Retention of nanocrystalline WNx layers exposed to high-fluence deuterium plasmas

For high-power plasma operation regimes in tokamak fusion devices the power load onto W divertor plates must be kept below acceptable limits for materials. N-2 gas is likely to be used to reduce the power load. However, because of erosion phenomena, WNx compounds will be produced in the divertor and tritium retention is issue of concern. We report recent experiments using the GYM linear plasma device that examined D retention in WNx compounds exposed to D plasma at divertor relevant fluence (similar to 10(24) m(-2)). It is shown that WNx compounds with different nitrogen concentration 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.