Models and simulation for divertor erosion following plasma disruption in tokomak reactors

Abstract

Erosion of plasma facing materials (PFMs) during a tokamak disruption limits the lifetime and increases the need of plasma facing components (PFCs) replacement in the reactor. During disruption, energetic plasma particles deposit high heat fluxes on the PFCs. It has been shown theoretically and experimentally that the deposited energy by plasma particles vaporizes the surface of the PFMs. Besides vaporization some selected metallic PFMs, such as tungsten and molybdenum, may suffer severe surface erosion due to melting. Melting and vaporization of metallic PFMs develop a boundary layer adjacent to the PFCs which shields such critical components as vapor shield, melt-layer shield or mixed melting/vapor shield. Part of the incoming heat flux is being absorbed by the dense and optically thick boundary layer evolved from the exposed surface, which significantly decreases the erosion of the PFCs. The accurate calculations of the net heat flux that hits the surface of PFCs during disruption are of great importance. In this study, the erosion of metallic PFMs is governed by vapor and droplet formation and their associated shielding effects. Fully selfconsistent erosion models are developed and implemented in the ETFLOW code in a new version (ETFLOW-BL) to model the PFMs response as they experience such disruption conditions. The melt-layer and vaporization losses following a disruption are calculated in this study for different values of incident plasma energies relevant to those expected in ITER. The calculated initial sharp rise in the PFMs erosion is due to the direct energy deposition on the PFCs surfaces. As disruption time goes on, boundary layers will accumulate adjacent to PFC surface and less energy penetrates to the original surface, which results in less boiling, scattering and vaporization. Comparisons between cases where both vaporization and melting process takes place are presented. Corresponding mass losses, and erosion thickness, are estimated for both cases.