Field quality in the ends of the Large Hadron Collider main dipole: Measurements and correlation to industrial assembly procedures

Magnetic field measurements are an important tool to monitor the LHC main dipole production. In this paper we analyse the data relative to a few tens of collared coils produced for the pre-series dipoles. Strong systematic differences between field at the magnet extremities are observed. Moreover, three different families of coil ends corresponding to the different coil manufacturers can be singled out. A 3D model of the coil ends is used to understand these differences in terms of the assembly parameters and the industrial procedures. We analyse the production trends in order to characterize the geometric parameters and the critical components for the field quality. The field components in the dipole ends are finally compared to the beam dynamics budget allowed for the whole dipole

An Estimate of Multipolar Errors in the LHC Dipoles

Magnetic measurements of 60 collared coils and of 14 cryomagnets are available for the LHC dipoles. These data are used to work out an estimate of the systematic and random components of the field harmonics, in the hypothesis of a complete mixing of the manufacturers

Impact of Coil Deformations on Field Quality in the Large Hadron Collider Main Dipole

In superconducting accelerator magnets the coils are usually pre-stressed in order to avoid conductor movements induced by electro-magnetic forces. In this paper we use a finite element mechanical model of the main LHC dipole to evaluate the coil deformations determined by the pre-stress and their impact on magnetic field quality. The model explains the origin of the offsets between the nominal multipole values and those measured at room temperature in prototype and pre-series dipole magnets. We also present an experiment carried out to analyse the impact on field quality and coil stresses of coil azimuthal spacers (pole shims). A 1 m long dipole collared coil has been re-assembled several times with pole shims of different thickness and the field components have been measured each time. Experimental data are compared to numerical computations based on the mechanical model.One finds that variations of shim thickness induce not only a change of the azimuthal coil length, but also a different pattern in coil deformations. A good agreement is found between measurements and simulations

Status Report on Field Quality in the Main LHC Dipoles

We give the present status of the field quality in the main LHC dipoles. Special emphasis is given to the collared coil data: a few tens of coils have been built, allowing a first analysis of the variability between producers, and estimates of the random part. Effects of the corrective actions implemented to fine tune the systematics components of low-order multipoles are presented. Correlations of collared coil data to the magnetic field measurements in operational conditions are discussed. Comparison to specifications imposed by beam dynamics allows to pin out the most critical requirements that will have to be met during the LHC dipole production

Performance of the Room Temperature Systems for Magnetic Field Measurements of the LHC Superconducting Magnets

The LHC will be composed of 1232 horizontally curved, 15-meter long, superconducting dipole assemblies and 474 Short Straight Sections containing various types of quadrupoles. These magnets are manufactured by several European companies and half of them are currently produced. The field quality at room temperature is strictly monitored to guide and validate the assembly at different stages of the production in the industry. Dipoles and quadrupoles are measured with two different rotating coil systems. These âﾜmolesâ travel inside the 50 mm aperture and accurately measure the field and gradient strength integrated over the length, the field direction and high order harmonics. We describe here these two systems, their performance and the experience gained through the two first years of operation

Optimization of the Even Normal Multipole Components in the Main Dipole of the Large Hadron Collider

In this paper we discuss even multipolar components of the Large Hadron Collider dipole in relation to the manufacturing features and target values required by beam dynamics. Due to the two-in-one collar geometry, systematic components are induced by the mutual influence of the two apertures and are strongly affected by the shape of the magnetic iron yoke. In order to optimize the normal quadrupole and octupole harmonics, a new design was chosen for the ferromagnetic insert between the iron yoke and the collars. Three different insert shapes were selected and installed in a full scale prototype. The measured dependence of the even multipoles on the insert shape shows a good agreement with simulations based on a magnetostatic code. A final design of the insert has been worked out and implemented in pre-series magnets. Data relative to even multipoles in pre-series magnets are presented, both at room temperature and at the operational temperature of 1.9 K. Comparison with target values required by beam dynamics is discussed

Analysis of Warm Magnetic Measurements of the First Series-Design Prototypes of the LHC Main Quadrupoles

The room temperature magnetic measurements of the first series-design prototypes of the LHC main quadrupoles are analysed. Data relative to the collared coils and to the assembled cold mass are considered. The averages of the multipoles along the magnet axis are interpreted as the systematic components. The agreement with the nominal design is verified, and possible explanations for discrepancies with regard to the multipole allowed by symmetry are worked out. The standard deviations of the multipoles along the axis are interpreted as the random components. We show that the latter can be interpreted in terms of random movements of up to 25-35 µm of the coil blocks, because of components and assembly tolerances. A good correlation between measurements made on collared coil and the assembled cold mass is found. The influence on field quality of a systematic radial misalignment of the coil conductor is also evaluated

Performance of Prototypes and Start up of Series Fabrication of the LHC Arc Quadrupoles

The construction of three prototype arc quadrupoles for the LHC machine has been concluded successfully. These magnets underwent warm and cold magnetic measurements as well as many other tests, both in CEA-Saclay's laboratory and at CERN. Their training qualifies them for use in the LHC machine and their measured field quality points to only very minor corrections. An excellent correlation is found between warm and cold magnetic measurements. The prototype quadrupole design has been fully retained for the series fabrication of the 400 magnets and their cold masses by industry. This paper describes the main tests and measurement results of all three prototypes. It further explains the logistics for the manufacturing of the series of cold masses. These cold masses contain not only the main quadrupole but also different combinations of corrector magnets. Thus, together with variants imposed by the cryogenic configuration of the machine, 40 different types of cold masses have to be fabricated by the firm, to which the contract has been adjudicated

Performance of Series-Design Prototype Main Quadrupoles for the LHC

After the successful construction of two first-generation prototypes of the main quadrupoles for the LHC, three series-design prototypes have been further manufactured at CEA-Saclay. Together with the sextupole-dipole corrector magnets and tuning quadrupoles, these twin-aperture main quadrupoles are assembled into the cold masses of the so-called short straight sections. Already during their fabrication, the collared coils and later the completed cold masses undergo warm magnetic measurements. Two of the main quadrupole cold masses have been mounted into their definitive machine cryostats and submitted to training and magnetic measurements. This paper presents the results of these cold tests by describing the quench behaviour, the transfer function in each of the apertures and the multipole components found at different levels of excitation. The field quality results, in cold conditions, will be compared to those measured at room temperatur

Measurement and Analysis of the Field Quality of LHC Prototype and Pre-series Superconducting Dipoles

We report the main results of the magnetic field measurements performed on the full-size LHC superconducting dipoles tested at CERN since summer 1998. Main field strength and field errors are summarised. We discuss in detail the contributions related to the geometry of the collared coil, the assembled cold mass, cool-down effects, magnetisation of the superconducting cable and saturation effects at high field. Dynamic effects on field harmonics, such as the field decay during injection and field errors during current ramps, are assessed statistically