Compensations of beamlet deflections for 1 MeV accelerator of ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; Dairaku, Masayuki; Tobari, Hiroyuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Inoue, Takashi; DeEsch, H. P. L.*; Grisham, L. R.*; et al.

AIP Conference Proceedings 1515, p.227 - 236, 2013/02

https://doi.org/10.1063/1.4792789

In a five stage multi-aperture multi-grid (MAMuG) accelerator for the ITER neutral beam injector (NBI), 1 MeV, 40 A D ion beam is required for 1 hour. However, beamlets are deflected due to (1) magnetic field for electron suppression and (2) space charge repulsion between beamlets, and consequently, cause excess grid heat load. A three dimensional beam analysis has been carried out to compensate the beamlet deflections. This paper shows that the beamlet deflections due to (1) and (2) are compensated by an aperture offset of only 0.6 mm applied to the aperture of 17 mm in diameter in the extractor and by a metal bar attached around aperture area beneath the extractor, respectively. When the metal bar is increased to 3 mm in thickness and installed 30 mm away from the aperture area, the beamlet is steered gently by the weaker electric field distortion. The beam optics was confirmed not deteriorated by those compensations. The presentation also discusses application of these compensation techniques to the ITER design.

Results of the SINGAP neutral beam accelerator experiment at JAEA

DeEsch, H. P. L.*; Svensson, L.*; Inoue, Takashi; Taniguchi, Masaki; Umeda, Naotaka; Kashiwagi, Mieko; Fubiani, G.*

Fusion Engineering and Design, 84(2-6), p.669 - 675, 2009/06

https://doi.org/10.1016/j.fusengdes.2009.01.017

Status of the ITER heating neutral beam system

Hemsworth, R. S.*; Decamps, H.*; Graceffa, J.*; Schunke, B.*; Tanaka, Masanobu*; Dremel, M.*; Tanga, A.*; DeEsch, H. P. L.*; Geli, F.*; Milnes, J.*; et al.

Nuclear Fusion, 49(4), p.045006_1 - 045006_15, 2009/04

https://doi.org/10.1088/0029-5515/49/4/045006

The ITER neutral beam (NB) injectors are the first injectors that will be operated under conditions and constraints similar to those in a fusion reactor. These injectors will be operated in a radiation environment and they will be activated due to the neutron flux from ITER. The injectors uses a single large ion source and accelerator that will produce 40 A 1 MeV D beams for pulse lengths of up to 3600 s. Design changes have been made to the ITER NB injectors over the past 4 years as follows: (1) Modifications to allow installation and maintenance of the beamline components with an overhead crane. (2) The RF driven negative ion source has replaced the filamented ion source. (3) The ion source power supplies will be located in an air insulated high voltage (-1 MV) deck located outside the tokamak building instead of inside an SF6 insulated HV deck located above the injector. This paper describes the status of the design as of December 2008 including the above mentioned changes.

Results of the SINGAP neutral beam accelerator experiment at JAEA

DeEsch, H. P. L.*; Svensson, L.*; Inoue, Takashi; Taniguchi, Masaki; Umeda, Naotaka; Kashiwagi, Mieko; Fubiani, G.*

AIP Conference Proceedings 1097, p.353 - 363, 2009/03

https://doi.org/10.1063/1.3112532

CEA Cadarache and JAEA Naka have entered into a collaboration in order to test a SINGAP accelerator at the Megavolt Test Facility (MTF) at Naka, Japan. Whereas at the CEA testbed the acceleration current was limited to 0.1 A, at JAEA 0.5 A is available. This allows the acceleration of 15 H beamlets in SINGAP to be tested and a direct comparison between SINGAP and MAMuG to be made. High-voltage conditioning in the SINGAP configuration has been quite slow, with 581 kV in vacuum achieved after 140 hours of conditioning. With 0.1 Pa of H gas present in the accelerator 787 kV could be achieved. The conditioning curve for MAMuG is 200 kV higher. A beamlet divergence better than 5 mrad was obtained. SINGAP accelerates electrons to a higher energy than MAMuG. 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.

High energy, high current accelerator development for ITER NBI at JADA

Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; DeEsch, H. P. L.*; Grisham, L. R.*; Svensson, L.*; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; et al.

Proceedings of 22nd IAEA Fusion Energy Conference (FEC 2008) (CD-ROM), 8 Pages, 2008/10

http://www-naweb.iaea.org/napc/physics/FEC/FEC2008/html/node376.htm#78335

At JAEA, beam parameters achieved by the MAMuG (multi-aperture multi-grid) accelerator were increased to 0.32 A H at the ion current density of 140 A/m and 796 keV at the beam energy. This was achieved as the result of countermeasures to handle unexpected heat load by backstream positive ions. A test of SINGAP (single-aperture single-gap) accelerator, which was performed at JAEA under an ITER R&D task agreement. The objective of this study was to compare the two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As the result, it was concluded that the MAMuG accelerator was more suitable for the ITER NBI because of its better voltage holding and less electron acceleration. A simulation is in progress for space charge repulsion of beamlets in the JT-60U accelerator. An aperture offset steering was suggested effective at exit of extractor for compensation of the beamlet deflection due to its own space charge.