Vapor shielding and erosion of walls during tokamak disruptions

In evaluating the lifetime of ITER plasma facing components (PFC) against heat loads that are not normal, credit is taken from the existence of a plasma shield which effectively protects the wall from excessive evaporation. The plasma shield formed from vaporized PFC material though beneficial for the PFC could become a potential threat for the tokamak because of the possible penetration of the impurity ions into the central plasma. This paper discusses various aspects of plasma shields for a rather wide-range of heat load conditions. Evaporation and melting of PFCs, physical properties of the plasma shields, plasma shield:efficiencies for tilted targets and estimations on impurity transport from the plasma shield into the SOL of the main plasma are addressed The numerical results for power densities 0.1-10 MW/cm(2) are obtained with the newly developed 2D radiation-magnetohydrodynamics (R-MHD) code FOREV-2. (C) 1998 Elsevier Science B.V. All rights reserved.