Effect of electron collisions on the plasma–sheath formation

The effects of electron collisions in the plasma–sheath are numerically investigated. We employ a one-dimensional electrostatic particle-in-cell code, with collisions incorporated using the Monte Carlo method. While it has been reported previously that the presheath potential drop increases with the ion collision frequency, the effects of electron collisions were not explored. The present study shows the inclusion of electron collisions reduces the potential drop, especially in the presheath region. The result is more or less the same when a weak magnetic field is imposed. We note that the reduced electron flux, caused by electron collisions, makes the presheath potential drop shallower as the required ion drift motions to balance the electron current are smaller.