High power fundamental and harmonic resonant ion cyclotron heating in a mirror machine

Radio frequency heating at powers up to 1 MW and pulse widths of ∼700 μsec was applied to a turbulently preheated hydrogen plasma in a large pulsed mirror machine. Energy analysis of charge exchange neutrals indicates that resonant heating occurred when the radio frequency matched either the ion cyclotron frequency or one of its harmonics. The behavior of the induced rf fluctuations in the plasma was observed by means of microwave scattering. These measurements show resonance phenomena and the presence of rf fluctuations at harmonics of the rf heating frequency. Diamagnetic loop measurements indicate that 310 ≤ (Te+Ti) ≤ 380 eV as a result of the heating, while measurements of the ion energy distribution by charge exchange energy analysis shows the ion energy distribution to be non-Maxwellian with a low temperature component of Ti ∼ 320 eV. Microwave interferometer measurements indicate densities of ∼2 to 3 × 1013 cm−3.