Potential and Density Fluctuation Characteristics of the Hot-Cathode-Biased Supersonic Plasma in TU-Heliac

In the Tohoku University Heliac (TU-Heliac), hot-cathode biasing experiment has been carried out. Poloidal Mach number exceeded unity, and reached 5 (supersonic regime). Increase of the electron density and decrease of the impurity influx were observed. It is important to study the anomalous transport for evaluation of the improvement. Then potential and density fluctuation (~600 kHz) measurement system were installed to the TU-Heliac. Characteristics of the fluctuations in the hot-cathode-biased supersonic plasma were measured. The fluctuation of (i) low frequency band (<10 kHz) and (ii) high frequency band (100~300 kHz) had large power spectra. The fluctuations between these bands (10~100 kHz) were suppressed. The potential fluctuation level was larger more than one order of the density fluctuation level in the low frequency band (<10 kHz), and comparable to the density fluctuation level in the high frequency band (100~300 kHz).