

A 170 GHz, 500 kW CW gyrotron has been developed for testing ITER transmission line components. Although specified as a 500 kW source, the electrical design has been conceived with the goal of generating up to 1 MW of continuous output power. The design employs a double-anode electron gun, an interaction cavity operating in the TE$_{31,8}$ cavity mode, a three-mirror internal converter to produce a fundamental Gaussian output beam, a CVD diamond output window and a depressed collector to safely dissipate the spent electron beam power. Fabrication of the gyrotron is nearly complete and initial high-power tests will soon be carried out. Details of the gyrotron design, results of low-power tests on the internal converter and initial high-power tests will be presented.   

Excitation of Modes During the Voltage Rise of a 1.5 MW, 110 GHz Gyrotron

We report measurement of the modes excited during the voltage rise of a 1.5 MW, 110 GHz pulse gyrotron operating in the TE$_{22,6}$ mode. The gyrotron operates at 96 kV and 40 A with a voltage rise time of less than 1 $\mu $s and a flat-top of 2 to 3 $\mu $s. Theoretical analysis predicts that competing higher frequency modes are excited during the voltage rise, possibly leading to operation in unwanted modes or the generation of unwanted spurious frequencies. A heterodyne receiver system with 20 ns time resolution was used to measure the frequency as a function of time during the voltage rise. We observed a lower frequency mode, the TE$_{21,6}$ mode near 108 GHz, at voltages up to 70 kV. Data were taken at different values of the magnetic field and operating voltage. The results confirm that low frequency modes are excited during the voltage rise, not high frequency modes. Analysis shows that these modes are backward wave oscillations excited far from cutoff, indicating that they would have a higher order axial field distribution. Additional theoretical research using the code MAGY is underway to explain these latest results.   

Numerical study of the start-up scenario of a 670 GHz gyrotron operation at TE$_{31,8}$ mode

In order to develop a system to detect concealed radioactive materials, we are designing a 670 GHz gyrotron with sufficient power to cause breakdown in the air. Design studies of the cavity and the magnetron injection gun (MIG) of this gyrotron had already been presented. We concluded study of simple start-up regime for this 670GHz gyrotron operating at TE$_{31,8}$ mode and found that at the fundamental cyclotron harmonics, the operating mode can be excited and the competitor modes will be suppressed. Currently we are studying gyrotron operating on the second cyclotron harmonics using the same electron gun. Preliminary studies show that if the higher harmonics mode is excited first, it will suppress competitors of the fundamental mode. Using available MIG data, we are performing numerical simulation using MAGY. The results of these simulations can be illustrative for our future experiments, and the results of the study will be presented at the conference.   

Experimental Program to Investigate the Technique of Remote Detection of Suspected Nuclear Materials With a 670 GHz Gyrotron

Planned experiments and diagnostics to investigate the technique of remote detection of concealed suspected nuclear materials (SNMs), utilizing gyrotron radiation at 670 GHz to cause air breakdown, are presented. The technique relies on the principle that ionizing radiation in the vicinity of SNMs creates number densities of free electrons that are orders of magnitude higher than background conditions, making breakdown highly likely at the focal region of the 670 GHz wave beam. The detection system is expected to be deployed in a wide range of atmospheric conditions, and thus testing of wave beam propagation and breakdown will include the presence of aerosols with and without elevated free electron densities. Diagnostics include a specially constructed calorimeter for the wave beam, optical and mass spectroscopy, and microwave scattering for the breakdown region.   

Effects of Random Circuit Fabrication Errors on Small Signal Gain and on Output Phase In a Traveling Wave Tube

Random fabrication errors may have detrimental effects on the performance of traveling-wave tubes (TWTs) of all types. A new scaling law for the modification in the average small signal gain and in the output phase is derived from the third order ordinary differential equation that governs the forward wave interaction in a TWT in the presence of random error that is distributed along the axis of the tube. Analytical results compare favorably with numerical results, in both gain and phase modifications as a result of random error in the phase velocity of the slow wave circuit. Results on the effect of the reverse-propagating circuit mode will be reported.   

Multiple frequencies per mode in a relativistic magnetron utilizing a diffraction output

Recently, relativistic magnetrons with diffractive RF outputs have been investigated both with PIC simulations and experimentally [1,2]. Diffractive outputs offer an alternate RF extraction method and may increase the efficiency over relativistic magnetrons that use a conventional power extraction scheme. We have independently verified some of these claims with our own PIC simulations. Furthermore, we have found that the diffractive output influences the modes of the relativistic magnetron by creating an axially overmoded structure. Results demonstrating there are multiple frequencies per mode, and that these can be selected by choosing the proper applied magnetic field and voltage, are presented. \\[4pt] [1] M. Daimon, K. Itoh, G. Imada, and W. Jiang, ``Experimental demonstration of relativistic magnetron with modified output configuration,'' \textit{Applied Physics Letters}, vol. 92, p. 191504, 2008\\[0pt] [2] M. Fuks, E. Schamiloglu, ``70{\%} Efficient Relativistic Magnetron with Axial Extraction of Radiation through a Horn Antenna,'' \textit{IEEE Transactions on Plasma Science}, vol. 38, p. 1302, 2010   

Equibrium and Stability of the Brillouin Flow in Recirculating Planar Magnetron

Simulation of the novel recirculating planar magnetron, RPM [1], has shown rapid formation of electron bunches in the inverted magnetron configuration. This bunching mechanism was recently simulated in a thin electron layer model [2], which exhibited negative, positive, and infinite mass behavior, depending on the magnitude and sign of the radial electric field. We analyze these properties for the relativistic, cylindrical Brillouin flow, to evaluate RPM startup. We make use of our recent discovery that the electrostatic potential and the vector potential satisfy a Buneman-Hartree like relation, and a Hull-cutoff like relation EVERYWHERE within the equilibrium Brillouin flow. \\[4pt] [1] R. M. Gilgenbach, et.al., IEEE Trans. Plasma Sci. 39, 980 (2011). \\[0pt] [2] D. M. French, et al., Appl. Phys. Lett. 97, 111501 (2010).   

Recirculating Planar Magnetron Modeling and Experiments

We present simulations and initial experimental results of a new class of crossed field device: Recirculating Planar Magnetrons (RPM) [1]. Two geometries of RPM are being explored: 1) Dual planar-magnetrons connected by a recirculating section with axial magnetic field and transverse electric field, and 2) Planar cathode and anode-cavity rings with radial magnetic field and axial electric field. These RPMs have numerous advantages for high power microwave generation by virtue of larger area cathodes and anodes. The axial B-field RPM can be configured in either the conventional or inverted (faster startup) configuration. Two and three-dimensional EM PIC simulations show rapid electron spoke formation and microwave oscillation in pi-mode. Smoothbore prototype axial-B RPM experiments are underway using the MELBA accelerator at parameters of -300 kV, 1-20 kA and pulselengths of 0.5-1 microsecond. Implementation and operation of the first RPM slow wave structure, operating at 1GHz, will be discussed. \\[4pt] [1] Patent pending   

Microwave Plasma Window Theory and Experiments

The microwave plasma window is an experiment designed to promote RF breakdown in a controlled vacuum-gas environment using a DC bias. Experimental data has shown that this DC bias will significantly reduce the RF power required to yield breakdown, a feature also shown in recent simulation [1]. The cross-polarized conducting array is biased at (100's V) DC on the surface of a Lucite vacuum window. Microwave power is supplied to the window's surface by a single 1-kW magnetron operating at 2.45 GHz CW. The goal of this project is to establish controllable characteristics relating vacuum pressure, DC bias, RF power required for surface breakdown, as well as RF transmission after the formation of plasma. Experimental data will be compared with multipactor susceptibility curves generated using a Monte Carlo simulation [1] which incorporates an applied DC bias and finite pressures of air and argon. \\[4pt] [1] P. Zhang et al., Phys. Plasmas 18, 053508 (2011)   

Evaluation of Breakdown Delay in High Power Microwave Dielectric Barrier Discharges

An essential element of distributed discharge limiter development is minimizing the delay time between high power microwave (HPM) incidence and diffuse plasma creation. We present a series of pulsed plasma experiments conducted in neon and argon from 80-760 torr designed to assess methods of reducing this delay time. Evidence is presented implicating a charge buildup effect on the dielectric window with a characteristic decay time constant on the order of tens of minutes to several hours. A detailed description of the experimental setup used in this study is provided and progress towards development of a high-frequency multi-moded signal acquisition system is also presented, including the development of a circuit analog absorber designed to provide greater than 30dB attenuation with a thickness of less than 2cm.   

