Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session YP8: Poster Session IX: Supplemental; Post-Deadline |
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Room: Hall BC |
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YP8.00001: SUPPLEMENTAL |
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YP8.00002: Probe measurements of penning electron spectra in the afterglow of nonlocal helium microplasma Anatoly Kudryavtsev, Denis Belskiy, Sergey Gutsev, Nikolay Kosykh, Anton Kryukov Method PLES [Blagoev A.B., Kolokolov, N.B., Kudryavtsev. Physica Scripta, 1994, v.50, p.371] is based on identification of atoms and molecules of impurities M by selective registration of groups of fast electrons e(f) created in Penning ionization: He(m) + M $\rightarrow$ He +M+ + e(f). The electron energy spectrum e(f) contains discrete peaks corresponding to the difference between the energy 19.8 eV of metastable helium atoms He(m) and the ionization energies Ei of impurities M. Since the ionization potential \textit{Ei} of each type of atom or molecule is a well-known, it is possible to identify the atoms or molecules M of the unknown impurity by their ionization potential \textit{Ei.} Probe registration of the energy spectra of penning electrons is carried out in the nonlocal afterglow plasma of pulsed microdischarge in helium and its mixtures with argon, krypton and air. In helium, the non-local plasma condition corresponds to $p \times L < 5$ Torr $\times$ cm, where $p$ is the gas pressure and $L$ is the plasma volume size. It is demonstrated that the obtained maxima appear at the characteristic energies corresponding exactly to the expected maxima for penning electrons of the known gas impurities used. [Preview Abstract] |
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YP8.00003: Numerical Studies of Hydrodynamic Instabilities Using Intense Ion Beams N.A. Tahir, A. Shutov, A.R. Piriz, C. Deutsch, Th. Stoehlker Intense particle beams can generate extremely high pressures in solid materials. Numerical simulations are presented to propose an experiments to study Richtmyer-Meshkov instability in the linear and non-linear regimes in solids as well as ideal fluids using intense uranium beams that will be generated at the FAIR facility at Darmstadt. These experiments form the basics of the experimental program, the HEDgeHOB collaboration, to study High Energy Density Physics problems at the FAIR facility in future. [Preview Abstract] |
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YP8.00004: Fully Implicit Energy and Charge Conserving, Discretely Consistent Moment System for Vlasov-Ampere System William Taitano, Dana Knoll, Luis Chacon, Guangye Chen, Bill Daughton [1][2] pioneered the implicit moment method (IMM) for kinetic plasma simulation. In the classic IMM approach, upon convergence of the discrete kinetic and fluid moment system within a timestep, a discretization truncation inconsistency between the two systems can exist. Additionally, when using the total stress tensor from the kinetic system as closure for the moment system, the stiff hyperbolic waves are not effectively decoupled from the kinetic system and accelerated in the moment system. In this presentation, we advance the original IMM approach by 1) addressing the discrete truncation consistency between the kinetic and moment system, and 2) improve the IMM approach by introducing the idea of density normalized stress tensor to efficiently isolate and implicitly step over the stiff hyperbolic isothermal wave in the moment system. We will present the significance of these improvements on the IMM method by discussing energy conservation and nonlinear convergence rate of the method for a multiscale two species ion acoustic shockwave problem. Additional results of the method accelerated via Anderson acceleration will be presented. \\[4pt][1] R.J. Mason, J. Comp. Phys., 1981. [2] J.U. Brackbill et al. J. Comp. Phys., 1982. [3] W.T. Taitano et al. SISC, 2012 in review. [Preview Abstract] |
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YP8.00005: 3-D electromagnetic PIC simulations of an electron collecting probe in an ExB drifting plasma Jonathon Heinrich, David Cooke Positive probe/plasma systems are inherently unstable with complicated dynamics that are not well described by standard probe theories, particularly in ExB drifting plasmas. While work has been done to understand ion collecting probes in ExB drifting plasmas, limited work has been done to understand their positively biased counterpart. Here, we have conducted a series of electromagnetic particle-in-cell simulations of a positive probe in an ExB drifting plasma that shed light on two fundamental problems: current closure in magnetized flowing plasmas and sheath dynamics of a positive probe in an ExB drifting plasma. We report on the results, which indicate the degree of legitimacy in current closure through Alfven waves, whistler waves, and diffusion (when magnetic field and ExB drift effects are important). Additionally, we report on sheath dynamics of a positive probe in an ExB drifting plasma, which were clearly resolved and indicated electron heating processes that include a quasi-trapped mode. [Preview Abstract] |
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YP8.00006: Improved basis set for low frequency plasma waves Paul Bellan It is shown that the low frequency plasma wave equation [Stringer, Plasma Physics \textbf{5}, 89(1963)] can be obtained much more directly than by the previously used method of solving for the determinant of a matrix involving the three wave electric field components $\tilde{E}_{x},\tilde{E}_{y},\tilde{E}_{z}.$ The more direct method uses a 2D wave current density vector space that is precisely equivalent to the previously used 3D electric field vector space. Unlike $\mathbf{\tilde{E}}$, the current density $\mathbf{\tilde{J}}$ is restricted by quasi-neutrality to a 2D vector space. Comparison with previously obtained dispersion relations is provided. An exact analytic method is presented for obtaining the three roots of the cubic dispersion relation. The commonly used kinetic Alfv\'{e}n dispersion is shown to be valid only for near-perpendicular propagation in a low $\beta $ plasma. It is shown that coupling between Alfv\'{e}n and fast modes vanishes when $\omega ^{2}=k^{2}c_{s}^{2}$ so that the Alfv\'{e}n mode reverts to its cold form even if $v_{A} < v_{Te}$. A method is prescribed by which measurement of $\mathbf{\tilde{J}}$ removes the space-time ambiguity previously believed to be an unavoidable shortcoming of single-spacecraft frequency measurements. [Preview Abstract] |
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YP8.00007: Kinetic simulation of Alfv\'{e}nic instabilities in tokamaks Y. Nishimura, C.Z. Cheng Toroidicity induced Alfv\'{e}n eigenmode in a tokamak geometry is studied by numerical simulation including both the high energy particles and bulk kinetic plasmas. To see the interaction between the high energy and the bulk (incorporate ions and electrons to statistically reliable level), effective parallelization is the key. Computational procedure of the simulation is discussed. [Preview Abstract] |
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YP8.00008: Symmetry of Momentum Conservation in Gyrokinetics Bruce Scott Gyrokinetic field theory is set up in terms of a Lagrangian with canonical structure -- dependent field variables appear only in the time component. The gyrokinetic and associated field equations are the resulting Euler-Lagrange equations for the gyrocenter coordinate positions and field amplitudes. Canonical structure leaves the symplectic part time-independent and axisymmetric, from which energy and canonical momentum conservation follow. Conversion from canonical to plasma momentum uses the charge conservation equation which follows from continuity. The specific role of the time-dependent polarisation current is emphasised. It is shown that the contributions in the zonal toroidal momentum transport equation due to higher-order field components in the Hamiltonian can be put into the same symmetric structure as the lowest-order piece. Hence arguments about symmetry and cancellation should be applied equally to all orders, not just the lowest. Some measurements of the PDF of these terms in computations are given. [Preview Abstract] |
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YP8.00009: Finite Time Lyapunov Exponents for magnetically confined plasmas Linda Sugiyama, Harinarayan Krishnan Finite Time Lyapunov Exponents (FTLEs) are applied for the first time to magnetically confined plasmas. The FTLE measures the local divergence or convergence of $n$-dimensional vector fields. Time-dependent FTLEs are directly related to Lagrangian Coherent Structures, which form the underlying structure of turbulent flows. Modern FTLE methods, developed over the past decade, are evolving rapidly and leading to new practical and theoretical insights into turbulent fluid dynamics. In contrast to fluids, an MHD plasma has two vector fields, the magnetic field and the plasma flow. Accurate methods for computing and visualizing FTLEs for the MHD fields have been developed, based on the VisIt visualization package. They are applied to time slices of a large sawtooth crash in a toroidal plasma, computed by the M3D extended MHD code. The plasma structures for both $\mathbf{B}$ and $\mathbf{v}$ have unexpected properties that are not brought out by conventional analyses. The sawtooth crash is also found to have well-organized ``flow'' structures in $\mathbf{v}\pm\mathbf{B}$. The FTLE appears to be a sensitive diagnostic for the structure of stochastic magnetic fields. The methods are not restricted to MHD, since they apply to almost any vector field. [Preview Abstract] |
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YP8.00010: Magnetic fusion: progress $\to$ stagnation $\to$ degradation Leonid Zakharov ``The theory of the failure of magnetic fusion,'' created in 2004 and presented to APS-2007 introduced the notion of the ``difficult'' and ``complicated'' stages of the program and described them details. At the first phase the emerging fusion science was created under strong leadership. Progress was visible on year to year basis, and the program was easy to manage. The complicated phase started in the late 1980s, when the plasma physics appeared to be incapable to implement the mission of ITER to test nuclear components of a fusion reactor. Then, the failure of TFTR (PPPL, USA) and JET (Culham, UK) in the mid 1990 to demonstrate $Q_{DT}=1$ and the blindness of their leaders to already visible means to resolve the problem, were a clear indication of an irreversible stagnation. In fact, right after 2007, it became clear that in the case of a large system of human ``particles'' (scientists) two phases have a continuation. The internal degrees of freedom, otherwise protected from external perturbations by a strong dedication to the scientific method, are now eroding and collapsing. The loss of science in addressing confinement, stability, power extraction, fueling, stationary regimes issues makes the current program irrelevant to fusion energy. A fresh approach should be taken. [Preview Abstract] |
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YP8.00011: Interaction of transport barriers with turbulent bursts in the tokamak edge K. Bodi, G. Ciraolo, E. Floriani, Ph. Ghendrih, Y. Sarazin The transport barrier in H-mode is usually considered to be a quiescent region, where turbulence effects are negligible. However, this region experiences intermittent interactions with the turbulent bursts, like blobs, which may breach the barrier and reach the scrape-off layer, while affecting the strength and width of the barrier. Fluctuations that penetrate through such transport barriers feed the turbulence in the SOL. Hence, interactions of transport barriers and convecting structures need to be understood. We study the interactions of the transport barrier with intermittent convecting structures, originating from edge turbulence in the 2-D fluid framework, using the nonlinear code TOKAM-2D. In the simulations we impose transport barriers through a biasing potential, characterized by its magnitude and the extent of its radial profile. We present the results of our investigation of the effect of the width of the barrier on the level of reduction of turbulent fluctuations inside the barrier. [Preview Abstract] |
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YP8.00012: Gyrokinetic finite-size scaling towards ITER Tobias Goerler, Daniel Told, Frank Jenko, Joerg Hobirk, Paola Mantica, Michael Barnes Though gyrokinetic simulations have become more and more mature and experimentally relevant, the majority of studies has been carried out by means of flux-tube computations, employing maximum physics but restricting to a minimal simulation volume in order to keep the computation time low, and consequently neglecting finite-size ($\rho^*$) effects. Global simulations, on the other hand, have often been employing reduced physics models like adiabatic electrons, electrostatic fluctuations, simplified magnetic equilibria, or collisionless dynamics. In this contribution, comprehensive global computations of actual ASDEX Upgrade and JET discharges [P.~Mantica et al., Phys.~Rev.~Lett.~102, 175002 (2009)] as well as ITER-like cases with the plasma turbulence code GENE are presented and compared to accompanying local simulations. This way it becomes possible to study finite-size effects in non-idealized systems and address the important question on the validity of the local approximation and the actual transport scaling in a more detailed manner. These investigations may be complemented by first results of simulations coupling the transport solver TRINITY [M.~Barnes et al., Phys.~Plasmas 17, 056109 (2010)] with the global GENE version, thus addressing long-time scale profile evolution. [Preview Abstract] |
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YP8.00013: Equilibrium and Transport in Strongly Coupled and Magnetized Plasmas Claude Deutsch, Hrachya B. Nersisyan, Guenter Zwicknagel Ultra-Cold plasmas obtained by ionization of atomic Rydberg states are qualified as classical and strongly coupled electron fluid.They are shown to share several common trends with ultra-cold electron flows used for ion beam cooling.They exhibit specific stopping behavior to charged particle beams,which may be used for diagnostics purposes [1]. Ultra-Cold plasmas are easily strongly magnetized.Then,one expects a strongly anisotropic behavior of low ion velocity slowing down when target electron cyclotron radius turns smaller than corresponding Debye length. \\[4pt] [1] C. Deutsch, H.B. Nersisyan and G. Zwicknagel, AIP Conf. Proc. 1421, 3-20[2012] [Preview Abstract] |
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YP8.00014: Electromagnetic analyses for stray fields due to gaps and ports on the shell of KTX W. You, W. Mao, C. Li, M. Tan, Tao Lan, Jinlin Xie, Adi Liu, Hong Li, Wandong Liu, Weixing Ding, C.J. Xiao In KTX reversed field pinch, two poloidal gaps and one toloidal gap on the shell are needed to allow the penetration of poloidal and toroidal fields into the shell. A number of ports on the shell are also needed for different diagnostics. The 3D finite element method was used to analyze the stray fields. By simulation, the eddy current and magnetic field are calculated and the electromagnetic force on the shell is estimated as well. In addition, three different methods to reduce the stray fields are presented and the difference among these methods is discussed. [Preview Abstract] |
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YP8.00015: Laboratory astrophysical collisionless shock experiments Hye-Sook Park, N. Kugland, J. Ross, B. Remington, C. Plechaty, D. Ryutov, A. Spitkovsky, G. Gregori, J. Meinecke, Y. Sakawa, T. Morita, G. Fiksel, M. Koenig, M. Grosskopf, R. Presura Astrophysical ``collisionless'' shocks form via plasma instabilities and self-generated magnetic fields. Laboratory experiments at large laser facilities can achieve the conditions necessary for the formation of collisionless shocks, and will provide a unique avenue for studying the nonlinear physics of shock waves. We are performing a series of experiments at the Omega and Omega-EP lasers in Rochester, NY, where collisionless shock conditions will be generated by the two high-speed plasma flows resulting from laser ablation of solid targets using 10kJ to 20 kJ of laser energy. The experiments will aim to answer several questions of relevance to collisionless shock physics: the importance of the electromagnetic filamentation (Weibel) instability in shock formation, the self-generation of magnetic fields in shock collisions, the influence of external magnetic fields on shock formation, and the signatures of particle acceleration in shocks. This paper will present simulations of our experimental results [1]. Our plan for experiments on the National Ignition Facility in Livermore, CA, using up to 1.8 MJ of laser energy will also be presented. \\[4pt] [1] H. S. Park et al., High Energy Density Physics, \textbf{8}, 38 (2012). [Preview Abstract] |
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YP8.00016: HYDRA Simulations for Collisionless Shock Experiments to be Performed on NIF Chris Plechaty, Nathan Kugland, Hye-Sook Park, Dmitri Ryutov, Radu Presura, Steven Ross, Bruce Remington Collisionless shocks are ubiquitous in the universe, and occur when the thickness of the shock is much smaller than the Coulomb collision mean free path. In astrophysical systems, collisionless shocks lead to the generation of magnetic fields, which are thought to play an important role in several different phenomena, such as particle acceleration, and the structuring of supernova remnants. The development and evolution of these self-generated magnetic fields is not entirely understood. To investigate the microphysics which plays a role in collisionless shock formation and magnetic field generation in the laboratory, experiments will be performed at the National Ignition Facility (NIF). In these experiments, two opposing polyethylene (CH$_{2})$ targets will be each irradiated with $\sim $ 10$^{16}$ W/cm$^{2}$ to produce counter-streaming flows. In preparation for these experiments, in this work we model the plasma flow in the context of radiation hydrodynamics, by employing the Arbitrary Lagrange-Eulerian (ALE) radiation hydrodynamics code HYDRA (Marinak 2001). References: M. M. Marinak, et al., Physics of Plasmas \textbf{8}, 2275 (2001). [Preview Abstract] |
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YP8.00017: Transient fields produced by a cylindrical electron beam flowing through a plasma Marie-Christine Firpo Fast ignition schemes (FIS) for inertial confinement fusion should involve in their final stage the interaction of an ignition beam composed of MeV electrons laser generated at the critical density surface with a dense plasma target. In this study, the out-of-equilibrium situation in which an initially sharp-edged cylindrical electron beam, that could e.g. model electrons flowing within a wire [1], is injected into a plasma is considered. A detailed computation of the subsequently produced magnetic field is presented [2]. The control parameter of the problem is shown to be the ratio of the beam radius to the electron skin depth. Two alternative ways to address analytically the problem are considered: one uses the usual Laplace transform approach, the other one involves Riemann's method in which causality conditions manifest through some integrals of triple products of Bessel functions.\\[4pt] [1] J.S. Green et al., \textit{Surface heating of wire plasmas using laser-irradiated cone geometries}, Nature Physics \textbf{3}, 853--856 (2007).\\[0pt] [2] M.-C. Firpo, http://hal.archives-ouvertes.fr/hal-00695629, to be published (2012). [Preview Abstract] |
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YP8.00018: The Effect of Non-Uniform and Finite Plasma on the Wakefield Amplitude in PWFA Yun Fang, Patric Muggli, Warren Mori In the plasma wakefield experiment performed at ATF (Accelerator Test Facility) of BNL (Brookhaven National Laboratory), the plasma is generated from a capillary discharge that is $2~cm$ long with a radius of $500~um$. The plasma density is non-uniform along the finite radius, and it has a certain density profile, e.g. cosine or parabolic profile. We study through simulation how this non-uniform and finite plasma may affect the wakefield amplitude and period driven by short electron bunches, and hence also the energy gain and loss of the drive and trailing bunch. This study is also important to understand the PWFA experiments at the Stanford Linear Accelerator Center (SLAC) with electron bunches and at the European Organization for Nuclear Research (CERN) with self-modulated proton bunches where laser-ionized plasma with radius on the order of the bunch radius or plasma skin depth will be used. The simulation are performed with particle-in-cell code OSIRIS, developed by UCLA and IST. [Preview Abstract] |
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YP8.00019: Effects of Ionization, Thermal Transport, and Radiation on Scaling Performance for Peak Pressure in Imploding Plasma Liners Formed by Converging Jets Milos Stanic, Jason Cassibry, Scott Hsu This paper is an extension of work done by (Cassibry et.al., in preparation) who performed similar research using Smoothed Particle Hydrodynamics Code (SPHC) with an ideal gas equation of state model, neglecting electron-thermal conduction, radiation conduction and radiation losses (in cases of optically thin plasma). SPHC has been modified to use a tabular equation of state, accounting for ionization effects and to include the mentioned thermal transport models. Series of simulations have been carried out and the results were analyzed in terms of recognizing the scaling laws for peak pressure and dwell time. Comparison with the previous work of (Cassibry et.al., in preparation) has also been carried out in an attempt to isolate and recognize the effects of ionization and thermal transport models. The work has been done in support of the Plasma Liner Experiment (PLX), which is a multi-institutional project working on validation of the imploding plasma liner concept for reaching High Energy Density (HEDP) regimes and a possible stand-off solution for Plasma Jet driven Magneto-Inertial Fusion (PJMIF). [Preview Abstract] |
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YP8.00020: PIC Modeling of Preplasma Effect on Fast Electron Generation and Transport in Cone-Wire Target R. Mishra, T. Yabuuchi, B. Qiao, M.S. Wei, H. Sawada, Y. Sentoku, R. Stephens, H. Mclean, P. Patel, F. Beg Collisional PIC simulations, using PICLS, are used to model an OMEGA EPexperiment\footnote{T Yabuuchi \textit{et al}, ICOPS 2010.} with cone-wire targets where fast electron energy coupling through a Au cone into a Cu wire was found to be significantly reduced ($\sim $7x) compared to Titan results with identical targets but 50x less energy in prepulse. Simulations with two different scale-lengths (L=3 {\&}15 $\mu $m) preplasma demonstratesd that a larger scale pre-plasma significantly reduces the energy coupling from heating laser to the wire due to larger offset distance of critical density surface and also wider divergence of electrons. Using simulation electron's phase information near source, such as propagation angle and offset distance of source from Wire, a reduction factor in electron flux reaching the wire for L=3 {\&}15 $\mu $m is estimated; which is consistent with flux arrived in the Wire. This factor is further used using realistic large preplasma and offset distance for EP experiment reproduces the experimentally observed energy coupling reduction. In addition, cone wall effect on the energy coupling to the wire is also investigated by comparing simulation in planar and cone geometries for these two preplasma scales. [Preview Abstract] |
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YP8.00021: ABSTRACT WITHDRAWN |
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YP8.00022: EM Dependence on Energy Transfer and Turbulence in Hypersonic and Laser-Induced Plasmas K.M. Williams, L.E. Johnson, A.B. Alexander, C. Akpovo, J. Martinez, J. Titus It has been previously reported that hypersonic weakly ionized Argon and Krypton plasmas created by electric discharge can display Stark and Zeeman profiles that are self-induced. Now evidence of the same Stark and Zeeman profiles are seen in laser induced plasmas as well. While the arc driven plasmas and laser induced plasmas are different systems, both exhibit a commonality with turbulent signatures in spectral profiles. Complexity analysis suggests that the internal plasma dynamics that contribute to the Stark and Zeeman profiles exhibit a lower complexity than profiles that are not Stark and Zeeman lines. Additionally, data also indicated a relationship between the frequency of the Stark and Zeeman and the energy transfer rate in the respective plasmas. [Preview Abstract] |
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YP8.00023: Oxygen Profile Evolution in NIF GDP Ablator Capsules H. Huang, D.M. Haas, J.J. Wu, R.B. Stephens, K.A. Moreno, A. Nikroo, J.D. Salmonson, S.W. Haan, M. Stadermann, S.D. Bhandarkar CH capsules, produced in Glow Discharge Plasma (GDP) coating, pick up oxygen continuously and irreversibly during storage. The added \hbox{x-ray} opacity from this oxygen affects the shock velocity during target implosion, requiring compensation in the shock timing. We developed a radiography technique that non-destructively characterizes the oxygen profile and have used it to track the evolution of the oxygen profiles in storage. Modified storage protocols have reduced the amount of pickup, and our database allows anticipation of the oxygen profile at shot time. The impact on target implosion will be discussed. [Preview Abstract] |
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YP8.00024: Simulation Analysis of Laser-driven Ion Acceleration Experiments with Defocussed Pulses Alex Robinson Recently Brenner et al. (Brenner et al. LPB (2011)) reported on a series of experimental observations of proton emission from 25nm CH foils irradiated by defocussed 40fs 0.65J 800nm laser pulses. Even with 60$\mu$m diameter spots and 10$^{16}$--10$^{17}$Wcm$^{-2}$ intensities proton spectra that extended up to 2~MeV were observed. We have carried out PIC simulations in order to better understand these observations. Here we we will report on the extent to which these simulations have elucidated the key aspects of the experimental observations. [Preview Abstract] |
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YP8.00025: Design and implementation of the Materials Analysis Particle Probe (MAPP) plasma-facing component diagnostic C.N. Taylor, B. Heim, S. Gonderman, J.P. Allain, R. Kaita, C.H. Skinner, R.A. Ellis, A.L. Roquemore, R. Majeski The Materials Analysis Particle Probe (MAPP) is capable of prompt shot-to-shot analysis of plasma-facing components samples exposed to NSTX plasma discharges. MAPP exposes four samples to individual plasma discharges in order to test novel materials and determine the effect on plasma-facing components. Spectroscopic analysis techniques include X-ray photoelectron spectroscopy, ion scattering spectroscopy, direct recoil spectroscopy, and thermal desorption spectroscopy. These techniques assess the chemical state of the near surface ($\sim $10 nm), the surface (1-2 monolayers), quantify hydrogen retention, and measure thermal desorption species, respectively. Characterization is performed during the between-shot time window without perturbing operations or other diagnostics. The present work discusses MAPP's current status, calibration, and implementation within LTX and NSTX. [Preview Abstract] |
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YP8.00026: An earth-isolated optically coupled wideband high voltage probe powered by ambient light Xiang Zhai, Paul Bellan An earth-isolated optically coupled wideband high voltage probe has been developed for pulsed power applications. The probe uses a capacitive voltage divider coupled to a fast LED that converts high voltage into an amplitude-modulated optical signal, which is then conveyed to a receiver via an optical fiber. A solar cell array powered by ambient laboratory lighting charges a capacitor that, when triggered, acts as a short-duration power supply for an on-board amplifier in the probe. The entire system has a noise level $\le$0.03 kV, a DC-$5$ MHz bandwidth and a measurement range from $-6$ to $2$ kV; this range can be conveniently adjusted. [Preview Abstract] |
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YP8.00027: ABSTRACT WITHDRAWN |
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YP8.00028: ABSTRACT WITHDRAWN |
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YP8.00029: Silicon-Class Ablators for NIC Ignition Capsules Darwin Ho, Jay Salmonson, Steve Haan We present design studies using silicon-class ablators (i.e., Si, SiC, SiB6, and SiB14) for NIC ignition capsules. These types of ablators have several advantages in that they: (a) require no internal dopant layers and are robust to M-band radiation; (b) have smooth outer surfaces; (c) have stable fuel-ablator interface; and (d) have good 1-D performance. The major disadvantage for some of the ablators in this class is the relatively smaller ablation stabilization. Consequently, the ablator is more susceptible to breakup caused by RT instabilities. However, smoother outer surfaces on this class of ablators can reduce the effect of RT instabilities. 2-D simulations of SiC ablators show ignition failure despite smooth surfaces and good 1-D performance. But SiB6 and SiB14 ablators exhibit promising behaviors. SiB6 (SiB14) ablators have high 1-D ignition margin and high peak core hydrodynamic pressure 880 (900) Gbar. The ablation scale length for SiB6 is longer than that for SiC and for SiB14 is comparable to that of plastic. Therefore, we expect acceptable performance for SiB6 and less RT growth for SiB14. 2-D simulations are now in progress. [Preview Abstract] |
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YP8.00030: Discovery of Quantum structure and A Theory of Everything Part I and Part II Meggie Zhang (Part I) During my research I discovered logical errors in the logic of science and in mathematics. These errors caused scientists missed out important information when interpreting data. This led me to revisit the method of science and the existing results and able to find new information, which lead to the discovery of photon's structure. A ``particle collision illumination'' experiment then provided direct evidence supported the structure. Analysis of the properties of the structure suggested an organized but not-continuous multi-dimension (n-D) space within. Therefore I formed a hypothesis of a not-continuous n-D space structure. In search for evidence, I turned into crystal technology, and found direct evidence supported the hypotesis, then further particle collision found more evidence support this finding. (Part II) Analysis of single electron buildup revealed star and galaxy formation is from a single particle following a predictable pattern. This pattern is also common in matter formation. Analysis of the quantum structure suggested the formation of a larger structure through the space expansion within the structure. Further experiment results support the finding and result revealed the expansion is through space folding. Result also suggested a violation of energy conservation law that energy is created during the formation of matter, and matter itself is moving from a lower energy state to a higher energy state. When putting all information together, I arrived to a theory of everything which gives explanations to all existing phenomenon in the universe including black hole, dark energy, star formation, consciousness. [Preview Abstract] |
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YP8.00031: POST-DEADLINE POSTERS |
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YP8.00032: Role of density ripples to resonant Terahertz radiation excitation in laser beating process Anil K. Malik, Sanjay K. Tomar, Hitendra K. Malik The Terahertz (THz) radiation has gained much attention of the researchers due to its applications in material characterization, imaging, topography and remote sensing, chemical and security identification, etc. Plasma based THz schemes are attractive because they are capable of producing high power radiation. Several experiments have employed plasma as a medium for the THz radiation generation using sub-picoseconds laser pulses and energetic electron beams. The role of obliqueness of the ripples in plasma density to the THz radiation generation in the process of laser beating is clarified. For this, we use two spatial-super-Gaussian lasers (different indices) having different frequencies and wave numbers but the same field amplitudes. Due to intensity gradient in transverse direction and obliqueness of the density ripples, a transverse component of nonlinear ponderomotive force is realized that produces transverse oscillatory current. This nonlinear current oscillating at beating frequency produces the THz radiation at the beating frequency. We discuss in detail the efficiency of the scheme and power and frequency of the THz radiation with due importance of the density ripples. [Preview Abstract] |
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YP8.00033: Investigation of Magnetic Field Geometry in Exploding Wire Z-Pinches via Proton Deflectometry Derek Mariscal, Farhat Beg, Mingsheng Wei, Jeremy Chittenden, Radu Presura It is often difficult to determine the configuration of B-fields within z-pinch plasma systems. Typical laser probing diagnostics are limited by the critical density, and electrical diagnostics are prone to failure as well as perturbation of the system. The use of proton beams launched by high intensity lasers, and the subsequent tracking of their deflected trajectories, will enable access to field measurements in previously inaccessible plasma densities.The experimental testing of this method is performed at the Nevada Test Facility (NTF) using the 10J 0.3ps Leopard laser coupled to the 1.6MA ZEBRA pulsed power generator. MHD simulations of the z-pinch plasmas are performed with the 3D resistive MHD code, GORGON. Protons are then injected and tracked through the plasma using the 3D PIC Large Scale Plasma code in order to produce possible proton image plane data. The first computational demonstration of protons propagating through single wire and x-pinch plasmas, along with comparison to recent experimental data will be presented. [Preview Abstract] |
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YP8.00034: Electro-optic phase grating streak spectrometer Fletcher Goldin The Electro-optic phase grating streak spectrometer (EOPGSS) generates a time-resolved spectra equivalent to that obtained with a conventional spectrometer/streak camera combination, but without using a streak camera (by far the more expensive and problematic component of the conventional system). The EOPGSS is based on a phase, rather than an amplitude grating. Further, this grating is fabricated of electro-optic material such as, for example, KD*P, by either etching grooves into an E-O slab, or by depositing lines of the E-O material onto an optical flat. An electric field normal to the grating alters the material's index of refraction and thus affects a shift (in angle) of the output spectrum. Ramping the voltage streaks the spectrum correspondingly. The streak and dispersion directions are the same, so a second (static, conventional) grating disperses the spectrum in the orthogonal direction to prevent different wavelengths from ``overwriting'' each other. Since the streaking is done by the grating, the streaked output spectrum is recorded with a time-integrating device, such as a CCD. System model, typical design, and performance expectations will be presented. [Preview Abstract] |
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YP8.00035: Polyethyleneterephthalate surface modification mechanisms by an atmospheric pressure RF plasma source Shujun Yang, Jiansheng Tang An atmospheric pressure plasma was generated by a RF capacitive discharge using Helium gas or a mixture of helium and oxygen. The plasma was used to modify polyethyleneterephthalate (PET) surfaces with extremely high throughput. The surface modification mechanisms were carefully investigated. The modification was determined to be mainly a chemical and photochemical process through the experiments and analysis on ions, UV light, oxygen atoms, and ozone molecules. [Preview Abstract] |
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YP8.00036: Double plasma layers for backward Raman compression Gennadiy Fraiman, Alexey Balakin, Nathaniel Fisch The possibility to suppress perturbations of the phase and the amplitude profiles of amplified pulse at fast backward Raman compression in inhomogeneous plasma is proposed. The method is based on using two-stage backward Raman amplification in plasma. At the first stage, the usual backward Raman compression takes place, which transfers energy from a long pump pulse to a short seed pulse [1]. In inhomogeneous plasma this produces a short intense seed pulse with strong transverse modulation of its phase profile. At the second stage, this short intense pulse is used as a pump for backward Raman amplification of the same seed, which has homogeneous transverse phase profile at the beginning. What is important is that for the second stage we can use plasma layer with very small length, where inhomogeneities of plasma density are weak. This two-stage scheme allows achieving the efficiency of compression of about 60\% in energy. \\[4pt] [1] V. M. Malkin, G. Shvets, N. J. Fisch, Phys. Plasmas {\bf 7}, 2232 (2000). [Preview Abstract] |
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YP8.00037: Electron-ion collision operator in strong electromagnetic fields Gennadiy Fraiman, Alexey Balakin The pair electron-ion collision operator is found for the kinetic equation describing the one-particle drift distribution in strong electromagnetic fields [1]. The pair collisions are studied under the conditions when the oscillation velocity of an electron driven by an external electromagnetic wave is much larger than the electron drift velocity. The operator is presented in the Boltzmann form and describes collisions with both small and large changes of the particle momentum. In contrast with the Landau collision operator, which describes diffusion in the momentum space, the collision operator that we propose describes a new and very important effect, namely, Coulomb attraction of a wave-driven oscillating electron to an ion due to multiple returns of the electron to the same ion. This effect leads to a large increase of the collision cross-section of electron-ion collisions in strong laser fields, to increased efficiency of the Joule heating in plasma, to the generation of fast electrons through $e$-$i$ collisions, etc. \\[4pt] [1] A. A. Balakin and G. M. Fraiman, Electron-ion collision operator in strong electromagnetic fields, EPL {\bf 93}, 35001 (2011). [Preview Abstract] |
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YP8.00038: Visualizing and Quantifying Blob Characteristics on NSTX William Davis, Stewart Zweben, James Myra, Daniel D'Ippolito, Matthew Ko Understanding the radial motion of blob-filaments in the tokamak edge plasma is important since this motion can affect the width of the heat and particle scrape-off layer (SOL) [1]. High resolution (64x80), high speed (400,000 frames/sec) edge turbulence movies taken of the NSTX outer midplane separatrix region have recently been analyzed for blob motion. Regions of high light emission from gas puff imaging within a 25x30 cm cross-section were used to track blob-filaments in the plasma edge and into the SOL. Software tools have been developed for visualizing blob movement and automatically generating statistics of blob speed, shape, amplitude, size, and orientation; thousands of blobs have been analyzed for dozens of shots. The blob tracking algorithm and resulting database entries are explained in detail. Visualization tools also show how poloidal and radial motion change as blobs move through the scrape-off-layer (SOL), e.g. suggesting the influence of sheared flow. Relationships between blob size and velocity are shown for various types of plasmas and compared with simplified theories of blob motion. This work was supported by DOE Contract DE-AC02-09-CH11466. \\[4pt] [1] J.R. Myra et al, Phys. Plasmas 18, 012305 (2011) [Preview Abstract] |
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YP8.00039: The Over-Barrier Emission Model for a Vertically-Aligned Single-Layer Graphene Sheet Shi-Jun Liang, Lay Kee Ang It is believed the unique properties of graphene make it an ideal emitter. Traditionally, the mechanism of electron field emission of materials is governed by Fowler-Nordheim Law (F-N law) [1]. Even some experimental researchers have employed the F-N law to study electron field emission of graphene. However, it is well-known that the F-N law was established under the situation of 3D materials, but graphene is quasi-2D material. Thus the usage of F-N law is incorrect for this case. What's more, our previous paper [2] has verified that the conventional F-N law is no longer valid in the case of single layer graphene. In the paper we present an electron emission mechanism of graphene --- over-barrier emission. The relativistic WKB method has been used to approximately calculate the tunneling probability and current density, by considering electron walking through two different barrier regions. After some calculations we found that the electron over-barrier emission of graphene can be tuned by a parameter determined over a wide range of relevant laser parameters.\\[0pt] [1] R. H. Fowler and L. Nordheim, Proc. R. Soc. London Ser. A 119, 173 (1928).\\[0pt] [2] S. Sun, L. K. Ang, D. Shiffler, J. W. Luginsland, Appl. Phys. Lett. 99, 013112 (2011). [Preview Abstract] |
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YP8.00040: Experimental measurement of electron energy distribution function of solitary electron holes Satyananda Kar, Mangi Lal, Subroto Mukherjee, Abhijit Sen A metallic disc electrode (exciter) is immersed in low pressure argon plasma. When the exciter is positively pulse biased, nonlinear solitary electron holes are excited [Kar et al., Phys. Plasmas, 17, 102113, (2010)]. The amplitude of SEHs decreases with distance from the exciter. So, for a change in the number of trapped electrons, the distribution function of SEHs would be changed. One should incorporate the electron energy distribution function (EEDF) to learn more about the microscopic details, e.g. the growth of holes in linearly stable plasmas, non-Maxwellian nature of distribution, temperature and density of trapped electrons moving with the SEHs, etc. We have measured the EEDF of SEHs for shorter and longer pulse widths compared to ion response time. To measure this EEDF, a disc Langmuir probe is used and the electron and ion currents are obtained for positive and negative bias to the probe respectively. From the $I-V$ characteristics of Langmuir probe, we can find the EEDF (first derivative) and the electron energy probability function (EEPF). In EEPF, the peak gives the trapped electron temperature and the area under the curve gives the density. In this way, we have measured the temperature and density of trapped electrons inside the SEHs. The distribution function is changed according to the number of trapped electrons. For both the pulse widths, the distribution function shows a bi-Maxwellian form. [Preview Abstract] |
