Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session CP8: Poster Session II: International Tokamaks; ITER; Next-Step Devices; Turbulence & Transport; Intense Beam and Radiation Sources; Dusty and Complex Plasmas |
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Room: Preservation Hall |
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CP8.00001: INTERNATIONAL TOKAMAKS; ITER; NEXT-STEP DEVICES; TURBULENCE \& TRANSPORT |
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CP8.00002: Experimental Measurements of the Lower Hybrid Electric Field and Induced Neutral Flow in Tore Supra by Optical Emission Spectroscopy E.H. Martin, C.C. Klepper, R.C. Isler, M. Goniche, J.B.O. Caughman Recently, the RF electric field vector (\textbf{E}$_{\mathrm{\mathbf{LH}}})$ in front of a lower hybrid (LH) launcher, operating at 3.7 GHz, at the low field side of the Tore Supra tokamak was determined by spectroscopic analysis of passive D$_{\mathrm{\beta }}$ spectral emission from the near-antenna plasma. The \textbf{E}$_{\mathrm{\mathbf{LH}}}$ was determined by globally minimizing the $\chi $ associated with the experimental and theoretical spectral line profile. The theoretical profile is calculated from a non-perturbative solution to the Schr\"{o}dinger equation, which includes the magnetic and dynamic electric field vectors. The magnitude, the direction, and the scaling with LH power of the measured \textbf{E}$_{\mathrm{\mathbf{LH}}}$ were fairly consistent with those calculated from a full-wave LH model. In addition to \textbf{E}$_{\mathrm{\mathbf{LH}}}$ the inboard and an outboard neutral flow was determined from the Doppler shifts associated with the D$_{\mathrm{\alpha }}$ and D$_{\mathrm{\beta }}$ spectral profiles. It was found that excitation of the LH wave induced both an inboard and outboard co-current neutral flow, which is linearly dependent on injected power; preliminary results indicate ICRH decreases the LH wave-induced co-current neutral flow. Neutral flow velocities are consistent with measurements of ion flow velocities obtained by charge exchange recombination spectroscopy. [Preview Abstract] |
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CP8.00003: Dependence of plasma rotation braking on ion temperature and non-axisymmetric magnetic field spectra in high normalized beta KSTAR plasmas Y.S. Park, S.A. Sabbagh, J.W. Berkery, J.M. Bialek, W.H. Ko, Y.M. Jeon, J.G. Bak, S.H. Hahn, J. Kim, S.G. Lee, S. Jardin, M.J. Choi, G.S. Yun, H.K. Park H-mode plasma operation of KSTAR has surpassed the ideal MHD $n =$ 1 no-wall limit by achieving high normalized beta up to 2.8 while reducing plasma internal inductance to near 0.7. Non-axisymmetric fields were applied using in-vessel control coils with varied $n$~$=$~2 field spectra, ECH, and supersonic molecular beam injection to alter the plasma toroidal rotation profile in high beta H-mode plasmas and to analyze their distinct effects on the rotation. The rotation profile was significantly altered in a self-similar fashion with rotation level reduced by more than 60{\%} without tearing activity or mode locking using the full range of techniques. Changes in the steady-state rotation profiles are analyzed to determine the physical aspects of NTV. The NTV scaling with $\delta B^{2}$ shows good agreement with the measured profile change. The NTV coefficient scales as $T_{i}^{2.27}$, in general agreement with the low collisionality ``1/$\nu $'' regime scaling of NTV theory. Resistive tearing stability determined by examining the classical tearing stability index is discussed, and the result is compared with two-fluid resistive MHD solutions from the M3D-C$^{1}$ code. The effect of plasma rotation profile on tearing stability is examined using the M3D-C$^{1}$ analyses. [Preview Abstract] |
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CP8.00004: Simulation Study of EAST Scenarios with the Tokamak Simulation Code C.E. Kessel, R.V. Budny, W.M. Solomon, Yong Guo, P.T. Bonoli The EAST experiment has upgraded its heating and current drive systems to allow significant non-inductive current drive. The goal of 100{\%} non-inductive plasma current is being sought with 10 MW of LH, 8 MW of NBI, and 12 MW of ICRF. For 2014, the target is H-mode for 30 s. A series of scenarios are examined for plasma currents of 350, 450, 550, and 650 kA, to examine the H/CD requirements and the rampup plasma strategies. The Tokamak Simulation Code is used with PF coils, strcutures, and feedback systems for plasma shape position and current. Based on previous EAST discharges that primarily used LH and ICRF, plasma and discharge parameters are determined. Examination of H/CD combinations, and energy transport models are reported. [Preview Abstract] |
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CP8.00005: TRANSP predictive modeling of EAST steady state plasmas R.V. Budny, W.M. Solomon, B. Grierson, X. Yuan, C. Kessel, S. Ding The EAST tokamak is starting operation with major upgrades to the heating, current drive, and diagnostic systems [1]. We use the plasma transport code TRANSP to predict performance [2] with nearly steady state non-inductive current conditions at plasma current near 500~kA and toroidal field near 2.3~T. The heating power is assumed to start with $\simeq$4~MW of beam injection and continue with $\simeq$3 MW of ICRH. Current drive of $\simeq$2~MW of LHCD is assumed. The GLF23 [3] predictive model incorporated in TRANSP is used to predict temperatures, and TGLF [4] to predict temperatures, toroidal rotation, and electron density profiles. We explore scans in parameters such as I$_p$, B$_0$, and boundary assumptions to maintain non-inductive and high performance. \\[4pt] [1] G.Wan, {\it et al.,} 41$^{st}$ EPS Conf, Berlin (2014) O2.104;\\[4pt] [2] R.V.Budny, Nucl. Fusion {\bf 52} (2012) 013001;\\[0pt] [3] R.Waltz, {\it et al.,} Phys. Plasmas {\bf 4} (1997) 2482;\\[0pt] [4] G.M.Staebler, {\it et al.,} Phys. Plasmas {\bf 14} (2007) 055909 [Preview Abstract] |
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CP8.00006: Gyrokinetic simulation of microturbulence in EAST tokamak Yong Xiao, Taige Zhang, Chen Zhao A complete understanding of anomalous transport is critical for designing future magnetic fusion reactors. It is generally accepted that the micro-scale turbulence leads to anomalous transport. For low beta toroidal plasmas, the electrostatic modes may dominate and ion temperature gradient (ITG) mode and trapped electron mode (TEM) are two very important candidates accounting for ion and electron turbulent transport respectively. Recently the massively parallel gyrokinetic simulation has emerged as a major tool to investigate the nonlinear physics of the turbulent transport. The newly-developed capabilities enable the gyrokinetic code GTC to simulate the turbulent transport for real tokamak plasma shape and profiles. These capabilities include a new gyrokinetic Poisson solver and zonal flow solver suitable for general plasma shape and profiles, improvements on the conventional four-point gyroaverage and newly-developed nonuniform initial marker loading. The GTC code is now able to import experimental plasma profiles and equilibrium magnetic field that come from the EFIT or TRANSP equilibrium reconstruction. Linear and nonlinear gyrokinetic simulations are carried out with the new capabilities in GTC for the electron coherent mode (ECM) recently observed in the EAST tokamak (EAST shot {\#} 38300). We found that in the pedestal region with strong electron temperature gradient, the unstable waves propagate in the electron diamagnetic direction, showing a trapped electron mode (TEM) feature. It is also found in the collisionless limit, the linear mode frequency is higher than that from the experiment. [Preview Abstract] |
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CP8.00007: Investigation of the high density discharges on the J-TEXT Tokamak Peng Shi, Ge Zhuang, Li Gao, Jie Chen, Qiang Li, Yang Liu, Xiaolong Zhang Recently, the operation region has been explored for J-TEXT Ohmically heated discharges by means of gas puffing. The results showed that the maximum achievable density has been significantly expanded, from 0.43 $n_{G} $ (Greenwald limit) to 0.85 $n_{G}$, after the stainless steel vacuum wall was covered by the graphite tiles. Nevertheless, the J-TEXT high density discharges were frequently terminated by a disruption. The investigation concluded that the maximum achievable density strongly relied on the total plasma current $I_{P} $, but very weakly depended on the edge safety factor $q_{a}$. Some features of such disruption have been identified by analyzing the measured data from the 17-channel (covering $-0.94a\sim 0.94a$ of the cross-section) FIR polarimeter-interferometer. For example, in the density ramp-up phase, asymmetry of density profile between the LFS (low field side) edge ($r>0.8a$) and the HFS (high field side) edge ($r<-0.8a$) would appear gradually. In addition, a reversed density gradient on the HFS edge occurred. Before the disruption, edge density on the HFS suddenly dropped to a lower level and tended to restore the symmetry of density profile between the LFS and HFS edge. Simultaneously, the radiation measurements, including CIII impurity radiations, soft X-ray emissions and so on, indicated that plasma radiation increased dramatically. Such lower density level at the HFS edge can maintain for $\sim 100ms$ when $q_{a} >5$, but less (or even null) for $q_{a} <3.5$ [Preview Abstract] |
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CP8.00008: Preliminary experimental observation of nonlocal transport due to SMBI on the J-TEXT tokamak Jinshui Xiao, Zhoujun Yang, Ge Zhuang, Chi Zhang, Minghai Liu Experimental studies of nonlocal electron heat transport have been carried out in J-TEXT ohmic plasmas exploiting Supersonic Molecular Beam Injection (SMBI) system. By cooling the very edge plasma, a prompt ($\sim$1ms) temperature rise of the plasma core can be induced. For a low density discharge with ne $= 1.1 \times 10^{19}$ m$^{-3}$, the amplitude of $\Delta $Te/Te exceeds 30{\%} at r/a$=$0.17 (a is the minor radius). The duration of NLT phenomena is about 10ms, which is comparable with the energy confinement time of J-TEXT. The Te inverse radius in this discharge locates at r/a$=$ 0.33 $\sim$ 0.4 and is outside the q$=$1 surface (r/a $\sim$ 0.3), which the latter is estimated from the sawtooth inverse position. As plasma density increases, the nonlocal phenomena decay. Repetitive nonlocal phenomena can be induced by modulated SMBI, which distinctly exhibits the strong dependence on electron density. The critical density is about 1.6 $\times$ 10$^{19}$ m$^{-3}$. [Preview Abstract] |
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CP8.00009: Halo and Runaway Currents in ITER Allen Boozer In ITER, halo currents can unacceptably increase maintenance requirements, and a strong current of runaway electrons cannot be allowed to occur. Halo-current mitigation may unacceptably exacerbate the problem of runaways. A strong halo current flows along magnetic field lines that intercept the walls just outside the main plasma body when the plasma becomes too kink unstable for the chamber walls to slow the growth rate. Basic physics constrains and simplifies the calculation of the effects of halo currents. The plasma current in ITER is naturally converted into a current of runaway electrons with a typical energy of about 10MeV by an exponential avalanche mechanism when the temperature drops much below 1keV for any reason. Pitch-angle scattering on high-$Z$ impurities may be important but has not been adequately studied. Scattering may explain anomalies in runaway production seen in experiments. Scattering also affects the anisotropy of runaways, $\epsilon_a\equiv j_r/en_rc$. The parallel current and number density of runaways are $j_r$ and $n_r$. The power that runaway electrons loose by drag on background electrons is $en_rE_c$. Runaway electron production is not energetically possible unless the parallel electric field satisfies $E_{||}\geq E_c/\epsilon_a$. [Preview Abstract] |
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CP8.00010: ITER Plasma at Ion Cyclotron Frequency Domain: The Fusion Alpha Particles Diagnostics Based on the Stimulated Raman Scattering of Fast Magnetosonic Wave off High Harmonic Ion Bernstein Modes V. Alexander Stefan A novel method for alpha particle diagnostics is proposed. The theory of stimulated Raman scattering, SRS,\footnote{ V. Alexander Stefan, ITER Plasma at Electron Cyclotron Frequency Domain: Tokamak Core Plasma Diagnostics Based on the Synergy of Stimulated Raman and Brillouin Scatterings, Bulletin of the American Physical Society , 54th Annual Meeting of the APS Division of Plasma Physics, Volume 57, Number 12, 2012; Abstract: TO6.00010} of the fast wave and ion Bernstein mode, IBM, turbulence in multi-ion species plasmas\footnote{ V. Alexander Stefan, \textit{Nonlinear Electromagnetic Radiation Plasma Interactions}, (Stefan University Press, La Jolla, CA, 2008).} is utilized for the diagnostics of fast ions, (4)He ($+$2), in ITER\footnote{ E. P. Velikhov, (Kurchatov Institute, Moscow, Russia), private communication in La Jolla, CA, 2007.} plasmas. Nonlinear Landau damping of the IBM on fast ions near the plasma edge leads to the space-time changes in the turbulence level, (inverse alpha particle channeling). The space-time monitoring of the IBM turbulence via the SRS techniques may prove efficient for the real time study of the fast ion velocity distribution function, spatial distribution, and transport. [Preview Abstract] |
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CP8.00011: Analysis and Measurements of 170 GHz ITER ECH Transmission Line Components Sudheer Jawla, Samuel Schaub, Michael Shapiro, Elizabeth Kowalski, Richard Temkin, Gregory Hanson In this paper we discuss two important issues related to the ITER 170 GHz ECH 63.5-mm diameter corrugated waveguide Transmission Lines (TL); 1) calculation of mode conversion losses in the expansion units for the TL, and, 2) determination of mode contents in corrugated waveguides. Expansion units are needed to accommodate expansion and contraction along the TL from the gyrotron to the tokamak. A numerical mode matching code has been developed to estimate power losses due to mode conversion of the operating mode, HE$_{11}$, to higher order modes as a result of the radial discontinuities in a sliding joint. Two designs were evaluated, a simple gap expansion unit and a more complex tapered expansion unit. We also present a novel method for determining the mode content of the linearly polarized (LP) modes of a corrugated waveguide using the method of moments. This method is based on calculating the low order irradiance moments of the measured radiated intensity profiles at several distances from the waveguide aperture. The proposed method is experimentally validated by the data measured from the 63.5-mm diameter corrugated waveguide using the vector network analyzer and a high purity HE$_{11}$ mode generator at 170 GHz built by General Atomics. [Preview Abstract] |
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CP8.00012: Designing Diagnostics to Survive in ITER Christopher Watts Adapting diagnostics to withstand the incredibly harsh environment of the ITER D-T plasma is a formidable engineering task. Hindrances include not only the nuclear environment, but also the high radiative heat fluxes, high particle fluxes and stray ECH radiation. Strategies to mitigate the impact of these run the gamut from shielding, through recessing, through appropriate materials selection, to refurbishment. Examples include the Langmuir probe system, where individual probes are protected by passive heat shields; retroreflectors recessed into the tokamak first wall in deep, baffled tunnels; plasma mirror cleaning systems; electronics components like piezo crystals and x-ray detectors vetted for the nuclear environment. These and other ITER diagnostic system designs will be highlighted to emphasize their strategies for dealing with the ITER environment. *The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. [Preview Abstract] |
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CP8.00013: Application of a GPU-Assisted Maxwell Code to Electromagnetic Wave Propagation in ITER S. Kubota, W.A. Peebles, D. Woodbury, I. Johnson, A. Zolfaghari The Low Field Side Reflectometer (LSFR) on ITER is envisioned to provide capabilities for electron density profile and fluctuations measurements in both the plasma core and edge. The current design for the Equatorial Port Plug 11 (EPP11) employs seven monostatic antennas for use with both fixed-frequency and swept-frequency systems. The present work examines the characteristics of this layout using the 3-D version of the GPU-Assisted Maxwell Code (GAMC-3D). Previous studies in this area were performed with either 2-D full wave codes or 3-D ray- and beam-tracing. GAMC-3D is based on the FDTD method and can be run with either a fixed-frequency or modulated (e.g.\ FMCW) source, and with either a stationary or moving target (e.g.\ Doppler backscattering). The code is designed to run on a single NVIDIA Tesla GPU accelerator, and utilizes a technique based on the moving window method to overcome the size limitation of the onboard memory. Effects such as beam drift, linear mode conversion, and diffraction/scattering will be examined. Comparisons will be made with beam-tracing calculations using the complex eikonal method. [Preview Abstract] |
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CP8.00014: Benchmarking FASTRAN vs TSC in Integrated ITER Modeling Simulations S.J. Diem, D.B. Batchelor, W.R. Elwasif, M. Murakami, J.M. Park, A.C. Sontag, F. Poli ITER steady state scenarios are examined using the Integrated Plasma Simulator (IPS) framework, which finds a self-consistent scenario of heating and current drive, MHD equilibrium, and transport. Both the FASTRAN solver and Tokamak Simulation Code (TSC) have been implemented in IPS to integrate a variety of models for transport, heating, CD and stability. The objective of this exercise is to benchmark the TSC/IPS time-dependent simulation with the FASTRAN/IPS steady-state solution procedure. The benchmark case is a fully non-inductive ITER steady-state scenario. Both simulations include ion cyclotron resonance heating, modeled using TORIC, and neutral beam heating, modeled using NUBEAM. The transport is modeled using GLF23 for both codes. Electron cyclotron heating was modeled using GENRAY. The results at several times of a time-evolving TSC simulation will be used as an initial guess for FASTRAN runs to compare the FASTRAN steady-state solutions to the time evolving TSC simulation. [Preview Abstract] |
