Effect of temperature on D retention in WNx layers exposed to low-energy, high-fluence D plasmas

For a burning plasma device (ITER), the removal of radiative power by seed impurities will be inevitable to avoid divertor damage by excessive heat flux [1]. N2 gas is likely to be used to reduce the power load. However, because of re-deposition phenomena, WNx compounds will be produced in the divertor and tritium retention is issue of concern. We report experiments using the GYM linear plasma device that examined D retention in WNx compounds exposed to D plasma at divertor relevant fluence (? 1024 m-2) as a function of sample temperature (Ts) in the range of 300-730 K. In order to determine the D retention, the WNx specimens were examined ex situ by Elastic Recoil Detection Analysis (ERDA). It is shown that WNx compounds have very similar D retention, lower than the case of the tungsten without nitrogen and in any case lower than the acceptable limit for operation in ITER [2]. W-N samples were prepared by reactive plasma sputtering system. The morphological properties and physical structure of the samples were investigated by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX).