Measurement and calculation of the radial electric field in the stellarator W7-AS

At the advanced stellarator W7-AS, active charge exchange recombination spectroscopy (CXRS) is used to measure the toroidal and poloidal impurity rotation velocity. The radial electric field E-r is determined experimentally from the radial force balance equation. In parallel, E-r is calculated by means of the neoclassical drift kinetic equation solver (DKES) transport code. Neoclassical calculation and measurement are, in general, in good agreement. A selection of discharges is presented in this paper which shows typical properties of E-r at W7-AS, and which highlights the mutual relationship between E-r and transport.