Protection of conduction cooled Nb3Sn SMES coil

A conduction cooled Nb₃Sn SMES coil requires a protection analysis different from that of the liquid helium cooled NbTi magnets. In an SMES coil constructed with a bronze processed Nb₃ Sn wire, hot spot temperature is high due to a slow normal zone propagation. In a conduction cooled system, the eddy current generated heating in the cryogenic interface enables a quench back. In order to design a proper protection scheme for a cryogen free Nb₃Sn SMES system operating at 10 K, a computer code has been developed. The code simulates the quench behaviour of the coil protected with any combination of a shunt resistor, subdivision and quench back. The modelling of the quench back requires the solution of the eddy current problem and the heat transfer between the coil and the interface. These are combined with the solution of the differential equations describing the protection with a shunt resistor or subdivision. Utilizing the developed code, the protection of a 0.2 MJ conduction cooled Nb₃ Sn SMES coil has been designed