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Author(s):
Y. Takeiri, A. Ando, O. Kaneko, Y. Oka, K. Tsumori, R. Akiyama, E. Asano, T. Kawamoto, T. Kuroda, M. Tanaka and H. Kawakami
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Title:
Development of an Intense Negative Hydrogen Ion Source with a Wide-Range of External Magnetic Filter Field
Date of publication:
Sep. 1994
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Key words:
negative hydrogen ion source, negative-ion-based NBI, external magnetic filter, high arc efficiency, low gas pressure operation, two-stage acceleration
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Abstract:
An intense negative hydrogen ion source has been developed, which has a strong external magnetic filter field in the wide area of 35 cm x 62 cm produced by a pair of permanent magnet rows located with 35.4 cm separation. The filter strength is 70 G in the center and the line-integrated filter strength is 850 G cm, which keeps the low electron temperature in the extraction region. Strong cusp magnetic field, 1.8 kG on the chamber surface, is generated for improvement of the plasma confinement. These resulted in the high arc efficiency at the low operational gas pressure. A 16.2 A of the H ^- ion current with the energy of 47 keV was obtained at the arc efficiency of 0.1 A/kW at the gas pressure of 3.8 mTorr in the cesium-mode operation. The magnetic field in the extraction gap is also strong, 450 G, for the electron suppression. The ratio of the extraction to the negative ion currents was less than 2.2 at the gas pressure of 3 mTorr. The two-stage acceleration was tried, and a 13.6 A of the H^- ion beam was accelerated to 125 keV.
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