Arc suppression snubbers for the energy extraction switchgear in the superconducting main circuits of the LHC Collider: Impact on the safety-critical quench protection system

A major challenge for operating a quench protection system for a chain of superconducting magnets and their interconnecting busbars is posed by the mandatory coexistence between the ultrasensitive and fast quench detectors and the high power systems, such as the power converter and the switchgear of the energy extraction (EE) facilities with their regular, occasionally violent, actions on the circuit elements. The eight, 13 kA, main dipole powering circuits of the recently inaugurated LHC Hadron Collider at CERN represents such circuits, for which a number of mitigation features has been designed and implemented in order to facilitate this coexistence. The introduction of snubber capacitor banks across the EE opening switches represents the most efficient method to enhance the commutation process by arc suppression and slow-down the fronts of the voltage waves penetrating the magnet chains, acting as transmission lines. The paper presents the measured properties and limitations of the combined switch/ capacitor-bank assemblies and describes the design and operation of the associated, short-circuit protection circuits. Furthermore, the paper details the improvements obtained to the original, analogue quench detection facilities and it describes how the application of such a scheme has helped lift some operational and performance limitations for tools related to the enhanced QPS systems, with specific emphasis on the so-called `symmetric´ quench detection tool.