In order to produce diagnostic helium neutral beam for alpha particle measurement in nuclear fusion plant of deuterium-tritium reaction, helium ion (He+) or helium-hydrogen ion (HeH+) beams of～20 keV have been considered as a primary beam. For He+ beam, it is important to produce focused high-current-density ion beam in order to pass through small apertures of alkali gas cell with an enough signal level. For HeH+ beam, conditions producing HeH+ has not been investigated in detail as yet. In order to extract these beams, focused high-current-density neutral beam system is applied. For He+ beam extraction of ～22 kV, it is confirmed that current density of ～86 mA/cm2 is achieved, whose value is close to necessary value in ITER. For HeH+ beam extraction in the case of ～300 V acceleration, the production rate of HeH+ component increases with the increase of helium gas pressure ratio to hydrogen gas pressure when its value is > ～75 %. In the case of 25 kV acceleration, if 15 % of total current (which includes H+, H+2 , H+3 , He+ and HeH+ components) is HeH+ component, current density of HeH+ is estimated as ～13 mA/cm2, whose value is larger than necessary value in ITER. From melted traces of the target plate, it is estimated that the divergence angle is about ±0.8 deg.
展开▼
