A generalized sufficient condition for velocity-space stability of fusion product distributions and application to heating of d-t tokamak reactors

A generalized condition is derived for the velocity-space distribution of suprathermal alpha- particles to be monotonically decreasing with energy — and hence stable to homogeneous plasma instabilities — during the heating phase of a tokamak reactor. This stability condition is easily satisfied for presently envisaged neutral-injection heating of reactors, but may be violated in strong heating of smaller plasmas or during fast compressional heating.