The Ion Velocity (Bohm-Chodura) Boundary Condition at the Entrance to the Magnetic Pre-Sheath in the Presence of Diamagnetic and ExB Drifts in the Scrape-Off Layer
In the absence of drifts, the Bohm-Chodura Criterion gives that the fluid velocity parallel to the magnetic field reaches the ion acoustic speed at the entrance to the magnetic pre-sheath. The changes to this Criterion dervied for the situation where peloidal E×B drifts are present. (It was shown earlier that diamagnetic drifts do not influence this Criterion). E×B drifts can cause the parallel fluid velocity at the magnetic pre-sheath entrance to become supersonic, subsonic or reversed (negative).