Contrib. Plasma Phys. 53, No. 1, 69 – 74 (2013) / DOI 10.1002/ctpp.201310012 Electric Probe Measurements at Edge Region During H-Mode Discharges in KSTAR J.G. Bak 1 ∗ , Y.S. Oh 2 , H.S. Kim 1 , S.H. Hahn 1 , S.W. Yoon 1 , Y.M. Jeon 1 , W.W. Xiao 1,3 , W.H. Ko 1 , W.C. Kim 1 , J.G. Kwak 1 , H.J. Woo 2 , K.S. Chung 2 , and the KSTAR project team 1 National Fusion Research Institute, Yusung, Daejeon, Korea 2 Hanyang University and Center for EDGE Plasma Sciences(CEPS), Seoul, Korea 3 Southwestern Institute of Physics, Chengdu, China Received 29 November 2011, accepted 11 May 2012 Published online 09 January 2013 Key words Fast reciprocating Langmuir probe assembly, fixed edge Langmuir probe array, characteristics of SOL and divertor, radial flux due to electrical turbulence, edge plasma, H-mode discharge, KSTAR. Electrical probe measurements are carried out at the scrape-off-layer (SOL) and divertor regions in order to in- vestigate 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 Te, 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 λ Te and that of density λ ne are 2 ∼ 4 cm and 1 ∼ 3 cm, respectively. The magnitude of v // near the last closed flux surface (LCFS) is 4 ∼ 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 ˜ Iis and floating potential ˜ V f obtained from the FRLPA measurement. The value of the flux is estimated as ∼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 ˜ jis(ω) near strike point decreases when the ELMs are suppressed or mitigated. 1 Introduction The characteristics of edge plasmas at the scrape-off-layer (SOL) and divertor regions during a plasma discharge in tokamaks have been investigated to study edge plasmas which gave boundary conditions affecting the plasma discharge performance [1], and to study the edge particle transport due to electrostatic turbulence [2]. Electric probe diagnostics (EPDs) have been used as one of useful tools for the experimental investigation at the edge region in tokamaks. In the Korea Superconducting Tokamak Advanced Research (KSTAR) device, various H-mode discharges have been able to be reproduced by injecting the neutral beam (NB) heating of 1.1 ∼ 1.6 MW for diverted plasmas (B T = 1.6 ∼ 2.4 T, I p = 0.6 ∼ 0.7 MA, n e = (1.2 ∼ 4.3) × 10 19 m -3 ,R ∼ 1.8 m, a ∼ 0.5 m, κ = 1.6 ∼ 2.0) since the first plasma of up to 100 kA had been successfully achieved 2 years ago. Several types of edge localized modes (ELMs) were observed during H-mode discharges in the KSTAR device. The control of the ELMs is one of key issues in future tokamak such as ITER because the ELM burst is strongly related to heat load on plasma facing components (PFCs) during H-mode discharges. It was observed that the ELMs were mitigated or suppressed by using the supersonic molecular beam injection (SMBI) or by non-axisymmetric magnetic perturbations due to the resonant magnetic perturbation (RMP) coils during the experimental campaign in the KSTAR device [3,4]. Thus, the investigation of the characteristics of edge plasmas at the SOL and divertor ∗ Corresponding author. E-mail: jgbak@nfri.re.kr, Phone: +82 42 879 5142, Fax: +82 42 879 5119 c  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim