Plasma wall interaction and its implication in an all tungsten divertor tokamak

Abstract

ASDEX Upgrade has recently finished its transition towards an all-W divertor tokamak, by the exchange of the last remaining graphite tiles to W-coated ones. The plasma start-up was performed without prior boronization. It was found that the large He content in the plasma, resulting from DC glow discharges for conditioning, leads to a confinement reduction. After the change to D glow for inter-shot conditioning, the He content quickly dropped and, in parallel, the usual H-Mode confinement with H factors close to one was achieved. After the initial conditioning phase, oxygen concentrations similar to that in previous campaigns with boronizations could be achieved. Despite the removal of all macroscopic carbon sources, no strong change in C influxes and C content could be observed so far. The W concentrations are similar to the ones measured previously in discharges with old boronization and only partial coverage of the surfaces with W. Concomitantly it is found that although the W erosion flux in the divertor is larger than the W sources in the main chamber in most of the scenarios, it plays only a minor role for the W content in the main plasma. For large antenna distances and strong gas puffing, ICRH power coupling could be optimized to reduce the W influxes. This allowed a similar increase of stored energy as yielded with comparable beam power. However, a strong increase of radiated power and a loss of H-Mode was observed for conditions with high temperature edge plasma close to the antennas. The use of ECRH allowed keeping the central peaking of the W concentration low and even phases of improved H-modes have already been achieved.

Transient Thermal and Structural Mechanics Investigation of the New Solid Tungsten Divertor Tile for Special Purposes at ASDEX Upgrade

“…Under the assumptions made by load conditions and fatigue material properties, in a f rst approach it can be generally said, that the structural part will not fail before 37 load cycles at least. This life cycle number in correlation with the value for regular tungsten tile [2] (without grooves and holes) of ∼1000 load cycles, under very similar thermal loading, shows the inf uence of the body shape features at the life cycle of the structural part.…”

“…Starting with the experimental campaign 2007, ASDEX was operated as a full tungsten experiment. More details about it can be found in [2]. The next step in the divertor improvement is the installation of a solid tungsten divertor made from powder metallurgy tungsten, to N. Jaksic is with the Integrated Technical Centre, Max Planck Institute for Plasma Physics, Garching 85748, Germany (e-mail: nikola.jaksic@ ipp.mpg.de).…”

Dynamic and static deuterium inventory in ASDEX Upgrade with tungsten first wall

“…This option is tested in ASDEX Upgrade (AUG) by using tungsten for PFCs. A stepwise transition from carbon to tungsten coated carbon tiles was selected to minimize the effort and to study material migration [1], [2], [3].…”

Experiences With Tungsten Plasma Facing Components in ASDEX Upgrade and JET

“…Consequently, the second W programme in AUG started in 1999 with the installation of W PFCs in the main chamber. Only in 2007 the W divertor tiles were installed and 100% W coverage was reached [6], representing the only full tungsten fusion device. All of the AUG W PFCs were produced by W coating on fine grain graphite.…”