Superconducting Coils for Small Nuclear Fusion Rocket Engines

This proposal focuses on the superconducting coils subsystem, a critical subsystem for the PFRC reactor and Direct Fusion Drive and other fusion and electric propulsion technologies. Our strategy for PFRC has evolved since our Phase I proposal, and we now propose a hybrid magnet approach: a combination of so-called “dry” conduction-cooled low-temperature (LTS) superconductor magnets and high-temperature (HTS) magnets that are operated at low temperature for maximum current at high fields. Conduction-cooled LTS magnets are becoming state-of-the-art for MRI machines, and reduce coolant requirements from 1000’s of liters of helium over the lifetime of the machine to a few liters in a closed cryocooler. This is with a mass penalty for cooling of only about 5%. These low-coolant LTS magnets, producing a field of 5 to 6 T, will have excellent safety margin in both critical current and field and will have a clear path to space applications. PFRC also requires higher-field nozzle magnets producing fields of 20 to 30 T. These would utilize HTS superconductors operated at low temperatures of about 10 K. All coils will require highly efficient cooling systems, excellent mechanical support, and overall low mass including structural components. Our partner, PPPL, is the only institution in the world where active research on the physics and technology of small, steady-state fusion devices is being performed. We propose a Phase II experiment to build a 0.5 Tesla LTS magnet with a split pair of winding packs, to mimic a subset of the PFRC magnets. A separate pulsed copper test coil to simulation the plasma will be used to study the effects on the magnet of FRC formation, which will occur in a fraction of a second and result in large increases in magnetic field at the windings. In parallel, we will continue to advance the design of the HTS nozzle magnets, seeking the lowest mass solution.