REBCO Magnets

High-temperature REBCO superconductor is the enabling conductor for the very high burner fields, though the plug still exceeds feasible coil stress.

Reaching 26.49 T at the plug and 17 T at the throat in steady state is beyond the practical range of the low-temperature superconductors used in older machines. The burner relies on REBCO (rare-earth barium copper oxide) high-temperature superconductor tape, which carries high current density at high field and operates with more temperature margin than earlier conductors.

REBCO is what makes fields of this class conceivable at all. It is a coated-conductor tape, wound into pancake or layer coils, and its performance at high field is the reason the burner and the breeder (Hyperion) both specify it. But conductor capability alone does not close the plug: the structure that must react the magnetic forces is the limiting factor.

Why REBCO

• High critical current density at very high field
• Larger temperature margin than low-temperature superconductors
• Steady-state operation at the plug and throat fields
• Common conductor choice across the Kronos machines
• Compatible with high-field, compact coil geometries

The honest boundary

REBCO removes the conductor as the bottleneck but not the structure. At 26.49 T the mechanical load on the plug coil exceeds the feasible structural limit by roughly 3–3.9x as specified. Better conductor does not lower that force; only stronger or re-architected structure, a smaller bore, or a lower field can. This is why the plug-coil-stress gate is stated as a structural, not a conductor, problem.

All figures are design-and-simulation values for a machine not yet built.