Instability of the ion hybrid wave in the presence of fusion alpha-particles

The propagation of the ion hybrid wave in a deuterium-tritium plasma and in the presence of a small population of fusion alpha-particles is analysed. A non-thermal distribution of alpha-particles is considered which is relevant to their distribution before they have slowed down. Non-thermal distributions are also relevant to large excursion orbit alpha-particles which give rise to ion cyclotron emission in the edge region of a tokamak. Numerical solutions of the full electromagnetic dispersion relation are presented which includes ion cyclotron damping of the deuterium and tritium ions, Landau and transit time damping of the electrons and the cyclotron resonance interaction of the alpha-particles. An analytic dispersion relation is used to identify the most unstable conditions. Unstable solutions for the ion hybrid wave are given for sub-Alfvacute enic alpha-particles. copyright 1996 American Institute of Physics