SINGAP: The European concept for negative ion acceleration in the ITER neutral injectors

In contrast to the multiaperture–multigrid concept of the International Thermonuclear Experimental Reactor (ITER) injector reference design in which D− acceleration to 40 A, 1 MeV is achieved through seven grids containing 1280 apertures each, the European SINGAP (single gap–single aperture) concept proposes acceleration of 1280 preaccelerated (20–50 keV) beamlets to 1 MeV in a single step. During acceleration the beamlets are merged into 16 groups of 80 beamlets. These 16 so-called 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 SINGAP physics is described here. The SINGAP beam optics is calculated to provide good beam transmission (86%) to the ITER.