BEAM SHEAR-ALFVEN INSTABILITY IN 2-COMPONENT TOKAMAK

The authors consider from a theoretical standpoint the excitation of shear-Alfven waves in a tokamak in which the plasma contains a fast ion group. It is assumed that the fast ions are formed as a result of fast neutral atoms injected into the tokamak. An expression is derived for the growth rate of the shear-Alfven oscillations, with an arbitrary relationship between the transverse wave length and the dimension of the Larmor and drift orbits. The authors analyse the part played by the finite orbit effect in the case of a longitudinal beam with a small Maxwellian velocity spread and an arbitrary ratio between the directed velocity V0 and the Alfven velocity cA. It is demonstrated that at a finite ratio V0/cA two physically different types of oscillations may build up, corresponding to the two signs of the ratio Ω/k| (Ω is the oscillation frequency, k| is the longitudinal wave number). The growth rate for perturbations with Ω/k|<0 is greater than for Ω/k∥>0. © 1979 Academia, Publishing House of the Czechoslovak Academy of Sciences.