Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session PP10: Poster Session VI (MFE: Energetic Particles, Heating, Current Drive and Fusion System Design; MFE: DIII-D Tokamak; ICF/HED: Diagnostics, X-Ray Sources and WDM; Pure-ion, Pure Electron, Anti-Matter Plasma and Strongly Coupled)Poster
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Room: Exhibit Hall 1 |
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PP10.00001: MFE: ENERGETIC PARTICLES, HEATING, CURRENT DRIVE AND FUSION SYSTEM DESIGN |
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PP10.00002: Building 1D resonance broadened quasilinear (RBQ) code for fast ions Alfvénic relaxations Nikolai Gorelenkov, Vinicius Duarte, Herbert Berk The performance of the burning plasma is limited by the confinement of superalfvenic fusion products, e.g. alpha particles, which are capable of resonating with the Alfvénic eigenmodes (AEs). The effect of AEs on fast ions is evaluated using a resonance line broadened diffusion coefficient [Berk et al., Phys.Plasmas v.3 (1996) 1827]. The interaction of fast ions and AEs is captured for cases where there are either isolated or overlapping modes. A new code RBQ1D is being built which constructs diffusion coefficients based on realistic eigenfunctions that are determined by the ideal MHD code NOVA [Cheng, Phys. Reports v.211 (1992) 1]. The wave particle interaction can be reduced to one-dimensional dynamics where for the Alfvénic modes typically the particle kinetic energy is nearly constant. Hence to a good approximation the Quasi-Linear (QL) diffusion equation only contains derivatives in the angular momentum. The diffusion equation is then one dimensional that is efficiently solved simultaneously for all particles with the equation for the evolution of the wave angular momentum. The evolution of fast ion constants of motion is governed by the QL diffusion equations which are adapted to find the ion distribution function. [Preview Abstract] |
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PP10.00003: Tridimensional Thermonuclear Instability in Subignited Plasmas and on the Surface of the Pulsars* A. Cardinali, B. Coppi Tridimensional modes involving an increase of the electron temperature can be excited as a result of $\alpha$-particle heating in subignited D-T fusion burning plasmas when a nearly time- independent external source of heating is applied. The analyzed modes [1] are shown to emerge from an axisymmetric toroidal configurations and are radially localized around rational magnetic surfaces corresponding to $q(r=r_{0})=m^{0}/n^{0}$ where $m^{0}$ and $n^{0}$ are the relevant poloidal and toroidal mode numbers. The radial width of the mode is of the order of the thermal scale distances $\delta_{T}=\left(D_{\perp e}^{th}}/D_{\parallel e}^{th}\right)^{1/4}\left({R}_{0}/{n}^{0}\right)} ^{1/2}\left( {d\ln q}/{dr}\right)_{0}^{-1/_2}$. The mode has a rather severe damping rate, that has to be overcome by the relevant heating rate. Thus the temperature range to be considered is that where the D-T plasma reactivity undergoes a relatively large increase as a function of temperature. This kind of theory has been applied to the plasmas that are envisioned to be associated with surface of pulsar and be subjects to (spatially) inhomogenous thermonuclear burning. *Sponsored in part by the US DOE. [1] B. Coppi, et al. Nucl. Fus., 55, 053011 (2015). [Preview Abstract] |
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PP10.00004: Alfven eigenmode stability and energetic particle transport using the TGLF model He Sheng, R.E. Waltz, G.M. Staebler The Trapped Gyro-Landau-Fluid (TGLF) transport model is a physically realistic and comprehensive theory based local quasilinear transport model fitted to linear and nonlinear GYRO gyrokinetic simulations [1]. This work presents the first use of the TGLF model to treat low-n Alfven eigenmode (AE) stability and energetic particle (EP) transport. TGLF accurately recovers the GYRO TAE and EPM mode linear growth and frequency rates for the fusion alpha case in Ref. [2]. TGLF is being set-up to quickly find the critical EP gradient profile for stiff AE EP transport based on the AE linear threshold conditions given the background plasma profiles in DIII-D [3]. The TGLF model for passive EP transport from high-n ITG/TEM micro-turbulence is compared with previous models. [1] G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 14, 055909 (2007). [2] E. M. Bass and R.E. Waltz, Phys. Plasmas 17, 112319 (2010). [3] R.E. Waltz, E.M. Bass, W.W. Heidbrink and M.A. VanZeeland, Nucl. Fusion 55, 123002 (2015). [Preview Abstract] |
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PP10.00005: Toroidal Alfv\'{e}nic Eigenmodes Driven by Energetic Particles with Maxwell and Slowing-down Distributions Yawei Hou, Ping Zhu, Zhihui Zou, Charlson C. Kim, Zhaoqing Hu, Zhengxiong Wang The energetic-particle (EP) driven toroidal Alfv\'{e}n eigenmodes (TAEs) in a circular-shaped large aspect ratio tokamak are studied using the hybrid kinetic-MHD model in the NIMROD code, where the EPs are advanced using the $\delta f$ particle-in-cell (PIC) method and their kinetic effects are coupled to the bulk plasma through moment closures. Two initial distributions of EPs, Maxwell and slowing-down, are considered. The influence of EP parameters, including density, temperature and density gradient, on the frequency and the growth rate of TAEs are obtained and benchmarked with theory and gyrokinetic simulations for the Maxwell distribution with good agreement. When the density and temperature of EPs are above certain thresholds, the transition from TAE to energetic particle modes (EPM) occurs and the mode structure also changes. Comparisons between Maxwell and slowing-down distributions in terms of EP-driven TAEs and EPMs will also be presented and discussed. [Preview Abstract] |
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PP10.00006: Progress in theory and simulation of ion cyclotron emission from magnetic confinement fusion plasmas Richard Dendy, Ben Chapman, Sandra Chapman, James Cook, Bernard Reman, Ken McClements, Leopoldo Carbajal Suprathermal ion cyclotron emission (ICE) is detected from all large tokamak and stellarator plasmas. Its frequency spectrum has narrow peaks at sequential cyclotron harmonics of the energetic ion population (fusion-born or neutral beam-injected) at the outer edge of the plasma. ICE was the first collective radiative instability driven by confined fusion-born ions observed in deuterium-tritium plasmas in JET and TFTR, and the magnetoacoustic cyclotron instability is the most likely emission mechanism. Contemporary ICE measurements are taken at very high sampling rates from the LHD stellarator and from the conventional aspect ratio KSTAR tokamak. A correspondingly advanced modelling capability for the ICE emission mechanism has been developed using 1D3V PIC and hybrid-PIC codes, supplemented by analytical theory. These kinetic codes simulate the self-consistent full orbit dynamics of energetic and thermal ions, together with the electric and magnetic fields and the electrons. We report recent progress in theory and simulation that addresses: the scaling of ICE intensity with energetic particle density; the transition between super-Alfv\'{e}nic and sub-Alfv\'{e}nic regimes for the collectively radiating particles; and the rapid time evolution that is seen for some ICE measurements. [Preview Abstract] |
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PP10.00007: Nonlinear dynamics of toroidal Alfvén eigenmodes in presence of tearing modes Jia Zhu, Zhiwei Ma, Sheng Wang, Wei Zhang A new hybrid kinetic-MHD code CLT-K is developed to study nonlinear dynamics of n$=$1 toroidal Alfvén eigenmodes (TAEs) with the m/n$=$2/1 tearing mode. It is found that the n$=$1 TAE is first excited by isotropic energetic particles in the earlier stage and reaches the steady state due to wave-particle interaction. After the saturation of the n$=$1 TAE, the tearing mode intervenes and triggers the second growth of the mode. The modes goes into the second steady state due to multiple tearing mode-mode nonlinear coupling. Both wave-particle and wave-wave interactions are observed in our hybrid simulation. [Preview Abstract] |
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PP10.00008: Simulation of Chirping Avalanche in Neighborhood of~TAE gap Herb Berk, Boris Breizman, Ge Wang, Linjin Zheng A new kinetic code, CHIRP, focuses on the nonlinear response of resonant energetic particles (EPs) that destabilize Alfven waves which then can produce hole and clump phase space chirping structures, while the background plasma currents are assumed to respond linearly to the generated fields. EP currents are due to the motion arising from the perturbed field that is time averaged over an equilibrium orbit. A moderate EP source produces TAE chirping structures that have a limited range of chirping that do not reach the continuum. When the source is sufficiently strong, an EPM is excited in the lower continuum and it chirps rapidly downward as its amplitude rapidly grows in time. This response resembles the experimental observation of an avalanche [1], which occurs after a series of successive chirping events with a modest frequency shift, and then suddenly a rapid large amplitude and rapid frequency burst to low frequency with the loss of EPs. From these simulation observations we propose that in the experiment the EP population is slowly increasing to the point where the EPM is eventually excited. [1]. M.Podesta et.al. Phys.Plasma, 16, 056104(2009) [Preview Abstract] |
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PP10.00009: High Voltage, Fast-Switching Module for Active Control of Magnetic Fields and Edge Plasma Currents Timothy Ziemba, Kenneth Miller, James Prager, Ilia Slobodov Fast, reliable, real-time control of plasma is critical to the success of magnetic fusion science. High voltage and current supplies are needed to mitigate instabilities in all experiments as well as disruption events in large scale tokamaks for steady-state operation. Silicon carbide (SiC) MOSFETs offer many advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities; however, these devices are limited to 1.2-1.7 kV devices. As fusion enters the long-pulse and burning plasma eras, efficiency of power switching will be important. Eagle Harbor Technologies (EHT), Inc. developing a high voltage SiC MOSFET module that operates at 10 kV. This switch module utilizes EHT gate drive technology, which has demonstrated the ability to increase SiC MOSFET switching efficiency. The module will allow more rapid development of high voltage switching power supplies at lower cost necessary for the next generation of fast plasma feedback and control. EHT is partnering with the High Beta Tokamak group at Columbia to develop detailed high voltage module specifications, to ensure that the final product meets the needs of the fusion science community. [Preview Abstract] |
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PP10.00010: Silicon Carbide MOSFET-Based Switching Power Amplifier for Precision Magnet Control Kenneth Miller, Timothy Ziemba, James Prager, Julian Picard Eagle Harbor Technologies, Inc. (EHT) is using the latest in solid-state switching technologies to advance the state-of-the-art in magnet control for fusion science. Silicon carbide (SiC) MOSFETs offer advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities. When comparing SiC and traditional silicon-based MOSFETs, SiC MOSFETs provide higher current carrying capability allowing for smaller package weights and sizes and lower operating temperature. To validate the design, EHT has developed a low-power switching power amplifier (SPA), which has been used for precision control of magnetic fields, including rapidly changing the fields in coils. This design has been incorporated in to a high power SPA, which has been bench tested. This high power SPA will be tested at the Helicity Injected Torus (HIT) at the University of Washington. Following successful testing, EHT will produce enough SiC MOSFET-based SPAs to replace all of the units at HIT, which allows for higher frequency operation and an overall increase in pulsed current levels. [Preview Abstract] |
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PP10.00011: Experimental Study of Convective Cells and RF Sheaths Excited by a Fast Wave Antenna in the LAPD Michael Martin, Walter Gekelman, Patrick Pribyl, Bart Van Compernolle, Troy Carter, Dirk Van Eester, Kristel Cromb\'e Ion cyclotron resonance heating (ICRH) will be essential for ITER where it is planned to couple 20 MW to the plasma. During ICRH, radio frequency (RF) sheaths may form on the antenna or farther away, and convective cells are suspected to form adjacent to ICRH antennas, negatively affecting both machine and plasma performance. The LAPD (n$_e \sim 10^{12-13} cm^{-3}$ , T$_e \sim$ 1-10 eV, B$_0 \sim$ 0.4 to 2 kG, diameter $\sim$ 60 cm, length $\sim$ 17m) is an ideal device for performing detailed experiments to fully diagnose these phenomena. A 200 kW RF system capable of pulsing at the 1 Hz. rep. rate of the LAPD and operating from 2 to 2.5 MHz has been constructed to perform such studies. B$_0$ can be adjusted so that this encompasses the 1$^{st}$ to 7$^{th}$ harmonic of f$_{ci}$ in H plasmas. Emissive, Mach, Langmuir, and B-field probes measured plasma potential, bulk plasma flows, wave patterns, n$_e$, and T$_e$ in 2D planes at various axial locations from the antenna. Plasma potential enhancements of up to 90 V along magnetic field lines connected to the antenna and induced ExB flows consistent in structure with convective cells were observed. Details of these observations along with power scaling of RF sheath voltage and convective cell flows will be presented. [Preview Abstract] |
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PP10.00012: High power fast wave experiments in LAPD: interaction with density fluctuations and status/plans for ICRH Troy Carter, Michael Martin, Bart Van Compernolle, Walter Gekelman, Pat Pribyl, Stephen Vincena, Shreekrishna Tripathi, Dirk Van Eester, Kristel Crombe The LArge Plasma Device (LAPD) at UCLA is a 17~m long, up to 60~cm diameter magnetized plasma column with typical plasma parameters $n_e \sim 10^{12}-10^{13}$cm$^{-3}$, $T_e \sim 1-10$eV, and $B \sim 1$kG. A new high-power ($\sim 200$ kW) RF system and antenna has been developed for LAPD, enabling the generation of large amplitude fast waves in LAPD. Interaction between the fast waves and density fluctuations is observed, resulting in modulation of the coupled RF power. Two classes of RF-induced density fluctuations are observed. First, a coherent (~10 kHz) oscillation is observed spatially near the antenna in response to the initial RF turn-on transient. Second, broadband density fluctuations are enhanced when the RF power is above a threshold a threshold. Strong modulation of the fast wave magnetic fluctuations is observed along with broadening of the primary RF spectral line. Ultimately, high power fast waves will be used for ion heating in LAPD through minority species fundamental heating or second harmonic minority or majority heating. Initial experimental results from heating experiments will be presented along with a discussion of future plans. [Preview Abstract] |
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PP10.00013: Simulations of microwave electron heating on field-reversed configuration driven by rotating magnetic field Xiaokang Yang, Yuri Petrov, Alf Koehn, Sam Cohen, Francesco Ceccherini, Laura Galeotti, Sean Dettrick, Michl Binderbauer The rotating magnetic field-driven field-reversed configuration (FRC), such as Rotamak [1] or PFRC experiment [2], was recently proposed as a test bench at Tri Alpha Energy to experimentally pioneer the study of microwave electron heating. In order to provide guidelines to the choice of microwave frequency and antenna position, as well as the desired target plasma profile, extensive simulations have been conducted with use of the GENRAY-C ray-tracing code for a wide range of frequencies from smaller than fundamental electron cyclotron resonant (ECR) frequency up to more than 30 harmonics of ECR. Based on the operational parameters of Rotamak plasma, simulations indicate that microwaves at a frequency around 10 GHz can heat electrons inside the separatrix layer. The physics of heating mechanism is similar for both the Rotamak and the C-2U [3] FRC plasma, meaning that the magnitude of magnetic field goes down along the direction of ray propagation, therefore the rays, after the O-X-B mode conversion, encounter a basin of high harmonic EC resonances and mostly damp the power in the vicinity of the upper-hybrid resonance layer Detailed simulation results and plans for a future test bench will be presented. [1] X. Yang, et al., PRL 102, 255004 (2009) [2] S. A. Cohen et al., PRL 98, 145002 (2007) [3] M. W. Binderbauer et al., PoP 22, 056110 (2015) [Preview Abstract] |
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PP10.00014: Lower Hybrid Wave Damping on Alpha Particles in ITER R.W. Harvey, Yu.V. Petrov, P.T. Bonoli An alpha particle source has been enabled in CQL3D-FOW[1], and this provides time-dependent nonthermal distributions for self-consistent damping of lower hybrid waves. Using the conventional ray damping in CQL3D[2], i\sout{on cyclotron damping at harmonics 125 to 160 are examined in preliminary work in an ITER equilibrium. The results are to be compared with alternative calculations of the ion damping [3,4,5], and will provide a basis for future work on alpha-particle channeling [6] for which CQL3D-FOW is well suited.} [1] Yu. V. Petrov and R.W. Harvey, this APS/DPP meeting (2016) [2] CQL3D Manual, http://www.compxco.com/cql3d.html [3] C.F.F. Karney, Phys. Fluids , 2188 (1979) [4] J. Schuss et al., Nucl. Fusion , 201 (1983) \sout{[5] P.T. Bonoli and M. Porkolab, Nucl. Fusion , 1341 ()} \sout{[6] }\sout{N.J. Fisch and J.-M. Rax, Nucl. Fusion, 549 (1992)} [Preview Abstract] |
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PP10.00015: Application of the Finite Orbit Width Version of the CQL3D Code to Transport of Fast Ions. Yu.V. Petrov, R.W. Harvey The CQL3D bounce-averaged Fokker-Planck (FP) code [1] now includes the "fully" neoclassical version in which the diffusion and advection processes are averaged over actual drift orbits, rather than using a 1st-order expansion. Incorporation of Finite-Orbit-Width (FOW) effects results in neoclassical radial transport caused by collisions, RF wave heating and by toroidal electric field (radial pinch). We apply the CQL3D-full-FOW code to study the thermalization and radial transport of high-energy particles, such as alpha-particles produced by fusion in ITER or deuterons from NBI in NSTX, under effect of their interaction with auxiliary RF waves. A particular attention is given to visualization of transport in 3D space of velocity$+$major-radius coordinates. [1] R.W. Harvey and M. McCoy, "The CQL3D Fokker Planck Code", www.compxco.com/cql3d [Preview Abstract] |
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PP10.00016: An improved rf-sheath boundary condition and implications for ICRF modeling J.R. Myra, H. Kohno To improve the fidelity of global ICRF codes for interactions with the scrape-off layer plasma, a newly improved sheath boundary condition has been formulated. Extending previous work, which employed a capacitive limit, the new boundary condition generalizes the formulation to a complex sheath impedance which additionally describes the effective sheath resistance at rf frequencies. The latter is important for modeling localized rf power deposition which could potentially cause damaging plasma material interactions. A generalized sheath model has been developed and is described by four dimensionless parameters: the degree of sheath magnetization, the magnetic field angle with the surface, the rf field strength and the degree of ion mobility set by the wave frequency. Characterization of the sheath impedance in this parameter space using fits and interpolations will be presented together with progress on testing and verification of the boundary condition in slab geometry using numerical codes. [Preview Abstract] |
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PP10.00017: Kinetic full wave analyses of O-X-B mode conversion of EC waves in tokamak plasmas Atsushi Fukuyama, Shabbir Ahmad Khan, Hiroe Igami, Hiroshi Idei For heating and current drive in a high-density plasma of tokamak, especially spherical tokamak, the use of electron Bernstein waves and the O-X-B mode conversion were proposed and experimental observations have been reported. In order to evaluate the power deposition profile and the current drive efficiency, kinetic full wave analysis using an integral form of dielectric tensor has been developed. The incident angle dependence of wave structure and O-X-B mode conversion efficiency is examined using one-dimensional analysis in the major radius direction. Two-dimensional analyses on the horizontal plane and the poloidal plane are also conducted, and the wave structure and the power deposition profile are compared with those of previous analyses using ray tracing method and cold plasma approximation. [Preview Abstract] |
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PP10.00018: The potential role of Neutral Beam Injection in EU DEMO Pietro Vincenzi, Jean-Francois Artaud, Tommaso Bolzonella, Gerardo Giruzzi EU DEMO studies for pulsed (DEMO1) and steady-state (DEMO2) concepts are currently in the pre-conceptual phase. Present DEMO1 design is based on ITER baseline H-mode scenario, while DEMO2 is based on advanced scenarios with moderate reversed q profile sustained by non-inductive currents. One of the possible flattop heating power systems currently considered is Neutral Beam Injection (NBI). In this work the role of NBI in DEMO1 and DEMO2 is investigated by means of integrated simulations of DEMO scenarios using METIS fast tokamak modelling tool. Limitations, requirements and benefits of the use of a NBI system are discussed. For DEMO1 pulsed concept, the role of NBI is mainly central plasma heating for scenario stability (high fusion power H-mode). As a by-product of the tangential injection, NBI is capable of current drive, which is favorable in order to extend the discharge duration. Regarding a steady-state DEMO2 concept, in addition to plasma heating, NBI becomes a direct actuator for the advanced scenario by driving a considerable part of the plasma current. This requires more than 100MW with off-axis injection. The effect of an increase of the injection energy on the driven current density profile is also presented for DEMO2. [Preview Abstract] |
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PP10.00019: Development of full wave code for modeling RF fields in hot non-uniform plasmas Liangji Zhao, Vladimir Svidzinski, Andrew Spencer, Jin-Soo Kim FAR-TECH, Inc. is developing a full wave RF modeling code to model RF fields in fusion devices and in general plasma applications. As an important component of the code, an adaptive meshless technique is introduced to solve the wave equations, which allows resolving plasma resonances efficiently and adapting to the complexity of antenna geometry and device boundary. The computational points are generated using either a point elimination method or a force balancing method based on the monitor function, which is calculated by solving the cold plasma dispersion equation locally. Another part of the code is the conductivity kernel calculation, used for modeling the nonlocal hot plasma dielectric response. The conductivity kernel is calculated on a coarse grid of test points and then interpolated linearly onto the computational points. All the components of the code are parallelized using MPI and OpenMP libraries to optimize the execution speed and memory. The algorithm and the results of our numerical approach to solving 2-D wave equations in a tokamak geometry will be presented. [Preview Abstract] |
