SELECTIVE GYROBROADENING OF ALPHA-PARTICLE ENERGY-SPECTRUM

Lower-hybrid alpha cyclotron waves driven by energetic alphas clue to relativistic mass variation and their interaction are studied with par ticle-in-cell simulations. In contrast to the anomalous thermalization of protons (whose driven instability is stable for the alphas), the i nteraction due to a different instability is selective (i.e., only alp has with perpendicular momentum above threshold are gyrobroadened) and it stops when they are slowed down to the threshold. An explanation i s given. The interaction persists in the case of a magnetic field with a sinusoidal non-uniformity. (C) 1998 Elsevier Science B.V.