Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session TP9: Poster Session VII: DIII-D I; Theory, Turbulence II, Non-neutral and Dusty Plasma II; Magneto Inertial Fusion; MFE Diagnostics & General Tokamak; Mini-conference: Dense Quantum Plasma Simulation |
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Room: Hall A |
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TP9.00001: DIII-D I |
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TP9.00002: Pedestal Plasma Control With Small 3D Magnetic Fields T.E. Evans Recent experiments on a variety of tokamaks have conclusively demonstrated that externally applied 3D magnetic fields can be used to control the confinement and stability of H-mode pedestal plasmas without destroying the edge transport barrier. These results have important practical implications and are of intrinsic scientific interest for understanding the physics of H-mode confinement and pedestal stability. For example, the applied fields predominantly act on the particle confinement with little effect on energy confinement. This is at odds with quasi-linear transport theory suggesting that either the induced pedestal magnetic topology differs from that observed in Ohmic plasmas or that physics other than parallel heat conduction along open stochastic field lines is dominate. Recent progress in our understanding of the pedestal plasma during the application of 3D magnetic fields will be discussed. In addition, implications of gaps in our ability to predict how these fields will affect the performance of plasmas with higher pedestal densities and temperatures such as those needed in ITER to achieve a fusion gain $Q_{DT} = 10$ will be presented. [Preview Abstract] |
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TP9.00003: Comparison of Plasma Response Model Predictions to Measurements in DIII-D RMP H-mode Discharges R.A. Moyer, J.H. Yu, D.M. Orlov, C. Chrobak, S. Mordijck, M.A. Van Zeeland, T.E. Evans, M.R. Wade, C.S. Chang, F. Waelbroeck, J.D. Callen Plasma response to resonant magnetic perturbations (RMPs) is important for predictive understanding of ELM suppression in ITER. Theoretical models predict that the RMP should only open islands on rational surfaces where the electron perpendicular velocity $\nu_{\perp e}\approx 0$ where $\nu_{\perp e}$ is the sum of the electron diamagnetic and $\vec{E}\times \vec{B}$ rotation. In the edge of low collisionality ITER-similar shape (ISS) ELMing \mbox{H-modes}, $\nu_{\perp e}\approx 0$ near the $q=8/3$ rational surface when the RMP is applied. The RMP modifies both the diamagnetic and $\vec{E}\times \vec{B}$ velocities; when the RMP suppresses ELMs, the $\nu_{\perp e}\approx 0$ point in the ELM-suppressed final state is at the $q=9/3$ surface. We investigate the correlation of $\nu_{\perp e}\approx 0$ with plasma and transport response at low and moderate collisionalities, and present the results of imaging of the plasma edge using beam emission, visible brehmsstrahlung, D$_\alpha$, and total visible light. [Preview Abstract] |
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TP9.00004: Metrics to Quantify Magnetic Field Stochasticity for DIII-D and ITER Discharges D.M. Orlov, S. Nogami, R.A. Moyer, T.E. Evans, M.J. Schaffer, N.M. Ferraro, E.A. Unterberg, A. Loarte, M.J. Lanctot, M.E. Fenstermacher Stochastic layers are created in tokamaks by adding small resonant magnetic perturbations (RMPs) to the equilibrium magnetic field using external coils. These stochastic fields are often quantified by the widely accepted Chirikov parameter. The Chirikov parameter was developed for a single toroidal mode, and becomes very complex and difficult to interpret when multiple toroidal harmonics are present. It can also be inapplicable for some codes. In this work, we present several metrics to quantify stochasticity, such as the vacuum island overlap width and the field line loss fraction, that have the advantage of automatic computation. We use these metrics to quantify stochasticity in vacuum and plasma response models to assess the impact of plasma response, to evaluate DIII-D RMP discharges, to improve the ELM suppression criterion, and to determine the optimum RMP coil currents and phasings. [Preview Abstract] |
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TP9.00005: ELM Size \& $\nu_{\perp e}\approx 0$ Location During RMP \mbox{H-mode} Plasmas in DIII-D M.E. Fenstermacher, R.A. Moyer, T.H. Osborne Previous studies [1,2] examined the correlation between vacuum island overlap region width and edge localized mode (ELM) size during $n=3$ resonant magnetic perturbations (RMPs) in DIII-D. For rotating H-mode plasmas it was proposed [3,4] that the resonant perturbation components would be screened by plasma response except at locations with the sum of the electron diamagnetic and $E\times B$ velocities, $\nu_{\perp e}=0$. One hypothesis for the mechanism of RMP ELM suppression is that the pedestal width is prevented from expanding to the peeling-ballooning instability boundary by plasma modes at a location where vacuum RMP fields penetrate. This would suggest that the $\nu_{\perp e}=0$ location would be closer to the plasma edge during ELM suppression than during ELM mitigation. This paper will examine the degree of correlation between $\nu_{\perp e}=0$ location and ELM size during RMP H-mode plasmas including those from the previous studies. \vskip3pt \noindent [1] M.E.\ Fenstermacher et~al., Phys.\ Plasmas {\bf 15} (2008) 056122.\par \noindent [2] M.E.\ Fenstermacher et~al., J.~Nucl.\ Mater.\ {\bf 390} (2009) 793.\par \noindent [3] M.~Heyn, et~al., Nucl.\ Fusion {\bf 48} (2008) 024005.\par \noindent [4] E.~Nardon, et~al., Nucl.\ Fusion {\bf 50} (2010) 034002. [Preview Abstract] |
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TP9.00006: Turbulence Dynamics During RMP-ELM Suppressed Discharges G.R. McKee, Z. Yan, O. Schmitz, R.J. Buttery, T.E. Evans, M.R. Wade, L. Schmitz, R.A. Moyer Long-wavelength density fluctuations in the plasma edge region ($0.75 < r/a < 1.0$) change markedly in response to applied resonant magnetic field perturbations, used to suppress ELMs. The RMP-enhanced fluctuations, measured with a 2D array of BES channels, have a radial correlation length of a few cm and span 50-400~kHz in frequency. Modulated RMPs are used to examine the fast temporal dynamics of the turbulence and related parameters. Inside of the pedestal ($0.8 < r/a < 0.9$), turbulence is found to change rapidly with the applied RMP, with a few ms response time, suggesting that enhanced turbulence may play a causative role in the observed increased particle and momentum transport. Fluctuations in the pedestal region exhibit a more complex response, initially decreasing with reduced RMP, but subsequently increasing as the pedestal pressure gradient increases. New measurements from upcoming experiments on the $q_{95}$ dependence of the turbulence and flow response to RMPs will also be presented. [Preview Abstract] |
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TP9.00007: Effect of Resonant Magnetic Perturbations on Fluctuations and Transport on DIII-D T.L. Rhodes, L. Zeng, E.J. Doyle, G. Wang, W.A. Peebles, L. Schmitz, J.C. Hillesheim, S. Mordijck, T.E. Evans, G.R. McKee, Z. Yan Resonant magnetic perturbations (RMPs) have been shown to suppress ELM activity during H-mode and so is a very attractive (but not well understood) technology for ITER and future burning plasmas. In a series of experiments conducted on DIII-D, RMPs are found to significantly affect fluctuations, flow, transport, and resulting profiles on the \mbox{DIII-D} tokamak. Intermediate-$k$ fluctuation levels ($1 \leq k\rho_s \leq 2$, measured by Doppler backscattering) and poloidal flow can increase in magnitude ($\tilde{n}/n$ increases of 20\%-30\% or larger) in the pedestal region during RMP. Linear growth rates from the trapped-gyro-Landau-fluid TGLF code indicate increased growth rates in this range of wavenumbers consistent with measurements. In addition, correlation electron cyclotron measurements of temperature fluctuations show a broadband increase during ELM suppressed RMP operation consistent with increased thermal transport. [Preview Abstract] |
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TP9.00008: RMP ELM Suppression with a Single Row of Coils in DIII-D J.S. deGrassie, R.J. Buttery, T.E. Evans, M.R. Wade, M.E. Fenstermacher, R.A. Moyer, D. Orlov, R. Nazikian, O. Schmitz ELM suppression with $n=3$ resonant magnetic perturbations (RMPs) has been obtained in DIII-D with a single row of coils, at one poloidal angle, but was investigated using only the same dominant window in $q_{95}$ as used for the standard two row suppression [1]. However, the single row imposes a richer density of spectral components as compared with the double row. Further experiments have been done with the single row to compare the efficacy of ELM suppression and the location and width of resonant windows in $q_{95}$ for suppression. We present calculations of the single row vacuum field resonances in $q_{95}$ and compare with experimental results. \vskip6pt \noindent [1] M.E. Fenstermacher et al., Nucl. Fusion {\bf 48}, 122001 (2008). [Preview Abstract] |
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TP9.00009: Interaction of NTM and RMP fields in DIII-D R. Nazikian, T.E. Evans, M.J. Schaffer, A.D. Turnbull Edge Localized Mode (ELM) suppression by external Resonant Magnetic Perturbations (RMPs) is sometimes accompanied by the growth of internal neoclassical tearing modes. Both Neoclassical Tearing Modes (NTMs) and RMP fields induce a density pump out effect in DIII-D. A question is whether there is a possible synergy between the externally applied RMP field and internal NTM field that could lead to enhanced stochasticity and/or ELM suppression in DIII-D plasmas. A large scalar database study did not reveal a significant correlation between the NTM level and the degree of density pump out observed during application of RMP fields, however individual discharges appear to show an effect. We will present vacuum field calculations of the superposition of modeled internal NTM fields and RMP fields for $n=2$ and $n=3$ perturbations in DIII-D in order to better understand the possible interaction of these two sources of magnetic perturbations. [Preview Abstract] |
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TP9.00010: Role of Magnetic Helicity in the Plasma Response to Non-axisymmetric Perturbations A.D. Turnbull, N.M. Ferraro, V.A. Izzo Plasma response to non-axisymmetric perturbations arising from external coils or linear instabilities can be treated as a dynamic stability problem using an extended MHD code or from a nearby perturbed equilibrium approach. The nearby equilibrium approach bypasses the detailed evolution and searches for the appropriate final state. However, there is no guarantee that the final state is the one among multiple states reached dynamically, or is even accessible. To assure final state accessibility, one needs to relate the 2D and nearby 3D system through a set of invariants or constraints. A suitable set of constraints may be obtained from considering the magnetic helicity, which is conserved exactly in ideal MHD but is broken at rational surfaces by non-ideal effects. Helicity has the advantage of a physical interpretation in terms of field line linkage that is conserved in ideal MHD but broken when the topology changes. The change can be calculated in principle from the topology changes and compared with solutions obtained from extended MHD calculations. [Preview Abstract] |
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TP9.00011: Experiments and ELM-Suppression in Double-Null \mbox{DIII-D} Plasmas E.A. Lazarus, T.E. Evans, M.E. Fenstermacher Experiments are underway on DIII-D to obtain ELM-suppression via resonant magnetic perturbations [1] in double-null (stellarator symmetric) configurations. While density pumpout was observed in these initial experiments, ELM suppression was not obtained. A previous attempt was unsuccessful. In this attempt we will investigate whether the difference in connection length between single and double null plays a critical role by varying the magnetic balance around a double-null configuration. Experimental results will be reported.\par \vskip8pt \noindent [1] T.E.~Evans, et al., Nature Physics {\bf 2}, 419 (2006). [Preview Abstract] |
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TP9.00012: Plasma Equilibrium Response to Slowly Rotating 3D Magnetic Perturbations in DIII-D RMP Experiments L.L. Lao, M.S. Chu, A.D. Turnbull, M.R. Wade, N.W. Ferraro, V.A. Izzo, E.A. Lazarus, W. Guo, Q. Ren, R. Srinivasan, Y.Q. Liu Slowly rotating non-axisymmetric magnetic perturbations have been routinely used in DIII-D experiments to study the plasma response to the applied perturbation fields. The slow changes in the perturbation amplitude allow the use of the DIII-D edge Thomson scattering measurements of electron temperature as an indicator to monitor the edge magnetic surface response in H-mode discharges. Although the applied perturbation fields are small, the edge magnetic surface responses can be large. For perturbations with $n=1$, a perturbation of 0.1\%-0.3\% of the poloidal equilibrium magnetic field can result in a 2\%-4\% change in the edge magnetic surface topology. The effects of the 3D perturbation fields on the equilibria with and without plasma response are being modeled using the 3D linear MHD code MARS-F, the 3D equlibrium codes VMEC and VMOM3D, and other MHD codes. Initial results indicate that plasma responses are important. Results will be presented. [Preview Abstract] |
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TP9.00013: ECE-Imaging of the H-mode Pedestal B.J. Tobias, R. Nazikian, C.W. Dormier, N.C. Luhmann, M.E. Austin ECE-Imaging has become a powerful diagnostic tool for optically thick core regions of tokamak plasmas, and a new synthetic diagnostic has now been applied to address questions of uniqueness in the interpretation of ECE-Imaging data from the plasma edge. Results pertaining to ELMs and externally applied 3D magnetic fields are presented herein. It has been shown that high pedestal pressure generally ensures adequate optical thickness very near the plasma edge, and that images from the pedestal and optically grey or thin regions beyond may be understood through a careful modeling of the interplay of emission and absorption along chords which exhibit short scale length inhomogeneities. A correlation analysis in the presence of MHD activity is consistent with kinetic modeling which predicts a spectral broadening of EC emission within the pedestal, accounting for anomalous emission that is routinely observed at frequencies well below the cold resonance frequency of the plasma edge. [Preview Abstract] |
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TP9.00014: Edge Soft X-Ray Imaging for Measurements of Magnetic Topology During 3-D Magnetic Perturbations M.W. Shafer, E.A. Unterberg, D.J. Battaglia, J.M. Canik, J.H. Harris, D.L. Hillis, R. Maingi, T.E. Evans A new tangential 2D soft x-ray imaging system (SXRIS) was recently installed on DIII-D to directly measure the edge island structure in the X-point region. Measurements of island structure are needed to understand the plasma response during the application of resonant magnetic perturbations (RMPs). Modeling of inverted images indicates integration times $\geq$1~ms with accurate equilibrium reconstruction are needed for small island ($\leq$3~cm) detection. The total signal-to-noise ratio is estimated to be $\geq$100, which provides enough sensitivity to extract the estimated 1\%-10\% island perturbations from the total SXR emissivity. First data from the diagnostic will be shown from DIII-D discharges with 3D magnetic perturbations applied. Initial image inversions are shown to provide estimates of the island structure in these discharges. This structure is compared to synthetic diagnostic estimates using modeled 3D SXR emissivity in L-mode and H-mode. [Preview Abstract] |
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TP9.00015: Role of Edge Turbulence and Flows in the Density Dependence of the L-H Transition Power Threshold on DIII-D G. Wang, T.L. Rhodes, W.A. Peebles, J.C. Hillesheim, E.J. Doyle, L. Schmitz, L. Zeng, M.E. Austin, Z. Yan, G.R. McKee, C.C. Petty, K.H. Burrell, J.C. DeBoo, W.M. Solomon The trigger mechanism of the L- to H-mode transition is not currently fully understood. Empirical scaling studies of the L-H transition power threshold have discovered global plasma parameter dependences, including a strong density dependence. The current work investigates the potential role of edge turbulence and flows in this density dependence by performing detailed measurements during a density scan experiment on DIII-D. Preliminary analysis indicates that the signatures of geodesic acoustic modes (GAMs) exist in both the perpendicular flow and electron temperature fluctuations ($\tilde{T}_e$) prior to the L-H transition. Both $\tilde{T}_e/T_e$ at the GAM frequency and $\tilde{T}_e/T_e$ of broadband fluctuations are observed to decrease with increasing density. Measurements of density turbulence, $E\times B$ flow, together with linear stability analysis will also be reported. [Preview Abstract] |
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TP9.00016: Testing the Paleoclassical Based Pedestal Model Against Measured DIII-D Pedestal Profiles S.P. Smith, R.J. Groebner, T.H. Osborne, A.W. Leonard, J.D. Callen Accurate prediction of kinetic profiles (densities and temperatures) in the pedestal is important in predicting the performance of future burning plasma experiments. A recently developed predictive model of the kinetic profiles includes the paleoclassical mechanism as the main, albeit minimum, cause of electron transport in the pedestal. The predictions of this model are compared to a database of measured DIII-D pedestal profiles to provide a quantitative test of the dominance of paleoclassical transport in the pedestal. The tests are performed at the symmetry point of the pedestal electron temperature profile (from a tanh fitting). The average ratio across the database of paleoclassical prediction to experimental measurement for the various quantities is: $\nabla T_e~ 1.1\pm 0.6$; $\nabla n_e/n_e~ 2.2\pm 0.9$. These results indicate that other processes besides paleoclassical are contributing to pedestal particle density transport. In probing the sensitivity of the temperature predictions to experimental inputs, it is found that the correlation of temperature prediction to measurement improves significantly by distributing the total power flow equally between the electron and ion channels. [Preview Abstract] |
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TP9.00017: Ion Orbit Loss and X-Loss Effects on the Interpretation of Transport in the Edge Pedestal W.M. Stacey Models have been developed for the calculation of i) standard ion orbit loss across the separatrix and of ii) X-loss of ions in the narrow, null-$B_\theta$ region extending into the plasma from the X-point in a divertor plasma, which are trapped poloidally while they $\nabla B$ drift radially outward through the X-point region (X-loss). Calculations of a \mbox{DIII-D} discharge indicate a significant non-diffusive transport of ion particles and ion energy in the edge pedestal due to these loss mechanisms. Taking this particle and energy loss into account when determining the conductive ion energy flux results in a significant reduction in the experimental thermal diffusivity interpreted from the measured temperature profile. [Preview Abstract] |
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TP9.00018: Numerical Investigation of Solving the Generalized Diffusion Equation in the Edge Pedestal with Extended Diffusion Theory Codes J.-P. Floyd, W.M. Stacey Radial and toroidal momentum balance requires the ion particle flux in the edge pedestal to satisfy a pinch-diffusion relation, $\Lambda = -D\nabla n+nV_r^{pinch}$, rather than the pure diffusion relation used to derive standard diffusion theory. Re-derivation of diffusion theory using the pinch-diffusion relation in the particle continuity equation yields a generalized diffusion equation [1] which, in principle, can be solved by modifying the standard diffusion theory methods and codes. We investigated this possibility using standard finite difference and Gauss reduction solution procedures for 1D diffusion theory to solve this equation. Analysis of the equation yields an expression for the numerical error of various finite-difference algorithms proportion to the square of the ratio of the mesh spacing to the characteristic scale length, $L \equiv \vert D_j/V_{rj}^{pinch}\vert$. The resulting implication is that smaller mesh spacing will be necessary in the edge pedestal where the inward pinch velocity is large, than is necessary for similar accuracy further inward where the pinch velocity diminishes. This was confirmed by numerical solution of the equation for a DIII-D shot.\\[4pt] [1]~W.M.~Stacey, Contrib.\ Phys.\ Plasmas {\bf 48}, 94 (2008). [Preview Abstract] |
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TP9.00019: QH-mode in Low Rotation, ITER-Similar Plasmas Using Static Non-axisymmetric Magnetic Fields A.M. Garofalo, K.H. Burrell, J.-K. Park, W.M. Solomon, M.E. Fenstermacher, M.J. Lanctot \mbox{DIII-D} experiments have shown that static 3D magnetic fields can be used to maintain the edge rotation shear required for ELM-stable operation in QH-mode even with zero-net torque from neutral beam injection (NBI). These results have been obtained in ITER-similar shape plasmas with ITER-level collisionality, normalized beta, and confinement quality. New experiments are planned to extend the previous results to conditions closer yet to those of ITER: 3D field application using coils external to the vessel, small co-$I_p$ NBI torque, and low $q_{95}\sim 3$. Results will be discussed. [Preview Abstract] |
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TP9.00020: Study of the Poloidal Variation of Edge Plasma Turbulence in QH-mode with PCI on DIII-D J.C. Rost, M. Porkolab, J.R. Dorris, A. Marinoni, K.H. Burrell The Phase Contrast Imaging (PCI) diagnostic has been used on DIII-D to measure plasma turbulence from 2 to 30 cm$^{-1}$ using three roughly vertical beam paths. Work here focuses on measurements of QH mode plasmas, with stationary plasma parameters and an outer gap scan that allowed the PCI to sample a range in poloidal angle and $k_r/k_\theta$. The results show the largest edge turbulence has $k_\theta\, \rho_i > 0.4$ and $f > 200$ kHz, consistent with the plasma velocity at the bottom of the $E_r$ well, and a radial coherence length much less than 1 cm. A sharp decrease in turbulence amplitude is seen between the midplane and $\mid\theta\mid = 20$ deg away from the X-point with no similar drop between the midplane and $\mid\theta\mid = 20$ deg toward the X-point. Another component to the turbulence is seen at roughly similar wavenumbers and $f<100$ kHz, consistent with the plasma velocity further inside the LCFS. [Preview Abstract] |
