Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session BO4: Magnetic Confinement Theory, Simulation and Modeling |
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Chair: Don Batchelor, Oak Ridge National Laboratory Room: Regency VI |
Monday, November 2, 2009 9:30AM - 9:42AM |
BO4.00001: System size and shear flow effects on ion temperature gradient turbulence Ben McMillan, Jolliet Sebastien, Trach-Minh Tran, Bottino Alberto, Villard Laurent We explore the role of system size ($\rho^*$ scaling) and shear flow levels on ion temperature gradient (ITG) turbulence in gyrokinetic simulations. Firstly, the scaling of heat flux level versus system size in plasmas with zero initial flow shear is reexamined. Averages over an ensemble of simulations are made to quantify errors in the mean flux estimate. Our scaling results are compared with others in light of this error. Secondly, the effect of poloidal shear flow on ITG turbulence is examined. Turbulence levels are suppressed when the flow shearing rate is similar to the ITG growth rate. Even at flow levels many times smaller than the supression threshold, nonlinear turbulence is only seen in the simulation if the initial perturbation is large: the system manifests subcritical turbulence. Inward or outward propagating avalanches and inward and outward shifted diffusivity profiles are seen according to the sign of the flow shear. In cases with strong flow shear almost all the flux is associated with avalanches, which propagate across the entire region with strong pressure gradient. The non-local and non-diffusive physics are explored by performing a second scan in system size. [Preview Abstract] |
Monday, November 2, 2009 9:42AM - 9:54AM |
BO4.00002: Gyrokinetic Particle Simulations of Toroidal Momentum Transport in Plasma with Kinetic Electrons I. Holod, Z. Lin Large scale gyrokinetic particle simulations find that momentum transport driven by microturbulence in magnetized plasmas includes both diffusive and off-diagonal (pinch and residual stress) components. Primitive separation of these momentum fluxes in toroidal plasma requires running simulations with a zero background rotation, a rigid rotation, and a sheared rotation, which give rise to the residual stress term, the pinch-like flux, and the diffusive flux, respectively. We have performed global gyrokinetic particle simulations using GTC code for the toroidal momentum transport in driftwave turbulence. Both ions and electrons are treated kinetically. We observe significant radial redistribution of toroidal momentum in cases with constant angular velocity (rigid rotation), which is the manifestation of residual stress and pinch fluxes. Momentum pinch is found to be enhanced by kinetic electrons. Using obtained off-diagonal fluxes we were able to subtract them from total flux in the sheared rotation case, getting as the result the diffusive flux. The ratio of momentum to heat diffusivity (Prandtl number) is found to be in good agreement with quasilinear estimates. The origin of off-diagonal fluxes has been studies through symmetry breaking mechanisms associated with zonal flow generation. [Preview Abstract] |
Monday, November 2, 2009 9:54AM - 10:06AM |
BO4.00003: Collision methods for particle simulations F.L. Hinton, C.S. Chang, E.S. Yoon Particle-in-cell simulations of magnetically confined plasmas require a method for incorporating the effects of Coulomb collisions, especially near the plasma edge, where these are especially important. We compare two possible types of methods: (1) Langevin, or Monte-Carlo, methods, which scatter the velocities of the particles, and (2) methods which change only the particle weights as a result of collisions. The weight-changing methods which we discuss use grid-based solutions of the Fokker-Planck equation, with interpolation between the grid and the particle velocities. For the Langevin methods, the errors in momentum and energy conservation are due to time-discretization, and accumulate in time. The weight-changing methods we discuss conserve momentum and energy exactly, assuming certain properties of the velocity-space shape functions for the particles. The details of these methods and their conservation laws will be presented. Also of interest are the effects of noise due to finite numbers of particles per grid cell. These are being investigated, and the results will be presented. [Preview Abstract] |
Monday, November 2, 2009 10:06AM - 10:18AM |