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PP10.00020: High Power, Solid-State RF Generation for Plasma Heating James Prager, Timothy Ziemba, Kenneth Miller, Chris Pierren Radio Frequency heating systems are rarely used by the small-scale validation platform experiments due to the high cost and complexity of these systems. Eagle Harbor Technologies (EHT), Inc. is developing an all-solid-state RF plasma heating system that uses EHT's nanosecond pulser technology in an inductive adder configuration to drive nonlinear transmission lines (NLTL). The system under development does not require the use of vacuum tube technology, is inherently lower cost, and is more robust than traditional high power RF heating schemes. The inductive adder can produce 0 to20 kV pulses into 50 Ohms with sub-10 ns rise times. The inductive adder has been used to drive NLTLs near 2 GHz with other frequencies to be tested in the future. EHT will present experimental results, including RF measurements with D-dot probes and capacitve voltage probes. During this program, EHT will test the system on Helicity Injected Torus at the University of Washington and the High Beta Tokamak at Columbia University. [Preview Abstract] |
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PP10.00021: Validation of quasilinear diffusion by electron Landau damping in toroidal geometry Xishuo Wei, Jungpyo Lee We study the conditions to validate quasilinear diffusion by electron Landau damping in toroidal geometry. As an example, the Landau damping by lower hybrid waves in a tokamak is considered. A particle code is used to calculate particle motion in phase space, and the diffusion coefficient in parallel direction is given by $D_{ql} =\left\langle {\Delta v^{2}} \right\rangle /\left( {2\Delta t} \right)$ over a period of time. For simiplicity, the particle motion is perturbed by the electrostatic waves only in the parallel direction, and the perpendicular motion is not taken into account in the diffusion coefficient with the assumption of significantly small gyro-radius and orbit width compared tothe perpendicular wavelength. The variation of parallel velocity due to the varying magnetic field in a flux surface is considered to include the effect of the toroidal geometry on the diffusion coefficient. The calculated coefficient is compared with the theoretical value of bounce-averaged Kennel-Engelmann(K-E) quasilinear diffusion coefficeint. Because the (K-E) diffusion coefficient is derived by the unperturbed particle orbit in a cylindrical geometry, we present some conditions to validate the theory in toroidal geometry. The conditions strongly depend on the variation of parallel velocity, the phase velocity of the wave, and the spectrum of broad band wave. [Preview Abstract] |
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PP10.00022: A new symmetric form of the bounce-averaged quasilinear diffusion coefficient in toroidal geometry Jungpyo Lee, David Smithe, Lee Berry, Erwin Jaeger, John Wright, Paul Bonoli Kennel-Engelmann (K-E) quasilinear diffusion coefficients are used in many RF wave codes to couple the Maxwell equation solver with a Fokker-Plank calculation. The diagonal component of the coefficient tensor in the speed direction should be positive in the quasi-linear assumption for the H-theorem. However, in the application to toroidal geometry, the bounce-average of the K-E coefficients does not guarantee positive values for an arbitrary wave spectrum due to the interference between the spectral modes. The negative bounce-averaged diffusion coefficients unexpectedly occur because the K-E coefficient is derived in a cylindrical limit, in which the resonance kernel (gyrofrequency, wave vector and parallel velocity) in the phase integral do not vary along the phase trajectory, while the bounce-average is computed in a toroidal geometry. To guarantee the positiveness, we derive a new form of the diffusion coefficient that keeps the symmetric form between the bounce-integral and the trajectory integral. The new coefficients are implemented in a code for ion cyclotron waves in a tokamak (TORIC). Using the new form, the error of quasilinear diffusion coefficients due to the negative values is reduced significantly, and the toroidal effects are well captured. [Preview Abstract] |
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PP10.00023: High-Performance Computational Modeling of ICRF Physics and Plasma-Surface Interactions in Alcator C-Mod Thomas Jenkins, David Smithe Inefficiencies and detrimental physical effects may arise in conjunction with ICRF heating of tokamak plasmas. Large wall potential drops, associated with sheath formation near plasma-facing antenna hardware, give rise to high-Z impurity sputtering from plasma-facing components and subsequent radiative cooling. Linear and nonlinear wave excitations in the plasma edge/SOL also dissipate injected RF power and reduce overall antenna efficiency. Recent advances in finite-difference time-domain (FDTD) modeling techniques [Jenkins \& Smithe, PSST {\bf 24}, 015020 (2015)] allow the physics of localized sheath potentials, and associated sputtering events, to be modeled concurrently with the physics of antenna near- and far-field behavior and RF power flow. The new methods enable time-domain modeling of plasma-surface interactions and ICRF physics in realistic experimental configurations at unprecedented spatial resolution. We present results/animations from high-performance (10k-100k core) FDTD/PIC simulations spanning half of Alcator C-Mod at mm-scale resolution, exploring impurity production due to localized sputtering (in response to self-consistent sheath potentials at antenna surfaces) and the physics of parasitic slow wave excitation near the antenna hardware and SOL. [Preview Abstract] |
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PP10.00024: Overview of the new capabilities of TORIC-v6 and comparison with TORIC-v5 R. Bilato, M. Brambilla, N. Bertelli Since its release[1], version 5 (v5) of the full-wave TORIC code, characterized by an optimized parallelized solver[2] for its routinely use in TRANSP package, has been ameliorated in many technical issues, e.g. the plasma-vacuum transition and the full-spectrum antenna modeling. For the WPCD-benchmark cases[3] a good agreement between the new version, v6, and v5 is found. The major improvement, however, has been done in interfacing TORIC-v6 with the Fokker-Planck SSFPQL solver to account for the back-reaction of ICRF and NBI heating on the wave propagation and absorption[4]. Special algorithms have been developed for SSFPQL for the numerical precision at high pitch-angle resolution and to evaluate the generalized dispersion function directly from the numerical solution. Care has been spent in automatizing the non-linear loop between TORIC-v6 and SSFPQL. In v6 the description of wave absorption at high-harmonics has been revised and applied to DEMO[5]. For high-harmonic regimes there is an ongoing activity on the comparison with AORSA[6]. [1]Brambilla, Bilato NF 46 (2006) S387.[2]Wright, et al. PoP 11 (2004) 2473.[3]Bilato, et al., 21st RF Conf. (2016) 1689.[4]Bilato, Brambilla NF 51 (2011) 103034.[5]Brambilla, Bilato NF 55 (2015) 023016.[6]Bertelli, et al. APS-DPP 2014 [Preview Abstract] |
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PP10.00025: Non-inductive current built-up by local electron cyclotron heating and current drive with a 28 GHz focused beam on QUEST Takumi Onchi, Hiroshi Idei, Makoto Hasegawa, Hiroaki Ohwada, Hideki Zushi, Kazuaki Hanada, Tsuyoshi Kariya, Kishore Mishra, Taichi Shikama The plasma current can be driven solely by injecting electron cyclotron waves (ECWs) in spherical tokamak (ST) configuration. A system of 28 GHz gyrotron (maximum power: 270 kW) is renewed and reinstalled on QUEST. A focused ECW beam, whose diameter is about 5 cm at the second harmonic resonance, is injected for local ECW heating and current drive. The local power density at resonance exceeds 75 MW/m$^2$ at an injection power of 150 kW. The incident ECW polarization can be adjusted employing the phase shifter consisting of two corrugated plates \footnote{ T.Ii $et$ $al.$, Rev. Sci. Instrum. 86, 023502 (2015)}. During 1.25 second pulse of ECH, plasma current is built up to $I_{\mathrm{p}}$ = 70 kA fully non-inductively with a core electron density of $n_{\mathrm{e}}$ $>$ 10$^{18}$ m$^{-3}$. The closed flux in such ST plasma is determined at the inboard limiter on the center stack. Energetic electrons are also responsible for the pressure and equilibrium. [Preview Abstract] |
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PP10.00026: Electromagnetic particle simulation of the effect of toroidicity on linear mode conversion and absorption of lower hybrid waves Jian Bao, Zhihong Lin, Animesh Kuley, Zhixuan Wang Effects of toroidicity on linear mode conversion and absorption of lower hybrid (LH) waves in tokamak have been studied by electromagnetic particle simulation using GTC$^{\mathrm{1,2}}$. The simulation confirms that the toroidicity induces an upshift of parallel refractive index when LH waves propagate from the tokamak edge toward the core, which affects the radial position for the mode conversion between slow and fast LH waves. Furthermore, moving LH antenna launch position from low field side toward high field side leads to a larger upshift of the parallel refractive index, which helps the slow LH wave penetration into the tokamak core. The broadening of the poloidal spectrum of the wave-packet due to wave diffraction is also verified in the simulation. Both the upshift and broadening effects of the parallel spectrum of the wave-packet modify the parallel phase velocity and thus the linear absorption of LH waves by electron Landau resonance. In the nonlinear electromagnetic simulation, nonlinear wave trapping of electrons is verified and a plasma current is nonlinearly driven. Preliminary results of the nonlinear parametric decay of LH waves will be presented. $^{\mathrm{1}}$J. Bao, Z. Lin, A. Kuley, Z. X. Wang, Phys. Plasmas 23, 062501 (2016). $^{\mathrm{2}}$J. Bao, Z. Lin, A. Kuley, Z. X. Wang, Nuclear Fusion 56, 066007 (2016). [Preview Abstract] |
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PP10.00027: 3D Modeling of Antenna Driven Slow Waves Excited by Antennas Near the Plasma Edge David Smithe, Thomas Jenkins Prior work with the 3D finite-difference time-domain (FDTD) plasma and sheath model used to model ICRF antennas in fusion plasmas has highlighted the possibility of slow wave excitation at the very low end of the SOL density range, and thus the prudent need for a slow-time evolution model to treat SOL density modifications due to the RF itself. At higher frequency, the DIII-D helicon antenna [1] has much easier access to a parasitic slow wave excitation, and in this case the Faraday screen provides the dominant means of controlling the content of the launched mode, with antenna end-effects remaining a concern. In both cases, the danger is the same, with the slow-wave propagating into a lower-hybrid resonance layer a short distance (\textasciitilde cm) away from the antenna, which would parasitically absorb power, transferring energy to the SOL edge plasma, primarily through electron-neutral collisions. We will present 3D modeling of antennas at both ICRF and helicon frequencies. We've added a slow-time evolution capability for the SOL plasma density to include ponderomotive force driven rarefaction from the strong fields in the vicinity of the antenna, and show initial application to NSTX antenna geometry and plasma configurations. The model is based on a Scalar Ponderomotive Potential method [2], using self-consistently computed local field amplitudes from the 3D simulation. [1] R. Pinsker et al., 21st Topical Conf. on RF Power in Plasmas, (2015). [2] J. R. Myra, et. al., Nucl. Fusion 46, S455 (2006). [Preview Abstract] |
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PP10.00028: Propagation of radio frequency waves through fluctuations in the scrape-off layer modeled by electromagnetic homogenization K. Hizanidis, F. Bairaktaris, S.-I. Valvis, A. K. Ram In tokamak plasmas, coherent fluctuations, such as blobs and filaments, are observed in the scrape-off layer (SOL). These fluctuations, embedded in background plasma, modify the spatial profile of the plasma permittivity. Radio frequency (RF) waves have to propagate through this spatially varying medium before depositing power in the core plasma. Any changes in the plasma permittivity modify the propagation properties of the waves, such as their polarizations and wave spectra. This, in turn, affects the spatial location and profile of the region where the waves deposit their energy on particles. Studies that have considered the scattering of RF waves by a single blob or filament are limited as they lack a global representation of the SOL. We have developed a special electromagnetic homogenization (EMH) technique to better model the SOL. The standard EMH model is for spherical dielectrics, small filling ratio, and for RF wavelengths longer than the inhomogeneity scale length. Our model is for ellipsoidal blobs of varying permittivity, and assumes that the filling ratio and the RF wavelengths are completely arbitrary. A description of our SOL model and its effect on the propagation of RF waves will be presented. [Preview Abstract] |
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PP10.00029: Global particle in cell simulation of radio frequency waves in tokamak$\backslash $fs20 Animesh Kuley, Z Lin, J Bao, C Lau, G.Y. Sun We are looking into a new nonlinear kinetic simulation model to study the radio frequency heating and current drive of fusion plasmas using toroidal code GTC. In this model ions are considered as fully kinetic (FK) particles using Vlasov equation and the electrons are treated as drift kinetic (DK) particles using drift kinetic equation. We have benchmarked this numerical model to verify the linear physics of normal modes, conversion of slow and fast waves and its propagation in the core region of the tokamak using the Boozer coordinates. In the nonlinear simulation of ion Bernstein wave (IBW) in a tokamak, parametric decay instability (PDI) is observed where a large amplitude pump wave decays into an IBW sideband and an ion cyclotron quasi-mode (ICQM). The ICQM induces an ion perpendicular heating, with a heating rate proportional to the pump wave intensity. Finally, in the electromagnetic LH simulation, nonlinear wave trapping of electrons is verified and plasma current is nonlinearly driven. Presently we are working on the development of new PIC simulation model using cylindrical coordinates to address the RF wave propagation from the edge of the tokamak to the core region and the parametric instabilities associated with this RF waves. We have verified the cyclotron integrator using Boris push method. [Preview Abstract] |
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PP10.00030: Nonlinear Burn Control in Tokamaks using Heating, Non-axisymmetric Magnetic Fields, Isotopic fueling and Impurity injection. Andres Pajares, Eugenio Schuster Plasma density and temperature regulation in future tokamaks such as ITER is arising as one of the main problems in nuclear-fusion control research. The problem, known as burn control, is to regulate the amount of fusion power produced by the burning plasma while avoiding thermal instabilities. Prior work in the area of burn control considered different actuators, such as modulation of the auxiliary power, modulation of the fueling rate, and controlled impurity injection. More recently, the in-vessel coil system was suggested as a feasible actuator since it has the capability of modifying the plasma confinement by generating non-axisymmetric magnetic fields. In this work, a comprehensive, model-based, nonlinear burn control strategy is proposed to integrate all the previously mentioned actuators. A model to take into account the influence of the in-vessel coils on the plasma confinement is proposed based on the plasma collisionality and the density. A simulation study is carried out to show the capability of the controller to drive the system between different operating points while rejecting perturbations. [Preview Abstract] |
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PP10.00031: First Results and Future Plans on HIDRA Daniel Andruczyk, Zehuan Song, Nirbhav Chopra, Daniel Johnson, Andrew Shone, David Ruzic, Jean Paul Allain, Davide Curreli The former WEGA stellarator, which operated in Greifswald at the Max Planck Institute for Plasma Physics, has been resurrected as the Hybrid Illinois Device for Research and Applications (HIDRA) at the University of Illinois. HIDRA is a five period, $l=$2, $m=$5 stellarator with major radius $R_{0}=$0.72 m and minor radius $r=$0.19 m. Initial heating is with 2.45 GHz ECR heating at $B_{0}=$0.087 T magnetic field and can be operated up to $B_{0}=$0.5 T. It has the ability to operate as both a stellarator and tokamak, mainly operating as a stellarator for long pulse studies. Expected parameters as a stellarator are Te$=$25 eV and ne$=$1x10$^{\mathrm{18\thinspace }}$m$^{\mathrm{-3}}$ and as a tokamak Te and ne can be up to 800 eV and 1x10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$ respectively. Research is dedicated to PMI studies using the wealth of knowledge and experience at the Center for Plasma Material Interactions. First experiments have started to be performed in HIDRA and soon it will become an integral step in the development of flowing lithium PFC concepts that will be implemented on EAST. This presentation will discuss the assembly of HIDRA along with first results from initial experiments and planned future experiments. [Preview Abstract] |
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PP10.00032: Experimental Characterization of a Plasma Deflagration Accelerator for Simulating Fusion Wall Response to Disruption Events Thomas Underwood, Keith Loebner, Mark Cappelli In this work, the suitability of a pulsed deflagration accelerator to simulate the interaction of edge-localized modes with plasma first wall materials is investigated. Experimental measurements derived from a suite of diagnostics are presented that focus on the both the properties of the plasma jet and the manner in which such jets couple with material interfaces. Detailed measurements of the thermodynamic plasma state variables within the jet are presented using a quadruple Langmuir probe operating in current-saturation mode. This data in conjunction with spectroscopic measurements of H$\alpha$ Stark broadening via a fast-framing, intensified CCD camera provide spatial and temporal measurements of how the plasma density and temperature scale as a function of input energy. Using these measurements, estimates for the energy flux associated with the deflagration accelerator are found to be completely tunable over a range spanning 150 MW m$^{-2}$ - 30 GW m$^{-2}$. The plasma-material interface is investigated using tungsten tokens exposed to the plasma plume under variable conditions. Visualizations of resulting shock structures are achieved through Schlieren cinematography and energy transfer dynamics are discussed by presenting temperature measurements of exposed materials. [Preview Abstract] |
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PP10.00033: Reduced Deuterium Retention in Simultaneously Damaged and Annealed Tungsten Michael Simmonds, Yongqiang Wang, Russell Doerner, Joseph Barton, Matthew Baldwin, George Tynan Fusion relevant displacement damage performed at elevated temperature in tungsten (W) and its influence on deuterium (D) retention is explored. Displacement damage performed in room temperature W allows defects to effectively become frozen-in. In this work, 5 MeV Cu ions produced up to 0.2 dpa damage in W samples at various temperatures up to 1243 K were subsequently exposed to D plasma at 383 K to a fluence of 10\textasciicircum 24 ions/m\textasciicircum 2. Subsequent Nuclear Reaction Analysis (NRA) and Thermal Desorption Spectrometry (TDS) show that increased temperature during damage creation reduces D retention. TDS clearly shows that the Cu ion induced traps are annealed and approach intrinsic concentrations as the simultaneous damage/heating approaches 1243 K. Lastly, analysis of the TDS data is shown to provide an estimate of 0.09 eV for the recovery activation energy, similar to the mobility energy calculated for self-interstitial atoms (SIA). [Preview Abstract] |
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PP10.00034: Helium and deuterium induced morphology on porous tungsten and effects on D retention Aveek Kapat, Jean Paul Allain, Eric Lang, Jonathan Hinks, Stephen Donnelly Tungsten is the material of choice for plasma facing components in the divertor region of future plasma-burning tokamak fusion reactors due to favorable thermo-mechanical properties. However, refractory metals are limited by possible detrimental ion-induced (He and D) surface morphologies that compromise confinement. Materials with increased defect sink domains could decrease vacancy trapping sites and decrease the probability for early-stage helium bubble formation intra-granularly. Previous work conjectured that an increase in defect sinks such as grain-boundary interfaces could provide increased resistance to helium-bubble formation. Thus higher grain boundary densities could potentially lead to an increased He fluence threshold. Based on the defect dynamics observed in the ultrafine grain tungsten, an internal free surface could also act as a defect sink and thus increases radiation tolerance, namely a material with a high surface-to-volume ratio such as porous tungsten. Moreover, very little is known about porous metals and their potential for increasing tolerance to radiation damage as a plasma-facing interface. Porous tungsten was irradiated in the MIAMI facility at the University of Huddersfield at room and\textasciitilde 1200\textdegree C temperature with He then with D as well as just with deuterium; all cases were observed with in-situ TEM. The observed defect dynamics as well as deuterium retention are presented. [Preview Abstract] |
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PP10.00035: Behavior of a SnLi liquid metal eutectic on D-irradiated, porous tungsten substrates Eric Lang, Aveek Kapat, J.P. Allain Tungsten (W) is a common PFC material in the divertor due to its beneficial thermomechanical properties and high sputter threshold [1]. Under helium irradiation, W develops surface morphology such as fuzz. Liquid metals, such as tin-lithium eutectics, have been proposed as PFCs to combat W erosion and allow for a self-healing surface. Tin-dominant eutectics have lower evaporation rates than pure lithium due to increased binding energies, yet exhibit decreased D retention and Li surface segregation [2]. In prior experiments of SnLi coatings on fuzzy W substrates, the SnLi layer has been shown to protect underlying fuzz. Additionally, the liquid metal better adhered to a fuzzy surface than a smooth one [3]. Fuzzy W samples have been coated with a 95 at.{\%} SnLi eutectic and exposed to 250eV D ions at elevated temperatures and fluences of \textasciitilde 10$^{\mathrm{17}}$ cm$^{\mathrm{-2}}$ . Experiments will be conducted in the IGNIS facility, a multi-functional, \textit{in-situ }irradiation and characterization facility at the University of Illinois. \textit{In-situ }XPS will be used to elucidate irradiation-driven liquid metal behavior to identify surface chemistry changes. Additionally, \textit{ex-situ }SEM will be used to identify surface morphology changes. [1] Naujoks, et al. \textit{Nucl. ~Fusion}. Vol 36,~No. 6 (1996) [2] R. Bastasz et al. \textit{Fus. Eng. Des.} 72 (2004) 111--119 [3] E. Lang, et al. Not yet published. 2016 [Preview Abstract] |
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PP10.00036: Engineering design point for a 1MW fusion neutron source Paul Sieck, Paul Melnik, Simon Woodruff, James Stuber, Carlos Romero-Talamas, John O'Bryan, Ronald Miller Compact fusion neutron sources are currently serving important roles in medical isotope production, and could be used for waste transmutation if sufficient fluence can be attained. The engineering design point for a compact neutron source with target rateof e17n/sbased on the adiabatic compression of a spheromak is presented. The compression coils and passive structure are designed to maintain stability during compression. The power supplies consist of 4 separate banks of \textasciitilde MJ each; Pspice simulations and power requirement calculations will be shown. We outline the diagnostic set that will be required for an experimental campaign to address issues relating to both formation efficiency and energy confinement scaling during compression. [Preview Abstract] |
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PP10.00037: Physicsdesign point for a 1MW fusion neutron source Simon Woodruff, Paul Melnik, Paul Sieck, James Stuber, Carlos Romero-Talamas, John O'Bryan, Ronald Miller We are developing a design point for a spheromak experiment heated by adiabatic compression for use as a compact neutron source. We utilize the CORSICA and NIMROD MHD codes as well as analytic modeling to assess a concept with target parameters R0$=$0.5m, Rf$=$0.17m, T0$=$1keV, Tf$=$8keV, n0$=$2e20m-3 and nf$=$ 5e21m-3, with radial convergence of C$=$R0/Rf$=$3. We present results from CORSICA showing the placement of coils and passive structure to ensure stability during compression. We specify target parameters for the compression in terms of plasma beta, formation efficiency and energy confinement. We present results simulations of magnetic compression using the NIMROD code to examine the role of rotation on the stability and confinement of the spheromak as it is compressed. [Preview Abstract] |
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PP10.00038: Numerical investigation of design and operational parameters on CHI spheromak performance J.B. O'Bryan, C.A. Romero-Talamas, S. Woodruff Nonlinear, extended-MHD computation with the NIMROD code is used to explore magnetic self-organization and performance with respect to externally controllable parameters in spheromaks formed with coaxial helicity injection. The goal of this study is to inform the design and operational parameters of proposed proof-of-principle spheromak experiment. The calculations explore multiple distinct phases of evolution (including adiabatic magnetic compression), which must be explored and optimized separately. Results indicate that modest changes to the design and operation of past experiments, e.g. SSPX [E.B. Hooper et al. PPCF 2012], could have significantly improved the plasma-current injector coupling efficiency and performance, particularly with respect to peak temperature and lifetime. Though we frequently characterize performance relative to SSPX, we are also exploring fundamentally different designs and modes of operation, e.g. flux compression. [Preview Abstract] |
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PP10.00039: Detecting Shielded Special Nuclear Materials Using Multi-Dimensional Neutron Source and Detector Geometries John Santarius, Marcos Navarro, Matthew Michalak, Aaron Fancher, Gerald Kulcinski, Richard Bonomo A newly initiated research project will be described that investigates methods for detecting shielded special nuclear materials by combining multi-dimensional neutron sources, forward/adjoint calculations modeling neutron and gamma transport, and sparse data analysis of detector signals. The key tasks for this project are: (1) developing a radiation transport capability for use in optimizing adaptive-geometry, inertial-electrostatic confinement (IEC) neutron source/detector configurations for neutron pulses distributed in space and/or phased in time; (2) creating distributed-geometry, gas-target, IEC fusion neutron sources; (3) applying sparse data and noise reduction algorithms, such as principal component analysis (PCA) and wavelet transform analysis, to enhance detection fidelity; and (4) educating graduate and undergraduate students. [Preview Abstract] |
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PP10.00040: MFE: DIII-D TOKAMAK |
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PP10.00041: DIII-D First Wall Metal Impurity Migration Trends C.P. Chrobak, H. Torreblanca, K. Holtrop, D. Thomas, E.A. Unterberg, D.C. Donovan, D. Buchenauer, P. Stangeby Metal accumulation on the entire graphite first wall of the DIII-D tokamak was measured using a novel X-Ray Fluorescence technique. The technique is sensitive to and distinguishes between various elements from Al to U. During a two week campaign, the DIII-D tokamak operated with W-coated Mo alloy (TZM) metal tiles in the divertor, arranged in two 5cm wide toroidally uniform rings. These rings provided a large localized source of W to enable the first measurements of whole-vessel high-Z metal migration from a known divertor source. We have also measured deposits of Ni, Cr, Fe, Cu, and Mo originating from various other sources including sputtering from neutral beam drift-duct port walls and RF antenna Faraday shields. The integrated deposition pattern for different elements originating from different sources during these campaigns will be compared. In addition, a detailed description of the intrinsic metal impurities in different unexposed grades of graphite will be presented. [Preview Abstract] |
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PP10.00042: Studies of short-range tungsten migration in DIII-D divertor D.L. Rudakov, P.C. Stangeby, J.D. Elder, R. Ding, T. Abrams, E.A. Unterberg, A. Briesemeister, D. Donovan, A.G. McLean, H.Y. Guo, D.M. Thomas, E. Hinson, W.R. Wampler, J.G. Watkins Two toroidal rings of 5 cm wide W-coated TZM inserts were installed in the lower divertor of DIII-D. Migration of W on the graphite tile surfaces 1-6 cm radially outwards from the outermost ring was studied in a series of 23 reproducible lower single null L-mode discharges with the Outer Strike Point (OSP) placed on the ring. The discharges used 3.2 MW of NBI heating power; plasma density and electron temperature at the OSP were about1x10$^{20}m^{-3}$ and 30 eV. W gross erosion rates were measured via monitoring 400.9 nm WI line and applying S/XB coefficient. W deposition was measured on a graphite DiMES sample used as a divertor collector probe. The sample featured two 1 mm wide radial inserts; one was exposed for the whole experiment, the other was exchanged every 4-8 plasma discharges. Measurements of the areal density of W on the inserts by post-mortem RBS analysis show that W deposition is largest in the area of net carbon deposition, possibly due to W re-erosion suppression by C deposits. Measured W coverage in the area of net C erosion is comparable to ERO modeling predictions. [Preview Abstract] |
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PP10.00043: First Measurements of W Erosion from Ultraviolet Emission in DIII-D C.A. Johnson, D.A. Ennis, S.D. Loch, S. Allen, B. Victor, C.M. Samuell, C.P. Ballance, T. Abrams, E. Unterberg Erosion of Plasma Facing Components (PFCs) will play a critical role in establishing the performance of future reactor-relevant fusion devices. Erosion can be diagnosed from spectral line emission together with atomic coefficients called 'ionizations per photon' (S/XB). New ultraviolet survey spectrometers (200 to 400 nm) have been commissioned on the DIII-D experiment for enhanced diagnosis of W erosion in the divertor region. Previous atomic calculations predict neutral W will radiate most strongly at ultraviolet wavelengths. Ultraviolet measurements from DIII-D experiments with W PFCs in the divertor have identified new candidate spectral lines for more accurately diagnosing neutral W erosion rates. For example, W emission lines at 265.65 and 363.19 nm were observed to be more intense than the widely used 400.89 nm. Complete UV spectra will be presented and compared to synthetic spectra generated by new atomic calculations of neutral W using ADAS for varying plasma conditions. [Preview Abstract] |
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PP10.00044: New \textit{R-}matrix calculations of neutral W electron-impact excitation and ionization for PFC erosion diagnostics S.D. Loch, D.A. Ennis, M.S. Pindzola, C.A. Johnson, C.P. Ballance, T. Abrams, E. Unterberg The erosion rate of tungsten PFCs can be diagnosed spectroscopically using spectral line intensity measurements combined with a set of `ionizations per photon’ coefficients (also called S/XB ratios). The accuracy of this diagnostic technique depends critically upon the quality of the atomic data comprising the S/XB ratio. This project aims to improve the accuracy of W excitation and ionization atomic data using non-perturbative methods. Synthetic spectra generated from existing perturbative W data are used to guide the size of the new $\textit{R}$-matrix calculations. The new data is used to generate a synthetic spectrum, which is compared with measured DIII-D ultraviolet spectra to determine the optimal lines for diagnosing W erosion. The new ionization rate coefficients are compared with literature values. The new S/XB ratio for the 400.9 nm line is compared with measured values and the density, temperature and metastable dependence of the S/XB ratios for new UV lines are investigated. [Preview Abstract] |
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PP10.00045: RMP effects on the W and C erosion/deposition balance on W test samples in DIII-D E.T. Hinson, H. Frerichs, O. Schmitz, T.E. Evans, H.Y. Guo, D.M. Thomas, D.L. Rudakov, T. Abrams, E.A. Unterberg, A. Briesemeister, C.J. Lasnier, A.G. McLean, M. Makowski, W.R. Wampler, J.G. Watkins, H.Q. Wang Clear evidence for alteration of the W and C erosion by resonant magnetic perturbation (RMP) fields has been obtained in an experiment exposing W-coated DiMES samples in the DIII-D divertor to outer strike point (OSP) sweeps in comparable series of discharges with and without the application of RMP. Gross erosion measurements of W and C during these sweeps using the S/XB method show that the 3-D boundary induced by the RMP significantly alters the erosion rate from DiMES. In particular, application of RMP smooths radial W erosion anisotropy seen for the axisymmetric case, where the W erosion rate for the OSP sweep in the outward direction significantly exceeds the erosion rate observed for the subsequent inward radial sweep over the sample. This finding is likely related to a change in the W/C erosion and redeposition balance in the C-dominated wall environment at DIII-D. Moreover, non-axisymmetric plasma structure on the W sample has to be considered. This challenge will be further examined by comparison of experimental results to EMC3-EIRENE modeling. [Preview Abstract] |
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PP10.00046: EUV Spectroscopy During the DIII-D Tungsten Divertor Campaign S.L. Allen, B.S. Victor, P. Beiersdorfer, E. Magee, V. Soukhanovskii, M. Weller, S. Loch, D. Thomas Two toroidal rings of tungsten-coated tile inserts were installed in the DIII-D lower divertor and a range of L- and H-mode plasma discharges were compared during a dedicated two week run campaign. A high resolution (1340 spectral channels) variable-ruling grating spectrometer viewing the core of the plasma was used to study the spectral region 10-70 {\AA}; a second spectrometer viewing $\sim20-150 {\AA}$ was also used. At DIII-D core plasma temperatures 2-3 keV, several emission lines from W38+ through W43+ were identified, including a quasi-continuum feature of W near 50 {\AA} whose structure depends on core $T_e$. Molybdenum (TZM substrate) emissions between 20-30{\AA} and near $\sim70{\AA}$ were also observed. ADAS calculations are used to guide the identification of W emission lines for the measured core plasma $T_e$ and $n_e$ profiles. The behavior of W emissions during both “benign”, pellet injection, and impurity accumulation conditions will be presented. [Preview Abstract] |
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PP10.00047: Intershot Analysis of Flows in DIII-D W.H. Meyer, S.L. Allen, C.M. Samuell, J. Howard Analysis of the DIII-D flow diagnostic data require demodulation of interference images, and inversion of the resultant line integrated emissivity and flow (phase) images. Four response matrices are pre-calculated: the emissivity line integral and the line integral of the scalar product of the lines-of-site with the orthogonal unit vectors of parallel flow. Equilibrium data determines the relative weight of the component matrices used in the final flow inversion matrix. Serial processing has been used for the lower divertor viewing flow camera 800x600 pixel image. The full cross section viewing camera will require parallel processing of the 2160x2560 pixel image. We will discuss using a Posix thread pool and a Tesla K40c GPU in the processing of this data. [Preview Abstract] |
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PP10.00048: Upgrades to OEDGE/DIVIMP for modeling the DIII-D W-rings experiments J.D. Elder, P.C. Stangeby, R. Ding, J. Guterl Several upgrades have recently been made to the OEDGE/DIVIMP interpretive code package to facilitate modeling of the tungsten rings experiments on DIII-D. OEDGE/DIVIMP can now import charge state resolved impurity fluxes and impact energies of an impurity from a previous run in order to more accurately simulate the source of a second impurity (e.g., C sputtering W). In addition, OEDGE now calculates the plasma potential based on integrating the parallel electric field calculated from Ohm’s law. The radial and poloidal electric fields are calculated along with the resulting ExB drifts which are applied to the impurity transport. Finally, a new model for prompt redeposition has been implemented in OEDGE/DIVIMP and in addition, OEDGE/DIVIMP has been coupled to the 3D ERO code to model near target impurity losses due to the sheath electric field. Initial results applying these features to modeling measurements from the tungsten rings experiment are presented. [Preview Abstract] |
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PP10.00049: DIII-D W-rings experiment: testing the Deposition Probe Hypothesis P.C. Stangeby, E.A. Unterberg, D.L. Rudakov, W.R. Wampler, D. Donovan, T. Abrams The hypothesis is tested that the deposition rate of W, which originates from toroidal W-rings at different poloidal locations in the DIII-D divertor, on a Deposition Probe (DP) in the outer midplane far SOL, is proportional to the W concentration in the confined plasma, $c_W$. The outer strike point, OSP, is placed on the inner edge of one of the W-rings. Small flux expansion ensures the other W-ring is not plasma-contacted. The source rate of W from the ring, $s_W$, is measured by line emission spectroscopy (WI 400.9 nm); also the deposition rate of W on the DP, $d_W$, using surface analysis; also the core concentration, $c_W$, inferred from core bolometry/spectroscopy. The experiment is repeated with the OSP placed half-way across the W-ring, thus reducing $s_W$ by $\sim 2X$. The DP Hypothesis is tested by examining if $c_W$ $\sim d_W \sim s_W$. This aids interpretation of the W-rings experiment since the DP probe, which is able to distinguish W-isotopes originating from the 2 isotopically-marked rings, can be used to infer $c_W$ due to each ring when the plasma contacts both rings simultaneously. [Preview Abstract] |
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PP10.00050: SOLPS modeling of inter/intra-ELM W transport DIII-D A.C. Sontag, E.A. Unterberg, J.M. Canik, L.W. Owen, T. Abrams, J. Watkins The concentration of impurities in the core plasma is determined by the impurity source rate, impurity transport in the SOL and core impurity transport. In order to study this impurity transport chain, tungsten coated molybdenum inserts have been installed in the DIII-D divertor carbon tiles to form two separate rings, one on the floor and one on the shelf above the pump duct. While both the tungsten source rate at the sputtering location and the tungsten concentration in the core plasma can be measured, there is no reliable method for predicting the core concentration given the source rate. SOLPS has been used to perform interpretive modeling of tungsten transport in the SOL of DIII-D and determine the relative importance of the friction force and the ion temperature gradient force on impurity transport. An outer midplane deposition probe provides additional data on the SOL tungsten density. ELM averaged pedestal profiles covering the last 20$\%$ of the ELM cycle are used to determine the inter-ELM transport, while individual pedestal profiles measured during the ELM cycle are used to examine intra-ELM tungsten transport. ELM resolved source flux measurements are used to model the intra-ELM transport. [Preview Abstract] |
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PP10.00051: Characterizing the DIII-D divertor conditions during the tungsten ring experiment J.L. Barton, J.G. Watkins, H.Q. Wang, R.E. Nygren, A. McLean, M. Makowski, E. Unterberg, D.M. Thomas, H.Y. Guo, J. Guterl, B. Buchenauer Tungsten (W) is the leading divertor material in tokamaks, but the core W impurity fraction must be kept below 5$\times$10$^{-5}$ in a reactor. The DIII-D tokamak, having all graphite PFCs, has done a series of experiments with two W-coated molybdenum rings in the lower divertor to track W migration after plasma exposure. We characterize the divertor plasma conditions at the DIII-D target plate in L- and ELMing H-mode, and ELM suppressed plasmas. We will present data from an array of Langmuir probes in the divertor and divertor Thomson-scattering. We also compare the heat flux from fast thermocouples (7.5 mm below the surface of the metal tile inserts) and IRTV heat flux profiles from graphite tiles. The plasma conditions will be used to benchmark ERO modeling to aid in understanding the migration of sputtered W onto other plasma facing surfaces and will be compared to post exposure W distribution measured on the graphite tiles. [Preview Abstract] |
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PP10.00052: Characterization and modeling of tungsten source during DIII-D tungsten ring experiments*, J. Guterl, T. Abrams, D. Elder, H.Y. Guo Two tungsten toroidal rings in the DIII-D divertor region were recently exposed to H-mode plasmas. During these experiments, the gross erosion rate of tungsten was spectroscopically monitored for various ELMy H-mode conditions to characterize the tungsten source in the divertor region (see e.g. [1]). However, only a small fraction of tungsten eroded particles eventually exits the divertor region because of the large tungsten local redeposition. Tungsten local redeposition and migration in the vicinity of the tungsten tiles are simulated using the ERO-OEDGE code package to link the effective tungsten source to the measured gross erosion rates between and during ELMs. It is shown that the energy and angular distributions of sputtered tungsten particles strongly affect the ratio of locally redeposited particles and thus the effective tungsten source. Effects of carbon deposition on tungsten tiles between ELMs on the tungsten erosion rate are also discussed. Preliminary studies of divertor screening on long-range tungsten transport in the SOL between ELMs are also presented.\par \vskip9pt \noindent [1] Fedorczak, N., et al Journal of nuclear materials 463 (2015): 85-90\par \noindent *Work supported in part by the US Department of Energy under DE-AC05-06OR23100 and DE-FC02-04ER54698 [Preview Abstract] |
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PP10.00053: Applications of Inductively Coupled Plasma Mass Spectroscopy to the Isotopically Enriched Tungsten Metal Ring Campaign at DIII-D D.C. Donovan, C. Eley, A. Maan, J. Duran, J. Auxier II, E.A. Unterberg, D.L. Rudakov, P. Stangeby, C. Chrobak, W.R. Wampler Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) was used to measure isotopic ratios of deposited W on collector probes inserted during the metal ring campaign. Two toroidal rings of 5 cm wide W-coated TZM inserts were installed in the lower divertor. The inner ring was coated in natural-W and the outer ring was coated with 93$\%$ isotopically enriched W-182. A triplet set of replaceable graphite collector probes were mounted at the outboard mid-plane. Over 100 collector probes were exposed. ICP-MS analysis of the collector probes has yielded isotopic ratios of the deposited W, which have been used with the Stable Isotope Mixing Model (SIMM) to estimate the amount of W from each of the divertor rings that contributed to the total W deposition on the probe. Comparisons in strike-point positioning, H-mode/L-mode, and Forward/Reverse $B_t$ are reviewed. [Preview Abstract] |
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PP10.00054: Inferring Core Tungsten Behavior Using SPRED During the DIII-D Metal Rings Campaign D.M. Thomas, D. Kaplan, R. Groebner, B. Grierson, Z. Unterberg, B. Victor The GA SPRED EUV spectrometer was used to study core emission of highly charged tungsten ions (W40+-W45+) in the 120-135{\AA} region during the recent Metal Rings Campaign. These experiments used two 5-cm wide toroidal rings of W-coated metal inserts exposed to a variety of DIII-D discharges to study effects of high-Z divertor erosion, migration, core uptake, and effects on advanced tokamak performance. For the proper core temperature range (2-4 keV), the measured multistate W emission forms a well defined spectral pattern that can be used to study the relative importance of strike point location, flux expansion, injected power, ELM characteristics and magnetic drift direction for high-Z core contamination in DIII-D. The spectra are fit using simple Gaussians to estimate concentrations using the historical SPRED intensity calibration. Calibration shots using known core dosages of pellet injected W are used to help infer the relative response of the instrument. [Preview Abstract] |
