C. Dorn

A fast scanning Langmuir probe system for ASDEX-Upgrade divertor

Abstract A fast scanning Langmuir probe system (LPS) for ASDEX-Upgrades divertor plasma investigations was designed, manufactured and operated. Profiles of ion saturation current density, Jsat, electron temperature, Ted, electron density, Ned, floating potential, Vfl, and Mach number have been recorded for ohmic (OH) and low/medium power neutral beam heated (NI) discharges. In these cases the probe can access both divertor legs, allowing comparison of plasma parameters in the two divertors and investigations of the private flux region. Strong divertor asymmetries, complex plasma flow patterns and changes in the power flow to the divertor targets, depending on ion gradB drift direction, density and divertor geometry, have been observed.

Spectroscopic investigation of the dynamics of ions and neutrals in the ASDEX Upgrade Divertor II

Abstract Detachment at the separatrix is a promising possibility to reduce the peak power load onto the divertor target plates. We investigated this topic spectroscopically at ASDEX Upgrade by measuring particle velocities using Doppler spectroscopy. The experimental data show a reduction of the chord averaged hydrogen velocity along the separatrix by about a factor of 3. Another important subject is flow reversal: after a brief discussion of 2D-code predictions and the conditions for detection we present spectroscopic evidence for flow reversal of C 2+ -ions in the ASDEX Upgrade divertor II. The comparison of these spectroscopic data with B2-EIRENE modeling shows good qualitative and quantitative agreement.

Completion of Assembly and Start of Technical Operation of ASDEX Upgrade

The last important steps of the tokamak machine assembly are described. A survey of precision and tolerances is given achieved for the vacuum vessel, the toroidal field (TF) magnet and the poloidal field (PF) coils. The first commissioning tests of vacuum vessel, TF magnet and PF coils are described together with certain features of the control and technical supervisory system. Remarks on improvements of the electric power supply system and the fast plasma control system follow. Finally the programme of the next future is briefly outlined.