IAEA Fusion Energy Conference 2010

Proceedings of the 23rd IAEA Fusion Energy Conference
Daejeon, 11-16 October 2010

Organized by the International Atomic Energy Agency
and hosted by the Government of the Republic of Korea


(ITR/2-4Rb) 1 MV Holding and Beam Optics in a Multi-Aperture Multi-Grid Accelerator for ITER NBI

M. Kashiwagi1), M. Taniguchi1), A. Kojima1), M. Dairaku1), M. Hanada1), R.S. Hemsworth2), T. Mizuno1), J. Takemoto1), M. Tanaka2), Y. Tanaka1), H. Tobari1), N. Umeda1), K. Watanabe1), M. Yamamoto1), T. Yamanaka1), K. Sakamoto1), T. Inoue1)
1) Japan Atomic Energy Agency, 801-1-Mukouyama, Naka 311-0193, Japan
2) ITER Organization, Cadarache Centre, 13067 St Paul lez Durance Cedex, France

Abstract.   At JAEA as the JApan Domestic Agency (JADA) for ITER, a multi-aperture multi-grid (MAMuG) accelerator has been developed for the ITER neutral beam heating & current drive (NB H&CD) system. A target is H- ion beam acceleration of 0.5 A (200 A/m2) at 1 MeV for several tens of seconds. In the tests to achieve the 1 MV holding, it was found that the voltage holding of the real accelerators was about a half of that obtained in an ideal small electrode. After applying necessary gap length and radii of edges of grid supports to lower the local electric field concentrations, the accelerator succeeded in sustaining 1 MV for more than one hour without feeding H2 gas. In the beam acceleration, the beamlet was deflected due to magnetic field and space charge repulsion. Consequently these deflections caused high heat load to the grids, and limited the beam pulse length. The beamlet deflection and its compensation methods, which are an aperture offset and so-called “field shaping plate”, were examined by a three-dimensional beam analysis. And then, these compensation methods were applied to the MAMuG accelerator. As results, beam parameters achieved by the MAMuG accelerator were increased to 879 keV, 0.36 A (157 A/m2) at perveance matched condition and 937 keV, 0.33 A (144 A/m2) slightly under perveance from 796 kV, 0.32 A (140 A/m2) reported in the previous conference.

Full paper and slides available (PDF)