Vacuum Calculations for the LHC Experimental Beam Chambers Collins I Knaster J R CERN Lepeule P Rossi A Veness R J M 2001 The vacuum stability is studied for the LHC experimental beam vacuum chambers of ALICE, ATLAS, and CMS. The present baseline design includes sputtered Non-Evaporable Getter (NEG) coating over the whole chamber inner surface providing distributed pumping and an antimultipactor coating. The data are presented for the dominant gas species (H2, CH4, CO and CO2) in a baked system. It results that the distributed pumping is necessary for vacuum stability of CO. Lumped pumping with Sputter Ion Pumps (SIP) is also indispensable for the stability of CH4. The operational constraints with NEG technology are described. research-article

Design Aspects of the RF Contacts for the LHC Beam Vacuum Interconnects Calatroni Sergio Caspers Friedhelm Couturier K Hilleret Noël CERN Knaster J R CERN Lepeule P Taborelli M Veness R J M Vos L 2001 The LHC requires a very low longitudinal and transverse beam coupling impedance, in particular at low frequencies. This implies an admissible DC contact resistance of less than 0.1 m$\Omega$ for the RF contacts inside the vacuum bellows which must carry the image current (up to 50 A peak) of the beam at each vacuum chamber interconnect. Technological aspects, measurement methods and test results are presented for the contacts which will be used in the LHC. The modified mechanical design and the justifications for specific choices will be discussed research-article

The SPS as a Vacuum Test Bench for the Electron Cloud Studies with LHC Type Beams Arduini Gianluigi Jiménez J M Weiss K 2001 The SPS machine has been operating with LHC-type beams with bunch intensities up to 8x1010 protons (70% of LHC nominal intensity). This paper will give evidence of the electron cloud phenomenon as the mechanism responsible for the pressure rises in the SPS in presence of LHC type beams. The dependence of the pressure rise and of the electron current measured with dedicated pick-ups on various beam characteristics such as proton bunch intensity, number of bunches needed to start the e-cloud phenomenon and the effect of missing bunches will be presented. The evolution of the pressure rise with the integrated current ('beam scrubbing') will be discussed. The observed effect of the dipole magnetic field and of the treatment of the stainless steel vacuum chambers with N2 glow discharge on the pressure rise and on its evolution with the integrated current will be also considered. Finally, the consequences of the electron cloud build-up on the SPS vacuum system for the LHC beam nominal intensity will be described. research-article

Currents in, Forces on and Deformations/Displacements of the LHC Beam Screen Expected during a Magnet Quench Caspers Friedhelm Pugnat P Rathjen C Russenschuck Stephan Siemko A 2001 Due to the field asymmetry of the LHC dipoles, the magnetic field integral calculated from the centre of the aperture to the outside of the cold mass does not vanish. During a magnet quench this asymmetry generates an electromotive force and thus a current with a resultant lateral force on the beam screen. This induced force was observed indirectly when measuring the deformation of the beam screen cross-section during a quench using a precision displacement transducer, which will be described. The transducer (based on optical gratings) was developed specially to study the beam screen deformation in cryogenic environments and high magnetic fields. The results of the measurements are compared to calculations and to direct measurements of the induced voltage along the current path. An estimation of the forces exerted on the cold bore by the beam screen and of the actual current induced in the beam screen will be given. research-article

Performance of Prototypes and Start up of Series Fabrication of the LHC Arc Quadrupoles Billan J Peyrot M Remondino Vittorio Rifflet J M Siemko A Simon F Smirnov N Tortschanoff Theodor 2001 The construction of three prototype arc quadrupoles for the LHC machine has been concluded successfully. These magnets underwent warm and cold magnetic measurements as well as many other tests, both in CEA-Saclay's laboratory and at CERN. Their training qualifies them for use in the LHC machine and their measured field quality points to only very minor corrections. An excellent correlation is found between warm and cold magnetic measurements. The prototype quadrupole design has been fully retained for the series fabrication of the 400 magnets and their cold masses by industry. This paper describes the main tests and measurement results of all three prototypes. It further explains the logistics for the manufacturing of the series of cold masses. These cold masses contain not only the main quadrupole but also different combinations of corrector magnets. Thus, together with variants imposed by the cryogenic configuration of the machine, 40 different types of cold masses have to be fabricated by the firm, to which the contract has been adjudicated. research-article

