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

Technical Report · Sun Sep 01 04:00:00 EDT 1991

DOI:https://doi.org/10.2172/5002759· OSTI ID:5002759

Berk, H L; Van Dam, J W; Guo, Z; Lindberg, D M

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 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. 44 refs., 13 figs., 1 tab.

• Research Organization: Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: FG05-80ET53088
• OSTI ID: 5002759
• Report Number(s): DOE/ET/53088-499; IFSR--499; ON: DE92002780
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700103 -- Fusion Energy-- Plasma Research-- Kinetics
700107 -- Fusion Energy-- Plasma Research-- Instabilities
700108* -- Fusion Energy-- Plasma Research-- Wave Phenomena
ALFVEN WAVES
ALPHA PARTICLES
ASPECT RATIO
CHARGED PARTICLES
CLOSED PLASMA DEVICES
DAMPING
DIFFERENTIAL EQUATIONS
EQUATIONS
EQUILIBRIUM
HYDROMAGNETIC WAVES
INSTABILITY
MHD EQUILIBRIUM
PARTIAL DIFFERENTIAL EQUATIONS
PLASMA INSTABILITY
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
WAVE EQUATIONS