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YP8.00041: Absolute intensity calibration of two-channel prototype ITER vacuum ultraviolet spectrometer with a collimating mirror. Changrae Seon, Joohwan Hong, Munseong Cheon, Sunil Pak, Hyeongon Lee, Wolfgang Biel, Robin Barnsley To optimize the design of ITER vacuum ultraviolet (VUV) spectrometer, a two-channel prototype spectrometer was implemented with No. 3 (14.4 nm -- 31.8 nm) and No. 4 (29.0 nm -- 60.0 nm) among the five channels. The prototype is composed of a toroidal mirror, and two toroidal diffraction gratings and two different detectors of the back-illuminated CCD and the micro-channel plate (MCP). To verify each optical component, the absolute intensity calibration was performed using the calibrated hollow cathode lamp. Inverse sensitivities of each spectrometer were derived by dividing the incident photon numbers with the measured detector counts. The measured sensitivity values were consistent with the sensitivities calculated from the grating and the detector efficiencies. Consequently the calibration curves of the two-channel VUV spectrometer were provided, and the mirror reflectivity and the detector efficiency could be confirmed experimentally. For the application of the calibrated spectrometer, measurements of impurity lines in KSTAR plasmas were performed, and the line integrated emissivity was derived from the calibration curve during impurity injection experiments. [Preview Abstract] |
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YP8.00042: A combined model for femtosecond laser induced photoemission with laser heating and quantum tunneling Mihir Pant, Lay Kee Ang Ultrafast laser induced electron emission has garnered considerable interest in recent years because of its application in imaging, future light sources and in the development of ultrafast optical transistors. The photoemission process involves multiple physical processes: laser heating, quantum tunneling and acceleration by the ponderomotive force. Previous models for photoemission have only included some of these effects. In this paper, we combine the simulations of non-equilibrium heating with time-dependent quantum simulations under a spatially varying field to obtain a model which can capture all three effects. We find that many features of the emission process can only be captured by the combined model. Furthermore, the assumptions made by older models are found to be valid only under certain conditions. Our model is also compared with the classical Einstein photoelectric effect and we find differences in the emission order because of heating and the finite pulsewidth. The relative contribution of different energy levels in the emission process is also studied. [Preview Abstract] |
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YP8.00043: 1D Optimization of Uniformly Cu Doped Beryllium Ignition Capsules Kristopher Yirak, Douglas Wilson, Andrei Simakov, John Kline, Jay Salmonson, Jose Milovich, Daniel Clark, Debbie Callahan, Scott Sepke An ignition capsule can be tuned by iteratively adjusting the laser pulses in 2D radiation hydrodynamic simulations of a capsule and hohlraum. However, a multitude of optimally tuned designs may be necessary to choose among design options, such as peak laser power and energy, dopant concentration, ablator thickness, DT ice thickness, and other parameters. We use a frequency dependent radiation source derived from 2D integrated calculations to explore the levels and timings of the radiation pulses created by four laser pulses across many 1D calculations. The first pulse is fixed at a level sufficient to melt the beryllium. The fourth pulse duration and length are determined by the laser energy and peak power. Pulse levels and timings are adjusted so that all shocks coalesce just inside the DT ice/gas interface (Munro et al., 2001). In addition to varying ablator and ice thickness (e.g. Haan et al., 2005) we have varied the laser energy, peak laser power, and dopant level, seeking designs optimizing several parameters, including yield (with and without alpha deposition), peak no-burn temperature, rho-r, and velocity. This optimization leads us to low dopant concentrations (0.1 to 0.3\%) with thick ablators ($\sim$160-190 microns) for further 2D analysis. [Preview Abstract] |
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YP8.00044: Calibrating Curved Crystals Used for Plasma Spectroscopy Michael Haugh, Ken Jacoby, Patrick Ross, Greg Rochau, Ming Wu, Sean Regan, Maria Barrios Curved crystals are used as diffraction elements for X-ray spectrometers in diagnosing laser plasma sources at the National Ignition Facility at Lawrence Livermore National Laboratory and on the Z machine at Sandia National Laboratories. Reflectivity curves for various curved crystals used at these facilities have been measured in National Security Technologies' (NSTec) X-ray laboratory. The X-ray source is a diode arrangement with a dual goniometer system that orients a monochromator and the sample crystal to the appropriate Bragg angles. The reflectivity curve is then measured at energies that ranged from 0.7 to 15.8 keV. This presentation covers reflectivity curve measurements on circular cylindrical KAP crystals and elliptical cylindrical PET crystals. The integrated reflectivity, the curve width, and the peak reflectivity were determined. The integrated reflectivity and the width of curved crystals were much larger than the values for the corresponding flat crystal, increasing as the radius of curvature decreases for a given photon energy. For a fixed radius of curvature, they increase as the photon energy increases. [Preview Abstract] |
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YP8.00045: The Spherical Tokamak MEDUSA for Costa Rica Celso Ribeiro, Ivan Vargas, Saul Guadamuz, Jaime Mora, Jose Ansejo, Esteban Zamora, Julio Herrera, Esteban Chaves, Carlos Romero The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R$<$0.14m, a$<$0.10m, B$_{T}<$0.5T, I$_{p}<$40kA, 3ms pulse)[1] is in a process of donation to Costa Rica Institute of Technology. The main objective of MEDUSA is to train students in plasma physics /technical related issues which will help all tasks of the very low aspect ratio stellarator SCR-1(A$\equiv $R/$\langle $a$\rangle \ge $3.6, under design[2]) and also the ongoing activities in low temperature plasmas. Courses in plasma physics at undergraduate and post-graduate joint programme levels are regularly conducted. The scientific programme is intend to clarify several issues in relevant physics for conventional and mainly STs, including transport, heating and current drive via Alfv\'{e}n wave, and natural divertor STs with ergodic magnetic limiter[3,4]. [1] G.D.Garstka, PhD thesis, University of Wisconsin at Madison, 1997 [2] L.Barillas et al., Proc. 19$^{th}$ Int. Conf. Nucl. Eng., Japan, 2011 [3] C.Ribeiro et al., IEEJ Trans. Electrical and Electronic Eng., 2012(accepted) [4] C.Ribeiro et al., Proc. 39$^{th}$ EPS Conf. Contr. Fusion and Plasma Phys., Sweden, 2012 [Preview Abstract] |
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YP8.00046: The Ultra-Low Aspect Ratio Stellarator SCR-1 Celso Ribeiro, Ivan Vargas, Jaime Mora, Esteban Zamora, Jose Asenjo, Leonardo Ribas, Saul Guadamuz The world most compact stellarator is currently being designed at the Costa Rica Institute of Technology (ITCR). The SCR-1(Stellarator of Costa Rica 1) is a 2-field period modular device with a circular cross-section vessel ($R_{o}=0.238m$, $a=0.097m$, $R_{o}$\textit{/a$\approx $2.5}, $0.014m^{3}$, \textit{4mm} thickness 6061-T6 aluminum). The expected D-shaped high elongated plasma cross section has a maximum average radius of $\langle $a$\rangle \approx $0.062m, leading to $R_{o}$/$\langle $a$\rangle \ge $3.8. Such compactness was reached after a SCR-1 earlier proposal [1] was redesigned, both based on the low shear stellarator UST{\_}1: $R_{o}$/$\langle $a$\rangle \approx $6, $\iota $=0.32/0.28 (core/edge) [2]. The set field at centre is 88mT produced by 12 copper modular coils, 8.7kA-turn each. This field is EC resonant at $R_{o}$ with a 2.45GHz $\mu $w, 1$^{st}$ harmonic, from 2/3kW magnetrons which will produce a second time-scale plasma pulse. The coil current will be produced by a bank of cell batteries. Poincar\'{e} and EC deposition plots will be presented using COMSOL Multiphysics software. SCR-1 will be synergetic to the ST MEDUSA currently under donation to ITCR [3]. Both will benefit of the local new activities in technological plasmas.\\[4pt] [1] Barillas L et al., Proc.19$^{th}$ Int.Conf. Nucl.Eng., Japan, 2011\\[0pt] [2] Queral V, Stellarator News, 118, 2008\\[0pt] [3] Ribeiro C et al., 54$^{th}$ APS, Plasma Phys. Div., US, 2012 [Preview Abstract] |
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YP8.00047: Simulation study of disruption characteristics in KSTAR Jongkyu Lee, J.Y. Kim, C.E. Kessel, F. Poli A detailed simulation study of disruption in KSTAR had been performed using the Tokamak Simulation Code(TSC) [1] during the initial design phase of KSTAR [2]. Recently, however, a partial modification in the structure of passive plate was made in relation to reduce eddy current and increase the efficiency of control of vertical position. A substantial change can then occur in disruption characteristics and plasma behavior during disruption due to changes in passive plate structure. Because of this, growth rate of vertical instability is expected to be increased and eddy current and its associated electomagnetic force are expected to be reduced. To check this in more detail, a new simulation study is here given with modified passive plate structure of KSTAR. In particular, modeling of vertical disruption that is vertical displacement event (VDE) was carried out. We calculated vertical growth rate for a drift phase of plasma and electromagnetic force acting on PFC structures and compared the results between in a new model and an old model. \\[4pt] [1] S.C. Jardin, N. Pomphrey and J. Delucia, J. Comp. Phys. 66, 481 (1986).\\[0pt] [2] J.Y. Kim, S.Y. Cho and KSTAR Team, Disruption load analysis on KSTAR PFC structures, J. Accel. Plasma Res. 5, 149 (2000). [Preview Abstract] |
