Propagation of waves generated in tandem-mirror end cells

Abstract

Slow waves generated by ion cyclotron instabilities in tandem-mirror end cells may propagate into the central cell where the waves may degrade ion confinement. Such propagation and degradation occurred in TMX, but not in TMX-U because of the improved neutral-beam injection geometry of the latter device. Fast waves observed in a central cell may arise by mode conversion near the ends of the central cell if the slow-wave amplitude is large there and if the slow and fast waves have comparable perpendicular wavelengths. Comparable wavelengths were present in TMX, but not in TMX-U; the fast-wave amplitudes observed in TMX-U which are much lower than those in TMX are thus consistent with mode-conversion theory.

Probe wave system for studying excitation of Alfvén eigenmodes in the ion cyclotron range of frequency

“…4 These modes are detected as axial eigenmodes determined from the plasma pressure profile in the axial direction. 5 The condition predicted by a theory 6 for the absolute instability is about one order of magnitude higher than that observed in the experiments. 7 The mechanism for the excitation of AIC modes in the GAMMA 10 plasma is not clear at present.…”

Eigenmode excitation of Alfvén ion cyclotron instability

“…14,15 Thus, it is of a crucial importance to study AIC modes in a tandem mirror. The first experimental observation of the AIC modes was made in the end-cell plasmas of the TMX ͑Tandem Mirror Experiment͒ device, 11,16 which were produced by perpendicularly injected highenergy neutral beams, and degradation of the confinement was reported. Stabilization of the AIC mode was achieved in the TMX-U device by reducing anisotropy with an oblique injection of a neutral beam.…”