FE Analyses of eddy currents in W7-X plasma vessel

Abstract

Wendelstein 7-X is the largest optimized stellarator, which is presently in operation in Greifswald, Germany. During possible fast plasma disruptions, relatively small plasma bootstrap current rapidly vanishes and consequently eddy currents are induced in all electrically conducting components including sophisticated Plasma Vessel (PV).This paper focuses on the evaluation of eddy currents induced in PV components due to plasma bootstrap current decay. This task was accomplished by means of a 3D PV FE model. Due to geometry complexity, special emphasis was on specific modelling issues (elements type, mesh density and excitation representation). At first, the PV structure was modelled without 254 ports, which were included subsequently. A procedure to allow quick and easy introduction or exclusion of ports from EM analyses was devised and implemented. In this way, the influence of these structures on the eddy currents could be evaluated efficiently.Peak value of total eddy current running around the PV structure without ports turns out to be around 20 kA Furthermore, results indicate that the ports presence leads to a relatively minor decrease of this value, around 5%. Current concentration around specific ports is highlighted.The paper presents also two examples of re-using FEM and results.