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PP10.00055: Detachment of helium plasmas in DIII-D A.R. Briesemeister, J.M. Canik, R.C. Isler, D.L. Hillis, M.W. Shafer, A.G. McLean, M.A. Makowski, M.E. Fenstermacher, W.H. Meyer, A.L. Moser, H. Wang, J.G. Watkins In low power, Ohmic plasmas, the high recycling regime typically seen as core density is increased in deuterium plasmas, was not observed in helium plasmas. When neutral helium beam heating was added, the high recycling regime returned as predicted using the SOLPS code. Modeling shows that increasing input power reduces neutral penetration across the separatrix, reducing radiation from the confined plasma and allowing a larger fraction of the input power to be carried into the scrape off layer. Detailed measurements including divertor ion and electron temperatures and densities and radiation emission patterns are presented at a variety of heating levels including both H and L-mode plasmas. An understanding of the differences between detachment in the helium and deuterium plasmas will be important for understanding how divertor conditions in the helium startup phase of ITER will differ from those in deuterium operation. [Preview Abstract] |
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PP10.00056: SOLPS modeling of an innovative small-angle slot divertor concept for low-density detachment B. Covele, C. Sang, H. Guo, L. Lao, P. Stangeby, D. Thomas SOLPS modeling offers insight into how a new Small-Angle Slot (SAS) divertor concept exploits the role of neutral trapping to exhaust power and particles at lower core densities than even highly slanted divertors. The special SAS baffling structure enhances volumetric power and momentum losses across the entire target profile, flattening temperatures even in the far SOL. SOLPS characterizes SAS heat and temperature handling for a spectrum of plasma and neutral source conditions, varying n$_{e,sep}$, P$_{SOL}$, heat flux width, gas puffing rates and locations, and pumping rates. Certain aspects of the baffling structure were also systematically varied to observe the effect on the neutral dynamics, particularly pressure gradients in D$_2$ near the target. Radial transport coefficients were controlled to match midplane profiles to experimental H-mode profiles. The SAS divertor is an excellent testbed for probing the interplay between plasma and neutrals at the onset of detachment. [Preview Abstract] |
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PP10.00057: Modeling of parallel transport and dissipation processes leading to detachment in DIII-D J.D. Lore, J.M. Canik, A. Briesemeister, A.W. Leonard, A. McLean A series of deuterium plasmas on DIII-D with extensive edge diagnostic coverage are simulated using the SOLPS-ITER code to validate processes leading to detached divertor conditions. The simulations will be used to quantify factors associated with an observed over prediction of the divertor electron temperature when matching upstream densities for detached cases, including parallel pressure and power losses and sources of divertor radiation. The detachment onset discrepancy is related to the deficit in outer divertor radiation found in fluid plasma edge modeling as compared to experiment, resulting in divertor conditions that are hotter and less dense than experiment when the upstream profiles are matched. Here modeling is performed using cross-field diffusivities chosen to match the ITPA scrape-off-layer heat flux width scaling and the separatrix temperature from experimental power balance. The simulation data are then compared to all available boundary diagnostics with the goal of quantifying the discrepancies and identifying the primary contributing processes. [Preview Abstract] |
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PP10.00058: Effects of impurity seeding on H-mode pedestal near divertor detachment H.Q. Wang, H.Y. Guo, A.W. Leonard, T.H. Osborne, P.B. Snyder, D.M. Thomas, J.G. Watkins Injection of $N_2$, Ne and Ar has been performed in DIII-D to assess the impact of impurities on type-I ELMy H mode plasmas near divertor detachment. Prior to detachment, both pedestal pressure and temperature in the impurity-seeded plasmas are comparable with that in non-seeded plasma. The transition to detachment leads to a pedestal temperature drop, which propagates from the edge to the core plasma, eventually degrading the global confinement. The pedestal pressure exhibits a strong correlation with the impurity content and the power across the pedestal. With $N_2$ seeding, radiation is predominantly localized in the divertor/SOL region and the pedestal temperature is only reduced by $\sim30\%$ at detachment, comparable with that in non-seeded plasmas. In contrast, Ar injection leads to significant core radiation, resulting in $\sim60\%$ reduction in pedestal temperature at the onset of detachment. In Ne-seeded plasmas, pedestal temperature is reduced by $\sim50\$% at detachment and remains nearly constant during the detachment phase. [Preview Abstract] |
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PP10.00059: Divertor ExB and Parallel Flows on the DIII-D Tokamak* J Boedo, D Rudakov E$\times$B convection is an important particle transport mechanism responsible for up to $\sim$50$\%$ of the total particle flux into the divertor, changing direction with B, and playing a role in divertor asymmetries. The gradient of the plasma potential, $V_p=V_f+2.5T_e$, reaches $\sim$5 kV/m across the SOL-private boundary, causing a poloidal particle flux, calculated as, $\Gamma_\theta = 2\pi{Rn_e}(V_{p1}-V_{p2})/B_T$, (along flux surfaces) of about $\sim$10${^2^2} s^_{-1}$, comparable to the target flow of 2$\times$10${^2^2} s^_{-1}$, and consistent with previous work [1]. Floating potential $V_f$, temperature $T_e$, density $N_e$, and $D^+$ flow were measured in the DIII-D divertor. The data will be compared to simulations by SOLPS and UEDGE. The $D^+$ parallel flow velocity, $V\|$, calculated by multiplying the Mach number by the local sound speed $c_s = (\gamma{ZkT_e}/m_i)^{1/2}$ show increasing velocity towards the plate in attached conditions and bulk sonic flows over the whole detached region in detached conditions. We compare measurements in the divertor to similar measurements made at the midplane to show how divertor conditions reflect upstream.\newline * J. Boedo, et al., Phys. Plasmas 7 (2000) 1075 [Preview Abstract] |
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PP10.00060: ELM resolved measurement of fuel recycling on divertor targets in DIII-D I. Bykov, E.M. Hollmann, R.A. Moyer, J.G. Watkins, M. Makowski, C.S. Lasnier, A. McLean, H. Wang Simultaneous measurements of different atomic and molecular contributions are important for determining D recycling from plasma-facing components (PFCs). A splitted filtered imaging of visible-range molecular and atomic emission was applied for the first time for synchronous measurements of D$_\alpha$ (656 nm), D2 Fulcher-$\alpha$ band (600 nm), and CD (430 nm) emissions in the strike point region of the lower divertor in DIII-D. Framing rate up to 1 kHz was sufficient to resolve intra- and inter-ELM phases of H-mode discharges. Radial profiles of atomic (molecular) fluxes of recycled D were deduced using respective S(D)/XB rate coefficients. We present the results of particle flux measurements for a series of shots with varying densities (n/n$_{GW}$ = 0.5-0.8), which affected the degree of the divertor detachment and the balance between individual channels of D recycling from PFCs. [Preview Abstract] |
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PP10.00061: Gyrokinetic-neoclassical study of resonant magnetic perturbations in DIII-D R. Hagar, C.S. Chang, R. Nazikian, N. Ferraro The gyrokinetic neoclassical, total-f, particle-in-cell code XGCa is utilized to study the kinetic effects of resonant magnetic perturbations (RMP) on a DIII-D H-mode plasma. Compared to the earlier efforts by G. Y. Park et al., [Phys. Plasmas 17, 102503 (2010), APS invited talk, Bull. Am. Phys. Soc. 56 (2011)] using the guiding center code XGC0, the gyrokinetic code XGCa adds important new capabilities to the study, such as a 2D Poisson solver and a fully nonlinear collision operator, which enhances the fidelity of the simulation in the H-mode pedestal and the scrape-off layer. [Preview Abstract] |
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PP10.00062: Nonaxisymmetric Divertor Striations via 3D Modulations in Upstream Transport M.W. Shafer, J.M. Canik, A.R. Briesemeister, J.D. Lore, R.S. Wilcox, A. Wingen, N.M. Ferraro, G.R. McKee A hypothesis presented here shows that divertor measurements during the application of resonant magnetic perturbations (RMPs) could be explained by toroidal modulations to upstream transport in the absence of any resonant field penetration. Experiments from multiple machines show helical lobes leading to 3D striations in the heat and particle flux. These observations are normally interpreted as a result of field penetration: either total (vacuum) or some level of screening (e.g. extended-MHD). However in the absence of tearing perturbations, these measurements can be shown to qualitatively result from toroidal modulations of upstream transport. Recent measurements and modeling show toroidal modulation of low-k turbulence at the outboard midplane with strong flow screening on DIII-D. This model may be able to reconcile 3D divertor measurements without the need for strong tearing perturbations in the pedestal, which can otherwise destroy the pedestal via stochasticity. [Preview Abstract] |
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PP10.00063: Fast-ion induced ablation of Li granules in DIII-D[1] A. Bortolon, G.J. Kramer, R. Maingi, D.K. Mansfield, A. Nagy, A.L. Roquemore, R. Lunsford, P.B. Parks, I. Bykov, R.A. Moyer In DIII-D, sub-millimeter Li spheres are injected at ${\textless120}$\hspace{2.5 mm}m/s to pace edge localized modes[2]. Typically, granule ablation, monitored by fast visible imaging, begins at the last closed flux surface (LCFS), with strong field-aligned emission from Li$^{1+}$. During counter $I_p$ neutral beam (NB) injection, non-field-aligned Li emission was observed from the vacuum region between the LCFS and wall, suggestive of a neutral cloud evaporating from the granules. This is ascribed to a relatively high density of fast-ions arising from 80 kV counter-$I_p$ NB injection. Simulations with the full-orbit Monte-Carlo code SPIRAL[3] find fast-ion densities up to 1x10$^{16}$ m$^{-3}$ with expected heat flux $\sim$50-100 W/cm$^2$ at the granule surface, sufficient to induce melting. The non-isotropic fast-ion pressure may cause droplets to leave the melted layer accelerating along characteristic trajectories, a phenomenon observed during injections at $\textless$50$\hspace{1.1 mm}$m/s.\par \vskip9pt \noindent [1] Supported by the U.S. Department of Energy (DE-AC02-09CH11466, DE-AC05-00OR22725, DE-FC02-04ER54698, DE-FG02-07ER54917).\par \noindent [2] A. Bortolon, NF 2016, 056008\par \noindent [3] G.J. Kramer, PPCF 2013, 025013 [Preview Abstract] |
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PP10.00064: Modeling of ELM-pacing by Lithium Granule Injection with M3D-C1 A. Fil, E. Kolemen, N. Ferraro, S. Jardin, A. Bortolon, R. Lunsford, R. Maingi, P.B. Parks We present first modeling results of ELM-pacing by Lithium Granule Injections (LGI) with the 3D full-MHD code M3D-C1. A newly implemented ablation model valid for sub-mm Li granules provides a realistic density source, allowing to model granule injections of realistic size and speed in DIII-D and NSTX-U plasmas. While DIII-D experiments have demonstrated a robust ELM-pacing with ELM triggering efficiency close to 80$\%$ for 0.9 mm Li granules, in some cases a strong variability of triggered ELM size was observed. To investigate numerically these phenomena, we first validate the code against experimental data from both DIII-D and NSTX-U discharges, specifically the measured granule ablation time, penetration depth and the increase of line integrated electron density. The maximum pressure gradient induced by LGI scales with the granule size. The injection velocity and angle have to be carefully chosen to reach maximum ablation when the granule is at the top of the pedestal. Then, 3D simulations of granule injections into a pedestal close to marginal stability are used to study ELM pacing efficiency, as a function of injection characteristics, i.e. granule size and speed. [Preview Abstract] |
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PP10.00065: DIII-D Pellet ELM Modeling Using M3D-C1 S.J. Diem, N. Ferraro, L. Baylor ELM pacing via rapid small deuterium pellet injection is being studied on various fusion experiments as a method to reduce the peak heat loads from ELMs on PFCs. Modeling of pellet ELM interactions is required to understand the mechanisms behind ELM triggering and scale the results from current experiments to larger scale devices such as ITER. M3D-C1, a code for solving the linear or non-linear extended-MHD equations in toroidal geometry, is currently being used for modeling pellet ELM triggering in DIII-D ITER-like plasmas. Initial M3D-C1 results run in linear mode show that the localized perturbation due to the pellet destabilizes peeling-ballooning modes. Calculations of linear peeling-ballooning stability as a function of the pellet size and deposition will be presented and compared to data from ITER-like plasma experiments on DIII-D. Additionally, a scan of the pellet perturbation size threshold for ELM triggering and nonlinear calculations of the expansion of an injected density cloud will be presented. [Preview Abstract] |
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PP10.00066: The influence of pedestal parameters on ELM energies and heat fluxes for DIII-D M. Knolker, J-W. Ahn, A. Bortolon, R. Nazikian, A.W. Leonard, H. Zohm – In our study of various H-mode shots with low electron collisionality on DIII-D, we find that the effective ELM wetted area decreases relative to the inter-ELM wetted area. A first extensive analysis does not reveal a clear pedestal pressure dependence of ELM energy density or ELM material load (defined by dividing the ELM rise energy by wetted area and square root of rise time). A database has been developed, tracing the distribution of ELM energies to the divertor, main chamber and radiated fraction. Using data from Langmuir probes, fast bolometers, and IR cameras, the role of collisionality and relevant quantities in the linear peeling ballooning model of the pedestal is studied and compared to the IR footprint in the divertor. Discharges are chosen where both the outer and inner strike point are seen on IR cameras simultaneously. Our preliminary observations encourage further research to identify the correct scaling properties of the ELM wetted area on DIII-D and to compare to observations on other devices. [Preview Abstract] |
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PP10.00067: Imaging divertor strike point splitting in RMP ELM suppression experiments R.A. Moyer, I. Bykov, D.M. Orlov, J.S. Lee, T.E. Evans, R. Nazikian, M. Makowski, C.S. Lasnier, H. Wang, T. Abrams, J.G. Watkins Fast visible imaging of the lower divertor has been implemented at DIII-D to study the structure and dynamics of lobes induced by 3D fields in RMP ELM suppression experiments. The sharpest imaging was obtained with spatially localized molecular D2 emission indicative of the D flux to the surface. Multiple D2 emission peaks are readily resolved during RMPs, in contrast to the heat flux profile (from IR), which often shows little structure. The brightest D2 lobe is often farthest from the primary inner strike point (ISP). Mitigated ELMs perturb the position and intensity of the ISP lobes and spread the outer strike point emission into the far SOL, where it may be caused by ELM filament propagation. RMP current ramps affect the lobe locations and separations. Implications of the lobe dynamics for plasma response is being studied. [Preview Abstract] |
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PP10.00068: Using Divertor Strike Point Splitting to Study Plasma Response and Its Sensitivity to Equilibrium Uncertainties J.S. Lee, D.M. Orlov, R.A. Moyer, I. Bykov, T.E. Evans, W. Wu, B.C. Lyons, L.E. Sugiyama Magnetic field perturbations (RMPs) split the strike points in divertor tokamaks. This splitting is measured using fast imaging of filtered visible light from the divertor. We compare the observed splitting during n=3 RMP experiments to vacuum and plasma response modeling to determine if the measured splitting provides a sensitive diagnostic for the plasma response to the RMP. We also investigate the sensitivity of the computed plasma response to uncertainties in the initial 2D equilibrium. Strike point splitting was also observed in ELMing H-mode without the RMP, possibly due to n=1 error- and error-field correction fields. We compare the measured splitting during ELMs to linear plasma response modeling of the divertor footprints, and to nonlinear M3D ELM simulations[1].\par \vskip6pt \noindent [1] L.E. Sugiyama and H.R. Strauss “Magnetic X-points, edge localized modes, and stochasticity” Phys. Plasmas 17, 062505 (2010) [Preview Abstract] |
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PP10.00069: Optimization of applied non-axisymmetric magnetic perturbations using multimodal plasma response on DIII-D D.B. Weisberg, C. Paz-Soldan, M.J. Lanctot, E.J. Strait, T.E. Evans The plasma response to proposed 3D coil geometries in the DIII-D tokamak is investigated using the linear MHD plasma response code MARS-F. An extensive examination of low- and high-field side coil arrangements shows the potential to optimize the coupling between imposed non-axisymmetric magnetic perturbations and the total plasma response by varying the toroidal and poloidal spectral content of the applied field. Previous work has shown that $n$=2 and $n$=3 perturbations can suppress edge-localized modes (ELMs) in cases where the applied field’s coupling to resonant surfaces is enhanced by amplifying marginally-stable kink modes. This research is extended to higher n-number configurations of 2 to 3 rows with up to 12 coils each in order to advance the physical understanding and optimization of both the resonant and non-resonant responses. Both in- and ex-vessel configurations are considered. The plasma braking torque is also analyzed, and coil geometries with favorable plasma coupling characteristics are discussed. [Preview Abstract] |
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PP10.00070: Model of ELM suppression by RMPs in DIII-D J.D. Callen, R. Nazikian, N.M. Ferraro, M.t. Beidler, C.C. Hegna, R.J. La Haye, C. Paz-Soldan Recent DIII-D experiments [1,2] explored effects of resonant magnetic perturbations (RMPs) near the minimum applied n=2 RMP amplitude required for ELM suppression in ITER-relevant low collisionality pedestals. Comprehensive tokamak forced magnetic reconnection (FMR) theory is used to describe and quantify the many physical processes involved in stages of RMP effects and an ELM crash response that lead to bifurcation into an ELM-suppressed state: 1) in ELMing equilibrium, flow-screening is strong with little magnetic reconnection; 2) the RMP at q=8/2 penetrates via FMR induced by an ELM crash and locks toroidal flow to the lab frame (like error field mode locking); 3) the ELM crash provides a 8/2 seed island (like NTMs) governed by a modified Rutherford equation; 4) if the total 8/2 RMP is large enough the internal tearing response and flow bifurcate and grow; and 5) flutter transport [3] reduces pedestal top gradients which stabilizes P-B modes and hence suppresses ELMs. This analysis is for discharge 158115 in DIII-D [1,2]; its potential universality is yet to be determined. [1] C. Paz-Soldan et al., Phys. Rev. Lett. 114, 105001 (2015); [2] R. Nazikian et al., Phys. Rev. Lett. 114, 105002 (2015); [3] J.D. Callen, C.C. Hegna and A.J. Cole, Nucl. Fusion 53, 113015 (2013). [Preview Abstract] |
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PP10.00071: Increased electron temperature turbulence and pedestal transport in ELM suppressed QH-Mode and RMP DIII-D plasmas C. Sung, T.L. Rhodes, W.A. Peebles, T. Osborne, G. Staebler, S. Smith, G. Wang New observations in DIII-D reveal significant levels of $T_e$ turbulence near the top of the pedestal during ELM-free H-mode operation. These large, increased levels of $T_e$ turbulence are observed in two different scenarios, quiescent H-mode (QH-mode) and resonant magnetic perturbations (RMP), where ELMs have been eliminated. These new results are significant because: 1)the $T_e$ turbulence increase, combined with $~{n}$, provide two distinct states for new and unique tests of nonlinear gyrokinetic simulation predictions; 2)these data provide new insights into the transport mechanisms just inboard of the pedestal top, a region where gyrokinetic simulations are challenging. In ELMing H-modes, the inter-ELM $T_e$ turbulence is close to the noise level and can increase to as much as $1.8\%$ with RMP ELM suppression and to $1.2\%$ in QH-mode. During QH-mode, the $T_e$ turbulence increases with lower collisionality and a similar, but smaller, increase in $T_e$ turbulence is observed in RMP ELM-suppressed plasmas. This is consistent with the growth of Trapped Electron Mode turbulence where destabilization occurs preferentially at lower collisionality. The physics relevance of these new measurements will be discussed in the context of linear stability (TGLF) and power balance analyses [Preview Abstract] |
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PP10.00072: Self-regulation of turbulence in low rotation DIII-D QH-mode with an oscillating transport barrier Kshitish Barada, T. L. Rhodes, K. H. Burrell, L. Zeng, Xi Chen We present observations of turbulence and flow shear limit cycle oscillations (LCOs) in wide pedestal QH-mode DIII-D tokamak plasmas (Burrell et al, PoP, 2016) that are consistent with turbulence self-regulation. In this low input torque regime, both edge harmonic oscillations (EHOs) and ELMs are absent. LCOs of ExB velocity shear and $\~n$ present predator-prey like behavior in these fully developed QH-mode plasmas. During these limit cycle oscillations, the ExB poloidal flows possess a long-range toroidal correlation consistent with turbulence generated zonal flow activity. Further, these limit cycle oscillations are observed in a broad range of edge parameters including $n_e$, $T_e$, floor Langmuir probe ion saturation current, and radial electric field $E_r$. TRANSP calculations of transport indicate little change between the EHO and LCO wide pedestal phases. These observations are consistent with LCO driven transport that may play a role in maintaining the profiles below ELM threshold in the EHO-free steady state wide pedestal QH-mode regime. [Preview Abstract] |
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PP10.00073: Characterization of broadband fluctuations in wide-pedestal QH-mode plasmas on DIII-D C.M. Muscatello, K.H. Burrell, N.C. Luhmann, Jr., G.R. McKee, B. Tobias Edge broadband fluctuations observed in wide pedestal quiescent H-mode plasmas may play an important role in driving transport necessary for stabilizing the edge to kink-peeling modes, thought to lead to ELMs. Density fluctuation measurements from BES and MIR independently observe periodic bursts in the pedestal that show up spectrally as broadband fluctuations. The period of the fluctuation bursts correlate with the period of enhanced bicoherence in the frequency range of the fluctuations, suggesting nonlinear coupling of turbulence. Time-delay estimation analysis of the 2D BES data shows strong evidence of a low-frequency zonal flow in the pedestal with a period matching that of the bursts. The carbon pressure gradient and E×B velocity, determined from CER, and ECE emission also oscillate with the same period. This behavior can be described as a quasi-stationary, limit-cycle oscillation and modeled by a set of predator-prey equations relating the zonal flow, equilibrium flow, and turbulence amplitude. [Preview Abstract] |
