Spectroscopic observations of beam and source plasma light and testing Cs-deposition monitor in the large area negative ion source for LHD-NBI

In the large area negative ion source for the LHD negative-ion-(H−)-based neutral beam system, (I) we used the spectrometer to measure caesium lines in the source plasma during beam shots. (II) With Doppler-shifted measurements, the Hα line at three different locations along the beam as well as the spectrum profile for cases of different plasma grid areas. (III) Caesium deposition monitor with a high speed shutter was tested to measure the weight of the deposited Cs layer. In the observation, cleaner spectra of Doppler-shifted Hα line with only a small level of background light were obtained at a new observation port which viewed the blueshifted light in the drift region after the accelerator of a LHD ion source. Both the amounts of CsI (852nm, neutral Cs0) and CsII (522nm, Cs+) in the source plasma light rose sharply when beam acceleration began, and continued rising during a 10s pulse. It was thought that this was because the cesium was evaporated/sputtered from the source back plate by the back-streami...