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TP9.00021: Turbulent SOL Transport in Limited Versus Diverted L mode Discharges in DIII-D D.L. Rudakov, J.A. Boedo, R.A. Moyer, R. Pitts, A.W. Leonard, P.C. Stangeby, J.G. Watkins Turbulent scrape-off layer (SOL) transport is measured near the outboard midplane of inner-wall limited (IWL) and lower single null (LSN) discharges on DIII-D using a reciprocating probe array. Scans of the plasma current ($q_{95}$), density, and heating power have been performed in both configurations. E-folding lengths for the SOL temperature and density in IWL configuration are on average larger than those in LSN configuration by a factor of 2.1-2.5 [1]. Overall turbulent cross-field transport is comparable near the separatrix of both configurations at similar discharge parameters but falls off much faster with radius in LSN configuration. The intermittent component of the transport associated with the radial motion of plasma blobs is up to an order of magnitude larger in the far SOL of IWL configuration compared to LSN. Blob radial velocity tends to increase with decreasing plasma current (increasing connection length).\par \vskip6pt \noindent [1]~D.L.\ Rudakov, et~al., J.~Nucl.\ Mater., in press. [Preview Abstract] |
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TP9.00022: Effect of Divertor Shaping on Plasma Performance and Divertor Power Loading on DIII-D T.W. Petrie, J.R. Ferron, A.W. Hyatt, A.W. Leonard, T.C. Luce, P.A. Politzer, C.T. Holcomb, M.E. Fenstermacher, D.N. Hill, C.J. Lasnier, J.G. Watkins Future generation tokamaks that produce significant fusion power will require a means of reducing damaging levels of both transient (ELM-induced) and steady power loads at the divertor targets. We report here on experiments at DIII-D that examine how certain variations in the divertor geometry affect both the capability to reduce heat flux at the outer divertor target and the H-mode quality of the main plasma. We focus specifically on documenting how core and divertor plasmas respond to changes in both the parallel path length of the outer divertor leg and the radial location of the outer divertor strike point, both in ``standard" ELMing H-mode (without gas puffing) and in radiating divertor. We also investigate how these geometric changes may mitigate transient ELM-induced heat fluxes. [Preview Abstract] |
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TP9.00023: An Isolated Divertor for Reactor Scale Tokamaks A.W. Leonard, M.A. Mahdavi, T.W. Petrie A divertor configuration is proposed to address the requirements of a reactor scale tokamak. A reactor divertor must dissipate heat flux over a wide area and reduce erosion to a tolerable level for component lifetime, while simultaneously allowing for a high performance core plasma at a density compatible with efficient current drive. A configuration with the divertor strike point at large major radius, similar to a ``Super-X" geometry reduces $q_{||}$ with magnetic flux expansion from the X-point to the divertor target. This may allow for containment of a cold dense detached plasma in the divertor region while maintaining a high pressure pedestal. Divertor baffling may also be designed for enhanced containment of the radiating divertor plasma. This configuration has the potential to provide heat flux control at a lower core density compared to a standard configuration. Initial experiments on DIII-D exploring this concept will be described. Concepts of how this approach may be pursued in DIII-D will also be presented. [Preview Abstract] |
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TP9.00024: Detailed OEDGE Modeling of Core-Pedestal Fueling in DIII-D J.D. Elder, P.C. Stangeby, A.W. Leonard, M.E. Fenstermacher, J.A. Boedo, D.L. Rudakov, B.D. Bray, N.H. Brooks, J.G. Watkins, E.A. Unterberg The OEDGE code is used to model the deuterium neutral density and ionization distribution inside the separatrix for an attached L-mode SAPP discharge and an attached ELMy H-mode discharge. The background plasma solution is determined by empirical plasma reconstruction matching as many diagnostic measurements as possible. Recycling fluxes are obtained from measurements by Langmuir probes and spectroscopic measurements of D$_\alpha$. The relative importance of wall, divertor and recombination sources to core and pedestal fueling are assessed. In addition, the sensitivity of the ionization source location to the details of the plasma solution in the divertor is examined. Several models for plasma-wall contact are used to estimate the strength of the wall recycling source. In the L-mode case, ionization profiles peak at the flux surface $\sim$1.3~cm inboard of the separatrix (mapped to the outer midplane). [Preview Abstract] |
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TP9.00025: Comparison of Sheath Power Transmission Factor for Neutral Beam Injection and Electron Cyclotron Heated Discharges in DIII-D D.C. Donovan, D.A. Buchenauer, J.G. Watkins, A.W. Leonard, C.J. Lasnier, P.C. Stangeby The sheath power transmission factor (SPTF) is examined in DIII-D with a new IR camera, a more thermally robust Langmuir probe array, fast thermocouples, and a unique probe configuration on the Divertor Materials Evaluation System (DiMES). Past data collected from the fixed Langmuir Probes and Infrared Camera on DIII-D have indicated a SPTF near 1 at the strike point. Theory indicates that the SPTF should be approximately 7 and cannot be less than 5. SPTF values are calculated using independent measurements from the IR camera and fast thermocouples. Experiments have been performed with varying levels of electron cyclotron heating and neutral beam power. The ECH power does not involve fast ions, so the SPTF can be calculated and compared to previous experiments to determine the extent to which fast ions may be influencing the SPTF measurements, and potentially offer insight into the disagreement with the theory. [Preview Abstract] |
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TP9.00026: Rotation in the Plasma Flow Frame of Marginal Neoclassical Tearing Mode Islands in DIII-D and NSTX R.J. La Haye, R.J. Buttery, S.P. Gerhardt, S.A. Sabbagh Small island effects inhibit the pervasive occurrence of neoclassical tearing modes. $m/n=2/1$ or 3/1 islands are reduced (by decreasing beta and thus the destabilizing bootstrap current density) to the self-stabilization size (``marginal point") in DIII-D and NSTX [1]. Non-zero island propagation in the plasma flow frame can produce a stabilizing polarization current provided it occurs in the direction of (but does not exceed) the ion diamagnetic drift [2]. This ``polarization threshold" naturally scales as a characteristic island size of several times the ion banana width, which is consistent with experiment. Comparison of measurements in \mbox{DIII-D} and NSTX discharges of similar cross-section (but different aspect ratio) with polarization current theory will be presented.\par \vskip6pt \noindent [1] R.J. La~Haye, et al., Proc.\ 38th EPS Conf.\ on Plasma Phys., Strasbourg, France, 2011, P2.088.\par \noindent [2] K.~Imada and H.R.\ Wilson, Proc.\ 38th EPS Conf.\ on Plasma Phys., Strasbourg, France, 2011, O3.116. [Preview Abstract] |
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TP9.00027: Measurements and interpretation of hard x-ray emission from runaway electrons in DIII-D A.N. James, E.M. Hollmann, V.A. Izzo, G.R. Tynan, J.H. Yu, M.E. Austin, N. Commaux, T.C. Jernigan, N.W. Eidietis, T.E. Evans, D.A. Humphreys, A.W. Hyatt, R.J. La Haye, E.J. Strait, J.C. Wesley The spatial distribution of runaway electron (RE) strikes to the wall during argon pellet initiated rapid shutdown of divertor or limiter plasma discharges in DIII-D is studied using an array of hard x-ray (HXR) scintillators. HXR emission from MeV level REs generated during the argon pellet injection is observed during the thermal quench (TQ) in divertor discharges from REs lost into the divertor. This prompt TQ loss is reduced in limiter discharges, suggesting improved TQ confinement of REs in this configuration. In the plateau phase, toroidally symmetric HXR emission from remaining confined REs is seen. Transient HXR bursts during this time suggest a possible instability. Eventually, abrupt final loss of remaining RE current occurs, with a spatio-temporal evolution that suggests the development of a kink instability. [Preview Abstract] |
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TP9.00028: Off-Axis-Fishbone Mode and Its Relevancy to the RWM Onsets M. Okabayashi, W.W. Heidbrink, Y. In, G. Matsunaga, M. Takechi, E.J. Strait, G.L. Jackson, R.J. La Haye, P.E. Sieck, M.J. Lanctot, J.M. Hanson In neutral beam injection heated plasmas with beta above the no-wall limit of the external kink and central safety factor $q(0)>1$, bursting off-axis fishbone modes (OFM) are often observed to trigger the resistive wall mode (RWM) in DIII-D. One of the relevant features of the OFM is the mode distortion in time on magnetics and ECE, as the mode amplitude increases. The distortion is peaked with the maximum mode amplitude. The mode then decays faster than the initial mode growth rate, which is not seen in classical fishbone modes. Based on the poloidal mode structure, a hypothesis is proposed that the distortion is related to the stable branch of external kink mode and the sinusoidal component is EP-driven branch. The relevancy to the RWM onset will be discussed from the view point of RWM avoidance and suppression. [Preview Abstract] |
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TP9.00029: Stability Analysis of Resistive Wall Mode in Rotating High-beta Plasmas in DIII-D V.A. Svidzinski, Y. In, J.S. Kim, M.S. Chu, Y.Q. Liu Stability of resistive wall modes (RWM) in rotating high beta DIII-D discharges is analyzed using the MARS-F code. The modes are calculated in axisymmetric toroidal equilibrium using the MHD plasma model with kinetic damping effects. RWM are analyzed for different spacing between the resistive wall and the plasma boundary and for different toroidal rotation profiles. Sensitivity study of the mode's stability on the plasma edge $q$-profile is made by varying both the edge current profile and the proximity of the plasma boundary to the real X-point geometry. The importance of the edge modeling on accurate RWM stability analysis is revisited. Scans of the mode's growth rate and frequency are made in these settings, and the mode's structure is explored. Quasilinear toroidal torque driven by $j\times B$ force due to current and magnetic field perturbations in the RWM is estimated and compared with the experimental estimate of the total toroidal torque on plasma. The dependencies of the RWM growth rate and frequency on the stability and torque parameters are presented. [Preview Abstract] |
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TP9.00030: Improved Error Field Correction in High Performance Plasmas Y. In, M. Okabayashi, G.L. Jackson, R.J. La Haye, P.E. Sieck, E.J. Strait, J.M. Hanson, H. Reimerdes Accurate error field correction (EFC) is highly desirable for high performance plasmas (e.g. steady-state, high-$\beta$ plasmas). Feedback-controlled ``dynamic error field correction'' (DEFC) helps us not only monitor the plasma response to non-axisymmetric error fields but also determine a better EFC waveform. In recent high-$\beta$ experiment, we confirmed that the use of ``revised'' EFC - in which the EFC waveform is pre-programmed to repeat the feedback output of a previous discharge - helped sustain the high-$\beta$ phase longer than otherwise possible. This experiment used DIII-D's C-coils, similar to ITER's external EFC coils. Additional iteration of the DEFC will allow us to asymptotically find the ``ideal'' EFC waveform, achieving higher-$\beta$ well above the $n=1$ no-wall stability limit. The combination of both internal and external coils in DIII-D, which would mimic the eddy current pattern in an ideal conducting wall, is expected to deliver substantially improved EFC. [Preview Abstract] |
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TP9.00031: Error Field Measurements Using the Torque on a Magnetic Island E.J. Strait, R.J. Buttery, A.M. Garofalo, R.J. La Haye, M.J. Schaffer, P.E. Sieck, F.A.G. Volpe, J.M. Hanson The toroidal position of a static $n=1$ magnetic island is determined by a balance between torques acting on the island. These include electromagnetic torques due to non-axisymmetric magnetic fields from external sources, as well as a possible viscous torque associated with plasma rotation. The amplitude and toroidal phase of an unknown $n=1$ error field can be inferred from analysis of the island position as an applied $n=1$ field is varied. In principle, the measurement can be accomplished in a single discharge. The results of error field measurements based on island torque balance in DIII-D will be compared to the standard method using mode-onset thresholds. [Preview Abstract] |
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TP9.00032: Hybrid-Like Discharges With 2/1 Flux-Pumping Due to ELM-NTM Coupling in DIII-D J.D. King, C.J. Lasnier, M.J. Lanctot, M.A. Makowski, C.T. Holcomb, S.L. Allen, W.H. Meyer, R.J. La Haye, C.C. Petty, T.H. Osborne, R.J. Groebner, T.C. Luce, F. Volpe, M.E. Austin, E.C. Morse Edge localized mode (ELM)-neoclassical tearing mode (NTM) coupling pumps poloidal flux from the core to the edge in hybrid discharges, contributing to flattening of the safety factor profile and avoidance of sawteeth. Direct motional Stark effect diagnostic analysis of internal magnetic field pitch angles show 2/1 NTMs exhibit stronger magnetic flux-pumping than typical hybrids, albeit at lower beta. This 2/1 flux-pumping is present during partial electron cyclotron current drive NTM suppression. This finding may lead to an alternative discharge with normalized fusion performance exceeding that required for $Q_{fus}=10$ operation in ITER. The strength of flux-pumping increases with beta and proximity of the NTM to the ELMing pedestal. Individual ELM-NTM coupling events are successfully modeled using the modified Rutherford equation (MRE). [Preview Abstract] |
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TP9.00033: New Plasma Discharge Development Tools for the DIII-D Plasma Control System A.S. Welander, N.W. Eidietis, D.A. Humphreys, A.W. Hyatt, J.A. Leuer, M.L. Walker A new set of discharge design tools has been implemented under the GA Tokamak System Toolbox (TokSys) [1]. A new equilibrium design tool enables development of target equilibria, and upgraded simulation tools enhance testing of new control algorithms for devices that share the DIII-D Plasma Control System (including DIII-D, NSTX, EAST, KSTAR and others). Such tools will be needed for high power devices such as ITER, which require extensive commissioning of discharges to minimize disruptions and maximize the scientific return. Control verification by simulation will enable ITER to focus on exploring the unknown while minimizing risks from the known. The {\em DIII-D simulation simserver} is a comprehensive simulation of the tokamak including power supplies, conductors, plasma, diagnostics, and actuators, which can be connected to the actual control system. It has been used extensively to test implementations and study multi-algorithm integrated control performance in DIII-D and other devices.\par \vskip6pt \noindent [1] D.A.\ Humphreys, et al., Nucl.\ Fusion {\bf 47} (2007) 943. [Preview Abstract] |
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TP9.00034: Robust Control of the Spatial Current Profile in the DIII-D Tokamak J. Barton, E. Schuster, M.L. Walker, D.A. Humphreys Advanced tokamak operating scenarios, characterized by large noninductively driven plasma currents, typically require active regulation of a specific current density profile. Non-model-based control of the $q$ profile has been tested at DIII-D. However, some present limitations of the controller motivate the design of a model-based controller that accounts for the dynamics of the whole $q$ profile in response to the control actuators. A control-oriented model of the current profile evolution in DIII-D was recently developed and used to design feedforward control schemes. In order to reject the effects of external disturbances to the system, a feedback control input needs to be added to the feedforward input. In this work, we report on the design of a robust feedback controller, on the implementation of the combined model-based feedforward + feedback controller in the DIII-D Plasma Control System, and on the experimental validation of the combined controller in the DIII-D tokamak. [Preview Abstract] |
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TP9.00035: Backstepping Control of the Current Profile in the DIII-D Tokamak M.D. Boyer, J. Barton, E. Schuster, M.L. Walker, D.A. Humphreys Control of the spatial profile of the plasma current in tokamaks has been demonstrated to be a key condition for advanced scenarios with improved confinement and steady-state operation. Non-model-based controllers tested at DIII-D have shown limitations, motivating the design of model-based controllers that account for the dynamics of the $q$ profile. In this work, we utilize a control-oriented model of the current profile evolution in DIII-D to design a backstepping boundary control law for regulating the current profile around a desired feed-forward trajectory. The control scheme makes use of the total plasma current, total power, and line averaged density as actuators. A simulation study is done to test the control law against uncertainties in the model parameters and initial conditions, as well as input disturbances. Finally, the implementation of the controller in the DIII-D plasma control system is discussed and experimental results are presented. [Preview Abstract] |
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TP9.00036: Robust Control of the Toroidal Rotation and Safety Factor Profiles in the DIII-D Tokamak W. Shi, W. Wehner, E. Schuster, M.L. Walker, D.A. Humphreys Because of the coupling between the different magnetic and kinetic plasma profiles, multi-input-multi-output (MIMO) model-based controllers are introduced to regulate the plasma rotation and safety factor profiles around particular target profiles. The approach is based on linear two-time-scale models identified from experimental data. The inputs are separated into slow and fast components by a low-pass filter that is incorporated into the overall plant. Then a singular value decomposition (SVD) of the plasma model is carried out to decouple the system and identify the most relevant control channels. Finally, the $H_\infty$ technique is used to determine a stabilizing feedback controller that minimizes the reference tracking errors and rejects disturbances with minimal control energy. Computer simulation results illustrate the performance of the robust profile controller, showing potential for improved performance. Experimental results in DIII-D are also reported. [Preview Abstract] |
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TP9.00037: Data-driven Modeling of the Toroidal Rotation and Safety Factor Profile Dynamics for AT Scenarios in \mbox{DIII-D} W. Wehner, W. Shi, C. Xu, E. Schuster, D. Moreau, D. Mazon, M.L. Walker, D.A. Humphreys, Y. In First-principle predictive models based on flux averaged transport equations often yield complex expressions not suitable for real-time control. As an alternative to first-principle modeling, data-driven modeling techniques involving system identification have the potential to obtain low-complexity, dynamic models without the need for ad hoc assumptions. This work focuses on the evolution of the toroidal rotation and safety factor profiles in response to magnetic, heating and current-drive systems. Experiments are conducted during the current flattop, in which the actuators are modulated in open-loop to obtain data for the model identification. The plasma profiles are discretized in the spatial coordinate by Galerkin projection. Then a linear model is generated by the prediction error method to relate the rotation and safety factor profiles to the actuators according to a least squares fit. [Preview Abstract] |
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TP9.00038: Commissioning of the off-axis neutral beamline on the DIII-D tokamak J.T. Scoville, C.J. Murphy, R.M. Hong One of the four neutral beam injection systems on DIII-D has recently been rebuilt to allow off-axis injection. A system of hydraulically operated pistons was fit to the beamline to allow tilting up to an angle of 16.5 deg, enabling injection of 5 MW of neutral beam power up to 40 cm below the plasma centroid. Off-axis injection required rebuilding the two ion sources to produce more strongly focused and narrower beams that can inject the power at an angle through the port box of the vacuum vessel. The internal beamline collimation system was replaced with a new system compatible with the stronger focused sources. An extensive alignment process was carried out for all beamline internal components and ion sources. Extensive analysis has been carried out using thermocouple and calorimetry data to document the performance of the collimation system, leading to an extension of the allowable pulse length. We present a description of the modifications that were made to the ion sources and collimation systems and the results of heating and performance studies for the off-axis beam injection system. [Preview Abstract] |
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TP9.00039: THEORY, TURBULENCE II, NON-NEUTRAL AND DUSTY PLASMA II |
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TP9.00040: Predictions and Explanations for the I-Regime: Relevant Heavy Particle Modes* Tianchun Zhou, Bruno Coppi The excitation of a new heavy particle mode [1,2] at the plasma edge is considered as the signature of the I-Regime [3]. The outward impurity transport produced by this mode is consistent with the observation that impurities are expelled from the main body of the plasma. The predicted mode phase velocity, in the electron diamagnetic velocity direction, has been confirmed by the experiments [4]. The plasma ``spontaneous rotation'' in the direction of the ion diamagnetic velocity is also consistent with the mode phase velocity direction, according to the ``Accretion Theory'' [5] of this phenomenon. Another feature of the mode consistent with the theory is that the I-Regime exhibits a temperature knee at the plasma edge but not that of the plasma density as the mode excitation involves relatively large values of $\eta_i$ ($\eta_i\equiv d\ln T_i/d \ln n_i$). The plasma current density appearing in the saturation stage of the mode evolution is associated with the observed poloidal magnetic field fluctuations accompanying the density fluctuations. The theoretical implications of the significant electron temperature fluctuations observed are discussed. *Sponsored in part by the U.S. DOE. \\[0pt] [1] B. Coppi, et al., Phys. Rev. Lett. {\bf{17}}, 377 (1966). [2] B. Coppi and T. Zhou, MIT(LNS) Report HEP 09/04 (2009), published in Phys. Lett. A. (2011). [3] A. Hubbard, et al., Phys. Plas. {\bf{18}}, 056115 (2011). [4] I. Cziegler, Private communication (2010). [5] B. Coppi, Nucl. Fusion {\bf{42}} 1 (2002). [Preview Abstract] |
