Study of hot tungsten emissive plate in high heat flux plasma on NAGDIS-I

Abstract

The high heat flux plasma in fusion devices sometimes makes a local hot spot on a plasma-facing material, generating sufficient electron emission from the surface to reduce the sheath voltage, resulting in a reduction in thermal insulation across the sheath. Experiments on hot tungsten emissive plate are performed in the linear divertor simulator NAGDIS-I with a steady state high heat flux plasma. Phase transitions due to the electron emission have been observed in the experiments. Results from SEM micrographs of the tungsten surface show that the microstructure of the tungsten surface is changed after the low energy and high flux plasma irradiation. An interesting ion species dependent surface modification is observed in experiments.