An important milestone was achieved in June 2020 with the successful test at CERN of a demonstrator - Demo 2 - of the cold powering system for the HL-LHC magnets. Demo 2 incorporates a superconducting 60-m long power transmission line, the Superconducting Link, which will later be used to connect the HL-LHC magnets in the LHC main tunnel to the power converters, delivering the current from the new HL-LHC underground caverns.

The Superconducting Link consists of a flexible cryostat housing cables made with magnesium diboride (MgB₂) superconductor, which will feed the HL-LHC Triplets and D2 magnets. The flexible cryostat, which circulates helium gas inside, has an innovative simplified design thanks to the higher operating temperature. The MgB2 conductor that forms the strands of the cables was developed by CERN with industry. The cables were developed at CERN before the production went out to industry for large-scale production. The final cable assembly, which was inserted inside the flexible cryostat at CERN, has an external diameter of about 80 mm and a total DC current capability of about 120 kA (60 kA each polarity) at 25 K. The flexible connection between the terminals of the MgB₂ cables and the current leads, which bring the current to room temperature, consists of cables of HTS (high temperature superconductor) of the REBCO type.

The test started by powering the 20 kA and the 7 kA circuits. A total current of 54 kA (27 kA each polarity) was successfully transferred in DC mode at a temperature as high as 30 K. This current represents a record of intensity for power transmission lines and for MgB₂ superconductor. Splices between superconducting cables as well as cryogenic and electrical transient conditions were successfully tested and validated, including quenches and fast ramp rates.

Demo 2 is the last development step of the cold powering systems for the HL-LHC Triplets. The successful achievement releases the series production of ten units: eight will be installed in the LHC underground areas and of the two spares, one system for the Triplets will used for powering the String of magnets at CERN in 2023. Indeed, in parallel with the Demo 2 milestone, the detailed design of the series cold powering systems has been progressing despite the Covid interruption. The distribution feedboxes DF cryostats (UK collaboration) and DFH cryostats (Uppsala collaboration) that interface to the extremities of the super conducting link in LHC tunnel and HL-LHC gallery respectively, are now entering their manufacturing phase.