Electromagnetic behavior and stress analysis of BT thermal shields

The ATLAS detector is one of the huge detectors used on the future LHC at CERN. Its magnet system is composed of a barrel toroid (BT) and two end-cap toroids (ECT) inserted at the ends of the BT, of an inner solenoid and of an iron shield close to the inner bore of the BT. The coil cryogenic system is designed to cool down the thermal shields by helium gas at 80 K. In the event of any variation of the magnetic flux, eddy currents are induced in these shields. This paper presents the computations of eddy currents in the shields using a variational formulation of the problem in terms of the electric vector potential and a finite element method. The worst case - fast discharge into dump diodes and resistors - is presented in the electrical behavior section. The evolution of eddy currents is computed using this method. Finally, anchor points are determined in the mechanical analysis in order to minimize the mechanical stresses on the shields.