Updated physics design ITER-SINGAP accelerator

In contrast to the Multi Aperture-MUlti Grid (MAMuG) concept of the ITER neutral beam injector reference design [1] in which D− acceleration to 40 A, 1 MeV is achieved through seven grids containing 1280 apertures each, the European SINgle GAP-SINGle Aperture (SINGAP) concept proposes acceleration of 1280 pre-accelerated (20-50 keV) beamlets to 1 MeV in a single step. During acceleration the beamlets are merged into 16 beam groups of 80 beamlets. These 16 beam groups (“hyperbeamlets”) then emerge from an exit grid containing only 16 very large apertures. This concept is expected to reduce cost and increase the tolerance to mechanical errors and stray magnetic fields. The physics of this concept and a design have been described before by ourselves [2]. Improved computational facilities have enabled us to calculate larger models and this has led to necessary modifications to the design which are described in this paper.