Rapid Formation of Distributed Plasma Discharges using X-Band Microwaves

Observations of rapidly formed (50-300 ns) distributed plasma discharges using X-band microwaves are presented. Two discharge test chambers are used to observe microwave breakdown in Ar and Ne gas from 10 to 760 torr. One is a brass rectangular WR650 waveguide and the other is a cylindrical stainless steel chamber, both enclosed with polycarbonate windows. The chamber is illuminated by the output of 25 kW, 0.8 $\mu$s pulse-width, 9.382 GHz magnetron through an X-band waveguide pressed against the polycarbonate window. Measured incident, reflected, and transmitted microwave power to a movable monopole antenna located beyond the discharge chamber are used to detect the discharge and attenuation characteristics as the pressure is varied. Observations of localized transmission spike measurements of -20 dB that occur within 50 ns caused by the plasma under certain conditions have been made. Additionally, an ICCD provides fast (10-50 ns) time-scale optical images of the plasma, revealing the plasma formation and decay processes. Progress on a Ku band interferometer and optical emission spectroscopy diagnostics will be discussed. Plasma modeling is used to compare the experimental data with theoretical behavior.   

Role of phase difference between superposing lasers and magnetic field for efficient terahertz radiation generation by tunnel ionization

The generation of terahertz (THz) radiation is an active field of research due to its applications in THz spectroscopy, material characterization, imaging, topography, etc. Since plasma can sustain high field and it is a nonlinear medium, the plasma based schemes are very attractive techniques for the THz radiation generation. In the present work, we make use of tunnel ionization, where quick ionization is achieved with the help of two femtosecond lasers having a phase difference. Then the generated plasma cylinder is caused to oscillate and radiate at the frequency in the THz range. An application of DC magnetic field on the plasma cylinder helps getting a directional THz radiation emission. The role of phase difference and the magnetic field for efficient THz radiation generation and a control on the emission of radiation are discussed. The conversion efficiency of the present scheme is $\sim $10$^{-3}$ and it supersedes several other schemes.   

Condition of Carbon Fiber Field Emitter Under Different DC Voltages

Field emission cold cathodes have the potential to provide high current density and low voltage operation for THz sources, high power microwave tubes etc. Each of these applications requires the cathode to exhibit long lifetime in the presence of deleterious condition. One type of cathode that is suitable is the carbon fiber field emitter (CFFE). CFFEs are robust and the current emission can easily be modified by surface treatment. The emission property of the CFFE depends critically on the condition of the cathode. Unfortunately, the morphology of the CFFE under different voltage is often unknown. Here, we describe results of a comprehensive experiment that aims to investigate the changes that occur to the CFFE during different DC voltages. SEM images of the CFFE are taken at a 1kV interval (up to 8kV), pre shot SEM images of the cathode are taken for reference. The amount of current produced for each interval is recorded. The evolution of the surface morphology, evidence of resistive heating and height of the CFFE for different voltages are obtained. Their effects on the electron emission are analyzed. A resistive heating model and Particle-in-cell simulations are performed to compare with the experiment.   

Underwater Laser Filamentation and Electrical Discharge Guiding

Techniques to trigger and guide underwater electrical discharges using a laser are currently being developed at NRL. This work may be useful for a variety of applications, including advanced micromachining. As part of this development we are studying underwater optical filaments. Optical filamentation is the extended propagation of a small diameter high-power laser beam, thought to result from a balance between Kerr self-focusing and ionization-induced defocusing, and typically includes a coincident plasma column. Laser heating and hydrodynamic expansion can also result in subsequent vapor channel formation. Both the plasma column and vapor channel can be useful structures for guiding electrical discharges. Our group has for the first time demonstrated and characterized ns underwater filaments. Using a 60 mJ, 5 ns, 532 nm laser, we measured filament diameters of $\sim$100 $\mu$m and propagation $>$ 30 Rayleigh lengths. Underwater optical filament measurements, as well as results from ongoing laser-guided underwater discharge experiments, will be presented.   

On anomalous Doppler instability in auroral and laboratory plasmas

This paper examines different conditions of appearance of anomalous Doppler instability when an electron beam moves under the presence of a strong magnetic field. The situations considered here are relevant to wave-particle interactions in space plasmas like lower-hybrid waves generated by Cherenkov and anomalous Doppler resonances [1] as well as to the experiment set at the University of Strathclyde, UK, to examine magnetized electron beams instabilities [2]. We consider growth rates produced by the relevant distribution functions with the beam drift velocity exceeding the wave velocity. Possible experiment configurations are addressed including a dielectric filled waveguide as well as a wave-slowing dielectric with a vacuum core at the axis for the electron beam. Possibilities to distinguish the anomalous Doppler resonance from other accompanying beam instabilities [3] are discussed. \\[4pt] [1] R. Bingham et al, J. Plasma Physics, 76, pp. 539-546 (2010) \\[0pt] [2] D. C. Speirs et al, Phys. Plasmas, 17, 056501 (2010) \\[0pt] [3] I. Vorgul et al, Phys. Plasmas, 18, 056501 (2011).   

Alternate Operating Scenarios for NDCX-II

NDCX-II is an accelerator facility being built at LBNL to study ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The baseline design calls for using twelve induction cells to accelerate 40 nC of Li+ ions to 1.2 MeV. During commissioning, though, we plan to extend the source lifetime by extracting less total charge. For operational flexibility, the option of using a helium plasma source is also being investigated. Over time, we expect that NDCX-II will be upgraded to substantially higher energies, necessitating the use of heavier ions to keep a suitable deposition range in targets. Each of these options requires development of an alternate acceleration schedule and the associated transverse focusing. The schedules here are first worked out with a fast-running 1-D particle-in-cell code ASP, then 2-D and 3-D Warp simulations are used to verify the 1-D results and to design transverse focusing.   

Characterization of the NDCX-II accelerator via simulation

The Neutralized Drift Compression Experiment-II (NDCX-II) will generate ion beams for use in driving targets for warm dense matter experiments and heavy ion fusion target studies and to do high-current beam physics.\footnote{see A. Friedman, et al., this meeting} It is designed to produce beams of Li$^+$ ions with energies of 1 to several MeV compressed to sub-nanosecond pulses with peak currents of 10 or more Amps. Here, we discuss characterization of the design with simulation, including optimization of the operating point, examination of error tolerances, and integrated source to target simulations for validation. There is some flexibility in the shaping and timing of the induction waveforms that provides a large operating space to optimize the performance of NDCX-II. Some examples will be discussed. Simulation has been used to characterize the tolerances for errors. The resulting requirements appear to be feasible. Full validation of the experiment requires self-consistent inclusion of the plasma dynamics. To this end, simulations that include a particle-in-cell plasma model have been carried out and will be discussed.   

Multiple Scattering of Slow Ions in a Partially Degenerate Electron Fluid

We extend former investigations to a partially degenerate electron fluid at any temperature for multiples slow ion scattering initially worked out at T=0. We implement an analytic and mean-field interpolation of the target electron dielectric function between T=0(Lindhard) and T$\to$Infinity (Fried-Conte). A specific attention is given to multiple scattering of proton projectiles in the keV energy range, stopped in a hot electron plasma at solid density [1].\\[4pt] [1]. R. Popoff, G. Maynard and C.Deutsch, Phys.Rev.E80, 046408 [2009]   

Prompt Gas Desorption Due to Ion Impact on Accelerator Structures

The repetition rate and peak current of high intensity ion accelerators for inertial fusion or other applications may be limited under certain conditions by the desorption of gas molecules and atoms due to stray ions striking the accelerator structure. We have measured the prompt yield of atoms in close proximity to the point of impact of the ions on a surface. Using the 300-keV, K+ ion beam of the Neutralized Drift Compression Experiment (NDCX-I), ions strike a metal target in a 5-10 microsecond bunch. The collector of a Bayert-Alpert style ionization gauge is used to detect the local pressure burst several centimeters away. Pressure transients are observed on a micro-second time scale due to the initial burst of desorbed gas, and on a much longer ($\sim $1 second) timescale, corresponding to the equilibration of the pressure after many ``bounces'' of atoms in the vacuum chamber. We report on these time dependent pressure measurements, modeling of the pressure transient, and implications for high-intensity ion accelerators.   

Thermodynamic Bounds on Nonlinear Electrostatic Fluctuations in Intense Charged Particle Beams

This work calculates nonlinear thermodynamic bounds on electrostatic perturbations in anisotropic charged particle beams with a wide range of initial beam parameters. Anisotropies develop naturally in accelerators and can drive Harris-type electrostatic instabilities. These can cause a deterioration of beam quality and degraded focusing, resulting in limits on the luminosity and minimum spot size attainable in experiments. This presentation places an upper bound on the field fluctuation energy of these instabilities. A method previously used to bound field energy in unstable plasmas [Davidson and Tsai, 1973; Davidson, 1985] is generalized to the case of an intense non-neutral beam, fully encompassing intense self-field effects. A bound on the fluctuation field energy is given for an arbitrary initial distribution and the results are applied to space-charge-dominated, emittance-dominated, and general anisotropic bi-Maxwellian distributions.   