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CP8.00015: Initial results for a 170 GHz high power ITER waveguide component test stand Timothy Bigelow, Alan Barker, Carl Dukes, Stephen Killough, Michael Kaufman, John White, Gary Bell, Greg Hanson, Dave Rasmussen A high power microwave test stand is being setup at ORNL to enable prototype testing of 170 GHz cw waveguide components being developed for the ITER ECH system. The ITER ECH system will utilize 63.5 mm diameter evacuated corrugated waveguide and will have 24 \textgreater 150 m long runs. A 170 GHz 1 MW class gyrotron is being developed by Communications and Power Industries and is nearing completion. A HVDC power supply, water-cooling and control system has been partially tested in preparation for arrival of the gyrotron. The power supply and water-cooling system are being designed to operate for \textgreater 3600 second pulses to simulate the operating conditions planned for the ITER ECH system. The gyrotron Gaussian beam output has a single mirror for focusing into a 63.5 mm corrugated waveguide in the vertical plane. The output beam and mirror are enclosed in an evacuated duct with absorber for stray radiation. Beam alignment with the waveguide is a critical task so a combination of mirror tilt adjustments and a bellows for offsets will be provided. Analysis of thermal patterns on thin witness plates will provide gyrotron mode purity and waveguide coupling efficiency data. Pre-prototype waveguide components and two dummy loads are available for initial operational testing of the gyrotron. [Preview Abstract] |
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CP8.00016: Transmission line component testing for the ITER Ion Cyclotron Heating and Current Drive System Richard Goulding, G.L. Bell, C.E. Deibele, M.P. McCarthy, D.A. Rasmussen, D.W. Swain, G.C. Barber, C.N. Barbier, I.H. Cambell, R.L. Moon, P.V. Pesavento, E. Fredd, N. Greenough, C. Kung High power RF testing is underway to evaluate transmission line components for the ITER Ion Cyclotron Heating and Current Drive System. The transmission line has a characteristic impedance $Z_{0} = 50 \Omega$ and a nominal outer diameter of 305 mm. It is specified to carry up to 6 MW at VSWR=1.5 for 3600 s pulses, with transient voltages up to 40 kV. The transmission line is actively cooled, with turbulent gas flow $(N_2)$ used to transfer heat from the inner to outer conductor, which is water cooled. High voltage and high current testing of components has been performed using resonant lines generating steady state voltages of 35 kV and transient voltages up to 60 kV. A resonant ring, which has operated with circulating power of 6 MW for 1 hr pulses, is being used to test high power, low VSWR operation. Components tested to date include gas barriers, straight sections of various lengths, and 90 degree elbows. Designs tested include gas barriers fabricated from quartz and aluminum nitride, and transmission lines with quartz and alumina inner conductor supports. The latest results will be presented. [Preview Abstract] |
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CP8.00017: Modeling ITER ECH Waveguide Performance M.C. Kaufman, C.H. Lau There are stringent requirements for mode purity and for on-target power as a percentage of source power for the ECH transmission lines on ITER. The design goal is less than 10\% total power loss through the line and 95\% HE$_{11}$ mode at the diamond window. The dominant loss mechanism is mode conversion (MC) into higher order modes, and to maintain mode purity, these losses must be minimized. Miter bends and waveguide curvature are major sources of mode conversion. This work uses a code which calculates the mode conversion and attenuation of an arbitrary set of polarized waveguide modes in circular corrugated waveguide with non-zero axial curvature and miter bends. The transmission line is modeled as a structural beam with deformations due to misalignment of waveguide supports, tilts at the interfaces between waveguide sections, gravitational loading, and the extrusion and fabrication process. As these sources of curvature are statistical in nature, the resulting MC losses are found via Monte Carlo modeling. The results of this analysis will provide design guidance for waveguide support span lengths, requirements for minimum alignment offsets, and requirements for waveguide fabrication and quality control. [Preview Abstract] |
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CP8.00018: Optimizing Antenna Layout for ITER Low Field Side Reflectometer using 3D Ray Tracing Code Sarah Newbury, Ali Zolfaghari The ITER Low Field Side Reflectometer (LFSR) is being designed to provide electron density profile measurements for both the core and edge plasma through the launching of millimeter waves into the plasma and the detection of the signal of the reflected wave by a receive antenna. Because the detection of the received signal is integral to the determination of the density profile, an important goal in designing the LFSR is to optimize the coupling between launch and receive antennas. This project investigates this subject by using Genray, a 3D ray tracing code, to simulate the propagation of millimeter waves launched into and reflected by the plasma for a typical ITER case. Based upon the results of the code, beam footprints will be estimated for different cases in which both the height and toroidal angle of the launch antenna are varied. The footprints will be compared, allowing conclusions to be drawn about the optimal antenna layout for the LFSR. This method will be carried out for various frequencies of both O-mode and X-mode waves, and the effect of the scrape-off layer of the plasma will also be considered. [Preview Abstract] |
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CP8.00019: Simulation of plasma current ramp-up with reduced magnetic flux consumption in JT-60SA using TOPICS transport code Takuma Wakatsuki, Takahiro Suzuki, Nobuhiko Hayashi, Shunsuke Ide, Yuichi Takase Feasibility of current ramp-up with reduced central solenoid (CS) magnetic flux consumption should be demonstrated to envision compact tokamak reactors such as SlimCS. In JT-60SA, issues concerning compact steady-state reactors can be investigated using a variety of heating and current drive combinations (positive and negative ion source based neutral beams and electron cyclotron waves). In this paper, plasma current ramp-up scenarios with reduced CS flux consumption has been investigated on JT-60SA using TOPICS transport code. Time evolution of the temperature profile is calculated using the CDBM model with prescribed density profile. In order to minimize the resistive flux consumption, we aim at ramping-up the plasma current from 0.6 MA to 2.1 MA maintaining a non-inductive full current drive (full-CD) condition. It has been found that a large bootstrap current fraction (\textgreater 60 {\%}) is needed to achieve a full-CD condition within the heating and CD capability planned in JT-60SA. This condition can be achieved with formation of a strong internal transport barrier. As a result, the resistive flux consumption can be reduced by a factor of 10. Since $\beta_{N}$ exceeds 4 x li(3) during the ramp-up phase, we will also discuss the MHD stability. [Preview Abstract] |
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CP8.00020: Progress in integrated modeling of JT-60SA plasma operation scenarios with model validation and verification Nobuhiko Hayashi, Jeronimo Garcia, Mitsuru Honda, Katsuhiro Shimizu, Kazuo Hoshino, Shunsuke Ide, Gerardo Giruzzi, Yoshiteru Sakamoto, Takahiro Suzuki, Hajime Urano Development of plasma operation scenarios in JT-60SA [1] has been progressing by using integrated modeling codes. In order to obtain an optimum set of models for the prediction, models are validated by using JT-60U and JET experimental data, and verified by integrated codes such as TOPICS and CRONOS. Predictive simulations are performed to assess the performance of each scenario and to develop optimum scenarios. In the scenario development, various physics aspects are studied by using various types of integrated modeling. The integrated divertor code SONIC showed that Ar seeding can reduce the heat flux on divertor plates below the preferable level (10 MW/m$^{2})$ with keeping low separatrix density in the full non-inductive current drive scenario, however, there are some amounts of Ar influx to core region. We integrate TOPICS with a core impurity transport code IMPACT and study the Ar accumulation in the core and its effect on the performance. Other studies with integrated modeling will be also presented. \\[4pt] [1] JT-60SA Research Plan v3.1, http://www.jt60sa.org/pdfs/JT-60SA\textunderscore Res\textunderscore Plan.pdf [Preview Abstract] |
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CP8.00021: Investigation of impurity radition in Wendelstein 7-X startup plasmas with EMC3-Eirene Florian Effenberg, Yuehe Feng, Sergey Bozhenkov, Heinke Frerichs, Hauke Hoelbe, Thomas S. Pedersen, Detlev Reiter, Oliver Schmitz The optimized stellarator Wendelstein 7-X will be operated in a limiter configuration during the first plasma operation phase. In this field configuration the plasma boundary does not include magnetic islands and the scrape-off layer is defined by five poloidal graphite limiters located at the bean shaped symmetry planes. The limiters define the position of the last closed flux surface and are positioned such that they prevent for high heat fluxes onto the unprotected main chamber wall and metallic frame structure of the later divertor targets. Considering startup plasmas with heating power up to 4MW and densities up to 9$\times$10$^{19}$m$^{-3}$ heat loads to plasma facing components (PFCs) and the generation of impurities due to plasma surface interaction become a concern. Plasma transport simulations are performed with the 3D fluid plasma edge and kinetic neutral transport code EMC3-Eirene. It is based on a fluid model for electrons and ions, a kinetic model for neutral particles, and a fluid approach for impurity ions. Results are discussed for a systematic scan of plasma scenarios assessing the production and transport of impurities. In particular radiation cooling is explored as means to reduce impurity production and heat loads to PFCs. [Preview Abstract] |
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CP8.00022: ITB Dynamics in Fusion Self-Heated Plasmas David Newman, P.W. Terry, Raul Sanchez Simple dynamical models have been able to capture a remarkable amount of the observed dynamics of the transport barriers found in many devices, including the often disconnected nature of the electron thermal transport channel sometimes observed in the presence of a standard (``ion channel'') barrier. The electron channel formation and evolution has been found to be even more sensitive to the alignment of the various gradients making up the sheared radial electric field then the ion barrier is. Because of this sensitivity and coupling of the barrier dynamics, the dynamic evolution of the fusion self-heating profile can have a significant impact on the barrier location and dynamics. To investigate this, self-heating has been added this model and the impact of the self-heating on the formation and controllability of the various barriers is explored. It has been found that the evolution of the heating profiles can suppress or collapse the electron channel barrier leading to the possibility of using NBI for profile/barrier control. Studies of different evolution scenarios will be presented. [Preview Abstract] |
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CP8.00023: Nuclei Separation Issue for p-B$^{11}$ Burning Plasmas* L. Merriman, B. Coppi Proton-Boron$^{11}$ fusing plasmas have the appealing characteristics of not producing neutrons but only charged particles and of involving easily available fuel nuclei. This feature has attracted the interest of distinguished scientists. On the other hand, as is well known, p-B$^{11}$ cannot ignite. In addition, there is an unexplored issue related to a transport process [1] due to the relatively large ratio of the masses of the two fuel nuclei. Since for equal temperatures of the two species, the difference between the squares of their thermal velocities is wide, a mode with a phase velocity between the two thermal velocities has been found [2]. This has the effect of transporting the two species in different directions radially and of enhancing the nuclei thermal energy transport. The obtained results, although not as critical as the lack of an ignition condition, should be taken into account in the burn simulations of p-B$^{11}$ plasmas that have to be carried out. *Sponsored in part by the U.S. DOE.\\[4pt] [1] B. Coppi, H. Furth, M. Rosenbluth and R. Sagdeev, \textit{Phys. Rev. Lett}. \textbf{17}, (1966) 377.\\[0pt] [2] B. Coppi, MIT (LNS) Report HEP 13/07, recommended publication in Physics of Plasmas, subject to a more complete presentation of its context. [Preview Abstract] |
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CP8.00024: Theoretical Issues for Plasma Regimes to be Explored by the Ignitor Experiment* A. Cardinali, B. Coppi, G. Sonnino At present, the Ignitor experiment is the only one designed and planned to approach and explore ignition regimes under controlled DT burning conditions. The machine parameters [1] have been established on the basis of existing knowledge of the confinement properties of high density plasmas. A variety of improved confinement regimes are expected to be accessible by means of the available ICRH heating power in addition to the prevalent programmable Ohmic heating power and relying on the injection of high velocity pellets for density profile control. The relevance of the various known confinement regimes to the objectives of Ignitor is discussed. Among other theoretical efforts, a non-linear thermal energy balance equation is investigated to study the onset of thermonuclear instability in the plasmas expected to be produced in Ignitor. The equation for the temperature profile in the equilibrium state is solved with the resulting profiles in agreement with those obtained by a full transport code and commonly adopted scalings for them. The evolution of the thermonuclear instability that relies on the solution of the time dependent energy balance equation is obtained. *Sponsored in part by the U.S. DOE.\\[4pt] [1] B. Coppi, et al. \textit{Nucl. Fus.} \textbf{53}, 104013 (2013). [Preview Abstract] |
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CP8.00025: Nonlinear Numerical Modeling of Shape Control in IGNITOR in the Presence of 3D Structures R. Albanese, G. Ambrosino, G. De Tommasi, A. Pironti, G. Rubinacci, F. Villone, G. Ramogida, B. Coppi IGNITOR is a high field compact machine [1] designed for the investigation of fusion burning plasmas at or close to ignition. The integrated plasma position, shape and current control plays an important role in its safe operation. The analysis of its behavior taking into account nonlinear and 3D effects can be of great interest for assessing its performances. In fact, the system was designed on the basis of an axisymmetric linearized model. To this purpose, we use a computational tool, called CarMa0NL, with the unprecedented capability of simultaneously considering three-dimensional effects of conductors surrounding the plasma and the inherent nonlinearity of the plasma behaviour itself, in the presence of the complex set of circuit equations describing the control system. Preliminary results already lead to the conclusion that the vertical position response is not much influenced by nonlinear and 3D effects, as the vertical stabilization controller is able to ``hide'' the differences in open-loop models. Here we assess the performance of the shape controller, by coupling the nonlinear plasma evolution in the presence of the 3D vessel with ports to the complex circuit dynamics simulating the integrated closed loop control system.\\[4pt] [1] B. Coppi, et al. Nucl. Fus. 53, 104013 (2013). [Preview Abstract] |
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CP8.00026: Developments for the ICRH System of the Ignitor Machine* M. Sassi, S. Mantovani, B. Coppi The ICRH system that is suitable for the high-density plasmas to be produced by the Ignitor machine[1] has been designed and components of it have been tested. This system will operate over the range 80-120 MHz, consistently with magnetic fields in the range 9-13 T. The maximum delivered power is in the interval 8 MW (at 80 MHz) to 6 MW (at 120 MHz) distributed over 4 ports. A full size prototype of the VTL between the port flange and the antenna straps, with the external support and precise guiding system has been constructed. The innovative quick latching system located at the end of the coaxial cable has been successfully tested, providing perfect interference with the spring Be-Cu electrical contacts. Vacuum levels of $10^{-6}$, compatible with the limit of material degassing, and electrical tests up to 12 kV without discharges have been obtained. *Sponsored in part by the US DOE.\\[4pt] [1] B. Coppi, et al. $\it{Nucl. Fus}. \bf{53}$, 104013 (2013). [Preview Abstract] |
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CP8.00027: Who will save the tokamak -- Harry Potter, Arnold Schwarzenegger, or Shaquille O'Neil? J. Freidberg, F. Mangiarotti, J. Minervini The tokamak is the current leading contender for a fusion power reactor. The reason for the preeminence of the tokamak is its high quality plasma physics performance relative to other concepts. Even so, it is well known that the tokamak must still overcome two basic physics challenges before becoming viable as a DEMO and ultimately a reactor: (1) the achievement of non-inductive steady state operation, and (2) the achievement of robust disruption free operation. These are in addition to the PMI problems faced by all concepts. The work presented here demonstrates by means of a simple but highly credible analytic calculation that a ``standard'' tokamak cannot lead to a reactor -- it is just not possible to simultaneously satisfy all the plasma physics plus engineering constraints. Three possible solutions, some more well-known than others, to the problem are analyzed. These visual image generating solutions are defined as (1) the Harry Potter solution, (2) the Arnold Schwarzenegger solution, and (3) the Shaquille O'Neil solution. Each solution will be described both qualitatively and quantitatively at the meeting. [Preview Abstract] |
