Overview of the LHC Magnets other than the Main Dipoles. oai:cds.cern.ch:466524

Abstract The Large Hadron Collider, due for commissioning in 2005, features a large and complex magnet system that includes about 3000 double aperture magnets and 5000 single aperture ones. Most of these magnets are superconducting, using conductors made of NbTi alloy, with a coil bore of 56 mm and operating in a static bath of superfluid helium at 1.9 K, fully exploiting the conductor limit at these low temperatures. Only a few particular magnets will operate at 4.5 K. For special applications in the long straight sections and for beam injection and extraction, highly specialised room temperature magnets are used. The paper discusses the underlying concepts, which lead to the design and layout of the interaction region magnets, required to obtain the very demanding beam parameters at the four main LHC experiments. The focus will then be on the magnetic elements of matching regions, dispersion suppressors and main arcs, with a discussion of the functionality of the different magnet families. The report will be concluded with a summary giving the present status of the design, procurement and testing of these magnets. LHC PARAMETERS AND LAYOUT The main performance parameters of the LHC are shown in EXPERIMENTAL INSERTIONS Detector magnets Large magnet systems are presently being built by the four main LHC experiments to be used for particle identification and momentum measurements ATLAS and CMS, the two general purpose p-p detectors use specially developed NbTi superconductors. The ATLAS magnet system is huge: 26 m long and 20 m in outer diameter. It comprises a central solenoid (5.3 m long and 2 T design field), a barrel toroid composed of eight coils symmetrically placed around the beam axis and two end-cap toroids placed at each end inside the barrel toroid. CMS features a large solenoid (12.5 m long with a design field of 4 T). The effect of these magnets on the LHC beams is relatively small but need correction. Toroids have no field along the beam axis. Solenoids however will produce coupling of the horizontal and vertical betatron motions, and distort the orbits due to the crossing angle of the beams at the interaction point (IP). Skew quadrupoles and dipole correctors are foreseen to cope with both effects respectively. ALICE and LHCb use room temperature magnets. ALICE incorporates the solenoid magnet presently being used by the L3 experiment at LEP and will run it at a field of 0.2 T. Both experiments feature a spectrometer arm each provided with a specifically developed dipole magnet of window frame design and which is traversed by the LHC beams. A local orbit compensation scheme is therefore needed in both cases. The inner triplets The strong focussing at the four collision points is obtained by the low-β quadrupoles of the inner triplets placed symmetrically at a distance of 23 m on each side of the I