2D heat flux in ASDEX Upgrade L-Mode with magnetic perturbation

Abstract

Power exhaust is one of the major challenges for a future fusion device like ITER. Future devices are foreseen to operate in a regime that exhibits periodic outbursts of particles and energy, so called edge localised modes (ELMs). These ELMs might limit the life time of the divertor target. One of the techniques that is studied in order to control ELMs is the application of a non-axisymmetric magnetic perturbation (MP). This technique leads to a 2D heat flux pattern at the divertor target.The 2D heat flux pattern is characterised for a perturbation with a toroidal mode number n = 2. The lobe structure is visible with a resonant configuration in a low density L-Mode. Varying the differential phase reduces the extent of the heat flux modulation compared to the axisymmetric reference. The heat flux distribution shows no significant modulation with the differential phase opposite to the resonant configuration. The toroidally averaged profile is described by an 1D diffusive model for all differential phases. No significant deviation between the axisymmetric reference and the averaged profiles is observed for both transport qualifiers, power fall-off length λq and divertor broadening S.It was reported from previous studies in ASDEX Upgrade, that in L-Mode both λq and S increase with increasing density. This dependence is confirmed for the axisymmetric reference phase. The toroidally averaged heat flux profiles with MP show the same increase with density as the reference without MP. The modulation of the heat flux decreases with increasing density. This is attributed to the increasing divertor broadening S which distributes the heat flux more uniformly.