Nonlinear effects of beam-plasma instabilities on neutralized propagation of intense ion beams in background plasma

In ion-beam-driven high energy density physics and heavy ion fusion applications, the intense ion beam pulse must propagate through background plasma before it is focused onto the target. The streaming of the ion beam relative to background plasma can cause the development of fast electrostatic collective instabilities. The nonlinear stage of these instabilities can affect the degree to which the ion beam can be focused onto the target. Simultaneously, the development of the instabilities is also affected by the ion beam focusing. In this paper we examine numerically three effects of instabilities on the beam focusing: heating of the beam ions, heating of the neutralizing background electrons inside the beam, and the nonlinear effect of the instabilities on the dynamical evolution of the electron return current. The scalings of the average de-focusing forces on the beam ions due to these effects are identified, and confirmed by comparison with numerical simulations. These scalings can be used in the development of realistic ion beam compression scenarios in present and next-generation ion-beam-driven experiments.   

Direct and Beat-Wave Excitation of Collective Beam Modes in the Paul Trap Simulator Experiment

The Paul Trap Simulator Experiment (PTSX) is a cylindrical Paul trap that simulates a long, thin charge bunch propagating through an equivalent kilometers-long magnetic alternating-gradient (AG) transport system. An external quadrupole drive is applied to excite collective modes, and experiments on PTSX show that when the charge bunch is driven either directly at the mode frequencies, or indirectly, using beat-wave excitation, the properties and dynamics of the charge bunch are strongly affected. Results are presented from experiments in which the drive amplitude, frequency, and drive duration are varied. The experimental data are compared with results of particle-in-cell (PIC) simulations performed using the WARP particle-in-cell (PIC) code.   

Beam-Plasma Interaction Experiments on the Princeton Advanced Test Stand

The Princeton Advanced Test Stand (PATS) is a compact experimental facility for studying the fundamental physics of intense beam-plasma interactions relevant to the Neutralized Drift Compression Experiment - II (NDCX-II). The PATS facility consists of a 100 keV ion beam source mounted on a six-foot-long vacuum chamber with numerous ports for diagnostic access. A 100 keV Ar+ beam is launched into a volumetric plasma, which is produced by a ferroelectric plasma source (FEPS). Beam diagnostics upstream and downstream of the FEPS allow for detailed studies of the effects that the plasma has on the beam. This setup is designed for studying the dependence of charge and current neutralization and beam emittance growth on the beam and plasma parameters. This work reports initial measurements of beam quality produced by the extraction electrodes that were recently installed on the PATS device. The transverse beam phase space is measured with double-slit emittance scanners, and the experimental results are compared to WARP simulations of the extraction system.   

Collective Mode Excitation by Asymmetric Fields in a Linear Paul Trap to Study Beam Stability

A second arbitrary function generator was used to apply trapping waveforms to the Paul Trap Simulator Experiment (PTSX) electrodes that do not have 90-degree-odd rotational symmetry as they do in a standard linear Paul trap. Time-oscillating transverse dipole, quadrupole, and uniform potentials were generated and their effects on the long term stability of the trapped charge bunch were studied as a function of perturbation amplitude, frequency, and duration. As expected, time-oscillating uniform potential perturbations have no effect. Dipole perturbations applied near the expected m = 1 dipole mode frequency result in strong emittance growth and particle loss. Changing the relative phase of the trap electrode waveforms also breaks the 90-degree-odd rotational symmetry and results in large amplitude particle excursions and particle loss. The results of these experiments are compared to an envelope equation model and also to the results of a particle-in-cell (WARP) code.   

Update on the Experimental Study of Current Filamentation Instability

Current Filamentation Instability (CFI) is of central importance for propagation of relativistic electron beams in plasmas. CFI has potential relevance to astrophysics, magnetic field/radiation generation in afterglow of gamma ray bursts, and inertial confinement fusion, energy transport in fast-igniter concept. An experiment is underway at Accelerator Test Facility at BNL with 60MeV electron beam and capillary discharge plasma. The goal is to conduct a systematic study and characterize CFI as function of beam (charge, transverse and longitudinal profile) and plasma (plasma density) parameters. The transverse beam profile is measured directly at the plasma exit with OTR from a gold-coated silicon window. Initial experimental results show reduction of the beam transverse size with the appearance of multiple beam filaments and the size and number of individual filaments depend on the plasma density. We will present early experimental results and outline next steps.   

Nonlinear Weibel Instability in collisonal and collisionless plasmas

The nonlinear stage of Weibel instability of a relativistic beam propagating through ambient plasma is studied analytically and supported by computationally efficient hybrid simulations. In our hybrid approach, beam electrons are modeled using numerical macroparticles while plasma electrons are modeled as a passive fluid instantaneously responding to the beam evolution. Assuming underdense beams, we find the self-similarity law for the nonlinear dynamics of the collisionless Weibel instability (WI). It is found that the electron energy distribution of the beam particles trapped in the filaments is close to Maxwellian. Using the Boltzmann distribution of the electron density in transverse plane, we derive a closed equation describing filament structure, yielding a modified Bennett pinch relation. Also, a theoretical model that utilizes the Bennett pinch relations is used to describe the nonlinear dynamics of the resistive WI and calculate the stopping time of the beam. It is found that the WI initially enhances beam deceleration but then reduces it when compared to a filamentation-suppressed beam (without WI), so that the overall stopping time of the beam is essentially unaffected by the instability.   

Simulation Studies of Adiabatic Thermal Beams in Periodic Solenoidal Magnetic Focusing Fields

Self-consistent simulations are performed to verify the theoretical predictions of adiabatic thermal beams in periodic solenoidal magnetic focusing fields [K.R. Samokhvalova, J. Zhou and C. Chen, Phys. Plasma \textbf{14}, 103102 (2007); J. Zhou, K.R. Samokhvalova and C. Chen, Phys. Plasma \textbf{15}, 023102 (2008)]. In particular, results are obtained for adiabatic thermal beams that do not rotate in the Larmor frame. For such beams, the theoretical predictions of the rms beam envelope, the conservation of the rms thermal emittance, the adiabatic equation of state, and the Debye length are verified in the self-consistent simulations.   

Spectroscopic Analyses of Electrode Plasmas Generated in High Intensity Electron Beam Diodes

The self magnetic pinch (SMP) electron beam diode is being investigated as an intense flash x-ray radiographic source. The diode produces a focused e-beam ($<$3mm diameter) at 7 MeV and 150kA with a 45ns FWHM pulsewidth. Since the vacuum gap is small ($\sim $ 1cm), plasmas formed on the electrode surfaces affect the diode impedance, x-ray spectrum, pulsewidth, and e-beam dynamics. Temporal and spatially resolved optical spectra are collected and analyzed using self-consistent, time-dependent, collisional radiative (CR) models which provide information about plasma species, densities, and temperatures. This data is used to verify plasma conditions and help benchmark hybrid PIC codes which simulate these plasma environments. Recent experimental results obtained for the SMP diode fielded on the RITS-6 accelerator are presented.   

System Radiographic Characterization of 7MV Self-Magnetic Pinch Diode on RITS-6

The 7 MV, 160 kA induction voltage adder RITS-6 is used as a test bed for research and development of sub-100 ns flash x-ray radiography of which the self-magnetic pinch (SMP) diode is an example. The x-ray source properties such as dose, source spatial distribution, and energy spectrum couple with the imaging detector sensitivity and blur to form the radiologic system performance which is also highly dependent on the imaging geometry. The system performance of some SMP diode configurations will be presented.   

Wakefields in Woodpile Accelerator Structures

The woodpile structure is a promising 3D photonic crystal for accelerating particles in a waveguide mode with speed-of-light phase velocity, driven by laser sources at optical frequencies. Using the simulation framework VORPAL, wakefields in possible woodpile structures have been simulated, with emphasis on eliminating unphysical transition radiation upon injecting the drive beam into the simulation. Operating at optical frequencies, the woodpile structure's small size would limit the maximum bunch change (though a high repetition rate would compensate for the high bunch charge, yielding a high current and eventually luminosity in an accelerator); calculation of the wakefields enables estimation of this maximum bunch charge.   

Simulations of Self-Pinching Heavy-Ion Beams

An unneutralized ion beam is subject to a self-pinching force and electrostatic defocusing, and normally the latter wins. However, if the transverse electrostatic forces can be reduced sufficiently, a net pinching can occur. There has been interest recently in utilizing this concept for heavy-ion fusion applications. We consider several approaches to reducing electrostatic defocusing. Two that have particular promise are use of closely spaced conducting foils transverse to the beam propagation direction, and introduction of a counterstreaming relativistic electron beam in a guide magnetic field. We present electromagnetic particle simulations (with the WARP code) that demonstrate pinching with both approaches. The conducting foil approach yields cleaner focusing in an idealized simulation, but is subject to limitations from non-ideal effects including field-emission of electrons and knock-on electrons.   

