ELMs and asymmetries at the COMPASS-D boundary

In this paper we report the effect of both edge localized modes (ELMs) and drifts on divertor plasma parameters in COMPASS-D. Profile changes during ELMs are measured with high spatial resolution, and power and particle losses per ELM are estimated. The time evolution of the divertor parameters is shown to be consistent with the ELM being associated with a fast collapse of the transport barrier. Asymmetries between inboard and outboard divertor targets in L-mode plasmas are shown to depend on the plasma parameters, in particular the direction of the toroidal magnetic field, the average plasma density and the input power. In general, the outer divertor region receives more power than the inner one, the asymmetry increasing for ion del B drift away from the X-point, contrary to observation in other devices. The E x B drift together with scrape-off layer (SOL) currents are suggested as possible mechanisms causing the asymmetry.