Design of a fast neutral He beam system for feasibility study of charge-exchange alpha-particle diagnostics in a thermonuclear fusion reactor

Measurement of velocity distributions of fusion produced alphas in a next stage magnetic plasma confinement device is a challenging topic in thermonuclear fusion research. Active beam probe diagnostic method based on high energy neutral beam of (3)He is considered promising. The beam can be produced by auto electron detachment from an energetic negative helium ion (He(-)) during the transport in field free space. To find critical issues in forming a diagnostic beam, a double-charge-exchange He source coupled to a simple beam transport systems is currently being constructed at Tohoku University. A He(+) beam of about 10 mA is extracted from the ion source and accelerated up to 10 similar to 25 keV for efficient charge exchange. The beam qualities of both double-charge-exchanged He- and auto detached neutral He (He(0)) will be investigated by emittance meters, beam profile monitors, and a calorimeter.