The Future Circular Collider study for a hadron-hadron collider (FCC-hh) foresees a collision energy of 100 TeV, which is about seven times higher than that of the LHC. For the experiments, this means that a much higher magnetic field is needed in order to bend the trajectories of particles within the detector volume, allowing the subsequent determination the basic properties of each particle from its trajectory and its ability to traverse matter.
One of the conceptual detector magnet designs currently being developed for FCC-hh is the twin solenoid and dipole detector magnet assembly, featuring a combination of very large superconducting magnets. The combination of solenoids and dipoles in close proximity presents a major engineering challenge. In terms of its size, this system is unlike any existing detector. The stored magnetic energy of 56 GJ and the corresponding cold mass of about 4000 tonnes are over 20 times higher than in the CMS detector, the current record holder with a stored energy of 2.7 GJ and a cold mass of 220 tonnes. In addition, the system also includes vacuum vessels, a support structure, trackers, calorimeters and muon chambers, for a total weight of 30,000 tonnes.
The unique configuration would provide substantial bending power for particles travelling in all directions. Bending particles with a solenoidal magnetic field works well for particles travelling perpendicular to the beam but less well for those travelling almost parallel to the beam, as the solenoidal field is also oriented parallel to the beam and does not influence its trajectory. For this purpose, superconducting dipoles are positioned in the forward direction, in which the field orientation is perpendicular to the beam, so that even the trajectories of particles travelling in the forward direction obtain a curvature.
Moving on from the experiments to the accelerator itself, experts in the Technology department at CERN have presented a first concept for the main bending magnets of the FCC electron collider (FCC-ee). This machine requires about 65 km of such magnets, to steer the counter-rotating electron and positron beams, before they collide at collision energies of 350 GeV.
The proposed design features a twin-aperture geometry, with a common iron yoke and two busbars, operated at room temperature. The FCC-ee does not require high dipole fields, therefore superconducting technology is not needed.
The design is very compact: at the moment the cross-section fits onto an A3 sheet. The concept will be further refined to match the evolving requirements of the other FCC-ee work packages, including those on beam dynamics and vacuum.
For more information about the FCC study, please visit the dedicated website.