Electrostatic Potentials of Stationary Plasma Flows Along Magnetic Well and Hill

In a collisionless supersonic plasma flow passing through a magnetic well along the field lines, a depression of plasma potential is observed to form around the magnetic well. The depression depth is of an order of T e /e ( T e : electron temperature, -e: electron charge). There appears a transition from depressed to hilled profile as neutral-gas pressure is increased, being ascribed to mirror trapping of ions due to the collisions. A further increase of the gas pressure results in a formation of MHD-flow potential profile. A plasma potential profile along a magnetic hill shows an asymmetric hilled shape which disappears with an increase in the gas pressure.