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YP8.00048: Plasma Electron Depletion via Cathode Spot Injection of Dielectric Particles Eric Gillman, John Foster A method for addressing communication blackout associated with the formation of a dense plasma around reentry vehicles is reported upon. Quenchant particles launched into a background plasma via cathode spots is investigated as a means for free electron depletion. Time resolved measurement of electron density evolution during cathode spot ``on times'' is inferred by monitoring variations in the electron saturation current. Corrections for magnetic effects are also taken into account in the interpretation of temporal variations in the electron saturation current. Measurements indicated depletion levels of over 95{\%} for model plasmas investigated. [Preview Abstract] |
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YP8.00049: Development of High-Resolution UV-VIS Diagnostics for Space Plasma Simulation Andrew Taylor, Oleg Batishchev Non-invasive far-UV-VIS plasma emission allows remote diagnostics of plasma, which is particularly important for space application. Accurate vacuum tank space plasma simulations require monochromators with high spectral resolution (better than 0.01A) to capture important details of atomic and ionic lines, such as Ly-alpha, etc. We are building a new system based on the previous work [1], and will discuss the development of a spectrometry system that combines a single-pass vacuum far-UV-NIR spectrometer and a tunable Fabry-Perot etalon. \\[4pt] [1] O. Batishchev and J.L. Cambier, Experimental Study of the Mini-Helicon Thruster, Air Force Research Laboratory Report, AFRL-RZ-ED-TR-2009-0020, 2009. [Preview Abstract] |
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YP8.00050: How to maintain the Pickup Ion ring distribution in reproducing the ENA ribbon? Peng Sun, J.R. Jokipii Numerical (hybrid) simulations are performed on various conditions to restrain the growth of the instability of pick up ion's ring distribution (Florinski, 2010) compared with linear theory estimates, which is an important assumption to the Heerikhuisen's (2010) explanation about the ENA ribbon discovered by IBEX. [Preview Abstract] |
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YP8.00051: Asymmetric Solutions of the Grad-Shafranov Equation Matsak Ainov, Alexander Mustafaev, Vladimir Semenov Grad-Shafranov (GS) equation describes the kinetic equilibrium of plasma embedded into magnetic field, in particular the space current sheets. GS equation can be derived from the Vlasov equations with self-consistent electromagnetic field. It is known (Walker, 1915), that the exact solutions of the GS equation can be obtained by use of a special complex function g($\xi$) which is responsible for the current sheet structure. Up to now were known only symmetric solutions which are not enough to describe the structure of the real space current layers. For example, the symmetric current sheet in the Earth's magnetotail happens to be only twice per year during the spring and autumn equinox. Therefore it was suggested to extend the well-known classes of the exact kinetic solutions (Harris, Fadeev, Kan and Manankova) of the GS equation for the asymmetric current sheet configurations by use the appropriate complex Walker function g($\xi$). As a result a new class of asymmetric kinetic current sheet equilibrium has been obtained and investigated. [Preview Abstract] |
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YP8.00052: Laser vaporization of the copper films obtained by electro-dispersion technology Pavel Petrov, Alex Mustafaev, Yuriy Anisimov In this work interaction of laser radiation with a copper dusting received on technology EDDS was investigated. The topography of a surface of a dusting on SZM was investigated, the assessment of thickness of a dusting also was made. As a theoretical part, in this work the EDDS elementary model in a circular field were simulated. The main conclusion of this model consists that if create EDDS suspension in a circular field, the suspension will fill an internal surface of a digit tube more evenly and consequently and if in this moment evaporate a suspension a longitudinal electric discharge, it is possible to achieve more uniform dusting in a digit tube. As within this model the charge of a flying suspension was estimated. [Preview Abstract] |
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YP8.00053: ABSTRACT HAS BEEN MOVED TO TP8.00130 |
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YP8.00054: Synthetic Reflectometry Applied to Realistic Plasma Simulation Code Lei Shi, Stephane Ethier, William Tang, Ernest Valeo, Weixing Wang Reflectometry is widely used in magnetically-confined plasma devices to measure both the density equilibrium profile and fluctuations. In order to better understand and thereby more effectively interpret the output, it is very useful to have a ``synthetic diagnostic''/numerical emulator for the reflectometer itself -- a synthetic reflectometer. In particular, instead of considering a collection of artificially created equilibrium and fluctuation profiles to test the efficacy of this tool, it is more relevant to apply this against realistic equilibria and fluctuations produced in an actual ``numerical experiment.'' In this work, we apply the synthetic reflectometer to a modern 3D gyrokinetic particle simulation code named GTS which is interfaced against realistic shaped-cross section tokamak equilibria and performs first principle simulations of the evolution of fluctuations. Results will be presented on progress toward our goal of producing -- for the first time -- the capability to generate synthetic diagnostic results from turbulence simulations that can be compared to those from experimental reflectometry measurements under similar plasma conditions. This could be used in realistically characterizing experimental results, verification, validation and uncertainty quantification. [Preview Abstract] |
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YP8.00055: Hybrid drift-kinetic electron/full kinetic ion PIC simulation of RF plasma discharge in magnetic mirror machine Evstati Evstatiev We present numerical simulations of a radio-frequency- (RF-) induced plasma discharge in magnetic mirror machines, with relevance to Electron Cyclotron Ion Source (ECRIS) devices. The simulations are done in 2D cylindrically symmetric geometry. The code \textbf{SIMPL} is a PIC code, which uses drift-kinetic electron and full kinetic ion description. The RF wave heating is implemented as a ``kick'' model, i.e., electrons get an increment in their perpendicular velocity when they cross the magnetic resonance surface. Atomic physics is for Argon and includes the following basic reactions: single ionization by electron impact, excitation, elastic scattering, and charge exchange. We will discuss the steady-state spatial structure of the discharge. [Preview Abstract] |
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YP8.00056: Anomalous Transport Model for GyroKinetic Code COGENT Justin Angus, Sergei Sergei, Ron Cohen, Tom Rognlien, Mikhail Dorf Cross field transport from the closed field line core of tokamaks to the open field line scrape off layer is often dominated by anomalous processes. This anomalous transport is largely a result of the ExB drift associated with electrostatic turbulence. Since the time scale of the turbulent fluctuations is typically much smaller than that of the mean transport, it is numerically expensive to fully resolve the turbulent fluctuations when simulating edge transport. For this reason, it is numerically economical to introduce models to represent the mean cross field transport due to anomalous process. We consider the anomalous kinetic flux to be a combination of advective and diffusive components and, for initial implementation and testing purposes, demonstrate how the coefficients can be chosen such that the velocity space moments of the flux reproduces known models used in fluid transport codes. The model has been implemented into the Gyrokinet code COGENT. [Preview Abstract] |
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YP8.00057: Development of DC plasma source for extremely low pressure operation Byung-Keun Na, In-Sik Bae, Shin-Jae You, Jung-Hyung Kim, Hong-Young Chang As the line width of semiconductor devices decreases less than 20 nm, development of a low pressure plasma source became a crucial issue. Moreover, as the atomic layer deposition is getting more important for the fine processing, the low density plasma source also became necessary. However, capacitive and inductive discharges, the most widely used plasma source, are not well generated below the pressure of 10 mTorr. The mean free path of electron under 10 mTorr is usually longer than the system size; hence the neutral gas is hardly ionized by the electron-neutral (e-n) collisions. In this presentation, a new type of DC plasma source which can be operated below 10 mTorr is introduced. A geometrical trick, instead of magnetic field, was used to increase free flight length of electron. A number of e-n collisions could occur through the longer flight length than the mean free path; finally plasma was generated even in extremely low pressure. The plasma generation could be confirmed by the anode current and Langmuir probe measurement. The plasma was generated at a few mTorr, and the plasma density was as low as $10^{8}$ cm$^{-3}$. This plasma source can be used for extremely fine processing. [Preview Abstract] |
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YP8.00058: Control of plasma oscillations in a short dc discharge making use of external auxiliary electrode Alexander Mustafaev, Artiom Grabovskiy, Vladimir Demidov, Igor Kaganovich A dc discharge with a hot cathode is the subject to current and voltage oscillations, which have deleterious effect on its operation. The oscillations can be inhibited by installing an auxiliary electrode, placed outside of anode. By collecting a modest current through a small opening in anode, we show that the discharge becomes stable, in certain pressure range. This method of avoiding current and voltage oscillations can be used, for example, for high current stabiliziers. [Preview Abstract] |
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YP8.00059: Xenon Additives Detection in Helium Micro-Plasma Gas Analytical Sensor Alexander Tsyganov, Anatoliy Kudryavtsev, Alexander Mustafaev Electron energy spectra of Xe atoms at He filled micro-plasma afterglow gas analyzer were observed using Collisional Electron Spectroscopy (CES) method [1]. According to CES, diffusion path confinement for characteristic electrons makes it possible to measure electrons energy distribution function (EEDF) at a high (up to atmospheric) gas pressure. Simple geometry micro-plasma CES sensor consists of two plane parallel electrodes detector and microprocessor-based acquisition system providing current-voltage curve measurement in the afterglow of the plasma discharge. Electron energy spectra are deduced as 2-nd derivative of the measured current-voltage curve to select characteristic peaks of the species to be detected. Said derivatives were obtained by the smoothing-differentiating procedure using spline least-squares approximation of a current-voltage curve. Experimental results on CES electron energy spectra at 10-40 Torr in pure He and in admixture with 0.3{\%} Xe are discussed. It demonstrates a prototype of the new miniature micro-plasma sensors for industry, safety and healthcare applications. [1]. A.A.Kudryavtsev, A.B.Tsyganov. US Patent 7,309,992. Gas analysis method and ionization detector for carrying out said method, issued December 18, 2007. [Preview Abstract] |