NIF science experiments on relativistic electron-positron plasma creation

High-flux jets of relativistic positrons with temperatures of MeV have recently been produced in experiments at 100-1000 J high-intensity laser facilities at LLNL and LLE. The pair parameters have been found to scale up with the input laser energies. We will perform an NIF science experiment to create high-density relativistic pair plasmas using the multi-kilojoule NIF ARC laser. It is expected that using multi-kilojoule, short-pulse lasers like Omega EP, Gekko LFEX and NIF ARC and advanced target designs, such experiments can create the first relativistic high-density pair plasmas in the laboratory - a completely novel system enabling detailed study of some of the most exotic and energetic systems in the universe. *This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.   

First-principles edge physics simulation in diverted tokamak geometry at SciDAC CPES

Primary mission of the SciDAC Proto-FSP CPES (Center for Plasma Edge Simulation) is (a) to build a new kinetic code applicable to realistic diverted edge geometry, (b) to create a new code integration framework to couple the multi scale edge physics including MHD and neutrals, and (c) to make scientific discoveries in the edge physics and the edge effect on the core confinement. Absence of a kinetic code applicable to realistic diverted edge geometry has been a critical missing element in the world fusion program. The insurmountable difficulties in building such a kinetic code has been in the requirement of the full-f approach instead of the popular delta-f approach, the complicated edge geometry, existence of the X-point, and the necessity of extreme scale computing. We have succeeded in building two such kinetic HPC codes XGC0 and XGC1, and in creating a state-of-the-art code integration framework EFFIS. The current capability of the XGC codes, including the kinetic ion-electron turbulence physics and 3D magnetic perturbation physics, will be described. Scientific discoveries on the edge neoclassical and turbulence physics, the non-local core-edge interaction, 3D RMP physics, pedestal physics, wall load, plasma rotation physics, and other edge physics will be reported.   

Polarization of Incoherent Thomson Scattering in Burning Plasmas

Incoherent Thomson scattering (TS) is routinely used for electron temperature measurement, with T$_{e}$ proportional to the width of the scattered spectrum. The polarization of the light is changed during the scattering process, an effect that becomes large in high-temperature burning plasmas and is typically described by the relativistic depolarization factor $q$. This factor quantifies the reduction of scattered spectral intensity collected by a detector with a specific polarization sensitivity. Our employment of the relativistic scattering operator, Stokes vectors and Mueller matrix formalism enables a more general approach that follows a major steps presented in [S. E. Segre and V. Zanza, Phys. Plasmas \textbf{7}, 2677 (2000)] with some important corrections and improvements. The superposition effect caused by a large number of randomly moving electrons in the scattering volume renders the scattered radiation partially polarized, and is quantified by the degree of polarization $p$. Because of different definitions of $q$ and $p$ their contribution to depolarization in TS is sometimes misinterpreted. The relationship between these two factors will be described.   

Unparticle, a special case of unmatter

The idea of unparticle was first considered by F. Smarandache in 2004, 2005 and 2006, when he uploaded a paper on CERN web site and he published three papers about what he called ``unmatter,'' which is a new form of matter formed by matter and antimatter that bind together. Unmatter was introduced in the context of ``neutrosophy'' (Smarandache, 1995) and ``paradoxism'' (Smarandache, 1980), which are based on combinations of opposite entities ``A'' and ``antiA'' together with their neutralities ``neutA'' that are in between. In 2006 E. Goldfain introduced the concept of ``fractional number of field quanta'' and he conjectured that these exotic phases of matter may emerge in the near or deep ultraviolet sector of quantum field theory, as a result of non-equilibrium dynamics and the onset of complex behavior. In the TeV sector the hypothetical high energy states consist of arbitrary mixtures of particles and antiparticles, which are similar to unparticles, and thus unparticles are particular cases of unmatter. H. Georgi proposed the theory of unparticle physics in 2007 that conjectures matter that cannot be explained in terms of particles using the Standard Model of particle physics, because its components are scale invariant. Unparticles are massless fields of nonintegral scaling dimensions.   

Fundamental Flaw in Kinetic Alfven Wave Dispersion

The well-known kinetic Alfven wave (KAW) dispersion is shown to be fundamentally incorrect because its derivation involves a mathematical error. The error results from the standard practice of setting to zero the dielectric tensor elements $K_{xy},$ $K_{yx}$ because these elements are of order $\omega/\omega_{ci}\ $ and $\omega/\omega_{ci}\ll1$. \ It is shown that in a warm electron, cold ion plasma the dielectric tensor elements $K_{yz},$ $K_{zy}$ are of order $\omega_{ci}/\omega$ so, when taking the full 3$\times $3 wave equation determinant, order of unity products of the sort $K_{xy}K_{yz}$ exist, are important, and are missing in the KAW derivation. This error was identified from the substantive discrepancy between the determinant of the matrix of a 3$\times$3 wave equation matrix reported by Hirose et al. [1] and the standard 2$\times$2 determinant used for deriving the KAW. The validity of the 3$\times$3 matrix elements and in particular the elements $K_{yz},K_{zy}$ was established by showing that 2- fluid theory gives the same matrix elements as the kinetic theory \ used in Ref. [1].\\[4pt] [1] A. Hirose et al. Phys. Letters A 330, 474 (2004).   

A High Repetition Rate Plasma Focus for High Energy Density Plasma Studies

Large, high energy density plasma sources such as Sandia's Z-machine or the National Ignition Facility are limited to low repetition rate operation ($\sim $1 shot per day). Intermediate facilities still have low data rates ($\sim $10 shots per day). Alameda Applied Sciences Corporation has demonstrated a plasma focus operating from 200- 500 kA, capable of firing shots at 0.1 Hz. A typical run gathers data over $\sim $1000 shots. Such high data rates allow validation and verification of numerical simulation codes with a statistically significant data set over a wide variety of operating conditions. A variety of terminal measurements (current and voltage), neutron yield, optical emission spectroscopy, hard x-ray images and zipper array data are used to characterize the source. Additional diagnostics such as interferometry, x-ray back lighting and soft x-ray spectroscopy are discussed.   

Preliminary results from the Pleiades experiment

We present preliminary experimental results from the Pleiades experiments, which were performed on the National Ignition Facility. The experiments consist of a 3.5 mm diameter hohlraum, which is irradiated by 80 laser beams with a total of 360 kJ In 2.5 ns. On the end of the hohlraum is a 200 micron long, 2 mm diameter SiO2 foam. We will present the requirements of the campaign as well as the diagnostic configuration. We will present hohlraum temperature measurements as well as radiographic measurements.   

3D CFDTD PIC Simulation Study on Low-Frequency Oscillations in a Gyrotron

Low-frequency oscillations (LFOs) have been observed in a high average power gyrotron and the trapped electron population contributing to the oscillation has been measured. As high average power gyrotrons are the most promising millimeter wave source for thermonuclear fusion research, it is important to get a better understanding of this parasitic phenomenon to avoid any deterioration of the electron beam quality thus reducing the gyrotron efficiency. However, understanding of the LFOs remains incomplete and a full picture of this parasitic phenomenon has not been seen yet. In this work, we use a 3D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method to accurately and efficiently study the LFOs in a magnetron injection gun (MIG) of a high average power gyrotron. Employing a highly parallelized computation, the model can be simulated in time domain more realistically. LFOs have been obtained in a 3D time domain simulation for the first time. From our preliminary simulation studies, it is found that not only magnetic compression profile but initial velocity or velocity ratio play an important role in the operation of a MIG electron gun. In addition, the secondary emission effects on the LFOs are also studied. Detailed results will be presented.   

Influence of ion effects on a space charge limited field emission flow: from non-relativistic to ultra-relativistic regimes

Influence of ion effects on a space charge limited field emission flow has been studied systematically, by employing both analytical and numerical approaches. In our model, the field emission of electrons is described by the Fowler-Nordheim equation. The cathode plasma and surface properties are considered within the framework of an effective work function approximation. Ionization effects at the anode as well as electron space-charge effects are described by Poisson's equation coupled with the energy conservation equation including the relativistic effects. The calculations are carried out self-consistently to yield the steady states of the bipolar flow. The electric field on the cathode surface is found to be saturated due to space charge effects and is determined by the effective work function approximately. In addition, the upstream ion current bas been treated as a tuning parameter. It is found that the field emission currents in the presence of saturated ion currents can be enhanced to be nearly 1.8, 1.5, and 1.4 times of the cases with no upstream ion current in non-relativistic, intermediate, and ultra-relativistic regimes, respectively. The solutions have also been verified using 1D PIC simulations, as implemented in the OOPD1 code developed by PTSG of UC Berkeley.   

