ИСТИНА

Processes occurring on the plasma-facing walls in the Large Helical Device (LHD) and in-vessel material migration were investigated using a technique of material deposition probes. Ten Si plates were located on the outer side of the first-wall surface in each 36⁰ toroidal section (Nos. 1–10) (Fig. 1). Long neon (Ne) and hydrogen (H) glow discharge cleanings (GDC’s) and then boronization using glow discharge with a mixture of helium (90%) and diborane (10%) gas were carried out at the beginning of the year 2012 plasma campaign. The plasma-facing components were exposed to high-power pulsed H plasma discharges and were also periodically subjected to He-GDC’s and Ti gettering. Mixed-material layers deposited on the probes during the year 2012 plasma campaign represented usually layers of carbon, which is the divertor tile material, containing hydrogen, helium, and metals from which the plasma-facing elements were made. Metallic impurities and hydrogen content in deposited layers were examined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA), respectively. The cross-sectional observations of the deposited mixed-material layers were performed with the help of a scanning electron microscope.