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CP8.00028: The Nonlinear Stationary State of Simple Interchange Turbulence Kenneth Gentle, W.L. Rowan, C.B. Williams, M.W. Brookman The Helimak is an approximation to the infinite cylindrical slab with a size large compared with turbulence transverse scale lengths, but with open field lines of finite length. Interchange modes are the dominant instability. Radially-segmented isolated end plates allow application of radial electric fields to modify the plasma flow transverse to B and the radial equilibrium gradient. Measurements of the ion flow velocity profile are made by Doppler spectroscopy of the argon plasma ion. The level of non-linearly saturated turbulence has been measured over a wide range of collisionality, parallel connection length, and flow pattern, but none of the processes found effective for setting the level of saturated turbulence for the weaker turbulence in the plasma interior are found applicable. Quasi-linear theory is inconsistent with the observations, zonal flows are not observed, and local flow shear does not correlate with local turbulence level. Weak correlations are found between turbulence level and radial correlation length for some restricted data subsets, but no broad correlation or predictive power exists. Work supported by the Department of Energy OFES DE-FG02-04ER54766. [Preview Abstract] |
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CP8.00029: Guiding center revisited and orbital spectral analysis for non-axisymmetric perturbations K. Hizanidis, P.A. Zestanakis, Y. Kominis, G. Anastasiou A systematic transformation algorithm from guiding center (GC) coordinates to action-angle variables for any type of magnetic equilibrium is presented. It exploits Hamiltonian methods for describing single and collective particle dynamics for various types of interactions. It accounts for finite orbit width effects and performs orbit averaging calculations for particles at any energy, pitch angle and radial position for any type of non-axisymmetric perturbations. Furthermore, the GC picture is revisited on the basis of the differential geometry features of the particle orbit and its transverse to the local magnetic field evolute. The latter yields the exact fully relativistic vectorial gyration radii which can be approximated by the respective Larmor ones under certain conditions. The approach incorporates inhomogeneous magnetic and electric fields as well as magnetic field perturbations. {\it This project is partially funded by EU Horizon 2020 Research and Innovation Programme under GA No. 633053 (the views and opinions expressed herein do not necessarily reflect those of the European Commission and the Hellenic NPTFR)}. [Preview Abstract] |
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CP8.00030: How to apply a turbulent transport model based on a gyrokinetic simulation for helical plasmas S. Toda, M. Nunami, A. Ishizawa, T.-H. Watanabe, H. Sugama A reduced transport model for the turbulent ion heat diffusivity due to the ion temperature gradient (ITG) mode was obtained from the gyrokinetic simulation using the GKV-X code for the high-$T_{i}$ Large Helical Device discharge [1]. This model is given by the function of the linear growth rate of the ITG mode divided by the square of the poloidal wavenumber integrated over the poloidal wavenumber space, $\mathcal{L}$ and the zonal flow decay time. The zonal flow decay time is calculated only at the initial state in the transport simulation, when the field configuration is temporally fixed. However, it takes a huge cost to carry out linear gyrokinetic simulations of the growth rate at each time step in the transport code. How to apply the reduced model to the temporal transport simulation is proposed with a low computational cost. Modeling of $\mathcal{L}$ is necessary to be involved with a parameter dependence of the plasma instability in the transport code. The ion temperature gradient scale length is chosen to apply $\mathcal{L}$ to the transport code for the ITG mode. The calculation in this study reproduces the results of the reduced model with an extremely low computational cost.\\[4pt] [1] M. Nunami, T. -H. Watanabe and H. Sugama, Phys. Plasmas Vol. 20. 092307 (2013) [Preview Abstract] |
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CP8.00031: Turbulence Parallel Wavenumbers in the Texas Helimak Chad Williams, Kenneth Gentle It is well known that wavenumbers, in particular the existence of a parallel wavenumber, play an important role in the classification of turbulence. In a paper published in 2010, Paolo Ricci and B.N. Rogers posit the existence of a previously undiscovered resistive interchange mode, similar to a tokamak resistive ballooning instability, that appears in simple magnetized toroidal plasmas at long connection length (PRL 104, 145001). As the pitch of the magnetic field lines is flattened, and thus the connection length is increased, the system was shown to undergo a transition from an ideal interchange mode with zero parallel wavenumber to a resistive interchange mode with nonzero parallel wavenumber. Additionally, the system undergoes a change in mode numbers. In this work we seek to measure the parallel wavenumber in the Texas Helimak at several long connection lengths in order to characterize the turbulence. By so doing we attempt to find the resistive interchange mode to provide verification of its existence in the Texas Helimak. [Preview Abstract] |
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CP8.00032: Gyrokinetic Simulation of HL-2A H-mode Turbulent Transports Hua-sheng Xie, Yong Xiao Gyrokinetic simulations using GTC code are carried out to study recent HL-2A H-mode experiments (shots {\#}19298, 14048, 14052). In those experiments, both low frequency (LFT) and high frequency (HFT) turbulences are found. The LFT is found to be mainly electrostatic (E.S.) with poloidal mode number m $\sim$ 14-33 and frequency f $\sim$ 25-65 kHz. Meanwhile, the HFT is found to be mainly electromagnetic (E.M.) with poloidal mode number m $\sim$ 16- 38, toroidal mode number n $\sim$ 6-14 and frequency f $\sim$ 100-400 kHz. In the E.S. simulation, a low-frequency unstable mode is found in the electron diamagnetic direction and no unstable mode is found when the electrons are treated adiabatic. Hence, the LFT is identified to be trapped electron mode (TEM). In linear stage, the most unstable mode is found to be n $\sim$ 20 and m $\sim$ 50-80. The dominant poloidal mode number will downshift to m $\sim$15-40 in the nonlinear stage, which is close to the experimental observation. In the E.M. simulation, strong ideal and high frequency kinetic ballooning modes (KBM) are found. To verify the KBM capability of GTC, detailed benchmarks with analytic equilibriums are also shown. [Preview Abstract] |
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CP8.00033: On fast radial propagation of parametrically excited Geodesic Acoustic Modes Liu Chen, Zhiyong Qiu, Fulvio Zonca It is known from linear theories that, Geodesic Acoustic Mode (GAM) linear group velocity is due to finite Larmor radius (FLR) effects, and is typically radially outward in consistency with GAM continuum associated with temperature profiles. In this work, we show that, since GAM is linearly stable, nonlinear effects must be considered to explain experimental observations. Our results show that the nonlinearly driven GAM propagates at a much larger group velocity, which is the mean of the linear group velocities of GAM and drift wave turbulence. The nonlinear theories presented here, can also be applied to interpret the discrepancies between the experimentally measured dispersion relation of GAM and that from linear theories. Further implications of these findings for proper understanding of experimental observations are discussed.\\[4pt] [1] N. Winsor, J. L. Johnson and J. M. Dawson, Phys. Fluids {\bf 11}, (1968) 2448.\newline [2] F. Zonca and L. Chen, Europhys. Lett. {\bf 83}, (2008) 35001.\newline [3] Z. Qiu, L. Chen and F. Zonca, Phys. Plasmas {\bf 21} (2014) 022304.\newline [4] D. Kong, A. Liu, T. Lan et al, Nucl. Fusion {\bf53} (2013) 113008. [Preview Abstract] |
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CP8.00034: Full-f gyrokinetic simulations for neoclassical toroidal viscosity in a perturbed tokamak configuration Seikichi Matsuoka, Yasuhiro Idomura, Shinsuke Satake A magnetic field perturbation in tokamak plasmas plays a key role in determining the intrinsic rotation and velocity shear, since even a small perturbation can break the axisymmetry in the toroidal direction and induces the finite neoclassical toroidal viscosity (NTV). A simulation study for the NTV evaluation in an axisymmetric tokamak with a small resonant magnetic field perturbation using the full-f gyrokinetic Eulerian code GT5D is presented. The magnetic field perturbation is included in the particle orbit of GT5D only through the Hamiltonian by replacing the axisymmetric magnetic field with the sum of the axisymmetric field and the perturbation, which enables us to perform GT5D simulations without changing the symplectic structure of the single-particle Lagrangian constructed for the equilibrium (axisymmetric) magnetic field. Numerical results are benchmarked with those obtained by the neoclassical transport code, FORTEC-3D, which solves the drift kinetic equation by two-weight $\delta f$ Monte Carlo method. The NTV of GT5D with a single-helicity perturbation is found to have a similar peaked profile around the resonant surface as that of FORTEC-3D. [Preview Abstract] |
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CP8.00035: Nonlinear Gyrokinetic Simulation of Electron-Driven Turbulence in HSX Benjamin Faber, M.J. Pueschel, Gavin Weir, Konstatin Likin, Joseph Talmadge, Simon Anderson, David Anderson The first nonlinear gyrokinetic simulations of plasmas in the Helically Symmetric eXperiment (HSX) are presented. Due to large electron cyclotron resonance heating (ECRH) and little ion heating, microtubulence in HSX is driven by electron dynamics and thus the simulations performed require two kinetic species. Linear growth rate calculations of plasmas at experimental parameters indicate HSX is unstable at low $k_y\rho_s$ to the Trapped Electron Mode (TEM) and the Electron Temperature Gradient (ETG) mode at high $k_y\rho_s$, especially in the core region where the normalized temperature gradient is significantly larger than the normalized density gradient. Nonlinear flux tube simulations show heat fluxes shift to smaller scales than for ion-driven turbulence, with the flux spectrum peaking at $k_y\rho_s \sim 0.9$ for TEM turbulence. Nonlinear simulations also show the evolution of zonal flows, which are a possible candidate for the nonlinear saturation mechanism. Calculation of the dependence of the saturated heat flux on the normalized electron temperature gradient provides a computational comparison with the stiffness measurements obtained in heat pulse propagation experiments.\footnote{G. M. Weir, invited talk, this conference} [Preview Abstract] |
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CP8.00036: Relaxation to neoclassical flow equilibrium in gyrofluid simulations Bruce Scott The theorem for toroidal angular momentum conservation within gyrokinetic field theory is used as a starting point for consideration of slow transport of flows under quasistatic force balance. If conserved/transported quantities are taken as given, the radial electric field is solved in terms of the neoclassical poloidal flow of each species and the total toroidal angular momentum. Standard result is recovered if the latter is small. In a gyro-kinetic or -fluid computation the collisional operator determines the parallel flow, which together with the momentum determines the radial electric field. Higher order drift terms included in the original Lagrangian yield contributions to these relations which can be measured by gyrokinetic computations. We find that for gyrofluid computations under conventional tokamak conditions that these are small. Finally, the pathway of relaxation to slowly varying conditions from an arbitrary initial state is detailed. The time scale hierarchy is separated to have Alfven and then geodesic oscillations damp away, and then on the ion collisional time scale the electric field is established, and then on the much slower confinement time the conserved quantities are transported. We detail these in a simple model and in gyroflluid computations. [Preview Abstract] |
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CP8.00037: Recently Discovered Features of the Quasi Coherent Mode* P. Montag, B. Coppi, L. Sugiyama, T. Zhou The Quasi Coherent Mode (QCM) is observed when the EDA H-Confinement regime is produced by the Alcator C-Mod machine and has been found [1] to 1) have a phase velocity in the direction of the electron diamagnetic velocity in the plasma reference frame 2) involve relatively high electron temperature fluctuations 3) be highly localized radially at the outer edge of the plasma column beyond the Last Closed Magnetic Surface (LCMS). A novel theoretical model is given for which; a) the relevant resistive mode driving factor is the sharp plasma pressure gradient that develops at the edge when the plasma enters the EDA H-Regime; b) the known ``disconnected mode approximation'' [2] cannot be applied to characterize the mode topology as the rotational transform $\iota\left(\psi\right)=1/q \left(\psi\right)=0$ on the LCMS; c) the mode localization in the poloidal direction (ballooning) is related to the limited region around the equatorial plane where the pitch of the magnetic field is about constant. The observed temperature fluctuations are consistent with the low values of the local longitudinal thermal conductivity. *Sponsored in part by the US DOE.\\[4pt] [1] B. Labombard, \textit{Bull. Am. Phys. Soc.} 58, (2013) 367.\\[0pt] [2] B. Coppi and G.Rewoldt, \textit{Phys. Rev. Lett.} 33, (1974) 3129. [Preview Abstract] |
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CP8.00038: Hybrid Gyrokinetic / Gyrofluid Simulation of ITG Turbulence Noah Mandell, William Dorland One of the main sources of disagreement between gyrofluid and gyrokinetic models is the inability of gyrofluid models to accurately describe zonal flows. These nonlinearly-driven sheared poloidal {\bf{E}} $\times$ {\bf{B}} flows have been shown to play a key role in determining the turbulence saturation level. While attempts have been made to improve gyrofluid modeling of zonal flows, we show here that improved zonal flow closures are insufficient. We introduce a new hybrid algorithm that simulates the zonal flow modes with a fully gyrokinetic model, while simulating the remaining modes with the newly developed GPU gyrofluid code GryfX. GryfX contains a new model of nonlinear FLR phase mixing by zonal flows, which in addition to accurate zonal flow modeling brings the heat flux predictions of the hybrid code into agreement with the gyrokinetic code GS2. The combination of GPU acceleration and the reduction of hundreds of velocity space grid points to six gyrofluid moments gives GryfX a roughly 7,000 times performance advantage over GS2. Further, due to supercomputer configurations that contain nodes with multiple CPUs per GPU, the hybrid fluid/kinetic code has minimal additional computation time cost and maintains a significant performance advantage over GS2. [Preview Abstract] |
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CP8.00039: Intrinsic momentum transport in tokamaks with tilted elliptical flux surfaces Justin Ball, Felix Parra, Michael Barnes, William Dorland, Gregory Hammett, Paulo Rodrigues, Nuno Loureiro Recent work demonstrated that breaking the up-down symmetry of tokamaks removes a constraint limiting intrinsic momentum transport, and hence toroidal rotation, to be small.\footnote{F.I. Parra, M. Barnes, and A.G. Peeters. Phys. Plasmas, 18(6):062501, 2011.} We show, through MHD analysis, that ellipticity is most effective at introducing up-down asymmetry throughout the plasma. Using GS2, a local $\delta f$ gyrokinetic code that self-consistently calculates momentum transport, we simulate tokamaks with tilted elliptical poloidal cross-sections and a Shafranov shift. These simulations show both the magnitude and poloidal dependence of nonlinear momentum transport. The results are consistent with TCV experimental measurements\footnote{Y. Camenen, A. Bortolon, B.P. Duval, et al. Phys. Rev. Lett., 105(13):135003, 2010.} and suggest that this mechanism can generate rotation with an Alfven Mach number of several percent in a tilted elliptical ITER-like machine. It appears that rotation generated with up-down asymmetry may be sufficient to stabilize the resistive wall mode in reactor-sized devices. [Preview Abstract] |
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CP8.00040: Interactions between Drift-Wave Microturbulence and the Tearing Mode S.D. James, D.P. Brennan, O. Izacard, C. Holland Turbulent dynamics are known to be affected by the presence of a magnetic island. The evolution of a magnetic island is also known to be affected by evolving turbulent fields. Capturing this interaction is a challenging computational problem due to the disparate scales involved. Using a Hasegawa-Wakatani model for the small spatial and temporal scale drift-wave microturbulence and coupling it to Ohm's Law for evolving the larger-scale magnetic island we can capture the dynamics of this interaction self-consistently. We have developed a new code, TURBO, to simulate this system using an equilibrium with prescribed turbulent drives and magnetohydrodynamic stability properties. We present progress toward understanding this interaction via comparisons with analytic predictions for a turbulent resistivity and turbulent viscosity. These two transport coefficients are calculated as integrals over the wave spectrum and the scaling with wave number is investigated. An extension to a five-field model including the ion temperature gradient is also presented. [Preview Abstract] |
