Superconducting Detector Magnets Baseline Designs for Particle Physics Experiments at the Future Circular Collider

In early 2014 a design study started at CERN for a Future Circular Collider. A new tunnel with a circumference of about 100 km for the collider magnets is foreseen as well as new general-purpose particle detectors to probe electron-positron (e^-e⁺), electron-hadron (eh), and hadron-hadron (hh) collisions, housed in large underground caverns. In the last four years baseline designs for the various detector magnets were developed. For the FCC-ee detector two magnet variants were defined: a 7.6-m bore and 7.9-m-long classical 2 T solenoid with 600 MJ stored energy, surrounding the calorimeters, and also a very challenging 4-m bore, 6-m-long, some 100-mm-thick ultrathin and radiation transparent 2 T solenoid with a stored energy of some 170 MJ, that surrounds only the inner tracker of the detectors. For the FCC-eh detector, the detector solenoid is combined with forward and backward dipole magnets required to guide the electron beam in and out of the collision point. This detector requires a 3.5 T solenoid, 2.6-m free bore and 9.2-m length with about 230 MJ of stored energy. Most demanding is the FCC-hh detector with a 14 GJ stored energy magnet system comprising three series connected solenoids, requiring 4 T in the main solenoid with 10-m free bore and a length of 20 m, in line with two 3.2 T forward solenoids with 5.1-m free bore and 4-m length. A quite challenging series of detector magnets is proposed, that needs to be further engineered in the coming years. The superconductor technology though is essentially the same in all the solenoids proposed: conductors comprising Rutherford type cables made of NbTi/Cu strands, stabilized by nickel doped pure aluminum and structurally reinforced with a high yield strength aluminum alloy. The cold masses are conduction cooled through helium cooling pipes welded to their outer support cylinder. The designs of the various baseline magnets as well as their engineering are presented.