R and D on a high energy accelerator and a large negative ion source for ITER

The R and D of a 1 MeV accelerator and a large negative ion source has been carried out at Japan Atomic Energy Research Institute (JAERI) for the ITER NB system. The R and D is in progress at present toward: 1) 1 MeV acceleration of H- ion beams at the ITER relevant current density of 200 A/m2, and 2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H- ion beams of 1 MeV, 140 mA level have been generated with a substantial beam current density (100 A/m2). In the uniformity study, it has been clarified that electron temperature in the ion extraction region is locally high (> 1 eV), which resulted in destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called 'magnetic filter' has been found effective to lower the local electron temperature, followed by an improvement of negative ion beam profile. (author)