Electrodynamic behaviour of the LHC superconducting magnet string during a discharge

A string of three dipole magnets and one quadrupole magnet, representing a half cell of the future LHC collider, has been assembled and tested at CERN. In order to avoid high temperatures in the magnets and high voltages between coils and ground in case of a quench, a reliable magnet protection system is necessary. The magnets are by-passed by protection diodes which are located in the cold mass. In case of a quench most of the stored magnetic energy is dissipated in the resistive parts of the magnets. Many natural and heater provoked quenches have been performed during the two experimental runs of the string at 1.9 K. This paper describes the electrodynamic behaviour during a fast discharge (i.e. after a quench) of the magnet string configuration. A simulation program was developed to evaluate parameters which cannot be directly measured, such as the current sharing between magnets and diodes, as well as the dissipated energy. The simulation program gives also the possibility for worst-case calculations, for example non-uniform magnet quench characteristics and protection heater delays.