Effect of E × B driven transport on the deposition of carbon in the outer divertor of ASDEX Upgrade

Reversal of the toroidal magnetic field and plasma current is observed to considerably change the re-deposition of 13C injected into the outer divertor scrape-off layer of ASDEX Upgrade. In forward field low-density L-mode plasmas, 24-32% of injected carbon is found locally re-deposited. The deposition tails are aligned toroidally both upstream and downstream of the exit holes and indicate transport towards the strike point. In reversed field with similar main plasma parameters, the re-deposition efficiency is a factor of 2 smaller. The deposition is more localized and shows transport towards the outer scrape-off layer. Numerical modelling with the SOLPS5.0 and ERO codes shows that these differences in 13C deposition can be attributed to the combination of the E × B drift reversal directly influencing the transport of carbon and changes in local plasma conditions due to the drift reversal.