Measurements in the X-Point Region at ASDEX Upgrade

It is now well known that the presence of the x-point in diverted tokamaks influences the turbulence in the scrape-off layer[1]. Turbulence plays an important role in fusion devices, as it is the main agent for the cross-field transport of particles and energy from the edge of the plasma into the scrape-off layer. This results in filamentary structures, which causes transport towards the plasma facing components of tokamak devices. Therefore, it is important to understand the turbulent transport to be able to predict the life time of the plasma facing components as well as the confinement of the plasma. However, due to scarcity of diagnostics particularly in the x-point region, the behaviour of plasma streaming in the scrape off layer as well as in the private flux region is not well understood. The x-point manipulator (XPM) at ASDEX Upgrade increases the diagnostic coverage in the divertor region. The XPM allows a full scan from the low field (LFS) scrape-off layer (SOL) into the high field side (HFS) and thus, allowing measurements in the private flux region (PFR). Fast imaging results from MAST show that filaments are elongated and sheared close to the x-point, thus resulting in a quiescent region[2]. The XPM makes it possible to investigate the quiescent region with an active diagnostic. Measurements using Langmuir probe are performed to investigate the quiescent region close to the x-point. This contribution will present the experimental results of the quiescent region at ASDEX Upgrade, which indicate a quiescent region in the SOL as well as in the PFR. The quiescent regions are characterised by a reduced fluctuation intensity. The quiescent regions are observed in L-mode plasma discharges and their existence seems to be independent of the heating scenario. The results are correlated to measurements from Langmuir probes mounted on the divertor plates.