Summary Notes of the GLM held on 17.09.01 2001 DSLLIB

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Summary notes of the GLM held on 29.10.2001 BAILEY R. 2001 DSLLIB

A High-power Superconducting H$^-$ Linac (SPL) at CERN Chiaveri Enrico 2001 The conceptual design of a superconducting H^- linear accelerator at CERN for a beam energy of 2.2 GeV and a power of 4 MW is presented. Using most of the superconducting RF cavities available after the decommissioning of LEP, it operates at 352 MHz and delivers 10^16 protons per second. At an early stage it will upgrade the performance of the PS complex by replacing Linac2 and the PS booster, by injecting protons directly into the PS. The brilliance of the LHC beam will thus be tripled. The present ISOLDE facility can be supplied with five times more beam current than to-day. In conjunction with an accumulator and a compressor, the purpose of its design is to be the proton driver of a neutrino factory at CERN.<br> research-article

Nucl. Instrum. Methods Phys. Res., A Nucl. Instrum. Methods Phys. Res., A 0167-5087 Results from the TARC experiment Abánades A Aleixandre J Andriamonje Samuel A Angelopoulos Angelos Apostolakis Alcibiades J Arnould H Belle E Bompas C A Brozzi Delecurgo Bueno J Buono S Carminati F Casagrande Federico Cennini P Cerro E Collar J I Del Moral R Dumps Ludwig Díez S Eleftheriadis C Embid M Fernández R García J Gelès C Giorni A González E González O Goulas I Gálvez J Heuer R D Hussonnois M Kadi Y Karaiskos P Kitis G Klapisch Robert Kokkas P Lacoste V Le Naour C Loiseaux J M Martínez-Val J M Méplan O Nifenecker H Oropesa J Papadopoulos I M Pavlopoulos P Perlado M Placci Alfredo Poza M Pérez-Enciso E Pérez-Navarro A Revol Jean Pierre Charles Rubbia Carlo Rubio Juan Antonio Sakelliou L Saldaña F Savvidis E Schussler F Sirvent C Tamarit J Trubert D Tzima A Viano J B Vieira S L Vlachoudis V Zioutas Konstantin 2002 478 577 730 research-article

The LEP Superconducting RF System Hübner K 2001 The basic components and the layout of the LEP RF system for the year 2000 are presented. The superconducting system consisted of 288 four-cell cavities operating at 352 MHz powered by 36 klystrons providing on average of 0.6 MW of RF power. This system was complemented by 56 cavities of the original copper RF system. A total accelerating voltage of 3630 MV could be provided routinely allowing operation up to 104 GeV. The installation schedule of the superconducting cavities is shown and comments are made about the evolution of the system over the years. The performance and the reliability of the final system are described.<br> research-article

Where to Install the I224 Detector Gatignon L 2001 Recently M.Ambrosio et al have submitted a Letter of Intent to the SPSC, in which they propose to expose a neutrino detector (much smaller but of a type similar to Monolith) to the neutrinos that accompany the M2 muon beam in the CERN North Area. In fact a significant neutrino flux (almost 2 10^9 nu per SPS cycle) is produced during the muon running of COMPASS at full intensity, out of which some 5 10^8 would traverse a detector with a section of 2 meters diameter. These neutrinos pass well below the COMPASS experiment, located in experimental hall EHN2. The neutrino detector will be housed in a new experimental hall, with a floor level, depending on the site chosen, several meters underground. On their way towards the detector, the neutrinos would traverse one or several RF cavities, recuperated from LEP, which may induce neutrino oscillations. Another part of the proposal addresses the question of speed of flight of the neutrinos by measuring the time difference between the neutrino interaction and the time of the muon from the same pion decay. This note compares and proposes suitable locations for the different detector components. PREPRINT

