Optimizing Secondary CLIQ for Protecting High-Field Accelerator Magnets

Future circular particle accelerators with collision energies significantly beyond the LHC will require magnets with higher magnetic field. Quench protection of such magnets is challenging for two main reasons. First, the high energy density and relatively high margin to quench require a high-performance quench protection system. Second, integration of the protection system in an accelerator machine foreseen to be operated for decades calls for easy-to-integrate, robust, and redundant elements. A new and promising protection method named Secondary CLIQ (S-CLIQ) has recently been proposed. It relies on auxiliary normal-conducting coils that are electrically insulated from the coils to protect but are magnetically coupled to them. Upon magnet quench detection, the coupled coils have dual functionality: first, they introduce high coupling loss in the superconductor, which is sufficient to transfer most of the windings to the normal state in a few milliseconds; second, they extract part of the magnet's stored energy by magnetic coupling. In this work, a S-CLIQ system based on auxiliary coils placed on the top and bottom of a racetrack magnet and made of a thin 1 mm
$^{2}$
wire is presented. It is shown that the quench protection performance in terms of hot-spot temperature and peak voltage to ground are superior to alternative methods such as energy extraction, quench heaters, and CLIQ.