Observation of High-Frequency Radiation and Anomalous Ion Heating on Low-Density Discharges in Alcator

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Abstract
A radiation spectrum ranging from 300 MHz to 5 GHz is observed in low-density discharges in Alcator. At the lower end this spectrum is strongly peaked at a frequency corresponding to the ion plasma frequency. The emission occurs if the ratio of the drift velocity to the thermal speed of the electrons exceeds 0.45 for discharges in hydrogen or 0.2 in deuterium. The onset of the radiation correlates with the production of energetic ions.