Ion Cyclotron Instabilities Driven by the Nearly Perpendicular Neutral Beam Injection in the Wendelstein VII-A Stellarator

摘要

The problem of ion cyclotron instabilities driven by the high power neutral beam injection is investigated for the conditions of the W VII-A stellarator by means of linear stability analysis. On the basis of only collisional (classical) slowing down, beam ion distribution functions are calculated by means of Monte Carlo simulation. In this report, various cases are considered: Transient beam ion distributions (i) immediately after switch on the neutral beam injection and (ii) after half of an average slowing down time; stationary beam ion distributions (iii) for confinement properties strongly improved by radial electric fields, transport and fast orbit losses are neglected for these situations, and (iv) for worse confinement properties for which the average beam ion confinement time is of the order of the average slowing down time. Furthermore, the distribution functions of the ions originating from the neutral beam injection are estimated for the early phase of the discharges with low temperatures and for the later phase with maximum ion temperatures. (ERA citation 13:005230)