Excitation of Alfven waves by trapped alpha particles in a tokamak reactor

Alfven wave instability in a tokamak caused by trapped alpha particles with non-monotonic energy distribution is investigated theoretically. It is shown that this kind of instability is associated with perturbations, the transverse wave-length of which is of the order of the banana width of trapped alpha particles. It occurs during resonance between the Alfven wave frequency and the bounce frequency of trapped alpha particles. The instability growth rate is of the order of the oscillation frequency multiplied by the ratio of the alpha-particle density to the plasma density. (author)