The LHC Magnetic Field Model Sammut Nicholas J Bottura Luca Micallef Joseph 2005 The compensation of the field changes during the beam injection and acceleration in the LHC requires an accurate forecast and an active control of the magnetic field in the accelerator. The LHC Magnetic Field Model is the core of this magnetic prediction system. The model will provide the desired field components at a given time, magnet operating current, magnet ramp rate, magnet temperature and magnet powering history to the required precision. The model is based on the identification and physical decomposition of the effects that contribute to the total field in the magnet aperture of the LHC dipoles. Each effect is quantified using data obtained from series measurements, and modeled theoretically or empirically depending on the complexity of the physical phenomena involved. This paper presents the developments of the new finely tuned magnetic field model and evaluates its accuracy and predictive capabilities over a sector of the machine. research-article

Testing of the LHC Magnets in Cryogenic Conditions Chohan Vinod 2005 For the Large Hadron Collider under construction at CERN and the testing of its 1706 Cryo-magnets in cryogenic conditions, considerable challenges had to be overcome since 2002 to arrive at the situation of today, with semi-routine operation of the purpose built tests facility. With the setting up of an Operation Team comprising of few non-expert CERN Accelerator operation staff, and a large external collaboration, it was essential to develop the methodology of working in light of external collaboration limits and base it on CERN-known techniques and experience in accelerator running-in, commissioning and routine operation. A flavour of the operation tools that were necessary or developed will be given, i.e., web-based tests follow-up management & information systems, development of precisely defined 'to do list' of tests sequences, associated methods, procedures and strict check-lists, electronic logbooks and so forth. The presentation will briefly outline the tests operation programme and its context & constraints, give a summary of the accomplishments so far, together with the outlook for the successful completion of the whole programme within the project goals. research-article

Field Quality and Alignment of the Series Produced Superconducting Matching Quadrupoles for the LHC Insertions Catalan-Lasheras Nuria Venturini Delsolaro W Kirby Glyn Ostojic Ranko Perez Juan C Prin Herve 2005 The production of the superconducting quadrupoles for the LHC insertions is advancing well and about half of the magnets have been produced. The coil size and field measurements performed on individual magnets both in warm and cold conditions are yielding significant results. In this paper we present the procedures and results of steering the series production at the magnet manufacturers and the assembly of cold masses at CERN. In particular, we present the correlation between coil sizes and geometrical field errors, the effect of permeability of magnet collars, and the analysis of warm-cold correlations and hysteresis of the main field multipoles. The results are compared with the target values for field multipoles and quadrupole alignment. research-article

The Construction of the Low-beta Triplets for the LHC Ostojic Ranko Bossert R Venturini Delsolaro W Di Marco Joseph Feher Sandor Karppinen Mikko Kerby James Kimura Nobuhiro Lamm Michael J Nakamoto Tatsushi Nicol Thomas H Nobrega Alfred Ogitsu T Ohuchi Norihito Page Thomas M Peterson Thomas J Rabehl Roger Jon Schlabach Philip Shintomi Takakazu Strait James Sylvester C D Tartaglia M Taylor Thomas Tsuchiya Kiyosumi Velev Gueorgui Yamamoto Akira 2005 The performance of the LHC depends critically on the low-b triplets, located on either side of the four interaction points. Each triplet consists of four superconducting quadrupole magnets, which must operate reliably at up to 215 T/m, sustain high heat loads and have an excellent field quality. A collaboration between CERN, Fermilab and KEK was set up in 1996 to design and build the triplet systems, and after nine years of joint effort the production will be completed in 2005. We retrace the main events of the project and present the performance of the low-b quadrupoles built by KEK and Fermilab and of other elements of the triplet. The assembly of the first triplet at CERN and plans for tunnel installation and commissioning in the LHC are also reported. research-article

Low-beta Quadrupole Designs for the LHC Luminosity Upgrade Ostojic Ranko Catalan-Lasheras Nuria Kirby Glyn Russenschuck Stephan 2005 Several scenarios are considered for the upgrade of the LHC insertions in view of increasing the luminosity beyond 1034 cm-2s-1. In the case of “quadrupole first” option, superconducting low-b quadrupoles with apertures in the range of 90-110 mm are required in view of increased heat loads and beam crossing angles. We present possible low-b quadrupole designs based on existing Nb$_{3}$Sn and LHC NbTi superconductors, present scaling laws for the magnet parameters and discuss relative advantages of the underlying triplet layouts. research-article

