Overview on plasma operation with a full tungsten wall in ASDEX Upgrade

Abstract

Operation with all tungsten plasma facing components has become routine in ASDEX Upgrade. The conditioning of the device is strongly simplified and short glow discharges are used only on a daily basis. The long term fuel retention was reduced by more than a factor of 5 as demonstrated in gas balance as well as in post mortem analyses. Injecting nitrogen for radiative cooling, discharges with additional heating power up to 23MW have been achieved, providing good confinement (H98y2=1), divertor power loads around 5MWm−2 and divertor temperatures below 10eV. ELM mitigation by pellet ELM pacemaking or magnetic perturbation coils reduces the deposited energy during ELMs, but also keeps the W density at the pedestal low. As a recipe to keep the central W concentration sufficiently low, central (wave) heating is well established and low density H-Modes could be re-established with the newly available ECRH power of up to 4MW. The ICRH induced W sources could be strongly reduced by applying boron coatings to the poloidal guard limiters.