Beam optics of the SINGAP 1 MeV 100 mA D- direct current accelerator for thermonuclear fusion

Injection of intense neutral beams (e. g., ITER up to 50 MW of neutral powe r) based on the neutralization of negative deuterium ions up to energies of 1 MeV is an important option for plasma heating and noninductive current d rive in future thermonuclear fusion machines. The objective of the SINGAP e xperiment is to demonstrate the acceleration of 100 mA of D- to 1 MeV in an electrostatic accelerator concept. It is composed of only two acceleration stages: a preacceleration to 60 keV in a multiaperture structure, and a po stacceleration to 1 MeV. The particular feature of the SINGAP accelerator i s that the postaccelerator by means of an electrostatic lens merges the 60 keV beamlets into a single beam and accelerates the merged beam to 1 MeV in a single gap. The present article is devoted to the SINGAP optics study (s imulation and experiment) for two geometric configurations: cylindrical and rectangular (more ITER relevant). Despite a higher measured divergence (8 mrad) than expected (4-5 mrad calculated) which is due to the magnetic fiel d of the electron suppression system, this study has proved that the SINGAP concept can meet the optical requirement (divergence <5 mrad) for multiamp eres injectors. (C) 1999 American Institute of Physics. [S0034-6748(99)0240 3-X].