Characterization of the impurity features deposited on the boronization tungsten tiles exposed in KSTAR tokamak using laser-induced breakdown spectroscopy

Abstract

Boronization is an important wall conditioning procedure for realizing the steady-state high performance operation of tokamaks such as KSTAR and ITER. The measurement of boron and its distribution on the first wall and divertor has a significant impact on studying the plasma-wall interaction (PWI) such as impurity generation, transportation and deposition behaviors. In this study, the laser-induced breakdown spectroscopic (LIBS) diagnostic method was applied in the lab for investigating the boron impurity deposited on the surface of different shaped tungsten (W) castellated tiles which were removed from the divertor region in the Korea Superconducting Tokamak Advanced Research (KSTAR). Meanwhile, other various impurity elements comprising carbon, silicon, calcium and copper were also observed. A subtraction method is proposed to eliminate the W line contribution for B deposition measurement. The depth profile of the impurity elements in the deposited layer also has been studied by the variation of spectral intensity with consecutive laser pulses. The lateral-distribution of the boron and carbon on the three tungsten castellated tiles (Rounded, Chamfered and Double chamfered) were carried out at 10−5 mbar vacuum condition. The distribution features of the impurities on the three different shaped tungsten tiles provide valuable information to understand PWI process in KSTAR. This study demonstrates that LIBS is a potential diagnostic approach for monitoring the impurity deposition in tokamak such as KSTAR or ITER.

Keywords

• Laser-induced breakdown spectroscopy
• Plasma-wall interaction
• Boron deposition
• Tungsten divertor
• KSTAR