Large temperature gradient toroidal (eta)(sub i) modes in fluid and kinetic descriptions

摘要

A study of the ion temperature gradient or (eta)(sub i) mode at larger (eta)(sub i) values (>>1), has been performed using gyrokinetic and fluid models. It is shown that there exists, in both models, an upper (eta)(sub i) stability threshold in the range about 10 or larger in addition to the already well known lower threshold at (eta)(sub i) around 1. The fluid description is found to reproduce the results of the gyrokinetic description with a good accuracy in the regimes b(sub o)<<1 and (epsilon)(sub n)<<1 whereas for larger b(sub o) and (epsilon)(sub n) the fluid model gives a lower upper (eta)(sub i) stability threshold than the gyrokinetic model. The lowest threshold occurs at wavelengths corresponding to b(sub o) around 1. Furthermore a steep density gradient ((epsilon)(sub n)<<1) is stabilizing -lowering the threshold and the growth rate. 30 refs, 11 figs. (Atomindex citation 28:029086)