PIC modeling of fast electron transport in plasmas

Understanding fast electron transport in plasma is crucial for fast ignition. A recent experiment [1] using the OMEGA EP laser (1 kJ/10 ps) study of fast electrons transport from the Au layer into hot (40 eV) dense (30 mg/cc) plasma created by shock heating of CH foam sandwiched between Au and Cu tracer layer, showed a strong reduction (20$\times )$ in Cu K$\alpha {\rm g}$yield compared to the cold target with a uniform and weak K$\alpha $ spot. To understand this transport experiment, 2D collisional PIC simulations, using the PICLS code, are performed to model fast electron transport in such plasma transport target. Simulations show a significant increase in fast electron divergence going from high density Au to less dense plasma transport layer due to strong B-fields generated at the Au/CH plasma interface. Fine B-field structures in plasma are also observed, possibly responsible for further electron scattering resulting in poor K$\alpha $ yield.\\[4pt] [1] T Yabuuchi, ``Study of fast electron transport in plasmas using a kJ-class laser pulse,'' IFSA 2011   

Banana Regime Neoclassical Ion Heat Flux with Retention of the Field Term in the Linearized Collision Operator

The standard calculation of neoclassical ion heat flux in the large aspect ratio, circular flux surface, banana regime limit uses a model collision operator where only pitch angle scattering is retained and an \emph{ad hoc} term is introduced to preserve conservation of momentum.\footnote{M.~N.~Rosenbluth, R.~D.~Hazeltine, and F.~L.~Hinton, Phys.~Fluids \textbf{15}, 116 (1972)} The full linearized collision operator contains also an energy diffusion term and a complicated field term which involves an integral over the perturbed distribution, both of which are dropped in the standard calculation. We reexamine the standard treatment by considering the field as well as the test particle portions of the linearized collision operator and by using an expansion in the eigenfunctions associated with the transit-averaged pitch angle scattering collision operator.\footnote{Y.~Xiao, P.~J.~Catto, and K.~Molvig, Phys.~Plasmas \textbf{14}, 032302 (2007)} We focus on modifications due to the field term to attempt to determine if corrections are needed to the standard result in the large aspect ratio limit.   

Time resolution constraints of x-ray crystal spectrometers on NIF

X-ray crystal spectrometers have been used successfully to measure the ion temperature within tokamaks. To apply this measurement to laser-heated plasmas, one would desire a very high time resolution to image the evolution of temperature over the duration of the shot. Standing in the way of the highest time resolution measurements is the fact that the path length of light from a finite source onto a crystal of finite size varies. Here we present the shortest time that could be resolved in a representative NIF shot as a function of crystal and source size.   

Multi-dimensional simulations of Magnetic Field Seeding of Plasma via Laser Beatwave Interaction

Assembling magnetized plasma for inertial fusion permits longer duration and smaller density-radius product fuel implosions by reducing the energy transport significantly. For fusion energy, however, the field must be created with a significant standoff distance. A promising technique for magnetic field production is the beat-wave interaction.\footnote{M. N. Rosenbluth and C. S. Liu, Phys. Rev. Lett. \textbf{29}, 701 (1972).} Some theoretical results have been confirmed by microwave experiments.\footnote{J. H. Rogers and D. Q. Hwang, Phys. Rev. Lett. \textbf{68}, 3877 (1992).} Recently, fully-kinetic 2D and 3D simulations of the interaction have been simulated using the L\textsc{sp} particle-in-cell code. We inject 2 CO$_{2}$ 100-micron transverse-extent lasers both with 10$^{13}$ W/cm$^{2}$ intensity into a peak 3x10$^{16}$ cm$^{-3}$ density plasma at various angles. The calculated interaction produces beatwaves at the predicted wavelength and frequency and drives magnetic fields up to 2.5 kG. We will examine the sensitivity of the efficiency of magnetic field production to laser parameters and plasma density scale length and discuss the application to the Plasma Liner eXperiment at LANL.   

Engage: The Science Speaker Series - A novel approach to improving science outreach and communication

Communicating the results and significance of basic research to the general public is of critical importance. At present, very few programs exist to allow young scientists the opportunity to practice their public outreach skills. Although the need for science outreach is recognized, graduate programs often fail to provide any training in making science accessible. Engage represents a unique, graduate student-led effort to improve public outreach skills. Founded in 2009, Engage was created by three science graduate students at the University of Washington. The students developed an interdisciplinary curriculum to investigate why science outreach often fails, to improve graduate student communication skills, and to help students create a dynamic, public-friendly talk about their research. The course incorporates story-telling, improvisational arts, and development of analogy, all with a focus on clarity, brevity and accessibility. This free, public-friendly speaker series is hosted at the University of Washington and has substantial public attendance and participation.   

Broadband THz Radiation from Two-color Laser-produced Plasma

We discuss the origin of broadband THz emission from two-color laser-produced plasmas. Previously, the emission of THz pulses was attributed to an ultrafast plasma current arising from tunneling ionization under an asymmetric two-color laser field. Here we find such mechanism produces ultra-broadband radiation, covering from tens of GHz to hundreds of THz, and investigate where such broadband radiation (THz supercontinuum) originates from. We first find that the onset of ultrafast photocurrent determines the radiation bandwidth, while its decay time sets the central frequency of radiation. We show that the nature of broadband radiation arises from the ultrashort timescale of photocurrent, substantially shorter than the laser pulse duration. We also consider other mechanisms such as self-phase modulation and spectral blue-shift generation by sudden plasma generation, which all broaden the fundamental and second harmonic laser spectra [1,2]. These also greatly broaden the THz radiation spectrum depending on the laser intensity and laser-plasma interaction length. \\[4pt] [1] I. Babushkin et al., PRL 105, 053903 (2010).\\[0pt] [2] Mark D. Thomson et al., Opt. Express 18, 23173-23182 (2010).   

Self-modulation of long SLAC particle bunches

The transverse self-modulation of ultra-relativistic particle bunches provides a path to the generation of large amplitude wakefields using long drivers [1]. In this work we show that the long electron or positron bunches that are available at SLAC could be used to demonstrate this mechanism. One-to-one OSIRIS simulations were performed in conditions that mimic the propagation of the electron beam available at SLAC in 1 meter long plasmas. The simulations showed that the transverse self-modulation of the electron beam occurs, and that this can lead to the generation of accelerating gradients in excess of 60 GeV/m. As a result, some of the beam electrons gained more than 5 GeV after one meter of propagation. The possibility to seed the transverse self-modulation instability with the initial wake provided by hard cut beams is also examined. In this case, the simulations revealed that stable accelerating gradients exceeding 10 GeV/m over the whole plasma length could be achieved. The asymmetries associated with the transverse self-modulation of electrons and positron beams were also explored.\\[4pt] [1] N. Kumar et al, Phys. Rev. Lett. 104, 255003 (2010).   

Speed of Opening a Relativistically Transparent Channel in an Overdense Plasma by a Linearly Polarized Wave

We investigated by theory and simulations how fast a relativistically transparent channel is opened by a linearly polarized relativistic laser pulse in an overdense plasma, which is classically opaque. The relativistic transparency has been well known: the dispersion relations were revealed for various steady states. However, as long as we understand, the answer to the question `how the relativistic channel is formed dynamically from an opaque plasma' has not been so clear. In this work, we focused on finding analytically the speed of such a channel opening. By employing the `channel-opening-time' concept, we could derive semi-analytically a simple formula, which showed excellent agreement with the one-dimensional PIC simulations. The theory was successfully applied in predicting the pulse shape after the interaction of an ultraintense linear polarized laser pulse and a thin foil both in one- and two-dimensional systems.   

Three-dimensional electromagnetic strong turbulence: II. Wave packet collapse and structure of wave packets during strong turbulence

Large-scale simulations are performed by numerically solving the three-dimensional (3D) electromagnetic Zakharov equations, focusing on individual wave packet collapses and on wave packets forming in strong turbulence. The structures of the Langmuir, transverse, and total electric field components of wave packets during strong turbulence are investigated over a range of $v_{e}/c$. For $v_{e}/c < 0.17$ strong turbulence is approximately electrostatic and wave packets have very similar structure to purely electrostatic wave packets. For $v_{e}/c > 0.17$ transverse modes become trapped in density wells and contribute significantly to the structure of the total electric field. At all $v_{e}/c$ the Langmuir energy density contours of wave packets are predominantly oblate. The transverse energy density contours of wave packets are predominantly prolate, with the major axis being perpendicular to the major axes of the Langmuir component. This results in wave packets becoming more nearly spherical as $v_{e}/c$ increases, and in turn generating more spherical density wells during collapse.   

