Microscopically nonuniform deposition and deuterium retention

The divertor surfaces in JET with ITER-like wall (ILW) have been studied using micro ion beam analysis (l-IBA) methods and scanning electron microscopy (SEM). Deposited layers with beryllium as main constituent had been formed during plasma operations through 2011–2012. The deuterium trapping and impurity deposition were non-uniform, frequently enhanced within pits, cracks and valleys, regions reaching in size from 10 lm to 200 lm. The impurity deposition and fuel retention were correlated with the surface slope with respect to the direction of ion incidence. Typically more than 70% of the total measured areal density of trapped D was found in less than 30% of the surface area. This is of consequence for the interpretation of other surface analyses and in extrapolation from fuel retention in JET with ITERlike wall and rough divertor surfaces to ITER with smoother surfaces.