Ion Cyclotron Instability of Energetic Plasma Confined in Magnetic Mirrors in the Model C Stellarator

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Abstract
A portion of the plasma in the Model C stellarator is heated by ion cyclotron resonance heating and contained within magnetic mirrors (1.02 ≤ R ≤ 1.3, B0 ≈ 35 kG). The plasma so formed (ne ≈ 1012-1013 cm−3) has little interaction with the main body of toroidal plasma, and has perpendicular ion temperature up to 4 keV while the electron temperature remains at less than 100 eV. New results show that the cooling of this energetic plasma, lasting several milliseconds, is accompanied by emission of radiation at frequencies close to the local ion cyclotron frequency and its harmonics. Experimental results are presented of observations of this rf activity, and related to theoretically predicted instabilities of the ion cyclotron type. It is concluded that the observed behavior can be satisfactorily explained by the presence of an electrostatic, temperature-anisotropy-driven instability. There is no correlation between the rf activity and the cooling time of the mirror-contained plasma; the containment time still seems to be limited by charge exchange.