Simulated Versus Experimentally Observed Quench Behavior of the HL-LHC Twin Aperture Orbit Corrector Prototype

This paper discusses the simulated and experimentally observed quench behavior of the first HL-LHC Twin Aperture Orbit Corrector Prototype, also known as the MCBRDp1 magnet. This superconducting magnet features two independently powered apertures. Each aperture comprises two concentric canted-cosine-theta-type Nb-Ti/Cu coils that together generate a dipolar magnetic field over the bore. These coils are held in place by conductive aluminum-alloy formers. The circuit is protected by a combination of energy extraction and quench-back in the coils. When the coils are discharged over an energy extractor, eddy currents are generated in the formers, and the resulting heat quickly and efficiently brings the Nb-Ti/Cu strands above their current sharing temperature, provided that the resistive voltage over the energy extractor is sufficiently large. This paper compares simulations and experimental observations. It is shown that with the BBQ tool, the initial voltage development after a training quench is correctly reproduced. The ProteCCT simulation tool is shown to be consistent with experimentally observed discharges of the MCBRDp1 prototype for different bath temperatures, energy extractor types, and initial operating currents. The baseline energy extractor resistor value of 1.5 Ω and the non-linear varistor option both give worst-case hotspot temperatures below the 200 K hotspot temperature limit. At ultimate current, the resulting hotspot temperatures are 143 and 167 K, and the peak voltages-to-ground are 590 and 440 V, respectively.