Continuum damping of low- n toroidicity-induced shear Alfven eigenmodes

Journal Article · Wed Jul 01 04:00:00 EDT 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860455· OSTI ID:7285274

Berk, H L; Van Dam, J W; Guo, Z; Lindberg, D M ^[1]

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1. Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)

The effect of resonant continuum damping is investigated for the low-mode-number, toroidicity-induced, global shear Alfven eigenmodes, which can be self-excited by energetic circulating alpha particles in an ignited tokamak plasma. Resonant interaction with the shear Alfven continuum is possible for these eigenmodes, especially near the plasma periphery, leading to significant dissipation, which is typically larger than direct bulk plasma dissipation rates. Two perturbation methods are developed for obtaining the Alfven resonance damping rate from the ideal fluid zeroth-order shear Alfven eigenvalue and eigenfunction. In both methods the real part of the frequency is estimated to zeroth order, and the imaginary part, which includes the damping rate, is then obtained by perturbation theory. One method, which is applicable when the eigenfunction is nearly real, can readily be incorporated into general magnetohydrodynamic (MHD) codes. In the second method, the zeroth-order eigenfunctions may be complex; however, the application of this method to general MHD codes needs more detailed development. Also, an analytical estimate is found for the next-order real frequency shift of the fluid global Alfven mode. Analytical and numerical studies of this continuum damping effect indicate that it can substantially reduce the alpha particle-induced growth rate. Thus, either it is possible to prevent instability or, if unstable, to use the Alfven resonance damping to estimate the saturation amplitude level predicted from quasilinear theory.

• DOE Contract Number: FG05-80ET53088
• OSTI ID: 7285274
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 4:7; ISSN PFBPE; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700340* -- Plasma Waves
Oscillations
& Instabilities-- (1992-)
ALFVEN WAVES
ALPHA PARTICLES
CHARGED PARTICLES
CLOSED PLASMA DEVICES
CONFINEMENT
DAMPING
EIGENFUNCTIONS
FLUID MECHANICS
FUNCTIONS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INSTABILITY GROWTH RATES
MAGNETOHYDRODYNAMICS
MECHANICS
PERTURBATION THEORY
PLASMA CONFINEMENT
THERMONUCLEAR DEVICES
TOKAMAK DEVICES