P. Collier

Present understanding of electron cloud effects in the Large Hadron Collider

We discuss the predicted electron cloud build up in the arcs and the long straight sections of the LHC, and its possible consequences on heat load, beam stability, long-term emittance preservation, and vacuum. Our predictions are based on computer simulations and analytical estimates, parts of which have been benchmarked against experimental observations at the SPS.

Electron cloud studies and analyses at SPS for LHC-type beams

A summary of the main results obtained so far from the electron cloud studies using strip detectors, pick-ups, COLDEX and a 100 MHz coaxial resonator will be presented. The spatial and energy distributions of the electrons in the cloud measured by the strip detectors will be detailed and compared to the results obtained with a conventional retarding field detector. The evidence of the scrubbing effect and of the NEG coatings as remedies to reduce the electron cloud activity will also be shown. In a second part, the improved hardware of the experiments will be presented together with the program of measurements foreseen for the 2003 SPS run.

Building a behemoth

The Large Hadron Collider makes extensive use of existing CERN infrastructure but is in many respects an unprecedented undertaking. It is a proton–proton collider; therefore, it requires two separate accelerator rings with magnetic fields of opposite polarity to guide the two beams in opposite directions around its 27-km circumference. In addition, the extraordinary energies and collision rates that it has been designed to attain pose huge challenges for controlling the beam and protecting the accelerator.

A dedicated multi-process controller for a LEP RF unit

The operation of each RF unit for the LEP (Large Electron Positron collider) requires that several control processes be run simultaneously. Local and remote access is required to around 2500 individual parameters and status indications inside the unit. Normal operation of the unit involves complex procedures requiring a considerable amount of sequential access equipment within the unit. Optimum performance and overall maintainability are achieved by calling up locally resident procedures. The needed surveillance and alarm monitoring can run locally, making a summary status available for the control center. The local process controller hardware is realized as a hybrid VME/G64 crate with a 68020 VME module as the main processor. Two 68000 VME slave processors having G64 ports handle communication with equipment buses. VME high-resolution graphics interfaces provide interactive local control via a touch screen and separate data display. A VME MIL-1553 interface provides the connection to the control system. Local control, remote control, and surveillance run concurrently on the main processor under the OS-9/68 K multitasking operating system.<<ETX>>

submitter : The technical challenges of the Large Hadron Collider

The Large Hadron Collider (LHC) is a 27 km circumference hadron collider, built at CERN to explore the energy frontier of particle physics. Approved in 1994, it was commissioned and began operation for data taking in 2009. The design and construction of the LHC presented many design, engineering and logistical challenges which involved pushing a number of technologies well beyond their level at the time. Since the start-up of the machine, there has been a very successful 3-year run with an impressive amount of data delivered to the LHC experiments. With an increasingly large stored energy in the beam, the operation of the machine itself presented many challenges and some of these will be discussed. Finally, the planning for the next 20 years has been outlined with progressive upgrades of the machine, first to nominal energy, then to progressively higher collision rates. At each stage the technical challenges are illustrated with a few examples.

Energy Calibration of the SPS with Proton and Lead Ion Beams

The momentum of the 450 GeV/c proton beam of the CERN Super Proton Synchrotron was determined by a high precision measurement of the revolution frequencies of proton and lead ion beams. To minimize systematic errors the magnetic cycle of the SPS had to be rigorously identical for both beams, and corrections due to Earth tides had to be taken into account. This paper presents how the beam momentum was determined from the RF frequency for which the beams are centered in the machine sextupoles. The measured beam momentum is 449.16 ± 0.14 GeV/c for a nominal momentum of 450 GeV/c, and the accuracy is limited by systematic errors.

Performance of the high level application software during LEP operation

Abstract After the first year of operating LEP, it was clear that a new generation of application software would be required to effectively exploit the accelerator. In response a new system of application software was developed. During 1992 and 1993 this software has been used exclusively to drive LEP in many different operational modes including polarization runs and 8 bunch pretzel operation. The software has performed well and has clearly enhanced the performance of the machine. For example, the turn around time has been significantly reduced, contributing an increase of around 20% to the integrated luminosity for 1992. The software has also made the accelerator accessible to less experience operators. After outlining the functionality of the system the impact of the software on various aspects of LEP performance is discussed. Comparative data from the last 3 years is presented.

LEP operation in 1992 with a 90/spl deg/ optics

The optics for physics operation in LEP was changed from 60/spl deg/ to 90/spl deg/ at the start of 1992 with a view to improved Z/sup 0/ production, preparation for future operation at higher energies and the use of the same optics in machine developments. The developments included running LEP with twice the number of bunches and using resonant depolarisation for energy calibration, Perturbation to steady operation was felt at the start of the year but was soon overcome as the benefits of smaller emittances were realised. The peak luminosity increased to 1.15 10/sup 31/ and the luminosity lifetime improved. New operational software halved the time taken between dumping one coast and the start of data taking on the next. The 8+8 bunch operation was introduced as routine operation for the last month. Overall, there was an increase in integrated luminosity from 17.6 inverse picobarns per experiment in 1991 to 28.6 in 1992. Along with improvements in detector efficiency, almost 3 million hadronic Z/sup 0/s were recorded by the four experiments, an increase from 1.27 million in 1991.<<ETX>>

Digital control of the LEP RF system

The RF system for the initial phase of LEP (Large Electron Positron collider) consists of eight identical units of 16 cavity assemblies with associated high-power and control equipment. Digital control is achieved by assigning a G64-based equipment controller crate to each major element of the unit. The crates are linked by a bus to a VME-based data manager with overall control and connection to the control network. The manager executes locally or remotely initiated complex control and surveillance procedures to simplify operation. The different classes of parameter and data are summarized. Interfacing and control within the equipment controllers and communication with the data manager are outlined. The equipment access functions and the development of complex control procedures are discussed. The implementation of corresponding functions at the control console level is examined. Experience with the six RF units presently installed is described. The modular approach to the controls of the LEP RF system, together with an interactive local control facility, has been found vital in commissioning and testing the RF system. It also allows additional units with superconducting cavities to be integrated gradually into the controls system with minimal disturbance to the operation of the accelerator.<<ETX>>

Acceleration of high intensity proton beams

In 1998 the CERN SPS accelerator finished a five years long program providing 450 GeV proton beams for neutrino physics. These experiments required the highest possible beam intensity the SPS can deliver. During the last five years the maximum proton intensity in the SPS has steadily been increased to a maximum of 4.8/spl times/10/sup 13/ protons per cycle. In order to achieve these intensities a careful monitoring and improvement of the vertical aperture was necessary. Improved feedback systems on the different RF cavities were needed in order to avoid instabilities. Also the quality (emittance and extraction spill) of the injector, the CERN PS, had been optimised.