M. Modena

LEP3: A High Luminosity

A strong candidate for the Standard Model Scalar boson, H(126), has been discovered by the Large Hadron Collider (LHC) experiments. In order to study this fundamental particle with unprecedented precision, and to perform precision tests of the closure of the Standard Model, we investigate the possibilities offered by An e+e- storage ring collider. We use a design inspired by the B-factories, taking into account the performance achieved at LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34 cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km circumference. The achievable luminosity increases with the bending radius, and for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision points appears feasible. Beamstrahlung becomes relevant at these high luminosities, leading to a design requirement of large momentum acceptance both in the accelerating system and in the optics. The larger machine could reach the top quark threshold, would yield luminosities per interaction point of 10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W pair production threshold (80 GeV per beam). The energy spread is reduced in the larger ring with respect to what is was at LEP, giving confidence that beam polarization for energy calibration purposes should be available up to the W pair threshold. The capabilities in term of physics performance are outlined.

e^+e^-

The LHC ring will contain 1232 main dipole and 382 main quadrupole double aperture magnets. All main magnets are superconducting and employ Nb-Ti/Cu Rutherford type cables operated at 1.9 K. The dipole production has reached the equivalent of almost three octants of cold masses and nearly four octants of collared coils. The quadrupole production has reached 75 cold masses and over 150 bare magnets. The ramping up of large scale magnet production has posed several challenges which will be discussed, like: the coil size uniformity, coil pre-stress control, cold mass welding technique and the geometrical shape issues. The magnetic measurement results at warm will be presented together with their usage for the quality control in the production. The common features and differences of the three dipole producers will be discussed. The latest version of the production schedule will be presented.

Collider to Study the Higgs Boson

Within the LHC cryo-dipole program, six full-scale superconducting prototypes of final design were built in collaboration between Industry and CERN, followed by launching the manufacture of pre-series magnets. Five prototypes and the first of the pre-series magnets were tested at CERN. This paper reviews the main features and the performance of the cryo-dipoles tested at 4.2 K and 1.8 K. The results of the quench training, conductor performance, magnet protection, sensitivity to ramp rate and field characteristics are presented and discussed in terms of the design parameters.

Status report on the LHC main magnet production

The LHC, a 7 TeV proton collider presently under construction at CERN, requires 1232, superconducting dipole magnets, featuring a nominal field of 8.33 T inside a cold bore tube of 50 mm inner diameter and a magnetic length of 14.3 in. This paper summarises the results of the program of the six LHC main dipole final prototypes and presents the performance measurements of the first magnets of the 90 pre-series units currently under manufacture by industry. Results of geometric and magnetic measurements are given and discussed. Finally, the major milestones towards the dipole magnets series manufacture are given and commented.

Performance of the LHC final prototype and first pre-series superconducting dipole magnets

A tunable hybrid quadrupole magnet design has been proposed for the final focus in the Compact Linear Collider (CLIC) that is currently under study. The proposed design is a combination of an iron dominated electromagnetic quadrupole with a bore diameter of 8.25 mm with permanent magnet blocks placed between the poles made of soft magnetic CoFe alloy “Permendur”. The possibility of using Sm₂Co₁₇ and Nd₂Fe₁₄B as material for the permanent magnet blocks has been investigated. It is shown that a very high field gradient of 530 T/m (Sm₂Co₁₇)and 590 T/m (Nd₂Fe₁₄B)can be achieved.

Final prototypes, first pre-series units and steps towards series production of the LHC main dipoles

The series production of the LHC main dipole magnets was completed in November 2006. This paper presents the organization implemented at CERN and the milestones fixed to fulfill the technical requirements and to respect the master schedule of the machine installation. The CERN organization for the production follow-up, the quality assurance and the magnet testing, as well as the organization of the three main contractors will be described. A description of the design work and procurement of most of the specific heavy tooling and key components will be given with emphasis on the advantages and drawbacks.

Design and Manufacture of a Hybrid Final Focus Quadrupole Model for CLIC

In 2015, the 1232 Nb-Ti dipole magnets in the Large Hadron Collider (LHC) have been commissioned to 7.8 T operational field, with 172 quenches. More than 80% of these quenches occurred in the magnets of one of the three cold mass assemblers (3000 series), confirming what was already observed in 2008. In this paper, the recent analysis carried out on the quench performance of the Large Hadron Collider dipole magnets is reported, including the individual reception tests and the 2008 and 2015 commissioning campaigns, to better understand the above-mentioned anomaly and give an outlook for future operation and possible increase of the operational field. The lower part of the quench probability spectrum is compatible with Gaussian distributions; therefore, the training curve can be fit through error functions. An essential ingredient in this analysis is the estimate of the error to be associated with the training data due to sampling of rare events, allowing to test different hypothesis. Using this approach, an estimate of the number of quenches required to reach 8.3 T (corresponding to the 7 TeV nominal energy) is given, and we propose to have two LHC sectors trained toward this target before the next warm up of the LHC.

Description of the Main Features of the Series Production of the LHC Main Dipole Magnets

The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.

submitter : Training Behavior of the Main Dipoles in the Large Hadron Collider

Two novel designs have been generated for permanent magnet-based quadrupoles for the Compact Linear Collider (CLIC) drive beam. The advantages of reduced heat load in the accelerator tunnel and very low operating costs over conventional electromagnets are significant to the project, hence the motivation for developing these designs. The drive beam lattice requirements can be met using two magnet designs. The higher strength design, which reaches over 60 T/m, has been successfully prototyped, and this paper will report on the measured mechanical and magnetic performance of this magnet. The lower strength design (over 43 T/m) is complete, and a prototype magnet is now being assembled at Daresbury Laboratory. The design of this magnet will be described in detail in the paper.

Retraining of the 1232 Main Dipole Magnets in the LHC

The LHC accelerator, at present under construction at CERN, Geneva, will make use of 1232 superconducting dipole magnets. The coils are wound with Rutherford type cable based on copper stabilized NbTi superconductors. The LHC machine will be operated at 1.9 K in superfluid helium. The unprecedented mass production of the superconducting dipole magnets, which involves three main contractors in Europe, is running steadily according to plan. This paper reports the outstanding technical issues encountered throughout the execution of the main manufacturing steps, which are the coil winding, curing and clamping in the collar structure, the 15-m long computer-controlled welding, the high-precision positioning operations for the cold mass finishing and the helium leak testing. The achieved production rates are discussed as well as the CERN plan for the completion of these important contracts