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TP9.00041: Quasi-Coherent Modes as Localized Viscous Ballooning Modes* B. Basu, B. Coppi, T. Zhou The quasi-coherent mode associated with the enhanced-$D_\alpha$ H-Regime produced by the Alcator C-Mod machine has been observed [1] as being well localized in the deep $E_r$ well at the edge of the plasma column and propagating in the ion diamagnetic direction in the plasma reference frame. This is explained as resulting from the excitation of a ``viscous ballooning mode'' with frequency close to $\omega_{di}$, where $\omega_{di}\equiv - k_\phi c/e B_\theta n dp_i/dr$ is the ion diamagnetic frequency. The deep $E_r$ well is shown to be responsible for the mode localization. For this we start our analysis from the model dispersion relation [2, 3], $\omega+i\gamma_\mu \omega-\omega_{di}=- \gamma^2_{RT}+ k^2_{stp} v^2_A 1+i D_m k^2_{\perp} \omega-\omega_{*e}$, in a plane geometry, where $\gamma_\mu$ is proportional to the ion transverse viscosity, $\gamma_{RT}$ is the Rayleigh-Taylor growth rate simulating the effects of the magnetic field line curvature, $v_A$ is the Alfv\'{e}n velocity, $D_m\equiv c^2\eta/4\pi$, $\eta$ is the plasma resistivity and $\omega_{*e}\equiv cT_e/e B r_0 d \ln n/dr$ is the electron drift wave frequency. *Sponsored in part by the U. S. DOE. \\[4pt] [1] I. Cziegler, Private communication (2010).\\[0pt] [2] G. Ara, et al., \textit{Annals Phys}. {\bf 112}, 443 (1978).\\[0pt] [3] B. Coppi, et al., \textit{Annals Phys.} {\bf 121}, 1 (1979). [Preview Abstract] |
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TP9.00042: Nonlinear plasma-wave interactions during ion cyclotron wave heating Nong Xiang, John R. Cary, C.Y. Gan Ion cyclotron resonant frequency (ICRF) heating has been proved to be an efficient method to heat ions in fusion devices. For present and future ICRF heating experiments, the input power is usually over mega-watt. As a result of such high input power, nonlinear wave-particle interaction may play a very important role in the process of ion heating. To fully account for the plasma-wave interaction physics, computer simulations are performed using the PIC code implemented in VORPAL framework (C. Nieter and J. R.Cary, J. Comp. Phys. 196, 448 (2004)). It is found that near the lower hybrid resonance(LHR), the parametric decay into an ion wave and a quasi-mode could be triggered as the incident wave frequency is larger than twice the ion cyclotron frequency. Ions are thus heated near the LHR. In addition, ion heating at half-harmonic cyclotron frequencies is also observed, and the heating mechanism is discussed. [Preview Abstract] |
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TP9.00043: Transport Barrier Restoration due to Particle Orbit Gyroaveraging Julio Martinell, Diego del-Castillo-Negrete Test particle $E\times B$ transport in a tokamak can be studied using a Hamiltonian approach in which the effect of drift waves acts as a perturbation on the background flow. For a zonal flow the nonmonotonic velocity profile gives rise to a nontwist Hamiltonian that has a robust central transport barrier at about the same position of the velocity maximum. This barrier can break for high enough level of the perturbation leading to global chaos of particle motion. When a gyroaveraging due to finite Larmor radius (FLR) is performed, several novel effects are observed: Bifurcations leading to separatrix reconnection appear at large FLR; Destroyed barriers can be restored for increasing FLR; Threshold radius for barrier destruction depends on perturbation strength and the threshold curve has a fractal structure. This curve is obtained for cases with both heteroclinic and homoclinic topologies. The effect of the changing barrier structure is studied for an ensemble of particles with a thermal distribution of Larmor radii. [Preview Abstract] |
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TP9.00044: Study of nonlinear dynamics among zonal flow, GAM, and turbulence on the HL-2A strongly heated L-mode plasmas Min Xu, George Tynan, Patrick Diamond, Christopher Holland, Peter Manz, Nicolas Fedorczak, Saikat Chakraborty Thakur, Jonathan Yu, Kaijun Zhao, Jiaqi Dong, Jun Cheng Experiments to directly measure the nonlinear energy exchange and interaction among turbulence, zonal flows, and GAMs were carried out on the HL-2A tokamak at the Southwestern Institute of Physics (SWIP) in China. The turbulent kinetic energy was clearly shown to transfer from turbulence with intermediate frequencies (20-60 kHz) to zonal flows (0-5 kHz) and GAMs ($\sim $10 kHz) and to turbulent fluctuations with high frequencies ($>$60 kHz), which also indicates that zonal flows and GAMs compete for turbulent energy as the heating power increased. The turbulent Reynolds stress $\left\langle {\tilde {v}_r \tilde {v}_{pol} } \right\rangle $ profiles were shown consistent with the time-averaged poloidal velocity profiles inferred by time-delay estimation. Other microphysical quantities together with the macro statistical results form a consistent picture that turbulent vortices mediate the energy, momentum, particle transport, and the formation of sheared flows in the edge of plasmas. [Preview Abstract] |
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TP9.00045: ABSTRACT WITHDRAWN |
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TP9.00046: Scaling Theory for Energy Distribution in Dissipated Mode Space P.W. Terry, D.R. Hatch, J.-H. Kim Recent gyrokinetic simulations reveal that ITG turbulence excites a large number of damped modes in the perpendicular wavenumber range of the instability. In this wavenumber range, these dissipative structures achieve equipartition of amplitude attenuation rate across the modes of a proper orthogonal decomposition (POD). Equipartition is equivalent to a scaling theory in mode space, with a power law energy distribution having POD damping rate as the scaling variable. This surprising manifestation of symmetry in a non-inertial turbulent energy transfer range is rooted in mode coupling. Energy from unstable modes is directly and simultaneously transferred to all damped modes in a parallel fashion, enabling a scaling theory even in a dissipation range. In contrast, the hydrodynamic cascade couples modes serially, requiring zero dissipation to achieve scaling and power law behavior. A mode coupling theory shows that all modes are in a dissipative balance, but that the few hundred modes with weakest damping, spill some energy into a wavenumber cascade to small perpendicular scale. [Preview Abstract] |
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TP9.00047: Role of stable modes in zonal flow regulated ITG turbulence K.D. Makwana, P.W. Terry, J.-H. Kim Stable modes are a ubiquitous mechanism for saturation of plasma turbulence. ITG turbulence is well known to be regulated by zonal flows. This work looks at the role of stable modes in ITG turbulence. First, a fluid model is investigated. By analyzing the energy dynamics in a simulation it is shown that the linear instability is saturated by nonlinear coupling with stable modes and zonal flows. It is shown that the zonal flow acts as a facilitator for energy transfer from unstable to stable modes. Three wave phase mixing is studied for triads involving different combinations of unstable, stable and zonal modes. It is found that triads involving one unstable, one stable and one zonal mode show the maximum phase matching. This explains the dominance of zonal modes ($k_{y}=0$ modes) in the nonlinear coupling. Amongst zonal modes, the dominance of zonal flows can be explained by looking at the strength of the nonlinear coupling coefficients. Gyrokinetic simulation results showing the nonlinear transfer of energy involving zonal flows will also be presented. [Preview Abstract] |
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TP9.00048: Parallel closures in the collisionless limit Jeong-Young Ji, Eric Held We have obtained closures in the collisionless limit by solving the drift kinetic equation (DKE) using the Fourier transform along the magnetic field line. When zeroth-order parallel gradients in the Maxwellian exist, integral parallel closures in the collisionless limit are obtained by solving the zeroth order DKE. When flux surfaces exist, however, the parallel gradients are first order and nontrivial closures are obtained by solving the first order DKE, which includes perpendicular gradients of the Maxwellian distribution. The closures are expressed in terms of perpendicular gradients of temperature and parallel derivatives of temperature and flow velocity. Modifications to existing neoclassical transport theory for the banana regime which uses a flux surface average will be discussed. [Preview Abstract] |
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TP9.00049: Energy-Conservation Constraint in Stochastic Structural Stability Theory J.B. Parker, J.A. Krommes The stochastic structural stability theory (SSST) is a technique, originally developed in the neutral-fluids community,\footnote{B. F. Farrell and P. J. Ioannou, J.\ Atmos.\ Sci.\ \textbf{60}, 2101 (2003)} that can be used for understanding the statistical behavior of drift-wave--zonal-flow (DW--ZF) systems. The technique involves parameterizing the nonlinear DW--DW interactions as white noise while keeping the correct behavior of the DW--ZF interactions. The SSST equations describe the dynamics of the zonal flow and the quadratic statistics of the drift waves, which are then simulated numerically. The SSST has been applied to the Modified Hasegawa--Wakatani system recently,\footnote{B. F. Farrell and P. J. Ioannou, Phys.Plasmas \textbf{16}, 112903 (2009).} and it has been demonstrated that the SSST equations exhibit ZF emergence. However, that work did not perform the DW--DW parameterization in a manner consistent with energy conservation. Here we apply the SSST to the Modified Hasegawa--Wakatani system while demanding that conservation of energy be satisfied. Preliminary results on how the energy-conservation constraint affects the dynamics of the SSST system will be reported. [Preview Abstract] |
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TP9.00050: Recurrence quantification analysis of simulations of near-marginal dissipative-trapped-electron-mode turbulence Raul Sanchez, Jose Angel Mier, Luis Garcia, David Newman Recurrence quantification analysis (RQA) is a powerful tool to study dynamical systems and to help us understand and characterize the underlying physics when a transition occurs. The idea is based on the fact that, given sufficiently long time lapses, every dynamical system returns to states arbitrarily close to those it had in the past. This fundamental property of dynamical systems is called recurrence. In this contribution, we analyze, using the RQA technique, the recurrence properties of time series obtained from a series of numerical simulations of a dissipative-trapped-electron-mode (DTEM) turbulence model in near-marginal conditions where a transition in the nature of turbulent transport was observed as a subdominant diffusive channel strength is increased from zero [J. A. Mier et al., \emph{Phys. Plasmas} \textbf{15}, 112301 (2008)] . The results of the RQA analysis clearly show that the degree of determinism and complexity of the dynamics closely follows the degree of non-diffusiveness in the observed transport. [Preview Abstract] |
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TP9.00051: Diamagnetic drifts and turbulent transport: non-diffusive effects David E. Newman, Raul Sanchez, Debasmita Samaddar Recently, much progress has been made toward understanding the fundamental dynamics of turbulent transport in the presence of sheared flows. The insights have come from following Lagrangian trajectories using both gyrokinetic simulations of ITG turbulence [R. Sanchez et al, Phys. Rev. Lett. 101, 205002 (2008)] and fluid models of drift-wave turbulence [D.E. Newman et al, Proc. 35 EPS Conf. (2008)]. In this work we examine the impact of simple diamagnetic drifts on the dynamics of the transport using numerical simulations of 2D-turbulence in slab geometry with the BETA code. By itself, a diamagnetic drift velocity can have a significant an impact on the transport dynamics both with and across flow. However, when coupled with a sheared flow, additional dynamics are observed which could lead to interesting profile control tools if separately controlled. These new dynamics are in part the result of coherent structure formation localized to particular regions of the flows. The transport dynamics and their possible uses will be discussed. [Preview Abstract] |
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TP9.00052: Implementation of 2D domain decomposition in the UCAN gyrokinetic PIC code for non-diffusive transport studies in tokamaks Jean-Noel Leboeuf, Viktor Decyk, David E. Newman, Raul Sanchez The massively parallel, nonlinear, 3D, toroidal, electrostatic, gyrokinetic, PIC, Cartesian geometry UCAN code, with particle ions and adiabatic electrons, has been successfully exercised to identify non-diffusive transport characteristics in DIII-D-like discharges. The limitation in applying UCAN to larger scale discharges is the 1D domain decomposition in the toroidal (or z-) direction for massively parallel implementation using MPI which has restricted the calculations to a few hundred ion Larmor radii per minor radius. To exceed these sizes, we have implemented 2D domain decomposition in UCAN with the addition of the y-direction to the processor mix. This has been facilitated by use of relevant components in the 2D domain decomposed PLIB2 library of field and particle management routines developed for UCLA's UPIC framework of conventional PIC codes. The gyro-averaging in gyrokinetic codes has necessitated the use of replicated arrays for efficient charge accumulation. Tests have shown that the 2D domain-decomposed UCAN2 code reproduces the original 1D domain results within round-off. Production calculations are ongoing to determine the optimal processor mix for UCAN2. [Preview Abstract] |
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TP9.00053: Toward the application of the Parareal algorithm to 5D gyrokinetic plasma turbulence Jose M. Reynolds Barredo, David E. Newman, Raul Sanchez, Debasmita Samaddar, Lee A. Berry, Wael Elwasif It has been shown that fully-developed plasma turbulence can be successfully parallelized in time using the Parareal algorithm [D. Samaddar et al, J. Comp. Phys. 229, 6558 (2010)]. Here, a detailed analysis of the error evolution is done in order to obtain a deeper understanding of the mechanisms of convergence. The analysis is done for slab 2D plasma drift wave turbulence in the case of long wavelengths [D.E. Newman et al, Phys. Fluids B 4, 599 (1992)] for two types of non-linearities: ExB and polarization. Some suggestions are put forward in order to understand why ExB nonlinearity has better convergence rate than the polarization one. The same technique is applied to gyrokinetic plasma turbulence simulated with GENE code [F. Jenko et al, Phys. Plasmas 7, 1904 (2000)] in order to study the applicability of Parareal to this kind of turbulence simulation, and first results of Gene simulations using the recently released IPS event based platform of Parareal are shown. [Preview Abstract] |
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TP9.00054: Non-diffusive turbulent transport of impurities in fusion plasmas S. Futatani, D. del-Castillo-Negrete, X. Garbet, S. Benkadda, N. Dubuit Non-diffusive impurity transport in tokamak plasmas is investigated using a three-dimensional fluid global code. The impurities are treated as an active scalar and the self-consistent interaction between the impurity concentration and the turbulence is studied. It is shown that the impurity concentration triggers intermittency that gives rise to a transition from Gaussian to stretched-exponential probability density functions of the ${\bf E} \times {\bf B}$ fluctuations. Proper orthogonal decomposition methods are used to unveil the multiscale spatio-temporal dynamics of the impurity concentration, the turbulence fluctuations, and the ion thermal flux. Spatio-temporal flux-gradient cross correlation functions are used to characterize the level of non-diffusive transport in the system. A novel diagnostic based on the use of Fourier-Laplace transforms is proposed and implemented to characterize the level of non-locality in space and time. [Preview Abstract] |
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TP9.00055: Lagrangian statistics and flow topology in resistive drift-wave turbulence B. Kadoch, D. del-Castillo-Negrete, W.J.T. Bos, K. Schneider A study of the relationship between Lagrangian statistics and flow topology in drift-wave turbulence is presented. The topology is characterized using the Weiss criterion, which provides a conceptually simple tool to partition the flow into topologically different regions. The turbulence model is based on the Hasegawa-Wakatani system, which is one of the simplest models of cross-field transport by electrostatic drift waves. The study is carried out for different values of the adiabaticity parameter $c$, in the Hasegawa-Wakatani model. In the $c >> 1$ adiabatic limit, the model reduces to a Hasegawa-Mima type equation, and for $c <<1$, the system reduces to a Navier-Stokes type equation. We follow a Lagrangian approach and perform the statistics on ensembles of tracers. The probability density functions (pdfs) of residence time in the topologically different regions are computed using the Lagrangian Weiss field, i.e., the Weiss field along the particles trajectories. In elliptic and hyperbolic regions, the pdfs of the residence time have self-similar algebraic decaying tails. In contrast, in the intermediate regions the pdf has exponential decaying tails. The conditional pdfs (with respect to the flow topology) of the Lagrangian velocity and acceleration are also computed. [Preview Abstract] |
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TP9.00056: Two-fluid analysis of the geodesic acoustic mode (GAM) in tokamaks Akira Hirose, Chijin Xaio, Yue Ding, Jan Weiland In the original prediction of electrostatic geodesic acoustic mode (GAM) in toroidal plasmas [1] based on single fluid MHD, the current perturbation along the magnetic field was not considered and incomplete charge neutrality condition was imposed. In low frequency modes in tokamaks, the parallel current is largely carried by electrons as shown in [2]. In electrostatic cases, the electron current is large and short-circuits the perpendicular electric field associated with the GAM. Consequence is that there is no electrostatic GAM in collisionless tokamak discharges. However, in collisional plasma as in edge region, the electron current is retarded and electrostatic dissipative GAM appears. The finding in this study clearly suggests that the GAM is an edge phenomenon confined in a narrow layer at the edge. In collisionless case, the GAM merely increases the Alfven frequency. \\[4pt] [1] N. Winsor et al., Phys. Fluids \textbf{11}, 2448 (1968).\\[0pt] [2] H. Nordman, et al., Phys. Fluids B \textbf{5}, 3469 (1993); A. Hirose, et al., Phys. Rev. Lett. \textbf{72}, 3993 (1994). [Preview Abstract] |
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TP9.00057: Collective particle kinetics in the lower hybrid drift instability Richard Dendy, James Cook, Sandra Chapman We study the coupled evolution of energetic minority ions, background majority ions, electrons, and electromagnetic fields in magnetised plasma undergoing the lower hybrid drift instability. The evolving distribution of a drifting ring-beam population of energetic ions is simulated using a particle-in-cell code, fully kinetic for all species, with one spatial and three velocity space co-ordinates. Bulk plasma parameters approximate tokamak core conditions, in a scenario motivated by observations of ion cyclotron emission and relevant to alpha channelling (Cook et al, PRL 105, 25503 (2010)). Resonant energy transfer occurs at the two gyrophase angles where the speed of an energetic ion on its cyclotron orbit matches the phase velocity of the lower hybrid wave along the simulation domain. Electron space-charge oscillations determine the wavelength of the propagating wave. This governs the bunching of energetic ions, in physical space and gyrophase angle (Cook et al, PPCF 53, 074019 (2011)), as they drive the instability. [Preview Abstract] |
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TP9.00058: Radial drift to diffusion ratio in asymmetry-induced transport D.L. Eggleston We are using a single-particle code with collisional effects to study asymmetry-induced radial transport in a non-neutral plasma. By following the time variation of the mean change and mean square change in radial position we can obtain the radial drift velocity $v_{\scriptscriptstyle D}$ and the diffusion coefficient $D$ as defined by the flux equation $\Gamma = - D\nabla n +nv_{\scriptscriptstyle D}$. As previously noted,\footnote{D.L. Eggleston, Bull. Am. Phys. Soc. {\bf 55}, 74 (2010).} for asymmetries of the form $\phi_1(r)\cos{(kz)}\cos {(\omega t - l\theta)}$ and low collisionality there are two sources for the observed transport: resonant particle transport and transport produced by axially trapped particles. This latter type, which is often dominant, occurs near radii where $\omega=l\omega_R$, where $\omega_R$ is the azimuthal rotation frequency. For resonant particle transport, we find that $v_ {\scriptscriptstyle D}$ and $D$ satisfy $v_{\scriptscriptstyle D}/D=r\omega_c(l\omega_{\scriptscriptstyle R}-\omega)/l\overline {v}^2$, a generalization of the Einstein relation for $\omega\ne 0$. For the transport produced by axially trapped particles, however, $v_{\scriptscriptstyle D}/D$ is significantly larger than this prediction. In constrast, our experiment\footnote {D.L. Eggleston, Phys. Plasmas {\bf 17}, 042304 (2010).} indicates that $v_{\scriptscriptstyle D}/D$ is significantly {\em smaller} than predicted. We suspect that these discrepancies indicate the need for a non-local determination of $v_{\scriptscriptstyle D}$ and $D$. [Preview Abstract] |
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TP9.00059: The non-neutral ion trap at Brigham Young University Bryan Peterson, Chad Williams, William Hall, Grant Hart We have constructed a non-neutral ion trap with the eventual goal of measuring the rate of decay of singly-ionized $^7$Be. Since $^7$Be decays exclusively by electron capture a Malmberg-Penning trap provides an ideal environment for this measurement due to the near absence of free electrons. We will use the FTICR (Fourier Transform Ion Cyclotron Resonance) mass spectrometry technique to measure the ratio of $^7$Be to $^7$Li to determine the decay rate. We are using an enriched boron carbide target (77.7\% $^{10}$B, 2.3\% $^{11}$B, 20\% $^{12}$C) to provide the ions for the test plasma. This allows us to test the FTICR technique through the presence of three different ions at very different concentrations. We will discuss the current status of the experiment. [Preview Abstract] |