Final Prototypes, First Pre-series Units and Steps Towards Series Production of the LHC Main Dipoles Modena M Bajko M Bottura L Buzio M Fessia P Pagano O Perini D Pugnat P Sanfilippo S Savary F Scandale Walter Siemko A Spigo G Todesco Ezio Vanenkov I Vlogaert J Wyss C 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. research-article

Geometric and Magnetic Axes of the LHC Dipole Bajko M Billan J Buzio M Deferne G Ferracin P García-Pérez J Scandale Walter Todesco Ezio 2001 The 15-m long superconducting dipoles of the Large Hadron Collider (LHC) with two-in-one design are curved by about 5 mrad to follow the beam trajectory. They are supported on three cold feet to minimise the vertical sagitta induced by their 35 tonnes weight. The cold masses contain at both ends local multipolar correctors to compensate for the detrimental effect of persistent current during injection. We discuss how we measure and control the geometrical shape of the cold mass and the alignment of the associated correctors and how we identify the magnetic axis of the field-shape harmonics with respect to the expected beam reference orbit. We present results relative to prototype dipoles obtained both at room temperature and in operational conditions at 1.9 K. research-article

Quench Heater Studies for the LHC Magnets Rodríguez-Mateos F Sonnemann F 2001 About 2000 LHC (CERN's Large Hadron Collider) superconducting magnets will be protected with quench heaters against development of excessive voltage and overheating after a resistive transition. The quench heater strips are powered by capacitor bank discharge power supplies. The strips are made of stainless steel partially plated with copper to reduce their resistance and to allow for the connection of quench heaters in series. The strips are embedded in between two polyimide foils. The initial power density and the current decay time determine the quench heater effectiveness. Since only one type of heater power supply will be available, the copper plating cycle is adapted for the various magnet types to keep the resistance of the heater circuit constant. Different quench heater designs have been tested on various prototype magnets to optimise the copper-plating cycle and the electric insulation of the heater strip. This paper summarises the experimental results and computations that allowed to finalise the heater strip layout for all LHC magnets. research-article

Energy Extraction for the LHC Superconducting Circuits Dahlerup-Petersen K Rodríguez-Mateos F Schmidt R Sonnemann F 2001 The superconducting magnets of the LHC will be powered in about 1700 electrical circuits. The energy stored in circuits, up to 1.3 GJ, can potentially cause severe damage of magnets, bus bars and current leads. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into a dump resistor installed in series with the magnet chain that is switched into the circuit by opening current breakers. Experiments and simulation studies have been performed to identify the LHC circuits that need energy extraction. The required values of the extraction resistors have been computed. The outcome of the experimental results and the simulation studies are presented and the design of the different energy extraction systems that operate at 600 A and at 13 kA is described. research-article

Status and Challenges of the LHC Construction Ostojic R 2001 The LHC is designed to provide proton beams of 7 TeV and nominal luminosity of 10**34 cm**-2s**-1. This objective is achieved at an affordable cost by pushing all major collider components to the limits of technology, by upgrading the existing CERN accelerators and infrastructure, and by involving the technical expertise, resources and dedication of accelerator laboratories world-wide. Following a decade of intensive R&D and technical validation of major collider systems, the LHC construction is now fully underway. Major industrial contracts have been awarded and are in execution for the procurement of the magnet, cryogenics and other systems. In this report, the status of the design and construction of the major LHC systems is presented. research-article

