Experimental investigation of turbulence at the transition from closed to open field lines

Investigations of turbulent transport at the transition from closed to open field lines are summarised. The data are from the toroidal low-temperature plasma of the torsatron TJ-K and the high-temperature plasma of ASDEX Upgrade. A close comparison of TJ-K data with results from the gyro-fluid code GEM shows a great structural similarity in all aspects analysed. This indicates the dominance of drift-wave turbulence. Data from both devices indicate a flow-shear layer at the separatrix incorporating pinch phenomena and the origin of SOL transport intermittency. The role of Reynolds stress in the generation of shear flows is studied on TJ-K with a novel poloidal array equipped with 128 Langmuir probes. (author)