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TP9.00060: A 1-D axisymmetric code to simulate oscillations in the vicinity of the cyclotron frequency Grant W. Hart, Ross L. Spencer, E. David Ballard We have created a new one-dimensional PIC code to model axisymmetric oscillations in the vicinity of the cyclotron frequency in a non-neutral plasma. This improves our ability to model the axisymmetric Bernstein modes compared to our previous 2D code because we can more fully populate the smaller phase space and therefore reduce the particle noise in the simulation. It runs significantly faster and has much smaller memory requirements. Problems at the origin are reduced by using $x=r^2$ as the variable and $\theta$ velocities are taken into account by using conservation of cannonical angular momentum. Using a kinetic-theory model we have analyzed the theory of these modes in a rigid-rotor thermal equilibrium. We find that in the constant-density region the perturbed velocity is proportional to J$_{1}(k r)$, with discrete values of $k$. There are two distinct modes with separate $\omega$s for each $k$. The value of $k$ is determined by the boundary condition that the perturbed pressure be zero at the boundary of the plasma. This value cannot be calculated directly from the theory because the theory breaks down in the region where the density goes to zero in the edge. The simulation also sees two families of modes at different frequencies for the same initial velocity perturbation in the plasma. The two modes behave similarly in the bulk of the plasma but behave differently in the edge. [Preview Abstract] |
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TP9.00061: Cavity Cooling of Ultracold Highly-Magnetized, One-Component Electron Plasmas Alex Povilus, Steven Chapman, Marcelo Baquero-Ruiz, Joel Fajans In order to optimize the efficency of recombination processes, it is of interest, particularly for the antihydrogen trapping groups at CERN, to have large numbers ($10^6$ to $10^8$) of ultracold ($\leq 10 \rm{K}$) electrons and positrons available without the presence of a background buffer gas. To realize this, we utilize the fact that particles in a Penning-Malmberg style trap are typically confined in a 0.8T-3.0T homogeneous background magnetic field and thus can radiate away energy through cycltron motion. Choosing a high-Q trapping cavity with geometry such that electromagnetic cavity modes match the cyclotron frequency of the individual leptons, we can strongly couple the particles to the thermal bath of the cavity walls allowing for quick, passive cooling of the plasma. Here we present the model for this cooling mechanism and a description of the new electron plasma experiment that is being commissioned to study this effect. [Preview Abstract] |
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TP9.00062: Vlasov Simulation of Mixing in Antihydrogen Formation Chukman So, Joel Fajans, Lazar Friedland, Jonathan Wurtele In the ALPHA apparatus, low temperature antiprotons (\={p}) and positrons ($e^{+}$) are prepared adjacent to each other in a nested Penning trap. To create trappable antihydrogen (\={H}), the two species must be mixed such that some resultant \={H} atoms have sub-Kelvin kinetic energy. A new simulation has been developed to study and optimize the autoresonant mixing [1,2] in ALPHA. The \={p} dynamics are governed by their own self- field, the $e^{+}$ plasma field, and the external fields. The $e^{+}$'s are handled quasi-statically with a Poisson-Boltzmann solver. \={p}'s are handled by multiple time dependent 1D Vlasov-Poisson solvers, each representing a radial slice of the plasma. The 1D simulatiuons couple through the 2D Poisson equation. We neglect radial transport due to the strong solenoidal field. The advantages and disadvantages of different descretization schemes, comparisons of simulation with experiment, and techniques for optimizing mixing, will be presented \\[4pt] [1] Andresen, G. B., \textit{et al} (ALPHA), Phys. Rev. Lett. \textbf{106}, 025002 (2011). \newline [2] Andresen, G. B., \textit{et al} (ALPHA), Phys. Lett. B \textbf{695}, 95-104 (2011). [Preview Abstract] |
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TP9.00063: New results on the autoresonant-spectrometric study of the vacuum system in ALPHA Marcelo Baquero-Ruiz Studying the residual gas composition in a cryogenic vacuum system is of particular interest to the ALPHA collaboration in our efforts to trap and study antihydrogen. A method based on autoresonant ion extraction from an electrostatic potential well was developed and tested during last year's experimental run in ALPHA, and a first set of results showed the feasability of such an implementation. New experimental data, as well as new computer simulations, have enabled us to have a better understanding of this spectrometric system, and to gain knowledge about the vacuum conditions in our apparatus. [Preview Abstract] |
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TP9.00064: Evaporative cooling of antimatter plasmas for the production of trappable antihydrogen Daniel Miranda Silveira Confinement of antihydrogen is likely required to achieve the goal of a sensitive test of CPT symmetry. Antihydrogen is produced from trapped plasmas of antiprotons and positrons and the chance of capturing it in a superposed magnetic trap can be maximized by the use of active cooling techniques for the charged plasmas. Forced evaporative cooling is a powerful technique for reducing the temperature of a sample bound to a potential well by removing the most energetic particles. Evaporation of antiproton plasmas held in Penning traps was pioneered by the ALPHA collaboration: temperatures as low as 9 K were obtained for samples containing initially 50,000 particles. More recently, evaporation was successfully applied to larger samples of positrons. The application of this technique to both species was instrumental in the recent demonstration of antihydrogen confinement. We describe our implementation of evaporation and its relevance for the observation of antihydrogen trapping. We present a model for the dynamics of evaporation as well as a discussion on the possible limits of the technique. [Preview Abstract] |
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TP9.00065: An Experimental Study of Waves in a Toroidal Electron Plasma M.R. Stoneking, F. Choudhury, J.W. Darrell, S.A. Exarhos, A.H. Wright Electron plasma is confined using a purely toroidal magnetic field ($R_{o}=$ 18 cm, $B <$ 550 G) for times ($\sim $1 s) that are much longer than any of the dynamical timescales of the system. Wave dynamics are compared for two experimental regimes: 1) a toroidal arc (or bent Penning-Malmberg trap) and 2) a fully toroidal trap in which the no electrostatic fields are used for confinement. Damping of the $m$=1 ($k$=0) diocotron mode is explored to assess the extent to which rotational and/or magnetic pumping transport mechanisms are operative. The frequency of the $m$=2 ($k$=0) diocotron mode is used to directly measure the transport rate and determine its scaling with control parameters. Resonant standing wave plasma modes ($m=$0) are excited in order to determine the Trivelpiece-Gould dispersion relation and identify toroidal and thermal effects. [Preview Abstract] |
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TP9.00066: Pure electron plasmas confined in a stellarator without internal objects Thomas Sunn Pedersen, Xabier Sarasola, Eric Winkler, Paul W. Brenner The Columbia Non-neutral Torus (CNT) is a simple stellarator built to investigate confinement and dynamics of non-neutral plasmas. One major goal of the experiment is to provide the necessary scientific basis for an electron-positron plasma experiment. Since such a plasma must be devoid of internal material objects (in order to avoid rapid positron annihilation on these objects), it has been a goal of CNT to create pure electron plasmas without internal objects, so that these could serve as a target for positron injection. After several years of development, plasmas surviving for more than 50 msec after removal of all internal objects have now been successfully created and measured. The confinement time is in this case very sensitively dependent on the neutral pressure, and is significantly shorter than for plasmas with internal objects, contrary to initial expectations. An ionization avalanche of the background neutrals may be responsible for the observed behavior. Plans for the positron-electron torus (PET) project are now under development and will be discussed. [Preview Abstract] |
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TP9.00067: Initial results on positron confinement in a magnetospheric configuration Haruhiko Saitoh, Zensho Yoshida, Yoshihisa Yano, Junji Morikawa Creation of positron-electron plasma in a laboratory is an interesting and challenging subject, which may open many scientific applications. Although single-component plasma is stably confined in linear traps, for example Penning-Malmberg trap, it is not straightforward to simultaneously confine electrons and positrons as plasma. Toroidal geometries have advantages for solving this problem. For this purpose, studies on toroidal non-neutral plasma have been conducted in the levitated magnetospheric configuration, RT-1. Stable confinement and self-organization of toroidal non-neutral plasma was realized in RT-1; rigid-rotating pure electron plasma is confined for more than 300s [Z. Yoshida et al., PRL 104, 235004 (2010)]. As the initial step toward the formation of magnetospheric antimatter plasmas, we installed a 1MBq Na-22 radiation source in RT-1. Annihilation gamma-rays were observed by a NaI(TI) scintillator detector, for the estimation of basic injection and confinement properties of positrons in the magnetospheric configuration. Numerical analysis of positron orbits in RT-1 and the initial experimental results will be presented. [Preview Abstract] |
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TP9.00068: Spin-dependent excitation of plasma modes in non-neutral ion plasmas Brian C. Sawyer, Joe W. Britton, John J. Bollinger We report on a new technique for exciting and sensitively detecting plasma modes in small, cold non-neutral ion plasmas. The technique uses an optical dipole force generated from laser beams to excite plasma modes. By making the force \mbox{spin- dependent} (i.e. depend on the internal state of the atomic ion) very small mode excitations ($<$ 100 nm) can be detected through spin-motion entanglement. Even when the optical dipole force is homogeneous throughout the plasma, short wavelength modes on the order of the interparticle spacing can in principle be excited and detected through the spin dependence of the force. We use this technique to study the drumhead modes of single plane triangular arrays of a few hundred Be$^{+}$ ions. Spin-dependent mode excitation is interesting in this system because it provides a means of engineering an Ising interaction on a 2-D triangular lattice.\footnote{Porras and Cirac, PRL {\bf 92}, 207901 (2004)} For the case of an \mbox {anti-ferromagnetic} interaction, this system exhibits spin frustration on a scale that is at present computationally intractable. [Preview Abstract] |
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TP9.00069: ABSTRACT WITHDRAWN |
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TP9.00070: Influence of Monomer Shape on Aggregates Jonathan Perry, Kevin Bombardier, Lorin Matthews, Truell Hyde Agglomeration of dust particles is the initial step in protoplanetary formation, with the precursors to planetesimals believed to form through the collisions of micron and submicron sized dust particles. Grains immersed in a plasma environment, as found in the neighborhood of a protostar, acquire a charge on their surface. The distribution of this charge on the surfaces of the particles impacts the morphology of the aggregates formed during collisions, which in turn influences the evolution of the dust cloud within the plasma. Recently, it has been shown that the shape of the individual dust grains can lead to widely varying morphologies of aggregate structures during collisions. This study seeks to extend this work by examining the morphologies of aggregates employing various monomer shapes as precursors and grown under generic astrophysical plasma parameters. [Preview Abstract] |
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TP9.00071: Phase Transitions in a Capacitively Coupled Dusty Plasma with Conducting Dust Jorge Carmona-Reyes, Lorin Matthews, Truell Hyde Complex plasma is present in a variety of environments including planetary rings, cometary tails, interplanetary clouds and semiconductor manufacturing and fusion environments. Understanding the physics behind such complex plasmas, particularly those comprised of conducting dust, is not well understood. In this work, a GEC reference cell is employed to examine the translational and orientational order of conducting dust contained within crystal lattice structures formed in a complex plasma. The Pair Correlation function, bond orientation function and Voronoi and polygon construction diagrams are used to measure dislocations and disclinations, yielding a quantitative measure of the overall phase of the structure. The role this phase transition process plays in the melting of conducting and non-conducting 2D structures will be discussed. [Preview Abstract] |
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TP9.00072: Interaction of Charged Aggregates in a GEC rf Reference Cell Kristen Deline, Brandon Doyle, Jorge Carmona Reyes, Lorin Matthews, Truell Hyde Dust aggregates are formed in a laboratory plasma as monodisperse spheres are accelerated in a self-excited dust density wave. Interactions between pairs of aggregates allow their charge, mass, and gas drag to be inferred. The asymmetric charge on the aggregates causes them to rotate as they interact with each other. Through these interactions, the charge and dipole moment can be estimated and compared to numerical models. [Preview Abstract] |
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TP9.00073: Dust acoustic wave growth measured in a drifting, moderately coupled, quiescent dusty plasma J.R. Heinrich, S.H. Kim, J.R. Meyer, R.L. Merlino By introducing a grid with a variable bias potential far from the anode of a dc-glow discharge device we developed a technique to produce a drifting dusty plasma. The biased mesh trapped a secondary dust cloud that was released when the grid was returned to its floating potential. The secondary dust suspension then drifted toward the anode, and when it reached a certain distance from the grid, dust acoustic waves (DAW) spontaneously appeared in the suspension. The DAWs began growing at the location where the ion drift velocity was presumably high enough to excite the ion-dust streaming instability. The observed DAWs grew from thermal density fluctuations in a dust cloud that was large enough to support many wavelengths. The amplitude of the DAWs were measured over time to obtain the growth rate. As the wave growth saturated, a transition from linear to nonlinear waves was observed. The measured wave frequencies, wavelengths and growth rates are compared with theoretical values obtained from both fluid and kinetic theory. [Preview Abstract] |
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TP9.00074: Faraday cup measurements of the charge on dust grains in magnetized Q machine plasma S.H. Kim, J.R. Heinrich, M. Miller, R.L. Merlino We have installed a Faraday cup (FC) detector to measure the charge on individual dust grains falling through a Q machine plasma. The Q machine plasma consists of singly-charged K ions and electrons confined by a solenoidal magnetic field with variable strength up to 0.4 T. The plasma is nearly fully ionized (background neutral pressure $\sim $ 10$^{-6}$ Torr), with plasma densities in the range of 10$^{15}$ m$^{-3}$, and electron and ion temperatures, T$_{e} \quad \approx $ T$_{i} \quad \approx $ 0.2 eV. Initial measurements were made using hollow glass microspheres with sizes in the range of 33 to 44 microns. The microparticles get charged as they pass through the plasma and fall into the Faraday cup where the charge is measured. We will report results of our preliminary experiments on the charging of dust in a plasma with a large concentration of negative ions. In future experiments we plan to investigate the effects of magnetic fields and neutral collisions on dust charging. [Preview Abstract] |
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TP9.00075: Observation of the Rayleigh-Taylor instability in a dusty plasma K.A. Pacha, R.L. Merlino, J.R. Heinrich, S.H. Kim Lord Rayleigh showed that the interface between two fluids of different densities, with the dense fluid above a fluid of lesser density, is unstable to the growth of downward moving irregularities which develop into finger-like structures. Taylor showed that this situation is equivalent to one in which a lighter fluid is accelerated into a heavier fluid. We have observed a Taylor-type instability in a dusty plasma formed in a dc-glow discharge in argon at P = 13 Pa. The glow discharge is formed using a 4 cm diameter anode disk biased at 300 V with respect to the walls of a vacuum chamber. An axial magnetic field $\sim $30 mT confines the glow to a cylindrical region protruding outward from the anode. Micron size spherical iron particles are incorporated into the discharge from a floating tray located below the anode. The conical dust suspension is separated into a region of high dust density near the anode and a low density region farther from the anode. Periodically, the boundary of the high density region is locally perturbed by a pressure disturbance from the low density region. The surface irregularity grows rapidly, forming a bubble and spike, classic signatures of the Rayleigh-Taylor instability. The instability is studied with laser light scattering and video imaging. [Preview Abstract] |
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TP9.00076: The 3MV Hypervelocity Dust Accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies A. Shu, A. Collette, K. Drake, M. Horanyi, S. Kempf, T. Munsat, P. Northway, S. Robertson, Z. Sternovsky, E. Thomas, E. Gruen, R. Srama Micrometeorite impacts and dusty plasma phenomena can be found in a wide variety of subjects. In many extraplanetary systems, such as in deep space and on airless bodies such as asteroids or the moon, dusty plasmas play a large role in the basic scientific evolution of the environment. Dust can also be captured and studied in \textit{dust astronomy} in order to better understand the evolution of our universe, similarly to how photons are used in traditional astronomy. At the Colorado Center for Lunar Dust and Atmospheric Studies, we have developed a 3MV hypervelocity dust accelerator in order to study these and other applications of dust and dusty plasmas. This facility is capable of accelerating micron sized dust particles up to 10's of km/s. In addition to this we have several vacuum chambers used for dusty plasma experiments. The large Lunar Environment Impact Laboratory (LEIL) test chamber will be used to study dust levitation, space weathering, and lunar exosphere evolution. A smaller ultrahigh vacuum chamber will be used to detect neutral species in micrometeorite impact ejecta and detect and analyze impact flashes. In addition to this work, graphite tokamak wall tile material will be placed into the beam path to determine damage characteristics from dust in fusion systems. [Preview Abstract] |
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TP9.00077: MAGNETO INERTIAL FUSION |
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TP9.00078: Simulated Spectral and Imaging Diagnostics for the Plasma Liner Experiment Igor Golovkin, Joseph J. MacFarlane, Pamela Woodruff, Dale Welch, Carsten Thoma, Nichelle Bruner, Scott C. Hsu, Tom Awe, F. Douglas Witherspoon, John Thompson, I. Nick Bogatu Imploding plasma liner formation using merging plasma jets will be tested on the Plasma Liner Experiment (PLX) at LANL. Several hydrodynamics and particle-in-cell codes (in particular, LSP) have been used to model the experiments. LSP is a hybrid particle-in-cell (PIC) code widely used to model various plasmas. We present the recent enhancements to a multi-dimensional collisional-radiative spectral analysis code, SPECT3D. It is designed to post-process the results of LSP or hydrodynamics codes and simulate experimentally observable spectra and images. This capability is important for successful planning and analysis of the PLX experiments. We will also discuss the models for computing detailed opacity and equation-of state data used in plasma dynamics simulations. This work is supported by the U.S. Department of Energy. [Preview Abstract] |
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TP9.00079: Overview of the Plasma Liner Experiment (PLX) S.C. Hsu, F.D. Witherspoon, J.T. Cassibry, M.A. Gilmore The Plasma Liner Experiment (PLX) is a multi-institutional collaboration that is exploring and demonstrating the formation of imploding spherical plasma liners to reach peak pressures exceeding 0.1 Mbar upon stagnation. The liners will be formed via the merging of 30 dense high Mach number plasma jets ($n\sim 10^{17}$~cm$^{-3}$, $M\sim 10$--35, $v\sim 50$~km/s, $r_{jet}\sim 2.5$~cm) in a spherically convergent geometry. We are aiming for two follow-on applications if this work is successful: (1)~assembling repetitive, macroscopic (cm and $\mu$s scale) plasmas suitable for fundamental HEDLP scientific studies and (2)~a standoff driver for magneto-inertial fusion. This is a staged project where scientific issues will be studied first at modest stored energies ($\sim 300$~kJ) before attempting to reach HED- relevant pressures (requiring $\sim 1.5$~MJ)\@. This poster provides an overview of the project's status/plans and emphasizes the progress made in the past year: completion of phase one facility and diagnostic construction, progress in numerical simulations, and initial experiments on single jet propagation and two jet merging. Finally, we describe cosmically-relevant collisionless shock experiments based on the head-on collision of two lower density but higher velocity plasma jets. [Preview Abstract] |
