Measurement of Small-Scale Density Fluctuation in JIPP T-II Plasma by Millimeter and Sub-Millineter Wave Scattering

The small-scale density fluctuations have been studied by both millimeter (2 mm) and sub-millimeter (337 µm) wave scattering technique in JIPP T-II plasmas. Experiments were performed in two types of plasma: tokamak and stellarator plasmas. In both plasmas, the density fluctuations are localized in outer region of the plasma column, and show the characteristics of the drift wave mode turbulence. The density fluctuation level is \(ñ/n₀{}1{-}1.5%\) around the plasma edge, and this value is inversely proportional to the mean electrondensity. Further, the dependence of the fluctuation level on the plasma parameters is studied and compared with the scaling law of the energy confinement time of the plasma. The diffusion coefficient estimated from the density fluctuation is about one third of the global diffusion coefficient.