EFFECTS OF NEUTRAL GAS COLLISIONS ON THE CONDUCTING-WALL INSTABILITY

The shallow angle of an oblique incidence of the magnetic field to the divertor plates (e. g. 1-degrees-3-degrees in in DIII-D) leads to a s patial extension of the sheath of the order of gyroradius (e. g. 0.3 m m) normal to the plate. Since the actual particle path along the field lines inside the sheath is around 1 cm, ionization processes within t he sheath become important and reduce the sheath potential. We show th at ionization due to electron-neutral collisions can reduce the end-lo ss current of the divertor plasma, contributing to a stabilizing effec t on the conducting wall-mode. Thus the neutral gas collisions can be used as a knob to control the conducting-wall-driven turbulence in the scrape-off layer (SOL) experimentally.