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CP8.00041: Turbulent Transport in Presence of Magnetic Island Olivier Izacard, Christopher Holland, Spencer James, Dylan Brennan Understanding the physics of both large-scale magnetohydrodynamic instabilities and small-scale drift-wave microturbulence is essential for predicting and optimizing the performance of magnetic confinement based fusion energy experiments. While both types of instabilities have been investigated individually for many years now, less attention has been given to quantifying the interaction mechanisms between them. We report progress on understanding these interactions using both analytic theory and numerical simulation, with BOUT$++$ [B. Dudson et al., Comput. Phys. Comm. 180, 1467 (2009)] used to evolve a simple four-field fluid model in a sheared slab geometry. This work focuses upon understanding the dynamics of the electrostatic ion temperature gradient instability in the presence of a background static magnetic island, as key parameters such as ion temperature gradient and magnetic gradients are varied. The simulation results are then used to calculate effective turbulent transport coefficients (e.g. viscosity, resistivity) that are compared against analytic predictions. As part of this work, a OMFIT module has been developed to enable execution of BOUT$++$ and post-processing on either local or remote systems. [Preview Abstract] |
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CP8.00042: A Quasilinear Description of Pedestal Transport induced by RMPs Christopher McDevitt, Xian-Zhu Tang, Zehua Guo The abrupt release of stored energy by large edge localized modes (ELM) and its subsequent deposition onto plasma facing components can place significant limitations on material lifetimes. Resonant magnetic perturbations (RMP) have been suggested as a means of tailoring pedestal profiles in order to suppress large ELM events. In this work, we utilize a quasilinear collision operator formulation in order to compute transport induced by a stochastic magnetic field. This formulation allows for phase transport induced by fluctuations (including field perturbations) as well as Coulomb collisions to be treated on an equal footing, hence allowing for general collisionality regimes to be treated. In addition, such a phase space formulation incorporates kinetic effects such as particle trapping as well as magnetic drifts, which are crucial to the description of pedestal transport. Particular emphasis is placed on determining the relative efficiency RMPs have on transporting density, current and heat in order to better understand how RMPs may be employed to shape pedestal profiles. Ongoing work is focused on the self-consistent description of the electric field induced by the response of the plasma to RMPs. [Preview Abstract] |
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CP8.00043: The Wave-Kinetic Landau Fluid Ilon Joseph, Andris Dimits Efficient representation of kinetic effects such as Landau damping and particle trapping is crucial for the accuracy of reduced fluid models used to describe collisionless plasma turbulence. A new method for representing nonlinear resonance effects has been developed for Landau fluid [1] models. Wave-kinetic basis functions that focus velocity space resolution on wave-particle resonances naturally generate correct linear and nonlinear Landau damping amplitudes. Perhaps surprisingly, closely spaced resonances are accurately treated using ``inverse'' or ``pseudo'' moments [2] in velocity space. The closure for the fluid moment system is equivalent to the choice of a companion matrix that determines the linear response. This freedom can be used to generate multiple families of closures that generate the same Pad\'{e} approximation to the linear response [1], but have different nonlinear behavior. Results have been formally generalized to include trapped particle effects and collisions. \\[4pt] [1] G. W. Hammett and F. W. Perkins, Phys. Rev. Lett. \textbf{64}, 3019 (1990).\\[0pt] [2] P. Amendt, Phys. Plasmas \textbf{8}, 1437 (2001). [Preview Abstract] |
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CP8.00044: Steady state gyrokinetic PIC simulation of ITG turbulence W.W. Lee, R. Ganesh, S. Ethier We will report the implementation of the two-weight scheme [1] in the global gyrokinetic PIC code - GTC [2], for studying turbulence transport in tokamak plasmas along with our initial attempts to also include the neoclassical transport physics. With the two-weight scheme, which is based on multiscale expansion $F = F_0 (\epsilon {\bf x}) + \delta f({\bf x})$, where $\epsilon$ is a smallness parameter and $F_0$ is the background Maxwellian, we are able to simulate the transition from $\delta f$ particles in the linear stage to a certain percentage of full $F$ particles in the nonlinear stage in the same run. Such a scheme would help us to assess the correctness of $\delta f$ runs when $\delta f$ becomes large as well as for the cases where there are sources and sinks in the simulation. The behavior of the entropy for the new scheme and the effect of collisions will also be reported along with the comparisons with the size scaling obtained earlier [3] using only the $\delta f$ simulation. \\[4pt] [1] W. W. Lee, T. G. Jenkins and S. Ethier, Comp. Phys. Comm. {\bf 182}, 564 (2011).\\[0pt] [2] Z. Lin, T. S. Hahm, W. W. Lee, W. M. Tang, and R. White, Science {\bf 281}, 1835 (1998).\\[0pt] [3] W. W. Lee, S. Ethier, R. Kolesnikov, W. X. Wang, and W. M. Tang. Comp. Sci. \& Disc. {\bf 1}, 015010 [Preview Abstract] |
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CP8.00045: Investigations of Turbulent Transport Channels in Gyrokinetic Simulations A.M. Dimits, J. Candy, W. Guttenfelder, C. Holland, N. Howard, W.M. Nevins, E. Wang Magnetic-field stochasticity arises due to microtearing perturbations, which can be driven linearly [1] or nonlinearly (in cases where they are linearly stable [2]), even at very modest values of the plasma beta. The resulting magnetic-flutter contribution may [1] or may not [2] be a significant component of the overall electron (particle and thermal) transport. Investigations of the effect of ExB flow shear on electron-drift magnetic-flutter diffusion coefficient $D_{edr}(r$,v$_{\vert \vert })$ using perturbed magnetic fields from simulations, using the GYRO code [3], of ITG turbulence show a significant effect for electrons with parallel velocities v$_{\vert \vert }$ surprisingly far from the resonant velocity. We further examine changes in the radial dependence of this diffusion coefficient vs. v$_{\vert \vert }$ and which resonant magnetic-field perturbations are important to the values and radial structure of $D_{edr}$. The resulting electron transport fluxes are compared with the simulation results. Improvements over [2] in treating the ambipolar field in the relationship between the magnetic (or drift) diffusion coefficients and the transport have been made in these comparisons. \\[4pt] [1] W. Guttenfelder, et al., Phys. Plasmas \textbf{19}, 056119 (2012).\\[0pt] [2] E. Wang, et al., Phys. Plasmas \textbf{18}, 056111 (2011).\\[0pt] [3] J. Candy and R. E. Waltz, J. Comput. Phys. \textbf{186}, 545 (2003). [Preview Abstract] |
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CP8.00046: Study of no-man's land physics in the total-f gyrokinetic code XGC1 Seung Hoe Ku, C.S. Chang, J. Lang While the ``transport shortfall'' in the ``no-man's land'' has been observed often in delta-f codes, it has not yet been observed in the global total-f gyrokinetic particle code XGC1. Since understanding the interaction between the edge and core transport appears to be a critical element in the prediction for ITER performance, understanding the no-man's land issue is an important physics research topic. Simulation results using the Holland case [1] will be presented and the physics causing the shortfall phenomenon will be discussed. Nonlinear nonlocal interaction of turbulence, secondary flows, and transport appears to be the key. \\[4pt] [1] C. Holland et al., Physics of Plasmas 16 052301 (2009) [Preview Abstract] |
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CP8.00047: MIB Probes for measurements of particle and energy fluxes in plasma of Wendelstein 7-X V.I. Demidov, M.E. Koepke, I.P. Kurlyandskaya, Y. Raitses Magnetically insulated baffled (MIB) probes and probe arrays that share the simplicity of simple Langmuir probes but supersede them in their ability to make real-time measurements of plasma potential, temperature and energy/particle fluxes in W7-X stellarator plasma~are being developed.~The probes offer the advantages of direct measurements of the plasma fluid observables, while being non-emitting and electrically floating. The principle of operation of the probe is based on the dependence of the voltage drop in the plasma-probe sheath on the direction of the local magnetic field. The core technology for these probes rests with the use of a special baffling configuration such that electron current to the probe is fully controllable in the closed, open or partially open orientation, by a simple rotation of the baffle with respect to the magnetic field alignment in the plasma. The baffled-probe designs proposed for edge diagnostics will increase the capability to characterize separately plasma properties in real-time for understanding of underlying physics in the edge plasma. [Preview Abstract] |
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CP8.00048: L-H Transition Dynamics and Power Threshold Minimum Mikhail Malkov, Patrick Diamond, Kazuhiro Miki, George Tynan The link between the microscopic and macroscopic attributes of the LH transition and their effect on power threshold scaling are investigated. Emphasis is placed on understanding the minimum in the power threshold. By extending a numerical 1D model to evolve electron and ion heat fluxes separately, we propose and examine the explanation that: (i) the initial trend of decrease in the power threshold with density is due to stronger collisional electron-to-ion heat transfer which enables the development of stronger diamagnetic electric field, crucial to the transition, (ii) the subsequent increase in the threshold is due to the increase in damping of shear flows with ion collisionality. Our studies reveal a power threshold minimum in density scans which is particularly pronounced for an electron heating dominating at low densities. The heating mix is important to the transition, again pointing to the interplay of electron-ion coupling. The model also demonstrates: (a) an increase in threshold power for off-axis electron heat deposition. This follows from the reduction of the transfer of energy from electrons to ions within a confinement time, (b) the absence of a clear threshold minimum for pure ion heat deposition. [Preview Abstract] |
(Author Not Attending)
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CP8.00049: Impurity effect on poloidal potential variation and plasma turbulence in edge pedestal Kyuho Kim, Janghoon Seo, S.-H. Ku, C.-S. Chang, M. Churchill, R. Hager, Daren Stotler The poloidal variation of electrostatic potential in the H-mode edge pedestal can be significant, especially in diverted geometry [1,2]. Impurity particles may enhance such a poloidal variation [3]. The total-f gyrokinetic code XGC1 is used to study the impurity effect on poloidal potential variation in diverted magnetic field geometry. Even though the ExB shearing rate is strong in the edge pedestal, residual turbulence can exist [1]. Impurity effect on the residual turbulence will also be reported. Implication to plasma and impurity transport across the separatrix surface and pedestal region will also be discussed. \\[4pt] [1] C.S. Chang et al., Phys. Plasmas \textbf{16}, 056108 (2009) \\[0pt] [2] M. Churchill, Invited Talk at this conference\\[0pt] [3] C.S. Chang and R.D. Hazeltine, Nucl. Fusion \underline {20}, 1397 (1980) [Preview Abstract] |
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CP8.00050: INTENSE BEAM AND RADIATION SOURCES . [Preview Abstract] |
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CP8.00051: Laser Absorption and Particle Acceleration at the Critical Surface J. May, J. Tonge, W.B. Mori, F. Fiuza, R. Fonseca, L.O. Silva Using high intensity lasers ($I \ge 5 \times 10^{19} W/cm^2$) to accelerate particles at the critical surface offers the potential to deliver high fluence particle beams into dense matter. Potential applications include Fast Ignition Inertial Confinement Fusion, Radiation Pressure Acceleration, and probing high-density matter for basic plasma research. In order to tailor the beam characteristics of laser conversion efficiency, energy spectrum, beam divergence, and accelerated species (ions or electrons) to the given application -- and of course to interpret the results of experiments -- it is key to have an understanding of the underlying absorption and acceleration mechanisms. Much theoretical and simulation work has been done on this regime in recent years, and although it has become clear that mechanisms often invoked at lower intensities (i.e. JxB and Bruenel heating) are less or unimportant in these systems, debate still exists as to exactly what mechanisms will play the dominant role in laboratory relevant scenarios. We present recent results of simulations with the Particle-in-Cell code OSIRIS which sheds light on these issues. [Preview Abstract] |
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CP8.00052: Discrete Variational Approach for Modeling Laser-Plasma Interactions J. Paxon Reyes, B.A. Shadwick The traditional approach for fluid models of laser-plasma interactions begins by approximating fields and derivatives on a grid in space and time, leading to difference equations that are manipulated to create a time-advance algorithm. In contrast, by introducing the spatial discretization at the level of the action, the resulting Euler-Lagrange equations have particular differencing approximations that will exactly satisfy discrete versions of the relevant conservation laws. For example, applying a spatial discretization in the Lagrangian density leads to continuous-time, discrete-space equations and exact energy conservation regardless of the spatial grid resolution. We compare the results of two discrete variational methods using the variational principles from Chen and Sudan [1] and Brizard [2]. Since the fluid system conserves energy and momentum, the relative errors in these conserved quantities are well-motivated physically as figures of merit for a particular method.\\[4pt] [1] X. L. Chen and R. N. Sudan, Phys. Fluids B, \textbf{5}, 1336 (1993).\\[0pt] [2] Alain J. Brizard, Phys. Plasmas, \textbf{5}, 1110 (1998). [Preview Abstract] |
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CP8.00053: Relativistic soliton-like collisionless ionization wave Alexey Arefiev, Matthew McCormick, Hernan Quevedo, Roger Bengtson, Todd Ditmire It has been observed in recent experiments with laser-irradiated gas jets that a plasma filament produced by the laser and containing energetic electrons can launch a relativistic ionization wave into ambient gas [Phys. Rev. Lett. 112, 045002 (2014)]. Here we present a self-consistent theory that explains how a collisionless ionization wave can propagate in a self-sustaining regime. A population of hot electrons necessarily generates a sheath electric field at the plasma boundary. This field penetrates the ambient gas, ionizing the gas atoms and thus causing the plasma boundary to expand. We show that the motion of the newly generated electrons can form a potential well adjacent to the plasma boundary. The outwards motion of the well causes a bunch of energetic electrons to become trapped, while allowing the newly generated electrons to escape into the plasma without retaining much energy. The resulting soliton-like ionizing field structure propagates outwards with a bunch of hot electrons that maintain a strong sheath field despite significant plasma expansion. We also present 1D and 2D particle-in-cell simulations that illustrate the described mechanism. [Preview Abstract] |
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CP8.00054: Interplay between Weibel, two-stream and oblique-mode instabilities of the ultrarelativistic electron beam Panpan Ruan, Vladimir Khudik, Xi Zhang, Gennady Shvets Electromagnetic and electrostatic instabilities of ultrarelativistic electron beam propagating in dense plasma are studied analytically and through simulations. We develop a hybrid reduced-description code and show that it describes the beam evolution quite close to that reproduced by first-principle PIC VLPL code [1]. We demonstrate that when electromagnetic Weibel instability is suppressed by the large beam temperature, the electrostatic oblique modes quickly grow. The growth rates of the perturbations [2] from the simulations and theory match each other at different temperatures of the beam and plasma. During the non-linear stage, we study the saturation of the instabilities through simulations. The redistribution of the initial beam energy among the beam, plasma, electric and magnetic fields with time is analyzed. The nature of the final non-linear stage of the instability is explained.\\[4pt] [1] A. Pukhov, J. Plasma Phys. 61, 425-433 (1999).\\[0pt] [2] A. Bret et al., Phys. Plasmas 17, 120501 (2010) [Preview Abstract] |
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CP8.00055: High repetition rate relativistic electron beam generation from intense laser solid interactions Thomas Batson, John Nees, Bixue Hou, Alexander Thomas, Karl Krushelnick Relativistic electron beams have wide-ranging applications in medicine, materials science, and homeland security. Recent advances in short pulse laser technology have enabled the production of very high focused intensities at kHz rep rates. Consequently this has led to the generation of high flux sources of relativistic electrons - which is a necessary characteristic of these laser plasma sources for any potential application. In our experiments, through the generation of a plasma by focusing a 5 x 10$^{18}$ W/cm$^{2}$, 500 Hz, Ti:Sapphire laser pulse onto a fused silica target, we have measured electrons ejected from the target surface having energies in excess of an MeV. The spectrum of these electrons, as well as the spatial divergence of the resulting beam, was also measured with respect to incident laser angle, prepulse timing and focusing conditions. The experimental results are compared to particle in cell simulations. [Preview Abstract] |
