A novel tubular superconductor stabilized with static pressurized helium

A new superconductor concept for encapsulated, medium-size magnets with a significantly increased stability margin is presented. A tubular superconductor (TSC) of a few millimeters outer diameter is drawn from a billet (normal metal+superconducting inserts). After winding, the TSC is filled with static gaseous helium under pressure, which serves as an enthalpy stabilizer. The approach is beneficial both for NbTi and Nb₃Sn magnets, including conductively cooled magnets. For example, Nb₃Sn TSC magnet for 8 T, 8 K operation has a stability margin up to 8 times greater than a corresponding magnet using a conventional conductor. The stability margin against slow (steady-state) and transient disturbances has been analyzed for TSC and cable-in-conduit conductors (CICC). Analytical expressions for the stability margin have been obtained and optimal helium cross-section have been determined. Results can be used to design helium-filled conductors for magnets operating to maximum stability margin