Radial transport in the far scrape-off layer of ASDEX Upgrade during L-mode and ELMy H-mode

Abstract

The radial turbulent particle flux and the Reynolds stress in the scrape-off layer (SOL) of ASDEX Upgrade were investigated for two limited L-mode (low confinement) and one ELMy H-mode (high confinement) discharge. A fast reciprocating probe was used with a probe head containing five Langmuir probes. One of the probe pins was protruding radially above the other pins. The radial electric field component was derived from the difference of the floating potentials of the protruding pin and another pin nearby. The poloidal electric field component was derived from the difference of the floating potentials of two probes on the same poloidal meridian. In both cases, equal electron temperatures on all probe pins had to be assumed. Of the other pins one was biased to ion saturation (−70 V), whereas one was swept to record the current–voltage characteristic. A detailed statistical analysis of the plasma conditions in L- and H-modes and, more specifically, also during and in between type-I edge-localized mode (ELM) events is presented. We found evidence for similarities in the statistics of transport in L-mode, during ELM events and in between ELMs, suggesting that in all three cases the transport is undertaken by blobs and filamentary structures, respectively. During the intervals in between ELMs the blob structures appear to be relatively smaller as compared with the L-mode.