Progress of negative ion measurements and understanding of negative ion transport

The authors introduced measurement devices related with negative ions into the vicinity of the negative ion generation region of the surface-generated hydrogen negative ion source, and experimentally verified the transport phenomenon from generation up to extraction of negative ions. The hydrogen negative ions generated on the surface of the plasma grid (PG) are uniformly distributed in the extraction region between PG and the filter magnetic field, and they form ionic plasma composed of H+ and H- due to a drastic decrease in electron density following an increase in hydrogen negative ion density. In ionic plasma, it was confirmed that the potential distribution of the plasma was strongly influenced by the potential of adjacent metal surfaces. It was also clarified that the Hα light emitted from the ionic plasma strongly depends on the mutual neutralization reaction of H+ and H-, and based on their two-dimensional distribution measurement, the negative ion reduction region associated with beam extraction was clarified. In addition, from the negative ion flow distribution using the laser-assisted photo-detachment method, it was confirmed that the negative ions generated on the surface are diffused in the direction of the magnetic field lines of the electron deflection magnetic field, and transported to negative ion PG by turning to the PG direction at the position around 20 mm from PG. (A.O.)