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 H(alpha) 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 H(alpha) 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 Cs I (852 nm, neutral Cs(0)) and Cs II (522 nm, Cs(+)) in the source plasma light rose sharply when beam acceleration began, and continued rising during a 10 s pulse. It was thought that this was because the cesium was evaporated/sputtered from the source back plate by the back-streaming positive ions. Cs deposition rate to the crystal sensor measured by adjusting the shutter open time was evaluated to be 2.9 nanograms/s cm(2) for preliminary testing. More neutral Cs tended to be evolved in the source after arc discharge. Much Cs could be consumed in a high rate-pulsed operation (such as LHD source).
Oka
Y
Y
National Institute for Fusion Science, Toki, Gifu, Japan. oka@lhd.nifs.ac.jp
Tsumori
K
K
Ikeda
K
K
Kaneko
O
O
Nagaoka
K
K
Osakabe
M
M
Takeiri
Y
Y
Asano
E
E
Komada
S
S
Kondo
T
T
Sato
M
M
Shibuya
M
M
Grisham
L R
LR
Ikeda
Y
Y
Hanada
M
M
Umeda
N
N