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YP8.00060: The ion distribution in a field-reversed configuration heated by odd-parity rotating magnetic field Chang Liu, Samuel Cohen The ion heating effect of odd-parity rotating magnetic field (oRMF) in a field-reversed magnetic configuration (FRC) is studied by a single particle Hamiltonian code. By varying the particle initial condition and assuming the ergodic hypothesis, we obtain a particle distribution on both configuration space and velocity space. The simulation shows that strong enough RMF will give high energy betatron orbit particles a strong concentration effect in the frame rotating with the RMF. Moreover, the RMF will accelerate the particles to form a double bump distribution rather than a Maxwellian. Both of those effect will improve the nuclear fusion efficiency and will increase the energy ratio of charged particles to neutrons when D-He$^{3}$ is used as fuel, which is good to future FRC-based nuclear fusion plant. [Preview Abstract] |
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YP8.00061: Scattering and absorption of electromagnetic waves in non-Maxwellian plasmas for the ion cyclotron range of frequencies Suwon Cho In radio-frequency heating of plasmas the launched wave undergoes tunneling, reflection, mode conversion, and damping near the resonance layer. The single pass scattering parameters can be estimated from the mode-conversion tunneling equation, whose solutions are known for Maxwellian plasmas. In this work, the analysis is extended to include the non-Maxwellian velocity distributions in inhomogeneous plasmas for the ion cyclotron range of frequencies. The rf power absorption profile and the velocity distribution are obtained by solving the mode-conversion tunneling equation and the quasilinear Fokker-Planck equation iteratively. The effects of the velocity distribution on the scattering parameters and absorption are examined in comparison with the case of Maxwellian distribution. [Preview Abstract] |
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YP8.00062: Investigation of efficient shock acceleration of ions using high energy lasers in low density targets P. Antici, M. Gauthier, E. D'humieres, B. Albertazzi, C. Beaucourt, J. B\"oker, S. Chen, V. Dervieux, J.L. Feugeas, M. Glesser, A. Levy, P. Nicolai, L. Romagnani, V. Tikhonchuk, H. Pepin, J. Fuchs Intense research is being conducted on sources of laser-accelerated ions and their applications that have the potential of becoming novel particle sources. In most experiments, a high intensity and short laser pulse interacts with a solid density target. It was recently shown that a promising way to accelerate ions to higher energies and in a collimated beam is to use under-dense or near-critical density targets instead of solid ones. In these conditions, simulations have revealed that protons are predicted to be accelerated by a collisionless shock mechanism that significantly increases their energy. We present recent experiments performed on the 100 TW LULI laser (France) and the TITAN facility at LLNL, USA. The near critical density plasma was prepared by exploding thin solid foils by a long laser pulse. The plasma density profile was controlled by varying the target thickness and the delay between the long and the short laser pulse. When exploding the target, we obtained proton energies that are comparable if not higher than what was obtained under similar laser conditions, but with solid targets which make them a promising candidate for an efficient proton source. [Preview Abstract] |
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YP8.00063: Magnetic fluctuations during fast magnetic reconnection with a finite guide field in TS-3 plasma merging experiment Akihiro Kuwahata, Taichi Ito, Boxin Gao, Hiroshi Tanabe, Michiaki Inomoto, Yasushi Ono Large amplitude magnetic fluctuations with ion cyclotron range frequency was observed inside the diffusion region during fast magnetic reconnection with a finite guide field in TS-3 plasma merging experiment. Magnetic fluctuation measurement was performed by three kinds of magnetic probe array: a radial array of pickup coils in the direction of current sheet length to measure magnetic fluctuations of reconnected field Bz, an axial array in the direction of current sheet width to measure reconnecting field B// fluctuations, and a 3-componets (B//, Bx, Bz) probe to measure the dispersion relation of the fluctuations. The guide field at the X-point Bx is comparable to B//. The magnetic field variation caused by the fluctuations is larger than 10\% of B//. Reconnection rate had a positive correlation with the amplitude of fluctuations. Our numerical calculation of dispersion relation yields that Kinetic Alfv\'en Wave (left-handed polarization) can propagate in the vicinity of the X-point. Fluctuation measurement of 3-magnetic components suggests that the observed fluctuations are left hand polarized wave. As a consequence, the observed magnetic fluctuations with characteristic of KAW have good correlation with the enhancement of reconnection rate in the presence of a guide field. [Preview Abstract] |
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YP8.00064: Numerical Simulations of Fine Structures within Reconnecting Current Sheets in Solar Flares Chengcai Shen, Jun Lin, Nicholas A. Murphy, John C. Raymond Solar flares occur when magnetic energy is quickly converted into heat and kinetic energy by magnetic reconnection in a current sheet (CS). Based on 2D MHD experiments, we simulate the development of instabilities and turbulence in a long CS. The simulations start with a vertical current sheet that is in mechanical equilibrium and line-tied at the lower boundary. Reconnection commences gradually due to an initially imposed perturbation, but becomes faster when plasmoids form and produce small-scale structures inside the current sheet. These structures include magnetic islands or plasma blobs flowing in both directions along the sheet, and X-points between pairs of adjacent islands. The various properties of the energy conversion in the reconnection region are studied through performing a 1D Fourier analysis. The results display a power law distribution for the energy versus the scale of small structures inside the CS, suggesting that the reconnection process is turbulent. [Preview Abstract] |
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YP8.00065: Optimization of marker particle distribution by particle merging/splitting for $\delta f$ PIC simulation Wenjun Deng, Guoyong Fu In typical $\delta f$ particle-in-cell (PIC) plasma simulations, a huge number of markers are loaded everywhere in phase space. Meanwhile, for some modes, e.g., Alfv\'en eigenmodes in toroidal geometry, the $\delta f$ mode structure mainly stays in a small portion of the phase space, which is usually the resonant regions, and $\delta f$ is nearly zero elsewhere. Markers in those $\delta f \approx 0$ regions can be reduced while retaining the same accuracy, and doing so can save a lot of computing time. Marker merging and splitting methods are being developed in this work to achieve this time saving effect. During simulation, the splitting method splits each marker into multiple markers to increase phase space resolution in the main $\delta f$ mode structure, while the merging method merges multiple markers into one in the $\delta f \approx 0$ regions to save computing time. This method is applied to a 1D electrostatic Vlasov-Poisson code and performed on both two-stream instability and bump-on-tail instability. The merging method can halve the overall number of markers while retaining the same accuracy. The splitting method is still under development. These two methods are also being implemented in the hybrid MHD gyrokinetic code M3D-K. [Preview Abstract] |
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YP8.00066: Electron heating during magnetic reconnection in the UTST merging experiment Kotaro Yamasaki, Shuji Kamio, Koichiro Takemura, Qinghong Cao, Takenori Watanabe, Hirotomo Itagaki, Takuma Yamada, Yasushi Ono, Michiaki Inomoto We have been investigating the electron heating at current sheet during magnetic reconnection in the UTST spherical tokamak merging experiment. The external magnetic pressure of PF coils accelerated / collided two ST plasmas together under the high guide field condition (typically B$_{t} \sim $ 0.2 T $\sim $ 10B$_{//}$ at X-point). Triple Langmuir probes were used to measure the radial profiles of electron density and temperature inside the current sheet. As the current sheet grew, the electron density inside the sheet was observed to increase from 0.5x10$^{19}$ to 3.0x10$^{19}$m$^{-3}$. After it reached the maximum value, the electron temperature around the X-point increased rapidly from 5eV to 15-20eV. The electron temperature profile was found to peak at the X-point which had strong toroidal electric field and toroidal guide field but almost zero poloidal magnetic field. This fact suggests that the toroidal electric field accelerates electrons toroidally along the X-line and that the Ohmic heating of the current sheet is the most probable cause for the peaked electron temperature profile. [Preview Abstract] |
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YP8.00067: Simulation of the Partially Ionized Negative Hydrogen Plasma Sergey Averkin, Nikolaos Gatsonis, Lynn Olson A High Pressure Discharge Negative Ion Source (HPDNIS) operating on hydrogen is been under investigation. The Negative Ion Production (NIP) section of the HPDNIS attaches to the 10-100 Torr RF-discharge chamber with a micronozzle and ends with a grid that extracts the negative ion beam. The partially ionized and reacting plasma flow in the NIP section is simulated using an unstructured three-dimensional Direct Simulation Monte Carlo (U3DSMC) code. The NIP section contains a low-pressure plasma that includes $\mbox{H}_2 $, vibrationally-rotationally excited $\mbox{H}_2^\ast $, negative hydrogen atoms $\mbox{H}^-$, and electrons. Primary reactions in the NIP section are dissociate attachment, $\mbox{H}_2^\ast +e\to \mbox{H}^0+\mbox{H}^-$and electron collisional detachment, $e+\mbox{H}^-\to \mbox{H}+2e$. The U3DSMC computational domain includes the entrance to the NIP nozzle and the extraction grid at the exit. The flow parameters at the entrance are based on conditions in the RF-discharge chamber and are implemented in U3DSMC using a Kinetic-Moment subsonic boundary conditions method. Neutral--neutral, ion-neutral, Coulomb collisions and charge-neutralizing collisions are implemented in U3DSMC using the no time counter method, electron-molecule collisions are treated by the constant timestep method. Simulations cover the regime of operation of the HPDNIS and examine the flow characteristics inside the NIP section. [Preview Abstract] |
