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ABSTRACT: The efficiency of ECRH experiment on the CASTOR tokamak at 18 GHz and 29 GHz is estimated. The power absorption during the
O-X-EBW conversion process is determined numerically.
Czechoslovak Journal of Physics 05/2012; 50:51-56. · 0.42 Impact Factor
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ABSTRACT: Large scale (16003-grid) entropic lattice Boltzmann (ELB) simulations are performed on the 27-bit model at sufficiently high Reynolds numbers
to find intermittency corrections to the Kolmogorov k
-5/3 inertial spectrum. Even though the transport coefficients in ELB and in the Large Eddy Simulation (LES) lattice Boltzmann
schemes have very different origins, there are strong similarities in their turbulence statistics from 5123-grid simulations. A new LB moment-space boundary condition algorithm is tested on the 2D backstep problem, with excellent
agreement with experimental data even up to a Reynolds number of 800.
The European Physical Journal Special Topics 04/2012; 171(1):167-171. · 1.56 Impact Factor
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ABSTRACT: Presented is a type-II quantum algorithm for superfluid dynamics, used to numerically predict solutions of the GP equation
for a complex scalar field (spinless bosons) in φ4 theory. The GP equation is a long wavelength effective field theory of a microscopic quantum lattice gas with nonlinear state
reduction. The quantum lattice gas algorithm for modeling the dynamics of the one-body BEC state in 3+1 dimensions is presented.
To demonstrate the method's strength as a computational physics tool, a difficult situation of filamentary singularities is
simulated, the dynamics of solitary vortex-antivortex pairs, which are a basic building block of morphologies of quantum turbulence.
The European Physical Journal Special Topics 04/2012; 171(1):9-14. · 1.56 Impact Factor
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ABSTRACT: It is shown that the alpha-particle contribution to the scattered power can be dominant in the coherent scattering of a CO2 laser in a Maxwellian plasma. For Ti = Te = 10 keV, the optimal forward-scattering angle is around 1.0°, with detection of the electron density fluctuation wavenumbers k⊥ >> k|| (relative to the toroidal magnetic field). A strong resonance occurs at the lower hybrid frequency. Because of the strong dependence of the scattered signal on the alpha-particle temperature and the alpha distribution function, it seems feasible that CO2 laser scattering, using heterodyne techniques, could give detailed local information on fusion alphas.
Nuclear Fusion 01/2011; 26(1):51. · 4.09 Impact Factor
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ABSTRACT: Scattering parameters (choice of incident radiation from CO2 sources through far-infra-red (FIR) and millimetre sources, forward scattering and orientation angles) are sought so that the one-dimensional alpha particle distribution can be deduced directly from the experimental data. This deduction can be optimized by using orientations with incident FIR and millimetre radiation at forward scattering angles θ. Backscattering angles can be used for longer wavelength millimetre sources, although the deduction will be more difficult than for θ < 90°. The use of CO2 scattering will be very difficult.
Nuclear Fusion 01/2011; 28(9):1595. · 4.09 Impact Factor
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ABSTRACT: Given a set of rotating helical current filaments within a cylindrical plasma and a set of fixed magnetic-field detectors at the edge of the plasma, a mathematical model is used to investigate the observable effect of rotation or longitudinal motion in the intervening plasma. If the soft-X-ray signals from magnetic islands indicate the instantaneous position of the helical current filaments within the plasma, then the phase difference between the X-ray signal and the magnetic fluctuations should provide a diagnostic of tokamak plasma rotation. The relative motion between the islands and the electron fluid is measured by the 'slip' S(r) = ω – kvz(r) – mvΘ(r)/r, where ω is the rotation frequency of the islands and is the electron fluid velocity. – The plasma velocity and the Hall effect are added to Rosenbluth's reduced equations to compute the phase difference between the island position and the perturbed magnetic field at the edge of the plasma as a function of the slip for a variety of resistivity profiles. The current profile within the islands is taken from the non-linear computer results of White, Monticello, Rosenbluth and Waddell. – Comparison with experiment indicates essentially locked electron fluid and mode motions, i.e. S(r) 0.
