Review of recent works in development and evaluation of high-Z plasma facing materials

Abstract

This paper reviews the recent activities and results in development and evaluation of new high-Z materials focusing on tungsten and its alloys. VPS-W coating on graphite and CFC showed superior high heat load properties by inserting sophisticated multilayer diffusion barriers (W/Re) between tungsten and substrate. For successful application it is necessary to know the temperatures for recrystallization and interdiffusion of rhenium and tungsten, which may degrade bonding properties. Sputtering by plasma impurities and damage by energetic charge-exchange neutrals must be considered. Retention of hydrogen isotopes strongly depends on material grade and production process. Dense bubbles and dislocations formed by helium bombardment may act as effective traps for hydrogen. It is anticipated that long range diffusion of helium induces embrittlement. Neutron irradiation is one of the major concerns for tungsten materials in fusion reactor application. The tungsten materials developed so far perform poorly under neutron irradiation and their brittle nature could limit their application as a fusion material. Further efforts are needed to improve ductility while keeping other desirable properties such as high thermal conductivity.