Bifurcation of temperature in the boundary region of advanced stellarators
The following paper discusses some problems of the island divertor in the Wendelstein 7-X configuration and the Helias reactor (HSR) configuration. These islands exist on the surface of the plasma boundary and will be utilized for impurity control in the Wendelstein 7-X experiment. The structure of this island region depends on the plasma pressure and the tendency is to become more and more ergodic with rising plasma pressure. Thermal transport in the divertor region is described by the transport equation, which is inherently three-dimensional. By averaging along the helical geometry of the island, this equation can be reduced to a two-dimensional one describing the temperature distribution on the poloidal plane. In this approximation, there is a strong similarity to tokamak geometry. Since the islands are modified by the plasma currents a finite beta equilibrium is computed as the starting point for the geometric analysis of divertor action. Anomalous transport strongly affects the width of the scrape-off layer and the width of the wetted area on the divertor target plates. The non-linearity of the radiation losses in the divertor region and the non-linearity of the boundary conditions can lead to a bifurcation of the temperature distribution and to multiple solutions. Some numerical examples of temperature profiles and bifurcation phenomena are studied by using phase space analysis.
Bibliographic Reference: Report: IPP III/262 EN (2000) 30 pp.
Availability: Available from Max-Planck-Institute, Garching bei M³nchen (DE)
Record Number: 200012724 / Last updated on: 2000-09-08
Original language: en
Available languages: en