EROSION OF PLASMA-FACING MATERIALS DURING A TOKAMAK DISRUPTION

The behavior of divertor materials during a major disruption in a toka mak reactor is very important to successful and reliable operation of the device. Erosion of material surfaces due to a thermal energy dump can severely limit the lifetimes of plasma-facing components and thus diminish the reactor's economic feasibility A comprehensive numerical model has been developed and used in this analysis, which includes all major physical processes taking place during plasma/material interact ions. Models to account for material thermal evolution, plasma/vapor i nteraction physics, and models for hydrodynamic radiation transport in the developed vapor cloud abo ve the exposed surface are implemented in a self-consistent manner to realistically assess disruption damage. The extent of self-protection from the developed vapor cloud in front of the incoming plasma particles is critically important in determini ng the overall disruption lifetime. Models to study detailed effects o f the strong magnetic field on the behavior of the vapor cloud and on the net erosion rate have also been developed and analyzed. Candidate materials such as beryllium and carbon are considered in this analysis . The dependence of divertor disruption lifetime on disruption physics and reactor conditions is analyzed and discussed. In addition, materi al erosion from melting of plasma-facing components during a tokamak d isruption is also a serious problem that limits reactor operation and economical reactor lifetime. In particular metallic low-Z components s uch as Be will be subjected to severe melting during disruptions and e dge localized modes (ELMs). Loss of the developed melt layer will crit ically shorten the lifetime of these components, severely contaminate the plasma, and seriously inhibit successful and reliable operation of the reactor. In this study mechanisms responsible for melt-layer loss during a disruption are also modeled and evaluated. Implications of m elt-layer loss on the performance of metallic facing components in the reactor environment are discussed.