ECR discharge cleaning and followed He GDC on HT-7 tokamak

A study of ECR discharge cleaning is conducted on HT-7. Radio frequency (RF) waves of 2.45 GHz were used under toroidal field of 0.088–0.066 T. Toroidally symmetric ECR plasmas were obtained, and the resonance layers were scanned by toroidal field. RF powers, neutral pressures and working gas species were investigated as parameters of cleaning. And ECR was compared with ICR discharge cleaning. After the cleaning, the enhancement of wall recycling and the increase of carbon and oxygen impurities were observed in the followed shots. Another ECR discharge cleaning was followed by He GDC, it was shown that the intensity of Hα radiation was much lower than that before cleaning. This indicates that D2 ECR discharge cleaning followed by He GDC is effective for wall conditioning.