FRP insulator column for high current accelerator of ITER; International thermonuclear experimental reactor

Inoue, Takashi

In ITER as a thermonuclear fusion experimental reactor being conducted by an international project, a large bore insulator ring of about 1.8 m in diameter is required for generation of 1 MeV, 40 A ion beam for plasma heating by Neutral Beam Injector. At JAEA, R&D has been carried out for development of such large bore insulator ring made of ceramics, and in parallel, ion beam experiments have been carried out with insulator rings made of FRP. The experiments have troubled with frequent high voltage breakdowns after outgas from FRP. Finding melt epoxy traces at triple junction (interface of vacuum, metal and FRP as dielectric material), local stress at the triple junction has been mitigated by mounting a large metal structure, so called stress ring. As a result, acceleration of 0.98 MeV, 185 A/m hydrogen negative ion beam has successfully achieved in short pulses, where the requirement by ITER is 1 MeV and 200 A/m.