Dynamics LFS and HFS density profiles at ASDEX Upgrade - Effect of magnetic configuration and divertor conditions

Abstract:
Future fusion devices, including ITER, will need to operate with a detached divertor regime. Divertor detachment is often linked to the formation of a high-density front on the high-field side (HFS) that significantly influences the profiles at the inboard midplane. HFS profiles are also remarkably sensitive to the magnetic configuration and, in particular, to the connection between the LFS and the HFS. The physics behind these observations is not yet fully understood as experimental data from the HFS is often scarce.

The O-mode reflectometer at ASDEX Upgrade is a valuable tool as it allows measuring the density profiles both on the LFS and HFS. In this work, we investigate the influence of ballooning transport and the high-density front in establishing HFS density profiles using as main experimental tolls scans in the magnetic configuration and in the divertor conditions. Our observations have shown that the high-density region is limited to the flux surface containing the secondary X-point and leads to inverted density gradients very close to the inner separatrix.