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

Journal Article · Tue Jan 15 00:00:00 EST 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4773177· OSTI ID:22113354

Bass, E. M. ^[1]; Waltz, R. E. ^[2]

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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)

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.

• OSTI ID: 22113354
• Journal Information: Physics of Plasmas, Vol. 20, Issue 1; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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