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CP8.00056: Proton probing using a ``table-top-terawatt'' laser Peter Kordell, Louise Willingale, Anatoly Maksimchuk, Karl Krushelnick, Eleanor Tubman, Nigel Woolsey The Tcubed laser at the University of Michigan can provide up to 20 TW of laser power in 400 fs pulses. Proton beams of up to 4 MeV can be accelerated with a sufficient flux for measuring on radiochromic film (RCF). We use a split-beam set-up to allow two, co-timed, relativistic intensity interactions; the first to produce the proton probe beam and the second to produce the interaction of interest. Our preliminary results of proton probing of a simple wire target interaction will be presented and future plans for this experiment will also be discussed. [Preview Abstract] |
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CP8.00057: Systematic investigation of plasma filaments generated by Sub-TW laser pulses in N2 gases Takamitsu Otsuka, Takeharu Hommyo, Kazuki Oguri, Yusuke Hyuga, Yasuhiko Sentoku, Noboru Yugami Intense ultrashort laser pulses propagating through gases and plasmas induce many interesting physical phenomena such as optical Kerr self-focusing, diffraction, and plasma induced defocusing, resulting in the formation of plasma filaments. Because the filaments can extend the Rayleigh length at high intensity, it is applicable to a wide range of applications, e.g. laser wakefield acceleration, and THz radiation. However, the characteristics and dynamics are not well defined, especially for laser-generated plasma filaments formed at lower gas pressure region. In this work, we have studied characteristics of plasma filament generated by a femtosecond laser pulse with less than critical power for giving rise to the relativistic effect. Plasma densities in the filament were observed using an interferometer under various conditions and compared with 1D-PIC calculation results. The experimental results agreed well with numerical calculation results. Shadowgraphs were also taken, and complex structures were observed in filaments formed under certain conditions. In this presentation the experimental results obtained and the results of the numerical calculations results will be compared. [Preview Abstract] |
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CP8.00058: Hole boring velocity measurements in near critical density plasmas by a CO$_{2}$ laser pulse Chao Gong, Sergei Tochitsky, Jeremy Pigeon, Chan Joshi Measurements of plasma dynamics during the interaction of a high-power laser pulse with an above critical density plasma is important for understanding absorption, transport and particle acceleration mechanisms. An important process that affects these mechanisms is hole boring occurring at the critical density because of the radiation pressure of the laser pulse. Yet, no systematic measurements of the hole boring velocity's (v$_{hb})$ dependence on laser intensity (I) have been made. In this talk, we present experimental results of v$_{hb}$ in near critical density plasmas produced by CO$_{2}$ laser as a function of I in the range of 1*10$^{15}$ to 1.6*10$^{16}$ W/cm$^{2}$. A novel four frame Mach-Zehnder interferometer using a 1ps, 532nm probe laser pulse was developed to record the evolution of the plasma density profile and the motion of the near critical density layer. Using this diagnostic, we observed the motion of the steepened plasma profile due to the incident, time-structured CO$_{2}$ laser pulse. Experimental results show the hole boring velocity increases from 0.004c to 0.007c as the laser intensity is increased from 1*10$^{15}$ to 1.6*10$^{16}$ W/cm$^{2}$. [Preview Abstract] |
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CP8.00059: Petawatt laser absorption bounded Matthew Levy, Scott Wilks, Max Tabak, Stephen Libby, Matthew Baring The interaction of petawatt ($10^{15}$ W) lasers with solid matter forms the basis for advanced scientific applications such as table-top relativistic particle accelerators, ultrafast charged particle imaging systems and fast ignition inertial confinement fusion. Key metrics for these applications relate to absorption, yet conditions in this regime are so nonlinear that it is often impossible to know the fraction of absorbed light $f$, and even the range of $f$ is unknown. In this presentation, using a relativistic Rankine-Hugoniot-like analysis, we show how to derive the theoretical maximum and minimum of $f$ [1]. These boundaries constrain nonlinear absorption mechanisms across the petawatt regime, forbidding high absorption values at low laser power and low absorption values at high laser power. Close agreement is shown with several dozens of published experimental data points and simulation results, helping to confirm the theory. For applications needing to circumvent the absorption bounds, these results will accelerate a shift from solid targets, towards structured and multilayer targets, and lead the development of new materials. \\[4pt] [1] Levy, M. C. et al. Nat. Commun. 5:4149 doi: 10.1038/ncomms5149 (2014). [Preview Abstract] |
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CP8.00060: Conical terahertz radiation from femtosecond laser created filaments Noboru Yugami, Takamitsu Otsuka, Kazuki Oguri, Takeharu Honmyo, Masataka Hideta, Yasuhiko Sentoku The mechanism of sub-THz emission with conical structure by laser and plasma interaction since the discovery of Yugami {\it et. al.} in 2006 has left unresolved.\footnote{N. Yugami {\it et.al}, Jpn. J. Appl. Phys. {\bf 45} L1051 (2006).} One tried to explain by the wakefield oscillation by laser pulse, however, it is impossible to generate sufficeint electric field for sub THz radiation due to high nutral gas pressure and low intense laser pulse. Furthermore, the radiation frequency is not identical to and much lower than the plasma frequency which is estimated by the initial gas density and laser intensity. In this presentation, we will present recent experimental data and explain the radiation generation mechanism by 2DPIC code by taking plasma density gradient and the electron current behind the laser propagatin into account.\footnote{H.-C.Wu {\it et.al}, Phys. Rev. E, {\bf 83}, 036407 (2011).} The calculation shows the existence of the radiation with lower than 1 THz, which is much lower than the local plasma freqency and distribution structure around focal point of the laser. [Preview Abstract] |
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CP8.00061: ABSTRACT WITHDRAWN |
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CP8.00062: Describing electron motion in ultra-high intensity laser plasma interactions: the inclusion of a stochastic radiation reaction force Christopher Ridgers At intensities soon to be reached by next-generation laser facilities (exceeding 5x10$^{22}$W/cm$^{-2}$) electrons are accelerated so violently in the laser fields that they radiate energy (as gamma-ray photons) comparable to that they gain from the laser pulse. In this case the radiation reaction force becomes important in determining their motion. However, at these intensities the electric field in the electron's rest frame approaches the Schwinger field; the critical field of quantum electrodynamics where quantum effects on the radiation reaction force become crucial. In particular, the force transitions from a deterministic classical force to a stochastic force. I will compare electron motion when the radiation reaction is treated classically and stochastically, showing that the two treatments give the same result in the classical limit (correspondence) and that, surprisingly, a modified deterministic force (called the ``semi-classical'' model) can also be used when quantum effects are strong. I will also demonstrate that the semi-classical treatment fails to predict the rate of pair production by the emitted gamma-ray photons. To describe pair production one needs to adopt a new model for electron motion where the motion is described in terms of the evolution of a probability function in phase space as opposed to motion along a classical (deterministic) worldline. [Preview Abstract] |
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CP8.00063: Ponderomotive Acceleration by Relativistic Waves Calvin Lau, Po-Chun Yeh, Onnie Luk, Joseph McClenaghan, Toshikazu Ebisuzaki, Toshiki Tajima In the extreme high intensity regime of electromagnetic (EM) waves in plasma, the acceleration process is found to be dominated by the ponderomotive acceleration (PA). While the wakefields driven by the ponderomotive force of the relativistic intensity EM waves are important, they may be overtaken by the PA itself in the extreme high intensity regime when the dimensionless vector potential $a_0$ of the EM waves far exceeds unity. The energy gain by this regime (in 1D) is shown to be (approximately) proportional to $a_0^2$. Before reaching this extreme regime, the coexistence of the PA and the wakefield acceleration (WA) is observed where the wave structures driven by the wakefields show the phenomenon of multiple and folded wave-breakings. Investigated are various signatures of the acceleration processes such as the dependence on the mass ratio for the energy gain as well as the energy spectral features. The relevance to high energy cosmic ray acceleration and to the relativistic laser acceleration is considered. [Preview Abstract] |
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CP8.00064: Ultra-high intensity laser scattering with quantum corrections Joana L. Martins, Marija Vranic, Jorge Vieira, Thomas Grismayer, Ricardo Fonseca, Luis O. Silva With the advances in plasma wakefield acceleration and in laser technology, electron beams with about 1 GeV of energy and ultra-high intensity lasers (up to 10$^{\mathrm{21}}$ W/cm$^{\mathrm{2}})$ are now available. These provide a means to explore regimes with a small ratio between the electric field in the electron rest frame and the Schwinger field ($\chi $ parameter). In this work the radiation spectrum of electrons undergoing nonlinear Thomson/Compton scattering at small $\chi $ is explored through PIC simulations combined with the radiation post-processing diagnostic jRad. Quantum corrections are modeled with a quantum corrected emissivity formula that generalizes that of Lieu {\&} Axford [ApJ vol 416, 700 (1993)] for arbitrary angles of observation. Scenarios with short ultra-intense linearly polarized laser pulses (a$_{\mathrm{0}}$ up to 30) interacting with electrons with up to few 10s GeV are modeled. Spatially resolved multidimensional (and integrated) spectra are presented and the effects of radiation damping and laser amplitude variation during the interaction are explored. Comparisons of the results with equivalent OSIRIS-QED simulations are also presented and the transition from the quantum corrected emissivity to QED Compton scattering is explored. [Preview Abstract] |
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CP8.00065: Nonlinear pulse propagation and phase velocity of laser-driven plasma waves Carlo Benedetti, Francesco Rossi, Carl Schroeder, Eric Esarey, Wim Leemans We investigate and characterize the laser evolution and plasma wave excitation by a relativistically intense, short-pulse laser propagating in a preformed parabolic plasma channel, including the effects of pulse steepening, frequency redshifting, and energy depletion. We derived in 3D, and in the weakly relativistic intensity regime, analytical expressions for the laser energy depletion, the pulse self-steepening rate, the laser intensity centroid velocity, and the phase velocity of the plasma wave. Analytical results have been validated numerically using the 2D-cylindrical, ponderomotive code INF\&RNO. We also discuss the extension of these results to the nonlinear regime, where an analytical theory of the nonlinear wake phase velocity is lacking. [Preview Abstract] |
(Author Not Attending)
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CP8.00066: Condition for the onset of the current filamentation instability of ultra-relativistic fireball bunches in plasmas Nitin Shukla, Jorge Vieira, Patric Muggli, Ricardo Fonseca, Lu\'Is Silva Current Filamentation Instability (CFI) is capable of generating strong magnetic fields relevant to explain radiation processes in astrophysical objects and lead to the on-set of particle acceleration in collisionless shocks. Probing such extreme scenarios in the laboratory is still an open challenge. It has been proposed that the available 20 GeV electron and positron bunches at the Stanford Linear Accelerator Center could be used to mimic these scenarios by exploring CFI associated with the propagation of a neutral e$^-$e$^+$ beam into a plasma [P. Muggli \textit{et al.}, arXIV 1306.4380 (2013)]. In this work, we investigate this possibility by performing numerical 2D PIC simulations using Osiris [R. A. Fonseca \textit{et al.}, Lect. Notes Comput. Sci. 2331, 342 (2002)]. We show that CFI can occur unless the rate at which the beam expands due to finite beam emittance, is larger than the CFI growth rate. We also explore the competition between CFI and the electrostatic two-stream instability (TSI) by changing the e$^-$e$^+$ bunch duration. We found that, by keeping the same number of particles, the CFI dominates over the TSI for shorter bunches with larger peak densities. [Preview Abstract] |
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CP8.00067: Radiation reaction and resulting photon emission from laser-irradiated solid targets David Stark, Alexey Arefiev, Manuel Hegelich Once completed, an ongoing upgrade of the Texas-PW laser system would allow us to achieve on-target laser intensities of up to $5\times10^{22}$ W/cm$^2$. As experimental confirmation of the radiation reaction force and the variety of models describing it remains a challenge, here we present a scenario that would enable us to observe the effect by detecting the resulting photon emission. A laser with our planned intensity could accelerate an electron to hundreds of MeV, but the radiation reaction and thus the photon emission would be relatively weak if the electron co-propagates with the wave. We consider a solid density target irradiated by a laser beam so that strong fields are generated due to charge separation. These fields can alter the electron trajectories, leading to strong radiation reaction and photon emission in the focal spot. Simulating this interaction using the particle-in-cell code EPOCH, we perform a target density scan that allows us to optimize the fraction of the laser energy converted into photons and to determine the photon spectrum. Knowing the spectrum and the angular emission is critical for measurements in the lab, since these photons must be distinguished from those from other processes. [Preview Abstract] |
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CP8.00068: Mono-energetic ion acceleration in the RPA regime: a tale of two temperatures Vladimir Khudik, Gennady Shvets We develop an analytical theory of the laser-accelerated plasma target irradiated by a circularly polarized laser pulse in the RPA regime. We demonstrate that relationship between electron and ion temperatures is the key to understanding the structure of the accelerated target. To illustrate this point, we discuss two simplest analytically treatable limiting cases of (1) cold ions and hot electrons [1], and (2) hot ions and cold electrons. In the first case, hot electrons bounce back and forth inside the potential well formed by ponderomotive and electrostatic potentials while the ions are force-balanced by the electrostatic and non-inertial fields. In the second case the situation is very different: hot ions are trapped in the potential well formed by the ion-sheath's electric and non-inertial potentials while the cold electrons are force-balanced by the electrostatic and ponderomotive fields. Using PIC simulations we study the target stability with respect to Rayleigh-Taylor instability [1,2].\\[4pt] [1] V. Khudik, S. A. Yi, C. Siemon, and G. Shvets, Phys. Plasmas, 21, 0013110 (2014).\\[0pt] [2] T.P. Yu, A. Pukhov, G. Shvets, M. Chen, T. H. Ratliff, S. A. Yi, and V. Khudik, Phys. Plasmas, 18, 043110 (2011). [Preview Abstract] |
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CP8.00069: Ion acceleration by relativistic laser pulses from semitransparent targets A.V. Brantov, E.A. Govras, V. Yu. Bychenkov, W. Rozmus A new, maximum proton energy, E$_{\mathrm{p}}$, scaling law with the laser pulse energy, E$_{\mathrm{L}}$, has been derived from the results of 3D particle-in-cell (PIC) simulations. According to numerical modeling, protons are accelerated during interactions of the femtosecond relativistic laser pulses with the plain semi-transparent targets of optimum thickness [Esirkepov, \textit{et al}. Phys. Rev. Lett. \textbf{96}, 105001 (2006)]. The scaling, E$_{\mathrm{p}}$ $\sim$ E$_{\mathrm{L}}^{0.7}$, has been obtained for the wide range of laser energies, different spot sizes, and laser pulse durations. Our results show that the proper selection of foil target optimum thicknesses, results in a very promising increase of the ion energy with the laser intensity even in the range of parameters below the radiation pressure (light sail) regime. The proposed analytical model is consistent with numerical simulations. [Preview Abstract] |
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CP8.00070: Simulation study of a destructed target effects on proton acceleration by a circularly polarized laser pulse Young-Kuk Kim, Myung-Hoon Cho, Hyong Ju Pack, Moon Youn Jung, Min Sup Hur In the laser-driven ion acceleration, usually the ASE or the pre-pulse of the laser pulse pre-ionize the target before the main pulse arrival. Depending on the pre-plasma condition formed in this way has been known to be influential on ion accelerations. In this simulation study, we assumed the destruction level of the target is controllable, and investigated the destructed target effect on proton acceleration by a circularly polarized pulse. For a given laser pulse intensity and the initial target density and thickness, the pulse penetration into the plasma depends on the plasma density profile formed by the target destruction. Too low penetration in a well-preserved target just yields the conventional radiation pressure dominant acceleration (RPDA), while too high penetration in over-destroyed target diminishes the ion acceleration by reduced coupling between the laser and plasma. For an optimized target destruction level, we observed the properly penetrated pulse heats the electrons, leading to a shock formation and mono-energetic ion beam generation. [Preview Abstract] |
