Simulation of a quench event in the upgraded High-Luminosity LHC Main dipole circuit including the 11 T Nb$_{3}$Sn dipole magnets

To achieve the goal of increased luminosity, two out of eight main dipole circuits of the accelerator will be reconfigured in the coming LHC upgrade by replacing one standard 14.3-m long, Nb-Ti-based, 8.3 T dipole magnet by two 5.3-m long, Nb$_{3}$Sn-based, 11.2 T magnets (MBH). The modified dipole circuits will contain 153 Nb-Ti magnets and two MBH magnets. The latter will be connected to an additional trim power converter to compensate for the differences in the magnetic transfer functions. These modifications imply a number of challenges from the point of view of the circuit integrity, operation, and quench protection. In order to assess the circuit performance under different scenarios and to validate the circuit quench protection strategy, reliable and accurate numerical transient simulations have to be performed. We present the field/circuit coupling simulation of the reconfigured main dipole magnet chain following the introduction of the MBH magnets. 2-D distributed LEDET models of the MBH's have been created to simulate the electrothermal transient occurring during a quench event, whereas the full electrical circuit of the main dipole chain, containing the 11 T magnets and their trim circuit, is simulated in PSpice. These two models are coupled through the STEAM cosimulation framework, calculating the electromagnetic and thermal transients in the magnets and circuit. The field/circuit coupling simulations performed with STEAM evaluate how the complex circuit affects the quenching magnet and vice versa. The results show a safe fast power abort of the system in the event of a quench in one of the MBH magnets, and support the validation of the correct functioning of the reconfigured main dipole circuit.