Vacuum Stability for Ion Induced Gas Desorption Collins I R Gröbner Oswald Malyshev O B Rossi A Strubin Pierre M Veness R J M 1999 Ion induced vacuum instability was first observed in the Intersecting Proton Storage Rings (ISR) at CERN and in spite of substantial vacuum improvements, it remained a limitation of the maximum beam current throughout the operation of the machine. Extensive laboratory studies and dedicated machine experiments were made during this period to understand the details of this effect and to identify ways of increasing the limit to higher beam currents. Stimulated by the recent design work for the LHC vacuum system, the interest in this problem has been revived with a new critical review of the parameters which determine the pressure run-away in a given vacuum system with high intensity beams. PREPRINT

Experimental Investigations of the Electron Cloud Key Parameters Anashin V V Baglin V Cimino R Collins I R Dostovalov R V Fedorov N V Gómez-Goñi J Gröbner Oswald Henrist Bernard Hilleret Noël CERN Krasnov A A Laurent Jean Michel Malyshev O B Pyata E E Pivi M 1999 Motivated by a potential electron cloud instability and the possible existence of electron mulitpacting in the LHC vacuum system, that may result in additional gas desorption and unmanageable heat loads on the cryogenic system, an extensive experimental research program is underway at CERN to quantify the key parameters driving these phenomena. Parameters, such as: photoelectron yield, photon reflectivity, secondary electron yield etc. from industrially prepared surfaces have been quantified. In addition to their dependence on photon dose the effect of temperature and presence of external fields has also been studied. PREPRINT

Studies of Decay and Snapback Effects on LHC Dipole Magnets Haverkamp M Bottura L Schneider M 2000 LHC model magnets have dynamic field imperfections of various nature. Two effects of particular importance are field component decay during injection and ''snapback'' during the first few seconds of acceleration, which happens over typically 15 to 20 mT. The dynamic behaviour of the model magnets was measured as a function of several parameters in the operation cycle and powering history. We demonstrate how the systematic variation of only one single operation cycle parameter can affect the behaviour of the sextupole component. research-article

High Temperature Superconducting Current Leads for the Large Hadron Collider Ballarino A 1999 The Large Hadron Collider (LHC) will be equipped with about 8000 superconducting magnets. Some 3380 leads will feed the currents ranging from 60 to 13000 A. To reduce the heat inleak into the liquid helium, CERN aims to use High Temperature Superconducting material for leads having current ratings between 600 and 13000 A. Specifications have been written for 13000 A current leads, incorporating a High Temperature Superconducting section, for the main magnets of the LHC, and contracts have been placed with several firms for the supply of prototypes for comparative testing. The leads used for feeding locally the 60 and 120 A dipole orbit correctors will be conventional conduction cooled resistive leads. An optimized lead of variable cross section has been tested, and an integral design has been initiated. This report describes the design status of the current leads for the LHC, emphasizing, for the different solutions, the principle of optimization and the choice of the cooling methods. PREPRINT

Photon Stimulated Desorption and the Effect of Cracking of Condensed Molecules in a Cryogenic Vacuum System Anashin V V Collins I R Gröbner Oswald Malyshev O B 2000 The design of the Large Hadron Collider (LHC) vacuum system requires a complete understanding of all processes which may affect the residual gas density in the cold bore of the 1.9 K cryomagnets. A wealth of data has been obtained which may be used to predict the residual gas density inside a cold vacuum system exposed to synchrotron radiation. In this study the effect of cracking of cryosorbed molecules by synchrotron radiation photons has been included. Cracking of the molecular species CO2 and CH4 has been observed in recent studies and these findings have been incorporated in a more detailed dynamic gas density model for the LHC. In this paper, we describe the relevant physical processes and the parameters required for a full evaluation. It is shown that the dominant gas species in the LHC vacuum system with its beam screen are H2 and CO. The important result of this study is that while the surface coverage of cryosorbed CH4 and CO2 molecules is limited due to cracking, the coverage of H2 and CO molecules may increase steadily during the long term operation of the machine. PREPRINT

Magnetic and Electric Field Effects on the Photoelectron Emission from Prototype LHC Beam Screen Material Anashin V V Collins I R Dostovalov R V Fedorov N V Gröbner Oswald Krasnov A A Malyshev O B Pyata E E 2001 This paper describes experimental studies of the effect of a dipole field on the photoelectron emission and on the photon reflectivities from LHC beam screen material. These studies were performed using synchrotron radiation from the VEPP-2M storage ring at BINP (Novosibirsk). The particular surface roughness and geometry of the prototype LHC beam screen material requires dedicated experimental measurements. The experiments were performed under conditions close to those expected in the LHC. An important result obtained is that a dipole magnetic field attenuates the photoelectron emission from surface by more than two orders of magnitude with the magnetic field aligned parallel to the surface. The measurements of photon reflectivities, forward scattered and diffuse, and the azimuthal distribution of emitted photoelectrons from the same material are reported. These experimental results are important input for the final design of the LHC beam screen. research-article

