Simultaneous measurements of plasma parameters and blob characteristics at the far-SOL region using a hybrid probe in KSTAR

• Published in: Fusion engineering and design 2021-11, Vol.172, p.112900, Article 112900
• Main Authors: Kim, Kwan-Yong, Son, Soo-Hyun, Hong, Suk-Ho, Park, Il-Seo, Kim, Ju-Ho, Lee, Jae-won, Chung, Chin-Wook
• Format: Article
• Language: English
• Subjects: Blob radial velocity; Discharge; Electric probe diagnostics; Electron energy; Far-SOL plasma; Fusion reactors; Hybrid probe; Ion flux; KSTAR; Optical properties; Parameters; Particle and heat fluxes; Plasma; Position measurement; Radial velocity; Time lag; Time measurement; Velocity; Weights & measures
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2021.112900

•A hybrid probe combined with an electrical and optical probe is developed to measure the far-SOL plasma parameters and the blob characteristics in the KSTAR.•The electron temperature and the ion flux are measured by the sideband harmonic method of the electrical probe, and the optical probe is used to measure the dα signals from the radial direction.•In ELMy H-mode discharge, the blob radial velocity is calculated by using the net time delay between the dα signal and the electrical probe current and the corresponding radial position (distance from the LCFS) of the electrical probe tip.•The blobs are propagated various radial velocities and the radial velocity decreases as the radial position increases from near the LCFS to the outer wall.•The average blob electron temperature, ion flux, and heat flux are about 2 to 10 times larger than the background plasma, respectively. The blob parameters decrease as the radial position increases and these show the same trend with the blob radial velocity. We developed a hybrid probe comprised of an electrical probe and optical probe to investigate the properties of the far scrape-off layer (SOL) plasma and the blob in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid probe is attached to a horizontal manipulator, and the radial profiles of plasma parameters such as electron temperature, ion flux, and the Dα signals are measured with time resolution (100 μs) by varying the radial position (0.15–0.4 m away from the last closed flux surface (LCFS)). In ELMy H-mode discharge, the blob radial velocity is obtained from the time delay between the start of the peak Dα signal and the peak electrical probe current and the corresponding radial position. The obtained blob radial velocity is in good agreement with the radial velocity of the filament obtained using the two radially separated electric probes at the far-SOL in the KSTAR. The profiles of the blob radial velocity for five discharges are obtained depending on the radial position in similar experimental parameters. The blob radial velocity is estimated as 44.1–250 m/s and 25.4–135 m/s at the radial position of 0.15 m (near the LCFS) and 0.4 m (near the outer wall), respectively. It is observed that the blobs are propagated to the outer wall with various radial velocities, and the radial velocity slows down as they get closer to the outer wall. The hybrid probe measurement found that the blob properties are about 2 to 10 times larger than the background