Energy shift with coupling (ESC): a new quench protection method

Abstract Quench protection of full-size, high-field accelerator magnets poses significant challenges. Maintaining the hot-spot temperature and peak voltage-to-ground within acceptable limits requires a protection system that quickly transitions most of the coil turns to the normal state. Existing magnet protection technologies, such as quench protection heaters or the coupling loss induced quench system (CLIQ), have been successfully applied. However, they both present shortcomings since they require either thin insulation between the heaters and the magnet conductor—in the case of heaters, or direct electrical connections to the magnet coil—in the case of CLIQ. A novel quench protection method, energy shift with coupling (ESC), is presented, which can achieve excellent quench protection performance without requiring any electrical connection or close physical contact with the coils to protect. ESC relies on normal-conducting auxiliary coils strongly magnetically coupled with the magnet coils to protect. Upon quench detection, capacitive units connected across the auxiliary coils introduce a high current change in the auxiliary coils, causing a rapid shift of magnet stored energy from the magnet coils to the auxiliary coils. This has three beneficial effects: sudden reduction of ohmic loss in the normal zone of the magnet conductor, introduction of high transient losses in the magnet conductor, thus causing a quick transition to the normal state, and extraction of a part of the magnet’s stored energy to the auxiliary coils. The applicability of the ESC concept on an existing magnet design is analyzed with electro-magnetic and thermal transient simulations performed with the STEAM-LEDET program. The advantages and disadvantages of ESC are discussed and compared to other conventional quench protection methods. Simulation results show that ESC can be applied to protect full-scale magnets with reasonable requirements in terms of size and location of the auxiliary coils, and of capacitive unit parameters.