Electron Cyclotron Heating in Toroidal Octupoles

J. C. Sprott
Department of Physics, University of Wisconsin, Madison, Wisconsin 53706
(Received 25 August 1969; final manuscript received 26 March 1971)


Microwave frequencies of 0.4-24 GHz at powers up to 100 kW have been used to heat electrons in regions of cyclotron resonance in a supported and in a levitated octupole magnetic field. A theoretical model has been developed to predict the heating rate of a cold, tenuous plasma in an arbitrary, nonuniform, magnetic field. The model predicts strong heating at places where del||B = 0 at resonance, and heating efficiencies approaching 100% for sufficiently high densities (wp^2 > w^2/Q). Scintillator probes have been used to verify the predicted localized heating and to measure the density at which total absorption occurs. Gun injected plasmas and microwave produced plasmas with n ~ 1 keV in the supported octupole and to ~ 10 keV in the levitated octupole. Upper off-resonance heating is also observed.

Ref: J. C. Sprott, Phys. Fluids 14, 1795-1802 (1971)

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