Main chamber sources and edge transport of tungsten in H-mode plasmas at ASDEX Upgrade

Abstract

In the fully tungsten clad ASDEX Upgrade, the sputtering rates of tungsten have been determined at all relevant plasma facing components using fast spectroscopic measurements with temporal resolution down to 0.5 ms. The sputtering strongly increases during an edge-localized mode (ELM) and the ELMs are often the dominant cause of tungsten sputtering. A modelling approach was employed to calculate the tungsten source at the limiters and the resulting tungsten density at the pedestal top inside the H-mode edge transport barrier (ETB). In the ETB, it is assumed that tungsten transport is collisional, i.e. behaves like other impurities. The collisional transport leads to strong inward drifts and steep density gradients in the ETB, which are flattened during an ELM causing an efflux of tungsten. The collisional transport in the ETB is also calculated for typical ITER conditions and the resulting tungsten density profiles as well as the transport of the helium ash through the ETB are evaluated.