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

Abstract

R&D pertaining to a 1 MeV accelerator and a large negative ion source has been carried out at the Japan Atomic Energy Research Institute for the ITER neutral beam system. The R&D is, at present, progressing towards: (1) 1 MeV acceleration of H− ion beams at the ITER relevant current density of 200 A m−2 and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H− ion beams of 1 MeV and 140 mA level have been generated with a substantial beam current density (100 A m−2). In the uniformity study, it was clarified that the electron temperature in the ion extraction region was locally high (>1 eV), which resulted in the 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 to be effective in lowering the local electron temperature, followed by an improvement of negative ion beam profile.

Deuterium trapping in tungsten damaged by high-energy hydrogen ion irradiation

“…Radiation damage was produced using a MeV accelerator MTF [14]. Negative ions of 300 and 700 keV H À were used for damage creation.…”

Blister formation on tungsten damaged by high energy particle irradiation

“…Details of this facility were reported elsewhere [15]. Tungsten samples were fixed on a sample holder made of copper.…”

Energetic ion transport by microturbulence is insignificant in tokamaks

“…Later work 79 reviewed NBI (E b ¼ 1 MeV) in ITER and determined that expected NBCD profile modification was minimal. It is worth noting that work considered fractional beam energy components (E b =2 and E b =3) that arise in standard neutral beams from molecular deuterium, 80 but MeV beams in ITER will use negative neutral sources 81 that produce only the full energy component. The inclusion of lower energy beam ions should tend to increase the modeled effect of turbulence-induced diffusion.…”