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Author(s):
Y. Takeiri, A. Ando, O. Kaneko, Y. Oka, K. Tsumori, R. Akiyama, E. Asano, T. Kawamoto, M. Tanaka and T. Kuroda
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Title:
High-Energy Acceleration of an Intense Negative Ion Beam
Date of publication:
Feb. 1995
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Key words:
negative ion source, high-energy acceleration, negative-ion-based NBI external magnetic filter, cesium seeding, neutralization efficiency
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Abstract:
A high-current H^- ion beam has been accelerated with the two-stage acceleration. A large negative hydrogen ion source with an external magnetic filter produces more than 10 A of the H^- ions from the grid area of 25 cm x 50 cm with the arc efficiency of 0.1 A/kW by seeding a small amount of cesium. The H ion current increases according to the 3/2-power of the total beam energy. A 13.6 A of H^- ion beam has been accelerated to 125 keV at the operational gas pressure of 3.4 mTorr. The optimum beam acceleration is achieved with nearly the same electric fields in the first and the second acceleration gaps on condition that the ratio of the first acceleration to the extraction electric fields is adjusted for an aspect ratio of the extraction gap. The ratio of the acceleration drain current to the H^- ion current is more than 1.7. That is mainly due to the secondary electron generated by the incident H^- ions on the extraction grid and the electron suppression grid. The neutralization efficiency was measured and agrees with the theoretical calculation result.
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