Development of a high current density, high temperature superconducting cable for pulsed magnets is the 2024 Superconductor Science and Technology paper in which 📝Charlie Sanabria and 63 co-authors qualify PIT VIPER, the low-AC-loss cable developed for the fast-ramping 📝central solenoid and 📝poloidal field coils of a high-field 📝tokamak.
Its predecessor solved a different problem. 📝VIPER: An Industrially Scalable HTS Cable qualified a conductor for magnets that sit at steady current, which is what a 📝toroidal field coil does. A central solenoid does the opposite — it ramps, and a changing field drives 📝AC loss in a 📝REBCO tape stack, depositing heat inside a magnet held near 20 kelvin, where removing heat is the expensive part.
PIT VIPER answers that by partitioning the conductor. Transposed copper petals, shaped to nest in a circular pattern, each carry a REBCO tape stack and are insulated from one another so induced currents cannot circulate between them. A stainless-steel jacket adds mechanical strength and doubles as the vessel for solder impregnation; a tube down the centre carries coolant; fibre-optic sensors sit beneath the tape stacks for 📝quench detection.
The qualification ran as part of the 📝SPARC central solenoid model coil program, and its results are measured rather than projected: AC losses fifteen times lower than VIPER's at roughly 5 tesla per second; 2 percent or less degradation in 📝critical current under electromagnetic loading above 850 kilonewtons per metre at the cable level; no detectable critical-current degradation up to 600 megapascals of transverse compression on the cable unit cell; cable-to-cable joint resistances near 15 nano-ohms at 20 kelvin; end-to-end magnet manufacture producing critical currents within 7 percent of prediction; and 📝distributed fiber-optic sensing fast and accurate enough to detect a quench without voltage taps. The byline runs to 64 names and closes with 📝Brandon Sorbom and 📝Dan Brunner; it includes 📝Theodore Golfinopoulos, 📝Philip C. Michael and 📝Rui Vieira, the MIT magnet engineers behind 📝The TFMC Engineering Papers.
VIPER got us to 20 📝tesla on the full-scale Toroidal Field Model Coil. PIT VIPER is designed to let a central solenoid ramp at that field without cooking itself, and we measured every one of those numbers on real cable rather than modeling them.