Fast particle finite orbit width and Larmor radius effects on low-n toroidicity induced Alfven eigenmode excitation

The effects of finite drift orbit width (FOW) and Larmor radius (FLR) of fast particles on the stability of low-n toroidicity-induced Alfven eigenmodes (TAE) are studied. The formulation is based on the solution of the low frequency gyrokinetic equation (omega much less than omega(c), where omega(c) is particle cyclotron frequency). A quadratic form has been derived in terms of invariant variables; energy epsilon, magnetic moment mu, and toroidal angular momentum P-phi;. The growth rate of the TAE is computed perturbatively using numerical averaging over the fast particle drift orbit. This new computational capability improves the NOVA-K code [G. Y. Fu, C. Z. Cheng, and K. L. Wong, Phys. Fluids B 5, 4040 (1994)] which included FOW effects in the growth rate calculation based on small radial orbit width approximation. The new NOVA-K version has been benchmarked for different regimes of particle TAE excitation. It is shown that both FOW and FLR effects are typically stabilizing; the TAE growth rate can be reduced by as much as a factor of 2 for tokamak fusion test reactor supershots [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. However, FOW may be destabilizing for the global modes, which are localized at the plasma edge. (C) 1999 American Institute of Physics. [S1070-664X(99)03107-9].