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 deduced from mode conversion experiments in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire, H. Adler, P. Alling et al., Phys. Plasmas 2(6), 2176 (1995)]. A comparison of the experimental loss rates with the theoretical prediction for the interaction of energetic ions with mode converted ion Bernstein waves showed the theory to underpredict the diffusion coefficient by a factor of 30-70. An anomalously high diffusion coefficient might enhance the advantageous channeling of energetic alpha particle energy in a tokamak reactor. Resolving this discrepancy is thus of importance from the standpoint of practical interest in an improved tokamak reactor as well as from the standpoint of academic interest in basic wave-particle theory. A mechanism is proposed for this accelerated diffusion involving the excitation of a contained mode, possibly similar to that used in explaining the ICE (ion cyclotron emission) phenomenon, near the edge of a tokamak.