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 of³He 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∼ 25 keV for efficient charge exchange. The beam qualities of both double-charge-exchanged He^-and auto detached neutral He (He⁰) will be investigated by emittance meters, beam profile monitors, and a calorimeter.