Nuclear Fusion 01/2011; 20(1):17. · 4.09 Impact Factor
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ABSTRACT: Spherical tokamaks (STs), which feature relatively high neutron flux and good economy, operate generally in high-beta regimes, in which the usual EC O- and X-modes are cut-off. In this case, electron Bernstein waves (EBWs) seem to be the only option that can provide features similar to the EC waves-controllable localized heating and current drive (H&CD) that can be utilized for core plasma heating as well as for accurate plasma stabilization. We first derive an analytical expression for Gaussian beam OXB conversion efficiency. Then, an extensive numerical study of EBW H&CD performance in four typical ST plasmas (NSTX L-and H-mode, MAST Upgrade, NHTX) is performed. Coupled ray-tracing (AMR) and Fokker-Planck (LUKE) codes are employed to simulate EBWs of varying frequencies and launch conditions. Our results indicate that an efficient and universal EBW H&CD system is indeed viable. In particular, power can be deposited and current reasonably efficiently driven across the whole plasma radius. Such a system could be controlled by a suitably chosen launching antenna vertical position and would also be sufficiently robust.
01/2011;
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ABSTRACT: Using a set of interleaved unitary collision-stream operators, a three-dimensional (3D) quantum lattice gas algorithm is devised which, on taking moments, recovers the Gross-Pitaevskii (GP) equation. If a zero-temperature Bose-Einstein condensate (BEC) is trapped in an a magnetic well, the evolution of the ground-state wave function satisfies the scalar GP equation, while if the BEC is trapped in an optical trap the ground-state wave function satisfies spin or GP equations. Quantum turbulence is studied in a scalar GP system on 5,7603 grid yielding not only the classical Kolmogorov k-5/3 cascade but also the quantum vortex k-3 spectrum. For a certain class of initial conditions, one finds an intermittent loss of tangled quantum vortices as the vortex cores attain minimal size, and thus prevent the Kelvin wave cascade (due to helical wave-wave coupling on the vortex). A coupled set of GP equations are solved for spin or BEC. Skrymions, which describe topologically-linked quantum vortices, are examined. One finds, for certain initial conditions that the incompressible kinetic energy spectrum for the condensate component of a vortex ring core rapidly departs from the k-3 linear quantum vortex spectrum.
High Performance Computing Modernization Program Users Group Conference (HPCMP-UGC), 2010 DoD; 07/2010
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37th EPS Conference on Plasma Physics, Dublin, Ireland; 01/2010
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ABSTRACT: ray-tracing (AMR) and Fokker-Planck (LUKE) codes. Deposition and driven current profiles under realistic spherical tokamak conditions are calculated for EBWs with various injection parameters. Key injection and plasma parameters are identified that influence the calculated profiles. These parameters are varied to investigate the robustness of the applied scenarios. The importance of relativistic corrections on the absorption of EBW is considered. The differences between various relativistic models are explored.
52nd Annual Meeting of the APS Division of Plasma Physics, Chicago, IL, USA; 01/2010
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ABSTRACT: We present a modeling of Electron Bernstein waves (EBWs) by recently coupled AMR (Antenna---Mode-conversion---Ray-tracing) and LUKE (3D Fokker-Planck) codes. The electrostatic EBW is a promising candidate for localized heating and current drive in high-$\beta$ plasmas, where the standard electron cyclotron O- and X-waves are cutoff. EBW heating and current drive is simulated here in spherical tokamak conditions, particularly in typical NSTX and MAST equilibria and also in equilibria predicted by transport modeling. The EBW injection parameters are varied in order to find optimized scenarios and a possible way to control the deposition location and the driven current. This task is rather challenging because EBW ray trajectories and $N_{\parallel}$ spectra are strongly dependent on the plasma parameters.
51st Annual Meeting of the APS Division of Plasma Physics, Atlanta, GA, USA; 01/2009
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AIP Conference Proceedings. 01/2009; 1187:465-468.
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ABSTRACT: The AMR (Antenna-Mode-conversion Ray-tracing) code [1, 2] has been recently coupled with the LUKE [3] Fokker-Planck code. This modeling suite is capable of complex simulations of electron Bernstein wave (EBW) emission, heating and current drive. We employ these codes to study EBW heating and current drive performance under spherical tokamak (ST) configurations-typical NSTX discharges are employed. EBW parameters, such as frequency, antenna position and direction, are varied and optimized for particular configurations and objectives. In this way, we show the versatility of EBWs.
Radio Frequency Power in Plasmas. 01/2009; 1187:465-468
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AIP Conference Proceedings. 01/2009; 1187:449-452.
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ABSTRACT: The WEGA stellarator [1] is well suited for fundamental electron Bernstein wave (EBW) studies. Heating and current drive experiments at 2.45 GHz and 28 GHz, carried out in WEGA's low temperature, steady state overdense plasmas, were supported by intensive modelling. We employ our AMR (Antenna-Mode-conversion-Ray-tracing) code [3] to calculate the O-X-EBW conversion efficiency with a full-wave equation solver, while the power deposition and current drive profiles using ray tracing. Several phenomena have been studied and understood. Particularly, EBW current drive was theoretically predicted and experimentally detected at 2.45 GHz. Simulations confirmed the presence of two (cold and hot) electron components and the resonant behaviour of the EBW power deposition and its dependence on the magnetic field configuration. Furthermore, the code is used to predict the 28 GHz heating and current drive performance and to simulate EBW emission spectra.
