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| P20 · Production of Helium and Helium-Hydrogen Positive Ion Beams for the Alpha Particle Measurement H. Sakakita1, S. Kiyama1, Y. Hirano1, H. Koguchi1, Y. Yagi1, M. Sasao2 1National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568, Japan
Abstract: 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+, H2+, H3+, 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.
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