100‐kV test of the prototype neutral beam injector for JT‐60

A prototype neutral beam injector for JT‐60 has demonstrated extraction of 100‐kV, 70‐A, 10‐s ion beams, delivering neutral beam power of 1.43 MW into the target chamber. The power‐flow measurements showed that all beam line components, including the ion sources, were operated successfully. This verified the validity of the design work related to the ion source and neutral beam cooling devices. No significant change in the beam divergence during the pulse has been observed up to the maximum rated beam extraction of 40 A at 100 kV for 10 s from each ion source. The measurement also indicated that the power distribution to the beam line components agreed well with independently obtained ion species ratio and gas pressure distribution. Efficiencies of 28% and 20% were obtained for the neutralization and neutral injection into the target, respectively, for 100‐kV, 70‐A, 10‐s operation.