Electrodynamic forces and stresses in the RFX toroidal field coils in fault conditions

During the pulse, the toroidal field winding of the RFX machine is connected to a capacitor bank and an oscillating current flows in the winding. The winding protection against faults is performed by short-circuiting the winding with a crow-bar, made of a set of ignitrons connected in parallel. The efficiency of this crow-bar strongly depends on its equivalent electrical resistance, which should be kept as low as possible to limit the voltage applied to the winding. On the other hand, the maximum current in the crow-bar must be low enough to be withstood even by a single ignitron, to avoid damages in case of an improper triggering. A compromise about the crow-bar resistance value is found on the basis of the analysis of the electrodynamic forces and stresses in the toroidal field coils during the crow-bar action. The paper presents the circuit model and simulations, the force distributions and the corresponding mechanical stress values in the coils, showing the dependence of the stresses on the crow-bar resistance