Ion cyclotron resonance heating and the Alfvén-ion cyclotron instability

Abstract

A simulation study of physical processes involved in ion cyclotron resonance heating and associated radio frequency plugging of a mirror confined plasma was carried out utilizing 1–2/2 dimensional magnetostatic particle code. Three heating regimes are discerned: weak, moderate and strong, characterized primarily by the pump wave amplitude. The pump waves induced other modes to various degrees, particularly so in the moderate and strong heating regimes. The heating increases ion magnetic moments; this property is applied to radio frequency plugging of a mirror. Modest improvements in confinement were observed in some moderate heating regimes. At the same time, pump-induced wave excitation enhances the velocity space diffusion of the ions, which tends to negate the increased magnetic moments. Induced excitation of Alfvén-ion cyclotron waves becomes intense when the heating results in a strongly anisotropic ion distribution, giving rise to the onset of the Alfvén-ion cyclotron instability. When the anisotropy becomes significant, the instability becomes rich in hydrodynamic characters and this is found to be very detrimental to confinement. A hydrodynamic model of this instability is constructed and examined in detail by simulation.