(IT/P7-4) High Energy, High Current Accelerator Development for ITER NBI at JADA

Mieko Kashiwagi1), M. Taniguchi1), M. Dairaku1), H.P.L. de Esch2), L.R. Grisham3), L. Svensson2), H. Tobari1), N. Umeda1), K. Watanabe1), K. Sakamoto1), T. Inoue1)
1)Japan Atomic Energy Agency, 801-1 Mukouyama, Naka 311-0193, Japan
2)CEA Cadarache, F-13108 St. Paul-lez-Durance CEDEX, France
3)Princeton University Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543, USA

Abstract.  The ITER neutral beam (NB) system is constructed so as to inject 33 MW of D0 beams from two NB injectors at the beam energy of 1 MeV. To meet the requirement, development of a high energy and high current accelerator is in progress at Japan Atomic Energy Agency (JAEA), utilizing two existing facilities. One is the MeV Test Facility (MTF) which is capable of 1 MeV and 0.5 A H- ion acceleration. In the multi-aperture multi-grid (MAMuG) electrostatic accelerator, called as MeV accelerator, consisting of five stages, acceleration of high current density beams (836 keV, 0.2 A H- at 146 A/m2) was reported in the previous conference. The present paper reports countermeasure against backstream positive ion beam as a new issue under high power operation and consequent increase in the beam current to 0.32 A H- at 796 keV, where the accelerated drain current including electrons was almost power supply limit. In a first beam acceleration test with a single-aperture single-gap (SINGAP) accelerator at the MTF under collaboration with JAEA and CEA, a notable difference of SINGAP from MAMuG was in a relatively high co-accelerated electron current. The mechanism of electron production and acceleration in the unique simple geometry is discussed in this paper. Another facility is the negative ion based NB system of the JT-60U, of which rated beam power is 500 keV and 22 A D- ion acceleration. A result of three dimensional analysis of JT-60U beamlets shows a beamlet deflection by space charge repulsion. An aperture offset at exit of extractor is suggested effective as the compensation for all beamlet deflections.

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