Low Velocity Ion Slowing Down in a Strongly Magnetized Plasma Target

An ion projectile slowed down at a velocity Vp smaller than target electron thermal velocity Vthe, in the presence of an arbitrary strong, constant and homogeneous magnetic field B, in a dense electron-ion target plasma is investigated within a novel diffusion formulation, based on Green-Kubo integrands evaluated within magnetized one-component plasmas(OCP) models, respectively framed on target ions and electrons [1]. Analytic expressions are reported for slowing down orthogonal and parallel to B, which are free from the usual uncertainties plaguing standard perturbative derivations either based on linear response (LR) or the binary collision approach (BCA).B and target temperature dependences of the given low velocity slowing down are further detailed for dense target of fast ignition concern and ultracold plasmas envisioned for ion beam cooling as well.\\[4pt] [1] C. Deutsch and R. Popoff, PRE 78, 056405 (2008) and NIMA606, 212(2009)   

Low Ion Velocity Slowing Down in a Demixing Binary Ionic Mixture

we pay attention to ion projectile slowing down at low velocity Vp $<$ Vthe, target thermal electron velocity, in a strongly coupled and demixing H-He ionic mixture. It is investigated in terms of quasi- static and critical charge-charge structure factors [1]. Non- polarizable as well as polarizable and partialy degenerate electron backgrounds are given attention. The low velocity ion slowing down can turn negative in the presence of long wavelength and low frequency hydromodes, signaling a first order critrical demixtion. Such a process is shown to document a superelastic energy transfer from target plasma ions to the incoming and slow ion projectile [2].\\[4pt] [1] D. Leger and C. Deutsch, Phys.Rev. A37, 4916, 4930 (1988)\\[0pt] [2] C. Deutsch, D. Leger and B. Tashev, Laser Part.Beams 29, 121 (2011)   

Low Velocity Ion Stopping in Binary Ionic Mixtures

We investigate the basic features underlying the low ion velocity (Vp) slowing down (LIVSD) in multicomponent and dense target plasmas built of quasi-classical electron fluids neutralizing binary ionic mixtures (BIM)such as deuterium-tritium of current fusion interest,proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam production of warm dense matter (WDM) at Bragg peak conditions [1]. The target plasma is taken in a multicomponent dielectric Fried-Conte formulation. We also focus attention on so-called critical Vp values featuring same LIVSD on target ions and electrons,respectively. BIM including negative hydrogen are also given attention [2].\\[4pt] [1] B. Tashev, F. Baimbetov, C. Deutsch and P. Fromy, PoP 15, 102701 (2008)\\[0pt] [2] B. Tashev, P. Fromy and C. Deutsch, PRSTAB 13, 10130 (2010)   

Transport and Removal experiment of Dust (TReD) for the Dust Particle Controls

The tokamak dust might be hazardous based on the radioactive from tritium or activated metals (e.g. tritium retention), toxic and/or explosive (or chemically reactive) in steam and air conditions. Therefore, controls of dust particle inventory can be treated a critical issue for safe operation of ITER and next step fusion devices. Although the dust removal experiments for fusion reactor had been tried in 1990s, it cannot directly applied to ITER and next step fusion reactors since scale issues does not solved. In this work, one developed the dedicated plasma device for the dust particle transport and removal tests to the level required in ITER or next step fusion reactors ($\sim$1 m dust particle transportation), which is called TReD (Transport and Removal experiments of Dust). The TReD also plan to test the dust particle detectors, such as electrostatic dust detector and capacitance diaphragm microbalance (CDM) used (or will be used) in fusion plasmas. The first experimental results of dust particle transport and removal will be explained along with the design concepts, assembly structure, also collaboration plans, etc.   

Plasma Flow Measurement via Laser-Induced Fluorescence and Mach Probe in Weakly Magnetized Plasmas

Although several un-magnetized Mach probe theories are available, they have not been completely calibrated and should be checked by comparative (or simultaneous) measurement with another diagnostic tools such as laser-induced fluorescence or optical emission spectroscopy. Most of the previous calibrations have been done in the low Mach number (say, less than 0.5), where the existing theories predict the very similar numbers, so that the validity of the calibration is still in doubt. In this work, the plasma flow velocity is measured via MP and laser-induced fluorescence in weakly magnetized Ar plasma in Diversified Plasma Simulator-II (DiPS-II). For meaningful comparison of MP and LIF, One increases the plasma flow velocity up to $0.5C_s$, where $C_s$ is the ion sound velocity. Although magnetic field are applied in plasma, the ion gyro-radius is still less than the probe radius. Hence, the MP results is analyzed by un-magnetized probe theories and these are compared to LIF results.   

Paradoxical behavior of electron fluxes for local EDF at moderate and high pressures in DC positive column plasmas

At moderate and high pressures when the characteristic discharge size L exceeds the electron energy relaxation length le $<$ L, electron distribution function EDF could be found in local approach. This means that terms containing space derivatives and radial field are discarded from a solution to the kinetic equation and the EDF is factorized in the form f(x,w) = F(w)Ne(x), where F is electron energy (w) distribution function EEDF and Ne is electron density. In these pressures, the energy balance of electrons is determined by the energy losses in elastic collisions and EEDF has the form of Druyvesteyn-Davydov distribution. Simulations for DC positive column plasmas revealed that electron fluxes are sensitive to energy dependence of elastic collision cross section. Paradoxical behavior of electron flux in spatial-energy space is presented. Electron flux in the elastic energy region (to the threshold of excitation) can be directed in different ways at different points in the radius (including against the direction of the external electric field).   

Rayleigh-Taylor instability in RPA regime of the ion acceleration by the laser pulse

Dynamics of acceleration of the ion target irradiated by a circularly polarized laser pulse is studied analytically and via particle-in-cell (PIC) simulations. A self consistent analytical model of the target with finite thickness is developed. In this 1-D kinetic model, target parameters are stationary in the center of mass of the system, and electrons are bouncing in the potential well formed by the laser ponderomotive and electrostatic potentials. They are distributed in the direction of acceleration by the Boltzmann law and over velocities by the Maxwell-Juttner law. The laser pulse interacts directly only with electrons in a thin sheath layer, and these electrons transfer the laser pressure to the target ions. In the fluid approximation it is shown that despite the distribution of the density in space, the target is still susceptible to the Rayleigh-Taylor instability [1]. Using PIC simulations we found the growth rate of initially seeded perturbations as a function of their wavenumber for different target parameters and compare it with analytical results. Useful scaling laws between this rate and laser pulse pressure and target parameters are discussed. Also, specially-designed numerical experiments are performed to reveal difference between instabilities of the accelerated target and Rayleigh-Taylor instability.\\[4pt] [1] T.P. Yu, A. Pukhov, G. Shvets, M. Chen, T. H. Ratliff, S. A. Yi, and V. Khudik, Phys. Plasmas, 18, 043110 (2011).   

Polarimeter to measure density and magnetic field of merging plasmas at General Fusion

General Fusion (GF) is currently building a plasma injector for a prototype magnetized target fusion reactor. A second injector is under construction to investigate the merging of two spheromaks. In the near future, a system is to be built to acoustically compress the merged plasma, which is intended to show break-even energy gain. The purpose of merging two spheromaks is to create a hotter, stationary target, which is more suitable for compression. The merged product can take several different forms depending on the relative helicities of the merging spheromaks, such as a new spheromak or a field-reversed configuration. To date, the GF plasma injector has formed and accelerated spheromaks to densities of $10^{15} \rm{cm}^{-3}$ and temperatures of 50eV, which will soon increase respectively to over $10^{16} \rm{cm}^{-3}$ and 100eV. Due to these harsh plasma conditions, it is highly desirable to use non-perturbing diagnostics that do not need to be immersed in the plasma. For these reasons, a three-beam, heterodyne polarimeter is being assembled at GF. Polarimeters take advantage of the Faraday rotation effect, where a magnetized plasma rotates the plane of polarization of a light beam. With multiple probing chords, the profile of the plasma's magnetic field and density can be estimated without perturbing the plasma.   

Importance of plasma-surface interaction to crater plasma mini-wakes and impact generated plasmas on the Moon

Recent progress is reported in understanding two regional plasma processes on the Moon through 2D kinetic simulations including a self-consistent plasma-surface interaction. (1) By direct analogy with the global plasma wake it is thought that crater ``mini-wakes'' form in permanently shadowed craters. Simulations of mini-wake formation in the vicinity of idealized, shadowed lunar topography are presented, and the importance of surface charging and crater shape in modulating the wake structure and particle fluxes to the surface is highlighted. (2) Laboratory experiments have shown that dust-like meteorite analogs are capable of vaporizing a target surface, creating an impact plasma that undergoes an ambipolar expansion process. The same process is thought to occur during meteorite impacts on the surface of the Moon. Preliminary simulations of impact plasma expansion in the vicinity of a lunar-like, charge-collecting surface are presented, and effects of the plasma-surface interaction are discussed.   

Nonlinear waves and inelastic effects in complex plasmas

Complex (dusty) plasmas are mixtures of micron-sized spheres with ion-electron plasmas. These spheres collect ions and electrons and acquire large negative electric charges. Due to collective interaction, they form crystal- or liquid-like structures. These structures can propagate linear and nonlinear waves such as solitons, and exhibit phase transitions. Our experiments were performed in a radio-frequency capacitively coupled gas discharge. Plastic microspheres were introduced into the plasma where they levitated above a powered electrode. A monolayer hexagonal lattice was formed, which was excited by applying electrostatic pulses. A series of experiments were performed in order to study soliton propagation in an inhomogeneous lattice, interaction of two counter-propagating solitons, as well as the influence of deformations on the crystal structure. The experiments were compared with molecular dynamics simulations based on the 5-th order Runge-Kutta solver of the equations of motion.   

