Interpretation of fast measurements of plasma potential, temperature and density in SOL of ASDEX Upgrade

Abstract

This paper focuses on interpretation of fast (1 µs) and local (2–4 mm) measurements of plasma density, potential and electron temperature in the edge plasma of tokamak ASDEX Upgrade. Steady-state radial profiles demonstrate the credibility of the ball-pen probe. We demonstrate that floating potential fluctuations measured by a Langmuir probe are dominated by plasma electron temperature rather than potential. Spatial and temporal scales are found consistent with expectations based on interchange-driven turbulence. Conditionally averaged signals found for both potential and density are also consistent; however, those for temperature show an unexpected ∼4 mm wide decrease by 10% at the very centre of a blob. In the wall shadow, temperature measured by the swept Langmuir probe yields values ∼10 eV, whilst the ball-pen temperature gradient is more steep and credible, dropping down to ∼1 eV.