Development of plasma neutralizer using DC arc discharge

A system efficiency of neutral beam injection (NBI) depend strongly on a neutralization efficiency of ion beam. Development of a plasma neutralizer (PN) is an attractive issue for the high power NBI, because the neutralization efficiency in PN is expected to be more than 80% which is higher than that of conventional gas neutralizers of 60%. To realize PN, a cylindrical multicusp large volume plasma source whose dimensions are 2000 mm in length and 600 mm in diameter was fabricated and tested. A smaller plasma source whose sizes are 1400 mm in length and 320 mm in diameter was also tested to compare plasma confinement properties. The results show that high degree of ionization was obtained at a lower gas pressure in the plasma generator with higher confinement property. This tendency was also confirmed by a numerical analysis. In an argon plasma discharge, a degree of ionization of 10% with the plasma line density of 4.5x1015 cm-2 was obtained, which is desirable values to demonstrate plasma neutralization experiment effectively. A high degree of ionization of 17% was obtained at 0.027 Pa when an arc discharge power was 30 kW. (author)