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Author(s):
Y. Takeiri, M. Osakabe, Y. Oka, K. Tsumori, O. Kaneko, T. Takanashi, E. Asano, T. Kawamoto, R. Akiyama and T. Kuroda
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Title:
Long-pulse Operation of a Cesium-Seeded High-Current Large Negative Ion Source
Date of publication:
Jan. 1997
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Key words:
negative ion source, negative-ion-based NBI, long pulse operation, cesium seeding, long-pulse arc discharge, grid thermal load, neutralization efficiency, grid aperture shaping, stripping loss
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Abstract:
A high-power large negative ion source has been operated for a long pulse duration. A three-grid single-stage accelerator is used, where the extraction grid is shaped so that the secondary electrons generated on the extraction grid would be prevented from leaking into the acceleration gap. A stable long-pulse arc discharge with an arc power of 100 kW has been obtained over 15 s by balancing an individual arc current flowing through each filament. The cesium-seeded operation is not influenced by a temperature rise of over 100 degree C of the plasma grid during the long-pulse arc discharge. As a result, the negative ion beam power of 330 kW (91 keV-3.6 A) was produced stably for 10 s from an area of 25 cm X 26 cm, where the current density was 21 mA/cm^2 and the negative ion power density was 1.9 kW/cm^2. The neutralization efficiency of accelerated negative ions has been measured including the residual positive and negative ion ratios by the water calorimetry of the beam dumps. The result agrees well with the calculation result.
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