CORE Metadata, citation and similar papers at core.ac.uk Provided by CERN Document Server EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN LIBRARIES, GENEVA ‘: ||l||\ll|lllll|Ull\I\ Nllllllllllllllllllllll CERN—AT-94-43 CERN AT/94-43 (MA) / LHC Note 298 .5%. ii {C13 Design Status of Superconducting Magnet for the LHC LHC Magnet Team, presented by N. Siegel Abslgact The LHC is a superconducting accelerator-collider to be installed in the LEP tunnel at CERN for high energy collisions in the multi~TeV range of p-p, heavy ions and e-p particle beams. The collider consists mainly of a ring of twin-aperture high field superconducting magnets operating in superfluid helium at 1.9 K. The layout of the machine and of the magnets will be described, which comprises 1250 dipoles of 14.2 m magnetic length and 400 quadrupoles of 3 m magnetic length. To reach the nominal 7 TeV proton beam energy, the main dipoles will operate at a field of 8.36 T and the main quadrupoles at a gradient of 210 T/ m. In total, more than 10000 superconducting magnets, including the regular arcs, the dispersion suppressors and the straight sections, must be built. The general design of these cryomagnets is described. Also the model and prototype work, together with the results achieved so far are presented. Among the short dipole models, one assembled at CERN with industrially made coils reached an ultimate field of 10.5 T and of the 10 m long industry made dipoles, the first reached the present nominal field without training quenches, showing that accelerator operation at that field is at hand. 14th Conference on Charged Particle Accelerators, Institute for High Energy Physics (HEP), Protvino, Russia, 25-27 October 1994 Geneva, Switzerland 2 February, 1995 OCR Output DESIGN STATUS OF SUPERCONDUCTING MAGNETS FOR THE LHC LHC Magnet Team, presented by N. Siegel CERN, European Organization for Nuclear Research, CH-1211 Geneva 23 Abstract The LHC is a superconducting accelerator-collider to be installed in the LEP tunnel at CERN for high energy collisions in the multi-TeV range of p-p, heavy ions and e-p particle beams. The collider consists mainly of a ring of twin-aperture high field superconducting magnets operating in superfluid helium at 1.9 K. The layout of the machine and of the magnets will be described, which comprises 1250 dipoles of 14.2 m magnetic length and 400 quadrupoles of 3 m magnetic length. To reach the nominal 7 TeV proton beam energy, the main dipoles will operate at a field of 8.36 T and the main quadrupoles at a gradient of 210 T/m. In total, more than 10000 superconducting magnets, including the regular arcs, the dispersion suppressors and the straight sections, must be built. The general design of these cryomagnets is described. Also the model and prototype work, together with the results achieved so far are presented Among the short dipole models, one assembled at CERN with industrially made coils reached an ultimate field of 10.5 T and of the 10 m long industry made dipoles, the first reached the present nominal field without training quenches, showing that accelerator operation at that field is at hand. 1. INTRODUCTION The CERN Large Hadron Collider essentially consists of a ring of high field superconducting magnets installed in the 27 km of the LEP timnel at CERN. The general design of this machine has been reported in several conference papers [1], [2], and a base-line design report was published in November 1993 [3]. The main parameters of the LHC for p-p collisions are given in Table I. TABLE1 MAIN PA1zAM1;r1zRs o1=rr—m LHC rox PRo·roN-PRoroN OPERATION Centre-of-mass collision energy (T eV) 14.0 Dipole field 8.36 Lurninosity (cm‘2s‘1) 1034 Injection energy (T eV) 0.45 Circulating current/beam (A) 0.53 Particles per beam 4.7 x 1014 Stored beam ener 332 An important asset of the LHC is that the existing accelerator infrastructure of CERN will provide the injection beams with the required characteristics with only a few additions to the present installations. Since the injector chain is composed of fast cycling classical accelerators, the LHC can be filled in a relatively short time of about 7 min, reducing the time at injection level, where the beams are more sensitive to perturbations like those coming from persistent currents. The layout of the LHC consists, as for LEP, of eight arcs separated by so·ca1led long straight sections. The two counter rotating beams circulate in two separate, horizontally spaced, magnetic channels. To achieve compact high field magnets, compatible with the cross-sectional dimensions of the existing LEP tunnel, they are designed of the