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Title: Gyrokinetic simulation of global and local Alfven eigenmodes driven by energetic particles in a DIII-D discharge

Abstract

The unstable spectrum of Alfven eigenmodes (AEs) driven by neutral beam-sourced energetic particles (EPs) in a benchmark DIII-D discharge (142111) is calculated in a fully gyrokinetic model using the GYRO code's massively parallel linear eigenvalue solver. One cycle of the slow (equilibrium scale) frequency sweep of the reverse shear Alfven eigenmode (RSAE) at toroidal mode number n=3 is mapped. The RSAE second harmonic and an unstable beta-induced Alfven eigenmode (BAE) are simultaneously tracked alongside the primary RSAE. An observed twist in the eigenmode pattern, caused mostly by shear in the driving EP profile, is shown through artificially varying the E Multiplication-Sign B rotational velocity shear to depend generally on shear in the local wave phase velocity. Coupling to the BAE and to the toroidal Alfven eigenmode limit the RSAE frequency sweeps at the lower and upper end, respectively. While the present fully gyrokinetic model (including thermal ions and electrons) constitutes the best treatment of compressibility physics available, the BAE frequency is overpredicted by about 20% against experiment here and is found to be sensitive to energetic beam ion pressure. The RSAE frequency is more accurately matched except when it is limited by the BAE. Simulations suggest that the experiment ismore » very close to marginal AE stability at points of RSAE-BAE coupling. A recipe for comparing the radial profile of quasilinear transport flux from local modes to that from global modes paves the way for the development of a stiff (critical gradient) local AE transport model based on local mode stability thresholds.« less

Authors:
 [1];  [2]
  1. University of California-San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States)
  2. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
Publication Date:
OSTI Identifier:
22113354
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 20; Journal Issue: 1; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ALFVEN WAVES; AUGER ELECTRON SPECTROSCOPY; BEAMS; COMPRESSIBILITY; CONFINEMENT; DOUBLET-3 DEVICE; EIGENVALUES; ELECTRIC DISCHARGES; IONS; PHASE VELOCITY; PLASMA; PLASMA INSTABILITY; PLASMA SIMULATION; SPECTRA; STABILITY; THERMONUCLEAR REACTORS; TRANSPORT THEORY

Citation Formats

Bass, E. M., and Waltz, R. E. Gyrokinetic simulation of global and local Alfven eigenmodes driven by energetic particles in a DIII-D discharge. United States: N. p., 2013. Web. doi:10.1063/1.4773177.
Bass, E. M., & Waltz, R. E. Gyrokinetic simulation of global and local Alfven eigenmodes driven by energetic particles in a DIII-D discharge. United States. doi:10.1063/1.4773177.
Bass, E. M., and Waltz, R. E. Tue . "Gyrokinetic simulation of global and local Alfven eigenmodes driven by energetic particles in a DIII-D discharge". United States. doi:10.1063/1.4773177.
@article{osti_22113354,
title = {Gyrokinetic simulation of global and local Alfven eigenmodes driven by energetic particles in a DIII-D discharge},
author = {Bass, E. M. and Waltz, R. E.},
abstractNote = {The unstable spectrum of Alfven eigenmodes (AEs) driven by neutral beam-sourced energetic particles (EPs) in a benchmark DIII-D discharge (142111) is calculated in a fully gyrokinetic model using the GYRO code's massively parallel linear eigenvalue solver. One cycle of the slow (equilibrium scale) frequency sweep of the reverse shear Alfven eigenmode (RSAE) at toroidal mode number n=3 is mapped. The RSAE second harmonic and an unstable beta-induced Alfven eigenmode (BAE) are simultaneously tracked alongside the primary RSAE. An observed twist in the eigenmode pattern, caused mostly by shear in the driving EP profile, is shown through artificially varying the E Multiplication-Sign B rotational velocity shear to depend generally on shear in the local wave phase velocity. Coupling to the BAE and to the toroidal Alfven eigenmode limit the RSAE frequency sweeps at the lower and upper end, respectively. While the present fully gyrokinetic model (including thermal ions and electrons) constitutes the best treatment of compressibility physics available, the BAE frequency is overpredicted by about 20% against experiment here and is found to be sensitive to energetic beam ion pressure. The RSAE frequency is more accurately matched except when it is limited by the BAE. Simulations suggest that the experiment is very close to marginal AE stability at points of RSAE-BAE coupling. A recipe for comparing the radial profile of quasilinear transport flux from local modes to that from global modes paves the way for the development of a stiff (critical gradient) local AE transport model based on local mode stability thresholds.},
doi = {10.1063/1.4773177},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 1,
volume = 20,
place = {United States},
year = {2013},
month = {1}
}