Energy Extraction in the CERN Large Hadron Collider: a Project Overview

In case of a resistive transition (quench), fast and reliable extraction of the magnetic energy, stored in the superconducting coils of the electromagnets of a particle collider, represents an important part of its magnet protection system. In general, the quench detectors, the quench heaters and the cold by-pass diodes across each magnet, together with the energy extraction facilities provide the required protection of the quenching superconductors against damage due to local energy dissipation. In CERN's LHC machine the energy stored in each of its eight superconducting dipole chains exceeds 1300 MJ. Following an opening of the extraction switches this energy will be absorbed in large extraction resistors located in the underground collider tunnel or adjacent galleries, during the exponential current decay. Also the sixteen, 13 kA quadrupole chains (QF, QD) and more than one hundred and fifty, 600 A circuits of the corrector magnets will be equipped with extraction systems. The extraction switch-gear is based on specially designed, mechanical high-speed DC breakers, in certain cases combined with capacitive snubber circuits for arc suppression. This paper is an overview of the complete project with emphasis on the arguments and motivation for the choice of equipment and methods. It presents the basic properties of the principal components, the operational aspects and the present state of advancement. Finally, it highlights the implications of the extraction process on other systems of the LHC collider.