Escaping Ion Measurement with High Time Resolution during Bursting Modes Induced by Neutral Beam Injection on CHS

Abstract

A bursting mode, whose time scale is a few milliseconds, is excited in low density neutral beam injected plasmas in the compact helical system. A scintillator-based probe equipped with a high speed video camera has been used to investigate the energetic ion losses induced by this fast evolving mode. This instrument reveals loss in a region of the gyroradius and the pitch angle space that occurs only during a burst. Namely, it was found that the bursting mode induces the transport of energetic ions to the region where the energetic ions cannot exist without such an enhanced transport. The dependence of the newly observed loss on the electron density and the neutral beam injected power was also investigated.