Speaker
Description
In 2017 the Wendelstein 7-X stellarator (W7-X) has performed the second experimental phase (OP 1.2a), introducing divertor operation with a inertially cooled test divertor unit (TDU), and graphite-covered first wall.
The divertor operation resulted in a substantial improvement of the plasma parameters and the inertially cooled TDU and the graphite walls also allowed much longer discharges with higher heating power. This could be observed by the possibility to increase the energy input up to 80 MJ, compared to the 4 MJ in the first phase (OP 1.1) without TDU. This was a first step in the mission of W7-X to achieve steady-state discharges at a high heating power.
This heating energy increase has been performed in several steps, in a dedicated procedure, identifying hotspots of localized energy deposition with thermography cameras and measuring the instantaneous temperature increase on the target plates, baffles and the walls as well as the slow temperature increase of divertor structures. Further, the plasma impurities have been monitored during the increase of the integrated power deposition in the device to detect a possible overloading of the first wall. The increase of integrated power deposition in the plasma was strongly depending on the magnetic configuration. The trim and control coils turned out to be good tools to adjust the wall loading.
Procedures to conduct this increase in the integrated power deposition and the results for several magnetic configurations will be discussed.
