Geometric and magnetic axes of the LHC dipole (original) (raw)
Related papers
Control of the Dipole Cold Mass Geometry at CERN to Optimize LHC Performance
IEEE Transactions on Applied Superconductivity, 2006
The detailed shape of the 15 m long superconducting LHC dipole cold mass is of high importance as it determines three key parameters: the beam aperture, nominally of the order of 10 beam standard deviations; the connectivity of the beam-and technical lines between magnets; the transverse position of non-linear correctors mounted on the dipole ends. An offset of the latter produces unwanted beam dynamics perturbations. The tolerances are in the order of mm over the length of the magnet. The natural flexibility of the dipole and its mechanical structure allow deformations during handling and transportation which exceed the tolerances. This paper presents the observed deformations of the geometry during handling and various operations at CERN, deformations which are interpreted thanks to a simple mechanical model. These observations have led to a strategy of dipole geometry control at CERN, based on adjustment of the position of its central support (the dipole is supported at three positions, horizontally and vertically) to recover individually or statistically their original shape as manufactured. The implementation of this strategy is discussed, with the goal of finding a compromise between conflicting requirements: quality of the dipole geometry, available resources for corrective actions and magnet installation strategy whereby the geometry tolerances depend on the final magnet position in the machine. Abstract 19 May 2006 MOA06PO10 1 Abstract-The detailed shape of the 15 m long superconducting LHC dipole cold mass is of high importance as it determines three key parameters: the beam aperture, nominally of the order of 10 beam standard deviations; the connectivity of the beam-and technical lines between magnets; the transverse position of non-linear correctors mounted on the dipole ends. An offset of the latter produces unwanted beam dynamics perturbations. The tolerances are in the order of mm over the length of the magnet. The natural flexibility of the dipole and its mechanical structure allow deformations during handling and transportation which exceed the tolerances. This paper presents the observed deformations of the geometry during handling and various operations at CERN, deformations which are interpreted thanks to a simple mechanical model. These observations have led to a strategy of dipole geometry control at CERN, based on adjustment of the position of its central support (the dipole is supported at three positions, horizontally and vertically) to recover individually or statistically their original shape as manufactured. The implementation of this strategy is discussed, with the goal of finding a compromise between conflicting requirements: quality of the dipole geometry, available resources for corrective actions and magnet installation strategy whereby the geometry tolerances depend on the final magnet position in the machine. Index Terms-dipole geometry, feed down, mechanic aperture
IEEE Transactions on Appiled Superconductivity, 2004
A full-scale and fully-instrumented working model of the LHC lattice cell has been tested at CERN between March and December 2002. Aside of the current, pressure and temperature sensors, controlled by an industrial supervision system, a novel device has been set to monitor magnet positions with respect to the surrounding cryostat. The series of operating modes to test cryogenics, current leads and quench recovery electronics offered the chance to investigate potentially harmful deformations of the superconducting structure. In this paper we present a survey of displacements and deformations experienced by the LHC cell magnets during thermal cycles, current ramps and resistive transitions. Although the system complexity prevented from complete modeling, a preliminary phenomena explanation is given.
IEEE Transactions on Appiled Superconductivity, 2002
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. Abstract 6 March 2002 1 1
The Geometry of the LHC Main Dipole
The main lines of discussion and analysis for the LHC dipole geometry are related to the shape of the cold mass at different stages of production and tests. The limitations in the stability of the cold mass shape induces constraints for the positioning of the spool pieces (feed down effects), for the flanges (interconnectivity) and the overall shape (aperture considerations). The geometry after acceptance in industry may change by the time of measurements at CERN. Tolerances that are needed by hardware and by beam physics will be reviewed.
Final prototypes, first pre-series units and steps towards series production of the LHC main dipoles
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001
The LHC, a 7 TeV proton collider presently under construction at CERN, requires 1232 superconducting dipole magnets, featuring a nominal field of 8.33 T inside a cold bore tube of 50 mm inner diameter and a magnetic length of 14.3 m. This paper summarises the results of the program of the six LHC main dipole final prototypes and presents the performance measurements of the first magnets of the 90 pre-series units currently under manufacture by industry. Results of geometric and magnetic measurements are given and discussed. Finally, the major milestones towards the dipole magnets series manufacture are given and commented.