Short Straight Sections in the LHC Matching Sections (MS SSS) Parma V Prin H Lutton F 2005 The LHC insertions require 50 specific superconducting quadrupoles in the matching sections, operating either in 1.9 K superfluid helium or in boiling helium at 4.5 K. These magnets are assembled together with corrector magnets in cold masses, and are inserted in individual cryostats to form the MS Short Straight Sections (MS SSS). The variety of quadrupoles and corrector magnets leads to 10 families of cold masses, with lengths ranging from 5 to 12 m and weights ranging from 60 to 140 kN. The MS SSS need to fulfil specific requirements related to the collider topology, its cryogenic layout and the powering scheme. Most MS SSS are standalone cryogenic and super-conducting units, i.e. they are not in the continuous arc cryostat, and therefore need dedicated cryogenic and electrical feeding. Specially designed cryostat end-caps are required to close the vacuum vessels at each end, which include low heat in-leak Cold-to-Warm transitions (CWT) for the beam tubes and 6 kA local electrical feedthrough for powering the quadrupoles. This paper presents the design of the MS SSS cryostats as an extension of the arc cryostat's design [1-3], to achieve a standard and consequently cost-effective solution, and the design solutions chosen to satisfy their specific functionalities. research-article

The Assembly of the LHC Short Straight Sections (SSS) at CERN Parma Vittorio Bourcey Nicolas Dos Santos de Campos Paulo M Feitor Rogerio C Gandel Makcim López R Schmidlkofer Martin Slits Ivo 2005 The series production of the LHC SSS has started in the beginning of 2004 and is foreseen to last until end 2006. The production consists in the assembly of 474 cold masses housing superconducting quadrupoles and corrector magnets within their cryostats. 87 cold mass variants, resulting from various combinations of main quadrupole and corrector magnets, have to be assembled in 55 cryostat types, depending on the specific cryogenic and electrical powering schemes required by the collider topology. The assembly activity features the execution of more than 5 km of leak-tight welding of stainless steel and aluminium cryogenic lines, designed for 20-bar pressure, according to high qualification standards and undergoing severe QA inspections. Some 2500 leak detection tests, using He mass spectrometry, are required to check the tightness of the cryogenic circuits. Extensive electrical control work, to check the integrity of the magnet instrumentation and electrical circuits throughout the assembly of the SSS, is also carried out. This paper presents the current status of production, the assembly facilities at CERN, work organisation and Quality Assurance issues, and the acquired assembly experience after one and a half years of production. research-article

Improvement of the Geometrical Stability of the LHC cryodipoles when Blocking the Central Support Post Seyvet Fabien Beauquis Jerome Fernandez-Cano Elena D Jeanneret Jean Bernard Poncet Alain Tommasini Davide 2005 The LHC will be equipped with 1232 horizontally curved 16 meter long super-conducting dipole magnets cooled at 1.9 K, supported within their vacuum vessel by three Glass Fiber Resin Epoxy (GFRE) support posts. The two support posts at the dipole extremities were initially designed free to slide longitudinally with respect to the vacuum vessel and the central support post free to slide transversely. However the magnet shape did not retain the tight geometrical tolerances, of the order of fractions of mm, imposed by machine aperture and magnetic corrector centering requirements. Thereafter a modification to the supporting system, removing the initial transversal degree of freedom of the lower flange of the central support post with respect to the vacuum vessel, was designed and implemented. This paper describes the design of the magnet/cryostat interface with and without blockage of the central support post, analyzes the additional mechanical loads related to the modification and reviews the experimental results with respect to the requirements for beam aperture and magnetic corrector centering. research-article

Recent Progress in Power Refrigeration below 2 K for Superconducting Accelerators Claudet Serge 2005 As a result of technico-economical optimization and quest for increased performance, 2 K cryogenics is now present in large accelerator projects using superconducting magnets or acceleration cavities. Consequently, large cryogenic systems producing refrigeration capacity below 2 K in the kW range and with high efficiency over a large dynamic range are needed. After CEBAF and SNS, this is the case for the Large Hadron Collider (LHC) project at CERN for which eight 2.4 kW @ 1.8 K refrigeration units are needed to cool each a 3.3 km long sector of high-field magnets. Combining cold hydrodynamic compressors in series with warm volumetric compressors, complete pre-series units as well as sets of series cold compressors have been intensively tested and validated from two different industrial suppliers. After recalling the possible 2 K refrigeration cycles and their comparative merits, this paper describes the specific features of the LHC system and presents the achieved performance with emphasis on the progress in terms of efficiency, operational compliance, reliability and maintenance. Perspectives of application to a future International Linear Collider (ILC) based on cold RF technology are then briefly evoked. research-article

Ultrathin Polyimide-Stainless Steel Heater for Vacuum System Bake-out Rathjen Christian Blanchard Sebastien Henrist Bernard Kölemeijer Wilhelmus Libera Bruno Lutkiewicz Przemyslaw 2005 Space constraints in several normal conducting magnets of the LHC required the development of a dedicated permanent heater for vacuum chamber bake-out. The new heater consists of stainless steel bands inside layers of polyimide. The overall heater thickness is about 0.3 mm. The low magnetic permeability is suitable for applications in magnetic fields. The material combination allows for temperatures high enough to activate a NEG coating. Fabrication is performed in consecutive steps of tape wrapping. Automation makes high volume production at low costs possible. About 800 m of warm vacuum system of the long straight sections of the LHC will be equipped with the new heater. This paper covers experience gained at CERN from studies up to industrialization. research-article