521548 oai:cds.cern.ch:CERN-SL-2001-052-BT DELETED

Optimization of Orbit Correction Systems using Generalized Response Matrices and its Application to the LHC Injection Transfer Lines Mertens V 2001 The LHC injection transfer lines will transport intense high-energy beams over considerable distances. Their relatively tight apertures require precise control of the trajectory. An analytic method has been developed to optimize the performance, reliability and cost of these lines. This method invokes a comprehensive set of performance criteria, makes detailed predictions on orbit correction effectiveness, configuration defects and critical elements, and gives indications for improvement. A path approaching an optimized configuration can thus be established based on well-defined quantitative criteria. research-article

Beam Based Measurements of Field Multipoles in the RHIC Low Beta Insertions and Extrapolation of the Method to the LHC Koutchouk Jean-Pierre Pilat F Ptitsyn V I 2001 The multipolar content of the dipoles and quadrupoles is known to limit the stability of the beam dynamics in super-conducting machines like RHIC and even more in LHC. The low-beta quadrupoles are thus equipped with correcting coils up to the dodecapole order. The correction is planned to rely on magnetic measurements. We show that a relatively simple method allows an accurate measurement of the multipolar field aberrations using the beam. The principle is to displace the beam in the non-linear fields by local closed orbit bumps and to measure the variation of sensitive beam observable. The resolution and robustness of the method are found appropriate. Experimentation at RHIC showed clearly the presence of normal and skew sextupolar field components in addition to a skew quadrupolar component in the interaction regions. Higher-order components up to decapole order appear as well. research-article

Summary Notes of the GLM held on 3.9.2001 BAILEY R. 2001 DSLLIB

Correction of the Long-Range Beam-Beam Effect in LHC using Electro-Magnetic Lenses Koutchouk Jean-Pierre 2001 The beams in LHC collide head-on in at most four experimental points. Due to the small bunch spacing, the beams experience more than one hundred 'near-misses' on either side of the collision points. The transverse beam separation at these places, limited by the quadrupole aperture, is in the range of 7 to 13 sigma. The non-linear part of these 'long-range' interactions appears to be the dominant mechanism for beam blow-up or beam loss in simulation. A simple non-linear model of the long-range interactions can be devised. It shows that the latter may be locally corrected with good accuracy using wires as correcting lenses. The non-linearity measured by the tune footprint is reduced by one order of magnitude. Pulsing the correcting lenses cancels the so-called PACMAN effect. research-article

Analysis and Measurement of coupling effects in the transfer line from PS to SPS for the LHC proton beam Arduini Gianluigi Chao Y Giovannozzi Massimo Klem J T Klem J Manglunki Django Martini Μ 2001 The tight emittance budget for injection into the LHC demands an accurate matching of the transfer line from the PS to the SPS to minimise blow-up at injection into the SPS. Precise two-dimensional beam profile measurements with Optical Transition Radiation (OTR) screens have recently pointed towards the presence of coupling in the LHC beam transfer. The new algorithms developed to analyse the profile data from the OTR screens and to quantify the observed coupling (in particular the determination of the complete 5?5 beam covariance matrix) are discussed. The results of the measurements and their dependence on the extraction conditions in the PS (trajectory and momentum) are presented and discussed in detail. research-article

Accelerator Aspects of a CLIC-1 $\gamma-\gamma$ Collider Schulte Daniel CERN Zimmermann Frank 2001 We consider an accelerator complex for a gamma\gamma collider based on CLIC-1 at 150 GeV c.m. energy, and present a rough estimate of the luminosity achievable at such a machine. Design challenges and open questions to be addressed are outlined. PREPRINT

The measurement of Q' and Q'' in the CERN-SPS by head-tail phase shift analysis Jones R Schmickler Hermann 2001 A so-called "Head-Tail" chromaticity measurement system has recently been installed in the CERN-SPS, which allows the chromaticity (Q') to be calculated from several hundred turns of data after transverse excitation. The measurement relies on the periodic dephasing and rephasing that occurs between the head and tail of a single bunch for non-zero chromaticity. By measuring the turn-by-turn position data from two longitudinal positions in a bunch it is possible to extract the relative dephasing of the head and the tail, and so to determine the chromaticity. In addition, by changing the orbit of the circulating beam this technique allows the variation of chromaticity with radial position (Q'') to be measured with a much higher resolution than is currently possible using RF modulation. This paper describes this "Head-Tail" measurement technique and discusses some recent results obtained using prototype LHC beam (25ns spacing) in the CERN-SPS. research-article