Bubbles Formation during Generation of Microscale Discharges in Liquids

Microscale discharges are generated in water electrolyte solutions by the application high voltage short duration pulses. In both positive and negative polarity configurations, voltages of 5kV-10kV and total energies of less than 10 millijoule result in discharges about 10 micrometers in diameter. The discharges are spherical in shape around the electrode tip similar to larger discharges referred in the literature to as primary streamer coronas. Temporally resolved and high intensity light imaging of the discharge indicates the presence of a bubble interface commensurate with the discharge diameter which grows from the sharp electrode. This bubble development is consistent with analytical estimates of several methods of rapid bubble formation including electro- hydraulic cracking, boiling, and electrolysis.   

Plasma Potential Profiles Near a Thin Cylindrical Wire

Although there are many experimental and theoretical works measuring plasma potential profiles near planar boundaries, there is little experimental data on the sheath and presheath of surrounding cylindrical wires. This paper presents experimental measurements of plasma potential profiles in the radial direction, perpendicular to a long (50 cm) and thin diameter (0.5 mm) circular stainless steel wire. Measurements were made using the inflection point in the limit of zero emission technique in an argon plasma in a multi-dipole dc hot filament device. Planar Langmuir probes were used to measure the plasma properties far from the sheath boundary. Sheath and presheath characteristics of the cylindrical geometry were examined for different Debye lengths and energy of the electrons emitted from the filaments.   

Development of a polarization resolved spectroscopic diagnostic for measurements of the magnetic field in the Caltech coaxial magnetized plasma jet experiment

Measurements of the magnetic field strength in current-carrying magnetically confined plasmas are necessary for understanding the underlying physics governing the dynamical behavior. Such a measurement would be particularly useful in the Caltech coaxial magnetized plasma gun, an experiment used for fundamental studies relevant to spheromak formation, astrophysical jet formation/propagation, solar coronal physics, and the general behavior of twisted magnetic flux tubes that intercept a boundary. In order to measure the field strength in the Caltech experiment, a non-perturbing spectroscopic method is being implemented to observe the Zeeman splitting in the emission spectra. The method is based on polarization-resolving spectroscopy of the Zeeman-split $\sigma $ components, a technique previously used in both solar and laboratory plasmas. We have designed and constructed an optical system that can simultaneously detect left- and right-circularly polarized emission with both high throughput and small extinction ratio. The system will be used on the 489.5 nm NII line, chosen because of its simple Zeeman structure and minimal Stark broadening.   

Progress of Rugby Hohlraum Experiments on Omega

The rugby hohlraum concept is predicted to enable better coupling and higher gains in the indirect drive approach to ignition [1-2]. A collaborative experimental program is currently pursued on OMEGA to test this concept in preparation for future megajoule-scale ignition designs [3]. A direct comparison of gas-filled rugby hohlraums with classical cylinders was recently performed, showing a significant (up to $\sim $40{\%}) observed x-ray drive enhancement and neutron yields that are consistently higher in the rugby case. This work extends and confirms our previous findings in empty rugby hohlraums [4-6]. [1] M. VandenBoomgaerde et al., Phys. Rev. Letters 99, 065004 (2007) [2] P. Amendt et al., Phys. Plasmas 14, 056312 (2007). [3] S. Laffite and P. Loiseau, Phys. Plasmas 17, 102704 (2010). [4] F. Philippe et al., Phys. Rev. Lett. 104, 035004 (2010). [5] H. Robey et al., Phys. Plasmas 17, 056313 (2010). [6] C.K. Li et al., Science 327, 1231 (2010).   

PETAL, a Multi PETAWATT Laser on the LMJ: Integration and Radiation Protection Issues

In 2015, PETAL, a multi-Petawatt laser beam, will be operated on the LMJ facility at the CEA/ Cesta research center. In addition to the LMJ nanosecond beams, it will provide an ultra-high-power short-pulse (500 fs to 10 ps), with a high-energy beam (few kJ compressed energy). To assess the potential exposure induced by PETAL experiments, three conservative source terms were evaluated. 1/ High energy photons (anisotropic) and photo-neutrons generated in thick and dense targets. 2/ Emission of protons driven by hot electrons in thin targets (directive emission) 3/ Isotropic production of fusion neutrons. For each source term, particle transport and material activation were estimated within the LMJ using the Monte-Carlo code MCNP-X. The final presentation will include the most recent information about on site commissioning, global architecture and radiation protection issues. This work is being performed under the auspices of the Conseil Regional d'Aquitaine, the French Ministry of Research and of the European Union, and with the technical supports of the Institut Lasers et Plasmas.   

Atomic force microscope measurement of a polyethyleneterephthalate surface modified by an atmospheric pressure air plasma source

An atmospheric pressure air plasma source was generated through dielectric barrier discharge (DBD). The modification of polyethyleneterephthalate (PET) surfaces by this plasma was investigated. PET strips were exposed to the plasma at the exit of the plasma source. Water contact angles were measured for surfaces modified with different processing parameters. Atomic force microscope (AFM) measurements on an unmodified PET surface and a modified PET surface showed the formation of a rougher surface by the plasma treatment. The PET surface profile change was due to an etching effect from the air plasma.   

Numerical Simulation of Colliding Ion Acoustic Solitons

The ion acoustic wave dispersion relation $\omega = k C_s $ we are familiar with, is in the long wave length limit. Inclusion of short wave-length (Debye length) scale through Poisson equation gives rise to the Korteweg de Vries (KdV) equation. We simulate propagation of solitary waves by solving the KdV equation in one dimensional and two dimensional planer geometries (Kadomtsev$-$Petviashvili equation).\footnote{ B.B.Kadomtsev, Doklady Akademii Nauk SSSR {\bf 192}, 753 (1970).}$^{,}$\footnote{Y.Nishida and T.Nagasawa, Phys. Rev. Lett. {\bf 42}, 379 (1979).} On the other hand, a different nonlinear term, ponderomotive force gives rise to Langmuir solitons by the interaction between high frequency Langmuir waves and low frequency ion acoustic waves.\footnote{V.E.Zhaharov, Sov. Phys. JETP {\bf 35}, 908 (1972).} We discuss our studies on 1d-1v Vlasov-Poisson system employing the splitting scheme\footnote{C.Z.Cheng and G.Knorr, J. Comput. Phys. {\bf 22}, 330 (1976).} (by the method of characteristics).   

Sawtooth Stabilization and Onset of Alfvenic Instabilities

Tokamak sawtooth instabilities can be stabilized by high energy particles as a consequence of conservation of the third adiabatic invariant.\footnote{D.J. Campbell {\it et al.}, Phys. Rev. Lett. {\bf 60}, 2148 (1988); F.Porcelli, Plasma Phys. Controlled Fusion {\bf 33}, 1601 (1991).} On the other hand, termination of the stabilized period is reported due to the onset of Alfvenic instabilities (and thus the absence of the stabilizing mechanism).\footnote{S.Bernabei {\it et al.}, Phys. Rev. Lett. {\bf 84}, 1212 (2000); steeping of the pressure gradient (of high energy particle components) triggers Alfvenic instabilities.} In this work, employing a kinetic-fluid model,\footnote{C.Z.Cheng and J.R.Johnson, J.Geophys. Res. {\bf 104}, 413 (1999).} the interaction of m=1 resistive kink mode and high energy particles is investigated. The onset of Alfvenic instabilities is examined as a function of the inversion radius location.   

A Stark broadening method to determine the electron temperature and density of the decay plasma in a LADPP 13.5 nm EUV source

In order to investigate the plasma expansion behaviors and the electrical recovery process after the maximum implosion in our tin fueled laser assisted discharge produced plasma (LADPP) 13.5 nm EUV source, we develop and evaluate a simple spectroscopic method to determine the electron temperature Te and density ne simultaneously using Stark broadenings of two Sn II isolated lines spontaneously emitted from the plasma. Spatial-resolved evolutions of Te and ne of the expansion plasma during 50-900 ns after the maximum implosion is obtained using this modified Stark broadening method. The expansion velocity of the electrons is estimated to be $\sim $1.2 $\times$ 104 ms$^{-1}$, and t he decay time constant of ne is measured to be 183$\pm$24 ns. Based on the theories of the plasma adiabatic expansion and the electron-impact ionization, the maximum repetition rate of our LADPP EUV source is estimated to be 16 kHz.   

Conceptual study of fusion-driven transmutation reactor with ITER physics and engineering constraints

A conceptual study of fusion-driven transmutation reactor was performed based on ITER physics and engineering constraints. A compact reactor concept is desirable from an economic viewpoint. For the optimal design of a reactor, a radial build of reactor components has to be determined by considering the plasma physics and engineering constraints which inter-relate various reactor components. In a transmutation reactor, design of blanket and shield play a key role in determining the size of a reactor; the blanket should produce enough tritium for tritium self-sufficiency, the transmutation rate of waste has to be maximized, and the shield should provide sufficient protection for the superconducting toroidal field (TF) coil. To determine the radial build of the blanket and the shield, not only a radiation transport analysis but also a burnup calculation were coupled with the system analysis and it allowed the self-consistent determination of the design parameters of a transmutation reactor. .   

