Abstract
Spurred by the question of the maximum allowable energy for the operation of the Large Hadron Collider (LHC), we have progressed in the understanding of the thermo-electric behavior of the 13kA superconducting bus bars interconnecting its main magnets. A deep insight of the underlying mechanisms is required to ensure the protection of the accelerator against undesired effects of resistive transitions. This is especially important in case of defective interconnections which can jeopardize the operation of the whole LHC.In this paper we present a numerical model of the interconnections between the main dipole and quadrupole magnets, validated against experimental tests of an interconnection sample with a purposely built-in defect. We consider defective interconnections featuring a lack of bonding among the superconducting cables and the copper stabilizer components, such as those that could be present in the machine. We evaluate the critical defect length limiting the maximum allowable current for powering the magnets. We determine the dependence of the critical defect length on different parameters as the heat transfer towards the cooling helium bath, the quality of manufacturing, the operating conditions and the protection system parameters, and discuss the relevant mechanisms.
Highlights
A few days after its start-up in September 2008, the particle accelerator Large Hadron Collider (LHC) at CERN experienced an incident causing considerable damages and delaying the restart of the machine by more than 1 year
In this paper we present a numerical thermo-electrical model of the LHC superconducting bus bars and interconnections, both for the Main Bending (MB) dipole and Main Quadrupole (MQ) magnets
Prior to the presentation of the parametric analyses, we report the validation of the model, which was performed by simulating experimental tests of an interconnection sample featuring a purposely built-in defect
Summary
A few days after its start-up in September 2008, the particle accelerator Large Hadron Collider (LHC) at CERN experienced an incident causing considerable damages and delaying the restart of the machine by more than 1 year. The incident was initiated by an electrical fault due to a defective interconnection (IC) between two adjacent main dipole magnets [1,2]. Large efforts were undertaken to measure the resistance of the interconnections in the machine both at warm and at cold [3]. They included a calorimetric technique and electrical measurements performed using either invasive or non-invasive diagnostics. In this paper we present a numerical thermo-electrical model of the LHC superconducting bus bars and interconnections, both for the Main Bending (MB) dipole and Main Quadrupole (MQ) magnets. The model aims at estimating the critical length of the interconnection defect. Parametric analyses are presented, in adiabatic and nonadiabatic conditions, as a function of the defect dimension, current decay time constant, RRR of the copper of the SC cable matrix and of the stabilizer, spatial distribution of the defect
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