Development, Fabrication & Test of the Round, Multi-Layer REBCO Cables of the Cold Powering Systems of the HL-LHC

The magnets of the High Luminosity Upgrade of the Large Hadron collider (HL-LHC) will be electrically connected through Cold Powering Systems incorporating superconducting, 100 kA class, power transmission lines to direct current power converters in service galleries. These transmission lines or ‘Superconducting Links’ are based on multi-circuit magnesium di-boride ($\text{MgB}_{2}$) cables in 74.5–120 m long flexible cryostats. In the LHC tunnel, the Superconducting Links are electrically connected via niobium-titanium to the HL-LHC magnets and in the service galleries through flexible, round, rare-earth-barium-copper-oxide (REBCO) cables to current leads. We have established at CERN the cabling and quality control capabilities required to produce the REBCO cables of the HL-LHC Cold Powering Systems. In Q1 2024, we have successfully completed the assembly and the electrical and cryogenic cold testing of the 1st full system transporting combined currents of 94 kA while cooled with a helium gas flow rate flow of ≤5 g/s. In this manuscript we report on the cabling of the REBCO cables, the quality control process and results as well as on the splice performance during the cold test of the Cold Powering System.