The Efficient Utilization of an R.F. Power Oscillator for Producing Low-pressure Plasmas†

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Abstract
In an ordinary arrangement for high-frequency plasma heating a discharge tube is placed inside an r.f. coil, as in the analogous case of the induction heating of metals, and the coil is connected to a standard power oscillator. If a low-pressure plasma is to be produced, i.e. in gas at 0.1–500 microns pressure, the energy transferred to the plasma then will be only a small fraction of the generator capacity, because of the low power factor of the load. Simple expedients are described which result in the attainment of a much increased r.f. magnetic flux density in the discharge tube. The resulting increase in the plasma conductivity, hence in the load power factor, is sufficient to effect high and efficient loading. The discussion centres around the use of a 15 kw, 450 kc/sec oscillator for plasma research studies. The usefulness of the generator is considerably increased by electronic control, which allows times of operation as brief as 0.05 sec. Short-time operation and low average loading permit the exceeding of normal oscillator current limits to obtain high r.f. fields for starting and maintaining low-pressure plasmas— extending the possible range of operation. Comprehensive performance data are presented.

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