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 "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 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 "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.
Abstract-Current installation of the Large Hadron Collider (LHC) particle accelerator at CERN has required the use of a harmonic coil magnetic measurement system to quantify the magnetic field harmonic quality of the superconducting, twin aperture LHC dipoles. Current and future needs for measuring fast changing magnetic fields necessitates the use of a rotating unit (RU) and associated electronics to drive this long shaft with increased speed and measurement bandwidth. Therefore, the Fast Magnetic Measurement Equipment (FAME) project has been launched to deliver such a system. A primary obstacle to achieving the goals of the FAME project is the possibility of amplifying mechanical vibrations due to increased speeds. This paper presents the methodology and results of an experimental investigation conducted to estimate mechanical vibrations of the long shaft within a cold-bore mounted anti-cryostat at various rotational speeds using magnetic measurements.
A self-calibrating digital instrument for flux measurements on magnets for accelerators used in basic research on subnuclear particles is proposed. The instrument acquires voltage arising from rotating coils transducers with a theoretical resolution of 10 ppt and a maximum sampling frequency of 800 kS/s. Then, samples are integrated on-line and suitably processed in order to improve time resolution and flux accuracy. This allows the limits of state-of-the-art digital fluximeters, related mainly to newgeneration rotating coils, with trigger rate of 20 kHz and coils speed of 10 rps, to be overcome. The instrument has been prototyped at Magnetic Measurement and Testing (MTM) Group of European Laboratory for Nuclear Research (CERN), under a framework of cooperation with the University of Sannio. Details on hardware and firmware conception, as well as on experimental results of the instrument principle validation, and of the preliminary metrological characterization of the prototype, are provided.
One of the main challenges of the Large Hadron Collider (LHC), the particle accelerator under construction at CERN (the European Organization for Nuclear Research) in Geneva, resides in the design and production of the superconducting dipoles used to steer the particles around a 27 km underground tunnel. These so-called cryodipoles are composed of an evacuated cryostat and a cold mass, that contains the particle tubes and the superconducting dipole magnet and is cooled by superfluid Helium at 1.9 K. The particle beam must be centred within the dipole magnetic field with a sub-millimetre accuracy, this requires in turn that the relative displacements between the cryostat and the cold mass must be monitored with accuracy.Because of the extreme environmental conditions (the displacement measurements must be made in vacuum and between two points at a temperature difference of about 300 degrees) no adequate existing monitoring system was found for this application. It was therefore decided to develop an optical sensor suitable for this application.This contribution describes the development of this novel sensor and the first measurements performed on the LHC cryodipoles. (CERN) [1]. The LHC will be installed in a 27 km long underground tunnel in the area near to Geneva and will accelerate two counter-rotating colliding proton beams, each at a 7 TeV energy. This project is aimed at studying the interactions of the basic constituents of the matter at the multi-TeV energy level; this is supposed to enlighten our knowledge on Higgs particles and on the theory of Supersymmetry. High magnetic fields are required to bend the proton beams to the desired curvature radius; they will be provided by 1232 dipole magnets, which will generate a 8.3 Tesla field. Superconducting technology makes this possible. Paper submitted to Measurement Science and TechnologyThe 1232 superconducting main dipole magnets will be distributed over eight arcs and will operate in a superfluid helium bath at 1.9 K. The cold masses of 15 m length will be made up of coils of superconducting niobium-titanium alloy cable mantained in shape and place by austenitic steel collars. These in turn are contained within a magnetic circuit consisting of low-carbon steel laminations with non-magnetic steel end-laminations. A welded austenitic stainless-steel shrinking cylinder, made up of two welded half cylinders (shells), surrounds the whole and also acts as the liquid helium vessel. A cross section of the LHC main dipole is given in figure 1.
A method based on an oscillating wire for measuring the field quality in accelerator magnets with small apertures of the order of 10 mm is proposed. The wire is positioned step-bystep on the generators of a cylindrical domain inside the magnet aperture, i.e. its end-points at the stages are moved on a circular trajectory. The amplitudes of the wire's forced oscillations are measured and related to field harmonics by a suitable analytical model. In this paper, the analytical model, the measurement procedure, and the measurement system architecture of the oscillating wire method are presented. The method is validated by comparison with the standard rotating-coil system. A case study on small-aperture, permanent-magnet quadrupoles constructed for the Linac4 injector at CERN is illustrated.
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