NEGATIVE-ION BEAM DEVELOPMENT AT CADARACHE

Neutral beam injection (NBI) is one of the candidates for plasma heati ng and current drive in the new generation of large magnetic fusion de vices (ITER). In order to produce the required deuterium atom beams wi th energies of 1 MeV and powers of tens of MW, negative D- ion beams a re required. For this purpose, multiampere D- beam production and 1 Me V electrostatic acceleration is being studied at Cadarache. The SINGAP experiment, a 1 MeV 0.1 A D- multisecond beam accelerator facility, h as recently started operation. It is equipped with a Pagoda ion source , a multiaperture 60 keV preaccelerator and a 1 MV 120 mA power supply . The particular feature of SINGAP is that the postaccelerator merges the 60 keV beamlets, aiming at accelerating the whole beam to 1 MeV in a single gap. The 1 MV level was obtained in less than 2 weeks, the a ccumulated voltage on-time of being similar to 22 min. A second test b ed MANTIS, is devoted to the development of multiampere D- sources. It is capable of driving discharges with current up to 2500 A at are vol tages up to 150 V. A large multicusp source has been tested in pure vo lume and cesiated operation. With cesium seeding, an accelerated D- be am current density of up to 5.2 mA/cm(2) (2 A of D-) was obtained. A m odification of the extractor is underway in order to improve this perf ormance. A 3D Monte Carlo code has been developed to simulate the nega tive ion transport in magnetized plasma sources and optimize magnetic field configuration of the large area D- sources. (C) 1996 American In stitute of Physics.