BO4.00004: Kinetic integrated modeling of tokamak plasmas by TASK3G A. Fukuyama, S. Murakami, A. Wakasa, H. Nuga, T. Okamoto Deviation of momentum distribution function from the Maxwellian is unavoidable in tokamak plasmas under heating and current drive. The deviation may affect transport, global stability, diagnostics and fusion reaction rate of burning plasmas. In order to describe the time evolution of the momentum distribution functions of plasma species self-consistently, we have developed a kinetic version of the integrated tokamak modeling code TASK3G as the third generation of the TASK code. Transport, heating and current drive are described by the bounce averaged Fokker-Planck equation. The calculated momentum distribution function is used for the analyses of wave propagation and absorption, global stability, and diagnostics. The bounce-averaged Fokker-Planck equation includes nonlinear Coulomb collision, quasi-linear wave interaction, neoclassical and turbulent-driven radial transport and particle source/sink. A typical example of TASK3G result for ITER burning plasma will be presented. [Preview Abstract] |
Monday, November 2, 2009 10:18AM - 10:30AM |
BO4.00005: Progress in the Development of an Integrated Modeling Tool to Support DIII-D and EAST Q. Ren, L.L. Lao, M.S. Chu, H.E. St. John, G. Abla, A. Collier, R. Prater, J.M. Park, G. Li, W. Guo, C. Pan, R. Srinivasan, M. Worrall Recent progress in the development of the IMFIT Integrated modeling tool is presented. The goal of IMFIT is to develop a modern and efficient integrated modeling platform to support DIII-D and EAST research, including the capability to simulate the behavior of tokamak discharges. Recent progress includes user-friendly and Python-based GUIs with multi-links to equilibrium, transport, and stability codes to facilitate modeling and analysis, and EFIT F90 upgrade with dynamic memory allocation and MPI option to support multiple devices and grid sizes. Through the GUI, straightforward analysis for kinetic EFIT reconstruction is made available. Ongoing developments include design of efficient algorithms to support interactions among physics modules such as EFIT/ONETWO/TGLF coupling for scenario development and transport flux analysis and EFIT/PEST3/TORAY coupling for modeling of tearing mode stability. Details will be presented. [Preview Abstract] |
Monday, November 2, 2009 10:30AM - 10:42AM |
BO4.00006: Model Data Fusion: developing Bayesian inversion to constrain equilibrium and stability theory Matthew Hole, J. Svensson, L.C. Appel, G. von Nessi, R.L. Dewar, J. Bertram, B.D. Blackwell, J. Howard Recently, a new probabilistic ``data fusion'' framework based on Bayesian principles has been developed on JET and W7-AS. The Bayesian analysis framework folds in uncertainties and interdependencies in the diagnostic data and signal forward-models, together with prior knowledge of the state of the plasma, to yield predictions of internal magnetic structure. A feature of the framework, known as Minerva (J. Svensson, A. Werner, Plasma Physics and Controlled Fusion 50, 085022, 2008), is the inference of magnetic flux surfaces without the use of a force balance model. We discuss results from a new project to develop Bayesian inversion tools that aim to (1) distinguish between competing equilibrium theories, which capture different physics, using the MAST spherical tokamak; and (2) test the predictions of MHD theory, particularly mode structure, using the H-1 Heliac. A novel spin-off application is development of a Tikhonov cross- validation method, that sequentially removes ``anomalous'' diagnostic data until the change in the inferred toroidal current is minimised. [Preview Abstract] |
Monday, November 2, 2009 10:42AM - 10:54AM |
BO4.00007: Collisional-radiative modeling of EBIT spectra from highly-charged high-Z ions of relevance to magnetic fusion Yuri Ralchenko, Ilija N. Dragani\'{c}, John D. Gillaspy, Joseph Reader, Joseph N. Tan, Joshua M. Pomeroy, Samuel M. Brewer Electron Beam Ion Traps (EBITs) are currently the primary source of spectroscopic information on highly-charged ions of heavy elements, e.g. tungsten, that are important for diagnostics of magnetic confinement fusion devices such as ITER. We will present some results on collisional-radiative (CR) modeling of low-density non-Maxwellian plasmas of EBITs and discuss how various physical processes affect spectral emission and ionization balance. Special attention will be given to the accuracy of radiative and collisional data used for the CR modeling. The simulated spectra will be compared with our recently measured x-ray and extreme-ultraviolet spectra of highly-charged (ion charge z=35-68) Hf, Ta, W, and Au. [Preview Abstract] |
Monday, November 2, 2009 10:54AM - 11:06AM |
