By David Carrillo (CERN), Mirko Pojer (CERN) and Daniel Wollmann (CERN)
The full series production of the Coupling-Loss Induced Quench (CLIQ) system has now been completed and delivered to CERN.
CLIQ is a novel protection technology developed at CERN for the superconducting magnets of the High-Luminosity LHC (HL‑LHC). CLIQ operates through the discharge of capacitors charged up to 600 or 1000 V, depending on the magnet type, and injecting approximately 3 kA AC current into the magnet coils. This mechanism produces inter-filament and inter-strand coupling losses that heat the conductor uniformly, ensuring a rapid and reliable quench. Each rack has a mass of about 620 kg and stores an energy of 20 kJ, combining robustness and high reliability for operation during the HL-LHC era.
The final version, CLIQ v3, integrates redundant systems, advanced monitoring electronics, and enhanced safety features. To validate its performance, an extensive qualification campaign was conducted. In addition to endurance and functional tests, a full electromagnetic compatibility (EMC) program was carried out, including radiated and conducted emissions, electrostatic discharge, surges, and fast transient bursts. Particular focus was put on immunity to spurious triggering, since an unintended discharge could perturb the circulating beam. Redundant sensors demonstrated fast and reliable detection, and no false triggers were observed during the entire campaign.
The full series production has now been completed by industry: 10 units were delivered in May 2025 and a final batch of 14 units arrived at CERN in August 2025. Factory acceptance tests were performed under CERN supervision early in 2025, and site acceptance tests are now starting. The units will be temporarily stored in the UW galleries at Points 1 and 5 before installation in the UR galleries during Long Shutdown 3 (LS3).
Figure 2. CLIQ3 units delivered (left), and acceptance tests ongoing (right) at CERN. Florence Thompson / CERN