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CP8.00071: ABSTRACT WITHDRAWN |
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CP8.00072: Thermal emittance from ionization-induced trapping in plasma accelerators Carl Schroeder, Jean-Luc Vay, Eric Esarey, Carlo Benedetti, Cameron Geddes, Wim Leemans, Stepan Bulanov, Lule Yu, Min Chen The minimum obtainable transverse emittance (thermal emittance) of electron beams generated and trapped in plasma-based accelerators using ionization injection is examined. The initial electron beam transverse phase space distribution following ionization and transit through the laser is derived. Expressions for the normalized transverse beam emittance, both along and orthogonal to the laser polarization, are presented. Results are compared to particle-in-cell simulations. Ultra-low emittance electron beams can be generated using laser ionization injection into plasma accelerators. [Preview Abstract] |
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CP8.00073: Generation of high energy electron accelerated by using a tapered capillary discharge plasma Minseok Kim, Inhyuk Nam, Taehee Lee, Seungwoo Lee, Hyyong Suk The tapered plasma density in a gas-filled capillary waveguide can suppress the dephasing problem in laser wakefield acceleration (LWFA). As a result, the acceleration distance and the gained electron energy are expected to be increased. For this purpose, we developed a tapered capillary waveguide, which can produce a plasma density of $\sim$ 10$^{18}$ cm$^{-3}$. Using this capillary discharge plasma, we performed the acceleration experiments with the high power laser system (20 TW/40 fs) constructed at GIST. In this presentation, the detailed electron acceleration experiments will be reported. [Preview Abstract] |
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CP8.00074: Generation of multiple, mono-energetic electron bunches via ionization injection in a laser wakefield accelerator C.J. Zhang, C.-K. Huang, J.F. Hua, C.-H. Chen, S.-Y. Chen, C. Joshi, W.B. Mori, J. Wang, W. Lu Electron bunches with multiple energy peaks are generated via ionization injection in a laser wakefield accelerator using a 40 fs, 10 TW laser. These electron bunches are highly asymmetric with an aspect ratio that varies from 2 to 5 and have a central energy about 80 MeV with multiple narrow-energy-spread peaks. Key features of the electron bunches seen in this experiment are observed in 3D PIC simulations using OSIRIS. In the simulations, ionization and injection of the inner-shell electrons is caused by the increase of laser intensity due to self-focusing (p/p$_{\mathrm{c}}\approx $1.1) and is subsequently terminated after a propagation distance of less than Z$_{\mathrm{R}}$ as a result of laser evolution. Acceleration of these electrons then leads to mono-energetic bunches. The interaction between the back of the laser pulse and the accelerated bunch stretches the latter leading to a highly asymmetric spot. [Preview Abstract] |
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CP8.00075: Ion-acoustic Shocks with Reflected Ions: Implications for laser-based proton accelerators Roald Sagdeev, Mikhail Malkov, Galina Dudnikova, Tatyana Liseykina, Patrick Diamond, C.-S. Liu, J.-J. Su Analytic solution for an ion-acoustic collisionless shock with reflected
ions is obtained. Its relation to classical non-reflecting solitons
propagating at Mach numbers strictly limited by $M |
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CP8.00076: Overcomingthe Dephasing Limit in the Bubble Regime by Synergybetween Direct Laser Acceleration and Laser Wakefield Acceleration Xi Zhang, Vladimir Khudik, Gennady Shvets Direct Laser Acceleration (DLA) in the bubble regime is an acceleration mechanism [1] that combines the traditional plasma wakefield acceleration inside the plasma bubble with energy gain directly from the laser pulse. Recent experiments [2] demonstrated one of the signatures of the DLA: highly efficient gamma-rays from resonantly excited betatron oscillations of accelerated electrons inside the plasma bubble. Here we propose another potential benefit of DLA: the reduction of dephasing between the accelerated electrons and accelerating field of the bubble. A simple semi-analytic model is developed to investigate the synergy between DLA and LWA acceleration mechanisms. We propose to enhance the DLA by adding a second time-delayed weak laser pulse capable of interacting with bubble electrons right after self-injection [3]. This scenario is validated by direct PIC modeling using the 2D VLPL code. The prospects for achieving high-energy electrons at the Texas Petawatt laser are discussed. \\[4pt] [1] A. Pukhov et al., Phys. Plasmas. 6, 2847 (1999).\\[0pt] [2] S. Cipiccia et al., Nature Phys. 7, 867-871 (2011).\\[0pt] [3] S. Kalmykov, S. A. Yi, V. Khudik, and G. Shvets, Phys. Rev. Lett. \textbf{,}135004 (2009). [Preview Abstract] |
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CP8.00077: Modeling of Laser wakefield acceleration in the Lorentz boosted frame using UPIC-EMMA and OSIRIS Peicheng Yu, Xinlu Xu, Viktor Decyk, Frank Tsung, Jorge Vieira, Ricardo Fonseca, Wei Lu, Luis Silva, Warren Mori We present the capability of investigating physics of laser wakefield accelerator (LWFA) in nonlinear regimes using various approaches. This includes simulating the physics using OSIRIS 3D code in the lab and boosted frame. We also implemented hybrid 3D algorithm into OSIRIS which uses an algorithm with a PIC description in r-z and a gridless description in phi [A.F. Lifschitz, et. al., JCP. 228, 1803 (2009)]. This algorithm greatly reduce the computation load by describing the three-dimensional (3D) physics problem of laser-plasma interaction with essentially two-dimensional if the expansion is truncated. The hybrid 3D OSIRIS code can be used to simulate the nonlinear physics in LWFA in both lab and boosted frames. Combining the hybrid 3D and boosted frame approaches potentially provides unprecedented speedups. Furthermore, we can simulate the same problems in a boosted frame using the spectral EM-PIC code UPIC-EMMA which solves the Maxwell's equation in Fourier space. By applying a recipe to systematically reduce the numerical Cerenkov instability (NCI) in the spspectral code, we are able to conduct LWFA Lorentz boosted frame simulation at arbitrary gamma with no signs of NCI. [Preview Abstract] |
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CP8.00078: Study on beam emittance evolution in a nonlinear plasma wake field accelerator with mobile plasma ions Weiming An, Chan Joshi, Warren Mori, Wei Lu We study the electron beam evolution in a nonlinear blowout PWFA when the accelerated beam has a very small matched spot size that can cause the plasma ions collapsing towards the beam. Contrary to the common belief, very small emittance growth of the accelerated electron beam is found when the plasma ion collapsing destroys the perfect linear focusing force in the plasma wake field. The improved quasi-static PIC code QuickPIC also allows us to use very high resolution and to model asymmetric spot sizes. Simulation results show that the accelerated beam will reach a steady state after several cm propagation in the plasma (which is why we can do simulations and not let the drive beam evolve). We find that for round beams the ion density (which is Li+) enhancement is indeed by factors of 100, but that the emittance only grows by around 20 percent. For asymmetric spot sizes, the ion collapse is less and emittance growth is zero in the plane with the largest emittance and about 20 percent in the other plane. [Preview Abstract] |
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CP8.00079: Self-modulation of a Long Electron Bunch in a Dense Plasma Patric Muggli, Jorge Vieira, Nelson Lopes, Ligia Diana Amorim, Spencer Gessner, Mark Hogan, Michael Litos, Selina Li, Navid Vafaei-Najafabadi, Chan Joshi, Kenneth Marsh, Chris Clayton, Erik Adli The self-modulation instability of long charged particle bunches in plasmas was recently proposed as a means to drive large amplitude wakefields.\footnote{N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010).} This instability transforms a long particle bunch into a train of shorter bunches with a periodicity approximately equal to that of the plasma wavelength. We proposed to study this instability at SLAC-FACET with electron and positron bunches.\footnote{J. Vieira et al., Phys. Plasmas 19, 063105.} The occurrence of the instability leads to three possible observables. First, bunch particles lose energy driving wakefields while the instability develops and after it has saturated. Second, the bunch particles are alternatively focused and defocused, leading to a transverse profile with a dense core and a waker halo. Third, the radius of the bunch becomes periodically modulated. Long particle bunches, meter-long high-density plasmas and well developed diagnostics are available at FACET. We present experimental results obtained with electron bunches that suggest the development of the instability. These results are supported by numerical simulations results. [Preview Abstract] |
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CP8.00080: Quasi-monoenergetic electron beam generation from laser wakefield acceleration with tapered capillary gas cell Inhyuk Nam, Minseok Kim, Seung-Woo Lee, Tae-Hee Lee, Hyyong Suk In this presentation, we experimentally investigated the enhancement of energy of electron beams with the untapered/tapered capillary gas cell. The energy of electron beams from the laser wakefield acceleration is mainly limited by the laser diffraction and the dephasing length. In order to overcome the dephasing the tapered plasma can increase the dephasing length which results in enhancement of the energy of electron beams. We have developed a tapered capillary gas cell with the variable gas pressure gradients by changing gas-feed line cross-sections. The capillary gas cell with untapered/tapered pressure will be used for high-energy electron acceleration experiments together with the 20 TW/40 fs laser system. We observed enhancement of the energy of electron beams with the tapered capillary gas cell. [Preview Abstract] |
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CP8.00081: Generation of High Brightness Electron Beams via Ionization Induced Injection by Transverse Colliding Lasers in a Beam-Driven Plasma Wakefield Accelerator F. Li, X.L. Xu, W. Lu, W.B. Mori, C. Joshi The production of ultra-bright electron bunches using ionization injection triggered by two transversely colliding laser pulses inside a beam-driven plasma wake is examined via three-dimensional (3D) particle-in-cell (PIC) simulations. The relatively low intensity lasers are polarized along the wake axis and overlap with the wake for a very short time. The result is that the residual momentum of the ionized electrons in the transverse plane of the wake is reduced and the injection is localized along the propagation axis of the wake. This minimizes both the initial ``thermal'' emittance and the emittance growth due to transverse phase mixing. Simulations show that ultra-short ($\sim$8 fs) high-current (0.4 kA) electron bunches with a normalized emittance of 8.5 and 6 nm in the two planes respectively and a brightness greater than $1.7 \times 10^{19} {\rm A\cdot rad^{-2}\cdot m^{-2}}$ can be obtained for realistic parameters. [Preview Abstract] |
(Author Not Attending)
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CP8.00082: Positron self-driven hollow channel in non-linear plasma wakefields Ligia Diana Amorim, Jorge Vieira, Ricardo A. Fonseca, Luis O. Silva Plasma based accelerators are capable of sustaining very high acceleration gradients when compared to conventional accelerators. In particular plasma based accelerators operating in non-linear regimes reached the 100GV/m. One of the challenges for a future plasma based collider is to accelerate positrons in non-linear regimes. Although novel techniques have been investigated to this end [1], it is still important to propose and explore other new configurations for positron acceleration in non-linear regimes. In this context we suggest a novel process for positron acceleration in non-linear plasma wakefields, where a tightly focused positron drive beam expels the plasma ions forming a hollow channel with large accelerating and focusing wakefields suitable for positron acceleration. We introduce the setup of the proposed scheme and illustrate it with analytical and numerical results of a 3D numerical simulations performed with the PIC code OSIRS [2]. Moreover, we discuss the optimal conditions for the positron drive beam stability.\\[4pt] [1] J. Vieira, J.T. Mendon\c{c}a, PRL 112, 215001 (2014);\\[0pt] [2] R. A. Fonseca et al., Lect. Notes Comput. Sci. 2331, 342 (2002). [Preview Abstract] |
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CP8.00083: Characterization of betatron x-ray emission from wakefield accelerators Karl Krushelnick, Chris McGuffey, Paul Cummings, Will Schumaker, Vladimir Chvykov, Franklin Dollar, Galina Kalintchenko, Takeshi Matsuoka, Michael Vargas, Victor Yanovsky, Alec Thomas We investigate betatron x-ray emission from laser wakefield accelerated electron beams using the HERCULES laser facility at the University of Michigan. The x-ray emission was observed to increase substantially after propagation of the generated electron beam beyond the plasma dephasing length. This was likely due to electron beam hosing instabilities seeded by interaction of the electron beam with the co-propagating laser pulse. The development of the hosing instability is confirmed by numerical modeling. We also investigate phase contrast imaging with this source at high x-ray energies and have compared the betatron emission with K-alpha emission from laser solid interaction in a similar experimental geometry. [Preview Abstract] |
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CP8.00084: Ferroelectric Plasma Sources for Ion Beam Neutralization A. Stepanov, E.P. Gilson, L.R. Grisham, R.C. Davidson A 40~keV Ar$^+$ beam with a dimensionless perveance of 4$\times$10$^{-4}$ is propagated through a Ferroelectric Plasma Source (FEPS) to determine the effects of charge neutralization on the transverse beam profile. Neutralization is established $~$5~$\mu$s after the FEPS is triggered, and lasts between 10 and 35~$\mu$s. When the beam is fully neutralized, the profile has a Gaussian shape with a half-angle divergence of 0.87$^\circ$, which is attributed to ion optics. The effects of the resistance and capacitance in the pulser circuit on the FEPS discharge are studied. The electron current emitted by the FEPS is calculated from measurements of the forward and return currents in the circuit. Electron emission typically begins $~$0.5~$\mu$s after the driving pulse, lasting for tens of $\mu$s, which is similar to the duration of ion beam neutralization. The total emitted charge does not depend significantly on the resistance, but depends strongly on the storage capacitance. Lowering the capacitance from 141~nF to 47~nF results in a near-complete shut-off of charge emission, although the amplitude of the applied voltage pulse is as high as when high-density plasma is produced. Overall, the data suggest that ferroelectric effects are significant in the physics of the FEPS discharge. [Preview Abstract] |
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CP8.00085: Numerical Studies of Electrode Plasma Formation and Expansion in High Power Charged Particle Beam Diodes I.M. Rittersdorf, S.B. Swanekamp, A.S. Richardson, R.J. Allen, J.W. Schumer High-power diodes that generate intense electron beams are useful in many applications, such as producing x-rays for flash radiography and nuclear weapon effects simulations. Desorption and ionization of gases from electrodes can form a plasma during operation. Expansion of this plasma into the gap leads to a short circuit, which limits the radiation production. It is difficult for particle-in-cell codes to model the surface physics or the subsequent expansion of the plasma. NRL is beginning a multi-year research effort to study such plasmas. This paper will summarize the relevant literature on plasma formation in high-power diodes with a goal of developing dynamic models that describe the formation and expansion of these plasmas that are suitable for PIC codes. [Preview Abstract] |
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CP8.00086: A Bi-Frequency Linear Slow Wave Device David Simon, Peng Zhang, Y.Y. Lau, Geoff Greening, Ronald Gilgenbach, Brad Hoff Bi-frequency sources are of interest to plasma processing, diagnostics, RF heating, and defense electronics. The recirculating planar magnetron [1] has been modified to produce two frequencies using two different slow wave structures in the planar regions. To highlight the coupling in the two frequencies, we consider here a linear TWT driven by a sheet beam inside such a structure. The cold tube dispersion is derived and is compared favorably with HFSS. The hot tube dispersion has also been derived, and is being compared with MAGIC simulations. Various nonlinear effects are explored, such as harmonic generation, parametric amplification, and intermodulation. \\[4pt] [1] R. M. Gilgenbach, et. al., IEEE Trans. Plasma Sci. 39, 908 (2011). [Preview Abstract] |
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CP8.00087: Experimental and Simulation Study of Electric Field Screenings of Carbon Fiber Field Emitters Wilkin Tang, Don Shiffler, Matthew LaCour, Ken Golby, Tim Knowles Field emitter arrays have the potential to provide high current density, low voltage operation, and high pulse repetition for radar and communication. It is well known that packing density of the field emitter arrays significantly affect the emission current. Previous experiments were conducted with 1000s of field emitters which makes the analysis of electric field screening difficult. Here we describe experiments in a dual-cathode and four-cathode configuration. The experiments used different number of carbon fiber field emitters (two and four) with variable spacing to investigate the effect of electric field screening on current emission. Emission characteristic is compared for the case of two and four field emitters with different spacing. Analytic model and Particle-in-cell simulations are performed to compare with the experiments. [Preview Abstract] |
