The regular lattice of the large Hadron collider (LHC) will make use of more than 1600 main magnets and about 7600 corrector magnets, all superconducting and working in pressurized superfluid helium bath. This complex magnet system will fill more than 20 km of the LHC underground tunnel. In this paper an overview of the cold test program and quality assurance plan to qualify all LHC superconducting magnets will be presented. The quench training performance of more than 1100 LHC main dipoles and about 300 main quadrupoles, cold tested to date, will be reviewed. From these results an estimate of the number of quenches that will be required to start operation of the whole machine at nominal energy will be discussed. The energy level at which the machine could be operated at the early phase of the commissioning without being disturbed by training quenches will be addressed. The LHC magnet program required the development of many new tools and techniques for the testing of superconducting magnet coils, magnet protection systems, cryogenics, and instrumentation. This paper will also present a summary of this development work and the results achieved.

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Review of Quench Performance of LHC Main Superconducting Magnets

During the hardware commissioning in 2008 more than 30 training quenches were performed in the main dipole circuits in sectors 4-5, 5-6, and 7-8. An overview of these quenches will be given, and the quench levels will be compared to the training observed in SM-18. Quench propagation to adjacent dipoles will be discussed, and an estimate will be given of the total number of training quenches required to reach 6, 6.5, and 7 TeV in all eight sectors. INTRODUCTION During the hardware commissioning in 2008 more than 30 training quenches were performed in the main dipole circuits in sectors 4-5, 5-6, and 7-8. Each sector contains 154 dipoles (MB) assembled by three different companies, Alstom (ALS), Ansaldo (ANS), and Noell (NOE), see Table 1. Note that the numbers for sector 3-4 denote the original distribution which will alter due to the repair work after the incident. Table 1: Distribution of the dipole magnets per sector for each of the three cold mass assemblers

http://cds.cern.ch/record/1172379/files/AV_1_01.pdf

Training the 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.

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

In superconducting magnets for particle accelerators the mechanical accuracy along the length of the Cold Mass is one of the crucial parameters to guarantee the field quality needed by beam dynamics. This issue is made even more challenging in the twin-aperture LHC superconducting dipole where tolerances in the 0.3-1 mm range shall be obtained over a length of 15 m, for a Cold Mass of about 30 t which, to minimize thermal losses, is supported in three points only. To reach this goal a number of geometrical checks and analyses are carried out at all stages of magnet assembly, handling, installation and operation. In this paper we present the structural model of the dipole based on which the checks and the analysis are performed, the nature of the geometrical imperfections identified and the temporary or permanent shape modifications predicted

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A Simplified Structural Model for the Analysis of Shape Deformations of the LHC Superconducting Dipole Cold Mass

This note presents the final assessment of the static heat loads in the LHC arc cryostats, using different experimental methods during the first commissioning period in 2007. This assessment further develops and completes previous estimates made during the commissioning of sector 7-8 [1]. The estimate of the helium inventory, a prerequisite for the heat load calculation, is also presented. Heat loads to the cold mass are evaluated from the internal energy balance during natural as well as powered warm-ups of the helium baths in different subsector. The helium inventory is calculated from the internal energy balance during powered warm-ups and matched with previous assessments. Furthermore, heat loads to the thermal shield are estimated from the non-isothermal cooling of the supercritical helium in line E. The comparison of measured heat loads with previous estimates and with budgeted values is then presented, while their correlation with some important parameters like insulation vacuum pressure and some heat interception temperatures is proposed and discussed.

/pdf/static-heat-loads-in-the-lhc-arc-cryostats-final-assessment-2chiv792o6.pdf

Static heat loads in the lhc arc cryostats: final assessment

The main superconducting dipoles for the LHC are being stored outdoors for periods from a few weeks to several years after conditioning with dry nitrogen gas. Such a storage before installation in the 27 km circumference tunnel may affect not only the mechanical and cryogenic functionality of the cryodipoles but also their quench and field performance. A dedicated task force was established to study all aspects of long term behavior of the stored cryodipoles, with particular emphasis on electrical and vacuum integrity, quench training behavior, magnetic field quality, performance of the thermal insulation, mechanical stability of magnet shape and of the interface between cold mass and cryostat, degradation of materials and welds. In particular, one specifically selected cryodipole stored outdoors for more than one year, was re-tested at cold. In addition, various tests have been carried out on the cryodipole assembly and on the most critical subcomponents to study aspects such as the hygrothermal behavior of the supporting system and the possible oxidation of the Multi Layer Insulation reflective films. This paper summarizes the main investigations carried out and their results

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Long Term Stability of the LHC Superconducting Cryodipoles After Outdoor Storage

The LHC will be equipped with 1232 horizontally curved 16 meter long super-conducting dipole magnets cooled at 1.9K, supported within their vacuum vessel by three Glass Fiber Resin Epoxy (GFRE) support posts. The two support posts at the dipole extremities were initially designed free to slide longitudinally with respect to the vacuum vessel and the central support post free to slide transversely. However the magnet shape did not retain the tight geometrical tolerances, of the order of fractions of mm, imposed by machine aperture and magnetic corrector centering requirements. Thereafter a modification to the supporting system, removing the initial transversal degree of freedom of the lower flange of the central support post with respect to the vacuum vessel, was designed and implemented. This paper describes the design of the magnet/cryostat interface with and without blockage of the central support post, analyzes the additional mechanical loads related to the modification and reviews the experimental results with respect to the requirements for beam aperture and magnetic corrector centering.

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Improvement of the Geometrical Stability of the LHC Cryodipoles when Blocking the Central Support Post

The LHC will be composed of 1232 horizontally curved, 15 meter long, superconducting dipole magnets cooled at 1.9 K. They are supported within their vacuum vessel by three Glass Fiber Reinforced Epoxy (GFRE) support posts. Each cryodipole is individually cold tested at CERN before its installation and interconnection in the LHC 27 km-circumference tunnel. As the magnet geometry under cryogenic operation is extremely important for the LHC machine aperture, a new method has been developed at CERN in order to monitor the magnet curvature change between warm and cold states. It enabled us to conclude that there is no permanent horizontal curvature change of the LHC dipole magnet between warm and cold states, although a systematic horizontal transient deformation during cool-down was detected. This deformation generates loads in the dipole supporting system; further investigation permitted us to infer this behavior to the asymmetric thermal contraction of the rigid magnet thermal shield during cool-down. Controlling the helium flow rate in the thermal shield of the cryomagnet enabled us to reduce the maximal deformation by a factor of approximately two, thus increasing significantly the mechanical safety margin of the supporting system during the CERN cold tests

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F. Seyvet

Papers

Long Term Stability of the LHC Superconducting Cryodipoles After Outdoor Storage

Improvement of the Geometrical Stability of the LHC Cryodipoles when Blocking the Central Support Post

Stability of the Horizontal Curvature of the LHC Cryodipoles During Cold Tests