Ion cyclotron wave generation in a two-ion plasma

Abstract

Exact calculation of the dispersion relation of a cold plasma shows that the plasma behaviour is different from that predicted by the usual approximate theory which neglects electron inertia in the low-density limit. For example, the limiting value of Ω for optimum coupling is different from 1, where Ω is the wave frequency divided by the ion cyclotron frequency. This fact was ascertained experimentally in the QP-machine.Experimental observations of optimum coupling of the ion cyclotron wave in a two-ion plasma in the QP-machine are presented as functions of the plasma density. The plasma was produced by a PIG discharge with a density from 1010 to 2 × 1012 cm−3. The wave was generated by a Stix-type coil (coil wavelength 50 cm), which was fed by a 4.4-MHz, 20-kW oscillator. Experimental data lay within the band of H+ concentration between 10–90% of the dispersion relation of a homogeneous cold plasma column with a sharp boundary. However, the dependence of optimum loading on the diameter of the plasma column disagrees with the theoretical prediction.