Feed-down effect in dipole alignment Verdier A Wildner E 2001 The field of strong super conducting magnets contains substantial multipole errors. An upper limit of their value is specified on the reference closed orbit. When the dipole is installed in a real machine, its axis cannot be exactly on the reference orbit, and "feed-down multipoles" are introduced. This paper describes an analytical approach to the alignment specification associated with this effect with an example from the LHC at CERN. research-article

The CLIC Study of Magnet Stability and Time-dependent Luminosity Performance Aleksa Martin CERN Assmann R W CERN Coosemans Williame CERN Guignard Gilbert CERN Leros Nicolas CERN Mayoud Michel CERN Redaelli S CERN Ruggiero F CERN Russenschuck Stephan CERN Schulte Daniel CERN Wilson Ian H CERN Zimmermann Frank CERN 2001 The present parameters of the CLIC study require the collision of small emittance beams with a vertical spot size of 1 nm. The tolerances on vertical quadrupole vi-bration (above a few Hz) are as small as a few nm in the linac and most of the Final Focus. The final focusing quadrupole has a stability requirement of 4 nm in the horizontal and 0.2 nm in the vertical direction. Those tol-erances can only be achieved with the use of damped support structures for CLIC. A study has been set-up at CERN to explore the application of stabilization devices from specialized industry and to predict the time-dependent luminosity performance for CLIC. The results will guide the specification of required technological im-provements and will help to verify the feasibility of the present CLIC parameters. CLINOT

Simulation of single bunch instabilities driven by electron cloud in the SPS Rumolo Giovanni Zimmermann Frank 2001 Photoemission, or gas ionization, and secondary emission can give rise to a quasi-stationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate single bunch instabilities driven by a quasi-stationary electron cloud by means of a computer simulation. The model that we apply makes use of two sets of macroparticles for both the bunch particles and for the electrons, which interact at one or more locations along the beam orbit. Two different schemes have been implemented for the electron cloud field calculation (PIC and soft-Gaussian), and their efficiencies are compared. The code is used to simulate possible instability mechanisms in the SPS. The options of a broad-band wake-field and space charge includuced tune spread have ben also introduced in order to follow the bunch evolution under the combined effect of the elctron-cloud and a broad-band impedance. research-article

Electron cloud studies for KEKB Rumolo Giovanni Zimmermann Frank Fukuma H Ohmi K 2001 Electron-cloud build up, incoherent tune spread and electron-induced beam instability are likely to be responsible for the vertical beam-size increase observed at the KEKB Low Energy Ring (LER). We report on recent simulations and analytical estimated, a ddressing the electron-cloud evolution for various magnet configurations, computing the beam size blow up predicted by three different simulation models (micro-bunches, multiparticle tracking with soft Gaussian approximation, particle-in cell) and finally discussing analytical expressions for the instability threshold. research-article

A study of fast bunch rotation in the negative mass region Rumolo Giovanni Hofmann I 2001 Fast bunch rotation of high-intensity proton or ion bunches above transition is - in principle - supported by the self-bunching effect of the attractive space charge force ("negative instabilities"). Due to the broad-band nature of the space charge impedance, the highest harmonics of this negative mass mode grow fast and inhibit compression, unless the bunch rotation is accelerated by a sufficiently high rf-voltage. Using particle-in-cell simulation we establish the threshold below which effective compression is still possible. We find that the required rf-voltage for compression of a given bunch above transition can be reduced at most by a factor 2 compared with compression below transition, where space charge requires extra voltage. research-article

