Electric probe diagnostics for measuring SOL parameters, wall and divertor fluxes in KSTAR

Abstract

Some components in electric probe diagnostics (EPDs) are improved in order to investigate characteristics of edge plasmas in the upstream scrape-off-layer (SOL) region and to measure wall and divertor fluxes during L-mode and H-mode plasma discharges in the Korea Superconducting Tokamak Advanced Research (KSTAR). From the upgrades in the EPDs, the measured error of the elapsed distance for the evaluation of the SOL profiles can be reduced up to 1% and the ion saturation current of up to 1.0A near an outer strike point (OSP) can be measured at the divertor region. In the SOL profile measurements during L-mode and inner wall limited plasma (B-T = 2.0T, I-p =0.4 MA), the e-folding lengths in the main SOL region lambda(Te) and lambda(ne) are evaluated as 3.5 cm and 2.1 cm, respectively. From particle flux measurement at the far SOL region during a diverted ELMy H-mode discharge (B-T = 1.8 T, I-p = 0.65 MA), peaked heat flux toward to outboard wall during ELM bursts is estimated up to similar to 20 k Wm(-2), which may be less than 1% of the peaked divertor heat flux expected for the neutral beam (NB) heating power P-NB of similar to 2.66 MW and stored energy W-TOT of similar to 0.38 MJ. In addition, the movement of the OSP during a diverted H-mode plasma (B-T = 2.4T, I-p = 0.5 MA) can be detected from the divertor probe measurement and peaked heat flux near the OSP is estimated as few MW m(-2) for P-NB = 3.0 MW, W-TOT = similar to 0.25 MJ. In this work, the technical details of the EPDs including its upgrades and some experimental results from EPD measurements are presented.