so-called "two-in-one" structure, incorporating the two beam channels in the same yoke and cryostat. Such a configuration, first studied at Brookhaven National Laboratory for fields up to 5 T at 4.2 K, results in smaller cross-sectional dimensions and more economic solution. [4]. A perspective view of the "two-in·one" dipole is shown in Fig. 1. The LHC magnets use N'bTi superconductors operating in a static bath of superfluid helium at 1.9 K pressurized at 1 bar [5]. The benefits of the superfluid helium are its very large heat conductivity and ability to penetrate through insulation porosities, thus permeating and cooling the conductor. By this mechanism heat dissipated in the conductor due mainly to beam losses and also to ramping and resistive losses is to be conducted away to the cold source within a limited temperature margin of the cable, which is 1.2 K at 8.65 T for the inner layer. Experiments studying heat transport of different types of insulated cables cooled by superfluid helium have been carried out at CEN, Saclay, (F), in view of optimizing the insulation parameters [6]. On the other hand, at 1.9 K, the thermal capacity of materials and of the cables are reduced by about an order of magnitude with respect to the ones at 4.2 K, inducing higher and faster temperature rises for a given heat deposition. The magnets become thus more sensitive to quasi-adiabatic heat development and propagation in the conductors caused by sudden motions. Considering further the high forces and the high stored electromagnetic energy, proportional to B2, underline the great care required in the construction of the force-retaining structure to prevent premature quenches. 2. LHC LAYOUT AND LATTICE The two interlaced LHC rings follow very closely the LEP geometry, in particular both machines must have the same revolution time to allow to convert them later into an e-p collider. The LHC, like LEP, is made of 16 half-octants, each of them 1.7 km long and made up of a long arc with a mean radius of 3.5 km, followed by the dispersion suppressor and a long straight section. The octant spans from mid-arc to mid-arc with services feeding it from the pit at the centre of the long straight section. The option to feed the LHC from the four even access points is being studied now in detail, due to its important cost savmg aspect. OCR Output As a result of funhcr optimization of thc machine from the point of vicw of beam stability, operational reliability, maximum dipole occupancy in the arcs and cost, the regular lattice is now based on 23 cells per half octant with the powering of the main quadrupoles separate from that of the dipoles, thus enabling to suppress the timing quadrupoles. The schematic layout of the new regular half-cell is shown in Fig. 2 and includes three long dipoles and one short suaight section about 6 m long. The dipole length is stretched to 14.2 m and the nominal Held is 8.36 T for a 7 TeV proton beam. The short straight section includes the 3 m long main quadrupole working at a gradient of 210 T/m for 90° phase advance, two corrector magnets one being either a skew quadrupole or an octupole, the other a combined sextupole/dipole, a beam monitor and the cryogenic service module. Attached to each main dipole are one small sextupole and one small decapole corrector to compensate in situ the tield errors introduced by the main magnets. The effect of these Held errors on the dynamic aperture has been reduced by enlarging the inner coil diameter from the previous 50 mm to 56 mm. 53.239 E ze 14.20 14.20 14.20 S WEE MB MB MB Dipole magnet MQ: Lattice quadmpoles MQSC: Skew quadrupole MQC: Landau octupole MSB: Combined sextupole and dipole corrector BPM: Beam Position Monitor - 0 —: Local Sextupole or Decapole Corrector Fig 1. Perspective View of the ··tWO_in_Onc·· dipole Fig. 2: Schematic layout of the LHC half-cell with 23 periods per octant 3. THE CRYOMAGNETS The LHC magnets represent a total of about 1400 tons of conductor of which 400 tons of high homogeneity NbTi alloy. The total mass to be kept at 1.8-1.9 K is 30000 tons covering about 24 km of the circumference of LEP. The main features and parameters of the magnets are outlined below. 3.1 Main dipole magnets 3.1.1 Design features: the design of the dipoles has to meet the following basic requirements: - Operational field of 8.36 T. Magnetic length of 14.2 m. Coil inner diameter of 56 mm. Distance between the axes of the apertures of 180 mm. Based on existing experience and on the given set of requirements, a new design was worked out, of which the main parameters are listed in Table H and a cross-section is shown in Fig.