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Title: Nonlinear low noise particle-in-cell simulations of electron temperature gradient driven turbulence

Abstract

In this Letter, it is shown that global, nonlinear, particle-in-cell (PIC) simulations of electron temperature driven turbulence recover the same level of transport as flux-tube codes when the level of statistical noise, associated with the PIC discretization, is sufficiently small. An efficient measure of the signal-to-noise ratio, applicable to every PIC code, is introduced. This diagnostic provides a direct measure of the quality of PIC simulations and allows for the validation of analytical estimates of the numerical noise. Global simulations for values of {rho}{sub e}{sup *}<1/450 (normalized electron gyroradius) show no evidence of a gyro-Bohm scaling.

Authors:
; ; ; ; ; ;  [1];  [2];  [3]
  1. Max-Planck-Institut fuer Plasmaphysik, IPP-EURATOM Association, Garching (Germany)
  2. (Germany)
  3. (Switzerland)
Publication Date:
OSTI Identifier:
20960075
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2428280; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELECTRON TEMPERATURE; ELECTRONS; ION TEMPERATURE; NONLINEAR PROBLEMS; PLASMA; PLASMA SIMULATION; SIGNAL-TO-NOISE RATIO; TEMPERATURE GRADIENTS; TURBULENCE; VALIDATION

Citation Formats

Bottino, A., Peeters, A. G., Hatzky, R., Jolliet, S., McMillan, B. F., Tran, T. M., Villard, L., Computer Center of the IPP and Max-Planck-Gesellschaft, Garching, and Centre de Recherches en Physique des Plasmas, EPFL, Lausanne. Nonlinear low noise particle-in-cell simulations of electron temperature gradient driven turbulence. United States: N. p., 2007. Web. doi:10.1063/1.2428280.
Bottino, A., Peeters, A. G., Hatzky, R., Jolliet, S., McMillan, B. F., Tran, T. M., Villard, L., Computer Center of the IPP and Max-Planck-Gesellschaft, Garching, & Centre de Recherches en Physique des Plasmas, EPFL, Lausanne. Nonlinear low noise particle-in-cell simulations of electron temperature gradient driven turbulence. United States. doi:10.1063/1.2428280.
Bottino, A., Peeters, A. G., Hatzky, R., Jolliet, S., McMillan, B. F., Tran, T. M., Villard, L., Computer Center of the IPP and Max-Planck-Gesellschaft, Garching, and Centre de Recherches en Physique des Plasmas, EPFL, Lausanne. Mon . "Nonlinear low noise particle-in-cell simulations of electron temperature gradient driven turbulence". United States. doi:10.1063/1.2428280.
@article{osti_20960075,
title = {Nonlinear low noise particle-in-cell simulations of electron temperature gradient driven turbulence},
author = {Bottino, A. and Peeters, A. G. and Hatzky, R. and Jolliet, S. and McMillan, B. F. and Tran, T. M. and Villard, L. and Computer Center of the IPP and Max-Planck-Gesellschaft, Garching and Centre de Recherches en Physique des Plasmas, EPFL, Lausanne},
abstractNote = {In this Letter, it is shown that global, nonlinear, particle-in-cell (PIC) simulations of electron temperature driven turbulence recover the same level of transport as flux-tube codes when the level of statistical noise, associated with the PIC discretization, is sufficiently small. An efficient measure of the signal-to-noise ratio, applicable to every PIC code, is introduced. This diagnostic provides a direct measure of the quality of PIC simulations and allows for the validation of analytical estimates of the numerical noise. Global simulations for values of {rho}{sub e}{sup *}<1/450 (normalized electron gyroradius) show no evidence of a gyro-Bohm scaling.},
doi = {10.1063/1.2428280},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • The problem of discrete particle noise has been studied based on direct fluctuation measurements from gyrokinetic particle-in-cell simulations of stable plasmas. From the statistical analysis of electrostatic potential time evolution, the space-time correlation function has been measured. Fluctuation spectra have been constructed and analyzed in detail. Noise-driven transport is calculated using the quasilinear expression for the diffusion coefficient and the obtained noise spectrum. The theoretical value of electron heat conductivity shows good agreement with that measured in the simulation. It has been shown that for the realistic parameters in actual turbulence simulations, the noise-driven transport depends linearly on the entropymore » of the system. This study makes it possible to estimate and subtract the noise contribution to the total transport during turbulence simulations.« less
  • Ion-temperature-gradient turbulence-based transport models have difficulties reconciling the recent DIII-D H-mode results ({ital Proceedings} {ital of} 17{ital th} {ital European} {ital Conference} {ital on} {ital Controlled} {ital Fusion} {ital and} {ital Plasma} {ital Heating} (EPS, Geneva, 1990), Vol. 1, p. 271), where the density profile is flat, but {chi}{sub {ital e}}{gt}{chi}{sub {ital i}} in the core region. In this work, a nonlinear theory is developed for recently discovered ion-temperature-gradient trapped-electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for {ital L}{sub {ital T}{sub {ital i}}}/{ital R}{approx lt}{ital k}{sub {theta}}{rho}{sub {ital s}}{approx lt} ({italmore » L}{sub {ital T}{sub {ital i}}}/{ital R}){sup 1/4}. They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave--particle--wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity.« less
  • It is shown that Ion Temperature Gradient turbulence close to the threshold exhibits a long time behaviour, with smaller heat fluxes at later times. This reduction is connected with the slow growth of long wave length zonal flows, and consequently, the numerical dissipation on these flows must be sufficiently small. Close to the nonlinear threshold for turbulence generation, a relatively small dissipation can maintain a turbulent state with a sizeable heat flux, through the damping of the zonal flow. Lowering the dissipation causes the turbulence, for temperature gradients close to the threshold, to be subdued. The heat flux then doesmore » not go smoothly to zero when the threshold is approached from above. Rather, a finite minimum heat flux is obtained below which no fully developed turbulent state exists. The threshold value of the temperature gradient length at which this finite heat flux is obtained is up to 30% larger compared with the threshold value obtained by extrapolating the heat flux to zero, and the cyclone base case is found to be nonlinearly stable. Transport is subdued when a fully developed staircase structure in the E × B shearing rate forms. Just above the threshold, an incomplete staircase develops, and transport is mediated by avalanche structures which propagate through the marginally stable regions.« less
  • In this Letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k{sub perpendicular{rho}s} < or approx. 10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of 2 decrease in the plasma effective thermal diffusivity.