Action-Angle variables defined on island chains

Straight-field-line coordinates are a particular case of action-angle variables, which, in standard Hamiltonian mechanics, are defined only for integrable systems. In order to describe 3-D magnetic field systems, a generalization of this concept was proposed in [1] that unified the concepts of ghost surfaces (almost-invariant tori defined by an action-gradient flow between O and X points of an island chain) and quadratic-flux-minimizing surfaces (QFMin tori, which minimize a weighted mean of the square of the normal component of \textbf{B}). This was based on a simple canonical transformation, generated by a change of variable $\theta = \theta(\Theta)$, where $\theta$ is the old poloidal angle and $\Theta$ a new one giving straight pseudo-orbits (approximate field lines [2]). This was illustrated using a perturbative construction of the transformation. Investigations of this idea using the Standard Map [3], with the analog of the same constraint as used implicitly in [1] to make $\Theta$ unique, show this constraint is not optimal in that $\theta(\Theta)$ ceases to be monotone beyond a certain nonlinearity.\\ \noindent[1] R.L. Dewar, S.R. Hudson and A.M. Gibson JPFR (2010) http://arxiv.org/abs/1001.0483; [2] R.L. Dewar, S.R. Hudson and A.M. Gibson CNSNS in press (2011) DOI:10.1016/j.cnsns.2011.04.022; [3] R.L. Dewar and A.B. Khorev, Physica D \textbf{85}, 66 (1995)   

Gyrokinetic simulations of toroidal angular momentum transport in electrostatic drift-wave turbulence

Comparative studies of toroidal angular momentum transport in collisionless trapped electron mode (CTEM) and ion temperature gradient (ITG) mode turbulence with kinetic electrons are presented. Diffusive, convective and residual components of momentum flux are separated. Significant intrinsic rotation is observed with the direction opposite for the CTEM and ITG turbulence. The perturbed momentum profile strongly correlates with the radial profile of self generated zonal flow. Momentum convective flux is separated into momentum pinch and particle convective parts. We demonstrate that outward particle flux can compete with inward momentum pinch, leading to the possible reversal of the direction of momentum convective flux. Parametric studies of the momentum pinch show no explicit dependence of pinch velocity on plasma temperature inhomogeneity scale length, but strong dependence on the density gradient scale length, for a given turbulence regime. The intrinsic Prandtl number, describing momentum diffusivity, is calculated for CTEM and ITG turbulence.   

Effects of Na+ and He+ pickup ions on the solar wind - Moon interaction: 3D hybrid modeling

The hybrid kinetic model used here supports comprehensive simulation of the interaction between different spatial and energetic elements for the Moon, solar wind, and Earth magnetosphere in the Earth-Moon system. Computational capabilities exist for MHD, kinetic, hybrid, drift kinetic, electrostatic and full kinetic modeling of the Lunar plasma environment. However, observations show the existence of several species of the neutrals and pickup ions like Na and He. The solar wind parameters are chosen for our work from ARTEMIS observations. The hybrid kinetic model allows us to take into account finite gyroradius effects of pickup ions and to estimate correctly the ions velocity distribution and the fluxes along the magnetic field. We will discuss the results of modeling, including separate species of pickup ions, (Na+, and He+) and their combinations. Modeling shows the formation of the asymmetric Mach cone, pickup ion tails, and another type of lunar-solar wind interaction.   

Edge Plasma Structure with Rotating Resonant Magnetic Perturbations at TEXTOR

Rotating Resonant Magnetic Perturbations impose a characteristic modulation to the electron density and temperature in the TEXTOR plasma edge ($r/a>0.9$). The modulation matches the position of the magnetic topology modeled in vacuum approximation for low relative rotation of $f_{rel}=-0.2\,kHz$ between RMP field and toroidal plasma rotation. With increasing relative rotation ($f_{rel}=1.8\,kHz$), the plasma structure at the outermost rational flux surface is shifted by $\pi/2$ in counter-$B_t$ direction due to internal plasma response. The shift is correlated to a smaller displacement of the plasma structure in front of the RMP coils of $0.1\pi$. This indicates a competition between the near-field of the RMP coils and the net magnetic field at the rational flux surface.   

Design of High-Performance Symmetry Capsule Implosions

Symmetry capsules (symcaps) are surrogate targets used in the National Ignition Facility (NIF) that are easier to field than regular DT capsules. Subject to the same implosion physics as their DT counterparts, symcaps have yet to achieve as high compression ratios or implosion velocities. A high performance symcap would facilitate experimental characterization of hohlraum drive asymmetry and implosion velocity. This work proposes such a symcap design that does not depart significantly from current DT capsule and radiation drive configurations. The increased capsule compression and implosion velocity are achieved by altering the shock timing of the driver pulse and reducing the density of the interior D-$^3$He gas. We characterize capsule performance through numerical simulations conducted with the production radiation-hydrodynamics code \textsc{hydra} and a simplified analytic model of spherical rocket drive.   

Shear flow instability observed in highly dissipative complex plasma

Complex Plasma is perfectly suited to study phenomena in fluid dynamics at the kinetic level of single particles. In this presentation its special properties allow the study of a shear flow instability of Rayleigh-Taylor type. The flow appears at the interface between two 3-D complex plasma clouds. The first cloud forms a toroidal vortex with poloidal flow and the second is stable, trapped in a stagnation zone. Experiments are performed in a parallel plate symmetrically driven rf discharge in argon. Gravity is partially compensated through a thermophoretic force. The microparticles (1.28 $\mu $m in diameter) are distributed all over the plasma volume and form a 3-D distribution. The flow is studied in 2-D at the kinetic level by resolving the trajectories of individual microparticles with high time and high spatial resolution. Hydrodynamic quantities such as flow velocity, vorticity and enstrophy density are determined and show that the two stream interface between flow and stagnation zone breaks up into a well developed multi-stream network due to Rayleigh-Taylor type perturbations. The origin of the observed instability is addressed theoretically.   

Gyrokinetic simulation of residual turbulence in transport barriers

One of the ultimate aims for gyrokinetic simulation is to describe the formation and evolution of transport barriers. An important step in that direction is the study of the residual turbulence in established barriers - a challenging task in itself, given that a wide range of spatio-temporal scales can be involved. In the present work, we employ the physically comprehensive, nonlocal gyrokinetic turbulence code GENE to study turbulence in both core and edge transport barriers. First, we apply GENE to a set of discharges in the TCV tokamak which exhibit electron ITBs. Nonlinear gyrokinetic simulations are used to examine the influence of a varying current profile on the strength of the barrier. For each case, the transport spectra reveal how much transport (for each channel) is done in the low-k, medium-k, and high-k regimes, respectively. The role of ETG turbulence is discussed. Second, we explore the role of ETG turbulence in a typical ASDEX Upgrade H-mode discharge. Numerical convergence is carefully examined, and new insights on the characteristics of ETG turbulence in the edge will be discussed, focusing particularly on the role of streamers, which had been found to be a necessary ingredient for experimentally relevant ETG transport in core plasmas. The radial dependence of the resulting electron heat diffusivity is also examined and a simple ETG model is presented which can be used in future edge modeling efforts.   

Finite-Temperature Orbital-free Density Functional Calculations for Warm Dense Lithium

Warm dense matter (WDM) defines the region between condensed matter and plasmas. This regime is characterized by high pressure and elevated temperature. The standard theoretical and computational approach, which is a combination of finite-temperature Kohn-Sham density functional theory (KS-DFT) and classical molecular dynamics, becomes computationally very expensive at elevated temperature. The orbital-free (OF) version of DFT is a less expensive alternative to the orbital-based methods. We have implemented finite-temperature Thomas-Fermi, second-order gradient expansion, and new generalized gradient approximation free energy functionals in an OF-DFT code. These non-interacting free-energy functionals are used in combination with zero-temperature exchange-correlation in local density approximation. Self-consistent OF-DFT calculations with these functionals are performed for lithium for the range of densities $\rho_{\rm Li}=0.5-10$ g/cm$^3$ and temperatures between 100 K and 100 kK. OF-DFT results are compared to the standard Kohn-Sham data. Local pseudopotentials used on OFDFT calculations are validated by comparison between Kohn-Sham results obtained with standard non-local pseudopotentials and with the same local pseudopotentials.   

Guiding center orbit following calculation of $\alpha$ particles in tokamaks

Guiding center orbit following code is developed to study $\alpha$ particle transport in tokamak plasmas. The equation of motion is derived from guiding center Lagrangian\footnote{R.G.Littlejohn, J. Plasma Phys. {\bf 29}, 111 (1983).} in a flux coordinate system incorporating electromagnetic perturbations. As an preliminary study, toroidal ripple induced transport\footnote{K. Tani, M.Azumi, H.Kishimoto and S.Tamura, J. Phys. Soc. Japan {\bf 50}, 1726 (1981).} is investigated.