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PP10.00074: Frequency-Poloidal Wave Number Spectral Analysis of Turbulence in QH-mode plasmas Measured with BES on DIII-D M. Ono, K. Ida, T. Kobayashi, M. Yoshinuma, G.R. McKee, Z. Yan, K.H. Burrell, X. Chen Quiescent H-mode (QH) is an ELM-free scenario with good energy confinement, constant density, and radiated power, with a pedestal localized electromagnetic mode (edge harmonic oscillation, EHO) providing continuous particle transport. The features and characteristics of QH-mode plasma turbulence in the wavenumber-frequency domain are crucial to understanding the mechanisms and dynamics of the enhanced particle transport. Frequency-wavenumber spectral analysis was applied to localized density fluctuation data measured with BES on DIII-D in the region of 0.8$\textless$\rho$\textless1.0. In the analysis, a Maximum Entropy Method is applied in the space domain, instead of an FFT, to estimate a well resolved \textit{k}-spectrum spectrum from truncated data. The fundamental frequency of the EHO was typically $\sim$10 kHz with long poloidal wavelength ($\textit{k}_\theta\sim0.02$ $cm^{-1}$), while broadband turbulence was observed in the range of 50–200 kHz with correlation lengths of a few cm. The broadband turbulence measured at ${\rho\sim0.9}$ was found to have poloidal phase velocity of $\sim10\hspace{1.1 mm}km/s$, which corresponds to the E$\times$B velocity. [Preview Abstract] |
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PP10.00075: Dependence of Critical Rotational Shear on Density and Toroidal Magnetic Field in DIII-D QH-mode Discharges T.M. Wilks, K.H. Burrell, Xi Chen, R.J. Groebner, J.W. Hughes Quiescent H-mode (QH-mode) has been identified as an attractive stationary operational regime in tokamaks due to the lack of edge localized modes (ELMs) in conjunction with good particle and impurity control due to the presence of an edge harmonic oscillation (EHO). The EHO allows operation of the QH mode edge near but also below the peeling-ballooning ELM stability limit, and has been shown to have a dependence on the edge rotational shear. Previous analysis has demonstrated the existence of a critical edge rotational shear necessary for the existence of typical low-n EHO MHD activity, particularly with the transition to a wide pedestal regime with broadband turbulence. We build upon these results by further exploring critical edge rotational shear existence for the transition from a QH-mode to a typical ELMy H-mode in DIII-D, along with its associated turbulence and dependence on collisionality. [Preview Abstract] |
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PP10.00076: UF-CHERS Measurements of Ion Temperature and Toroidal Rotation Fluctuations Associated with the Edge Harmonic Oscillation in Quiescent H-mode Plasmas D.D. Truong, R.J. Fonck, G.R. McKee, Z. Yan, B.A. Grierson The UF-CHERS (Ultra Fast CHarge Exchange Recombination Spectroscopy) diagnostic at DIII-D measures local, long-wavelength ion temperature and toroidal velocity fluctuations at turbulence-relevant spatiotemporal scales from emission of the CVI n=8$\to$7 transition. During Quiescent H-mode (QH-mode) plasmas, which offer ELM-free improved confinement, UF-CHERS measurements observed coherent, low frequency ${(f_o\sim10\hspace{2 mm}kHz)}$ pedestal oscillations in $T_i$ and $v_{tor}$ at the Edge Harmonic Oscillation (EHO) frequency while several modes between 35-75 kHz are suppressed when the EHO appears. Although broadband ion temperature and density fluctuations were reduced by the EHO, the toroidal rotation showed increased fluctuation amplitude. Investigating ion temperature and toroidal fluctuations associated with the EHO may provide insights into the saturated instability driving the EHO. [Preview Abstract] |
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PP10.00077: Validation of theoretical models of intrinsic torque in DIII-D B.A. Grierson, W.X. Wang, D.J. Battaglia, C. Chrystal, W.M. Solomon, J.S. deGrassie, G.M. Staebler, J.A. Boedo Plasma rotation experiments in DIII-D are validating models of main-ion intrinsic rotation by testing Reynolds stress induced toroidal flow in the plasma core and intrinsic rotation induced by ion orbit losses in the plasma edge. In the core of dominantly electron heated plasmas with T$_e$=T$_i$, the main-ion intrinsic toroidal rotation undergoes a reversal that correlates with the critical gradient for ITG turbulence. Residual stress arising from zonal-flow ExB shear and turbulence intensity gradient produce residual stress and counter-current intrinsic torque, which is balanced by momentum diffusion, creating the hollow profile. Quantitative agreement is obtained for the first time between the measured main-ion toroidal rotation and the rotation profile predicted by nonlinear GTS gyrokinetic simulations. At the plasma boundary, new main-ion CER measurements show a co-current rotation layer and this is tested against ion orbit loss models as the source of bulk plasma rotation. [Preview Abstract] |
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PP10.00078: Main-ion and impurity flows in the DIII-D tokamak C.M. Samuell, S.L. Allen, W.H. Meyer, A.E. Jaervinen, A.R. Briesemeister, J. Howard Plasma flows and drifts are integral to determining the bulk transport of particles and energy throughout the tokamak. Helium discharges provide an opportunity to observe velocities of both main-ion (HeII) and impurity (CIII) species. Coherence Imaging Spectroscopy (CIS) on DIII-D has been used to generate a polodially-complete view of the SOL velocity profiles, which was used to investigate the transition from lower single null (LSN) to upper single null (USN) topologies. Main-ion and impurity velocities up to 30 km/s were observed with the fastest velocities appearing near limiter and target surfaces. A change in flow direction was observed during the transition from LSN to USN. This transition caused a much more gradual change on the outboard mid-plane compared to the inboard side where the transition was sharp. Highly localized flow reversal associated with high emissivity was observed on the in-board midplane highlighting the need for fully-2D flow measurements. [Preview Abstract] |
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PP10.00079: Real-Time Variation of the Injected Neutral Beam Energy on the DIII-D Tokamak,* J.T. Scoville, B.J. Crowley, D.C. Pace, J.M. Rauch A powerful new technique for smoothly controlling the time evolution of injected energy from neutral beams has recently been implemented on the DIII-D tokamak. Upgrades to the high voltage circuitry of the neutral beams and to the tokamak’s Plasma Control System have enabled the first-ever continuous variation of beam voltage during plasma shots. This avoids the perturbative effects of pulse modulation, which was the previously employed method for changing the injected beam power. The new technique allows much finer control of the injected energy, with beam voltage able to be varied smoothly over a 20 kV range (within the 45-85 kV beam operating space) in 0.5 sec. This capability enables fundamentally new experiments that require precise control of beam ion phase space, including the minimization of undesirable energetic ion instabilities and scans across low torque regimes at fixed power. We present a description of the beam system modifications and initial results from plasma experiments using the new variable beam energy capability on the DIII-D tokamak. [Preview Abstract] |
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PP10.00080: Operational performance and plans for the ECH system on DIII-D J. Lohr, M. Cengher, Y.A. Gorelov, D. Ponce, A. Torrezan, L. Ives, M. Read, A. Leviness The ECH system on the DIII-D tokamak currently comprises 6 gyrotrons operating at 110 GHz and injecting 3.5 MW for administratively limited pulse lengths up to 5 sec. A 7th gyrotron generating $\sim$1.5 MW at 117.5 GHz is planned for installation late in 2016. Production of this tube was delayed due to issues related to reflected electrons resulting in internal arcs during initial testing. Performance reliability of the individual gyrotrons in the DIII-D complex has exceeded 90$\%$ for a wide variety of operational modes, including fast modulation and rapid poloidal sweeping of the rf beams using high speed dc motors and magnetic position encoders. Measures have been taken to reduce the risk of damage to launcher hardware and diagnostics from inadvertent operation of the tokamak at densities such that the right hand cutoff frequency is present in the plasma. The system has occasionally been used in non-fusion applications. The most recent of these has been testing a CVD diamond waveguide blocking window at the Brewster angle. [Preview Abstract] |
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PP10.00081: New developments in RF power and polarization measurements on the ECH System on DIII-D M. Cengher, J. Lohr, Y. Gorelov, C.P. Moeller, D. Ponce, A. Torrezan The rf power injected at the tokamak by the electron cyclotron heating (ECH) system is measured and calibrated on a shot to shot basis for the six 110 GHz, 1 MW class gyrotrons. A new technique for ECH power measurement at the tokamak using a 4-port rf monitor was tested. Polarization scans for each system show H-plane and E-plane rf waveforms can be combined to provide a reliable calibrated power signal at the closest access point near the tokamak. Previous attempts to calibrate the power at this end were limited by the pickup of only one polarization angle at the last miter bend. Calorimetric measurements in the relevant gyrotron cooling circuits in conjunction with the 4-port RF monitors with orthomode transducers can be used to calibrate the rf power. Other alternative approaches showing proportionality with the input power like the inline power monitor and in-vessel measurements are discussed. Future plans include mode content measurements at the tokamak end of the transmission line using the 4-port RF monitors and mode sensitive directional couplers. [Preview Abstract] |
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PP10.00082: Improvements and new features for the diagnostics and control system of the ECH system on DIII-D A.C. Torrezan, D. Ponce, Y.A. Gorelov, M. Cengher, J. Lohr, R.A. Ellis In this work we discuss improvements and new features for the diagnostics and controls of the electron cyclotron heating (ECH) system on the DIII-D tokamak. As for diagnostics, a new mapping system to measure the power density on a gyrotron collector, which should not exceed 500 W/cm$^2$, has been designed and assembled. The new mapping system was designed to enable the test of new depressed collector gyrotrons that requires more RTD channels and for easier servicing and expansion compared with a previous system. First results from this diagnostic will be presented. As for controls, obsolete timing generators and auxiliary circuitry are being replaced by a more flexible approach using a FPGA. Besides being a simple replacement, the FPGA design will also add new features to the ECH control system such as an attempt to restart RF generation after RF loss or the recovery of selected interlocks. Upgrades made to the ECH launchers and issues found in the last experimental campaign as well as planned improvements will also be described. [Preview Abstract] |
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PP10.00083: ICF/HED; DIAGNOSTICS, X-RAY SOURCES AND WDM |
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PP10.00084: First experiment on LMJ facility : pointing and synchronisation qualification, sequences qualification. Olivier Henry, Dominique Bretheau, Michel Luttmann, Herve Graillot, Michel Ferri, Frederic Seguineau, Emmanuel Bar, Loic Patissou, Phillipe Canal, Fran\c{c}oise Sautarel, Yves Tranquille Marques, Didier Raffestin The LMJ (Laser mega Joule) facility at the CESTA site (Aquitaine, France) is a tool designed to deliver up to 1.2 MJ at 351 nm for plasma experiments. The experiment system will include 11 diagnostics: UV and X energy balances, imagers (Streak and stripe camera, CCD), spectrometers, and a Visar/pyrometer. The facility must be able to deliver, within the hour following the shot, all the results of the plasma diagnostics, alignment images and laser diagnostic measurements. These results have to be guaranteed in terms of conformity to the request and quality of measurement. The end of 2014 was devoted to the qualification of system pointing on target and synchronization within and between beams. The shots made with one chain (divided in 2 quads -- 8 laser beams) have achieved 50 \textmu m of misalignment accuracy (chain and quad channel) and a synchronization accuracy in the order of 50 ps . The performances achieved for plasma diagnostic (in the order of less 100 \textmu m of alignment and timing accuracy less than 150 ps) comply with expectations. At the same time the first automatic sequences were tested. They allowed a shot on target every 6h:30 and in some case twice a day by reducing preparation actions, leading to a sequence of 4h:00. These shooting sequences are managed by an operating team of 7 people helped by 3 people for security aspects. [Preview Abstract] |
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PP10.00085: Development of experimental platform for high energy density sciences using high-intensity optical lasers at the SACLA x-ray free electron laser facility Toshinori Yabuuchi, Makina Yabashi, Yuichi Inubushi, Akira Kon, Tadashi Togashi, Hiromitsu Tomizawa Combinations of high intensity optical laser and x-ray free electron laser (XFEL) open new frontiers in high energy density (HED) sciences. An experimental platform equipped with high-power Ti:Sapphire laser systems is under commissioning for HED sciences at the XFEL facility, SACLA. The Ti:Sapphire laser system is designed to deliver two laser beams with a maximum power of 500 TW in each to the sample chamber. A hard x-ray beamline of SACLA is also transported to the chamber with a beam focusing capability down to a few microns using sets of compound refractive lenses. The second optical laser pulse or the energetic particles and photons generated by the laser pulse can provide additional flexibilities for HED-related pump-probe experiments, which have been generally performed using single optical laser and XFEL. The development status and future perspectives of the experimental platform will be presented. [Preview Abstract] |
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PP10.00086: Thin liquid sheet target capabilities for ultra-intense laser acceleration of ions at a kHz repetition rate Adam Klim, J.T. Morrison, C. Orban, S. Feister, G.K. Ngirmang, J. Smith, K. Frische, A.C. Peterson, E.A. Chowdhury, R.R. Freeman, W.M. Roquemore The success of laser-accelerated ion experiments depends crucially on a number of factors including how thin the targets can be created. We present experimental results demonstrating extremely thin (under 200 nm) water sheet targets that can be used for ultra-intense laser-accelerated ion experiments conducted at the Air Force Research Laboratory at Wright-Patterson Air Force Base. Importantly, these experiments operate at a kHz repetition rate and the recovery time of the liquid targets is fast enough to allow the laser to interact with a refreshed, thin target on every shot. We present results from liquid water targets which are useful for proton acceleration experiments via the mechanism of Target Normal Sheath Acceleration (TNSA). In future work, we will create thin sheets from deuterated water in order to perform laser-accelerated deuteron experiments. [Preview Abstract] |
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PP10.00087: High-energy-density Targets Fabricated by The University of Michigan Sallee Klein, J. S. Davis, L. Gao, R. S. Gillespie, M.J. MacDonald, G. Malamud, M. J.-E. Manuel, W.C. Wan, R.P. Young, C. C. Kuranz, P.A. Keiter, R P. Drake The University of Michigan has been fabricating their own targets for high-energy-density physics experiments for well over the past decade. We utilize the process of machined acrylic bodies and tightly toleranced mating components that serve as constraints, enabling our group to build repeatable targets. We favor traditional machining, utilizing 3D printing when it suits, taking advantage of the very best part of both of these methods of creating precision parts for our targets. Here we present several campaigns shot at the OMEGA, Titan and Trident facilities and methods used to those fabricate targets. [Preview Abstract] |
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PP10.00088: Optimized shielding design for the time-resolved Magnetic Recoil Spectrometer (MRSt) on the NIF* C. Wink, J. Frenje, M. Gatu Johnson, C.K. Li, F. Seguin, R. Petrasso, T. Hilsabeck, R. Bionta, H. Khater To meet the goals for the MRSt to measure the neutron spectrum at the NIF with a time resolution of \textasciitilde 20 ps and an accuracy of \textasciitilde 5{\%}, a S/B \textgreater 5 for the down-scattered neutron measurement is required. As the MRSt-detector design consists of a pulse-dilation drift tube with a CsI photocathode positioned at the focal plane of the spectrometer and a microchannel plate (MCP) for signal gain, the S/B requirement can be met if the number of secondary electrons (SE) produced by neutron and $\gamma $-ray background in these components is reduced 50-100 times. It has been shown in ref. [1] that the SE generated by the neutron and $\gamma $-ray background in the CsI is insignificant and won't affect the MRSt measurement. However, the MCP poses a greater S/B challenge due to higher background sensitivities. In this paper, we discuss an MRSt SE generation model, which includes the CsI photocathode and MCP, and the MRSt shielding design required to reduce the MCP background to the required level for a down-scattered neutron measurement.$^{\mathrm{\mathbf{\thinspace \thinspace \thinspace \thinspace }}}$[1] C. Wink et al., RSI (2016). [Preview Abstract] |
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PP10.00089: A compact, high-efficiency charged-particle spectrometer for studies of stellar nucleosynthesis and kinetic implosion physics at OMEGA and the NIF G.D. Sutcliffe, E. Armstrong, J.A. Frenje, M. Gatu Johnson, C.K. Li, L.M. Milanese, R. Simpson, C. Wink, H. Sio, F.H. Seguin, R.D. Petrasso, A. Zylstra, T.C. Sangster, H.-S. Park, R. Bionta A compact and highly efficient magnet-based spectrometer (called MOS, for Mini Orange Spectrometer) has been designed for measurements of energy spectra of low-energy protons and alphas in experiments at the OMEGA laser facility and the National Ignition Facility (NIF). The MOS brings a much needed capability to these laser facilities, able to measure charged-particle spectra with high accuracy and high energy resolution at energies \textless 5 MeV for yields \textless 5x10$^{\mathrm{8}}$. High efficiency is accomplished by maximizing the solid angle. The MOS enables studies of low-probability stellar nucleosynthesis reactions like the $^{\mathrm{3}}$He$+^{\mathrm{3}}$He reaction, which is part of the solar proton-proton chain. It will also enable other basic science experiments, including studies of stopping power in ICF-relevant plasmas, astrophysical shocks and kinetic physics. The optimization of the MOS design utilized simulated magnetic fields and particle tracing with the software COMSOL. Performance requirements of the MOS system, including desired detection efficiencies and energy resolution, are discussed. [Preview Abstract] |
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PP10.00090: The MIT HEDP Accelerator Facility for Diagnostic Development for OMEGA, Z, and the NIF C.E. Parker, M. Gatu Johnson, A. Birkel, N.V. Kabadi, B. Lahmann, L.M. Milanese, R.A. Simpson, H. Sio, G.D. Sutcliffe, C. Wink, J.A. Frenje, C.K. Li, F.H. Seguin, R.D. Petrasso, R. Leeper, C.L. Ruiz, T.C. Sangster The MIT HEDP Accelerator Facility utilizes a 135-keV linear electrostatic ion accelerator, DT and DD neutron sources, and two x-ray sources for development and characterization of nuclear diagnostics for OMEGA, Z, and the NIF. The accelerator generates DD and D$^{\mathrm{3}}$He fusion products through the acceleration of D$^{\mathrm{+}}$ ions onto a $^{\mathrm{3}}$He-doped Erbium-Deuteride target. Accurately characterized fusion product rates of around 10$^{\mathrm{6}}$ s$^{-}^{\mathrm{1}}$ are routinely achieved. The DT and DD neutron sources generate up to 6x10$^{\mathrm{8}}$, and 1x10$^{\mathrm{7}}$ neutrons/s, respectively. One x-ray generator is a thick-target W source with a peak energy of 225 keV and a maximum dose rate of 12 Gy/min; the other uses Cu, Mo, or Ti elemental tubes to generate x-rays with a maximum energy of 40 keV. Diagnostics developed and calibrated at this facility include CR-39-based charged-particle spectrometers, neutron detectors, and the particle Time-Of-Flight (pTOF) and Magnetic PTOF CVD-diamond-based bang time detectors. The accelerator is also a valuable hands-on tool for graduate and undergraduate education at MIT. [Preview Abstract] |
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PP10.00091: Improved characterization of the CR-39 efficiency for detecting DD neutrons based on data from OMEGA, NIF and the MIT HEDP Accelerator Facility L. M. Milanese, B. Lahmann, J. A. Frenje, M. Gatu Johnson, F. H. Seguin, R. D. Petrasso, V. Yu. Glebov, T. C. Sangster, M. J. Eckart, G. P. Grim, E. P. Hartouni, R. Hatarik, D. B. Sayre, R. Bionta, C. Yeamans, K. Hahn, B. Jones CR-39 nuclear track detectors are extensively used to measure fluences and spectra of charged particles produced in Inertial Confinement Fusion (ICF) implosions. An accurate determination of the CR-39 response to neutrons is important both to perform direct neutron fluence measurements and to estimate the level of neutron-induced background impacting charged-particle measurements. The CR-39 efficiency for detecting neutrons depends on several factors, including the manufacturing process of the CR-39, etching conditions and characteristics of the scanning system employed to detect the neutron-induced tracks. The CR-39 response to DD neutrons has been characterized using implosions at OMEGA and the NIF as well as a neutron generator at the MIT HEDP Accelerator Facility. A new approach provides significantly better precision than previously demonstrated in the literature. This method will be used to characterize DD fusion isotropy at the Z Facility. [Preview Abstract] |
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PP10.00092: Absolute x-ray and neutron calibration of CVD-diamond-based time-of-flight detectors for the National Ignition Facility A. Rosenthal, N. V. Kabadi, H. Sio, H. Rinderknecht, M. Gatu Johnson, J. A. Frenje, F. H. Seguin, R. D. Petrasso, V. Glebov, C. Forrest, J. Knauer The particle-time-of-flight (pTOF) detector at the National Ignition Facility routinely measures proton and neutron nuclear bang-times in inertial confinement fusion (ICF) implosions. The active detector medium in pTOF is a chemical vapor deposition (CVD) diamond biased to 250 -- 1500 V. This work discusses an absolute measurement of CVD diamond sensitivity to continuous neutrons and x-rays. Although the impulse response of the detector is regularly measured on a diagnostic timing shot, absolute sensitivity of the detector's response to neutrons and x-rays has not been fully established. X-ray, DD-n, and DT-n sources at the MIT HEDP Accelerator Facility provide continuous sources for testing. CVD diamond detectors are also fielded on OMEGA experiments to measure sensitivity to impulse DT-n. Implications for absolute neutron yield measurements at the NIF using pTOF detectors will be discussed. [Preview Abstract] |