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CP8.00088: Temporally Gated Liquid Scintillator Neutron Detectors John T. Morrison, Kyle D. Frische, W. Melvyn Roquemore Laser based neutron sources are of interest for non-destructive testing of materials and detection of sensitive materials. These sources typically also generate large numbers of secondary x-rays and gammas which can saturate Photo Multiplier Tubes (PMT's) measuring scintillating time of flight detectors if there is not sufficient time for them to recover before the arrival of the neutron signal. Improving the response time of scintillating of medium allows for closer placement of the detectors and improved sensitivity. Liquid scintillators have been employed to reduce the decay time of the scintillating medium and temporal gating of the PMT's prevents saturation of the PMT's by the preceding gamma flash. Detector design and results of the detector calibration will be presented. [Preview Abstract] |
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CP8.00089: DUSTY AND COMPLEX PLASMAS |
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CP8.00090: Dropper for micron and submicron size powders for a plasma mass filter Eugene S. Evans, Stewart J. Zweben, Renaud Gueroult, Nathaniel J. Fisch, Fred Levinton The goal of the Plasma Mass Filter (PMF) experiment at PPPL, in collaboration with Nova Photonics, Inc., is to achieve separation between high-Z and low-Z atoms, for possible application to processing of nuclear waste to remove the highly radioactive high-Z components. The PMF features a rotating plasma column in which centrifugal forces push high-mass ions out of the plasma radially, while low-mass ions exit the plasma axially. In order to control the injection location, high-Z materials are introduced in powder form into the PMF plasma. The current experiment is limted to $\sim$1~kW RF, giving a calculated maximum flow rate of $\sim$0.1~mg/s. An electron temperature of a few eV and assumptions about the residence time of the dust particles in the PMF plasma limits the calculated maximum particle size to $\sim$1~$\mu$m. While previous dusty plasma experiments have dealt with particles on the order of 2-3~$\mu$m, submicron particles are comparatively more difficult to manipulate under vacuum due to increased Van Der Waals and electrostatic forces. A powder dropper capable of reliably dropping micron and submicron-size particles at this flow rate is being developed, consisting of a mesh-bottomed container that is coupled to vibration motors. [Preview Abstract] |
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CP8.00091: Experimental investigation of differential confinement effects in a rotating helicon plasma Renaud Gueroult, Eugene Evans, Stewart J. Zweben, Nathaniel J. Fisch, Fred Levinton Although plasmas have long been considered for isotope separation, challenges presented by nuclear waste remediation and nuclear spent fuel reprocessing have recently sparked a renewed interest for high-throughput plasma based mass separation techniques. Different filter concepts relying on rotating plasmas have been proposed to address these needs. However, one of the challenges common to these concepts is the need to control the plasma rotation profile, which is generally assumed to be provided by means of dedicated electrodes. An experimental effort aiming to evaluate the practicality of these plasma filter concepts has recently been started at PPPL. For this purpose, a linear helicon plasma source is used in combination with concentric ring electrodes. Preliminary biasing experiments results indicate floating potential profiles locally suitable for mass discrimination for different gas mixtures (Ar/Ne, Ar/N$_2$, Ar/Kr). Radially resolved spectroscopic measurements and neutral gas composition analysis at two different axial positions are being planned to assess the mass separation effect. [Preview Abstract] |
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CP8.00092: Nucleation, growth, and dynamics of water-ice grains in laboratory plasmas Paul Bellan, Kil-Byoung Chai An rf discharge with LN$_{2}$ cooled electrodes has been used to study nucleation, growth, and dynamics of water-ice grains spontaneously formed in weakly ionized H, D, He, Ne, Ar, or Kr plasmas. Ice grain nucleation occurs only when plasma exists and its density is below a critical value that is proportional to ambient gas pressure. Nonspherical, fast grain growth occurs when the water molecule mean free path exceeds the ice grain screening length corresponding to molecules incident on the ice grain having collisionless trajectories. Up to 10:1 elongated ice grains have been observed. Ice grains grow larger in lighter gas plasmas and in particular grow up to 500 $\mu $m long in H plasma. Magnetic fields sufficiently strong to make the electron gyro radius smaller than the ice grain screening length impede nonspherical growth by reducing the charge residing on water-ice grains. Ice grains are aligned along the sheath electric field and rotate about their alignment axis with $\sim$ 10$^{2}$ Hz angular frequency. Dust acoustic waves are observed in low pressure, low rf power plasmas. [Preview Abstract] |
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CP8.00093: Simulation of ablation cloud shielding effects on Tungsten dust transport in edge plasmas R.J. Hajjar, R.D. Smirnov, S.I. Krasheninnikov, A.Y. Pigarov, E.D. Marenkov, T.D. Rognlien Significant amount of dust are expected to be produced during plasma/PFCs interactions in next generation tokamaks. To study dust transport in tokamaks, numerical codes such as DUSTT, were developed using plasma-dust interaction models based on OML theory. However in high temperature plasmas, dust grains are always surrounded by dust material vapor cloud, which when dense enough can alter the dust-plasma interactions for grain radii larger than $\sim$ 1-10$\mu$m depending on plasma parameters. This reduces the grain ablation rate and extends its lifetime and penetration towards the plasma core as compared to models neglecting the cloud effects. A new model describing dust shielding effects for high-Z materials is developed and implemented in DUSTT code. This model considers the reduced heat flux to the dust grain in edge plasma, where it is shown to be due to electron heat conduction. In this work, we investigate the vapor induced shielding effects on dust dynamics and transport, as well as its impact on parameters of ITER-like plasma using the modified DUSTT code. Impact of the shielding effects on the maximum tolerable amount of tungsten dust produced in ITER is investigated. The simulation results are also compared to those previously obtained using an \textit{ad hoc} dust shielding factor. [Preview Abstract] |
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CP8.00094: Dust Transport in Low Voltage Glow Discharges C.A. Romero-Talamas, E.M. Bates, W.F. Rivera, W. Birmingham Results from experiments of dust hopping under different electrode configurations are presented. The purpose of these experiments is to investigate conditions that lead to the dust in a low voltage dusty plasma to be transported and clumped on the lower electrode, by hopping throughout the bottom electrode. The setup consists of a pair of parallel electrode plates that can be oriented with respect to gravity and can have their separation changed without breaking vacuum. The electrodes are suspended by insulating rings in the vacuum chamber, away from walls, and both the top and bottom of each conducting plate is exposed. This configuration allows a glow discharge on all faces of the electrodes, with the glow between the plates having a low enough voltage to charge, but not to levitate the dust grains. Several initial conditions are tested, including the amount of dust on the plate, its distribution, and the presence of any obstacles. This research is relevant to the transport and accumulation of dust in high temperature plasma discharge chambers, as well as in airless planetary bodies. [Preview Abstract] |
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CP8.00095: Mass Spectrometry of 3D-printed Materials in Vacuum W.F. Rivera, C.A. Romero-Talam\'as, E.M. Bates, W. Birmingham We present the design and preliminary results of a mass spectrometry system to assess vacuum compatibility of 3D-printed parts. The setup consists of a vacuum chamber with a residual gas analyzer (RGA), a radiation heater, and windows for optical measurements of samples. The signal from the RGA is analyzed by creating a system of equations from the calibration signal from a large number of molecular spectra (the so-called cracking patterns). The equations are then inverted to find the most likely true elements in the chamber. The setup can be used as a stand-alone system, or attached to another vacuum chamber at higher pressure using differential pumping. The latter mode will be used in the Dusty Plasma Experiment at UMBC, since many of the plasma facing parts are 3D-printed. Mass spectra of electroplated plastic parts, which have a much better vacuum compatibility than non-plated plastic parts, is also obtained and compared to those without electroplating. [Preview Abstract] |
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CP8.00096: Development of a Split Bitter-type Magnet System for Dusty Plasma Experiments Evan Bates, Carlos A. Romero-Talamas, William J. Birmingham, William F. Rivera A 10 Tesla Bitter-type magnetic system is under development at the Dusty Plasma Laboratory of the University of Maryland, Baltimore County (UMBC). We present here an optimization technique that uses differential evolution to minimize the omhic heating produced by the coils, while constraining the magnetic field in the experimental volume. The code gives us the optimal dimensions for the coil system including: coil length, turn thickness, disks radii, resistance, and total current required for a constant magnetic field. Finite element parametric optimization is then used to establish the optimal design for water cooling holes. Placement of the cooling holes will also take into consideration the magnetic forces acting on the copper alloy disks to ensure the material strength is not compromised during operation. The proposed power and cooling water delivery subsystems for the coils are also presented. Upon completion and testing of the magnet system, planned experiments include the propagation of magnetized waves in dusty plasma crystals under various boundary conditions, and viscosity in rotational shear flow, among others. [Preview Abstract] |
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CP8.00097: Cooling System Design for a Split High Field Bitter-type Electromagnet William Birmingham, Evan Bates, Carlos Romero-Talamas, William Rivera For the purpose of analyzing magnetized dusty plasma at the University of Maryland Baltimore County (UMBC), we are designing a split resistive electromagnet. When completed, the magnet will be capable of generating fields of 10 T for 10 seconds. The type of design proposed here was originally developed by Francis Bitter, and achieves high magnetic fields by helically stacked disk-shaped solenoids with axially oriented cooling channels. In order to ensure the safety and functionality of the apparatus, the geometry and placement of the cooling passages must be designed to establish a manageable temperature profile throughout the coil. The estimated power consumption from resistive losses is nearly 7 MW, thus it is imperative to optimize the cooling capacity of the system. The cooling capacity is limited by the mass of chilled water available at one time and the maximum achievable mass flow through the coils. The system is also designed to withstand the resultant mechanical stresses from the Lorentz force. Slot-shaped cooling channels are used. The number and placement of these channels is optimized through an iterative and integrated design process which combines analytic calculations with finite element analyses. The methodology and results of the design process is presented. [Preview Abstract] |
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CP8.00098: Initial Results from the Magnetized Dusty Plasma Experiment (MDPX) Edward Thomas, Uwe Konopka, Brian Lynch, Stephen Adams, Spencer LeBlanc, Darrick Artis, Ami DuBois, Robert Merlino, Marlene Rosenberg The MDPX device is envisioned as a flexible, multi-user, research instrument that can perform a wide range of studies in fundamental and applied plasma physics. The MDPX device consists of two main components. The first is a four-coil, open bore, superconducting magnet system that is designed to produce uniform magnetic fields of up to 4 Tesla and non-uniform magnetic fields with gradients up to up to 2 T/m configurations. Within the warm bore of the magnet is placed an octagonal vacuum chamber that has a 46 cm outer diameter and is 22 cm tall. The primary missions of the MDPX device are to: (1) investigate the structural, thermal, charging, and collective properties of a plasma as the electrons, ions, and finally charged microparticles become magnetized; (2) study the evolution of a dusty plasma containing magnetic particles (paramagnetic, super-paramagnetic, or ferromagnetic particles) in the presence of uniform and non-uniform magnetic fields; and, (3) explore the fundamental properties of strongly magnetized plasmas (``i.e., dust-free'' plasmas). This presentation will summarize the initial characterization of the magnetic field structure, initial plasma parameter measurements, and the development of in-situ and optical diagnostics. [Preview Abstract] |
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CP8.00099: Filamentation of a Magnetized, Radio Frequency Discharge Uwe Konopka, Brian Lynch, Pintu Bandyopadhyay, Devendra Sharma, Edward Thomas A filamentation instability has been observed in a radio-frequency (rf) discharge that was subject to an externally applied, homogeneous magnetic field. The instability arises in a uniform rf-discharge after the magnetic field strength is sufficiently increased. First, the plasma shows target-like glow structures, followed by spiral structures at higher fields. Finally, the plasma breaks up into individual, string-like, magnetic field aligned filaments that seem to repel each other. A variety of filamentation states can be observed, but their overall shapes follow the aforementioned rule of magnetic field strength dependency. The detailed picture of the discharge glow, however, depends on experiment specific conditions as the geometric shape and type of the discharge electrodes, the discharge pressure and power. In an effort to verify that the observed effect is universal, we compare experimental measurements made using two different high magnetic field, dusty plasma experiment facilities: the experiment that was located at the Max Planck Institute in Garching, Germany and the newly built MDPX (magnetized dusty plasma experiment) at Auburn University, Alabama. In both experimental setups we could observe filamentation. [Preview Abstract] |
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CP8.00100: Real-Time 2-Dimensional Particle Tracking in Magnetized Plasmas Brian Lynch, Uwe Konopka, Edward Thomas Complex plasmas are a four component plasma system consisting of electrons, ions, neutral particles, and electrically charged (nanometer to micrometer) sized ``dust'' particles. In laboratory plasmas, collisional processes lead to a net negative charge residing on the dust grain surface. As a result, dust clouds may be suspended in a plasma sheaths vertical electric field and studied using digital imaging systems with laser sheet illumination. Particle Tracking Velocimetry (PTV) is an analysis technique in which each dust particle is tracked through imaging data. The velocity fields extracted using PTV provide a spatially resolved dust particle phase space distribution (PSD) function, which can be used to calculate transport and thermal properties of the system. In this presentation, we apply ``real-time'' PTV analysis to the Magnetized Dusty Plasma Experiment (MDPX). The introduction of a magnetic field is shown to significantly modify the global dust cloud PSD as well as individual dust particle dynamics. Finally, we present preliminary plans for the development of a new experimental study to use real-time PTV to observe single particle deflection in a magnetic field - as a means to investigate ion drag and charging of the dust grain. [Preview Abstract] |
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CP8.00101: Observations and analysis of poloidal flows in dusty plasmas Stephen Adams, Shane Moorhead, Christian Polka, Daniel Robinson, Uwe Konopka, Edward Thomas, Manjit Kaur, Prabal Chattopadhyay, Devendra Sharma Dusty plasmas are a four-component plasma system consisting of electrons, ions, neutral atoms, and charged nanometer- to micron-sized micro particles (i.e., ``dust''). In recent experiments at the Institute for Plasma Research (IPR), observations of toroidally shaped dust rings, with strong poloidal rotation were reported. The Auburn dusty plasma group has reproduced these experiments using the large, octagonal vacuum chamber designed for the Magnetized Dusty Plasma Experiment. These studies use a dc discharge plasma at high pressure (p $>$ 200 mTorr), over a broad range of discharge currents (up to 10 mA), to produce toroidal, semi-toroidal, disc-shaped, or ring-like dust structures. Frequently, these structures exhibit a steady-state poloidal flow. In these studies, particle image velocimetry (PIV) is used to characterize the transport of the charged microparticles. Initial results will be presented on the evolution of the particle flow as a function of the experimental parameters and a preliminary analysis of the particle motion using a balance between ion drag and gravitational forces will be presented. [Preview Abstract] |
