Superconducting magnets for detectors of large colliders

Abstract

The magnetic systems for the LHC Detectors (ATLAS and CMS) are based on large superconducting magnets indirectly cooled by two-phase liquid helium at atmospheric pressure. The ATLAS system is composed by 3 toroids (2 end caps and 1 barrel) and one solenoid. The barrel toroid has a stored energy of 1250 MJ; the end caps toroids 200 MJ each. The CMS solenoid generates a magnetic field of 4 T in a bore of 5.9 m; the stored energy is 2850 MJ. The required magnet technology can be not considered a simple extrapolation of the ideas developed for the previous large detector solenoids CELLO, ALEPH, DELPHI, …). The basic guidelines are: 1) Indirect cooling, 2) Pure aluminium stabilized conductors, made by the co-extrusion technique, 3) Inner layer winding, 4) Full epoxy resin impregnation. In order to verify that these techniques are really suitable for magnets having 10 times stored energy, with respect to the last generation, a careful R&D activity is required. The aim is the understanding of the conductors and magnets feasibility through the studies of the engineering problems as well as the basic problems related to the use of superconducting materials. In this framework the stability against thermal disturbances and the quenching to the normal state appear to be analyzed with special attention.