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The LHC will incorporate about 7600 superconducting single aperture corrector magnets mounted in the main magnet cold masses. In order to follow up their production, we have designed and built 12 different benches for warm magnetic measurements based on rotating coils. Each bench was manufactured in two copies, one installed at the industry sites and the other kept at CERN for cross checks and monitoring of the measurement quality. These systems measure the main field, the field quality and the position and orientation of the field relative to the mechanical construction, all properties that are required for an effective use of the magnets. After calibration, the benches automatically refer the measured quantities to the mechanical interfaces used to align the correctors in the cold masses (pin holes or keys). In this paper we evaluate the global uncertainty achieved with the benches and compare the field measurements performed at room temperature in industry with measurements at 1.9 K performed at CERN on samples of each corrector type.

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moles” 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.

The Large Hadron Collider (LHC) (1995), a proton-proton superconducting accelerator, will consist of about 8400 superconducting magnet units, all operating in superfluid helium at a temperature of 1.9 K. The design of the superconducting main dipole magnets for the LHC is guided by the requirement of an extremely high field quality in the magnet aperture which is mainly defined by the layout of the superconducting coil and the position of the conductors. In order to avoid conductor movements within the magnet cross-section, the superconducting coils are held in place by surrounding stainless steel collars. In this paper, we review the dependence of field harmonics in the LHC main dipoles on dimensions of the hardware components of the collared coils. An analysis of the dimensional measurements of these components which are used in the collared coils produced so far is given. Sensitivity tables which are worked out through a coupled magneto-static model give the variation of the multipoles on collars, copper wedge dimensions and cable geometry. A Monte Carlo method is used to simulate the effects of possible errors on the multipoles.

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 analyze 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.

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.

A novel method to localize and characterize the origin of a quench in a superconducting dipole has been developed during the tests of the Large Hadron Collider (LHC) 1-m-long superconducting dipole models. It consists of an extended analysis of the voltage signals generated at the onset of a quench in pickup coils distributed along the inside of the magnet bore in conjunction with the pole voltage signals. The authors discuss the measurement method and the main results obtained during the training of these magnets, reaching a bore field of 10 T. >

The field quality measurements at room temperature of around 100 collared coils of the main LHC dipoles are analysed. Using correlations to field measurements at 1.9 K, comparison with beam dynamics limits are discussed. Both random and systematic components are analysed, allowing to pin out the most critical multipoles. Corrective actions that have been taken during the pre-series phase are presented; we focus on the low order systematic multipoles that are shown to be the most difficult components to steer. A preliminary analysis of the integrated main field and of its implications on the possible scenarios for the installation are also carried out.

More than 10% of the collared coils of the main LHC dipoles have been produced. In this paper, we compare the measured field quality to beam dynamics targets using correlations to measurements at 1.9 K. The present status of field quality is given and corrective actions carried out to center field quality on optimal values are presented. Differences among the three manufacturers are analyzed, and the main results that concern correlation between cold and warm measurements are outlined. Present trends in the production and open points are discussed.

In this paper, we review the tools used for controlling the production of the LHC main dipoles through warm magnetic measurements. For the collared coil measurements, control limits are based on the statistics relative to the pre-series production. For the cold mass, the difference between collared coil and cold mass is considered, allowing a very stringent test. In both cases, measurements are split in straight part average, variations and coil ends contributions. Two different alarm levels exist in case the measured field is out of limits. The analysis can be carried out at the manufacturer and allows detection of anomalies in the measured magnetic field. These can be either due to wrong measurements or caused by assembly defects. Techniques used to work out information on the magnet assembly from the field harmonics are outlined. We summarize the experience gathered on about 180 collared coils and 120 cold masses, pointing out the bad cases and investigating the reliability of the measurements.

The behaviour of some isolation amplifiers irradiated at the CERN PSAIF facility is described. These components were irradiated to total integrated neutron fluences varying from 1.2/spl times/10/sup 13/ n/cm/sup 2/ (E>140 keV) to 1.34/spl times/10/sup 14/ n/cm/sup 2/ (E>140 keV). The degradation of the electrical characteristics was measured versus doses. These amplifiers could be used for the superconducting magnet protection of LHC. They will be placed inside the tunnel and they will be exposed to 2.5/spl times/10/sup 13/ n/cm/sup 2/ (E>140 keV) during 10 year operation life time.

The LHC dispersion suppressors and matching sections will be equipped with individually powered superconducting quadrupoles with an aperture of 56 mm. In order to optimise the parameters and cost of the magnets and of their powering, the quadrupole has been designed on the basis of an 8.2 mm wide Rutherford-type cable for a nominal current of 5300 A, corresponding to a gradient of 200 T/m at 1.9 K. In order to validate the design two 1-m single-aperture quadrupoles and one twin-aperture quadrupole have been built and tested. In this report we describe the construction features of the magnets and present the results of the magnet tests. (4 refs).

The quench protection system for the superconducting magnets of the CERN Large Hadron Collider (LHC) is described. The system is based on the so called "cold diode" concept. In a group of series connected magnets if one magnet quenches then the magnetic energy of all the magnets will be dissipated in the quenched magnet so destroying it. This is avoided by by-passing the quenched magnet and then rapidly de-exciting the unquenched magnets. For the LHC machine it is foreseen to use silicon diodes situated inside the cryostat as by-pass elements-so called "cold diodes". The diodes are exposed to some 50 kGray of radiation during a 10 year operation life-time. The high energy density of the LHC magnets (500 KJ/m) coupled with the relatively slow propagation speed of a "natural" quench (10 to 20 m/s) can lead to excessive heating of the zone where the quench started and to high internal voltages. It is therefore necessary to detect quickly the incipient quench and fire strip heaters which spread the quench out more quickly over a large volume of the magnet. After a quench the magnet chain must be de-excited rapidly to avoid spreading the quench to other magnets and over-heating the by-pass diode. This is done by switching high-power energy-dump resistors in series with the magnets. The LHC main ring magnet will be divided into 16 electrically separated units which has important advantages. >

An unexpected magnetisation of the thin nickel layer of the LEP dipole vacuum chamber has been identified as the main cause of the large horizontal to vertical optical coupling found during the LEP commissioning. Even though the betatron coupling could be much weakened by changing the difference between the tunes from 8 to 6, it was decided, after some tests, to suppress the source itself by demagnetizing the nickel layer of every chamber. An "in situ" method avoiding a removal of the chambers has been developed. The coupling has been reduced by more than a factor 5. The demagnetization suppresses a constraint on the betatron tunes and weakens the horizontal betatron spin resonances. >

The series production of a total of 814 quadrupole magnets of two types for the Large Electron Positron accelerator is approaching its end as is the production of 510 sextupole magnets, also of two types. After a review of the design of these lenses, the experience gained during their manufacture is discussed. The results of systematic measurements of their excitation characteristics and field quality are linked to the quality of the low-carbon steel sheet used for their magnetic circuits and to that of the geometry achieved in the assembly of the magnets. >