Fluctuation measurements in the X-point region of ASDEX Upgrade

Density fluctuations in the X-point region are characterized using ion-saturation current measurements obtained from Langmuir probes. These are mounted on the X-point manipulator (XPM) available at the ASDEX Upgrade, which provides the unique possibility of increased poloidal coverage for measuring continuous time series. To characterize the filamentary structures, we implement the Filtered Poisson Process (FPP) model [1] as it provides a way to unify the observations of a probability density functions (PDF), power spectral density (PSD), and the conditional averaged profile (CA). The FPP models a given time series as the superposition of uncorrelated pulses with the assumption that they arrive according to a Poisson distribution. The pulses are also assumed to be independent and their amplitudes are exponentially distributed. Due to the successful implementation of this model in different tokamaks [2, 3, 4] to characterize the filamentary structures in the SOL at the outboard midplane, we implement this method to investigate whether the underlying assumptions of this model is able to describe fluctuations in the X-point region. This provides a fair way to compare the statistics of the fluctuations observed at the outboard midplane to those in the X-point region.