Design, modelling and fabrication of a fault tolerant 1 T superconducting applied-field module for a kW-class plasma rocket

In 2022, Paihau-Robinson Research Institute developed a 1 T superconducting electromagnet cooled by a space rated cryocooler and successfully integrated it with a kilowatt-class plasma rocket, in collaboration with the Shockwave and Space Propulsion Laboratory at Nagoya University. The use of superconductors reduced the input power by over 99%, generated magnetic fields three times stronger, and by using a space-rated miniaturised cryocooler, the use of liquid cryogen was eliminated. Therefore, for thrusters that require a strong external magnetic field – such as applied-field magnetoplasmadynamic thrusters – this represents the first system that could reasonably be flown in space. This paper discusses the design, fabrication, and testing of the superconducting coils at Paihau-Robinson for plasma thrusters. Special attention is paid to preventing a ‘quench’, a major fault mode for superconducting coils. If part of the cryogenic coils is heated above the critical temperature, the superconducting state is destroyed and the energy stored in the magnetic field is dissipated suddenly, which can permanently destroy the superconducting system. Despite numerous tests with the plasma rocket above the kilowatt power level, the superconducting electromagnet never quenched, even with large heat loads during plasma generation. This paper therefore also discusses and demonstrates how this fault tolerance was achieved.