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PP10.00093: Neutron Diagnostic Development for the Z Accelerator Kelly Hahn, G.A. Chandler, C.L. Ruiz, B. Jones, M.R. Gomez, P.F. Knapp, A.B. Sefkow, S.B. Hansen, P.F. Schmit, E.C. Harding, E. Norris, J.A. Torres, G.W. Cooper, J.D. Styron, J. Frenje, B. Lahmann, M. Gatu-Johnson, F. Seguin, R. Petrasso, D. Fittinghoff, M. May, L. Snyder, K. Moy, R. Buckles, V.Yu. Glebov We are studying Magnetized Liner Inertial Fusion (MagLIF) and Gas Puff fusion neutron sources on the Z accelerator. MagLIF experiments have produced up to 3e12 primary DD neutrons with 2-3 keV ion temperatures and 1-2 ns burn widths. Gas puff experiments have produced up to 5e13 primary DD neutrons with higher ion temperatures, longer burn times, and evidence of non-thermonuclear production. For MagLIF, the yield is expected to increase rapidly with increased energy coupling, yet it remains unclear if Gas Puffs would scale as attractively. We review neutron measurements for these experiments and plans for developing neutron diagnostics for these two very different sources. [Preview Abstract] |
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PP10.00094: Laser and Pulsed Power Electron Density Imaging Through Talbot-Lau X-ray Deflectometry. Maria Pia Valdivia Leiva, Dan Stutman, Christian Stoeckl, Chad Mileham, Ildar Begischev, Wolfgang Theobald, Jake Bromage, Sean Regan, Salee Klein, Gonzalo Muñoz-Cordovez, Milenko Vescovi, Vicente Valenzuela-Villaseca, Felipe Veloso A Talbot-Lau X-ray Deflectometer was deployed using laser driven and x-pinch x-ray backlighters. The Talbot-Lau X-ray Deflectometer is an ideal electron density diagnostic for High Energy Density plasmas with the potential to simultaneously deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single image with source limited resolution. Grating survival and electron density mapping was demonstrated for 10-29 J, 8-30 ps laser pulses using Cu foil targets at the Multi-TeraWatt facility. An areal electron density of \textasciitilde 0.050 g/cm$^{\mathrm{2}}$ was obtained at the center of a fluoro-nylon fiber of \textasciitilde 300 mm diameter with a source FWHM of \textasciitilde 80 \textmu m and resolution of \textasciitilde 50 \textmu m. Grating survival and Moir\'{e} pattern formation was demonstrated using a Cu x-pinch plasma of FWHM \textasciitilde 27 \textmu m, driven by the 350 kA, 350 ns Llampudken pulsed power generator. These results closely match simulations and laboratory results. It was demonstrated that the technique can detect both sharp and smooth density gradients in the range of \textasciitilde 2x10$^{\mathrm{23}}$ to \textasciitilde 2x10$^{\mathrm{25}}$ cm$^{\mathrm{-3}}$, thus allowing implementation of the electron density technique as a HED plasma diagnostic in both laser and pulsed power experiments [Preview Abstract] |
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PP10.00095: Polarization-Sensitive Measurements Of Magnetic Fields In Magnetized Plasmas Using Zeeman Broadening Diagnostics Showera Haque, Matthew S. Wallace, Paul Neill, Radu Presura The Zeeman effect has been used to measure the magnetic field in high energy density plasmas. The measurements are difficult in this regime because the line broadening due to the high plasma density and temperature surpasses the Zeeman splitting. Using an idea proposed by Tessarin \textit{et al}. (2011), we have measured the field in magnetized laser plasmas and in the current-driven exploding wire plasmas. Time-gated spectra with one-dimensional space-resolution were obtained at the Nevada Terawatt Facility for laser plasmas created by 20 J, 1 ns Leopard laser pulses, and expanding in the azimuthal magnetic field produced by the 0.6 MA Zebra pulsed power generator, and for wire array plasmas driven by the 1 MA configuration of the Zebra generator. We explore the response of the Al III 4s $^{\mathrm{2}}$S$_{\mathrm{1/2\thinspace }}$-- 4p $^{\mathrm{2}}$P$_{\mathrm{1/2,3/2}}$ doublet components to the external magnetic field spatially along the plasma in two orthogonal polarizations. In these measurements the Zeeman splitting was not resolved, but the magnetic field strength was measured from the difference between the widths of the line profiles. [Preview Abstract] |
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PP10.00096: Bent crystals for x-ray diagnostics evaluated with synchrotron radiation Nino Pereira, Al Macrander, Woody Vandervort, Heath LeFevre, Elena Baronova The bent crystals that are used extensively in plasma x-ray spectroscopy are usually assumed to reflect x-rays in substantially the same way as flat crystals. The x-rays diffract coherently from specific crystal planes, which are assumed to bend as in an isotropic solid. While these assumptions are valid enough for many practical purposes, detailed measurements on typical bent crystals obtainable at a synchrotron show that x-ray reflection from bent crystals may have interesting features that deviate from the ideal. This paper presents some of the measurements done recently on various bent crystals, some used and some newly made, and discusses their possible relevance for the interpretation of bent-crystal based x-ray diagnostics. [Preview Abstract] |
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PP10.00097: Development of a High Fluence, High Conversion Efficiency X-Ray Silver Metal Foam Source at the NIF M. J. May, J.D. Colvin, G.E. Kemp, D. Thorn, K Widmann, B.E, Blue High x-ray conversion efficiency (XRCE) L-shell Ag sources are being developed for High Energy Density experiments. The targets are nominally 4 mm in diameter, 4 mm tall cylinders of free standing Ag metal foam with densities of 10 - 30 mg/cm$^{3}$ and made by a new technique of freeze drying an aqueous suspension of Ag nano wires. 192 laser beams from NIF are used to heat the targets with $\sim$150 TW of power in a 4 ns square in time pulse depositing $\sim$600 kJ into the target. XRCEs from these targets have been measured by using the Dante diode spectrometer to be $\sim$7\% which is much less than the predictions from simulations. The nano wires at nominal solid density might not be homogenized sufficiently by the laser heating pulse which could limit the XRCE. To increase the XRCE, we plan to use a laser prepulse of $\sim$1 kJ to preheat the nano wires in the target before the main laser heating pulse. The results of these experiments will be discussed. This work was performed under the auspices of the US Department of Energy by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. [Preview Abstract] |
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PP10.00098: Heat Loss in a Laser-Driven, Magnetized, X-Ray Source with Thermoelectric Terms J.L. Giuliani, A.L. Velikovich, G.E. Kemp, J.D. Colvin, J. Koning, K.B. Fournier The efficiency of laser-driven K-shell radiation sources, i.e., pipes containing a gas or a metal foam, may be improved by using an axial magnetic field to thermally insulate the pipe wall from the hot interior. A planar, self-similar solution for the magnetic and thermal diffusion is developed to model the near wall physics that includes the thermoelectric Nernst and Ettingshausen effects. This solution extends previous work [1] for the MagLIF concept to include the full dependence of the transport coefficients on the electron Hall parameter. The analytic solution assumes a constant pressure. This case is matched with a 1D MHD code, which is then applied to the case allowing for pressure gradients. These numerical solutions are found to evolve toward the self-similar ones. The variation of the time integrated heat loss with and without the thermoelectric terms will be examined. The present work provides a verification test for general MHD codes that use Braginskii's or Epperlein-Haines' transport model to account for thermoelectric effects. [1] A.L. Velikovich, J.L. Giuliani, S.T. Zalesak, Phys. Plasmas, 22, 042702 (2015). [Preview Abstract] |
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PP10.00099: Non-LTE modeling of multifluid plasmas Hai Le We present a collisional-radiative model to simulate non-LTE plasmas using the classical multifluid approximation. The effect of non-zero relative drift velocities of the colliding particles is taken into account in the rate formulation\footnote{Le \& Cambier, PoP \textbf{22}, 093512 (2015), PoP \textbf{23}, 063505 (2016).}. We show that the multifluid collision rates deviate from standard results when the kinetic energy of the relative drift motion is comparable to the average thermal energy. Numerical results are presented to demonstrate the impact of this effect on the overall kinetics of the system. [Preview Abstract] |
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PP10.00100: Spectral and Atomic Physics Analysis of Xenon L-Shell Emission From High Energy Laser Produced Plasmas Daniel Thorn, G. E. Kemp, K. Widmann, R. D. Benjamin, M. J. May, J. D. Colvin, M. A. Barrios, K. B. Fournier, D. Liedahl, A. S. Moore, B. E. Blue The spectrum of the L-shell (n$=$2) radiation in mid to high-Z ions is useful for probing plasma conditions in the multi-keV temperature range. Xenon in particular with its L-shell radiation centered around 4.5 keV is copiously produced from plasmas with electron temperatures in the 5-10 keV range. We report on a series of time-resolved L-shell Xe spectra measured with the NIF X-ray Spectrometer (NXS) in high-energy long-pulse (\textgreater 10 ns) laser produced plasmas at the National Ignition Facility. The resolving power of the NXS is sufficiently high (E/$\partial $E \textgreater 100) in the 4-5 keV spectral band that the emission from different charge states is observed. An analysis of the time resolved L-shell spectrum of Xe is presented along with spectral modeling by detailed radiation transport and atomic physics from the SCRAM code and comparison with predictions from HYDRA a radiation-hydrodynamics code with inline atomic-physics from CRETIN. [Preview Abstract] |
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PP10.00101: Anomalous He-like ion resonance-to-intercombination line intensity ratios in discharge and laser produced plasmas. Vyacheslav Shlyaptsev, G. Avaria, J. Li, F.G. Tomasel, M. Busquet, M. Klapish, A.Ya. Faenov, J.J. Rocca Highly anomalous resonance-to-intercombination line intensity ratios were observed in He-like ions spectra from plasmas created in high current density microcapillary channels by ultrafast current pulses ($\le $ 4ns risetime). The emission from discharges containing Si or Al impurities show intercombination line intensities to exceed the resonance line intensities by nearly an order of magnitude. The analysis and detailed hydrodynamic/atomic physics model simulations suggest that the effect responsible for the spectral anomaly reported here is different from those observed to cause similar abnormalities in other plasmas, and is related instead to a new phenomenon in which the very different optical depths in the transverse and axial directions generate triplet level populations greatly exceeding the singlet state populations. The modeling suggests that for different experimental conditions there could be even much larger line ratios observed. The model predictions were tested in wide range parameters and methods of plasma creation including laser produced plasma. [Preview Abstract] |
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PP10.00102: X-ray Emission Line Anisotropy Effects on the Isoelectronic Temperature Measurement Method Duane Liedahl, Maria Barrios, Greg Brown, Mark Foord, William Gray, Stephanie Hansen, Robert Heeter, Leonard Jarrott, Christopher Mauche, John Moody, Marilyn Schneider, Klaus Widmann Measurements of the ratio of analogous emission lines from isoelectronic ions of two elements form the basis of the isoelectronic method of inferring electron temperatures in laser-produced plasmas, with the expectation that atomic modeling errors cancel to first order. Helium-like ions are a common choice in many experiments. Obtaining sufficiently bright signals often requires sample sizes with non-trivial line optical depths. For lines with small destruction probabilities per scatter, such as the 1s2p--1s2 He-like resonance line, repeated scattering can cause a marked angular dependence in the escaping radiation. Isoelectronic lines from near-Z equimolar dopants have similar optical depths and similar angular variations, which leads to a near angular-invariance for their line ratios. Using Monte Carlo simulations, we show that possible ambiguities associated with anisotropy in deriving electron temperatures from X-ray line ratios are minimized by exploiting this isoelectronic invariance. [Preview Abstract] |
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PP10.00103: Kr X-ray spectroscopy to diagnose NIF ICF implosions A. Dasgupta, N. Ouart, J. L. Giuliani, R. W. Clark, M. B. Schneider, H. A. Scott, H. Chen, T. Ma, J. P. Apruzese X ray spectroscopy is used on the NIF to diagnose the plasma conditions in the ignition target in indirect drive ICF implosions [1]. High-energy emission spectra from mid to high atomic number elements can provide estimates of electron temperature near stagnation of an ICF implosion. A platform is being developed at NIF where small traces of krypton are used as a dopant to the fuel gas for spectroscopic diagnostics using krypton line emissions. The fraction of krypton dopant was varied in the experiments and was selected so as not to perturb the implosion. Simulations of the krypton spectra using a 1 in 104 atomic fraction of krypton in direct-drive exploding pusher with a range of electron temperatures and densities show discrepancies when different atomic models are used. We use our non-LTE atomic model with a detailed fine-structure level atomic structure and collisional-radiative rates to investigate the krypton spectra at the same conditions. Synthetic spectra are generated with a detailed multi-frequency radiation transport scheme from the emission regions of interest to analyze the experimental data and compare and contrast with the existing simulations at LLNL. $^{\mathrm{1}}$ T. Ma, et al., RSI submitted (2016) [Preview Abstract] |
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PP10.00104: Extraction of the spatial distribution of electron temperature and density in Magnetized Liner Inertial Fusion implosion plasmas Kyle Carpenter, Roberto Mancini We are testing polychromatic tomography to extract the spatial distribution of electron temperatures and densities in the cylindrical implosion plasmas created during MagLIF. Motivation for this technique stems from its successful application to spherical implosion core plasmas on Omega through the analysis of spatially resolved spectra (SRS) collected via pinhole imaging. In MagLIF, collections of SRS can be extracted from the images created by the slit imaging CRITR spectrometers. These spectra can be complemented with pinhole monochromatic images and spectra recorded with a spherical crystal spectrometer. One axially resolved and one radially resolved CRITR are field during MagLIF and information extracted from one of these SRS would be spatially integrated over a plane of finite thickness given by the spatial resolution of the instrument. In our method, we couple a model that creates synthetic sets of spectra, like those obtained from an experiment, with a Pareto genetic algorithm which searches in parameter space for the spatial distribution which best simultaneously and self-consistently fits the set of SRS/ Solutions obtained are used as the initial solution for a Levenberg-Marquadt minimization algorithm to provide a final ``fine-tuned'' solution. We are testing this method by creating synthetic ``experimental'' data and using the technique to search for the spatial distribution. The results of these feasibility studies will be discussed. [Preview Abstract] |
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PP10.00105: Ion Heating of Plasma to Warm Dense Matter Conditions for the study of High-Z/Low-Z Mixing R. Roycroft, G.M. Dyer, E. McCary, C. Wagner, A. Bernstein, T. Ditmire, B.J. Albright, J.C. Fernandez, W. Bang, P.A. Bradley, D.C. Gautier, C.E. Hamilton, S. Palaniyappan, M.A. Santiago Cordoba, E.L. Vold, L. Yin, B.M. Hegelich The evolution of the interface between a light and heavy material isochorically heated to warm dense matter conditions is important to the understanding of electrostatic effects on the hydrodynamic models of fluid mixing. In recent experiments at the Trident laser facility, the target, containing a high Z and a low Z material, is heated to around 1eV by laser accelerated aluminum ions. In preparation for continued mixing experiments, we have recently heated aluminum to \textasciitilde 20eV by laser accelerated protons on the Texas Petawatt Laser. We fielded a streaked optical pyrometer to measure surface temperature. The pyrometer images the rear surface of a heated target on a sub-nanosecond timescale with 400nm blackbody emissions. This poster presents the details of the experimental setup and pyrometer design, as well as results of ion and proton heating of aluminum targets, and ion heating of high-Z/low-Z integrated targets. [Preview Abstract] |
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PP10.00106: Thermal conductivity measurements of warm dense iron at the LCLS A. McKelvey, S. Jiang, G. Collins, R. Shepherd, S. P. Hau-Riege, M. P. Hill, C. R. D. Brown, E. Floyd, J. D. Fyrth, J. W. Skidmore, R. Hua, F. N. Beg, M. Kim, B. Cho, J. Lee, J. King, R. R. Freeman, H. J. Lee, E. Galtier, P. Audebert, A. Levy, Y. Ping Accurate knowledge of conductivity characteristics in the strongly coupled plasma regime is extremely important for ICF processes such as the onset of hydrodynamic instabilities, thermonuclear burn propagation waves, shell mixing, and efficient x-ray conversion of indirect drive schemes. Recently, an experiment was performed at the LCLS at SLAC to measure the thermal conductivity of warm dense iron. The experiment used 6.8 keV x-rays to differentially heat thin bi-layer Au/Fe targets and establish a prompt temperature gradient at the layer interface. We used a SOP and a FDI to measure the rear layer's time-resolved temperature, expansion velocity, and reflectivity. Data from the time-resolved diagnostics for 100 nm Au and 50 to 100 nm Fe targets will be presented along with analysis and comparison with various models in the strongly coupled plasma regime. [Preview Abstract] |
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PP10.00107: Time- and space- resolved pyrometry of dense plasmas heated by laser accelerated ion beams Gilliss Dyer, Rebecca Roycroft, Eddie McCary, Craig Wagner, Xuejing Jiao, Rotem Kupfer, D. Cort Gauthier, Woosuk Bang, Sasikumar Palaniyappan, Paul A. Bradley, Christopher Hamilton, Miguel A. Santiago Cordoba, Erik L. Vold, Lin Yin, Juan C. Fernandez, Brian J. Alibright, Todd Ditmire, Bjorn Manuel Hegelich Laser driven ion sources have a variety of possible applications, including the rapid heating of matter to dense plasma states of several eV. Recent experiments at LANL and The University of Texas have explored ion heating in the context of mixing at high-Z / low-Z plasma interfaces, using different laser-based ion acceleration schemes. Quasi-monoenergetic and highly directed Al ions from ultra-thin foils were used in one set of experiments, while TNSA accelerated protons from an F/40 focused petawatt laser were used in the other. Using spatially and temporally resolved streaked optical pyrometry we have gained insight into the degree and uniformity of heating from various configurations of ion source and sample target. Here we present data and analysis from three experimental runs along with hydrodynamic modeling of the heated targets and geometric considerations. [Preview Abstract] |
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PP10.00108: Target design for materials processing very far from equilibrium* John J. Barnard, Thomas Schenkel Local heating and electronic excitations can trigger phase transitions or novel material states~that can be stabilized by rapid quenching.~~An example on the few nanometer scale are phase transitions induced by the passage of swift heavy ions in solids where nitrogen-vacancy color centers form locally in diamonds when ions heat the diamond matrix to warm dense matter conditions at \textasciitilde 0.5 eV [1].~~We optimize mask geometries for target materials such as silicon and diamond to induce phase transitions by intense ion pulses (e. g. from NDCX-II [2] or from laser-plasma acceleration).~~The goal is to rapidly heat a solid target volumetrically and to trigger a phase transition or local lattice reconstruction followed by rapid cooling.~~The stabilized phase can then be studied ex situ.~~We performed HYDRA [3] simulations that calculate peak temperatures for a series of excitation conditions and cooling rates of crystal targets with micro-structured masks. A simple analytical model, that includes ion heating and radial, diffusive cooling, was developed that agrees closely with the HYDRA simulations. The model gives scaling laws that can guide the design of targets over a wide range of parameters including those for NDCX-II and the proposed BELLA-i. 1.~~J. Schwartz, et al, J. Appl. Phys. (2014). 2.~P. Seidl, et. al. NIM A \textbf{800}, 98 A (2015); J. J. Barnard, et al., NIM A \textbf{733}, 45 (2014). 3.~M.M. Marinak, et al Phys. Plasmas \textbf{8} 2275 (2001). *This work was performed under the auspices of the U.S. DOE under contracts DE-AC52-07NA27344 (LLNL), DE-AC02-05CH11231 (LBNL) and was supported by the US DOE Office of Science, Fusion Energy Sciences. LLNL-ABS-697271 [Preview Abstract] |
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PP10.00109: PURE-ION, PURE ELECTION, ANTI-MATTER PLASMA AND STRONGLY COUPLED |
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PP10.00110: The BX-U linear trap applied to test two-fluid plasma effect by using lithium and electron fluids Haruhiko Himura The BX-U linear trap, a modified version of the Penning–Malmberg trap was developed wherein both positive and negative harmonic potential wells were created by using multi-ring electrodes (H. Himura, Nucl. Inst. Methods Phys. Res., Sect. A, {\bf 811}, 100 (2016).). In the machine, pure lithium and electron plasmas are not only produced independently but also trapped simultaneously. Confinement properties of those non-neutral plasmas were investigated recently (S. Kawai, H. Himura {\it et al.}, Phys. Plasmas {\bf 23}, 022113 (2016).) Data were obtained by a micro-channel plate followed by a phosphor screen (H. Himura {\it et al.}, Rev. Sci. Instrum. {\bf 87}, 063306 (2016); S. Yamada and H. Himura, Rev. Sci. Instrum. {\bf 87}, 036109 (2016).). In this meeting, we present our recent results along with detailed description of the BX-U. Also, we explain our method of testing two-fluid effects by using the pure lithium and electron plasmas. [Preview Abstract] |
