Phase mixing and nonlinearity in geodesic acoustic modes

Journal Article · Sun Sep 15 00:00:00 EDT 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4820941· OSTI ID:22220574

Hung, C. P.; Hassam, A. B. ^[1]

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1. University of Maryland at College Park, College Park, Maryland 20742 (United States)

Phase mixing and nonlinear resonance detuning of geodesic acoustic modes in a tokamak plasma are examined. Geodesic acoustic modes (GAMs) are tokamak normal modes with oscillations in poloidal flow constrained to lie within flux surfaces. The mode frequency is sonic, dependent on the local flux surface temperature. Consequently, mode oscillations between flux surfaces get rapidly out of phase, resulting in enhanced damping from the phase mixing. Damping rates are shown to scale as the negative 1/3 power of the large viscous Reynolds number. The effect of convective nonlinearities on the normal modes is also studied. The system of nonlinear GAM equations is shown to resemble the Duffing oscillator, which predicts resonance detuning of the oscillator. Resonant amplification is shown to be suppressed nonlinearly. All analyses are verified by numerical simulation. The findings are applied to a recently proposed GAM excitation experiment on the DIII-D tokamak.

• OSTI ID: 22220574
• Journal Information: Physics of Plasmas, Vol. 20, Issue 9; Other Information: (c) 2013 AIP Publishing LLC; 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
AMPLIFICATION
DOUBLET-3 DEVICE
ELECTRON TEMPERATURE
ION TEMPERATURE
MAGNETIC SURFACES
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
NUMERICAL ANALYSIS
OSCILLATION MODES
OSCILLATORS
PLASMA CONFINEMENT
PLASMA INSTABILITY
PLASMA SIMULATION
PLASMA WAVES
REYNOLDS NUMBER
WALL EFFECTS