The short straight sections for the LHC Tortschanoff Theodor Parma Vittorio Rohmig P Peyrot M Rifflet J M Védrine P Vincent D 1998 During more than five years a close collaboration between CERN and CEA-Saclay led to the development and construction of two prototype quadrupole magnets and the integration of one of them into the short straight section of the LHC half-cell test string at CERN. In the frame of the special host country contribution to the LHC project this collaboration has been extended to the CNRS laboratory in Orsay and covers besides the quadrupole magnets the complete cold mass assembly (CEA) and the integration into the short straight section cryostat (CNRS). The short straight sections include not only the main lattice quadrupoles with their protection diodes, they also house different corrector magnets and the beam position monitors. Further, they provide the cryogenic feed units for a half-cell with all the magnet interconnections and the jumper connection to the separate cryo-line. The paper will show the general lay-out of these complex units and elaborate the different aspects of their assembly. research-article

State of the LHC Main Magnets Perin R 1998 The main features of the dipole magnet design have been frozen in 1996 and important steps for the preparation of their series production are being taken in the current year. To finilize the technical specifications of the superconducting cables and other components, a number of detail variants are being validated with the construction and test of short and long magnets. Thus, beside a number of 1 m long models, four 10 m long models of the main dipoles and two 14.2 m prototypes are being assembled in industry and at CERN. The fabrication of a further set of 3 full length dipoles is also starting in industry to verify the reproducibility of production performance. The lifetime and fatigue test of the String Test Facility, consisting of three dipoles and one quadrupole and simulating the basic periodic cell of the LHC, has been successfully concluded. The String was repetitively cycled between the injection field of 0.6 T and the operational field of 8.4 T, 24 hours per day, and has accumulated more than 2100 cycles, corresponding to about ten years of machine operation. The final design of the main quadrupoles, based on the use of the dipole coil outer layer cable, is being worked out by CEA, Saclay and the construction of two new prototypes has been launched. research-article

Experiments and cycling at the LHC prototype helf-cell Casas-Cubillos J Collier Paul Cruikshank P Dahlerup-Petersen K Desforges B Hilbert B Krainz G Momal F Rijllart A Rodríguez-Mateos F Saban R I Schmidt R Serio L 1998 The first version of the LHC prototype half-cell has been in operation since February 1995. It consists of one quadrupole and three 10-m twin aperture dipole magnets which operate at 1.8 K. This experimental set-up has been used to observe and study phenomena which appear when the systems are assembled in one unit and influence one another. The 18-month long experimental program has validated the cryogenic system and yielded a number of results on cryogenic instrumentation, magnet protection and vacuum in particular under non-standard operating conditions. The program was recently complemented by the cycling experiment: it consisted in powering the magnets following the ramp rates which will be experienced by the magnets during an LHC acceleration. In order to simulate 10 years of routine operation of LHC, more than 2000 1-hour cycles were performed interleaved with provoked quenches. The objective of this experiment was to reveal eventual flaws in the design of components. The prototype half-cell performed to expectations showing no sign of failure of fatigue of components for more than 2000 cycles until one of the dipoles started exhibiting an erratic quench behavior. research-article

Mechanical design and layout of the LHC standard half-cell Brunet J C Cruikshank P Erdt W K Genet M Parma Vittorio Poncet Alain Rohmig P Skoczen Blazej Van Weelderen R Vlogaert J Wagner U Williams L R 1998 The LHC Conceptual Design Report issued on 20th October 1995 [1] introduced significant changes to some fundamental features of the LHC standard half-cell, composed of one quadrupole, 3 dipoles and a set of corrector magnets. A separate cryogenic distribution line has been adopted containing most of the distribution lines previously installed inside the main cryostat. The dipole length has been increased from 10 to 15 m and independent powering of the focusing and defocusing quadrupole magnets has been chosen. Individual quench protection diodes were introduced in magnet interconnects and many auxiliary bus bars were added to feed in series the various families of superconducting corrector magnets. The various highly intricate basic systems such as: cryostats and cryogenics feeders, superconducting magnets and their electrical powering and protection, vacuum beam screen and its cooling, support and alignment devices have been redesigned, taking into account the very tight space available. These space constraints are imposed by the desire to have maximum integral bending field strength for maximum LHC energy, in the existing LEP tunnel. Finally, cryogenic and vacuum sectorisation have been introduced to reduce downtimes and facilitate commissioning. research-article

Dynamic Effects and their Control at the LHC Bailey R Bordry Frederick Bottura L Burla P Collier Paul Henrichsen K N Koutchouk Jean-Pierre Lauckner R J Parker R Pett John G Proudlock Paul Schmickler Hermann Schmidt R Walckiers L Wolf R 1998 Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magnetic field of quadrupole, sextupole and corrector magnets.This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects.The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams.The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b3) and decapolar (b5) field components in the dipole magnets will be derived. To meet these requirements a deterministic control system is envisaged. research-article

