Plasma Heating by collisional magnetic pumping

Collisional magnetic pumping as a plasma heating method is investigated theoretically, computationally, and experimentally. Improvement of the efficiency of this heating method is also achieved. The theoretical treatment yields solutions to the energy transfer equations. The solution is presented in the form of an energy increase rate, which gives quantitatively the amount of energy increase per RF driving cycle. The RF wave adds a small perturbation to the background steady state DC magnetic field that confines the plasma. Depending on the type of waveform used, the energy increase rate obtained can be of first or second order in the amplitude of the magnetic field perturbation.

Two waveforms are used in this work. The first is a sinewave with variable frequency and amplitude. The energy increase rate in this case is proportional to the second power of the magnitude of the perturbation. This yields a small amount of heating for small perturbations. The second waveform used is a sawtooth with adjustable frequency and amplitude. The energy increase rate in this case is proportional to the first power of the magnitude of the perturbation. This yields an improvement of several orders of magnitude over the previous case.

Two circuits have been implemented to study experimentally the effects of the above mentioned perturbations on a cylindrical plasma generated by a classical Penning discharge. The circuit generating the sinusoidal perturbation is a high-Q parallel resonant circuit with tunable resonance frequency. The circuit generating the sawtooth perturbation is a switch-mode configuration using state-of-the-art metal-oxide-semiconductor transistors capable of switching on and off in few tens of nanoseconds and of handling high curents and voltages. The experimental heating data collected in both cases is presented and discussed.