The Large Hadron Collider, A Megascience Project Lebrun P 2001 The Large Hadron Collider (LHC) will be the next particle accelerator built to serve the world's high-energy physics community at CERN, the European Organisation for Nuclear Research. Reusing the 26.7-km circumference tunnel and infrastructure of the existing LEP collider, the LHC will make use of advanced technology - high-field superconducting magnets operated in superfluid helium - to push the energy frontier up by an order of magnitude, while remaining economically feasible. The LHC demonstrates on a grand scale several typical features of megascience projects, such as the need for international funding, world-wide co-operation and integration in the local environment, which we review in the following. research-article

Industrial Surfaces Behaviour Related to the Adsorption and Desorption of Hydrogen at Cryogenic Temperature Moulard G Jenninger B Saitô Y 2000 The determination of the hydrogen adsorption capacity on different industrial surfaces has been carried out by measuring isothermal adsorption. First results show that the adsorption capacity is mainly determined by surface porosity. Therefore, the samples may be classified in two categories: smooth surfaces and porous surfaces. Thermal desorption spectra reveal two adsorption energy levels for hydrogen physisorbed on porous materials, but only a single one on smooth samples. The value of the lowest energy level seems to be independent on the substrate nature. The physisorption process studied at low coverage, well below a monolayer, shows that these two levels are not well defined but an energy distribution exists for each of them.The influences of the isotherm temperature and an annealing at 7 K of an adsorbed monolayer on hydrogen adsorption capacity have been studied. PREPRINT

Superconducting Magnets and RF Cavities for the LHC Taylor T 2001 The Large Hadron Collider (LHC) presently under construction at CERN relies on superconducting technology both for the complex magnet system and the radio frequency accelerating structure. The technologies adopted for these systems are described. research-article

Integrating the Latest Technologies into a Java Process Control MMI Momal F 1999 The LHC/IAS (equipment control) Group is developing supervisory systems by means of industrial SCADA packages. For the past four years, we have provided Web remote access to the data coming from our supervisory and control systems. Combining our findings, an architecture and a strategy have been set-up for a generic Java interface which offers a remote and unique access to all kinds of control data. Using the object-oriented technology, the architecture dissociates the data access layer from the presentation one. Thus, the interface may be used to access different types of data. The data are stored in the interface together with a set of related information (acquisition date, unit, etc.). The graphical interface is based on components which may be stored independently and which can be accessed on demand. Attention has been given to easing the integration of commercial components. To help non-specialists in creating components, a graphical scripting language has been developed. PREPRINT

From a UNIX to a PC Based SCADA System Momal F 1999 In order to facilitate the development of supervisory applications involved in slow process control (such as cryogenic control), the LHC/IAS Group (Equipment Controls Group) opted, a few years ago, for an industrial SCADA package which runs on UNIXÒ platforms. However, to reduce costs and following market trends, it has been decided to move over to a PC-based package. Several processes relating to the testing of the prototypes of the LHC magnets are already controlled in this way. However, it was still necessary to provide all the services previously available to the users, for example, data archiving in central databases, real-time access through the Web, automatic GSM calls, etc. This paper presents the advantages and drawbacks of a PC-based package versus a Unix-based system. It also lists the criteria used in the market survey to arrive at the final selection, as well as, the overall architecture, highlighting the developments needed to integrate the package into the global computing environment. PREPRINT

New Long-term Historical Data Recording and Failure Analysis System for the CERN Cryoplants Barbeau H Barth K Baud R Dauvergne J P Delikaris D 1999 CERN uses several liquid helium cryoplants (total of 21) for cooling large variety of superconducting devices namely: accelerating cavities, magnets for accelerators and particle detectors. The cryoplants are remotely operated from several control rooms using industrial standard supervision systems, which allows the instant display of all plant data and the trends, over several days, for the most important signals. The monitoring of the cryoplant performance during transient conditions and normal operation over several months asks for a long-term recording of all plant parameters. An historical data recording system has been developed, which collects data from all cryoplants, stores them in a centralized database over a period of one year and allows an user-friendly graphical visualization. In particular, a novel tool was developed for debugging causes of plant failures by comparing selected reference data with the simultaneous evolution of all plant data. The paper describes the new system, already in operation with 11 cryoplants. PREPRINT

Overview of Single-particle Nonlinear Dynamics Todesco Ezio 1998 We give an overview of the single-particle non linear dynamics in circular accelerators. The main topics are: integration of equations of motion, fast symplectic tracking, dynamic aperture definition, long-term methods, quality factors and lattice optimization. Special emphasis is put on ideas and tools developed during the last decade. research-article