Radio Frequency Power in Plasmas. 01/2009; 1187:449-452
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ABSTRACT: In the past several years we have been developing simulation techniques for electron Bernstein wave (EBW) physics in toroidal fusion devices. EBW simulations are rather difficult for several reasons. EBWs are electrostatic waves, whose propagation is strongly affected by the plasma parameters. EBWs cannot propagate in a vacuum and must be coupled to X- and/or O-modes. The conversion efficiency must be in general computed numerically by a full-wave solver.
Details of our code AMR are described. This includes electrostatic ray-tracing, EBW root finder and 1D full-wave adaptive finite elements solver of the EBW-X-O mode conversion. The plasma configuration is handled by independent modules and typically obtained from experimental results. A Python driver script handles user configuration files and is able to parallelize the simulation.
We describe applications of AMR to support various experiments. It is used to interpret EBW emission from the spherical tokamaks MAST and NSTX, to confirm the resonant EBW heating on the WEGA stellarator, to model its new 28 GHz system and to predict the applicability of the designated EBW emission radiometer for COMPASS.
Journal of Plasma and Fusion Research SERIES. 01/2009; 8:1153-1157.
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ABSTRACT: In the past several years we have been developing simulation techniques for electron Bernstein wave (EBW) physics in toroidal fusion devices. EBW simulations are rather difficult for several reasons. EBWs are electrostatic waves, whose propagation is strongly affected by the plasma parameters. EBWs cannot propagate in a vacuum and must be coupled to X- and/or O-modes. The conversion efficiency must be in general computed numerically by a full-wave solver.
Details of our code AMR are described. This includes electrostatic ray-tracing, EBW root finder and 1D full-wave adaptive finite elements solver of the EBW-X-O mode conversion. The plasma configuration is handled by independent modules and typically obtained from experimental results. A Python driver script handles user configuration files and is able to parallelize the simulation.
We describe applications of AMR to support various experiments. It is used to interpret EBW emission from the spherical tokamaks MAST and NSTX, to confirm the resonant EBW heating on the WEGA stellarator, to model its new 28 GHz system and to predict the applicability of the designated EBW emission radiometer for COMPASS.
Journal of Plasma and Fusion Research SERIES. 01/2009; 8:1153-1157.
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ABSTRACT: Three dimensional free-decaying MHD turbulence is simulated by lattice Boltzmann methods on a spatial grid of 8000 3 for low and high magnetic Prandtl number. It is verified that ∇· B = 0 is automatically maintained to machine accuracy throughout the simulation. Isosurfaces of vorticity and current show the persistence of many large scale structures (both magnetic and velocity) for long times — unlike the velocity isosurfaces of Navier-Stokes turbulence.
COMMUNICATIONS IN COMPUTATIONAL PHYSICS Commun. Comput. Phys. 10/2008; 4:624-646.
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International Congress on Plasma Physics, Fukuoka, Japan; 01/2008
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ABSTRACT: Lattice Boltzmann algorihms are a mesoscopic representation of nonlinear continuum physics (like Navier-Stokes, magnetohydro dynamics (MHD), Gross- Pitaevskii equations) which are ideal for parallel supercomputers because they transform the difficult nonlinear convective macroscopic derivatives into purely local moments of distribution functions. The macroscopic nonlinearities are recovered by relaxation distribution functions in the collision operator whose dependence on the macroscopic velocity is algebraically nonlinear and thus purely local. Unlike standard computational fluid dynamics codes, there is no loss in parallelization in handling arbitrary geometric boundaries, e.g., using bounce-back rules from kinetic theory. By encoding detailed balance into the collision operator through the introduction of discrete H-function, the lattice Boltzmann algorithm can be made unconditionally stable for arbitrary high Reynolds numbers. It is shown that this approach is a special case of a quantum lattice Boltzmann algorithm that entangles local qubits through unitary collision operators and which is ideally parallelized on quantum computer architectures. Here we consider turbulence simulations using 2,048 PEs on a 1,6003-spatial grid. A connection is found between the rate of change of enstrophy and the onset of laminar-to- turbulent flows.
DoD High Performance Computing Modernization Program Users Group Conference, 2007; 07/2007
