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Title: Excitation of high-n toroidicity-induced shear Alfven eigenmodes by energetic particles and fusion alpha particles in tokamaks

The stability of high-n toroidicity-induced shear Alfven eigenmodes (TAE) in the presence of fusion alpha particles or energetic ions in tokamaks is investigated. The TAE modes are discrete in nature and thus can easily tap the free energy associated with energetic particle pressure gradient through wave particle resonant interaction. A quadratic form is derived for the high-n TAE modes using gyro-kinetic equation. The kinetic effects of energetic particles are calculated perturbatively using the ideal MHD solution as the lowest order eigenfunction. The finite Larmor radius (FLR) effects and the finite drift orbit width (FDW) effects are included for both circulating and trapped energetic particles. It is shown that, for circulating particles, FLR and FDW effects have two opposite influences on the stability of the high-n TAE modes. First, they have the usual stabilizing effects by reducing the wave particle interaction strength. Second, they also have destabilizing effects by allowing more particles to resonate with the TAE modes. It is found that the growth rate induced by the circulating alpha particles increase linearly with toroidal mode number n for small {kappa}{sub {theta}}{rho}{sub {alpha}}, and decreases as 1/n for {kappa}{sub {theta}}{rho}{sub {alpha}} {much gt} 1. The maximum growth rate is obtained atmore » {kappa}{sub {theta}}{rho}{sub {alpha}} on the order of unity and is nearly constant for the range of 0.7 < {upsilon}{sub {alpha}}/{upsilon}{sub A} < 2.5. On the other hand, the trapped particle response is dominated by the precessional drift resonance. The bounce resonant contribution is negligible. The growth rate peaks sharply at the value of {kappa}{sub {theta}}{rho}{sub {alpha}} such that the precessional drift resonance occurs for the most energetic trapped particles. The maximum growth rate due to the energetic trapped particles is comparable to that of circulating particles.« less
Authors:
;
Publication Date:
OSTI Identifier:
5077248
Report Number(s):
PPPL-2852
ON: DE92016804
DOE Contract Number:
AC02-76CH03073
Resource Type:
Technical Report
Research Org:
Princeton Univ., NJ (United States). Plasma Physics Lab.
Sponsoring Org:
DOE; USDOE, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALFVEN WAVES; EXCITATION; ALPHA PARTICLES; TRAPPED-PARTICLE INSTABILITY; DISTRIBUTION FUNCTIONS; KINETIC EQUATIONS; LANDAU DAMPING; MAGNETIC FIELDS; MHD EQUILIBRIUM; SHEAR; TOKAMAK DEVICES; CHARGED PARTICLES; CLOSED PLASMA DEVICES; DAMPING; ENERGY-LEVEL TRANSITIONS; EQUATIONS; EQUILIBRIUM; FUNCTIONS; HYDROMAGNETIC WAVES; INSTABILITY; PLASMA INSTABILITY; PLASMA MACROINSTABILITIES; THERMONUCLEAR DEVICES 700310* -- Plasma Confinement-- (1992-); 700340 -- Plasma Waves, Oscillations, & Instabilities-- (1992-)