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PP10.00111: Axisymmetric Bernstein modes in a finite-length non-neutral plasma: simulation and kinetic theory. Grant Hart, Bryan G. Peterson, Ross L. Spencer We are using a 2-D PIC code to model high-frequency (near the cyclotron frequency) axisymmetric oscillations in a finite-length pure-ion plasma. We previously modeled these modes for infinite-length plasmas, where they are not detectable in the surface charge on the walls because of axisymmetry and lack of z-dependence. This is not true in a finite-length plasma, however, because the eigenfunction of the oscillation has to have nodes a short distance beyond the ends of the plasma. This gives the modes a $\cos(k_z z)$ or $\sin(k_z z)$ dependence, with a $k_z$ such that an integral number (approximately) of half-wavelengths fit into the plasma. This $z$-dependence makes the mode detectable in the surface charge on the walls. The modes also have $r$-dependence. The radial-velocity eigenfunctions of the modes behave as J$_1(k_r r)$. We have simulated the plasma with different $k_z$ and $k_r$ values and find that increasing $k_z$ introduces a small frequency shift, either upward or downward depending on which mode is measured. The damping of the modes also increases as $k_z$ or $k_r$ increases. We are developing an appropriate kinetic theory of these modes that will include both the finite-Larmour-radius effects and the axial bouncing motion of the particles. [Preview Abstract] |
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PP10.00112: Numerical and Analytical Calculation of Bernstein Resonances in a Non-Uniform Cylindrical Plasma D.K. Walsh, D.H.E. Dubin This poster presents theory and numerical predictions of electrostatic Bernstein modes in a cylindrical non-neutral plasma column with multiple ion species. These modes propagate radially across the column until they are reflected when their frequency matches the local upper hybrid frequency, setting up an internal normal mode on the column, and also mode-coupling to the electrostatic surface cyclotron wave (which allows the normal mode to be excited and observed using external electrodes). Using our linear Vlasov code discussed last year, we present several numerical results at various magnetic fields, $e^{i \ell \theta}$\hbox{-dependencies}, and plasma profiles in order to make quantitative predictions of future cyclotron wave experiments. These results are compared to the semi-analytic WKB theory in order to determine under what conditions Bernstein waves are measurable at the wall. [Preview Abstract] |
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PP10.00113: Collisional heating of a plasma column slowly forced across a squeeze potential D.H.E. Dubin When equilibrium plasmas have two or more locally-trapped particle populations, perturbations to the equilibrium can produce phase-space discontinuities in the distribution function that strongly enhance transport, plasma loss, and wave damping. This poster presents a simple version of this process, wherein a plasma is heated as it is slowly forced back and forth across a squeeze potential (at a frequency $\omega $ that is small compared to the particle bounce frequency) that traps particles on either side of the squeeze. Adiabatic theory is developed for the distribution function, showing that trapped and passing particles have different responses to the forcing that produces a collisional boundary layer at the separatrix. Expressions for both the adiabatic and non-adiabatic distribution functions are presented, and the heating rate caused by the collisional boundary layer at the separatrix is derived. The heating is proportional to $\surd (\nu $ $\omega )$, where $\nu $ is the collision rate. [Preview Abstract] |
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PP10.00114: Non-Resonant Particle Heating Due to Collisional Separatrix Crossings F. Anderegg, M. Affolter, D.H.E. Dubin, C.F. Driscoll We observe plasma heating when a pure ion column is forced back and forth across a partial trapping barrier. Here, an externally applied axisymmetric ``squeeze" potential $V_s$ creates a velocity separatrix between trapped and passing particles. Weak collisions between these two populations at rate $\nu_c$ causes diffusion across the separatrix, leading to irreversible heating. The observed heating rate scales as $ \dot{T} / T \propto \left ( \delta L / L \right )^2 \; \sqrt{\nu_c \;f_{sl}}\;\;V_s^2 / T^2$, where $\delta L / L$ is the amplitude of the forced ``sloshing" oscillation, and $f_{sl}$ is the applied sloshing frequency. These experiments verify the $ \left ( \delta L / L \right )^2$, and the $\sqrt {f_{sl}}$ dependence that is characteristic of collisional separatrix crossing. The particle velocity distribution function of the oscillating plasma is measured directly with coherent Laser Induced Fluorescence, and shows passing and trapped particles having an out of phase response with respect to the applied oscillations which is responsible for the observed heating. [Preview Abstract] |
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PP10.00115: Test of Long-Range Collisional Drag via Plasma Wave Damping C.F. Driscoll, M. Affolter, F. Anderegg In magnetized plasmas, where the cyclotron radius r$_{\mathrm{c}}$ is less than the Debye length $\lambda_{\mathrm{D}}$, classical collision theory is incomplete, since it neglects long-range collisions with impact parameters $\rho $ in the range r$_{\mathrm{c}}$ \textless $\rho $ \textless $\lambda_{\mathrm{D}}$. We present the first experimental confirmation of a new theory* predicting enhanced parallel velocity slowing due to these long-range collisions in magnetized plasmas. The experiments measure the damping rate of plasma waves in multi-species pure ion plasmas confined in a Penning-Malmberg trap. In certain regimes, this damping is dominated by interspecies collisional drag. The measured damping rates exceed classical predictions of collisional drag damping by as much as an order of magnitude, but agree with the new long-range collision theory. $^{\mathrm{\ast }}$D.H.E. Dubin, Phys. Plasmas \textbf{21}, 052108 (2014) [Preview Abstract] |
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PP10.00116: Parametric Decay Instability of Near-Acoustic Waves in Fluid and Kinetic Regimes M. Affolter, F. Anderegg, C.F. Driscoll, F. Valentini We present quantitative measurements of parametric wave-wave coupling rates and decay instabilities in the range 10 meV \textless T \textless 1 eV. These experiments are conducted on a laser cooled pure ion plasmas confined in a cylindrical Penning-Malmberg trap. The axisymmetric, standing plasma waves have near-acoustic dispersion $\omega $(k$_{\mathrm{z}})\propto $ k$_{\mathrm{z}}-\alpha $k$_{\mathrm{z}}^{\mathrm{3}}$, discretized by the axial wave number k$_{\mathrm{z}}=$ m$_{\mathrm{z}}(\pi $/L$_{\mathrm{p}})$. The parametric coupling rates are measured between m$_{\mathrm{z}}=$ 2 waves with large amplitude $\delta $n$_{\mathrm{2}}$/n$_{\mathrm{0}}$, and small amplitude m$_{\mathrm{z}}=$ 1 waves, which have a small frequency detuning $\Delta \omega =$ 2$\omega_{\mathrm{1}}-\omega_{\mathrm{2}}$. On cold plasmas, the parametric coupling rates $\Gamma \propto $ ($\delta $n$_{\mathrm{2}}$/n$_{\mathrm{0}})$ are consistent with cold fluid, 3-wave instability theory, and the decay instability occurs when $\Gamma $ \textgreater $\Delta \omega $/2. In contrast, at higher temperatures, the m$_{\mathrm{z}}=$ 2 wave is more unstable. The instability threshold is reduced from the cold fluid prediction as the plasma temperature is increased, which is in qualitative agreement with Vlasov simulations, but is not yet understood theoretically. [Preview Abstract] |
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PP10.00117: Flux-driven algebraic damping of m=2 diocotron mode C.Y. Chim, T.M. O'Neil Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of $m=2$ diocotron modes.\footnote{A.A. Kabantsev \textit{et. al.}, Phys. Rev. Lett. \textbf{112}, 115003, 2014.} Due to small field asymmetries a low density halo of electrons is transported radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius $r_{\text{res}}$, where $f=mf_{E\times B}(r_{\text{res}})$. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from the exponential spatial Landau damping in a linear wave-particle resonance. This poster uses analytic theory and simulations to explain the new flux-driven algebraic damping of the mode. As electrons are swept around the nonlinear ``cat's eye" orbits of the resonant wave-particle interaction, they form a quadrupole $(m=2)$ density distribution, which sets up an electric field that acts back on the plasma core. The field causes an $E\times B$ drift motion that symmetrizes the core, i.e. damps the $m=2$ mode. [Preview Abstract] |
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PP10.00118: Mitigation of ion-induced drift instability in electron plasma by a transverse current through the Landau-resonant layer. A.A. Kabantsev, C.F. Driscoll Experiments and theory on electron columns have characterized an \textit{algebraic} damping of diocotron modes, caused by a flux of electrons through the resonance (critical) layer [1]. This flux-driven damping also eliminates the ion-induced \textit{exponential} instability of diocotron modes. Our plasmas rotate at rate $\omega_{E\times B} $, and the (nominally stable) diocotron modes are described by amplitude $A_{d} ,k_{z} =0,m_{\theta } =1,2,..,$ frequency $\omega_{d} (m_{\theta } )$, and a wave/plasma critical radius $r_{c} (m_{\theta } )$, where $\omega_{E\times B} (r_{c} )={\omega_{d} } \mathord{\left/ {\vphantom {{\omega_{d} } {m_{\theta } }}} \right. \kern-\nulldelimiterspace} {m_{\theta } }$. External fields produce a low density (1/100) halo of electrons moving radially outward from the plasma core, with flux rate $F\equiv ({-1} \mathord{\left/ {\vphantom {{-1} {N_{e} ){dN_{e} } \mathord{\left/ {\vphantom {{dN_{e} } {dt}}} \right. \kern-\nulldelimiterspace} {dt}}}} \right. \kern-\nulldelimiterspace} {N_{e} ){dN_{e} } \mathord{\left/ {\vphantom {{dN_{e} } {dt}}} \right. \kern-\nulldelimiterspace} {dt}}$. We find that \textit{algebraic }damping of the diocotron modes begins when the halo reaches the critical radius $r_{c} (m_{\theta } )$, proceeding as $A_{d} (\Delta t)=A_{d} (0)-\gamma \Delta t$, with $\gamma =\beta (m_{\theta } )F$. We also investigated the diocotron instability which occurs when a small number of ions are transiting the electron plasma [2]. Dissimilar bounce-averaged drifts of electrons and ions polarize the diocotron mode density perturbations, developing instability analogous to the classical flute instability. The exponential growth rate $\Gamma $ is proportional to the fractional neutralization $({N_{i} } \mathord{\left/ {\vphantom {{N_{i} } N}} \right. \kern-\nulldelimiterspace} N_{e} )$ and to the separation between electrons and ions in the wave perturbation. We have found that the \textit{algebraic} damping can suppress the exponential ion-induced instability only for amplitudes satisfying $A_{d} \le {\beta F} \mathord{\left/ {\vphantom {{\beta F} \Gamma }} \right. \kern-\nulldelimiterspace} \Gamma $. [1]A.A. Kabantsev \textit{et al}., PRL \textbf{112}, 115003 (2014). [2]A.A. Kabantsev and C.F. Driscoll, Fusion Sc. and Tech. \textbf{51}, 96 (2007) [Preview Abstract] |
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PP10.00119: Dynamics of electron plasma vortex under time-dependent external strain N. C. Hurst, J. R. Danielson, D. H. E. Dubin, C. M. Surko The behavior of two-dimensional vortex structures is of key interest in a number of important physical systems, including geophysical fluids\footnote{\small D.~G.~Dritschel and B.~Legras, {\it Phys. Today} {\bf 46}, 44 (1993).} and strongly magnetized plasmas.\footnote{\small P.~W.~Terry, {\it Rev. Mod. Phys.} {\bf 72}, 1 (2000).} Specifically, vortices can be stripped and destroyed by external forcing (for example, from boundaries or other nearby vortices).\footnote{\small R. R. Trieling, G. J. F. Van Heijst, \textit{Fluid Dyn. Research} \textbf{23} 319-341 (1998).} The research presented here focuses on the behavior of an initially axisymmetric vortex subjected to external straining flow fields which vary in time. Experimental results are obtained using an electron plasma confinement device, which models the 2D Euler equations for ideal fluid flow.\footnote{\small C.~F.~Driscoll \textit{et. al.}, {\it Physica C} {\bf 369}, 21 (2002)} Vortex-in-cell simulation results are also presented to complement and extend the laboratory results. Specific behaviors under consideration include details of the vortex destruction mechanism, vortex adiabaticity, and vortex splitting \textit{via} the Kelvin-Helmholtz instability. [Preview Abstract] |
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PP10.00120: Intense positron beam as a source for production of electron-positron plasma M.R. Stoneking, J. Horn-Stanja, E.V. Stenson, T. Sunn Pedersen, H. Saitoh, U. Hergenhahn, H. Niemann, N. Paschkowski, C. Hugenschmidt, C. Piochacz We aim to produce magnetically confined, short Debye length electron-positron plasma and test predicted properties for such systems. A first challenge is obtaining large numbers of positrons; a table-top experiment (system size \textasciitilde 5 cm) with a temperature less than 5 eV requires about 10$^{\mathrm{10}}$ positrons to have more than 10 Debye lengths in the system. The NEPOMUC facility at the FRM II research reactor in Germany is one of the world's most intense positron sources. We report on characterization (using a retarding field energy analyzer with magnetic field gradient) of the NEPOMUC beam as delivered to the open beam port at various beam energies and in both the re-moderated and primary beam configurations in order to design optimal trapping (and accumulation) schemes for production of electron-positron plasma. The intensity of the re-moderated (primary) beam is in the range 2 -3 x 10$^{\mathrm{7}}$ /s (1 -- 5 x 10$^{\mathrm{8}}$ /s). The re-moderated beam is currently the most promising for direct injection and confinement experiments; it has a parallel energy spread of 15 -- 35{\%} and the transverse energy spread is 6 -- 15{\%} of the parallel energy. We report on the implications for injection and trapping in a dipole magnetic field as well as plans for beam development, \textit{in situ} re-moderation, and accumulation. We also report results demonstrating a difference in phosphor luminescent response to low energy positrons versus electrons. [Preview Abstract] |
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PP10.00121: Dipole configuration for confinement of positrons and electron-positron plasma E. V. Stenson, H. Saitoh, J. Horn-Stanja, U. Hergenhahn, N. Paschkowski, T. Sunn Pedersen, M. R. Stoneking, M. Dickmann, M. Singer, S. Vohburger, C. Hugenschmidt, L. Schweikhard, J. R. Danielson, C. M. Surko Laboratory creation and confinement of electron-positron plasmas, which are expected to exhibit atypical plasma physics characteristics, would enable tests of many theory and simulation predictions (e.g., the stabilization of anomalous transport mechanisms). This is the goal of APEX/PAX (A Positron-Electron eXperiment/Positron Accumulation eXperiment). Following demonstration of efficient (38\%) {\bf E}$\times${\bf B} injection and subsequent confinement ($\tau$ = 3--5 ms) of cold positrons in a dipole magnetic field (H. Saitoh, {\it et al.}, NJP {\bf 17},103038 (2015)), the system is undergoing upgrades from a supported permanent magnet to a supported HTSC (high-temperature superconductor) coil, then to a levitated HTSC coil suitable for the simultaneous confinement of electrons and positrons. This contribution will report on the design and testing of the new systems and subsystems (e.g., for cooling, excitation, and levitation) and, if available, on results of upcoming experiments using a ``rotating wall'' to generate inward particle flux deeper into the confinement region. [Preview Abstract] |
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PP10.00122: Antihydrogen gravity Apparatus Joel Fajans, Chukman So ALPHA first measured the gravitational mass of antihydrogen atoms in a magnetic minimum trap in 2013, limiting anomalous forces coupled to the antiatoms to <75 times of gravity. A new apparatus is being designed to tighten the limit to much better than order unity. It entails a magnetic trap with a vertical long axis and maximal height to improve gravity signal. The magnets creating the trap are designed to ensure a magnetic up-down asymmetry <1e-5 T, a level of field control achieved by taking into account the effect of fabrication error, the inter-connections between current loops, the current leads into/out of the magnets, wire splices, and other fine, uncontrolled details inside the superconducting wires. [Preview Abstract] |
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PP10.00123: Combining the Strong Drive Regime with Evaporative Cooling to Control Plasma Parameters in the ALPHA Experiment Celeste Carruth, Joel Fajans To make antihydrogen at the ALPHA experiment at CERN, we need to produce antiproton and positron plasmas with consistent plasma parameters. We developed a technique that allows us to eliminate initial variations in the density and the number of particles by combining evaporative cooling and the strong drive regime. The strong drive regime is a non-neutral plasma regime driven by a rotating electric field, where the drive frequency synchronizes with the plasma rotation frequency; this controls the density.\footnote{J. R. Danielson and C. M. Surko, "Radial compression and torque-balanced steady states of single-component plasmas in Penning-Malmberg traps", Physics of Plasmas \textbf{ 13}, (2006), 055706} Evaporative cooling is a space-charge dominated effect where a potential well is completely filled with the space charge of a plasma and one side is lowered, which sets the on-axis potential. For cold non-neutral plasmas, the density and on-axis potential give a unique solution to the plasma parameters, so we want to simultaneously combine these two techniques. Experimental results using electron plasmas show this combination of techniques does an excellent job at producing plasmas with the same number of particles and densities from a wide range of initial conditions. [Preview Abstract] |
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PP10.00124: A Laser-Cooled Ion Source to Sympathetically Cool Positrons in the ALPHA Experiment Muhammed Sameed, Daniel Maxwell, Niels Madsen The ALPHA experiment at CERN studies the properties of antimatter by making precision measurements on antihydrogen. Antihydrogen atoms are produced by mixing a cloud of cold antiprotons with a dense positron plasma inside a magnetic trap. The formation of antihydrogen, of which only the coldest atoms remain trapped, depends principally on the kinetic energy of the constituent plasmas. Presently, the trapping rate is approximately two atoms in a seven minute cycle. During mixing, the antiprotons thermalize in the positron plasma prior to antihydrogen production. Colder positron temperatures would therefore result in an increased fraction of trapped antihydrogen atoms in the ALPHA mixing trap. At present, the positrons used for antihydrogen production in ALPHA reach energies of about $50$ K. Much colder positron plasmas may be achieved by sympathetically cooling the positrons using laser-cooled beryllium ions. Preliminary results in the development of a low flux and low energy beryllium ion source using a pulsed ablation laser are presented. Precision ablation techniques coupled with laser-cooling can subsequently be used to effectively cool positrons. A provisional design of an ablation source is also presented for installation in the ALPHA apparatus in 2017. [Preview Abstract] |
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PP10.00125: Characteristic coupling time between axial and transverse energy modes for antihydrogen in magnetostatic traps Mike ZHong, Joel Fajans For upcoming ALPHA collaboration laser spectroscopy and gravity experiments, the nature of the chaotic trajectories of individual antihydrogen atoms trapped in the octupole Ioffe magnetic trap is of importance [1]. Of particular interest for experimental design is the coupling time between the axial and transverse modes of energy for the antihydrogen atoms. Using Monte Carlo simulations of semiclassical dynamics of antihydrogen trajectories, we quantify this characteristic coupling time between axial and transverse modes of energy. There appear to be two classes of trajectories: for orbits whose axial energy is higher than 10\% of the total energy, the axial energy varies chaotically on the order of 110 seconds, whereas for orbits whose axial energy is around 10\% of the total energy, the axial energy remains nearly constant on the order of 1000 seconds or longer. Furthermore, we search through parameter space to find parameters of the magnetic trap that minimize and maximize this characteristic coupling time. [1] A I Zhmoginov, A E Charman, R Shalloo, J Fajans, J S Wurtele, Nonlinear dynamics of antihydrogen in magnetostatic traps: implications for gravitational measurements, Class. and Quantum Grav., 30 205014 2013,doi:10.1088/02649381/30/20/205014. [Preview Abstract] |
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PP10.00126: Transport Theory for Plasmas that are Strongly Magnetized and Strongly Coupled Scott Baalrud, Jerome Daligault Plasmas with components that are magnetized, strongly coupled, or both arise in a variety of frontier plasma physics experiments including magnetized dusty plasmas, nonneutral plasmas, magnetized ICF concepts, as well as from self-generated fields in ICF. Here, a species is considered strongly magnetized if the gyroradius is smaller than the spatial scale over which Coulomb interactions occur. A theory for transport properties is described that treats a wide range of both coupling and magnetization strengths. The approach is based on an extension of the recent effective potential transport theory [1] to include a strong magnetic field. The underlying kinetic theory is based on an extension of the Boltzmann equation to include a strong magnetic field in the dynamics of binary scattering events. Corresponding magnetohydrodynamic equations are derived by solving the kinetic equation using a Chapman-Enskog like spectral method. Results are compared with classical molecular dynamics simulations of self-diffusion of the one component plasmas [2], and with simulations of parallel to perpendicular temperature equilibration of an initially anisotropic distribution. [1] S.D. Baalrud, and J. Daligault, PRL 110, 235001 (2013). [2] T. Ott and M. Bonitz, PRL 107, 135003 (2011). [Preview Abstract] |
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PP10.00127: Effective momentum-dependent potentials for atomic bound states and scattering in strongly coupled plasmas A. Christlieb, G. Dharuman, J. Verboncoeur, M.S. Murillo Modeling high energy-density experiments requires simulations spanning large length and time scales. These non-equilibrium experiments have time evolving ionization and partial degeneracy, obviating the direct use of the time-dependent Schrodinger equation. Therefore, efficient approximate methods are greatly needed. We have examined the accuracy of one such method based on an effective classical-dynamics approach employing effective momentum dependent potentials (MDPs) within a Hamiltonian framework that enables large-scale simulations. We have found that a commonly used formulation, based on Kirschbaum-Wilets MDPs [1] leads to very accurate ground state energies and good first/second-ionization energies. The continuum scattering properties of free electrons were examined by comparing the momentum-transfer cross section (MTCS) predicted by KW MDP to a semi-classical phase-shift calculation. Optimizing the KW MDP parameters for the scattering process yielded poor MTCSs, suggesting a limitation of the use of KW MDP for plasmas. However, our new MDP yields MTCS values in much better agreement than KW MDP.[1] Phys. Rev. A 51, 266 (1995) [Preview Abstract] |