Detection of Resistive Transitions in LHC Superconducting Components Denz R Rodríguez-Mateos F 2001 The LHC has entered the construction phase. It will incorporate a large number of superconducting components like magnets, current leads and busbars. All these components require protection means in case of a transition from the superconducting to the resistive state, the so-called quench. Key elements in the protection system are electronic quench detectors, which have to be able to identify a quench in any state of the powering cycle of the accelerator. According to the different properties and characteristics of the superconducting elements and circuits, a set of quench detectors adapted to their specific tasks has been developed. research-article

The Interconnections of the LHC Cryomagnets Jacquemod A Poncet Alain Skoczen Blazej Tock J P 2001 The main components of the LHC, the next world-class facility in high-energy physics, are the twin-aperture high-field superconducting cryomagnets to be installed in the existing 26.7-km long tunnel. After installation and alignment, the cryomagnets have to be interconnected. The interconnections must ensure the continuity of several functions: vacuum enclosures, beam pipe image currents (RF contacts), cryogenic circuits, electrical power supply, and thermal insulation. In the machine, about 1700 interconnections between cryomagnets are necessary. The interconnections constitute a unique system that is nearly entirely assembled in the tunnel. For each of them, various operations must be done: TIG welding of cryogenic channels (~ 50 000 welds), induction soldering of main superconducting cables (~ 10 000 joints), ultrasonic welding of auxiliary superconducting cables (~ 20 000 welds), mechanical assembly of various elements, and installation of the multi-layer insulation (~ 200 000 m2). Defective junctions could be very difficult and expensive to detect and repair. Reproducible and reliable processes must be implemented together with a strict quality control. The interconnection activities are optimized taking into account several constraints: limited space availability, tight installation schedule, high level of quality, high reliability and economical aspects. In this paper, the functions to be fulfilled by the interconnections and the various technologies selected are presented. Quality control at different levels (component/ interconnect, subsystem, system) is also described. The interconnection assembly sequences are summarized. Finally, the validation of the interconnection procedures is presented, based in particular on the LHC prototype cell assembly (STRING2). research-article

The Commissioning of the LHC Test String 2 Bordry Frederick Bozzini D Casas-Cubillos J Cruikshank P Dahlerup-Petersen K Denz R Herzog R Puccio B Rodríguez-Mateos F Saban R I Schmidt R Serio L 2001 String 2 [1,2] is a full-size model of an LHC cell of the regular part of the arc. It is composed of six dipole magnets with their correctors, two short straight sections with their orbit and lattice corrector magnets, and a cryogenic distribution line running alongside the magnets. The commissioning of String 2 Phase 1, with one half-cell and the following quadrupole, has started in April 2001. As for String 1 [3], the facility was built to individually validate the LHC systems and to investigate their collective behaviour during normal operation (pump-down, cool-down and powering) as well as during exceptional conditions such as quenches. String 2 is a stepping stone towards the commissioning of the first sector (one eight of LHC) planned for 2004. It is expected to yield precious information on the infrastructures, the installation, the tooling and the procedures for the assembly, the testing and the commissioning of the individual systems, as well as the global commissioning of the technical systems. This paper describes the procedures followed for the commissioning and details the preparation for the first cool-down and for the powering. research-article

The Preparation of the Cryomagnets and the Assembly of the LHC Test String 2 Andujar O Bozzini D Calzas-Rodriguez C Cruikshank P Desebe O Dobers T Jacquemod A Kos N Lepeule P Maan W Missiaen D Parma Vittorio Riddone G Rodríguez-Mateos F Rohmig P Saban R I Schneider G Serio L Skoczen Blazej Tock J P Veness R J M Vuitton C 2001 The numerous complex activities required to prepare the cryomagnets for the installation in String 2 are described. These include the configuration of the mechanical interfaces, thee conditioning of the beam tubes, the installation of beam screens and the instrumentation as well as the final checks. The preparation of the cryomagnets for String 2 has been a dress rehearsal for the preparation that the cryomagnets will undergo before their installation in the tunnel. After a description of the interconnection procedures of the components for String 2, the tests carried-out to release the String for operation are described. A brief account of the lessons learnt is also given. research-article