Electric Probe Measurements at Edge Region During H-Mode Discharges in KSTAR

Abstract

Electrical probe measurements are carried out at the scrape-off-layer (SOL) and divertor regions in order to investigate the characteristics of edge plasmas during H-mode discharges in the Korea Superconducting Tokamak Advanced Research (KSTAR) device. Radial profiles of plasma parameters such as electron temperature T-e, plasma density n(e), and parallel flow velocity v(//) are measured by using a fast reciprocating Langmuir probe assembly (FRLPA) at the SOL region. From the FRLPA measurements, it is found that the decay length of temperature gimel T-e and that of density gimel(ne) are 2 similar to 4 cm and 1 similar to 3 cm, respectively. The magnitude of v(//) near the last closed flux surface (LCFS) is 4 similar to 15 km/s. The radial flux due to edge turbulence at the SOL region is investigated by using spectra analysis on electrostatic fluctuation levels such as ion saturation current (I) over tilde (is) and floating potential (V) over tilde (f) obtained from the FRLPA measurement. The value of the flux is estimated as similar to 10(20) particle m(-2) s (-1) near the LCFS. The poloidal distribution of the ion saturation current density j(is) is measured by fixed edge Langmuir probe array (ELPA) at the divertor region, and it is found that the positions of strike points from the ELPA measurement agree well with those reconstructed from the EFIT result using magnetic diagnostic data. From the spectrum analysis on the ELPA measurements at the divertor region during edge localized modes (ELMs) control in the H-mode discharges, it is observed that the magnitude of (j) over tilde (is)(omega) near strike point decreases when the ELMs are suppressed or mitigated.