Using MAXFEA code in combination with ANSYS APDL for the simulation of plasma disruption events on EU DEMO

Abstract

Plasma disruptions are one of the major concerns in the design phase of fusion devices. The very high eddy and Halo currents, induced in the passive structures, crossing the electromagnetic field generate huge loads. A Vertical Displacement Event (VDE) begins with a loss of position control that could be triggered by a plasma perturbation (e.g. ELMs, L-H and H-L transitions, minor disruptions, etc.) acting as a source of vertical and horizontal plasma displacements. At a certain point a fast Thermal Quench (TQ) takes place. After that the plasma current abruptly decreases (Current Quench (CQ) phase). During the plasma evolution, especially during the TQ and CQ, toroidal and poloidal eddy currents are induced in the metallic components, respectively due to the dynamic effect of plasma Poloidal Field Variation (PFV) and Toroidal Field Variation (TFV). The plasma time evolution and the effects of such events on the passive structures can estimated through 2D axisymmetric codes, such as MAXFEA. However, the presence of 3D structures (e.g. ports, divertor, etc.) generates non-trivial currents paths and distribution of EM loads. In order to estimate the 3D effects, MAXFEA has been used in combination with ANSYS APDL code, allowing to estimate both PFV and TFV consequences on the 3D model. Considering the DEMO PMI configuration and a fast upper Vertical Displacement Event (VDE), the procedure was successfully benchmarked, comparing the MAXFEA and APDL results, in a case where the 3D Vacuum Vessel (VV) was considered axisymmetric. The methodology has been then exploited and applied to estimate the EM load distribution on the real DEMO VV.