Measuring system qualification for LHC arc quadrupole magnets

Currently the LHC Project at CERN has reached the construction phase. The superconducting magnets of this new accelerator work at superfluid helium temperature. The "arc quadrupoles" (360 pieces), which focus the beam have to be measured at a temperature of 1.9 Kelvin with outstanding precision: The measurement aims to reach a reproducibility of 1.5 · 10^-4 for the field integral, 2 ppm for the harmonic content of the main field and 0.15mm for the position of the axis. A specially developed scanner allows the simultaneous measurement of the field axis and quality. This thesis demonstrates that the system as it stands fulfils the high requirements with respect to the magnetic measurement and the magnetic axis and thus provides the desired unique versatile equipment. The assessment was performed based on experimental results, direct calibration and using a new simulation tool. The main defects treated are mechanical torsion and vibration of moving parts, electrical noise and power supply ripple

A Tool for Simulating Rotating Coil Magnetometers

When investigating the quality of a magnetic measurement system, one observes difficulties to identify the "trouble maker" of such a system as different effects can yield similar influences on the measurement results.We describe a tool in this paper that allows to investigate numerically the effects produced by different imperfections of components of such a system, including, but not limited to vibration and movements of the rotating coil, influence of electrical noise on the system, angular encoder imperfections. This system can simulate the deterministic and stochastic parts of those imperfections. We outline the physical models used that are generally based on experience or first principles. Comparisons to analytical results are shown. The modular structure of the general design of this tool permits to include new modules for new devices and effects

Magnets for Low Emittance Storage Rings an Overview

Low emittance machines require lattices with many magnets of short length. Furthermore, successful lattices require strong gradients with strong dipole fields. These lattices are popular today, as MAX IV has demonstrated that a diffraction limited synchrotron light source can be based on such a lattice. This paper gives an overview of the various magnets used by the various diffraction limited light sources available, under construction or designed. It compares the different magnet design and technology used and presents the magnet parameters in a consistent fashio

Magnetic Measurement of Alignment of Main LHC Dipoles and Associated Correctors

We discuss the method developed for the verification of alignment of magnetic elements contained in the LHC cryodipole cold mass during series tests at CERN. First, we outline motivations and requirements and then we focus on test strategy, equipment and procedures. Our goal is to express the magnetic field of the dipole and of its associated correctors w.r.t. the reference beam line, not accessible during cryogenic tests. To do so, we use traveling harmonic coil probes ("moles") that allow simultaneous measurement of the field and of the coil position. A laser tracker is used to relate these measurements to fiducials. In the dipole, the axis of the Quadrupole Configured Dipole (QCD) is used as an intermediate reference for the transfer. We provide details on the devices used for measurements in warm and cold conditions, some results from prototypes and pre-series dipoles and an assessment of the precision expected for the series tests

Sensitivity and Accuracy of the Systems for the Magnetic Measurements of the LHC Magnets at CERN

Beam optics of the LHC accelerator require stringent control of the field quality of the main dipole and quadrupole magnets. The field quality measurements need challenging accuracy given the small size of the aperture (50 mm) : relative strength of the magnets within 2×10-4, harmonics in the ppm range, axis determination within 0.1 mm, main field direction within 0.2 mrad. We present a detailed analysis of the accuracy and reproducibility obtained with the equipment presently available for the qualification tests of the first series magnets

Roots of Unity: Representations of Quantum Groups

Representations of Quantum Groups U_q (g_n), g_n any semi simple Lie algebra of rank n, are constructed from arbitrary representations of rank n-1 quantum groups for q a root of unity. Representations which have the maximal dimension and number of free parameters for irreducible representations arise as special cases.Comment: 23 page

A System for Series Magnetic Measurements of the LHC Main Quadrupoles

More than 400 twin aperture lattice quadrupoles are needed for the Large Hadron Collider (LHC) which is under construction at CERN. The main quadrupole is assembled with correction magnets in a common cryostat called the Short Straight Section (SSS). We plan to measure all SSS's in cold conditions with an unprecedented accuracy: integrated gradient of the field within 150 ppm, harmonics in a range of 1 to 5 ppm, magnetic axis of all elements within 0.1 mm and their field direction within 0.2 mrad. In this paper we describe the automatic measurement system that we have designed, built and calibrated. Based on the results obtained on the two first prototypes of the SSS's (SSS3 and SSS4) we show that this system meets all above requirements