RECEIVED
MAR 13 1996
S-T .
PPPL-3143, Preprint Date: December 1995, UC-420, 427
Nonlinear Theory of Collisionless Trapped Ion Modes
T.S. Hahm and W.M. Tang
Princeton University, Princeton Plasma Physics Laboratory
P.O. Box 451, Princeton, NJ 08543
Abstract
A simplified two field nonlinear model for collisionless trapped-ion-mode turbulence has
been derived from nonlinear bounce-averaged drift kinetic equations. The renormalized
thermal diffusivity obtained from this analysis exhibits a Bohm-like scaling. A new nonlin-
earity associated with the neoclassical polarization density is found to introduce an isotope-
dependent modification to this Bohm-like diffusivity. The asymptotic balance between the
equilibrium variation and the finite banana width induced reduction of the fluctuation po-
tential leads to the result that the radial correlation length decreases with increasing plasma
current. Other important conclusions from the present analysis include the predictions that
(i) the relative density fluctuation level n/no is lower than the conventional mixing length
estimate, Ar/La; (ii) the ion temperature fluctuation level 6T/T significantly exceeds the
density fluctuation level 8n/no; and (iii) the parallel ion velocity fluctuation level 5viI/vTi is
expected to be negligible.
'PACS numbers:52.35.Ra, 52.25.Gj, 52.25.Fi, 52.55.Fa
DiSTR UT1N OF THIS DOCUMENT IS UI.MTAST