Observation of Low-Frequency Beat Waves in GAMMA-10

Abstract

In the ion cyclotron range of frequency (ICRF) heating experiments on GAMMA 10, wave-wave and wave-particle interactions are investigated. Low-frequency fluctuations of around 100 kHz with beat frequencies among the AIC modes have been observed. These low-frequency modes are also detected in the signal of electrostatic probes in the central cell and in the signal of end-loss high-energy ion detector. Axial transport (velocity space diffusion) of high-energy ions due to beat waves among the AIC modes is clearly indicated. On the other hand, radial transport of high-energy ions due to the drift-type fluctuations has been observed in the central cell. The excitation of low-frequency magnetic fluctuations of which frequencies, f_LF, are less than 1 MHz and satisfy the relation of f_LF = f_ICRF - f_AIC, where f_ICRF is the frequency of the heating ICRF wave and f_AIC the frequency of the AIC modes. The parametric decay of the heating ICRF waves to the AIC modes and low-frequency waves will be a possible mechanism.