Wendelstein 7-X

Starting in July 2015: Collaborative grant with the Auburn University  for work on island divertor physics at Wendelstein 7-X, Germany

Title:“Impact of three-dimensional equilibrium stability on island divertor performance at Wendelstein 7-X”

Public Abstract:

Three-dimensional (3D) plasma edge transport and plasma material interaction (PMI) critically influence plasma stability and performance in stellarators. There is a strong coupling between the plasma equilibrium and boundary plasma characteristics since the overall 3D equilibrium determines the edge magnetic topology and hence plasma interaction with material surfaces. Neutral and impurity sources released from this 3D PMI can be transported back into the main plasma. This inward impurity transport not only defines possible divertor operating conditions (e.g. a radiative divertor, detachment) but also can determine core plasma performance limits due to impurity accumulation. From a reactor perspective, impurities and in particular helium fusion ash has to be efficiently exhausted. This collaborative research enterprise between Auburn University and the University of Wisconsin-Madison investigates key aspects of this self-consistent feedback loop between plasma wall interaction, edge and core plasma transport and stability of 3D stellarator equilibria in an attempt to optimize the core-edge coupling for high performance, steady state operation of Wendelstein 7-X. This research will enable understanding of the link between finite beta and trim coil effects on the 3D equilibrium of W7-X and the resultant specific edge transport characteristics during the startup and initial operations of Wendelstein 7-X. The research effort includes development and application of a sophisticated fractional impurity neutral pressure measurements system to study and optimize impurity exhaust in general and helium exhaust in particular with the island divertor at Wendelstein 7-X for the first time.

Personell: Ass. Prof. Oliver Schmitz, Ass. Scientist Heinke Frerichs, Dipl. Phys. Florian Effenberg, BSc Thierry Kremeyer