Magneto-acoustic cyclotron instability due to neutral beam injection

Abstract

Instabilities driven by energetic ion beams injected for ion heating in magnetically confined plasmas have attracted considerable interest in connection with both plasma heating and containment. In this paper, the range of fast-ion distribution functions resulting from near-perpendicular neutral injection into Doublet-3 is determined using a numerical Fokker-Planck code and a guiding-centre Monte Carlo code. Guided by these results, we consider the possibility of exciting magnetosonic cyclotron instability due to anisotropic non-Maxwellian energetic ions streaming at an arbitrary angle with respect to the magnetic field, and show the possibility of unstable waves with fairly large growth rates. The threshold condition and the range of physical parameters where such a growth is possible are obtained. We also consider the contribution of magnetically trapped energetic beam particles to the growth of such magneto-acoustic cyclotron waves.