Effect of Ne Glow Discharge on Ion Density Control in LHD

Neon glow discharge cleaning was firstly attempted in Large Helical Device （LHD）instead of He glow discharge to remove hydrogen neutrals and to control the ion density n;. TheNe glow discharge continued for 8 hours overnight after a three-day experiment. At the secondnight H;emission became weaker than the emission usually observed in the He glow discharge. Aclear reduction of the hydrogen influx was also observed in neutral beam injection （NBI） dischargeswith Ne puff, whereas the neon recycling was strongly enhanced with appearance of a flat densityprofile. As a result, the lowest density limit was further reduced down to 0.2×10～（13） cm～（-3）. Theuse of Ar puff formed a peaked density profile with a high T;of 7 keV.