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,
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