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TP9.00080: Hybrid Algorithms for Modeling Plasma Jet Transport and Merging Nichelle Bruner, Carsten Thoma, Robert Clark, Dale Welch New algorithms have been developed which enable more stable and accurate modeling of high energy density (HED) plasmas. These algorithms have been incorporated in a hybrid particle framework within the fully electromagnetic, implicit particle-in-cell (PIC) code {\sc Lsp}. The hybrid framework combines a treatment of thermal plasma species governed by fluid equations of motion with more energetic, non-Maxwellian particle species treated fully kinetically. The hybrid PIC approach enables modeling of the dynamics of HED plasmas which are inaccessible in a magnetohydrodynamic code, such as kinetic instabilities, turbulence, finite mean-free-path effects, charge separation, complex ion orbits, and strong Hall physics. The new algorithms include a stabilizing remap technique for kinetic particles, a charge-conserving fluid algorithm, and a treatment for multiple-ionization states, and an equation-of-state (EOS) formalism. The improved model is used to simulate HED plasma jet transport and merging under conditions expected for the upcoming Plasma Liner Experiment (PLX) at Los Alamos National Laboratory. For this configuration, the kinetic treatment is required to accurately model dynamics during jet interpenetration. [Preview Abstract] |
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TP9.00081: Magnetized Target Fusion: Improving the plasma target T. Intrator Magneto Inertial Fusion (MIF) inertial adiabatic compression of a plasma fuel target takes advantage of embedded magnetic field to reduce thermal conduction and enhance alpha-particle heating. Magnetized Target Fusion (MTF) is a subset of MIF, requiring target plasma formation plus ejection into a solid flux conserving compressor shell or liner that implodes and compresses a plasma target. The liner has much larger mass than the compressed fuel, which increases the dwell time because it scales as the square root of the total mass. It appears possible to exceed the typical figure of merit eta*G $>$ 10 which is the product of (high) driver efficiency eta and (small) fusion gain G. We describe our efforts to improve the plasma target lifetime by using plasma guns. We also show recent data including experimental engineering test shots in a collaboration with Kirtland Air Force Research Laboratory to realize a physics demonstration of MTF. [Preview Abstract] |
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TP9.00082: Ion Kinetic Effects in Hybrid-PIC Simulations of Merging Plasma Jets Carsten Thoma, Nichelle Bruner, Robert Clark, Dale Welch, Joseph MacFarlane, Igor Golovkin Merging plasma jets will be used to form imploding plasma liners for generating HED plasma and as a standoff driver for magneto- inertial fusion. In the upcoming Plasma Liner Experiment (PLX) at Los Alamos National Laboratory a spherical array of 30 plasma jets generated by compact accelerators will be merged. We present simulation results of plasma jets in the PLX parameter regime ($n_i \sim 10^{17}$ cm$^ {-3}$, $T_e$, $T_i \sim 1$ eV) using the Hybrid particle-in-cell (PIC) code LSP. Electron macroparticles are treated as Lagrangian fluid elements while ion macroparticles may be treated either as a fluid or a kinetic species. The kinetic approach for ions captures non-maxwellian behavior and finite mean-free-path effects such as inter- penetration in jet merging. We present results for acceleration, transport, and merging of argon plasma jets, and compare the results for simulations with fluid and kinetic ions. [Preview Abstract] |
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TP9.00083: High Speed Argon Plasma Jet Merging Studies In Support of PLX Andrew Case, Sarah Messer, Samuel Brockington, Lin Chun Wu, Ray Elton, Douglas Witherspoon Formation of an imploding plasma liner for the Plasma Liner Experiment (PLX) requires individual plasma jets to merge into a uniform shell of plasma converging on the target region. Understanding dynamics of the merging process requires knowledge of the plasma phenomena involved. We present here results from the study of the merging of two and three plasma jets in two dimensional (coplanar) and three dimensional geometry. The experiments were performed using HyperV Technologies Corp. one centimeter MiniRailguns using a preionized Argon plasma armature on a vacuum chamber designed to partially reproduce the port geometry of the PLX vacuum chamber. Diagnostics include fast imaging, spectroscopy, interferometry, deflectometry, fast pressure probes, B-dot probes, and high speed spatially resolved photodiodes, permitting measurements of plasma density, temperature, velocity, stagnation pressure, magnetic field, and density gradients. These experimental results are compared with simulation results from the LSP 3D hybrid PIC code. [Preview Abstract] |
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TP9.00084: Construction of the Plasma Liner Experiment (PLX) C.S. Adams, T.J. Awe, J.P. Dunn, S.C. Hsu, J.S. Davis, D.S. Hanna, J.A. Schwartz, S. Brockington, D. van Doren, F.D. Witherspoon, E.C. Merritt, A.G. Lynn, M.A. Gilmore The Plasma Liner Experiment (PLX) will investigate the behavior and interaction of spherically convergent plasma jets in forming imploding spherical plasma liners for HED and MIF-relevant studies. Numerous hardware systems have been assembled for the new PLX facility at Los Alamos National Laboratory to prepare for first plasma. A three meter diameter spherical vacuum tank is coupled to an oil-free vacuum pump system reaching sub-$10^{-6}$~torr pressures on the first pump-down. A modular, distributed, and portable 60~kV pulsed-power system has been constructed for initial experiments on single jet propagation and two jet merging, with each plasma gun source having 70~kJ of stored energy. In addition, a capacitor test stand has been constructed in order to test each of the 180 required capacitors to the expected operational voltage. Finally, the experiment will be controlled via FPGA/LabView to interact with numerous custom-built pieces of electronics for interlock, control, triggering, and data acquisition. [Preview Abstract] |
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TP9.00085: Plasma-Jet Convergence Calculations John Santarius Converging plasma jets may be able to reach the regime of high energy density plasmas (HEDP, $\sim10^{11}\ J\ m^{-3}$). If plasma jets can be used for magneto-inertial fusion (MIF) [1], the resulting heating by fusion products might generate even higher energy density plasmas. This poster reports the results of using the UW's 1D Lagrangian, rad-hydro, fusion code BUCKY to investigate two cases of converging plasma jets formulated in Ref.\ 2. The BUCKY code solves single-fluid equations of motion with ion-electron interactions, PdV work, table-lookup equations of state, fast-ion energy deposition, and one or two temperatures. Extensions to the code include magnetic field evolution as the plasmoid compresses, B-field pressure, plus dependence of the thermal conductivity on the magnetic field. Some parametric explorations are also reported. \\[4pt] [1] Y.C. F. Thio, et al.,``Magnetized Target Fusion in a Spheroidal Geometry with Standoff Drivers,'' in Current Trends in Int'l Fusion Research, E. Panarella, ed. (NRC--Canada, Ottawa, Canada, 1999), p. 113. \newline [2] R. Samulyak, P. Parks, and L. Wu, ``Spherically Symmetric Simulation of Plasma Liner Driven Magnetoinertial Fusion,'' Physics of Plasmas 17, 092702 (2010). [Preview Abstract] |
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TP9.00086: Single Jet Studies on the Plasma Liner Experiment Thomas Awe, Scott Hsu, Colin Adams, Joshua Davis, John Dunn, Jacob Schwartz, Elizabeth Merritt, Alan Lynn, Mark Gilmore, F. Douglas Witherspoon, Sam Brockington, David van Doren The Plasma Liner Experiment (PLX) will generate imploding plasma liners via an array of high-Mach-number (M) plasma jets. Initial experiments examine the evolution of an argon plasma jet with velocity $\sim $50-70 km/s, number density $\sim $10$^{16-17}$ cm$^{-3}$, M $>$10, cross sectional radius $\sim $2.5 cm. Single-jet physics issues include jet expansion/stability, cooling, and atomic physics effects. Photodiode data determine the jet velocity. Intensified gated imaging details the jet geometry, expansion, and stability. A gated broad-band visible light spectrometer provides information on the plasma temperature and ionization state and will inform the design of a high-resolution spectrometer for future experiments. Finally, a multi-chord interferometer provides temporally resolved line-integrated density data and potentially Abel-inverted jet radial density profiles. A collaborative modeling effort is underway to generate simulated data based on experimental jet parameters and diagnostic configurations. Experimental data and comparisons with simulated data are presented. [Preview Abstract] |
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TP9.00087: Creation of a high density, high flux target plasmoid for magneto-inertial fusion Thomas Weber, Thomas Intrator, Jason Sears Magneto-inertial fusion utilizes embedded magnetic fields to reduce thermal transport and enhance alpha particle heating during an implosion reducing the required areal density, implosion speed, and convergence for fusion ignition. This enables the use of efficient inexpensive pulsed power, reducing the gain required for breakeven (e.g. $\eta G = 0.5*10$ (MIF), $= 0.05*100$ (ICF)). The FRX-L and FRCHX experiments at Los Alamos National Laboratory and the Air Force Research Laboratory at Kirtland AFB are investigating a subset of MIF called Magnetized Target Fusion (MTF) in which a Field Reversed Configuration (FRC) plasmoid is injected into a converging solid, conductive liner and compressed to fusion conditions. Traditional FRC formation techniques utilizing ringing-$\theta$ pre-ionization have proved to be incapable of forming target plasmoids with enough density and magnetic flux, limiting the particle inventory, confinement, and lifetime. An alternative formation technique utilizing magnetoplasmadynamic arc sources has been developed to increase the density and trapped flux of the target plasmoid. Plasma source technology and operation are presented, as well as changes to the target formation process, plasmoid characteristics, and implications to MTF. [Preview Abstract] |
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TP9.00088: A 1D (radial) Plasma Jet Propagation Study for the Plasma Liner Experiment (PLX) J.R. Thompson, I.N. Bogatu, S.A. Galkin, J.S. Kim, D.R. Welch, C. Thoma, I. Golovkin, J.J. MacFarlane, A. Case, S.J. Messer, F.D. Witherspoon, J.T. Cassibry, T.J. Awe, S.C. Hsu The Plasma Liner Experiment will explore the formation of imploding spherical ``plasma liners'' that reach peak pressures of 0.1 Mbar upon stagnation. The liners will be formed through the merging of dense, high velocity plasma jets (n$\sim $10$^{17}$ cm$^{-3}$, T$\sim $3~eV, v$\sim $50 km/s) in a spherically convergent geometry. The focus of this 1D (radial) study is argon plasma jet evolution during propagation from the rail gun source to the jet merging radius. The study utilizes the Large Scale Plasma (LSP) PIC code with atomic physics included through the use of a non-Local Thermal Equilibrium (NLTE) Equation of State (EOS) table. We will present scenarios for expected 1D (radial) plasma jet evolution, from upon exiting the PLX rail gun to reaching the jet merging radius. The importance of radiation cooling early in the simulation is highlighted. [Preview Abstract] |
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TP9.00089: Effect of Atomic and Spatial processes on Implosion of Plasma Liners for Magneto-Inertial Fusion Roman Samulyak, Heungkeun Kim, Lina Zhang, Paul Parks The effect of ionization and oblique shock waves generated by the merger of high Mach number plasma jets in the concept of plasma liner driven magneto-inertial fusion have been investigated using the FronTier code. For deuterium liners, an analytic EOS containing Saha equations for dissociation and ionization has been used. For high-Z materials such as argon and xenon, an average ionization EOS model that reduces the system of coupled Saha equations to a differential equation has been developed and validated. Energy sinks due to atomic processes caused the increase of the Mach number and the stagnation pressure. In some simulations, the fusion energy gain increased by 30\%. 3D simulations of the merger of plasma jets have demonstrated a strong effect of oblique shock waves heating the liner and reducing the Mach number. The stagnation pressure in 3D liners have been reduced by up to two orders of magnitude compared with 1D liners. An influence of non-ideal vacuum in the chamber on the self-implosion of liners has also been investigates. [Preview Abstract] |
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TP9.00090: Effect of Magnetic Shear on Magneto-Rayleigh-Taylor Instability Peng Zhang, Y.Y. Lau, I.M. Rittersdorf, M.R. Weis, R.M. Gilgenbach, S.A. Slutz, D.B. Sinars, M.C. Herrmann, M.E. Cuneo Because of diffusion of the azimuthal magnetic field into a cylindrical liner which encloses a plasma that is embedded in an axial magnetic field [1], the magnetic field within the liner may exhibit a strong magnetic shear, offering the interesting possibility of shear stabilization of the magneto-Rayleigh-Taylor instability (MRT). Here, we use the ideal MHD model to study this effect of magnetic shear in a finite slab. It is found that magnetic shear reduces the MRT growth rate in general. However, the feedthrough factor is virtually independent of magnetic shear. The limiting cases of zero magnetic shear and infinite magnetic shear are consistent with the generalized analytic model [2]. \\[4pt] [1] S. A. Slutz \textit{et al}., \textit{Phys. Plasmas} \textbf {17}, 056303 (2010). \\[0pt] [2] Y. Y. Lau \textit{et al}., \textit{Phys. Rev. E.} \textbf {83}, 066405 (2011); M. R. Weis \textit{et al}., in this conference. [Preview Abstract] |
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TP9.00091: Interferometry Results from Initial Experiments on the Plasma Liner Experiment (PLX) Elizabeth Merritt, Alan Lynn, Mark Gilmore, Scott Hsu The Plasma Liner Experiment (PLX) is exploring and demonstrating the feasibility of forming HED and potentially MIF relevant imploding spherical ``plasma liners'' that can reach peak pressures $\sim $ 0.1 Mbar at stagnation. Liners will be formed via merging of 30 dense, high Mach number plasma jets (M $\sim $ 10-35, v $\sim $ 50 km/s, jet diameter $\sim $ 5 cm) in spherically convergent geometry. Determining n$_{e}$ during liner formation, convergence, and stagnation, in comparison to simulation, is imperative for understanding the underlying plasma dynamics and for optimizing the liner formation and implosion. Simulations predict a wide parameter range for n$_{e}$ over the liner evolution, from densities of 10$^{22 }$- 10$^{26}$ m$^{-3}$. A primary density diagnostic is an 8-chord, fiber-optic, heterodyne, 561 nm interferometer. This poster overviews the interferometer design, and will present results from initial experiments including single jet propagation and two jet merging. [Preview Abstract] |
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TP9.00092: Anisotropy and Feedthrough in Magneto-Rayleigh-Taylor Instabilities Matthew Weis, Ian Rittersdorf, Yue Ying Lau, Peng Zhang, Ronald Gilgenbach, Jacob Zier The magneto-Rayleigh-Taylor instability (MRT) in a finite slab is studied analytically using the ideal MHD model. The slab may be accelerated by an arbitrary combination of magnetic pressure and fluid pressure, thus allowing an arbitrary degree of anisotropy intrinsic to the acceleration mechanism [1]. The magnetic field in different regions may assume arbitrary magnitude and direction tangential to the interface. In general, MRT retains robust growth if it exists. However, feedthrough may be substantially reduced if there are magnetic fields on both sides of the slab, and if the MRT mode invokes bending of the magnetic field lines. The analytically tractable eigenmode solutions allow an evaluation of the temporal evolution of MRT from random initial surface roughness. \\[4pt] [1] Y. Y. Lau \textit{et al}., \textit{Phys. Rev. E83}, 066405 (2011). [Preview Abstract] |
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TP9.00093: MiniRailgun Pressure and Magnetics Measurements Sarah Messer, Andrew Case, Sam Brockington, Linchun Wu, F. Douglas Witherspoon We present pressure and magnetic data from both a single 1 inch square bore minirailgun and from the merging of jets from several 1 cm minirailguns. The magnetic probes are in the wall of the minirailguns and monitor current distribution and propagation in the bore. The pressure probe array measures stagnation pressure simultaneously at several points in a plane downstream from the gun and shows how the pressure changes through the merge process at various distances from the gun. Stagnation pressure is influenced by density, temperature, and velocity, and serves as a check on spectroscopic and interferometric measurements. Unlike optical measurements, stagnation pressure is taken at a definite location. These guns are similar to the initial gun recently installed on the Plasma Liner Experiment at LANL. The jet-merging results are compared to objectives for PLX. [Preview Abstract] |
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TP9.00094: Eulerian and Lagrangian Plasma Jet Modeling for the Plasma Liner Experiment Richard Hatcher, Jason Cassibry, Milos Stanic, John Loverich, Ammar Hakim The Plasma Liner Experiment (PLX) aims to demonstrate the feasibility of using spherically-convergent plasma jets to from an imploding plasma liner. Our group has modified two hydrodynamic simulation codes to include radiative loss, tabular equations of state (EOS), and thermal transport. Nautilus, created by TechX Corporation, is a finite-difference Eulerian code which solves the MHD equations formulated as systems of hyperbolic conservation laws. The other is SPHC, a smoothed particle hydrodynamics code produced by Stellingwerf Consulting. Use of the Lagrangian fluid particle approach of SPH is motivated by the ability to accurately track jet interfaces, the plasma vacuum boundary, and mixing of various layers, but Eulerian codes have been in development for much longer and have better shock capturing. We validate these codes against experimental measurements of jet propagation, expansion, and merging of two jets. Precursor jets are observed to form at the jet interface. Conditions that govern evolution of two and more merging jets are explored. [Preview Abstract] |
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TP9.00095: CO2 Laser Beat-Wave Current Drive in an Unmagnetized Plasma Fei Liu, David Hwang, Robert Horton, Russell Evans, Zhuo Fan Huang, Sean Hong The ability to remotely generate plasma current in dense plasmas is a basic yet important investigation in experimental plasma physics. Plasma current can be generated through nonlinear beat-wave mixing process by launching two intense electromagnetic waves into an unmagnetized plasma. The beat wave formation process is efficient if the difference frequency of the two pump waves corresponds to the local plasma frequency. Beat wave can accelerate plasma electrons via quasi-linear Landau process, which has been demonstrated in low-density plasma using micro-waves [1]. The high tunability of the CO$_{2}$ lasers provides many options for the wave-particle interaction experiment at a variety of CTIX plasma densities. Two sections of Lumonics TEA CO$_{2}$ lasers have been modified at power over 100MW. The development of the tunable CO$_{2}$ lasers and diagnostics system will be described. A high-density plasma test source and density diagnostics system will also be presented. This line of research will impact experiment such as the PLX facility under initial operation at Los Alamos National Lab.\\[4pt] [1] Rogers, J. H. and Hwang, D. Q., Phys. Rev. Lett. v68 p3877(1992). [Preview Abstract] |
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TP9.00096: 3D modeling of merging plasma jets John Loverich, Ammar Hakim, Sean Zhou PLX is a new experiment at LANL investigating imploding plasma liners formed via merging plasma jets. In the future, an imploding plasma liner could be used as a standoff driver for MIF implosions. In this paper we present 3D simulation results of multiple interacting jets with and without magnetic fields including a general equation of state and simple radiation models using the Tech-X code Nautilus. A brief description of the algorithms and plasma models used will also be presented. [Preview Abstract] |
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TP9.00097: Plasma Jet Modeling for PLX Caroline F. Mason, Rodney J. Mason, R.J. Faehl, R.C. Kirkpatrick The implicit simulation code ePLAS has been applied to plasma jets generated with mini-rail guns for plasma production and compression aimed at use with PLX. The rails are typically planar, 2.5 cm apart and arranged to transport an initial 1 cm or wider vertical plasma fill some 10 cm into a void. The driving magnetic field is 3.2 T. The plasma singly ionized argon at 10$^{17}$ cm$^{-3}$. We use ePLAS in both its traditional implicit/hybrid form [1] where it is restricted by an electron Courant time step, and in a new super-hybrid form that extracts the main electron moments from the \textit{E{\&}B}-field solutions. This provides numerical stability at \textit{ion} Courant limits, for at least a 10 times larger time step, thus probing microsecond jet dynamics with computational economy. We examine possible field penetration at the cathode and anode gun electrodes. Cathode erosion and EMHD $B-$Field penetration are possible at lower jet densities [2]. We examine jet transport beyond the gun, modeling possible ionization with either analytic or tabular EOSs. We study the merger of jets with ions represented as either fluids or particles.\\[4pt] [1] R. J. Mason and C. Cranfill, IEEE Trans. Plasma Sci. \textbf{PS-14}, 45 (1986)\\[0pt] [2] R. Mason, et al., Phys. Fluids \textbf{B, 5}, 1115 (1993). [Preview Abstract] |
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TP9.00098: High Current Systems for HyperV and PLX Plasma Railguns S. Brockington, A. Case, S. Messer, R. Elton, F.D. Witherspoon HyperV is developing gas fed, pulsed, plasma railgun accelerators for PLX and other high momentum plasma applications. The present 2.5 cm square-bore plasma railgun forms plasma armatures from high density neutral gas (argon), preionizes it electrothermally, and accelerates the armature with 30 cm long parallel-plate railgun electrodes driven by a pulse forming network (PFN). Recent experiments have successfully formed and accelerated plasma armatures of $\sim$4 mg at 40 km/s, with PFN currents of $\sim$400 kA. In order to further increase railgun performance to the PLX design goal of 8 mg at 50 km/s, the PFN was upgraded to support currents of up to $\sim$750 kA. A high voltage, high current linear array spark-gap switch and flexible, low-inductance transmission line were designed and constructed to handle the increased current load. We will describe these systems and present initial performance data from high current operation of the plasma rail gun from spectroscopy, interferometry, and imaging systems as well as pressure, magnetic field, and optical diagnostics. High current performance of railgun bore materials for electrodes and insulators will also be discussed as well as plans for upcoming experimentation with advanced materials. [Preview Abstract] |
