Results of the SINGAP neutral beam accelerator experiment at JAEA

Abstract: IRFM (CEA Cadarache) and JAEA Naka have entered into a collaboration in order to test a Single Gap, Single Aperture (SINGAP) [H.P.L. de Esch, R.S. Hemsworth, P. Massmann, Updated physics design ITER-SINGAP accelerator, Fusion Eng. Des. 73 (2005) 329.] accelerator at the JAEA Megavolt Test Facility (MTF) at Naka, Japan. Whereas at the CEA testbed the acceleration current was limited to 0.1A, at JAEA 0.5A is available. This allows the acceleration of 15 H− beamlets in SINGAP to be tested and a direct comparison between SINGAP and Multi Aperture, Multi Grid (MAMuG) [M. Taniguchi, T. Inoue, N. Umeda, M. Kashiwagi, K. Watanabe, H. Tobari, M. Dairaku, K. Sakamoto, Acceleration of ampere class H− ion beam by MeV accelerator, Rev. Sci. Instrum. 79 (2008) 02C110.] to be made. High voltage conditioning in the SINGAP configuration has been quite slow, with 581kV in vacuum achieved after 140h of conditioning. With 0.25Pa of H2 gas present in the accelerator 787kV could be achieved. The conditioning curve for MAMuG is 200kV higher. SINGAP beam optics appears in agreement with calculation results. A beamlet divergence better than 5mrad was obtained. SINGAP accelerates electrons to a higher energy than MAMuG. Measurements of the power intercepted on one of the electron dumps have been compared with EAMCC code [G. Fubiani, H.P.L. de Esch, A. Simonin, R.S. Hemsworth, Modeling of secondary emission processes in the negative ion based electrostatic accelerator of the International Thermonuclear Experimental Reactor, Phys. Rev. ST Accel. Beams 11 (2008) 014202.] calculations. Based on the experiments described here, electron production by a SINGAP accelerator scaled up to ITER size was estimated to be too high for comfort. [Copyright &y& Elsevier]