Abstract
A spectrally selective imaging system has been developed to obtain a distribution of Hα 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 Hα distribution in the range up to 20 mm from the PG surface was clearly observed. The reduction area for Hα emission caused by beam extraction was widely distributed in the extraction region near the PG surface.
Highlights
A distribution of negative hydrogen ion (H− ) and its extraction behavior are the important contents to produce a homogeneous beam which is a critical issue for stable and highpower operation for a large-scaled and high-energy neutral beam injectors (NBI) that used arc discharge H− sources[1, 2] and will use radio frequency (RF) discharged source.[3]
A line of sight (LOS) of the imaging system passed through the center of the viewing port arranged parallel to the plasma grid (PG) surface with the distance of 11 mm
H− ions generated at the PG surface are widely distributed during arc discharge in the optimal Cs condition, it decreases caused by the particle loss owing to the beam extraction
Summary
A distribution of negative hydrogen ion (H− ) and its extraction behavior are the important contents to produce a homogeneous beam which is a critical issue for stable and highpower operation for a large-scaled and high-energy neutral beam injectors (NBI) that used arc discharge H− sources[1, 2] and will use radio frequency (RF) discharged source.[3]. Excited-state (n = 3) neutral hydrogens are produced by this reaction, and it emits hydrogen Balmer-α spectrum (Hα ) during the transition of energy level (n = 3 → 2). For this reason, an optical emission spectroscopy (OES) diagnostic for hydrogen Balmer line emission had been carried out in the negative ion source for monitoring negative ion densities.[4] In order to investigate behavior of H− ions, we developed an imaging diagnostic method with a high voltage insulation for negative ion source for NBI. The intensity of Hα emission dropped during beam extraction, the area of which was widely distributed in the extraction region
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