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Observation of Low-Frequency Beat Waves in GAMMA-10

M. Ichimura et al.

Fusion Science and Technology / Volume 55 / Number 2T / February 2009 / Pages 59-62

Technical Paper / Seventh International Conference on Open Magnetic Systems for Plasma Confinement /

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, fLF, are less than 1 MHz and satisfy the relation of fLF = fICRF - fAIC, where fICRF is the frequency of the heating ICRF wave and fAIC 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.

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