First experimental determination of ion flow velocities and temperatures in the ASDEX Upgrade divertor

Abstract

For the analysis of ion dynamics (i.e. ion temperature and ion flow velocity distributions) in the divertor I of ASDEX Upgrade an optical spectroscopic system with high spectral, temporal and spatial resolution was brought into operation. Integrated along up to 74 lines of sight with different orientations to the magnetic field lines, emission spectra of atoms and ions were recorded with high resolution by an Echelle spectrometer and a 2D CCD camera. With this setup, ion flow velocities and temperatures in a divertor plasma could be determined experimentally for the first time. In the attached high-recycling divertor regimes analysed, neutrals such as helium do not flow preferentially parallel to any of the installed lines of sight. In contrast, all the ions investigated always showed pronounced Doppler shifts. The corresponding ion flow is directed towards the target plates, in the outer as well as in the inner divertor. For typical L- and H-mode discharges (attached high-recycling divertor conditions) the ions flow at speeds of about in the L-mode and in the ELMy H-mode phases. The temperatures of the ions near the divertor plates range from about 5 eV (L-mode) to up to 20 eV (ELMy H-mode phases). The comparison of these results with computer code calculations showed good agreement.