Development of high performance negative ion sources and accelerators for MeV class neutral beam injectors

Taniguchi, Masaki; Hanada, Masaya; Iga, Takashi*; Inoue, Takashi; Kashiwagi, Mieko; Morishita, Takatoshi; Okumura, Yoshikazu; Shimizu, Takashi*; Takayanagi, Tomohiro*   ; Watanabe, Kazuhiro; Imai, Tsuyoshi

A high power neutral beam injector (NBI) has been designed for ITER. A key component of the NBI system is a high power beam source which produces a 40A D ion beams at the energy of 1 MeV. JAERI has developed a vacuum insulated beam source (VIBS). The VIBS insulates the high voltage of 1 MV by immersing the ion source and accelerator in vacuum. So far the VIBS succeeded in acceleration of 37 mA (power supply drain current) beam up to 970 keV for 1 s. The achieved beam energy is nearly equal to the required value for the ITER NBI system. The negative ion source for the ITER beam source has been also developed. One of the key issues for the negative ion source is reduction of the operating pressure. By optimizing the filter magnetic field for negative ion production even at low pressure, a H ion beam of 31 mA/cm was extracted at 0.1 Pa. Although the pulse length was very short (0.1 s) the ITER requirement on the current density was demonstrated at 1/3 of the ITER design pressure (0.3 Pa), which could reduce the heat loading on the accelerator grids.