Experimental test of Godyak and Sternberg´s collisional sheath model

Summary form only given, as follows. An emissive probe is used to measure sheath potential profiles in an argon dc glow discharge operated at 0.1 or 1.0 Torr. The emissive probe is operated in the limit of zero electron emission. Experimental data are found to be in a good qualitative agreement with the new boundary condition (a finite electric field) based on the works of Godyak and of Godyak and Sternberg. The ion velocity at the sheath edge (inferred from the measured electric field) is found to be much smaller than the ion sound speed (as predicted in the model). Ion velocities much less than the Bohm velocity are a consequence of ion collision mean-free-paths that are comparable to or smaller than the electron Debye length as first described by Persson. A fluid equation based analysis is presented to demonstrate the transition from Bohm-like behavior at low collisionality to Persson-like behavior at high collisionality making clear the role of electric fields at the sheath boundary.