Statistical Analysis of Fluctuation Characteristics at High- and Low-Field Sides in L-mode SOL Plasmas of JT-60U

Detailed comparison between fluctuation characteristics at high-field-side (HFS) and low-fieldside (LFS) scrape off layers (SOLs) has been made, for the first time, in the L mode plasma of JT-60U tokamak using reciprocating Langumuir probes. Statistical analysis based on probability distribution function (PDF) was employed to describe intermittent (non-diffusion) transport in SOL plasma fluctuations. It was found that the positive bursty events appeared most frequently at LFS midplane associated with blobby plasma transport, then the PDF is strongly skewed positively, while the PDF in HFS SOL is close to Gaussian distribution. Conditional averaging analysis of the positive bursty events at LFS midplane indicates the intermittent feature with a rapid increase and a slow decay is similar to that of plasma blobs theoretically predicted. Statistical self-similarity was also investigated with Fourier power spectrum, and statistics of waiting-time and duration-time of the fluctuation. It was found, for the first time, that clear statistical self-similarity was observed at LFS SOL, showing fractal property of the fluctuation. The scaling exponent of duration time statistics disagrees with the predictions for the self-organized criticality (SOC) paradigm.