Change of the scrape-off layer power width with the toroidal B-field direction in ASDEX upgrade

The change of the scrape-off layer power width in dependence of the toroidal magnetic field direction is investigated in L-mode discharges in the upper single null (USN) configuration in ASDEX Upgrade. The heat flux onto the outer and inner divertor plates is measured using a fast 2D infrared camera. The heat flux distribution is described by an exponential power fall-off length lambda(q) and a diffusive broadening in the divertor region S. In this paper the parameters, S and lambda(q), for the inner and outer divertor target are compared for both toroidal magnetic field directions. For the divertor broadening S no dependence on the toroidal magnetic field direction is observed. The comparison between the near scrape-off layer electron temperature fall-off length lambda(Te) and the power fall-off length lambda(q) are in agreement with the 2-point model. It is concluded that electron conduction is the main contribution for the scrape-off layer parallel transport in these discharges. The ratio between inner, lambda(inner)(q), and outer, lambda(outer)(q), power fall-off length is dependent on the toroidal magnetic field direction. The numerical values are lambda(inner)(q)/lambda(outer)(q) = 0.44 for favourable B x del B ion drift direction and lambda(inner)(q)/lambda(outer)(q) = 0.85 for non-favourable drift direction. The different ratios are explained by vertical drifts, which are dependent on the toroidal magnetic field direction.