Spectroscopic Studies on Carbon Coating in Heliotron E

Visible and vacuum ultraviolet (VUV) spectroscopic studies on carbon coating were described. In Heliotron E, carbon coating was performed on the vacuum chamber wall to reduce metallic impurities. The carbon layer was deposited on the wall using glow discharge with CH4 and H2 mixed gases. The CH(A 2Δ-X 2Π) spectrum was observed in the CH4+H2 glow discharge, and its excitation mechanism was discussed in relation to H2 and Hα emissions. The reduction of iron impurity by the carbon coating was confirmed measuring multiply ionized iron emissions by a calibrated VUV monochromator in the neutral beam heated plasmas. The behavior of the retained hydrogen, which was absorbed in the carbon layer during the glow discharge, was also studied observing Hα and Dα emissions in the RF-heated plasmas by the ion cyclotron range of frequency (ICRF).