Multiphysics modelling of the LHC main quadrupole superconducting circuit

Superconducting magnets that bend and focus the particle beams are one of the key parts of a particle accelerator. In this thesis the LHC Main Quadrupole (MQ) magnet-circuit is the point of investigation. Simulation of the complex electrical, magnetic, and thermal transients occurring in the magnet is critical for analyzing the magnet behaviour and assessing the impact of failure cases. Within this study this complex system was modelled using the STEAM [1] (Simulation of Transient Effects in Accelerator Magnets) framework, which was developed in the Performance Evaluation (PE) section at CERN. The main goal of this thesis is the development, validation, and characterization of the model of the LHC main quadrupole magnet and its circuit. Both models were independently tested and validated against measurement results. Furthermore, both models were coupled in a cooperative simulation (co-simulation) [2], where the circuit model and the magnet model exchange signals across physical domains to reproduce the behaviour during the quench of one of the magnets in the circuit. The simulated results from the co-simulation were validated as well. After finalizing this project, the new models became a part of the library of LHC superconducting circuit models developed with the STEAM framework. In addition, an improved diode model of the cold by-pass diode [3] used in the LHC circuits has been developed and validated against measurement results. Therefore, this thesis is mainly addressed to those responsible of simulating different transient effects in superconducting magnets and circuits and are interested in coupling magnet and circuit models within a co-simulation