Evolution of the Conceptual FCC-hh Baseline Detector Magnet Design

As a part of the future circular collider conceptual design study for hadron-hadron physics (FCC-hh), conceptual designs of detector magnets are being developed to facilitate the measurement of particle products resulting from the 100-TeV collisions. This paper discusses the design evolution leading from a 65-GJ twin solenoid with forward dipoles design to the present baseline design that features three superconducting solenoids. The central magnet produces 4 T over a free bore of 10 m and a length of 20 m. The forward solenoids provide additional bending power to facilitate tracking of high-pseudo-rapidity particles. The combined stored energy of this system is 13.8 GJ. This design is discussed in terms of powering and quench protection, conductor composition, mechanical properties of the cold masses and vacuum vessels, stray fields, and heat loads. In addition, alternative designs are discussed, including an ultrathin superconducting solenoid concept with comparatively low stored magnet energy. Like the ATLAS central solenoid, this solenoid provides a magnetic field to the tracker, and particles have to tunnel through the solenoid before reaching the calorimeters. An iron yoke returns the flux, thus providing bending power for muon tagging and giving complete magnetic shielding.