Simulation of voltage and current development in the Wendelstein 7-X coil system taking into account fault conditions

At present the Wendelstein 7-X stellarator experiment is under construction at the Greifswald branch of the Max-Planck-Institut für Plasmaphysik. During operation the plasma will be confined by the magnetic field of superconducting coils which will store a magnetic energy of about 620 MJ at 3 T average field strength at the magnetic axis. In a fast shut down this energy will be mainly absorbed by discharge resistors which heat up in the process and change their resistances to about four times the initial value. These changing resistances not only decrease the time constants of the discharge process but also determine the voltages applied to the coils. The paper describes the simulation of the currents and voltages during shut down and gives an example for increased coil currents due to a shut down failure which would lead to higher magnetic forces acting on the coils.