Plasma and Fusion Research

Volume 2, 022 (2007)

Letters

Negative Ion Production in High Electron Temperature Plasmas

Hiroyuki TOBARI, Takayoshi SEKI, Naoyuki TAKADO¹⁾, Masaya HANADA, Takashi INOUE, Mieko KASHIWAGI, Akiyoshi HATAYAMA¹⁾ and Keishi SAKAMOTO

Fusion Research and Development Directorate, Japan Atomic Energy Agency
1): Keio University

(Received 16 February 2007 / Accepted 10 April 2007 / Published 4 June 2007)

Abstract

In our recent experiment, it was found that intense negative ion beams could be extracted from high-density and high-electron temperature plasmas under a Cesium seeded condition. This indicates that such plasmas contribute to the surface production of negative ions, and that the negative ion production exceeds the destruction process via electron detachment. Thus, it has been suggested that highly ionized and dissociated plasmas are suitable for the surface production of negative ions. This paper reports the results of specific experiments to confirm the negative ion production in plasmas with high-electron temperature. In these experiments, high electron temperature plasmas were produced by (1) placing filaments (acting as cathodes) near the extraction area, and (2) reducing the magnetic filter strength, both to allow fast electrons access to the beam extraction area. The results support the production of high-density H^- ions even in plasmas with high-electron temperature. Also included is a discussion on the surface production mechanism of negative ions under a Cs-seeded condition.

Keywords

NBI, negative ion source, beam uniformity, surface production, magnetic filter

DOI: 10.1585/pfr.2.022

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This paper may be cited as follows:

Hiroyuki TOBARI, Takayoshi SEKI, Naoyuki TAKADO, Masaya HANADA, Takashi INOUE, Mieko KASHIWAGI, Akiyoshi HATAYAMA and Keishi SAKAMOTO, Plasma Fusion Res. 2, 022 (2007).