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TP9.00099: Development of MiniRailguns for the Plasma Liner Experiment (PLX) F.D. Witherspoon, S. Brockington, A. Case, S.J. Messer, L. Wu, R. Elton, S.C. Hsu, J.T. Cassibry, M.A. Gilmore Plasma guns are being developed for use on the Plasma Liner Experiment (PLX) located at LANL. The collapsing plasma liner will be formed via merging of 30 dense, high Mach number plasma jets (n$\sim$ 10$^{16-17}$~cm$^{-3}$, $M\sim$10--35, $v\sim$50--70~km/s, $r_{\rm jet}\sim $5~cm) in a spherically convergent geometry. Small parallel-plate railguns are being developed for this purpose. Each gun will operate at $\sim$300-600~kA peak current, and launch up to $\sim$8000 $\mu$g of high-Z plasma (Ar, Xe) using a $\sim$50~kJ pfn. We now routinely operate with very fast gas valve injection of Ar, and have recently achieved $\sim$4000 $\mu$g at 40 km/s at $\sim$400 kA. Work continues to increase both the mass and velocity using higher current and pulse shaping aided by MACH2 simulations. We describe these experimental efforts and the first prototype gun recently installed on PLX. [Preview Abstract] |
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TP9.00100: Numerical Simulations of Plasma Jets for PLX L. Wu, S. Messer, A. Case, M. Phillips, F.D. Witherspoon, D. Welch, C. Thoma, I.N. Bogatu, S. Galkin, J.R. Thompson, J.S. Kim, J. Macfarlane, I. Golovkin Two and three-dimensional simulations are performed using the hybrid particle-in-cell code LSP to study liner formation for the Plasma Liner Experiment (PLX). These include studies of plasma transport within small parallel-plate MiniRailguns, issues related to detachment of the jet from the nozzle, and the subsequent propagation of single jets in Cartesian coordinates. Merging of plasma jets is studied mainly in cylindrical coordinates at present. Varied number of railguns (or jets) are used in this study with initial velocity of 50-100 km/s, initial argon number density of 10$^{16}$~cm$^{-3}$ to 10$^{17}$~cm$^{-3}$, and initial temperature of $\sim$3 eV. The effects on liner formation from jet initial profiles (density, velocity and temperature distribution) are studied to explore behavior. Simulation results are presented and compared with experimental data from merging jet experiments currently being conducted at HyperV using 1cm bore MiniRailguns. The LSP code is used to perform the simulations using improved fluid algorithms and equation-of-state models from Voss and atomic data from Prism. Work supported by the U.S. DOE Office of Fusion Energy Sciences. [Preview Abstract] |
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TP9.00101: Pulsed Polarimeter instrument for the Magnetized Target Fusion program R.J. Smith, T. Intrator, G.A. Wurden, J. Sears, T. Weber Pulsed polarimetry, a Lidar-\textit{like} technique, promises to provide internal measurements of the distributions of $n_{e}$, $B_{\vert \vert }$ and $T_{e}$ for the MTF program, the FRX-L and FRCHX FRC experiments at at LANL and Air Force Research Lab, Albuquerque. The instrument in its final form is mostly finished and testing is in progress. The optical system: collection and collimating optics, polarimeter, spectrometer and condensing optics are built. The laser and streak camera have been commissioned. A versatile instrument has been designed which is capable of covering a 30 cm depth of field for FRX-L plasma, has selectable spectrometers for different $T_{e}$ ranges for the FRCHX plasma and can be stationed at discrete distances of 3, 4 and 5 $m$ from the plasma. The design and performance and plans to implement the diagnostic on the FRX-L device at Los Alamos will be presented. [Preview Abstract] |
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TP9.00102: Fast Temperature Rise and Saturation of Al Surface Plasma Generated by Pulsed MG Fields Stephan Fuelling, Thomas Awe, Bruno Bauer, Irvin Lindemuth, Richard Siemon In pulsed power system, the performance of current carrying surfaces is limited by plasma generation. Experiments with thick (diameter 0.5 -- 1.25 mm) aluminum rods, performed on the 1 MA Zebra generator at the Nevada Terawatt Facility reveal a threshold of 2.2 MG surface fields for plasma formation, independent of the initial diameter. For 1-mm thick loads, emission spectra obtained by extreme ultraviolet spectroscopy (8-18 nm spectral range) compare well with a modeled aluminum plasma temperature (PrismSPECT) of about 15 eV, both in early and late (peak current) plasma emissions. Time-gated, intensified imaging show spotty plasma formation at early times. This suggests that the temperature in the early spotty plasma quickly rises to 15 eV. At peak current, the intensity of the 15 eV plasma emissions reaches a maximum, suggesting that more of the same 15 eV plasma covers the surface of the aluminum rod. [Preview Abstract] |
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TP9.00103: Bounce-free spherical hydrodynamic implosion Grigory Kagan, Xian-Zhu Tang, Scott C. Hsu, Thomas J. Awe In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. A solution family realizing such a regime has been explicitly found. This regime found is most naturally applied and would be of most benefit to plasma liner driven magneto-inertial fusion (MIF). That is, this version of inertial confinement relies on maintaining the compressed hot spot within the thermonuclear burning condition for as long as possible, rather than on initiating the burn wave. Consequently, in MIF it is the best-case scenario that the fuel target persists in the state of maximum compression after reaching stagnation. Also, the plasma liner driven MIF provides substantial freedom in shaping the profiles of the imploding flow (i.e. liner) pressure, density and fluid velocity. By comparing the fuel disassembly time against that of a stationary imploding flow case, we find that shaping this flow appropriately is likely to increase the dwell time and fusion gain by a factor of four or more. Moreover, in this newly found regime the shocked region of the liner is at rest. That is, the kinetic energy of the original liner is entirely converted into internal energy. Hence, our result supports the idea of using the deuterium-tritium in the inner parts of the liner or the so-called ``after-burner,'' which upon becoming shocked will also burn, thus further increasing the gain. [Preview Abstract] |
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TP9.00104: The Tendency of Plasma Liners Formed by Hypersonic Jets to Evolve Toward Good Spherical Symmetry During Implosion Jason Cassibry, Milos Stanic, Richard Hatcher, Scott Hsu, Doug Witherspoon, Mark Gilmore, Weiwei Luo The Plasma Liner Experiment (PLX) is studying the implosion of a spherical liner formed via the merging of plasma jets. We are modeling the liner formation and evolution for 30 jets in 3D with SPH. The main results of this poster are (1) comparable peak pressure observed in 3d simulations of symmetric liner implosion and an equivalent case of the implosion of 30 discrete jets and (2) that gradients produced by the discrete jets smear such that the uniform and discrete jet simulations tend to converge on a common flow evolution at late times. Peak pressures occur at the center, and the rate of decrease of pressure is low until the liner has fully stagnated. Precursor jets occur at the jet merging interfaces, and the amplitude of these jets decreases during the implosion. The process is largely stable to Raleigh-Taylor instability growth for most of the implosion. Some mixing occurs which may cool the central hotspot. Further assessment is needed to evaluate whether the remaining asymmetry at the inner liner boundary is tolerable for compressing magnetized fuel to fusion conditions. [Preview Abstract] |
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TP9.00105: Target FRC Formation and Foil Liner Implosion Demonstrations for the Foil Liner Compression Experiment George Votroubek, John Slough, David Kirtley, Chris Pihl, Richard Milroy, George Marklin The Foil Liner Compression Experiment aims to demonstrate the compression of a Field Reversed Configuration (FRC) plasma with megagauss fields generated by an imploding foil liner. The liner is driven by a theta-pinch coil using sub-megajoule energies. This energy limit and the FRC lifetime at smaller scale ($\sim$ a few cm) must be balanced against the liner mass (and thickness), implosion velocity and liner material properties to arrive at the optimal system parameters. A two pronged experimental effort is underway: 1) formation of the target FRC utilizing FRC merging, 2) demonstration of an efficient foil liner implosion resulting in the high implosion velocities needed for compression. The FRC formed through merging of two supersonic FRCs creates a well positioned, stationary target suitable for compression. Foil liner dynamics have been studied with the aid of FEM analysis (ANSYS), where liner properties and initial implosion field strength can easily be varied, and have been found to agree with experimental results. Details of the experimental setup and results will be detailed. In addition, numerical codes are being developed to provide accurate and predictive capabilities of the plasma/foil liner compression. These efforts will also be discussed. [Preview Abstract] |
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TP9.00106: Characterizing MagLIF Preheated Plasmas Using Self-Thomson Scattering D.S. Montgomery, M. Geissel, E.C. Harding, A.B. Sefkow, D.B. Sinars Magnetized Liner Inertial Fusion (MagLIF) is a novel concept where GJ-class fusion yields might be achieved in the laboratory by pulsed-power driven implosions of cylindrical liners onto preheated (100-500 eV), magnetized ($>$ 10 T) deuterium-tritium (D-T) fuel. Preliminary experiments are being planned at the Z-facility to test the MagLIF concept using deuterium-deuterium (D-D) fuel. Analytic calculations and simulations indicate that a cm-scale liner filled with $\sim$3 mg/cc D-D gas can be preheated to 200-500 eV using 5-10 kJ of 527-nm light provided by the Z-beamlet laser. We propose using self-Thomson scattering from the Z-beamlet laser to diagnose electron temperature and density of the preheated plasma. Details of the experimental design and estimates of the Thomson scattered spectrum will be reported. The benefits of trace amounts of Ne or Ar in the D-D fuel for measuring the ion temperature will also be discussed. [Preview Abstract] |
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TP9.00107: MHD simulation of direct laser-driven magnetic-flux compression with Nautilus C.D. Zhou, J. Loverich, A. Hakim Direct laser-driven magnetic-flux compression is an innovative approach to achieve magneto-inertial fusion (MIF). A cylindrical target with initial seed magnetic field is compressed by energetic laser beams. The magnetic field that is ``frozen-in'' the plasma gets compressed with the target. The resulting high magnetic field reduces electron thermal conductivity and improves alpha particle confinement, thus providing an additional thermal insulation of the fuel forming the hot spot. Numerical simulations of magneto-inertial fusion implosions require realistic equation of states, thermonuclear fusion energy generation and laser energy deposition coupling with MHD equations. These simulations are important in stability and scaling studies of MIF implosions. Nautilus is a multidimensional shock-capturing MHD simulation framework developed at Tech-X. Incorporated with PROPACEOS equation of states, fusion reaction and laser ray tracing modules, it is utilized to perform direct laser-driven magnetic-flux compression implosions. Simulation results and relevant Nautilus features are discussed. [Preview Abstract] |
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TP9.00108: MFE DIAGNOSTICS AND GENERAL TOKAMAK |
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TP9.00109: Stabilization of RWM -- Comparison between RFP and Tokamak Shichong Guo, Zhirui Wang, Yueqiang Liu In the present work, we make a comparison of the instability behavior of Resistive Wall Modes (RWM) between Reverse Filed Pinch (RFP) and Tokamak configurations, where both MHD and kinetic theories are applied on this study. Since the investigation is carried out in cylindrical and toroidal geometries, CMR-F code [1] and Mars-K code [2] are adopted for the numerical computation. The analysis of potential energy components has been performed in order to obtain a physical understanding of the two different systems. It is shown that due to the different magnetic configuration, the roles of the toroidal coupling effects lead to different mode spectrum and structures. Furthermore, the stabilization by plasma rotation requires rather different conditions of the flow velocity, which can be predicted just by the dissipative MHD theory. The kinetic effects (particle-wave resonance) on the mode stabilization in the two configurations are also investigated and compared. The influence of the kinetic stabilization on the current driven and pressure driven RWMs will be presented. In addition, the plasma responses to the feedback stabilization in the two devices will be also discussed. \\[4pt] [1] Z.R. Wang, S.C. Guo, Nucl. Fusion 51, 053004(2011).\\[0pt] [2] Y.Q. Liu, et al., Phys. Plasmas 15, 112503(2008). [Preview Abstract] |
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TP9.00110: HBT-EP Program: Active MHD Mode Dynamics {\&} Control G.A. Navratil, S. Angelini, J. Bialek, A.H. Boozer, P. Byrne, B. Debono, P. Hughes, J.P. Levesque, L. Bi, M.E. Mauel, D.A. Maurer, Q. Peng, D. Rhodes, N. Rath, C. Stoaffer, D. Shiraki The HBT- EP active mode control research program aims to advance understanding of ITER and fusion relevant modular feedback control coil configurations. This poster describes progress with our enhanced active mode control facility (i) to quantify external kink dynamics and multimode response to applied magnetic perturbations, (ii) to understand the relationship between control coil configuration, conducting and ferritic wall effects, and active feedback control effectiveness, and (iii) to explore advanced feedback algorithms and internal feedback control coil configurations. Initial results show the first high-resolution detection of 3D multi-mode magnetic response of wall-stabilized tokamak discharges. Our successful multiple-input/output (MIMO) digital control system has been improved using a GPU. Combined with improved capability from the VALEN 3D feedback modeling code, we aim to optimize the use of modular feedback coils to control instability growth near the ideal wall stabilization limit. [Preview Abstract] |
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TP9.00111: Multimode Measurements of Resistive Wall Modes near the Ideal Wall Stability Limit J.P. Levesque, J. Bialek, P.J. Byrne, B.A. DeBono, B. Li, M.E. Mauel, D.A. Maurer, G.A. Navratil, N. Rath, D. Shiraki An important instability that limits plasma performance in tokamaks is the resistive wall mode (RWM). When there are two or more unstable modes, or when a mode is near marginal stability, multimode effects may become important [1]. Multimode plasma response to feedback may be responsible for loss of RWM control in high $\beta$ machines such as NSTX [2]. Typical HBT-EP plasmas operate near the ideal wall limit, where multimode effects are measurable. The recent HBT-EP upgrade has enabled high-resolution, high-sensitivity measurements of magnetic fluctuations from kink modes. We report measurements of natural multimode RWM activity in HBT-EP. Mode behavior is studied with respect to (i) proximity of the plasma to the ideal wall limit and (ii) geometry of the movable conducting wall. Measured mode structures and structural evolution are compared with predictions of DCON and VALEN. Rigidity of modes during growth, saturation, and decay is investigated. Supported by U.S. DOE Grant DE-FG02-86ER53222. \\[4pt] [1] Boozer A.H. 2003 Phys. Plasmas \textbf{10} 1458 \newline [2] Sabbagh S.A. \emph{et. al.} 2010 Nucl. Fusion \textbf{50} 025020 [Preview Abstract] |
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TP9.00112: High-Resolution Multimode MHD Spectroscopy Experiments on HBT-EP D. Shiraki, B.A. Debono, J.P. Levesque, M.E. Mauel, D.A. Maurer, N. Rath, G.A. Navratil The HBT-EP experiment has a unique high-resolution 216 point magnetic diagnostic system, allowing detailed measurements of plasma response to external perturbations. This includes 134 poloidal and 82 radial sensors, allowing measurements of the external field, plasma response, and wall currents. In addition, a high-power modular control coil array allows the application of multimode external field structures. The static and dynamic response of the stable resistive wall mode (RWM) to these perturbations has been measured as a function of perturbation amplitude, phase, and helicity, as well as edge $q$ and mode rotation. The driven response is observed to have the same structure as unstable RWM's. The plasma response is seen to clearly peak with the perturbation helicity and edge $q$. A large rise in the resonant field amplification is also observed as the natural mode rotation is slowed down with the application of an edge bias and resulting $jxB$ torque. The amplitude of the plasma response as a function of perturbation amplitude appears to have both a linear regime and a nonlinear saturated regime. Details of the measurement techniques are presented for both single-mode and multimode behavior, as well as comparisons to modeling. Supported by U.S. DOE Grant DE-FG02-86ER5322 [Preview Abstract] |
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TP9.00113: GPU based, real-time tracking of perturbed, 3D plasma equilibria N. Rath, J. Bialek, P.J. Byrne, B. DeBono, J.P. Levesque, B. Li, M.E. Mauel, D.A. Maurer, G.A. Navratil, D. Shiraki The new high-resolution magnetic diagnostics and actuators of the HBT-EP tokamak [1] are used to evaluate a novel approach to long-wavelength MHD mode control: instead of controlling the amplitude of specific preselected perturbations from axisymmetry, the control system will attempt to control the 3D shape of the plasma. This approach frees the experimenter from having to know the approximate shape of the expected instabilities ahead of time, and lifts the restriction of the control reference having to be the perfectly axisymmetric state. Instead, the plasma can be maintained in an arbitrary perturbed equilibrium [2], which may be selected for beneficial plasma properties. The increased computational demands on the control system are handled by a graphical computing unit (GPU) with 448 computing cores that interfaces directly to digitizers and analog output boards. The control system is designed to handle 96 inputs and 64 outputs with cycle times below 5 and I/O latencies below 10~microseconds. We report on the technical and theoretical design of the control system and give experimental results from testing the system's observer module which tracks the perturbed plasma equilibrium in real-time. This work was supported by US-DOE grant DE-FG02-86ER53222.\\[0pt] [1] D.A. Maurer et~al., \emph{PPCF} 53(2011)\\[0pt] [2] A.H. Boozer, \emph{PoP} 6(1999) [Preview Abstract] |
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TP9.00114: Edge biasing effects on MHD instabilities and plasma response to external magnetic perturbations in HBT-EP Bryan DeBono, Dave Maurer, Michael Mauel, Jeff L., Daisuke S., Niko R., Gerald Navratil, Sarah A., Pat B., Thomas Pedersen A biased electrode inserted into a tokamak plasma edge can be used to apply torque on the plasma and change the rotation rate of MHD instabilities, including the resistive wall mode (RWM). RWM's in HBT-EP have a natural frequency of +4-9 kHz, however with appropriate bias the plasma rotation can be adjusted both positively and negatively. We present a study of the effect of biased plasma rotation on MHD instabilities; a comparison is made between plasma rotation rate and the plasma response to external resonant magnetic perturbations (RMP). The Boozer tokamak plasma reluctance equation $ \rho = - (\frac{1}{s-i\alpha} +1)\frac{1}{L_p}$ suggests that the plasma response to RMP's is greatly enhanced as the toroidal torque dissapation coefficient $\alpha \rightarrow 0$. Moderate biasing ($\approx$ 50V) slows down the RWM rotation to 2-3kHz, and an increase in the plasma responsivity to RMP's is seen. Strong positive bias ($\approx +300V$) accelerates the mode in the direction opposite to its natural rotation at $\approx$ -40 kHz. At this high rotation frequency the mode is being dragged at too rapid a rate for it to penetrate the wall. Therefore, the conducting shells behave like an ideal wall and a saturated ideal external kink is observed instead of a RWM. [Preview Abstract] |
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TP9.00115: Multimode MHD Stability Investigations using Plasma Shaping on HBT-EP P. Byrne, D. Shiraki, J.P. Levesque, D.A. Maurer, M.E. Mauel, N. Rath We describe the design and installation of a ``zero net turns'' shaping coil that will allow the systematic investigation of plasma shaping. This coil will permit formation of a diverted plasma and the study of MHD characteristics such as multimode plasma response and stability in a shaped plasma in HBT-EP for the first time. The design, and construction of a capacitive power source is also discussed. Using HBT-EP's 40 element control coil set, computational studies into the multimode response of a shaped plasma to resonant magnetic perturbations (RMP's), are undertaken. The effects of the RMP's on a shaped plasma have been simulated using the TokaMac and Valen codes. In addition, the control coils allow for great flexibility in perturbing the equilibrium flux surfaces with high resolution. These coilsets have been used to increase the squareness of the plasma via n=0, m=3 shaping on the low field side, as a preliminary investigation into the effects of shaping on MHD activity. Supported by US DOE Grant: DE-FG02-86ER53222. [Preview Abstract] |
