Study of Wall Recycling and Conditioning on the Hanbit Mirror Device

The wall recycling effect dominantly appears in the ICRH discharge with ω < ω_ci in the HANBIT plasma. The methods and evaluation of wall conditioning are described. The progress of wall conditioning is monitored with neutral pressure and plasma parameters. Electron cyclotron resonance–discharge cleaning(ECR-DC) is applied to improve wall conditioning, and then electron impact desorption(EID) by filament heating is utilized in order to desorb the impurities from the wall. The impurities are analyzed quantitatively by quadrupole mass spectrometer(QMA). We also install new baking system by Halogen lamp radiation with 2 kW in the HANBIT central cell. It is also observed that Hα emission reduces after lamp heating. The evolution of neutral pressure profiles are carefully evaluated during discharge and monitored discharge cleaning effect after several hundred of radio frequency(rf) shots. The partial pressure of light impurities much reduced after rf discharges The line integrated density and edge density much decreased after rf shots, while edge temperature increases. After ECR-DC, also line density decreases, but edge temperature much increases. Plasma beta goes up more than three times after 250 rf shots.