Analysis of collisional sheath structure in an argon DC discharge

The electric fields of the sheath region in an argon DC discharge were measured using a laser optogalvanic spectroscopy in a pressure range from 0.88 to 10 torr, where collisions are significant in the sheath region. The sheath width is estimated as the position where the electric field becomes zero, and the pressure dependence of the measured sheath width was obtained to be (pressure)^-13/. The measured electric fields agree well with two-dimensional simulation results but are slightly different from collisional sheath theory in the mobility limited region. The discrepancy of the theory from the experiment and simulation results was found to be caused by the change of ion current density due to ion collisions in the sheath region.