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TP9.00116: Multi-Point Thomson Scattering Upgrade for HBT-EP C. Stoafer, P. Byrne, B. DeBono, J. Levesque, B. Li, M. Mauel, D. Maurer, G. Navratil, Q. Peng, N. Rath, D. Shiraki, H. McLean A recent acquisition of the Thomson Scattering (TS) system from SSPX has allowed for significant upgrades to the TS system at HBT- EP. The equipment allows for ten spatial point measurements, an improvement over the previous single point system. The new source laser is a Continuum Nd:YAG with a 1064 nm wavelength and 2 J per 10 ns pulse. The installation of this new instrumentation will be described along with the necessary adjustments to the existing Thomson system. The multipoint system will enhance our equilibrium reconstruction and improve stability analysis of HBT-EP discharges. To illustrate the use of multipoint measurements in future experiments, we present the results of a sensitivity study where equilibria are reconstructed with and without the use of the Thomson scattering measurements. We show the additional pressure profile information will allow for a more accurate equilibrium reconstruction of the HBT-EP plasmas for further understanding of the plasma characteristics during resistive wall mode (RWM) activity, and active control experiments. [Preview Abstract] |
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TP9.00117: Design of Wall Segments for Ferritic Wall Mode studies on HBT-EP P. Hughes, J. Bialek, A.H. Boozer, M.E. Mauel, D.A. Maurer, G.A. Navratil Low-activation ferritic steels are leading material candidates for use in next-generation fusion development experiments such as a prospective US component test facility and DEMO [1]. Understanding the interaction of plasmas with a ferromagnetic wall will be crucial physics for these experiments. Although there has been a linear FRWM experiment [2], the FRWM has not yet been observed in toroidal geometry. Using its high-resolution magnetic diagnostics, HBT-EP will explore the dynamics and stability of plasma interacting with ferromagnetic materials. We describe an analysis of the plasma-wall coupling constant as a function of ferritic segment configuration and plasma position, as well as comparing material options for magnetic properties, cost, and ease of fabrication. Also, initial modeling, design, and installation of moderate permeability~($\mu \approx 5$) wall segments on HBT-EP will be discussed. Supported by U.S. DOE Grant DE-FG02-86ER53222. \\[4pt] [1] {\sc Kurtz, R.J., et al.} 2009 {\em J Nucl Mater \/} {\bf 386-388}, 411-417. \newline [2] {\sc Bergerson, W., et al.} 2008 {\em Phys Rev Lett \/} {\bf 101}, 235005. [Preview Abstract] |
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TP9.00118: Advanced RWM Feedback with Truncated Balanced Realization Dov Rhodes, J. Bialek, A.H. Boozer, M.E. Mauel, D.A. Maurer, G.A. Navratil, N. Rath Stabilizing the resistive wall mode (RWM) requires advanced control techniques. State-space methods such as truncated balanced realization have shown promise in VALEN simulations [1]. Advanced control theory is particularly relevant to large tokamaks such as ITER. In this presentation, we make use of a balanced realization, which highlights the plasma modes that are simultaneously controllable and observable, and optimizes the efficiency of the controller. Furthermore, the {\it truncated} balanced realization approximates the system with a reduced model in order to minimize the computational load, a critical factor in real-time control of large systems. Since finding the optimal truncation remains an open problem [2], it is essential to compare the effectiveness of different truncation models with the full balanced realization, as well as other control schemes. We present theoretical and simulation-based predictions of the different feedback models, soon to be implemented in real-time using a GPU computer at HBT-EP. \\[4pt] [1] {\sc Katsuro-Hopkins, O., et al.} 2007 {\em Nucl. Fusion \/} {\bf 47}, 1157. \newline [2] {\sc Dullerud, G.E. \& Paganini, F.} {\em A Course in Robust Control Theory \/}. Springer: 2000. [Preview Abstract] |
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TP9.00119: Initial Results from the $\mathrm{D_\alpha}$ Photodiode Array on HBT-EP Sarah Angelini, P. Byrne, B. DeBono, P. Hughes, J.P. Levesque, D.A. Maurer, M.E. Mauel, G.A. Navratil, N. Rath, C. Stoafer, D. Shiraki A 20-channel photodiode array diagnostic has recently been assembled for use on HBT-EP. Combining the high-speed measurements of light fluctuations from this photodiode array with HBT-EP's high-resolution magnetic diagnostics creates a method by which the structure of naturally appearing or control coil-induced kink instabilities can be measured. HBT-EP's photodiode array diagnostic is designed to respond to $\mathrm{D_\alpha}$ emissions at 656nm and to filter light emissions from other sources. Since these $\mathrm{D_\alpha}$ emissions are proportional to the product of the neutral density and the plasma density, structural information about the plasma response and its instabilities can be reconstructed using the perturbations from the time-averaged emission profile. In this poster, the viewing geometry and calibration method used to transform the chord-integrated measurement into a radial emission profile is described. The emission fluctuations will be analyzed and the correlations with the external magnetic diagnostics will be explored. [Preview Abstract] |
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TP9.00120: L- to H-mode power threshold and confinement characteristics of H-modes in KSTAR Hyun-Seok Kim, Young-Mu Jeon, Joon-Wook Ahn, Si Woo Yoon, Laurent Terzolo, Ki Min Kim, Yong-Su Na The KSTAR project has achieved H-mode with about 0.9$\sim $1.4 MW of NBI heating and about 0.25 MW of ECRH in the 3$^{rd}$ and 4$^{th}$ campaigns of KSTAR experiments. In this work, the L- to H-mode threshold power(P$_{TH})$, the energy confinement time($\tau _{E})$ and the confinement enhancement factor(H) were calculated in KSTAR. Firstly, in the procedure to calculate the power loss to the separatrix, the ohmic heating power, the fast ion loss power and the radiation loss power were simulated using a 1.5-D integrated plasma transport code, ASTRA and a Monte-Carlo code for NBI simulation, NUBEAM. With respect to P$_{TH}$, a trend of discrepancy between the P$_{TH}$ of KSTAR and that of multi-machine empirical scaling was observed in the regime of relatively low plasma density. Secondly, in order to evaluate confinement of KSTAR H-modes, a H$_{exp}$ was introduced defined as the ratio of total energy confinement time between the L-mode phase and the H-mode phase and compared with conventional H factors such as H$_{89-p}$. [Preview Abstract] |
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TP9.00121: Equilibrium of KSTAR Plasma K.-I. You, D.-K. Lee, S.G. Lee, J.G. Bak, S.H. Hahn, L. Lao We have installed the EFIT code on our computing system and made some modification to reconstruct the plasma equilibrium of KSTAR (Korea Superconducting Tokamak Advanced Research). KSTAR PF and TF coil systems use a CICC (Cable-In-Conduit Conductor) type superconductor. The CICC jacket material for most PF and all TF coils is Incoloy 908, which is a magnetic material with relative magnetic permeability greater than 10 in low external field. We newly introduced Diamagnetic Loop and variational Motion Stark Effect signals to equilibrium reconstruction. In this paper, we present some results of equilibrium reconstruction with the EFIT code, assess the effects of newly introduced diagnsotics signal on the equilibrium reconstruction and compare the EFIT results with the various diagnostics data in various plasma conditions including H- and L- modes. In addition, we will show the Incoloy908 effects on the plasma equilibrium. [Preview Abstract] |
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TP9.00122: Non-linear MHD Simulation of ELMs including Pellet Triggered ones for KSTAR tokamak Hyunsun Han, G. Park, H. Strauss, J.Y. Kim Three-dimensional non-linear MHD simulations have been conducted to investigate the qualitative characteristics of ELM(Edge Localized Mode)s including pellet induced ones using the M3D code [1]. A linearized velocity perturbation of initial equilibrium is employed to trigger the ELM instability for the simulation of natural ELM, while a density blob, which represents the ionized pellet ablation and is located within the edge pedestal, is adopted in an adiabatic condition for that of pellet induced one. The initial equilibrium is constructed based on a H-mode plasma of KSTAR(Korea Superconducting Tokamak Advanced Research) device. It is found that characteristics of natural ELM simulation are in qualitative agreement with the experimental observations including that density perturbation is much larger than temperature one during ELM instability. Regarding the pellet induced ELM, it is observed that the locally increased pressure due to the fast parallel heat conduction compared to the spread of density perturbation triggers the peeling-ballooning instability resulting in ELM- like relaxation. Detailed results will be presented in the discussion of underlying mechanism and application to KSTAR tokamak.\\[4pt][1] H. Strauss et al., Phys. Plasmas 7, 250 (2000) [Preview Abstract] |
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TP9.00123: Study of the Bursting Behavior of Type-I ELM Filaments on KSTAR by 2-D ECE Imaging System J. Lee, G.S. Yun, M.J. Choi, W. Lee, H.K. Park, J.H. Lee, C.W. Domier, N.C. Luhmann, Jr., A.J.H. Donn\'e, B. Tobias Edge Localized Modes (ELMs), repetitive relaxation of the excess pressure and/or current density at the edge of the H-mode plasmas, have been studied in 2-D during the 2010 KSTAR campaign using an electron cyclotron emission imaging (ECEI) diagnostics [1]. More comprehensive picture of type-I ELMs compared to the previous campaign has been obtained in 2011 and the complex crash dynamics of the ELM filaments have been investigated in more detail. The growth rate, the filament size, and the poloidal flow are compared between type-I ELMs and type-III ELMs. In particular, type-I ELMs are observed to involve larger change in the poloidal flow during the crash phase and have much longer transient phase ($\sim 10$ ms), a critical stage characterized by an abrupt change in the poloidal mode number preceding the crash.\\[4pt] [1] G.S. Yun et al., to be published in Phys. Rev. Lett. [Preview Abstract] |
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TP9.00124: Investigation of MHD instabilities and their dependence on plasma rotation in KSTAR* Y.S. Park, S.A. Sabbagh, J.W. Berkery, J.M. Bialek, Y.M. Jeon, S.H. Hahn, J. Kim, K.-I. You, S.G. Lee, J.G. Bak, K.D. Lee, W.H. Ko, Y.S. Bae A goal of the Korea Superconducting Tokamak Advanced Research (KSTAR) is to perform physics studies in support of ITER. With co-directed neutral beam injection, one expected difference between KSTAR and ITER is the degree and profile of the plasma rotation, which affects plasma stability. The present work examines instabilities that exist in KSTAR under plasma rotation conditions spanning the entire KSTAR operational space. Mode characteristics measured by electron cyclotron emission are compared to values computed from reconstructed plasma equilibria. Frequencies of the modes tied to plasma rotation are compared to measurements from an X-ray crystal spectrometer and charge exchange recombination spectroscopy. A first experiment producing non-resonant alteration of the plasma rotation profile by neoclassical toroidal viscosity will be attempted to access a low rotation operating space most applicable to ITER and examine the dependence of beta-limiting instabilities on rotation and rotation shear. Proximity of this new operational regime to MHD stability limits will be examined, as well as implications for n = 1 feedback stabilization planned for future KSTAR operation. *Work supported by U.S. DOE grant DE-FG02-99ER54524. [Preview Abstract] |
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TP9.00125: Development of Numerical Methods to Estimate the Ohmic Breakdown Scenarios of a Tokamak Min-Gu Yoo, Jayhyun Kim, YoungHwa An, Yong-Seok Hwang, Seung Bo Shim, Hae June Lee, Yong-Su Na The ohmic breakdown is a fundamental method to initiate the plasma in a tokamak. For the robust breakdown, ohmic breakdown scenarios have to be carefully designed by optimizing the magnetic field configurations to minimize the stray magnetic fields. This research focuses on development of numerical methods to estimate the ohmic breakdown scenarios by precise analysis of the magnetic field configurations. This is essential for the robust and optimal breakdown and start-up of fusion devices especially for ITER and its beyond equipped with low toroidal electric field (E$_{T}\le $0.3 V/m). A field-line-following analysis code based on the Townsend avalanche theory and a particle simulation code are developed to analyze the breakdown characteristics of actual complex magnetic field configurations including the stray magnetic fields in tokamaks. They are applied to the ohmic breakdown scenarios of tokamaks such as KSTAR and VEST and compared with experiments. [Preview Abstract] |
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TP9.00126: Recent Sawtooth Studies on the Tokamak a Configuration Variable Duccio Testa, Gustavo Canal, Stefano Coda, Basil Duval, Lucia Federspiel, Federico Felici, Silvano Gnesin, Timothy Goodman, Jonathan Graves, Federico Halpern, Miho Janvier, Josef Kamleitner, Alexander Karpushov, Doohyun Kim, Kyungjin Kim, Antoine Pochelon, Holger Reimerdes, Olivier Sauter We report recent studies performed on the Tokamak a Configuration Variable on the sawtooth instability and its relation with Tearing Modes (TMs). The primary long-term aim of this work is to provide understanding of the relation between sawteeth and TMs so that reliable real-time schemes can be devised for combined sawtooth and TM control in burning plasma experiments such as ITER. Hence, our work has focused on studying: dynamical relation between sawtooth crash and subsequent onset of TMs, sometimes leading to disruptions, as a function of the plasma shape and current profile; coupling of the low m/n modes generated at the sawtooth crash; dynamical evolution of the toroidal rotation during sawteeth; real-time control techniques for the sawtooth period using localized electron cyclotron heating and current drive; distribution function of high energy electrons generated at the sawtooth crash. [Preview Abstract] |
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TP9.00127: Sawtooth period pacing and locking by EC power control on TCV Timothy Goodman, Federico Felici, Jonathan Graves, Olivier Sauter, Gert Witvoet, Menno Lauret, Marco De Baar, Gerd Vandersteen Recent experiments on TCV have demonstrated two new techniques to precisely control the timing of each individual sawtooth crash by modulating the power of sawtooth stabilizing EC waves. The first technique, known as sawtooth pacing [1], the EC power is controlled in real-time and is reduced at a pre-determined interval after the previous sawtooth crash. This causes the following crash to occur at a predictable and repeatable time after each reduction of the power. The second method [2] uses a pre-programmed EC modulation waveform with a given period and duty cycle. For certain combinations of period and duty cycle the sawtooth period locks to the period of the modulation with a given relative phase. The approaches are closely related and both have been used to reliably control the sawtooth cycle period, known to affect Neoclassical Tearing Mode triggering. \\[4pt] [1] T.P. Goodman, et.al, Phys. Rev. Lett., vol. 106, 245002\\[0pt] [2] G.Witvoet, et al., Nucl. Fusion (submitted) [Preview Abstract] |
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TP9.00128: ELM control by edge ECH on TCV J.X. Rossel, F. Felici, J.-M. Moret, T.P. Goodman, O. Sauter, S. Coda, B.P. Duval, D. Testa, Y. Martin The control of ELMs is a crucial requirement for future Tokamak reactors. The possibility to achieve ELM pacing using ECH locally deposited near the pressure pedestal has been explored on TCV. With constant power, the frequency of type I ELMs was observed to increase by a factor 1.5 to 2 when the deposition region was moved towards the edge, despite the decreased absorption. Power modulation synchronized with the ELM cycle was also used for a real-time control of individual ELM occurrence as well as ELM frequency and regularity, measured by the standard deviation of their period. An ad-hoc 0-D model for the ELM cycle is proposed in support to these observations. [Preview Abstract] |
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TP9.00129: Gyrokinetic Particle Simulation of Internal Kink Mode in Toroidal Geometry Joseph McClenaghan, Zhihong Lin Magnetohydrodynamic (MHD) instabilities excited by equilibrium current in toroidal fusion devices play important roles in plasma stability and confinement. Kinetic effects are important in the excitation and saturation of the MHD modes, as well as resulting transport. In this work, we have applied Gyrokinetic Toroidal Code (GTC) to study kinetic effects in current-driven MHD modes. As the first step, we have performed GTC simulation of the n=m=1 internal kink mode, which has been studied extensively in tokamak experiments, theory and MHD simulations. We will compare the dispersion relation and mode structure from the simulation to the ideal MHD theory in a low beta, large aspect ratio limit to verify the gyrokinetic simulation of current-driven MHD modes. [Preview Abstract] |
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TP9.00130: First X-point tokamak operations in the RFX-mod experiment A. Zemengo, L. Zanotto, P. Bettini, R. Cavazzana, L. Grando, G. Marchiori, L. Novello, A. Soppelsa, T. Luce, G. Jackson RFX-mod is a Reversed Field Pinch which can be run as a low current ohmic tokamak, thanks to the flexibility of the power supply systems. RFX-mod is equipped with an MHD control system, based on a set of 48x4 saddle coils individually fed by current controlled power amplifiers, which represents the state-of-art in the field of MHD control of magnetized plasmas. This system has been successfully exploited in Tokamak discharges to study MHD stability issues relevant to next step devices as ITER. Recently, the possibility of performing tokamak discharges in X-point configuration has been explored, assessing the impact on the machine systems. A first experimental campaign was run in April 2011 with the aim of check the feasibility of a Double Null (DN) X-point tokamak scenario, first with vacuum shots and then with preliminary plasmas with open loop transition from circular to DN shaping. The paper will report the outcome of the campaign, which has successfully demonstrated that the transition to the DN X-point shape is possible without any particular problem. Reconstructions of the shape obtained will be presented, which proves the capability of controlling the plasma shape. This opens interesting opportunities towards the path of achieving an H-mode plasma. [Preview Abstract] |
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TP9.00131: A Model for Incomplete Reconnection in Sawtooth Crashes Matthew Beidler, Paul Cassak Large sawteeth are deleterious for fusion because they spoil core confinement. The Kadomtsev model fails to explain why the sawtooth cycle ends before all available magnetic flux is reconnected, i.e., the reconnection is incomplete. We present a model for incomplete, or partial, reconnection in sawtooth crashes. When the high pressure core and low pressure edge of a tokamak convect toward the m=n=1 reconnection site due to self-consistent dynamics of magnetic reconnection, the pressure gradient at the reconnection site increases. Reconnection shuts off before all available magnetic flux is reconnected if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain observations of incomplete reconnection. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER. [Preview Abstract] |
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TP9.00132: Neoclassical transport fluxes inside transport barriers in tokamaks K.C. Shaing Inside the transport barriers in tokamaks ion energy losses sometimes are smaller than the value predicted by the standard neoclassical theory. This improvement can be understood in terms of the orbit squeezing theory in addition to the sonic poloidal $E\times B$ Mach number $U_{p.m} $ that pushes the tips of the trapped particles to the higher energy. In general, $U_{p.m} $ also includes the poloidal component of the parallel mass flow speed. These physics mechanisms are the corner stones for the transition theory of the low confinement mode (L-mode) to the high confinement mode (H-mode) in tokamaks. Here, detailed transport fluxes in the banana regime are presented using the parallel viscous forces calculated earlier. It is found, as expected, that effects of orbit squeezing and the sonic $U_{p.m} $ reduce the ion heat conductivity. The former reduces it by a factor of $\vert S\vert ^{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}$ and the later by a factor of $R\left( {U_{p,m}^2 } \right)\exp \left( {-U_{p,m}^2 } \right)$ with $R\left( {U_{p,m}^2 } \right)$, a rational function. A nonlinear equation for $U_{p.m}$, similar to the bifurcation equation for L-H transition, is derived. Discussions between the theory presented here and earlier with that from a different group will be presented. [Preview Abstract] |
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TP9.00133: Measurement of Type-I ELM Pulse Propagation in SOL Using MSE/BES Diagnostics in JT-60U Takahiro Suzuki, Naoyuki Oyama, Nobuyuki Asakura Propagation of plasma ejected by type-I ELM (ELM pulse) is measured in scrape-off layer (SOL) in JT-60U, using optical system of motional Stark effect (MSE) diagnostics as beam emission spectroscopy (BES) diagnostics. This MSE/BES diagnostics measures $D_{\alpha}$ emission from heating neutral beam that is excited by collisions with the ejected plasma, and hence, the emission intensity is proportional to the ejected plasma density. ELM pulse propagation is evaluated as the radial propagation of the plasma density increase in the SOL, after eliminating the background light (e.g. bremsstrahlung) component from the BES signal. Also a conditional averaging technique to eliminate signal intensity modulation induced by photo-elastic-modulator for the conventional MSE diagnostics enables this measurement and the safety factor measurement, simultaneously [1]. Applying the technique to several JT-60U discharges having different global plasma parameters, dependence of ELM pulse propagation on global plasma parameters is investigated. \\[4pt] [1] T. Suzuki {\it et al.}, Rev. Sci. Instrum. {\bf 81} (2010) 043502. [Preview Abstract] |
