Fueling and heating of tandem mirror end cells using rf at the ion-cyclotron frequency

Fueling and heating of tandem mirror end cells by rf at the ion-cyclotron frequency have been studied experimentally in the Phaedrus Tandem Mirror. The end cell density is found to increase linearly with rf voltage. The total plasma energy is observed to increase with rf power with no evidence of saturation at high power. The plasma axial length decreases with increasing rf power down to a length of approximately the distance between the two resonance locations in the end cell. The highest density and average ion energy are achieved with the resonance closest to the midplane. It is necessary to assume that the rf electric field at the resonance decreases with increasing density and with distance from the antenna in order to model the ion particle and power balance. The particle and power balance model predicts that dense, hot end cells may be maintained with E₊∼1V/cm and a fueling efficiency of a few percent when the resonance is close to the midplane because of better ion confinement and small plasma volume. Monte Carlo simulation of the trapping process shows that E²₊ ∝T_ic^1.5 is required to maintain a given rf trapping efficiency.