Estimating the Radial Profile of Edge Plasma Electrical Fluctuations in the IR-T1 Tokamak

The radial dependence of edge plasma turbulence is investigated in the IR-T1 tokamak. The radial profile of the fluctuation level and spectra are measured using an array of Langmuir probes (rake probe) in the r/a=0.75–1.2 region. In all radial positions the edge plasma is turbulently unstable, with a broad band fluctuation spectrum in the frequency range f= 10–1000 kHz. The relative fluctuation level, as monitored by the ion saturation current J₊, is always highest near the wall and decreases monotonically toward the plasma center, while the shape of the fluctuation power spectra is almost unchanged. The result of this experiment shows that in contrast to the more inner regions, the plasma near the wall does not simply have a small density fluctuation about a mean, but rather a shredded structure in which one can imagine that discrete shreds of plasma interact with one another rather than with the average background.