1 MeV, ampere class accelerator R&D for ITER

Inoue, Takashi; Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Watanabe, Kazuhiro; Sakamoto, Keishi

The JAERI MeV accelerator has been designed extrapolating vacuum insulation design guidelines (the clump theory and Paschen law) to Mega Volt and long vacuum gap. Reduction of electric field concentration at triple junction by a large stress ring was effective to prevent flashover along insulator surface. By the vacuum insulation technology above, the accelerator sustained 1 MV for 8,500 s continuously. Strong enhancement of negative ion surface production has been attained by stopping vacuum leaks due to SF permeation through Viton O rings and a damage of port by backstream ions, followed by increase of the H ion current density without saturation. Operating the KAMABOKO source with high power arc discharge ( 40 kW), H ion beams of 146 A/m (total ion current: 0.2 A) have been obtained stably at the beam energy of 836 keV (pulse length: 0.2 s). Bremsstrahlung generation in the accelerator is also estimated from EGS4 analysis, and then discussion on the breakdown possibility follows.