A Technique for Measuring the Fast ³He⁺⁺ Distribution During ³He⁺⁺ Minority Icrf Heating

A technique for measuring the fast ³He⁺⁺ distribution during ³He⁺⁺ minority ion cyclotron resonance frequency heating is discussed. The technique involves the use of 10- to 100-keV neutral helium beams to neutralize the fast ³He⁺⁺ ions by double charge-exchange (³He⁺⁺ + ⁴He⁰ → ³He⁰ + ⁴He⁺⁺). The neutralized fast ³He atoms then escape from the plasma and are detected by conventional neutral particle analyzing apparatuses. By the use of such a technique, the effectiveness of the coupling of the ion cyclotron waves to the ³He⁺⁺ minority can be measured.