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CP8.00102: Probe Diagnostics on the Magnetized Dusty Plasma Experiment (MDPX) Spencer LeBlanc, Ami DuBois, Mark Cianciosa, Uwe Konopka, Edward Thomas The Magnetized Dusty Plasma Experiment (MDPX) has recently begun operation at Auburn University. The MDPX device uses a superconducting magnet system to study plasmas at high magnetic field strengths of up to 4 Tesla. As a newly operating plasma experiment, it is essential to have careful measurements of the plasma parameters. However, the performance of in-situ plasma diagnostics at high magnetic fields strengths is not well understood. In order to characterize the plasma, initial measurements will be performed using single and triple cylindrical Langmuir probes without a magnetic field. These probes, in addition to a disk shaped probe, will then be used to make plasma measurements with increasing magnetic field strength. Understanding the measurements obtained from these diagnostics will be essential in order to study the charging properties of a plasma as particles are magnetized, as well as the evolution of a dusty plasma containing magnetic particles. This presentation will summarize the probe measurements obtained without magnetic fields and make comparisons with the probe performance at increasing magnetic field strengths. It will be shown that at high magnetic field strengths, the probes are strongly impacted by flux-tube limited collection. [Preview Abstract] |
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CP8.00103: Investigating Ion Drag In Perturbed Dusty Plasmas Taylor Hall, Edward Thomas, Uwe Konopka Complex, or dusty, plasmas are plasmas which contain charged microparticles, for example small silicon dust grains. In this study, we are particularly interested in the interaction between the charged dust particles and plasma ions through the ion drag force in a dc glow discharge plasma. Measurements of the dust particles are carried out through a technique called Particle Image Velocimetry (PIV) which calculates the average velocity field based on small particle groups. As an electrostatic perturbation is applied to the dust cloud, the particle motion is observed to change its direction of motion as the gas pressure is increased. Density and temperature measurements on the background plasma are conducted for both low and high voltage states of the perturbation. An analysis of the dust particle motion and background plasma parameters suggests that there is a competition between the electrostatic force and the ion drag force on the particles. This presentation will discuss techniques and results of the calculations as well as the implications for future work on microgravity experiments. [Preview Abstract] |
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CP8.00104: Time-resolved measurement of global synchronization in a weakly-coupled dusty plasma system Jeremiah Williams A complex (dusty) plasma is a four-component system composed of ions, electrons, neutral particles and charged microparticles. The presence of the microparticles gives rise to new plasma phenomena, including collective modes such as the dust acoustic wave (DAW). This naturally-occurring wave mode has been the subject of intense theoretical and experimental study since it was predicted in 1990 and experimentally identified in 1995. In the experimental studies of this wave mode, it has been observed that the naturally-occurring wave mode is the superposition of several wave modes and that the natural wave mode can be synchronized to an external modulation. In this presentation, a time-resolved Hilbert Transform [J. D. Williams, Phys Rev E 89, 023105 (2014)] is applied to high speed video imaging to provide a spatiotemporal measurement of the global synchronization of the DAW with an external modulation in a weakly-coupled dusty plasma in a dc glow discharge plasma. [Preview Abstract] |
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CP8.00105: Experiments and simulations of the expansion of three dimensional dusty plasmas John K. Meyer, Robert L. Merlino, Vikrant Saxena, Avinash Khare, Abhijit Sen The expansion of a three-dimensional dust cloud was studied experimentally, and using molecular dynamics simulations. The dust clouds are composed of spherical glass particles of one micron diameter formed in a DC glow discharge in argon. The dust clouds are confined by an electrostatic potential structure formed by a biased mesh electrode. The cloud expansion is initiated either by turning off the bias on the mesh or by turning off the anode voltage, or both. The cloud expansion is studied by imaging the particles with a thin sheet of 532 nm laser light and a fast video camera. Cloud expansions were studied for various neutral gas pressures. The simulation model is zero dimensional, which solves the equation of motion of screened dust particles along with temporal evolution equations for plasma density and electron temperature which determine the Debye length and the dust charge. The effect of background neutral gas enters through loss terms in the plasma density and electrons temperature evolution equations. In the high pressure regime the electron temperature decays faster than the plasma density while in the low pressure regime opposite is true. Results from the simulations at different background pressure are obtained and compared with the experimental observations. [Preview Abstract] |
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CP8.00106: A comparison of the local field approximation and the local mean energy approximation in a dusty plasma Althea Wilson, Mohammad Davoudabadi, Babak Shotorban Two methods of determining rate coefficients, the local-field approximation and the local-mean-energy approximation, are compared for a dusty plasma. A low pressure cylindrical RF argon reactor is modeled computationally. Then multiple small dust grains are released and tracked in a three-dimensional framework. Gravity, neutral drag, ion drag, and grain-grain interaction forces are considered to act on dust. The differences in the plasma properties and in the resulting dust crystal generated through two methods are examined. [Preview Abstract] |
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CP8.00107: Discrete Stochastic Charging of Dust Aggregates Immersed in Plasma Abbey Haines, Lorin Matthews, Babak Shotorban, Truell Hyde Numerical simulations treating the charge as a continuous variable have been used to model stochastic charge fluctuations on dust aggregates. These stochastic fluctuations in turn lead to differences in the interactions and dynamics of charged dust aggregates [Matthews et al., ApJ, 2013]. The continuity assumption is strictly valid when the overall charge collected on the grain is substantially larger than the elementary charge. However, small grains (with radii less than 1 $\mu$m) or grains in a tenuous plasma environment are sensitive to single additions of electrons or ions, as their overall gained charge is comparable in magnitude to the elementary charge.~ In this work, a discrete stochastic method is employed to allow for integer increments of fluctuations of elementary charges collected on dust grains. Dynamic charging calculations during particle interactions are used to resolve the effects of the changing charge distribution due to stochastic charging effects. [Preview Abstract] |
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CP8.00108: Measurement of the Charge Reduction and Asymmetrical Interaction Force Created by the Ion Wakefield in a Dusty Plasma Mudi Chen, Razieh Yousefi, Jie Kong, Ke Qiao, Jorge Carmona-Reyes, Lorin Matthews, Truell Hyde The manner in which the ion wakefield forms has strong implications on the structure, stability and dynamics of a complex plasma. The majority of vertically aligned, ordered dust particle structures observed in a complex plasma result from a combination of the ion wakefield and the external confinement. The ion wakefield is also responsible for other interesting phenomena, such as the reduction in charge seen for a down-stream particle in a vertically aligned dust particle chain and the asymmetrical interaction force between the up-stream and down-stream particles. Unfortunately, few experimental measurements of these phenomena are available. In this experiment, one dimensional (1-D) dust particle structures (i.e., particle chains) are formed in a GEC RF reference cell within a glass box sitting on the powered, lower electrode. The charge reduction on the downstream particle and the asymmetric interaction force are examined using an externally produced DC bias applied to the lower electrode and a diode pumped solid state laser (Coherent VERDI) for perturbation. [Preview Abstract] |
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CP8.00109: Using Dust Particle Clusters as Probes for Mapping Trapping Potentials in Complex Plasmas Bo Zhang, Jie Kong, Lorin Matthews, Truell Hyde Dust particle clusters often manifest interesting phenomena when externally driven inside a complex plasma. Double vortices, structural phase transitions and aligned string structures have all been observed within the central region of such clusters. This paper examines whether dust particle clusters can be used as in-situ probes for investigating the trapping potential of the external confinement (driving) field within a rf discharge plasma in argon. The experiments to be discussed, were conducted inside a transparent, conductive, indium tin oxide (ITO) glass box with the walls of the box biased positively and negatively. By switching the biasing potential on and off while maintaining constant rf power, the morphology of the dust cloud can be analyzed providing insight on the topology of the trapping potential inside the ITO box. [Preview Abstract] |
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CP8.00110: A small body in a plasma: effects of ion flow and capture on the potential and fluid flow velocities Christos Stavrou, Umberto de Angelis, John Allen, Michael Coppins Although the potential, ion density and fluid velocity profiles of a flowing plasma around a small charged object can be obtained by means of PIC simulations, a theoretical approach allows an easier understanding of the role of the basic parameters: the ion flow speed, the dust radius and the ion to electron temperature ratio. These results allow for the calculation of ion drag, a problem of basic importance for fusion. We investigate how the potential, ion density and ion fluid velocities are modified when ion streaming and capture by the object are taken into account by using the simplest possible model of linear kinetic theory. The point-sink model is used, with the assumption that all the effects (presence of charged object, capture of ions, ion flow) introduce a ``small'' perturbation in the ion distribution function. Both supersonic and subsonic velocities are investigated. The calculations are compared with PIC simulations. [Preview Abstract] |
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CP8.00111: Particle in cell calculation of plasma force on a small grain in a non-uniform collisional sheath Ian H. Hutchinson Dusty plasma experiments often involve grains suspended in a sheath. The plasma forces on them are complicated by several factors. Ion-neutral collisions, essential to the pre-sheath physics, control the ion velocity distribution and can directly affect the ion drag force; there is no length-scale separation between the non-uniformity of the sheath itself and the grain's plasma perturbation; and non-linearity is important in the ion-grain interactions. The multidimensional particle in cell code COPTIC has been used to calculate fully self-consistently the plasma force, when charge and height in a (charge-exchange) collisional DC plasma sheath are specified. The background sheath ion velocity distribution functions for the unperturbed sheath are observed to vary substantially with collisionality. The grain force is found to agree quite well with a combination of sheath electric field force plus ion drag force. However, the drag force must take account of the non-Maxwellian (and spatially varying) ion distribution function, and the collisional drag enhancement. Practical formulas are provided to enable equilibrium including other forces such as gravity to be calculated. [Preview Abstract] |
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CP8.00112: Orbital-motion-limited theory of dust charging and plasma response Xianzhu Tang, Gian Luca Delzanno The foundational theory for dusty plasmas is the dust charging theory that provides the dust potential and charge arising from the dust interaction with a plasma. The most widely used charging theory for negatively charged dust particles is the so-called orbital motion limited (OML) theory, which predicts the dust potential and heat collection accurately for a variety of applications, but was previously found to be incapable of evaluating the dust charge and plasma response in any situation. Here we report a revised OML formulation that is able to predict the plasma response and hence the dust charge. It involves a corrected OML ion density expression for the background plasma where the plasma potential rises faster than $1/r^2,$ which is always the case in the Debye shielding region. We also provide the first calculation of the plasma potential and the dust charge using the OML theory. Significant deviation from the Whipple approximation of the dust charge is found when the dust size is comparable to or larger than the Debye shielding length, which is a case of importance to laboratory applications, particularly magnetic fusion. This is attributed to the fundamental role of angular momentum conservation in setting the plasma electron and ion density near the dust particle. [Preview Abstract] |
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CP8.00113: Breakdown of the Orbital-Motion-Limited charging theory in the positively charged regime Gian Luca Delzanno, Xian-Zhu Tang The Orbital-Motion-Limited theory (OML) is the most widely used theory for charging of a spherical dust grain in a plasma. It is normally applicable to grains whose radius is much smaller than the plasma Debye length, although Particle-In-Cell simulations have shown that, when the grain is negatively charged, OML is still accurate even for moderately large grains. In this work, we show that OML can become inapplicable in the positively charged regime when the grain is an electron emitter [1]. It can completely miss the transition between negatively and positively charged dust (thus predicting a positive dust potential when simulations show a negative dust potential) and overestimates the power collected by the grain. This is due to the development of a non-monotonic potential (a potential well) near the grain, which affects the electron emission current. A parametric study of the critical parameters controlling the breakdown is presented, together with a revised OML theory that remains accurate when potential well effects are important. \\[4pt] [1] G.L. Delzanno, X.Z. Tang, ``Charging and heat collection by a positively charged dust grain in a plasma,'' to appear in Physical Review Letters (2014). [Preview Abstract] |
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CP8.00114: Ion response in a magnetized flowing plasma Hanno K\"ahlert, Jan-Philip Joost, Patrick Ludwig, Michael Bonitz We investigate the influence of an external magnetic field on streaming ions in a dusty plasma. The magnetic field is chosen parallel to an external electric field, which accelerates the ions and gives rise to a non-Maxwellian distribution function~[1]. The ion susceptibility is derived from a kinetic equation, where ion-neutral collisions are taken into account via a Bhatnagar-Gross-Krook collision term. The properties of the response function and the angular dependence in the anisotropic plasma are discussed. The modified ion response significantly changes the effective interaction between the dust particles. Here, we use the response function to study the influence of magnetized flowing ions on the dispersion of dust density waves and compare the screened dust potential with calculations based on a shifted Maxwellian distribution~[2]. [1] A. V. Ivlev, S. K. Zhdanov, S. A. Khrapak, and G. E. Morfill, Phys. Rev. E \textbf{71}, 016405 (2005)\\[4pt] [2] J.-P. Joost, P. Ludwig, H. K\"ahlert, C. Arran, and M. Bonitz, submitted for publication, arxiv.org/abs/1407.1645 [Preview Abstract] |
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CP8.00115: ABSTRACT WITHDRAWN |
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CP8.00116: Effect of dust rotation on the stability of dust ion-acoustic surface waves in a kappa plasma Myoung-Jae Lee, Kyu-Sun Chung In many literature, dust grains in astrophysical environments or terrestrial laboratories were often assumed to be negatively charged point particles, hence their geometrical features were neglected. However, the dust grains in space or laboratory are often non-spherical and sometimes elongated or flattened. The non-spherical dusts can have non-zero dipole moment and can acquire a rotational motion due to the oscillating electric field or due to their interaction with photons or particles of surrounding gas. Therefore, the dispersive properties of dusty plasma should be modified by the influence of the dust rotation. Meanwhile, plasmas encountered in space and laboratories are not in thermally equilibrium states and often well described by a kappa distribution function because it can effectively represent the properties of the superthermal plasma particles in the high energy tail. In this work, the temporal behavior of electrostatically perturbed dust ion-acoustic surface wave propagating in a kappa plasma containing elongated and rotating dust grains is investigated. For this purpose, we employ the Vlasov-Maxwell system and the specular reflection condition to derive the dispersion relation. We have found that the wave is stable against the linear perturbation for the full spectrum of the wave number and the damping rate is obtained. We also have found that the increase of angular frequency of rotating dust grains can enhance the damping of the wave. [Preview Abstract] |
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CP8.00117: Experimental and Simulation Studies on Dust Instabilities at the Microscopic Level Katherine Pacha Dust instabilities have been widely studied for many years in RF and DC discharge devices as well as using computer analysis. By using a direct simulation in conjunction with the experiment, the microscopic picture of the instabilities can be studied in more detail. This is particularly helpful when looking in detail at the turbulent structures that at edges of clouds and when looking into regions where dust is not as dense. These studies were looked at as a fluid and as a granular flow with surprising results. [Preview Abstract] |
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