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 C 2+ ions flow at speeds of about 10 km s −1 in the L-mode and 10-20 km s −1 in the ELMy H-mode phases. The temperatures of the C 2+ 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.

Modelling of the Edge Plasma with Account of Self-Consistent Electric Fields

“…Hence, on one side, part of the impurity poloidal velocity changes due to E × B drift but on the other side, its parallel velocity also changes due to the drag of the main ions in the opposite direction, while the total poloidal velocity of impurities remains almost the same. Hence the distribution of the lowly charged impurities is similar to earlier results obtained without drifts [22]- [23], which are consistent with experiments on AUG. Fig. 7 The scheme of the poloidal and radial current distribution in the SOL.…”

The role of friction in SOL pressure balance in Alcator C-Mod

“…Parallel drift measurements have also recently been made in the divertor of ASDEX-Upgrade [14]. As in this study, ion velocities are found to be generally directed towards the divertor plate, with magnitudes being a significant fraction of the ion acoustic speed.…”

Measurements and ERO simulations of carbon flows in the high-field side main SOL in AUG

“…Impurity transport is related to material migration, tritium co-deposition, and core contamination -issues that are crucial for ITER and commercial fusion power. The radial profiles of the SOL flow has been measured in ASDEX Upgrade (AUG) close to the x-point for both divertor legs using a reciprocating Langmuir probe [3] and spectroscopy [4], and in the low field side (LFS) midplane using a Langmuir probe [5]. Also, charge exchange recombination spectroscopy (CXRS) core rotation measurements exists for both the HFS [6] and LFS [7].…”