The possibility of high amplitude driven contained modes during ion Bernstein wave experiments in the tokamak fusion test reactor

Extremely high quasilinear diffusion rates for energetic beam ions can be d educed from mode conversion experiments in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire, H. Adler, P. Alling , Phys. Plasmas 2(6), 2176 (1995 )]. A comparison of the experimental loss rates with the theoretical predic tion for the interaction of energetic ions with mode converted ion Bernstei n waves showed the theory to underpredict the diffusion coefficient by a fa ctor of 30-70. An anomalously high diffusion coefficient might enhance the advantageous channeling of energetic alpha particle energy in a tokamak rea ctor. Resolving this discrepancy is thus of importance from the standpoint of practical interest in an improved tokamak reactor as well as from the st andpoint of academic interest in basic wave-particle theory. A mechanism is proposed for this accelerated diffusion involving the excitation of a cont ained mode, possibly similar to that used in explaining the ICE (ion cyclot ron emission) phenomenon, near the edge of a tokamak. (C) 2000 American Ins titute of Physics. [S1070-664X(00)03107-4].