Proposed 14 T Nb3Sn magnet designs for a future energy-frontier circular collider often call for wires with higher Jc, larger diameter and lower copper to non-copper (Cu:nonCu) ratio. As well as pushing Nb3Sn superconducting wire technology to its performance limits, these characteristics all prove challenging for magneto-thermal stability.
This study investigates the stability of Nb3Sn wires using an unconventional approach to measure the Minimum Quench Energy (MQE), employing an ultra-violet (UV) laser to initiate quenches. The use of a pulsed laser offers an advantage over traditionally used resistive heaters, depositing the energy within nanoseconds – much faster than the characteristic time of temperature diffusion in the samples tested.
Stability has been experimentally studied for a range of internal tin Nb3Sn wire designs, comparing samples differing in Cu:non-Cu ratio, layout and copper residual resistance ratio (RRR). In each case, the MQE has been determined in external applied fields in the range of 6 T – 15 T and at both 1.9 K and 4.2 K. The stability of the tested wires is benchmarked against the well-established Restacked Rod Process (RRP®) wire with 108/127 layout employed in the quadrupole (MQXF) magnets for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC project).
Additionally, a novel Hypertech wire design with high heat capacity (Cp) inserts has been tested for its MQE. These results are benchmarked against a control wire of the same design, but with copper in place of the high-Cp inserts.
