Time-resolved ion temperature measurements on the HBTX1A reversed field pinch

Abstract

The energy distribution of the neutral particle emission (200 eV–2 keV) from the HBTX1A reversed field pinch has been observed, using a five-channel analyzer, at 20-μs intervals throughout the duration of the discharge. The relative number of high-energy neutrals emitted increases with currents up to 250 kA above which there is little change. Preliminary analyses show that the ion temperature of the bulk of the plasma is in the range 70–120 eV, rather than the few electron volts expected from electron–ion collisions. Equally, the rapid evolution to this temperature (<0.5 ms) is not accountable by equipartition (τeq∼3 ms). Long thermalization times (∼1 ms), compared with short time-scale excursions (∼100 μs) in the high-energy neutrals indicate that there are nonthermal ions at ∼10 times the Maxwellian temperature.