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TP9.00134: SOL Electron Temperature and Density Profiles using Ratios of Minority Helium-I Emission in ICRH-heated Tokamak Discharges on TEXTOR E.A. Unterberg, O. Schmitz, H. Stoschus, D.H. Fehling, C.C. Klepper, D.L. Hillis, J.M. Munoz-Burgos, G. Van Wassenhose Characterizing the scrape-off layer (SOL) and last-closed-flux-surface (LCFS) region around an ion cyclotron resonant heating (ICRH) launch antenna during high-power RF heating of tokamak discharges is needed to better understand the heating mechanisms on the core plasma. A new diagnostic that uses a 1-D array of filtered photomultiplier tubes has recently been installed in front of an ICRH antenna on TEXTOR. This diagnostic uses narrow-bandpass (10{\AA}) visible filters to isolate various emission lines of helium-I. The helium is a minority species ($<$ 1{\%}) of an otherwise pure ($\sim $ 98{\%}) deuterium discharge. Using this data and an enhanced collisional-radiative model, the electron density and temperature are determined at high spatial ($\sim $ 1 mm) and temporal (down to 1 ms) resolution. Simultaneous profiles of electron temperature and density from $\sim $ 1cm in front of the antenna out to $\sim $2-3cm inside the LCSF have been obtained -- giving a $\sim $ 5cm full profile. Details of the diagnostic technique and profile data from discharges with ICRH power up to 1.2 MW will be shown. [Preview Abstract] |
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TP9.00135: Diagnostics for particle control in toroidal plasmas Jennifer Baerny, Simon Woodruff, James Stuber To monitor vacuum conditioning and particle control in a toroidal plasma undergoing a compression, three optical diagnostics have been designed an built: a single-chord HeNe (633nm) heterodyne interferometer [1], a collimated soft X-ray/UV bolometer, and an H-alpha detector (similar to [2]). The interferometer will measure the line-average density in the range 1e20 to 1e22m-3. The design and calibration of instruments is presented. 1D modeling of the density profile and recycling coefficients for a toroidal plasma undergoing compression obeying adiabatic scaling relations is presented.\\[4pt] [1] D. Kumar et al. Rev. Sci. Instr,, 77, 083503 (2006)\\[0pt] [2] H. S. McLean et al Rev. Sci. Instr. 72, 1556-561 (2001) [Preview Abstract] |
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TP9.00136: Wide Radial Coverage Electron Cyclotron Emission Imaging (ECEI) System for EAST Calvin Domier, Kerry Kong, Liubing Yu, Alexander Spear, Shao Che, Neville Luhmann, Jr., Chen Luo, Bingxi Gao, Changxuan Yu A wide bandwidth Electron Cyclotron Emission Imaging (ECEI) system has been developed and installed on the EAST tokamak in China. Unlike similar ECEI systems installed on DIII-D, KSTAR and ASDEX-UG, the EAST system delivers twice the number of radial channels per imaging antenna element for a total of 384 channels (24 vertical by 16 radial) from a single imaging array. The increased radial coverage has been achieved by extending the instantaneous IF coverage from 2 to 16.4 GHz (was previously limited to 9.2 GHz) using a novel frequency extender approach compatible with existing ECEI electronics. The EAST system is also equipped with an extremely large vertical zoom capability similar to that existing on DIII-D and KSTAR. Details of both the optical and electronic design will be presented. [Preview Abstract] |
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TP9.00137: Heavy Neutral Beam Probe Development and Space Poten tial Measurements of Helimak Alvaro Garcia de Gorordo, Gary A. Hallock, Kenneth W. Gentle The Heavy Neutral Beam Probe (HNBP) is an extension of the Heavy Ion Beam Probe that can probe plasmas with low electron temperature and densities. The HNBP's beam operates at $U\simeq 10\,keV$, and the probing ions, Na, are neutralized in a Cs based neutralizer. Even with Na neutrals, the signal current is low (tens of nanoAmperes), and so a phase sensitive detection system is used to raise low frequency signals out of the noise by modulating the neutral Na beam. The HNBP has been specifically developed for measuring the Helimak plasma device, which is an approximation to the infinite cylindrical slab with open field lines. We will present measurements of the plasma potential accross magnetic field lines and along the direction of various gradients including density, temperature, and magnetic field strength gradients. These are the first space potential measurements of a plasma of electron temperature below $T_e\simeq 40\,eV$; the Helimak's HNBP is extending beam probing to the $T_e\simeq 10\,eV$ regime. [Preview Abstract] |
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TP9.00138: ABSTRACT WITHDRAWN |
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TP9.00139: The behaviors of the ion temperature and impurity rotation profiles from charge exchange spectroscopy during H-mode in KSTAR Won-Ha Ko, H. Lee, K. Ida, S. Oh, H.M. Wi, K.D. Lee, S.H. Jeong, S.W. Yoon, J.H. Lee, J.G. Kwak, M. Kwon Ion temperature and impurity rotation velocity profiles were obtained on KSTAR by using the charge exchange emission of spectral lines in the neutral beam modulated plasma. The ion temperature and impurity rotation profiles are achieved in typical H-mode and the measured temperature profiles have a strong increase near pedestal at H-mode. The measured profile gradients in KSTAR are examined for evidence of the presence and location of the transport barrier region during the H-mode. This work supported by the Ministry of Education, Science and Technology. [Preview Abstract] |
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TP9.00140: Initial operation of the tangential x-ray pinhole camera system for KSTAR plasma Siwon Jang, S.G. Lee, M.K. Moon, C.H. Lim, S.H. Lee, Wonho Choe The tangential soft x-ray pinhole camera (TXPC), which is a fast, two-dimensional (2-D), soft x-ray imaging system with a toroidal view, has been developed for studying MHD activities and transport in KSTAR plasmas. It consists of 50x50 channels multi-wire proportional counter (MWPC) filled with a gas mixture of 78{\%} Kr, 20{\%} C2H6, and 2{\%} CF4 at atmospheric pressure. It can measure 2-D x-ray emissivity with a high and controllable intrinsic gain ($>$ 10$^{4})$, high spatial ($<$ 2 cm) and high temporal ($>$ 100 kHz) resolution with a 100 MHz DAQ system. They can assist analysis of plasma profile, MHD modes, localization and effects of auxiliary heating and transport phenomena from core to edge. Also, the TXPC employs a duplex multi-wire proportional x-ray (DMPX) detector that combines two MWPCs in series. It will provide simultaneous measurements of plasma x-ray emission in two spectral ranges using the first MWPC as an absorber filter for the second one. The signals of the first and the second MWPC allow providing the fast 2-D measurement of the plasma electron temperature. The TXPC system is installed on KSTAR in 2011, and initial plasma data and an assessment of the system performance are presented. [Preview Abstract] |
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TP9.00141: Laboratory Investigation of the Phase Reconstruction by Microwave Imaging Reflectometry I. Hong, W. Lee, M. Kim, Y. Nam, J. Leem, G.S. Yun, H.K. Park, N.C. Luhmann, Jr., C.W. Domier Microwave Imaging Reflectometry (MIR) has been developed for a precise measurement of 2D electron density fluctuations in fusion plasmas. The MIR can overcome the limitations of the conventional reflectometry by minimizing the loss of phase information with large imaging optics and an array of detectors. The precise design of optics and detection system is critical for the reconstruction of the fluctuations. The integrated system of the KSTAR MIR optics and detector system has been tested using a corrugated solid target representing the density fluctuations at the cutoff surface. The reconstructed phase has been compared to the direct measurement of corrugations considering the rotational speed of the target. The influence of optical aberrations and imperfection of the optical components on the phase reconstruction have been studied by the 2D phase/amplitude measurement of the reflected beam and diffraction-based optical simulations. [Preview Abstract] |
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TP9.00142: Development of Microwave Imaging Reflectometry for KSTAR W. Lee, I. Hong, Y. Nam, M. Kim, J. Leem, G.S. Yun, H.K. Park, Y.G. Kim, K.W. Kim, C.W. Domier, N.C. Luhmann, Jr. A microwave imaging reflectometry (MIR) system for KSTAR is being developed to measure 2-D (poloidal $\times$ radial) image of the electron density fluctuations for turbulence based transport study. Prior to the full system, two-frequency prototype system will be tested for the 2012 KSTAR campaign. The system is capable to measure poloidal wave numbers from 0.5 to 2 cm$^{-1}$ with a 16 channel array of detectors that can image $\sim 13$ cm length of the poloidal plane. Due to the standing wave problem of lens based system (sharing optics with 2nd ECEI system), a new system based on reflective optics is being designed. The RF electronics, capable of simultaneous measurement of the reflected beams from two cut-off layers, has been developed and the laboratory test results with a corrugated reflecting target will be presented. [Preview Abstract] |
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TP9.00143: X-Ray Spectroscopic Imaging of Tokamaks with Photon-Counting Hybrid Pixel Array Detectors (PAD) K.W. Hill, M. Bitter, L. Delgado-Aparicio, N. Pablant, P. Beiersdorfer, M.L. Reinke, Y. Podpaly, J.E. Rice, S.G. Lee, Y. Shi, Ch. Broennimann, E. Eikenberry Hybrid PADs, such as Pilatus (www.dectris.com) offer the possibility of 1D and 2D x-ray spectroscopic imaging of tokamaks with good spatial and temporal resolution, using pinhole x-ray cameras. These cameras can be either radially viewing (1D) or tangentially viewing (2D), and can provide fast profiles of electron temperature, impurity concentration and transport, and non-thermal electron distributions. Each pixel counts x-ray photons having energy above a threshold value, and different groups of pixels are set to different thresholds to provide spectral discrimination. X-ray camera designs, simulations of performance, and progress on energy- threshold calibration on a per-pixel basis will be presented. [Preview Abstract] |
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TP9.00144: Diagnostic Systems for the Ignitor Experiment F. Bombarda, F. Giammanco The main purpose of the Ignitor experiment ($R_0\cong 1.32 \textnormal{ m}, a \times b\cong 0.47\times 0.83 \textnormal{ m} ^2, B_T \leq 13 \textnormal{ T}, I_p\leq 11 \textnormal{ MA}$) is that of establishing the reactor physics in regimes close to ignition ($T_e\cong T_i\cong 11 \textnormal{ keV}, n_0 \cong 10^ {21} \textnormal{m}^{-3}$). The pulse evolution at the maximum machine parameters is characterized by a ramp-up phase of the plasma current of 4 s and 4 s of flat-top, which allow to reach fully relaxed current profiles. The set of baseline diagnostic systems includes, among others, the advanced neutron spectrometer originally proposed for Ignitor and later adopted on JET, Thomson Scattering, ECE, High Resolution X-ray Spectrometer. A Dispersion-Interferometer operating at 1 $\mu$m instead of the conventional Two-color Interferometer at 10 $\mu$m is being considered for plasma density measurements. The high plasma density and temperature, together with the use of tritium, impose some limitations on diagnostic systems based on NB injection, escaping particles or in direct connection with the high vacumm of the plasma chamber. The high neutron flux is also expected to challenge the systems more directly exposed to it, although the low fluences do not pose particular concerns on material survival. The conceptual design of the main diagnostic systems has been carried out and the present lay-out around the machine is shown. [Preview Abstract] |
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TP9.00145: High Gain and Frequency Ultra-Stable Integrators K.E. Miller, T.M. Ziemba, J.R. Prager, D.E. Lotz Eagle Harbor Technologies has received DOE Phase I SBIR funding to continue the development of high gain and stability integrators that are capable of high bandwidth measurements over long pulse operation. The present design operates with a 10 us RC time, for pulse durations up to the second time scale, with a frequency response in excess of 10 MHz, and typical drift errors of under 10 mV. This integrator development effort consists of two primary tasks. The first is to demonstrate stable operation over the much longer time scales required by ITER. When a proper comparison between available integrator designs is made that normalizes for gain and operation time, the existing integrators are the best available and meet ITER requirements for stability. However, this stability needs to be demonstrated over the hour type time scales relevant to ITER, as opposed to the very high gain second type operation typically used within the ICC community. The second primary task is to incorporate the integrators into the National Instruments (NI) platform to allow for easy operation with modern DAQ systems. [Preview Abstract] |
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TP9.00146: Spectroscopic investigations of tungsten EUV spectra for fusion plasma diagnostics Joel Clementson, Thomas Lennartsson, Peter Beiersdorfer, Ulyana Safronova, Tomas Brage, Jon Grumer The Livermore WOLFRAM spectroscopy project consists of experimental and theoretical investigations of tungsten ions of relevance to the diagnostics of magnetically confined fusion plasmas. A recent effort has focused on the complex extreme ultraviolet spectra of few-times ionized tungsten atoms that are expected to be abundant in ITER divertor plasmas. The tungsten ions were produced and excited in the Livermore EBIT-I electron beam ion trap by scanning the electron-beam energy between 30 and 300 eV. The emission was studied using a broad-band grazing-incidence spectrometer covering 150 -- 300 {\AA} and a high-resolution spectrometer covering the 180 -- 220 {\AA} region. Experimental spectra are presented together with analysis based on calculations using the FAC, GRASP, Cowan, HULLAC, and RMBPT codes. Part of this work was performed under the auspices of the US DOE by LLNL under Contract No. DE-AC52-07NA-27344. [Preview Abstract] |
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TP9.00147: ABSTRACT WITHDRAWN |
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TP9.00148: MINI-CONFERENCE: DENSE QUANTUM PLASMA SIMULATION |
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TP9.00149: A Different Time-Dependent Variational Principle Approach: Going Beyond Wave Packet Molecular Dynamics Paul Grabowski, Andreas Markmann, Michael Murillo, Frank Graziani During inertial confinement fusion, matter evolves from a solid condensed matter phase through the warm dense matter (WDM) regime to a hot dense matter. In WDM, quantum mechanical effects are important because of both Fermi-Dirac statistics and the rate of electrons transitioning in and out of bound states is large. The time-dependent temperature and quickly changing local environment require a time-dependent quantum method. A converged dynamical quantum simulation is intractable for more than a few particles. Instead, we take as a feasible goal to match the statistical properties of a warm dense plasma. The time-dependent variational principle gives a framework for producing equations of motion. A commonly used ansatz is a Hartree product of isotropic Gaussian wave packets (wave packet molecular dynamics). The resulting dynamics do not produce the right statistics. We therefore introduce a plane wave basis and discuss its advantages and test its ability to reproduce radial distribution functions produced by hyper-netted chain calculations. [Preview Abstract] |
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TP9.00150: Configuration Path Integral Monte Carlo Michael Bonitz, Tim Schoof, Simon Groth, Alexei Filinov, David Hochstuhl A novel path integral Monte Carlo (PIMC) approach for correlated many-particle systems with arbitrary pair interaction in continuous space at low temperatures is presented. It is based on a representation of the N-particle density operator in a basis of (anti-)symmetrized N-particle states (``configurations'' of occupation numbers) [1]. The path integral is transformed into a sum over trajectories with the same topology and, finally, the limit of M to infinity, (M is the number of high-temperature factors), is analytically performed. This yields exact expressions for the thermodynamic quantities and allows to perform efficient simulations for fermions at low temperature and weak to moderate coupling. Our method is applicable to dense quantum plasmas in the regime of strong degeneracy where conventional PIMC, e.g. [2], fails due to the fermion sign problem. \\[4pt] [1] T. Schoof, M. Bonitz, A. Filinov, D. Hochstuhl, and J.W. Dufty, Contrib. Plasma Phys. (2011), DOI 10.1002/ctpp.201100012;.\\[0pt] [2] ``Introduction to computational methods for many-body physics,'' M. Bonitz and D. Semkat (eds.). Rinton Press, Princeton 2006, chapter 4. [Preview Abstract] |
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TP9.00151: Classical Representation of a Quantum System at Equilibrium Sandipan Dutta, James Dufty A quantum system at equilibrium is represented by a corresponding classical system, chosen to reproduce the thermodynamic and structural properties. The objective is to develop a means for exploiting strong coupling classical methods (e.g., MD, integral equations, DFT) to describe quantum systems. The classical system has an effective temperature, local chemical potential, and pair interaction that are defined by requiring equivalence of the grand potential and its functional derivatives with respect to the external and pair potentials for the classical and quantum systems. Practical inversion of this mapping for the classical properties is effected via the hypernetted chain approximation, leading to representations as functionals of the quantum pair correlation function (similar in spirit to the approach of Dharma-wardana and Perrot [1]). The parameters of the classical system are determined such that ideal gas, weak coupling RPA, and strong coupling pair limits are preserved. The potential advantages of this approach are discussed. Research supported by US DOE Grant DE-SC0002139. \\[4pt] [1] M. W. C. Dharma-wardana and F. Perrot, Phys. Rev. Lett. 84, 959 (2000). [Preview Abstract] |
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TP9.00152: Studies of Particle Wake Potentials in Plasmas Ian Ellis, Frank Graziani, James Glosli, David Strozzi, Michael Surh, David Richards, Viktor Decyk, Warren Mori Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and with BEPS using various cell sizes. In this poster, we compare the wakes we observe in these simulations with each other and predictions from Vlasov theory. [Preview Abstract] |
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TP9.00153: The Kinetic Theory Molecular Dynamics Method Chris Fichtl, Michael Murillo, Frank Graziani We are interested in simulating plasmas under thermonuclear burn conditions relevant to NIF. As such, we have recently developed the Kinetic Theory Molecular Dynamics (KTMD) method, which takes advantage of the fact that the plasma electrons are typically moderately degenerate and weakly coupled, whereas the ions are classical and moderately to strongly coupled. The basic approach of KTMD is to describe the fully non-equilibrium electron dynamics with an appropriate kinetic equation while leaving the ion dynamics to MD. The current version of KTMD self-consistently follows the time evolution of a Fermi gas via the time-dependent, fully nonlinear Wigner-Poisson system. Our approach, its associated implementation, and preliminary physics benchmarking results, such as nonlinear plasma waves and instabilities, will be presented. We describe a Langevin approach designed to mitigate numerical errors causing the Fermi distribution to relax towards a Maxwellian during long simulations. Ideas for extending the current capability, such as extending the mean-field approach by including collisions and quantum mechanical smearing, will be outlined. [Preview Abstract] |
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TP9.00154: Linear Response Screening Models for Dense, Strongly-Coupled Plasmas Liam Stanton, Michael Murillo, John Benage, Frank Graziani Needs for accurate EOS and transport models of warm/hot dense matter have increased with the advent of new experiments that are able to more accurately probe these areas of phase-space. Molecular dynamics (MD) methods are often used for this, as they are apt for strongly-coupled systems. Unfortunately, the traditional Coulomb and Yukawa pair-potentials begin to fail at lower temperatures as degeneracy effects of the electron gas arise, and a more sophisticated treatment is required. We present a class of effective ion-ion interactions derived within the framework of linear response, which go beyond screening in the long-wavelength limit. These new potentials not only improve the accuracy of screening effects without contributing to the computational complexity of the model, but they also add physics entirely missing from Yukawa models (such as the onset of Friedel oscillations). [Preview Abstract] |
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TP9.00155: Direct numerical simulations of structure and transport in dense plasmas Heather D. Whitley, John I. Castor, Michael S. Murillo, Frank R. Graziani In recent years, high power laser facilities, such as NIF, and advanced diagnostics have enabled the determination of detailed properties of dense plasmas over unprecedented regimes. Understanding such plasmas, which may be partially degenerate and/or moderately coupled, represents a major challenge to the plasma physics community. We examine the accuracy and applicability of approximate effective potentials in the study of structural and dynamic properties of one and two component systems in the partially and fully ionized regimes. The diffractive Coulomb potential is derived from an exact quantum solution for a pair of particles while the fermionic character of the electrons is handled via an effective Pauli potential. We utilize classical hypernetted chain and molecular dynamics (MD) simulations to calculate static structure factors that can be compared to recent x-ray Thompson scattering experiments. We also examine whether these approximate potentials can be used to simulate electronic transport properties, such as thermal conductivity, and compare to recent quantum molecular dynamics calculations for hydrogen plasmas. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-490775 [Preview Abstract] |
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TP9.00156: Thermalization simulations of strongly/weakly coupled mixtures David Michta, Frank Graziani, Michael Surh, James Glosli In plasmas where certain pairs of species are strongly coupled and others weakly coupled, the assumptions that can be made in deriving simplified kinetic models are often unclear. Molecular dynamics simulation is a robust tool for probing physics in these regimes. In this study, the particle-particle particle-mesh (PPPM) molecular dynamics code ddcMD is used to simulate temperature relaxation of electron, proton, and Argon-doped mixtures. Thermalization rates are calculated and compared to theoretical models. The practicality of a simplified treatment of electrons as a Langevin bath is also explored. [Preview Abstract] |
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