ANSYS Model to Predict Magnetic Fields and Loads in Alcator C-Mod’s New Outer Divertor During a Disruption

Abstract

A new outer divertor is being designed for installation on Alcator C-Mod. This divertor will be toroidally continuous such that the currents during a disruption will be driven in the toroidal direction and not cross Alcator’s large toroidal field and it eliminates leading edges. However, currents will still cross the poloidal fields, and so it is important to properly predict the poloidal fields in the area of the divertor so that we can properly predict the loads on the divertor during a disruption. To that end, an ANSYS model has been built which can predict the fields and field transients in C-Mod given two inputs, the currents for the toroidal and poloidal field coils which come from measured data taken during a discharge, and the current in the plasma, which comes from another model that solves Maxwell’s equations to reconstruct the plasma as 24 current carrying filaments. The advantage of using this method to predict fields is that it provides the ability to create a model based on actual measured data and to model whichever type of disruption, whether a midplane disruption or a vertical displacement event, is deemed necessary for the design. The ANSYS model then is able to predict the fields, including the shielding effects of the structures in the vessel, and the currents induced in the vessel and these structures. These results can then be mapped to a sub-model of the divertor to predict loading and stress during the disruption.