LHCb exploits the forward region of proton collisions and requires a dipole field with a free aperture of ±300 mrad horizontally and ±250 mrad vertically.
Tracking detectors in the magnetic field have to provide momentum measurement for charged particles with a precision of about 0.4% for momenta up to 200 GeV/c. This demands an integrated field of 4 Tm for tracks originating near the primary interaction point.
A good field uniformity along the transverse co-ordinate is required by the muon trigger. The lateral aperture of the magnet is defined by the longitudinal extension of the detectors, placed upstream of the magnet. The magnet’s two coils are each 7.5 m long, 4.6 m wide and 2.5 m high.