The novel Coupling-Loss-Induced-Quench (CLIQ) concept will be part of the quench protection system of the High Luminosity Large Hadron Collider (HL-LHC) Inner Triplet superconducting magnets at CERN. Several units of two distinct CLIQ prototype variants were produced to validate the CLIQ novel protection concept and define the system parameters for the required performance. Subsequently, these units were further enhanced by introducing additional redundancy, advanced monitoring systems, and improved safety features. These improvements culminated in the development of the third and final version. This paper provides insights into the evolution from prototypes to the final version to be installed in the machine, shedding light on the outcomes of comprehensive safety and electromagnetic compatibility (EMC) tests, coupled with extensive operational assessments.

The Quench Heater Discharge Power Supplies (HDS) are magnet protection devices installed in the Large Hadron Collider (LHC) that, upon detection of a magnet quench, release energy into the copper-plated stainless-steel strip heaters, inducing a resistive transition all along the superconducting coils. Such a distributed internal heating ensures an even energy dissipation across the entire volume, preventing local overheating and magnet damage. Over 6000 HDS units have been operational in the LHC tunnel since 2007. The new HDS design for protection of the High Luminosity LHC (HL-LHC) Inner Triplet magnets, to be installed in the Long Shutdown starting in 2026, calls for a more advanced design with up-to-date components resulting in a higher reliability of the HDS units. Several HDS prototypes were produced at CERN, eventually culminating in the development of the HL-LHC HDS version to be installed in the accelerator. This paper describes the design of the upgraded HDS units and the comprehensive safety and electromagnetic compatibility (EMC) tests, coupled with extensive operational tests, including irradiation tests, that have been conducted.