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3 results on '"Guy Deferne"'

1. Mathematical formulation to predict the harmonics of the superconducting Large Hadron Collider magnets: III. Precycle ramp rate effects and magnet characterization

Author

Nicholas Sammut, Luca Bottura, Guy Deferne, and Walter Venturini Delsolaro

Subjects
Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798
Abstract

The Large Hadron Collider (LHC) at CERN is equipped with a feed-forward control system known as the field description for the LHC (FiDeL) which is designed to predict the magnetic field and its multipoles, hence reducing the burden on beam based feedback. FiDeL consists of a physical and empirical parametric field model based on magnetic measurements at warm and in cryogenic conditions. It is particularly critical during beam injection when the field decays and at the beginning of acceleration when the field snaps back. It is known that the decay amplitude is largely affected by the powering history of the magnet, particularly by the precycle flattop current and duration and the preinjection preparation duration. Recently, we have collected data that quantify the dependence of the decay amplitude on the precycle ramp rate. This paper presents the results of the measurements performed to investigate this effect, and the method included in FiDeL to model the precycle dependence. With this complete picture of dynamic changes, we finally discuss the effect on the data taken at nominally constant field, along the magnet loadline. We show that a correction for dynamic changes is required for adequate magnet characterization.

Published
2009
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2. High-temperature superconducting screens for magnetic field-error cancellation in accelerator magnets

Author

Jeroen van Nugteren, Mariano Pentella, Torsten Koettig, Lorenzo Bortot, Gijs de Rijk, Matthias Mentink, Carlo Petrone, Arjan Verweij, Sebastian Schöps, Juan Carlos Perez, Francois-Olivier Pincot, Stephan Russenschuck, Guy Deferne, and Glyn Kirby

Subjects
High-temperature superconductivity, Materials science, screening currents, law.invention, Error cancellation, law, High-temperature superconductors, Materials Chemistry, Electrical and Electronic Engineering, physics.acc-ph, Condensed matter physics, superconducting coils, Metals and Alloys, High temperature superconducting, Condensed Matter Physics, Accelerators and Storage Rings, Finite element method, Magnetic field, magnetic field quality, High-temperature superconductors, magnetic field quality, screening currents, persistent magnetization, superconducting magnetic screens, finite-element analysis, superconducting coils, accelerator magnets, Magnet, Ceramics and Composites, finite-element analysis, persistent magnetization, Superconducting Coils, superconducting magnetic screens, accelerator magnets
Abstract

Accelerators magnets must have minimal magnetic field imperfections to reduce particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the magnetization due to persistent currents adds an undesired field contribution, potentially degrading the magnetic field quality. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field component, such that only the undesired field components are compensated. The screens are self-regulating, and do not require any externally applied source of energy. Measurements in liquid nitrogen at 77 K show for dipole-field configurations a significant reduction of the magnetic field error up to a factor of four. The residual error is explained via numerical simulations accounting for the geometric defects in the HTS screens, achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at 4.5 K , field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets.

Published
2021

3. Upgrade of the LHC magnet interconnections thermal shielding

Author

Dimitrios Damianoglou, Alain Bastard, Max Duret, Guy Deferne, Gilles Villiger, Loren Wright, Michael Guinchard, Graeme Barlow, Maryline Charrondiere, Anna Chrul, H. Prin, Arnaud Vande Craen, Gaëlle Dib, Michal Strychalski, and Andrea Musso

Subjects
Cryostat, Engineering, Large Hadron Collider, Physics::Instrumentation and Detectors, business.industry, Nuclear engineering, Electrical engineering, Shields, Particle accelerator, Superconducting magnet, law.invention, law, Shield, Magnet, Electromagnetic shielding, business
Abstract

The about 1700 interconnections (ICs) between the Large Hadron Collider (LHC) superconducting magnets include thermal shielding at 50-75 K, providing continuity to the thermal shielding of the magnet cryostats to reduce the overall radiation heat loads to the 1.9 K helium bath of the magnets. The IC shield, made of aluminum, is conduction-cooled via a welded bridge to the thermal shield of the adjacent magnets which is actively cooled. TIG welding of these bridges made in the LHC tunnel at installation of the magnets induced a considerable risk of fire hazard due to the proximity of the multi-layer insulation of the magnet shields. A fire incident occurred in one of the machine sectors during machine installation, but fortunately with limited consequences thanks to prompt intervention of the operators. LHC is now undergoing a 2 years technical stop during which all magnet's ICs will have to be opened to consolidate the magnet electrical connections. The IC thermal shields will therefore have to be removed...

Published
2014
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