Alpha particle destabilization of the toroidicity‐induced Alfvén eigenmodes

C. Z. Cheng
1991 Physics of Fluids B Plasma Physics  
Tlae high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be,driven unstable by the circulating and/or trapped a-particles through the wave-particle resonances. Satisfying the resonance condition requires that the o_-particle birth speed Vet __. VA/21m-nql, where VAis the Alfven speed, m is the poloidal mode number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the _particle pressure gradient free
more » ... sure gradient free energy must overcome the velocity space Landau damping due to both the c_-particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aidof the NOVA-K code. Stability criteria in terms of the a-particle beta 13ct, a-particle pressure gradient parameter (o./oh) (co. is the ox-particle diamagnetic drift frequency), and (va/v_ parameters will be presented for TFTR, CIT, and ITER tokamaks. The volume averaged u-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged o_-particle beta threshold is in the order ofl0 _. Typical growth rates of the n=l TAE mode canbe in the order of 102_A, where OA = vA/qR. Other types of global Alfven waves are stable in D-T tokamaks due to toroidal coupling effects. m
doi:10.1063/1.859618 fatcat:rdsyc4rzufgyzgmrnjyo6izq2m