SOL width and intermittent fluctuations in KSTAR

Highlights: • This manuscript is the proceeding paper from the 22nd PSI conference in Rome 2016, invited contribution I2. • Probe measurements on KSTAR augments the tokamak SOL profile database, revealing significant profile broadening of the far-SOL with increasing line-averaged density in L-mode plasmas. • The statistical properties of plasma fluctuations are revealed by analysis of a ion saturation current data time series of several second duration under stationary plasma conditions. • Analysis of level crossing rates and excess time statistics, ultimately determining the degree of plasma-surface interactions in reactors, is presented for the first time for a magnetically confined plasma. • All fluctuation statistics are demonstrated to be in excellent agreement with a novel stochastic model for intermittent fluctuations in the tokamak scrape-off layer. - Abstract: Radial profiles of the ion saturation current and its fluctuation statistics are presented from probe measurements in L-mode, neutral beam heated plasmas at the outboard mid-plane region of KSTAR. The results are consistent with the familiar two-layer structure, seen elsewhere in tokamak L-mode discharges, with a steep near-SOL profile and a broad far-SOL profile. The profile scale length in the far-SOL increases drastically with line-averaged density, thereby enhancing plasma interactions with the main chamber walls. Time series from the far-SOL region are characterised by large-amplitude bursts attributed to the radial motion of blob-like plasma filaments. Analysis of a data time series of several seconds duration under stationary plasma conditions reveals the statistical properties of these fluctuations, including the rate of level crossings and the average duration of periods spent above a given threshold level. This is shown to be in excellent agreement with predictions of a stochastic model, giving novel predictions of plasma–wall interactions due to transient transport events.