Influence of nitrogen pre-irradiation at different temperatures on surface blistering and deuterium retention in tungsten

Nitrogen seeding is considered to be used to reduce the power load onto tungsten divertor armors in tokamaks. Consequently, plasma-material interactions will be affected by seeded nitrogen impurities. The influence of nitrogen pre-irradiation on deuterium induced blistering and deuterium retention in rolled tungsten has been investigated at different pre-irradiation temperatures in the linear plasma device STEP with ion flux >10²¹ m⁻² s⁻¹. Commercially rolled W samples were sequentially exposed to nitrogen plasma (380 K and 470 K) and deuterium plasma (510 K). Surface observations show that nitrogen pre-irradiation suppresses deuterium-induced surface blistering. Thermal desorption spectroscopy measurements indicate that deuterium retention in the rolled tungsten is reduced due to nitrogen pre-irradiation, and it significantly changes with the pre-irradiation temperature. These phenomena are supposed to be related to the formation and change of WN_xs at different temperatures which is validated by X-ray photoelectron spectroscopy analyses.