Density dependence of electron cyclotron heating rate in a toroidal octupole

Electron cyclotron heating rates have been measured for low density plasmas (ωpe≪ω) in a toroidal octupole by the sweep method with resonance zones situated near the minor axis of the torus. The energy absorbed by the plasma from the 100 mW frequency sweep oscillator is determined from the broadening of the cavity modes. The scaling of heating rate with plasma density differs from previous results of high frequency (9.6 GHz) cavity mode measurements. The difference is explained by the accessibility of the waves to the resonance zones.