Selective gyrobroadening of alpha particle energy spectrum

Lower-hybrid alpha cyclotron waves driven by energetic alphas due to relativistic mass variation and their interaction are studied with particle-in-cell simulations. In contrast to the anomalous thermalization of protons (whose driven instability is stable for the alphas), the interaction due to a different instability is selective (i.e., only alphas with perpendicular momentum above threshold are gyrobroadened) and it stops when they are slowed down to the threshold. An explanation is given. The interaction persists in the case of a magnetic field with a sinusoidal non-uniformity.