ИСТИНА

As part of the Future Circular Collider conceptual design study for hadron-hadron physics (FCC-hh), several designs of detector magnets are being developed to facilitate the measurement of particle products resulting from the 100 TeV collisions. This paper discusses three topics. Firstly, the previous FCC-hh detector magnet designs and subsequent design choices leading to the present design are discussed. In this process the evolution was toward lower complexity and more compact and cost-effective designs, at the cost of a larger stray field, a field reduction from 6 T to 4 T, and less space for the tracker and calorimeters inside the bore tube of the main solenoid. Secondly, the details of the current conceptual baseline design are discussed. This design features three superconducting magnets, in which the main solenoid produces 4 T over a free bore of 10 m and a length of about 20 m and where two forward solenoids generate additional bending power to track high-pseudo-rapidity particles. This combination of solenoids results in a net Lorentz force on each forward solenoid of about 60 MPa, toward the interaction point. The combined stored energy of the system is 13.8 GJ, the weight of the main solenoid and its vacuum vessel is 2 kt, and the combined weight of each forward solenoid is 80 t. Aluminum-stabilized Nb-Ti/Cu-based conductors carrying a nominal operating current of 30 kA are used to power both the main and the forward solenoids, optimized to resist the Lorentz forces during operation and to avoid excessive temperatures during a quench. An electrical scheme is used where the solenoids are powered by a single power supply, but such that the coils are electrically decoupled during a quench. In this scheme, three 30 kA surface-to-cavern leads are required with all the services located at the surface, about 300 m removed from the experimental cavern. Vacuum vessels are designed for the main and forward solenoids, which are sufficiently strong to carry the trackers and calorimeters in their bore tubes, even when considering gravity, seismic loads, possible misalignments, buckling, and the non-zero Lorentz forces upon the cold masses. Axial and radial tie rods are designed resulting in a total heat load (Radiation + heat conduction) of 6.8 kW upon the 50 K thermal shields and 360 W upon the cold masses. The third topic discussed in this paper is alternative conceptual detector magnet designs, with an emphasis on an “Ultra-thin solenoid” design, where the main solenoid is placed inside the calorimeters rather than around them and where the flux is returned with an iron yoke. In this design, the magnetic field is thus concentrated on the tracker and the muon chambers, so that the overall stored magnetic energy is lowered.