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 spatial extension of the sheath of the order of gyroradius (e.g. 0.3 mm) normal to the plate. Since the actual particle path along the field lines inside the sheath is around 1 cm, ionization processes within the sheath become important and reduce the sheath potential. Ionization due to electron-neutral collisions can reduce the end-loss current of the divertor plasma, contributing to a stabilizing effect 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.
Sheath constraints on turbulent magnetised plasmas