CMS coil thermal shields final design

The Compact Muon Solenoid (CMS) is one of the detectors that is under construction in the framework of the Large Hadron Collider (LHC) project at CERN. The design field of the CMS magnet is 4 T in a 6 m diameter and 12.5 m long bore leading to a stored energy of 2.7 GJ. The coil cryogenic system is designed to cool the thermal shields by helium gas at 60 K and protect the cold mass at 4.5 K from the thermal radiation. The thermal shield design must take into account cryogenics, eddy currents, mechanical and realization considerations. This paper presents a detailed analysis of the eddy currents induced in the thermal shield, using a variational formulation of the problem in terms of the electric vector potential and a finite element method. The thermal and mechanical design are then described.