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Non-Linear Dependence of Deflection Angle on Beam Steering Control Grid Displacement in Accelerator for N-NBI

Junichi HIRATSUKA, Masaya HANADA, Naotaka UMEDA, Atsushi KOJIMA, Mieko KASHIWAGI, Kazuhiro WATANABE, Hiroyuki TOBARI and Masafumi YOSHIDA

Japan Atomic Energy Agency (JAEA), 801-1 Mukoyama, Naka-shi, Ibaraki 311-0193, Japan

(Received 25 November 2014 / Accepted 18 March 2015 / Published 16 April 2015)

Abstract

To produce high current density (> 200 A/m²), high-energy (> 1 MeV) negative ion beams for long pulse duration time (1 hour) for International Thermo-nuclear Experimental Reactor (ITER), the suppression of the direct interception of the negative ions with the grids has been carefully investigated with studying the deflection angle by aperture displacement technique. The non-linear dependence of the deflection angle appears at the aperture diameter of > 14 mm on a steering control grid (SCG). From this dependence, the aperture diameter and the offset distance of the SCG has been designed to be 16 mm and 0.7 mm, respectively and tested in a prototype accelerator for ITER. Each of the beamlets on the multiple apertures is properly steered with compensation of the deflection due to the residual magnetic field in the accelerator and the grid power loading was significantly reduced. It resulted in a 10% enhancement of the accelerated beam current.

Copyright (c) 2015 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

ITER, neutral beam injection, accelerator, negative ion, beam steering control, electrostatic lens, space charge, MeV accelerator

DOI: 10.1585/pfr.10.3405045

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This paper may be cited as follows:

Junichi HIRATSUKA, Masaya HANADA, Naotaka UMEDA, Atsushi KOJIMA, Mieko KASHIWAGI, Kazuhiro WATANABE, Hiroyuki TOBARI and Masafumi YOSHIDA, Plasma Fusion Res. 10, 3405045 (2015).