<RESEARCH REPORT>Measurement of Density Fluctuations on the JIPP T-II Tokamak Plasma by Millimeter and Sub-Millimeter Wave Scattering
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Scattering experiments with a 2-mm microwave oscillator (E.I.O.) and a 337-μm HCN laser were performed to measure density fluctuations on the JIPP T-II/T-IIU tokamak in a wide range of the plasma density. We observed an instability and an externally excited wave during rf heating experiment. It is found from the measurements of the frequency and wavenumber spectra of the instability that the density fluctuation shows characteristics of a turbulence which is originated in the instability of drift type. The dependence of the fluctuation level on the plasma parameters was investigated and compared with the scaling law of the energy confinement time of the plasma. The relation between the density fluctuation level and the confinement time was obtained. The fluctuation level decreases as the electron density is increased. The plasma temperature dependence of the density fluctuation was also investigated. During the rf heating in the ion-cyclotron range of frequency (ICRF) the increase in the density fluctuation level was observed in low-frequency and long-wavelength region. The temporal behavior of the density fluctuation was correlated with the MHD oscillation observed by magnetic probes. The excited wave during the ICRF heating experiment was studied by the HCN laser scattering. The frequency and wavenumber spectra of the excited wave observed during the heating are found to be consistent with the theoretically estimated wave dispersion of the ion Bernstein wave which is mode-converted from the fast wave in the vicinity of the ion-ion hybrid resonance layer. The influence of MHD activity on the mode-converted ion Bernstein wave was examined. When the MHD activity grows and the plasma becomes unstable, the scattered signal from the ion Bernstein wave decreases, being accompanied with large pulsation.
- 核融合科学研究所の論文
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