BO4.00008: Gauging MRI Ison Herron, Jeremy Goodman Axisymmetric stability of viscous resistive magnetized Couette flow is re-examined, with emphasis on flows that would be hydrodynamically stable according to Rayleigh's criterion: opposing gradients of angular velocity and specific angular momentum. A uniform axial magnetic field permeates the fluid. In this regime, magnetorotational instability (MRI) may occur. It is proved that MRI is suppressed, in fact no instability at all occurs, with insulating boundary conditions, when the magnetic resistivity is sufficiently large. This shows conclusively that small magnetic dissipation is a feature of this instability for all magnetic Prandtl numbers. A criterion is provided for the onset of MRI. [Preview Abstract] |
Monday, November 2, 2009 11:06AM - 11:18AM |
BO4.00009: ABSTRACT WITHDRAWN |
Monday, November 2, 2009 11:18AM - 11:30AM |
BO4.00010: Results from an International MHD Data Mining Collaboration B.D. Blackwell, D.G. Pretty, S. Yamamoto, K. Nagasaki, E. Ascasibar, R. Jimenez-Gomez, S. Sakakibara, F. Detering New data mining techniques have been successfully applied to MHD data on H-1, TJ-II and Heliotron-J, and are being implemented on LHD and W-7AS data. The motivation for automated mining of fusion databases is to distil and classify data for inclusion in fusion physics databases, and to highlight physically-interesting, previously unnoticed modes. We present results from data mining of more than 10,000 shots from H-1, TJ-II and Heliotron J, showing a range of Alfv\'{e}nic and non-Alfv\'{e}nic modes, many with well-defined poloidal mode structure and clear relation to heating configuration and plasma geometry. In the case of H-1, the dispersion relations for several of these modes have been examined in detail exploiting H-1's high resolution in rotational transform. Examples of use of this relation to provide information about rotational transform (a form of Alfven spectroscopy) are given. We also discuss possible real-time application of the cluster technique to preliminary mode identification as data is being acquired, and some initial work on application of image processing techniques to MHD spectrogram analysis. [Preview Abstract] |
Monday, November 2, 2009 11:30AM - 11:42AM |
BO4.00011: Hiro currents, current spikes and forces in tokamak disruptions Leonid E. Zakharov The talk gives resolution of the oldest (known since 1963) puzzle in tokamak physics, related to such bright phenomena as the positive current spike (negative voltage spike) in tokamak disruptions. It is shown that the electric contact between plasma and the wall plays crucial role in tokamak disruptions. When the safety factor $q$ at the plasma boundary crosses the resonant value and a kink mode is excited, two effects follows. One is the generation of the surface, called ``Hiro'', current at the plasma boundary, unrelated to the resonant character of $q$-value. Another is the excitation of the stabilizing eddy currents in the wall, negligible when $q$ is resonant. The kink mode starts its development as a fast, invisible magnetically ideal mode with no wall effect present. As soon as plasma touches the wall, the surface Hiro currents from the plasma will be driven through the wall. This stops fast instability and convertw it into a slower resistive mode. The Hiro currents are always opposite to the plasma current. This is consistent with toroidal asymmetry in the plasma current measurements on JET due to m/n=1/1 kink mode. The same Hiro currents, generated by $m >1$ modes are responsible for positive plasma current spikes (and negative voltage spikes) in conventional disruptions. [Preview Abstract] |
Monday, November 2, 2009 11:42AM - 11:54AM |
BO4.00012: Resonant Field Amplification in JET Advanced Regimes Mikhail Gryaznevich, T.C. Hender, Y. Liu, I.T. Chapman, D. Howell, C.D. Challis, E. Joffrin, R. Koslowski, P. Buratti Resonant Field Amplification (RFA) has been systematically measured on JET, in two domains favourable for ITER steady-state operations: broad q-profiles with qmin ~ 1 and qmin ~ 2. MARS-F code modelling reproduces RFA data at low and high beta and suggests a new method of how the RFA data should be used to determine the no-wall limit experimentally. Although there is no strong evidence of a beta-limit connected with the RWM even at betaN~4 and performance was limited by internal n=1 modes, the observed (using RFA data) decrease in the no-wall limit with the increase in qmin is in agreement with the same dependence of the experimentally achieved highest beta values. [Preview Abstract] |
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