Design and Commissioning of the Energy Extraction Systems for the LHC Corrector Magnet Circuits

CERN is currently commissioning the world´s largest particle accelerator, the large hadron collider (LHC). The machine makes extensive use of superconducting technology for magnets, busbars and current leads. It is built in a circular tunnel of 27 km circumference, ready to receive proton beams in the summer of 2008. In case of a resistive transition (quench) in a superconducting magnet or busbar of a LHC corrector circuit, a time window of maximum 60 ms is given for the detection of the quench and the activation of the energy extraction (EE) system, after which the risk of overheating may seriously affect the integrity of the circuit. Fast and reliable extraction of the stored energy (up to 150 kJ) is needed to prevent such damage caused by local dissipation of the energy stored in the magnet chain. For reasons of redundancy the energy extraction breakers were designed with multiple and independent release systems for deviation of the magnet excitation current into energy absorbing resistors (series-inserted system). For all 600 A DC circuits of the LHC, which have external energy extraction, electro-mechanical switch gear, fast enough to eliminate the risk of thermal damage, was chosen. Opening breakers with two independent release systems were especially developed in collaboration with Russian industry. Because of the high inductance of the circuits, varying from 12 to 1200 mH, capacitors were introduced to assist the commutation process and minimize the arc, herewith reducing the opening time and increasing the lifetime of the breaker contacts.