INTRODUCTION 1 2 THE CERN-LHC PROJECT AND ITS MAGNETS 4 2.1 The Large Hadron Collider 4 2.2 Accelerator layout and experiments 7 2.3 The magnets 2.4 The main dipole 2.4.1 General description 2.4.2 The superconducting cables 2.4.3 The coils 2.4.4 The mechanical structure 2.5 Magnetic field quality 3 MECHANICAL AND MAGNETIC MODELS OF THE DIPOLES 3.1 The mechanical finite element model 3.1.1 The coils 3.1.2 The collars 3.1.3 The yoke and the cylinder 3.1.4 The contact interfaces 3.2 The magnetic model IV 4 MECHANICAL PROPERTIES MEASUREMENTS 4.1 Capacitive force transducers 4.2 Coils elasticity curve 4.3 Coils prestress at room and at cryogenic temperature 4.3.1 Check of contraction coefficient of the coils 4.3.2 Modeling the prestress loss from room to cryogenic temperature 5 RESULTS OF THE FINITE ELEMENT MODEL OF THE DIPOLE 5.1 General remarks 5.2 ANSYS output 5.3 Decomposition of displacements 5.4 Mechanical tolerances 5.4.1 General remarks on the problem 5.4.2 Methods to evaluate tolerances effects on field quality 5.4.3 Tolerances on coils 5.4.4 Tolerances on collars 5.5 Monte Carlo analysis 5.5.1 Estimate of several tolerances effects 5.5.2 Monte Carlo method 5.5.3 Application to coil length 5.5.4 Application to collar tolerances V
Performance of the first LHC pre-series superconducting dipoles
IEEE Transactions on Appiled Superconductivity, 2003
Within the LHC magnet program, a preseries production of final design, full-scale superconducting dipoles has presently started in industry and magnets are being tested at CERN. The main features of these magnets are: two-in-one structure, 56 mm aperture, six-block two layer coils wound from 15.1 mm wide graded NbTi cables, and all-polyimide insulation. This paper reviews the main test results of magnets tested to date in both supercritical and superfluid helium. The results of the quench training, conductor performance, magnet protection, sensitivity to ramp rate, and magnetic field quality are presented and discussed in terms of the design parameters and the aims of the LHC magnet program. LHC Division Abstract 12 December 2002
A method to determine the flexural rigidity of the main dipole for the large Hadron collider
IEEE Transactions on Appiled Superconductivity, 2003
The Large Hadron Collider (LHC) superconducting dipole cold mass is a cylindrical structure 15 m long, made of a shrinking cylinder which contains iron laminations and collared coils. This structure, weighing about 28 ton is horizontally bent by 5 mrad. Its shape should be preserved from the assembly phase to the operational condition at cryogenic temperature. Hence an accurate comprehension of the mechanical behavior of the cold mass is required. In particular the flexural rigidity in horizontal and vertical directions represents one of the foremost properties to be aware of. To determine the flexural rigidity, deformations of the cold mass induced by the self weight have been measured and compared with the predictions of an analytical structural model. A particular care has been taken in reducing the experimental error by an appropriate fitting procedure.
Towards series measurements of the LHC superconducting dipole magnets
Proceedings of the 1997 Particle Accelerator Conference (Cat. No.97CH36167)
Extensive power tests of the LHC dipole magnets required the development of new techniques to study the quench and training behaviour. Magnetic measurements of short and long model dipoles have allowed to understand and quantify the time dependent behaviour of the field quality during the current flat top needed during beam injection. The experience gained is employed for the design of the measuring tools presently under construction for the series measurements of the LHC dipole magnets. The economically important issue of how many magnets have to be measured in the superconducting state is addressed in view of the field quality required for the performance of the LHC.