Characterization of the Copper Resistance in the LHC Main Dipole Bypass Diode Leads

A fundamental component of the quench protection system of the large hadron collider (LHC) superconducting dipole magnets are bypass diodes. During a quench, the high current powering the magnet coil is redirected through the parallel diode. The resistance of diode current lead contacts is essential due to the risk of overheat. There is no possibility to measure their resistances, as the superconducting magnet coil acts as a short-circuit. Those measurements are possible when the magnet is in the resistive state. The most important point is the contact surface between the magnet busbar and the diode current lead. The resistance of this contact is not possible to measure when the cryostat is closed, so an indirect method that includes the resistance of the copper parts has to be developed. This article describes the methodology of measurements and calculations and summarizes the results of the resistance measurements of copper current leads of the LHC dipole bypass diodes. The measurements have been performed in a wide temperature region, to reproduce different environmental parameters of the LHC. It was proven that the temperature of measured samples has a significant influence on obtained results and a systematic approach is essential. Precise values of the resistance parameters have been obtained and will be used in the future measurements of the quality of connection of those diodes and, in consequence, will be used in the quality assurance of the quench protection system.