Design Enhancements of the MBRD Magnet for the High Luminosity LHC: The Ongoing Status of the Series Production

The upcoming enhancement for the Large Hadron Collider (LHC), known as the High-Luminosity LHC, is designed to increase the collision rate of the accelerator by a factor of ten. This ambitious objective entails the replacement of the dipole and quadrupole magnets situated before and after the interaction region of the ATLAS and CMS experiments. Among these, the separation-recombination dipole MBRD (Main Bending Recombination Dipole, also known as D2) stands out, featuring a target integral magnetic field of 35 Tm within a double aperture of 105 mm. Following the successful testing of the full-length prototype MBRDP in 2022–23, the first magnet in the series, MBRD1, has been finalized, delivered to CERN in October 2023. During the acceptance tests at CERN, a damage in one quench heater wire was found and the magnet was sent back to ASG Superconductors for repairing in July 2024. The foreseen delivery date of the fixed MBRD1 is at the end of October 2024. The MBRD2 has been built in ASG, delivered to CERN in April 2024 and accepted in June after all the compliance tests. This magnet is now under integration in the cold mass with the multipole correctors and will be cold tested in January 2025. While the other four magnets of the series production are being built in industry and the end of the construction phase is expected in January 2026. Due to significant cross-talk between the two apertures and the high sensitivity of the field to the as-built size of the coils, a revised cross-section for the series magnets has been devised compared to the prototype. For each coil, a dedicated and optimized insulation scheme has been identified to achieve the most favorable and consistently reproducible field harmonics, guided by measurements performed on the prototype at cold and on the series at room temperature (RT). This contribution provides an update on the construction progress at ASG Superconductors, details the enhancements made to the coil cross-section to meet the stringent requirements for field quality in this dipole, and discusses the current status of testing for MBRD2 at CERN.