Scattering of High Energy Ions due to Spontaneously Excited Alfven Waves

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In the GAMMA 10 tandem mirror, plasmas with the strong temperature anisotropy are created when the ion cyclotron range of frequency (ICRF) heating is applied. The Alfven ion cyclotron (AIC) modes are spontaneously excited in the plasma due to such the strong temperature anisotropy. In this research, we studied the excitation mechanism of the Alfven waves and the correlation between high energy ions and spontaneously excited waves. Obtained results are summarized as followings ;1. The AIC modes in the GAMMA 10 tandem mirror are observed to be unstable in the parameter range below an order of magunitude lower than the parameters predicted by the theory. The AIC modes are excited as eigenmodes which have the boundary in the axial direction. The boundary is determined by the plasma pressure.2. We constructed a diagnostics system to evaluate the plasma parameters by injecting low power ICRF waves. The antenna loading and the amplitude of the excited waves are measured. It becomes clear the antenna loading decreases and the waves are resonantly excited in the frequency range of the AIC modes with a positive growth rate. This indicates the AIC modes are firstly excited by the external antenna.3. We constructed another diagnostic system with a semi-conductor detector to measure the pitch angle distribution of high energy ions in the central cell. It becomes clear the pitch angle distribution of high energy ions is determined from the effects of the heating by ICRF waves and the scattering by spontaneously excited waves.4. The end loss ions have strong correlation with the amplitude of the AIC mode in the central cell. It becomes clear experimentally the hot ions created in the central cell are scattered into the loss cone and lossed to the end by the AIC modes.