Status of the LHCb magnet system

The LHCb experiment focuses on the precision measurement of CP violation and rare decays in the B-meson system. It plans to operate with an average luminosity of $2\times 10^{32}$~cm$^{-2}$s$~^{-1}$, which should be obtained from the beginning of the LHC operation. The LHCb detector exploits the forward region of the pp collisions at the LHC collider. It requires a single-arm spectrometer for the separation and momentum measurement of the charged particles with a large dipole magnet of a free aperture of $\pm 300$~mrad horizontally and $\pm 250$~mrad vertically. The magnet is designed for a total integrated field of 4~Tm. The pole gap is 2.2 to 3.5~m vertically (the direction of the field) and 2.6 to 4.2~m horizontally. The overall length of the magnet (in beam direction) is 5~m and its total weight about 1500~t. The power dissipation in the aluminium coils will be 4.2~MW. The magnet yoke is constructed from low carbon steel plates of 100~mm thickness. The maximum weight of one plate does not exceed 25~t. The coils are wound from large hollow aluminium conductor of $50~{\rm mm}\times 50~{\rm mm}$ cross-section with a central cooling channel of 25~mm diameter for the pressurized demineralized water. Each of the two coils is composed of 15~monolayer pancakes of 15~turns per pancake. To reach good field quality the coils are bent by 45$^\circ$ towards the gap along the horizontal aperture of $\pm 300$~mrad and the pole pieces have large shims. The underlying magnet design, its present status and milestones will be reviewed.