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Origin of Non-Uniformity of the Source Plasmas in JT-60 Negative Ion Source

Masafumi YOSHIDA, Masaya HANADA, Atsushi KOJIMA, Takashi INOUE, Mieko KASHIWAGI, Larry R GRISHAM¹⁾, Noboru AKINO, Yasuei ENDO, Masao KOMATA, Kazuhiko MOGAKI, Shuji NEMOTO, Masahiro OHZEKI, Norikazu SEKI, Shunichi SASAKI, Tatsuo SHIMIZU and Yuto TERUNUMA

Japan Atomic Energy Agency, 801-1 Mukoyama, Naka 311-0193, Japan

1)

Princeton Plasma Physics Laboratory, Princeton, USA

(Received 6 December 2012 / Accepted 14 August 2013 / Published 15 November 2013)

Abstract

In order to investigate the origin of the non-uniformity of the source plasmas in the JT-60 negative ion source, the distribution of H⁺ ions and H⁰ atoms, which were converted to H⁻ ions on the cesium covered surface, were measured by Langmuir probes and emission spectroscopy. Both of H⁺ ions and H⁰ atoms at the top and bottom of the ion source were about twice higher and lower than those in the center region, respectively. In particular, they were highly localized near the side wall of the top of the ion source. The analyses of the primary electron trajectories showed that this non-uniformity was due to the B x grad B drift of primary electrons emitted from filaments. These results suggest that the non-uniformity of the negative ions results in a locally poor beam optics and significant direct interception of the H⁻ ions on the acceleration grid. This is the reason why the negative ion beams are non-uniform in the JT-60 negative ion source.

Copyright (c) 2013 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

negative ion source, neutral beam injection, arc discharge, Langmuir probe and emission spectroscopy

DOI: 10.1585/pfr.8.2405146

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This paper may be cited as follows:

Masafumi YOSHIDA, Masaya HANADA, Atsushi KOJIMA, Takashi INOUE, Mieko KASHIWAGI, Larry R GRISHAM, Noboru AKINO, Yasuei ENDO, Masao KOMATA, Kazuhiko MOGAKI, Shuji NEMOTO, Masahiro OHZEKI, Norikazu SEKI, Shunichi SASAKI, Tatsuo SHIMIZU and Yuto TERUNUMA, Plasma Fusion Res. 8, 2405146 (2013).