Destruction of magnetic surfaces in an RFP by field errors from ports and gaps.

摘要

Geometric disturbances such as ports and gaps in the shell give rise to magnetic error fields, which may result in the formation of magnetic islands in the neighbourhood of rational magnetic surfaces. These islands have a deteriorating effect on plasma confinement. In this work the formation of these islands and their effect on plasma confinement are studied and the results are applied to the Extrap T1-Upgrade device, which is a large aspect-ratio device possible to operate in RFP-mode. The plasma is modelled with a polynomial function model. A static model for the field errors from ports in the shell shows that several magnetic islands are formed and that an overlap of islands occurs. The results suggest that a conducting grid should be positioned over the ports. In the case of field errors from gaps in the shell a simple model is used, with the approximation that all currents flow at the edges of the gaps. It shows that especially the m = 1 perturbations are considerably large and that there will be confinement problems even with the use of conducting plates for shielding of the error fields. (au). (Atomindex citation 24:034471)