Modulated active charge exchange fast ion diagnostic for the C-2 field-reversed configuration experiment

A diagnostic technique for measuring the fast-ion energy distribution in a field-reversed configuration plasma was developed and tested on the C-2 experiment. A deuterium neutral beam modulated at 22 kHz is injected into the plasma, producing a localized charge-exchange target for the confined fast protons. The escaping fast neutrals are detected by a neutral particle analyzer. The target beam transverse size (∼15 cm) defines the spatial resolution of the method. The equivalent current density of the target beam is ≤0.15 A/cm(2), which corresponds to a neutral density (∼6 × 10(9) cm(-3)) that highly exceeds the background neutral density in the core of C-2. The deuterium fast-ions due to the target beam (E ∼27 keV), are not confined in C-2 and thus make a negligible contribution to the measured signals.