Neutral flux measurements during neutral‐beam injection on Doublet III (abstract)

摘要

Neutral particle flux parallel and perpendicular to the plasma current and at energies equal to and below the injection energy has been observed with the parallel and perpendicular charge exchange spectrometers on Doublet III. Initial neutral injection is marked by a rapid increase in the high‐energy neutral efflux which usually relaxes over tens of milliseconds to a lower equilibrium value. As injected power is increased by the stepped addition of more neutral beams, the measured flux is not linearly additive, often increasing slightly or not at all. For very high values of injected power, in the 5–7‐MW range, the neutral particle flux is often observed in bursts correlated with the rapid fall of giant sawteeth on soft x‐ray signals. In many of these shots the fishbone instability is present and is observed with the perpendicular spectrometer, however the parallel flux does not correlate with fluctuations observed with magnetic probes unless the instability terminates rapidly, in which case both a soft x‐ray drop and a burst of neutrals occurs. Some aspects of these measurements have been modeled by a particle transport code with particular emphasis on changes in the neutral density profile during high‐power neutral injection.