Results of the 1 MV SINGAP experiment

Injection of intense neutral beams based on the neutralisation of negative deuterium ions up to energies of 1 MeV is an important option for plasma heating and non-inductive current drive in future thermonuclear fusion machines. The objective of the SINGAP experiment is to demonstrate the acceleration of 100 mA of D− to 1 MeV in an electrostatic accelerator concept which is substantially simpler than the multi-aperture, multi-grid accelerator system foreseen for the ITER neutral beam injectors. Voltage holding without beam has been demonstrated at above 1 MV after only 35 min of integrated voltage on-time. H− beams have been produced up to 860 kV, 40 mA in 1 s pulses and without caesium seeding of the ion source. With caesium admixture, D− beams of 105 mA have been accelerated to 630 keV for 1 s. These results were obtained at energies lower than 700 keV because of the bushing deterioration. The measurements of the beam profiles are in good agreement with the results obtained from 3D trajectory calculations.