Development of spectrally selective imaging system for negative hydrogen ion source

Abstract

A spectrally selective imaging system has been developed to obtain a distribution of H α emissions at the extraction region in a hydrogen negative ion source. The diagnostic system consisted of an aspherical lens, optical filters, a fiber image conduit, and a charge coupled device detector was installed on the 1/3-scaled hydrogen negative ion source in the National Institute for Fusion Science. The center of sight line passes beside the plasma grid (PG) surface with the distance of 11 mm, and the viewing angle has coverage 35 mm from the PG surface. Two dimensional H α distribution in the range up to 20 mm from the PG surface was clearly observed. The reduction area for H α emission caused by beam extraction was widely distributed in the extraction region near the PG surface.

Installation of spectrally selective imaging system in RF negative ion source

“…A spectrally-selective imaging system has been developed and installed in the arc discharge type negative hydrogen ion (H − ) source in the National Institute for Fusion Science (NIFS) 1,2 . This system has been well performed to visualize a reduction in the distribution of hydrogen Balmer-α emission (H α ) owing to H − ions; these findings have contributed to the high performance and safety operation for a neutral beam injector (NBI) in the Large Helical Device (LHD).…”

Evaluation of negative ion distribution changes by image processing diagnostic

“…The bias insulator is sandwiched between the magnetic filter flange and the PG flange to control PG potential by bias voltage. We install an optical sapphire window and a spectrally selective imaging system, which consists of a H α band-pass interference filter and CCD detector [10] on the outside of the bias insulator. Figure 1(a) shows the configuration of line of sight (LOS) for a spectrally selective imaging system.…”

“…H α intensity was strongly related to the H -density because the excitation process for mutual neutralization between H + and H -ions is dominant in the low temperature plasma and rich H -condition. By utilizing this phenomenon, we have developed the spectrally selective imaging system to investigate the H -behavior in the wide range area near the PG aperture [10,11]. Then, we have found the interesting structure of the distribution of H α reduction.…”