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PP10.00128: Bayesian inference of x-ray diffraction from warm dense matter using the one-component-plasma model Jean Clerouin, Nicolas Desbiens, Vincent Dubois, Philippe Arnault We show that the Bayesian inference of recently measured x-ray diffraction spectra from laser-shocked aluminum [L. B. Fletcher \textit{et al}., Nature Photonics 9, 274 (2015)] with the one-component-plasma (OCP) model performs remarkably well at estimating the ionic density and temperature. This statistical approach requires many evaluations of the OCP static structure factor, which were done using a recently derived analytic fit. The atomic form factor is approximated by an exponential function in the diffraction window of the first peak. The electronic temperature is then estimated from the comparison of this approximated form factor with the electronic structure of an average atom model. Out-of-equilibrium states, with electrons hotter than ions, are diagnosed for the spectra obtained early after the pump, whereas at late time delay the plasma is at thermal equilibrium. [Preview Abstract] |
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PP10.00129: Modification of microparticles due to intense laser radiation Dietmar Block, Frank Wieben, Jan Schablinski Recent experiments have demonstrated that it is possible to build an optical tweezer for dusty plasmas. It allows to trap and manipulate single particles from a 2-d plasma crystal. However, as soon as a particle is trapped it is exposed to intense laser radiation. To investigate the influence of intense laser radiation on the particle, the trapping and detrapping processes are studied with high spatial and temporal resolution. Our measurements show, that the trapped particle properties are different and that this change is reversible once the particle is detrapped. [Preview Abstract] |
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PP10.00130: Generation of two-dimensional binary mixtures in complex plasmas Frank Wieben, Dietmar Block Complex plasmas are an excellent model system for strong coupling phenomena. Under certain conditions the dust particles immersed into the plasma form crystals which can be analyzed in terms of structure and dynamics. Previous experiments focussed mostly on monodisperse particle systems whereas dusty plasmas in nature and technology are polydisperse. Thus, a first and important step towards experiments in polydisperse systems are binary mixtures. Recent experiments on binary mixtures under microgravity conditions observed a phase separation of particle species with different radii even for small size disparities. This contradicts several numerical studies of 2D binary mixtures. Therefore, dedicated experiments are required to gain more insight into the physics of polydisperse systems. In this contribution first ground based experiments on two-dimensional binary mixtures are presented. Particular attention is paid to the requirements for the generation of such systems which involve the consideration of the temporal evolution of the particle properties. Furthermore, the structure of these two-component crystals is analyzed and compared to simulations. [Preview Abstract] |
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PP10.00131: Dust Effects on a Free Presheaths in Weakly Magnetized Plasmas I.J. Kang, M.K. Bae, S.G. Chp, S.Y. Kim, S.H. Hong, H.G. Choi, Y.S. Oh, H.T. Oh, I.S. Park, T. Lho, K.S. Chung Dust effects on a diffusion coefficient and a connection length at a free presheath regions have been investigated as a part of experimental simulation of dust interaction with plasmas and plasma edge transport at Divertor Plasma Simulator -- 2 (DiPS-2) with the following conditions: plasma density 1\textasciitilde 10 × 10$^{\mathrm{12}}$ cm$^{\mathrm{3}}$, electron temperature 1 \textasciitilde 10 eV and magnetic field \textasciitilde 1 kG, where the characteristics of DiPS-2 is the following: 12 V and 280 A for LaB$_{\mathrm{6}}$ heating, 50 -- 100 V and 20 -- 40 A for plasma discharge. Pulsed laser beams by a 250 mJ Nd:YAG laser were injected to a tungsten target for production of dust particles. Free presheaths were artificially generated by inserting a tungsten perturbing object with diameter $=$ 1.5 cm at the center of plasmas in DiPS-2. Radial plasma profiles were measured by using a fast scanning probe (FSP) system with triple probe (TP) and Mach probe (MP) and a laser induced fluorescence (LIF) system. Dust effects on a diffusion coefficient and a connection length in the presheath region were analysed by comparing the plasma parameter of dusty and pure plasmas. [Preview Abstract] |
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PP10.00132: Transport and mixing in strongly coupled dusty plasma medium Vikram Dharodi, Amita Das, Bhavesh Patel The generalized hydrodynamic (GHD) fluid model has been employed to study the transport and mixing properties of Dusty plasma medium in strong coupling limit. The response of lighter electron and ion species to the dust motion is taken to be instantaneous i.e. inertia-less. Thus the electron and ion density are presumed to follow the Boltzman relation. In the incompressible limit (i-GHD) the model supports Transverse Shear wave in contrast to the Hydrodynamic fluids. It has been shown that the presence of these waves leads to a better mixing of fluid in this case. Several cases of flow configuration have been considered for the study. The transport and mixing attributes have been quantified by studying the dynamical evolution of tracer particles in the system. The diffusion and clustering of these test particles are directly linked to the mixing characteristic of a medium. The displacement of these particles provides for a quantitative estimate of the diffusion coefficient of the medium. It is shown that these test particles often organize themselves in spatially inhomogeneous pattern leading to the phenomena of clustering. [Preview Abstract] |
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PP10.00133: Dusty plasma microparticle cloud control and rapid electrostatic mutual-repulsion expansion in a DC glow discharge Eric Gillman, Bill Amatucci Microparticles in plasma discharges rapidly charge up, typically collecting a net negative charge due to the relatively high mobility of electrons compared to ions. Electrostatic forces can be utilized to control charged microparticle behavior and motion in a plasma discharge. In these experiments a metal wire loop is supplied with an electric potential that can be controlled independently from the DC plasma glow discharge electrodes. By varying the voltage on the wire loop, we can attract, trap, manipulate, suspend, and/or repel microparticles that originate from the DC glow discharge. Experiments studied the properties of electrostatic self-repulsion of a cloud of charged microparticles. By pulsing the plasma and controlling wire loop potential, a cloud of trapped microparticles is released and allowed to rapidly expand. A simple force balance simulation code is used as a model to compare and benchmark actual experimental results. *This work was supported by the Naval Research Laboratory base program. [Preview Abstract] |
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PP10.00134: Collisional enhancement of wakes in streaming complex plasma Sita Sundar, Hanno Kaehlert, Jan-Philip Joost, Patrick Ludwig, Michael Bonitz Wake effect and dynamical screening of grains in streaming plasmas have received considerable attention over the years from experimentalists as well as theoreticians. However, recently it was shown that the characteristic features of the wake potential for flowing non-Maxwellian plasma are qualitatively distinct from Maxwellian streaming ions. The difference observed is due to the modification in the distribution function itself during collisions and the presence of external fields. Herein, we compute the electrostatic potential of a dust grain in collisional streaming ions using 3D particle-in-cell(PIC) code `COPTIC' [1] and Linear Response (LR) theory. In contrast to the Maxwellian case, simulations demonstrate the enhancement of the wake potential with collisionality for the non-Maxwellian streaming plasmas. We investigate the effect of collisions and compare our results with the wake potential obtained from the LR formalism for Maxwellian and non-Maxwellian cases. We discuss the physics of distribution function and flux around the grain and present a parametric study of collision frequency ${\nu}$ vs. wake peak characteristics. $[1]$I H Hutchinson Phys. Plasmas {\bf 18}, 032111 (2011). [Preview Abstract] |
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PP10.00135: Volumetric measurement of 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). The dust acoustic wave (also known as the dust density wave) is low-frequency, longitudinal mode that propagates through the dust component of the dusty plasma system and is self-excited by the free energy from the ion streaming through the dust component. In the laboratory setting, the majority of the self-excited dust acoustic waves that are observed are nonlinear, which allows for detailed studies of the nonlinear properties of waves at the kinetic level. One such nonlinear process is synchronization, where a self-excited wave or oscillations interacts with a driving force causing an adjustment of the wave or oscillation frequency. In this presentation, we report on experimental measurements of the volumetric nature of the synchronization process of the naturally-occurring dust acoustic wave with an external modulation in an rf discharge. [Preview Abstract] |
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PP10.00136: Properties of ordered structures with and without magnetic fields in the Magnetized Dusty Plasma Experiment Edward Thomas, Uwe Konopka, Robert Merlino, Marlene Rosenberg The Magnetized Dusty Plasma Experiment (MDPX) at Auburn University has observed the formation of ordered structures of dust particles (from 0.5 micron up to 3 micron diameter) at high magnetic field (above 1 T) in which the spatial pattern of the particles is determined by a wire mesh that is embedded in an electrode that is ~30 to 40 mm away from the particles. The most recent experiments have shown the dust particles can mirror the shape of the electrode up to separations of 60 to 70 mm. However, it remains unclear what processes are present in the strongly magnetized background plasma that leads to this pattern formation. In this presentation, we will discuss the formation of a “standard” plasma crystal and compare it with the “imposed, ordered” structure. Results may be presented on the transition from one spatial configuration to the other. [Preview Abstract] |
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PP10.00137: Dust Particle Dynamics in The Presence of Highly Magnetized Plasmas Brian Lynch, Uwe Konopka, Edward Thomas, Robert Merlino, Marlene Rosenberg Complex plasmas are four component plasmas that contain, in addition to the usual electrons, ions, and neutral atoms, macroscopic electrically charged (nanometer to micrometer) sized ``dust'' particles. These macroscopic particles typically obtain a net negative charge due to the higher mobility of electrons compared to that of ions. Because the electrons, ions, and dust particles are charged, their dynamics may be significantly modified by the presence of electric and magnetic fields. Possible consequences of this modification may be the charging rate and the equilibrium charge. For example, in the presence of a strong horizontal magnetic field (B \textgreater 1 Tesla), it may be possible to observe dust particle \textbf{g }x \textbf{B }deflection and, from that deflection, determine the dust grain charge. In this poster, we present recent data from performing multiple particle dropping experiments to characterize the \textbf{g} x \textbf{B} deflection in the Magnetized Dusty Plasma Experiment (MDPX). [Preview Abstract] |
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PP10.00138: Characterization of Imposed Ordered Structures in MDPX Taylor Hall, Edward Thomas, Uwe Konopka, Robert Merlino, Marlene Rosenberg It is well understood that the microparticles in complex, or dusty, plasmas will form self-consistent crystalline patterns at the proper plasma parameters. In the Magnetized Dusty Plasma Experiment (MDPX) device, studies have been made of imposed, ordered structuring of the dust particles to a two dimensional grid. At high magnetic field (B \textgreater 1 Tesla), the dust particles are shown to become spatially oriented to the structure of a wire mesh embedded in an electrically floating, upper electrode while the particles are suspended in a plasma that is generated by the powered, lower electrode in the experiment. With even higher magnetic field (B \textgreater 2 Tesla), the particles become strongly confined to the mesh pattern with the particles constrained to a quasi-discreet motion that closely follows the mesh pattern. This presentation characterizes the structure of the potential energy well in which the dust particles are trapped through observation of particle motion and measurement of the thermal properties of the particles. [Preview Abstract] |
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PP10.00139: Ion-dust interactions at high magnetic field Spencer LeBlanc, Edward Thomas, Uwe Konopka, Robert Merlino, Marlene Rosenberg While complex plasma have been studied for over three decades, many of the mechanisms of interactions between ions and charged dust grains are not yet fully understood and remain a topic of intense study in the field. In particular, in the presence of a magnetic field, as the ions become magnetized, this can have a profound influence on the ion-dust interaction as it is anticipated that the Debye screen around the dust grain will become asymmetric with increasing magnetic field. In the Magnetized Dust Plasma Experiment (MDPX), recent studies have focused on the creation of probe-induced dust-free regions (i.e. voids) and characterizing the influence of the magnetic field on the void region. Other recent experiments focus on the role of ion-dust interaction in the formation of waves and studies of dust heating (with and without magnetic fields). [Preview Abstract] |
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PP10.00140: Evolution of self-organized poloidal dust rotation with discharge parameters P. K. Chattopadhyay, Sayak Bose, M. Kaur, J. Ghosh, D. Sharma, Y. C. Saxena Stationary self-organized, poloidally rotating and toroidally symmetric structure of mono-dispersed micro-particles are obtained in parallel plate DC glow discharge plasma with modified cathode geometry [1]. The evolution of the vortices with discharge parameters is presented. A transition from a filled-vortex (poloidal cross-section of the toroidal structure) to a vortex with void at the centre is observed with increase in neutral gas pressure accompanied by a decrease in vortex height from cathode surface. The variation of the velocity profile of the dust particles constituting the vortex is investigated using PIV analysis with discharge parameters. Interestingly, the velocity of the dust particles is observed to increase with an increase in neutral gas pressure. The observed experimental results and its causes are presented in details.\newline $[1]$Kaur et al., Phys. Plasmas 22, 033703 (2015). [Preview Abstract] |
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PP10.00141: Experimental Validation of an Electromagnet Thermal Design Methodology for Magnetized Dusty Plasma Research W. J. Birmingham, E. M. Bates, C. A. Romero-Talamás, W. F. Rivera An analytic thermal design method [1] developed to aid in the engineering design of Bitter-type magnets, as well as finite element calculations of heat transfer, are compared against experimental measurements of temperature evolution in a prototype magnet designed to operate continuously at 1 T fields while dissipating 9 kW of heat. The analytic thermal design method is used to explore a variety of configurations of cooling holes in the Bitter plates, including their geometry and radial placement. The prototype has diagnostic ports that can accommodate thermocouples, pressure sensors, and optical access to measure the water flow. We present temperature and pressure sensor data from the prototype compared to the analytic thermal model and finite element calculations. The data is being used to guide the design of a 10 T Bitter magnet capable of sustained fields of up to 10 T for at least 10 seconds, which will be used in dusty plasma experiments at the University of Maryland Baltimore County. Preliminary design plans and progress towards the construction of the 10 T electromagnet are also presented. \\ \,\,[1] W. J. Birmingham, E. M. Bates, and C. A. Romero-Talamás, J. Thermal Sci. Engr. Appl. 8, 021008 (2015) [Preview Abstract] |
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PP10.00142: Single-Camera Stereoscopy Setup to Visualize 3D Dusty Plasma Flows C. A. Romero-Talamas, T. Lemma, E. M. Bates, W. J. Birmingham, W. F. Rivera A setup to visualize and track individual particles in multi-layered dusty plasma flows is presented. The setup consists of a single camera with variable frame rate, and a pair of adjustable mirrors that project the same field of view from two different angles to the camera, allowing for three-dimensional tracking of particles. Flows are generated by inclining the plane in which the dust is levitated using a specially designed setup that allows for external motion control without compromising vacuum. Dust illumination is achieved with an optics arrangement that includes a Powell lens that creates a laser fan with adjustable thickness and with approximately constant intensity everywhere. Both the illumination and the stereoscopy setup allow for the camera to be placed at right angles with respect to the levitation plane, in preparation for magnetized dusty plasma experiments [C. A. Romero-Talamas, et al. IEEE T Plasma Sci 44, 535 (2016)] in which there will be no direct optical access to the levitation plane. Image data and analysis of unmagnetized dusty plasma flows acquired with this setup are presented. [Preview Abstract] |
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PP10.00143: BETA (Bitter Electromagnet Testing Apparatus) Design and Testing Evan Bates, William Birmingham, William Rivera, Carlos Romero-Talamas BETA is a 1T water cooled Bitter-type magnetic system that has been designed and constructed at the Dusty Plasma Laboratory of the University of Maryland, Baltimore County to serve as a prototype of a scaled 10T version. Currently the system is undergoing magnetic, thermal and mechanical testing to ensure safe operating conditions and to prove analytical design optimizations. These magnets will function as experimental tools for future dusty plasma based and collaborative experiments. An overview of design methods used for building a custom made Bitter magnet with user defined experimental constraints is reviewed. The three main design methods consist of minimizing the following: ohmic power, peak conductor temperatures, and stresses induced by Lorentz forces. We will also discuss the design of BETA which includes: the magnet core, pressure vessel, cooling system, power storage bank, high powered switching system, diagnostics with safety cutoff feedback, and data acquisition (DAQ)/magnet control \textit{Matlab} code. Furthermore, we present experimental data from diagnostics for validation of our analytical preliminary design methodologies and finite element analysis calculations. BETA will contribute to the knowledge necessary to finalize the 10 T magnet design. [Preview Abstract] |
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PP10.00144: Precursor solitons in a flowing complex (dusty) plasma Surabhi Jaiswal, Pintu Bandyopadhyay, Abhijit Sen We report the first experimental observation of precursor solitons in a flowing dusty plasma. The nonlinear solitary dust acoustic waves (DAWs) are excited by a supersonic mass flow of the dust particles passing over an electrostatic potential hill. In a frame where the fluid is stationary and the hill is moving the solitons propagate in the upstream direction while wake structures consisting of linear DAWs are seen to propagate in the downstream direction. The experiments have been carried out in a $\Pi $-shaped Dusty Plasma Experimental (DPEx) device where kaolin particles are immersed in a DC discharge argon plasma to form the dusty plasma and a floating wire mounted on the cathode creates a potential hill. The dust flow is induced by sudden changes in the hill height and the solitary structures are seen only for supersonic flows and up to an upper limit of the flow. A theoretical model description of the phenomenon will be provided and some practical implications of such precursor excitations for a charged object moving in a plasma will be discussed. [Preview Abstract] |
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PP10.00145: Accretion growth of water-ice grains in astrophysically-relevant dusty plasma experiment Kil-Byoung Chai, Ryan Marshall, Paul Bellan The grain growth process in the Caltech water-ice dusty plasma experiment has been studied using a high-speed camera equipped with a long-distance microscope lens. It is found that (i) the ice grain number density decreases four-fold as the average grain length increases from 20 to 80 um, (ii) the ice grain length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge so the agglomeration growth is prevented by their strong mutual repulsion. It is concluded that direct accretion of water molecules is in good agreement with the observed ice grain growth. The volumetric packing factor of the ice grains must be less than 0.25 in order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains; this conclusion is consistent with ice grain images showing a fractal character. [Preview Abstract] |
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PP10.00146: O-X mode conversion in a non-symmetric torus at electron cyclotron frequencies Harold Weitzner Earlier work on linear wave propagation over a symmetric background state , Phys. Plasmas 11, 866 (2004) is simplified and extended to non-symmetric equilibria. With the exception of one special case, which reduces to the case of a perpendicularly stratified medium, it is shown that mode conversion in symmetric or non-symmetric equilibria satisfies the same set of equations. An examination of the coupling of the geometrical ray optics solution to the mode conversion system provides a relatively simple and physical characterization of the incoming wave structure necessary to achieve effective mode conversion. Part of the work was done while visiting the Max=Planck-Insititute-for Plasmaphysics, Greifswald , Germany. its support is gratefully acknowledged. [Preview Abstract] |
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