Recent Results of Studies of Plasma Fluctuations in Stellarators by Microwave Scattering Technique

Plasma density fluctuations in the heating region of the L-2M stellarator were measured from microwave scattering at the second harmonics of the heating gyrotron radiation. Probability distribution functions of density fluctuations were analyzed by EN-algorithm. In the TJ-II stellarator, a separate 2-mm microwave source was used to produce a probing beam; the measurements were performed at the middle of the plasma radius. In TJ-II, plasma density fluctuations were studied in experiments with the neutral beam injection. It is shown that fluctuations at the middle radius (r/a equal 0.5) of TJ-II can be attributed to drift-dissipative instability. Plasma density fluctuations in the heating region of the LHD stellarator were measured from microwave scattering at the fundamental harmonic of the heating gyrotron radiation. New results were obtained with the use of a small-angle scattering of the heating gyrotron radiation in LHD. (Author)