Drift motion in the scrape-off layer during hard disruptions

As a result of plasma-wall contact during hard disruptions, intense vaporization of the divertor plates is initiated. The evolving vapour layer intercepts a fraction of the incident energy carriers, thus shielding the plates. The plasma particles of different energies and masses moving along the skewed magnetic field lines penetrate the vapour layer to different depths, thus causing charge separation there and the onset of an electrostatic field. It is shown in a one dimensional approximation that, owing to the constraints imposed on the electric field and on the current components at the plate surface, a rather intense lateral drift motion of the vapour evolves in the scrape-off layer (SOL). The analysis shows that drift velocities of the order of 103 to 104 m/s are to be expected, which may notably impair the shielding characteristics of the vapour layers and increase the erosion rates of the divertor plates