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YP8.00068: Simulation of gradient drift instabilities in Hall thruster plasmas with the BOUT++ code Winston Frias, Andrei Smolyakov, Yevgeny Raitses, Igor Kaganovich, Maxim Umansky Hall thrusters plasma is a subject of several instabilities related to gradients of plasma density and electron temperature, gradient of magnetic field as well as the equilibrium electron flow due to the equilibrium axial electric field. The effect of electron collisions and electron inertia are studied using the fluid BOUT++ code and the results compared and validated with the existing analytical theory. In the future, computer simulations of nonlinear stage and associated turbulent transport in Hall thrusters will be performed. Also connections with other instabilities in Hall plasmas will be investigated. [Preview Abstract] |
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YP8.00069: Rogue Waves Associated with Circularly Polarized Waves in Magnetized Plasmas I. Kourakis, J. Borhanian, V. Saxena, G. Veldes, D.J. Frantzeskakis Extreme events occur in abundance in the ocean: an ultra-high ``ghost wave" often appears unexpectedly, against an otherwise moderate-on-average sea surface elevation, propagating for a short while and then disappearing without leaving a trace. Rogue waves are now recognized as proper nonlinear structures on their own. Unlike solitary waves, these events are localized in space and in time. Various approaches exist to model their dynamics, including nonlinear Schrodinger models, Ginzburg-Landau models, kinetic-theoretical models, and probabilistic models. We have undertaken an investigation, from first principles, of rogue waves in plasmas in the form of localized events associated with electromagnetic pulses. A multiple scale technique is employed to solve the fluid-Maxwell equations for nonlinear circularly polarized electromagnetic pulses. A nonlinear Schrodinger (NLS) type equation is shown to govern the amplitude of the vector potential. A set of non-stationary envelope solutions of the NLS equation is presented, and the variation of their structural properties with the magnetic field are investigated. [Preview Abstract] |
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YP8.00070: Plasma Jet Diagnostic for Runaway Electron Beam-Plasma Interaction I.N. Bogatu, J.R. Thompson, S.A. Galkin, J.S. Kim, S. Brockington, A. Case, S.J. Messer, F.D. Witherspoon FAR-TECH's recently developed C$_{60}$/C plasma jet has the potential to rapidly and significantly increase electron density, deep into tokamak plasma, hence to change the `critical electric field' as well as the runaway electrons (REs) collisional drag, during different phases of REs dynamics. Suitably chosen visible/UV lines emitted by the injected C ions can then be used for line intensity quantitative spectroscopy, allowing the diagnostic of the RE beam-plasma interaction. The C$_{60}$ delivered in $\sim1$ ms by the prototype plasma jet system, estimated to be $\sim75$ mg, carries $\sim4\times10^{21}$ C atoms and $\sim2.4\times10^{22}$ electrons, and would lead to an electron density $n_{e}\sim2.4\times10^{21}$ m$^{-3}$, i.e. $\simeq60$ times larger than typical DIII-D pre-disruption value ($n_{e0}\approx 4\times10^{19}$ m$^{-3}$). While the prototype's C$_{60}$/C plasma jet mass is not sufficient to achieve the Rosenbluth electron density in DIII-D, it delivers a total number of electrons $\sim5$ times larger than that of the Ar pellet, with the advantage of a much faster response and precisely chosen delivery time. We will present several proposed diagnostic schemes using rapid C$_{60}$/C plasma jet injection capability in different phases of the discharge in DIII-D. [Preview Abstract] |
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YP8.00071: Progress of the 2012 KSTAR experimental campaign Yeong-Kook Oh, W.C. Kim, S.G. Lee, J.Y. Kim, H.L. Yang, K.R. Park, Y. Chu, M.K. Park, Y.S. Bae, H,K, Kim, J.G. Kwak, H. Park, W.H. Choe, K.S. Chung, Y.S. Na, Y.S. Hwang, S.Y. In, M. Walker, D. Mueller, J. Park, J.W. Ahn, S.A. Sabbagh, S. Zoletnik KSTAR device has been operated with a mission to explore the advanced physics and technologies at high performance steady-state plasma that are essential for ITER and fusion reactor development. The 2012 KSTAR campaign is conducted with experimental goals to extend H-mode over 10 sec at the plasma current in the level of 0.6 $\sim $ 1 MA by adopting the real-time shaping control, to investigate physics issues including L- to H-mode transition and ELM mitigation, and to support various experiments proposed by domestic and international collaborators. The available heating power in 2012 is about 5.5 MW in total including 3.5 MW NBI, 1 MW ICRF, 1 MW ECH/CD, and 0.3 MW LHCD. The upgraded diagnostic systems are Thomson scattering system, BES, two ECEI, VUV spectrometer, imaging bolometer, and FIR interferometer. In this presentation, the progress of the KSTAR experiments will be described including the hardware upgrade and physics research results. [Preview Abstract] |
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YP8.00072: The study on the self-consistent eigenfuction of resistive wall modes and perturbed equilibria including kinetic effects Zhirui Wang, Jong-Kyu Park, Jonathan Menard, Yueqiang Liu It is known that the kinetic effects can play an important role in determining Resistive Wall Mode (RWM) stability as well as perturbed equilibria in tokamaks. The toroidal hybrid code Mars-K, which self-consistently incorporates drift kinetic effect into MHD formulation, has already shown that the kinetic resonance can substantially change RWM eigenfuntion particularly near the plasma edge. These results imply in fact that the perturbed equilibria with external perturbations can be also largely modified by such kinetic effects. To understand the self-consistent solutions in both RWM stability and perturbed equilibria, first we performed the careful benchmark between Mars-K code in the fluid limit and IPEC code. We found an excellent agreement between the two codes in a simple tokamak as well as in a challenging NSTX equilibrium. Then the code associated with the potential energy analysis is applied to further study the modification of RWM eigenfunction and the shielding effect of perturbed equilibria due to kinetic effects. Furthermore, the undergoing development including the energy dependent collision operator into Mars-K kinetic calculation will be presented and the equivalence between the neoclassical toroidal torque and the kinetic potential energy will be discussed. [Preview Abstract] |
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YP8.00073: Experimental Results on the First Short Pulse Laser Driven Neutron Source Powerful Enough For Applications In Radiography Nevzat Guler Short pulse laser driven neutron source can be a compact and relatively cheap way to produce neutrons with energies in excess of 10 MeV. It is based on short pulse laser driven ions interacting with a converter material to produce neutrons via separation or breakup mechanisms. Previous research on the short pulse laser driven ion acceleration has mainly concentrated on surface acceleration mechanisms, which typically yield isotropic emission of neutrons from the converter. Recent experiments performed with a high contrast laser at TRIDENT facility at LANL demonstrated laser driven ion acceleration mechanism based on the concept of relativistic transparency. This produced an intense beam of high energy (up to 80 MeV) deuterons directed into a Be converter to produce a forward peaked neutron flux with a record yield, on the order of 4.4x10$^9$ n/sr. The produced neutron beam had a pulse duration less than a nanosecond and an energy range between 2-80 MeV, peaking around 12 MeV. The neutrons in the energy range of 2.5 to 15 MeV were selected by the gated neutron imager to radiograph tungsten blocks of different thicknesses. We will present the results from the two acceleration mechanisms and the first short pulse laser generated neutron radiograph. [Preview Abstract] |
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YP8.00074: Turbulent eddy-mediated transport in the edge of HL-2A tokamak plasma Min Xu, George Tynan, Patrick Diamond, Kaijun Zhao, Jun Cheng, Jiaqi Dong, Peter Manz, Nicolas Fedorczak, Saikat Thakur, Jonathan Yu, Wenyu Hong, Longwen Yan, Qingwei Yang, Xiangming Song, Yuan Huang, Laizhong Cai, Wulv Zhong, Zhongbing Shi, Xuantong Ding, Xuru Duan, Yong Liu We report the first experimental evidence that turbulent eddies mediate the heat, particle, momentum and vorticity transport at the edge of a tokamak plasma so as to amplify the shear layer at the last closed flux surface (LCFS). We find that turbulent eddies with relative negative vorticity (opposite to B field) and positive azimuthal momentum (electron-diamagnetic drift direction) are drawn from both sides of and move towards the region about 1 cm inside separatrix; while eddies with relative positive vorticity (i.e. parallel to the B field) and negative azimuthal momentum (ion-diamagnetic drift direction) propagate away from this location towards to the core and scrape-off layer (SOL) plasma regions. Thus negative vortices act to concentrate positive momentum into the region just inside the LCFS, and plasma in this region acquires an ExB drift in the electron drift direction. This physical picture links the macroscopic confinement to the microscopic transport dynamics. Also since the vortcity drive gets stronger as the heating power is increased, it should naturally lead to a very strong shear flow that can suppress the turbulent transport and ultimately can lead to H-mode with sufficient heating. [Preview Abstract] |
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YP8.00075: Adiabatic invariants of alpha particles in the presence of time dependent perturbations B. Huang, Y. Nishimura, C.Z. Cheng Theoretical and numerical analysis is done for the fast particles in tokamaks in an analogy with the nonlinear pendulum with slowly changing string length (A.Einstein, Solvay Conference, 1912). The two important parameters are the ratio between mode frequency and bounce frequency $\omega / \omega_b$ (change in string length versus pendulum frequency), as well as the perturbation amplitudes. Toroidal drift eigenmode structure is applied to the analysis.\footnote{C.Z.Cheng, Phys. Fluids {\bf 25}, 1020 (1982).} [Preview Abstract] |
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