Beam Induced Multipacting Gröbner Oswald 1998 Beam induced multipacting driven by the electric field of successive bunches, as first observed in the ISR proton-proton storage ring [1] may arise from a resonance motion of a cloud of secondary electrons bouncing back and forth between opposite walls of the vacuum chamber. Under conditions where the average secondary electron yield of this process exceeds unity, the electron cloud may increase exponentially. A consequence for the vacuum system is strong electron stimulated gas desorption and the associated pressure increase which may affect the beam lifetime. A simple criterion for the onset of multipacting and an estimate of the average secondary electron yield is derived and will be applied to typical vacuum chambers and to the specific conditions found in the LHC. research-article

Mechanical Design Aspects of The LHC Beam screen Cruikshank P Artoos K Bertinelli F Brunet J C Calder R Campedel C Collins I R Dalin J M Feral B Gröbner Oswald Kos N Mathewson A G Nikitina L I Nikitin I N Poncet Alain Reymermier C Schneider G Sexton J C Sgobba Stefano Valbuena R Veness R J M 1998 Forty-four kilometers of the LHC beam vacuum system [1,2] will be equipped with a perforated co-axial liner, the so-called beam screen. Operating between 5 K and 20 K, the beam screen reduces heat loads to the 1.9 K helium bath of the superconducting magnets and minimises dynamic vacuum effects. Constructed from low magnetic permeability stainless steel with a 50 mm inner layer of high purity copper, the beam screen must provide a maximum aperture for the beam whilst resisting the induced forces due to eddy currents at magnet quench. The mechanical engineering challenges are numerous, and include stringent requirements on geometry, material selection, manufacturing techniques and cleanliness. The industrial fabrication of these 16 metre long UHV components is now in its prototyping phase. A description of the beam screen is given, together with details of the experimental programme aimed at validating the design choices, and results of the first industrial prototypes. research-article

Systems Layout of the Low-$\beta$ Insertions for the LHC Experiments Ostojic R Taylor T M Weisz S 1998 The LHC experimental insertions consist of a low-beta triplet, a pair of separation dipoles, and a matching section of four quadrupoles. The superconducting low-beta quadrupoles must accommodate separated beams at injection, provide high field gradients and low multipole errors for colliding beams, and sustain considerable heat load from secondary particles generated in the high luminosity ATLAS and CMS experiments. In the other two proposed experiments, ALICE and LHCb, the separation dipoles and matching sections share the available space with the injection equipment. In this report we present the systems layout of the experimental insertions for the LHC, and review the requirements for the superconducting magnets. research-article

Quench Performance and Field Quality Measurements of the First LHC low-$\beta$ Quadrupole Model Ostojic R Kirby G A Schmidt R Taylor T M Milward S R Morris J Nobes S Smith K Street A J Townsend M C Treadgold J R Wiatrzyk J M Gourlay S A Strait J B 1998 As part of the LHC magnet development program, CERN in collaboration with Oxford Instruments has designed, built and tested a one metre model of a 70 mm aperture low-beta quadrupole. The magnet features a four layer coil, and is designed for 250 T/m at 1.9 K. We review the results of the magnet training and quench propagation studies performed at 4.3 K and 1.9 K, and report on the magnetic field measurements. research-article

The LHC Vacuum System Gröbner Oswald 1998 The Large Hadron Collider (LHC) at CERN, involves two proton storage rings with colliding beams of 7 TeV. The machine will be housed in the existing LEP tunnel and requires 16 m long superconducting b ending magnets. The vacuum chamber will be the inner wall of the cryostat and hence at the temperature of the magnet cold bore, i.e. at 1.9 K and therefore a very good cryopump. To reduce the cryogeni c power consumption, the heat load from synchrotron radiation and from the image currents in the vacuum chamber will be absorbed on a 'beam screen', which operates between 5 and 20 K, inserted in the magnet cold bore. The design pressure necessary for operation must provide a lifetime of several days and a further stringent requirement comes from the power deposition in the superconducting magnet coils due to protons scattered on the residual gas which could lead to a magnet quench. Cryopumping of gas on the cold surfaces provides the necessary low gas densities but it must be ensured that the vapour pressure of cryosorbed molecules, of which H2 and He would be the most critical species, remains within acceptable limits. In the room temperature sections of the LHC, specifically in the exper iments, the vacuum must be stable against ion induced desorption and ISR-type 'pressure bumps'. research-article

Control and operational models for vacuum equipment Strubin Pierre M Trofimov N N 1998 perational models which describe the behaviour and the physical values associated with the vacuum equipment as seen by an operator have been studied for some time at CERN. Recently, they have been completed by control models, which define in a formal way the data structures required to access the physical values described in the operational model. The control models also define the operations that an application program has to send to the vacuum equipment to modify its state. Object Modelling Techniques (OMT) have been used to formalise the description of the models. In order to test the validity of the concepts, we have made a working prototype in the LEP accelerator. This prototype is being built on top of the CERN SL-Equip equipment access package and uses the "cdev" C++ library, developed at TJNAF, for the interface to application programs. SL-Equip is used for data transmission between front-end computers and vacuum equipment. We use the "cdev" networking facilities to communicate between the workstation and the front-end computers, and the "cdev" generic server as the framework for implementing the vacuum controls software. These packages were used in order to minimise the required software investment, but also to prove that these models are hardware and software independent. research-article