Status and Recent Developments of the Analog Signal Observation System at CERN PS Alvarez P Deghaye S Gagnaire A Heinze W Serrano J 2001 The nAos (new Analog observation system) at CERN's PS complex allows visualization of some 1500 analog signals in any of the workstations connected to the controls network. Signals are digitized close to their source using VXI oscilloscope modules and sent to the users via Ethernet. A sophisticated application program conveys the signal selection and settings to the VXI front-ends and displays all the requested signals in one virtual oscilloscope window. The trigger pulses for the VXI oscilloscope modules are produced centrally near the Main Control Room of the PS and sent to the VXI crates oscilloscopes through long dedicated copper cables. To get to a sharper time definition, a new trigger production method has been tested with successful results. Timing events, encoded with an ultra-stable 10 MHz clock are sent as 32-bit messages through an optical fiber and converted locally into trigger pulses. The precision achieved with this method is better than 1 ns. The paper describes the current system, presents its performances in operation and details the recent development on the trigger generation. PREPRINT

Measurement of Driving Terms Schmidt F Tomás R Faus-Golfe A 2001 In 2000 a series of MDs has been performed at the SPS to measure resonance driving terms. Theory predicts that these terms can be determined by harmonic analysis of BPM data recorded after applying single kicks at various amplitudes. Strong sextupoles were introduced to create a sizeable amount of nonlinearities. Experiments at injection energy (26 GeV) with single bunch as well as one experiment at 120 GeV with 84 bunches were carried out. The expected nonlinear content is compared to the experimenteal observation. research-article

Measurements of the SPS transverse impedance in 2000 Arduini Gianluigi Burkhardt H Cornelis Karel Klem J T Zimmermann Frank Zorzano-Mier M P 2001 We report on measurements of coherent tune shifts, head-tail growth rates, and current-dependent betatron phase advances at the CERN SPS in the year 2000. Comparing results obtained at two different energies shows that there is no notable contribution from space charge. Within the measurement resolution the impedance is the same as in 1999, consistent with the expected small effect from changes to ony a small number of pumping ports. In 2000, data were taken over an expanded range of chromaticities, which increases the sensitivity to the impedance frequency distribution. Measuremeents of the current-dependent phase advance around the ring help localizing the most important impedance sources. research-article

Overview of the CLIC Collimation design Assmann R W CERN Burkhardt H CERN Fartoukh Stéphane David CERN Jeanneret J B CERN Pancin J CERN Redaelli S CERN Risselada Thys CERN Zimmermann Frank CERN Schreiber H J DESY 2001 The collimation system of the Compact Linear Collider (CLIC) should simultaneously fulfill three different functions. It must (1) provide adequate halo collimation to render the detector background acceptable, (2) ensure collimator survival and machine protection against mis-steered beams, and (3) not significantly amplify incoming trajectory fluctuations via the collimator wake fields. We describe the present layout of CLIC post-linac collimation and characterize its potential performance. CLINOT

Failure modes in CLIC Schulte Daniel CERN Zimmermann Frank 2001 Several CLIC failure modes may cause beam loss at colimators between the linac and the collision point. Studying sample failures by computer simulation, we derive performance requirements for the CLIC collimation system. In particular, we discuss the effect of energy variations due to rf phase jitter, reduced current, or malfunction of one drive beam sector on the multi-bunch emittance. CLINOT

The crossing angle in CLIC Schulte Daniel CERN Zimmermann Frank 2001 Lower limits on the crossing angle at the interaction-point (IP) of the compact linear collider (CLIC) are set by the multi-bunch kink instability, which, at 3 TeV centre-of-mass energy, is strongly affected by coherent pairs. Aperture requirements for the spent beam introduce a second limitation. Finally, synchrotron radiation in the detector solenoid field, in the solenoid fringe field, and in the final quadrupole field mposes an upper limit on the crossing angle. technical-report

The electron cloud instability Zimmermann Frank 2001 Electron-cloud effects presently limit the performance of several accelerators operating with high beam current, notably the SLAC and KEK B factories, the CERN SPS, the CERN PS, and the Los Alamos PSR. They are a major concern for many future projects, e.g. the CERN LHC and the SNS. An electron cloud is generated in the vacuum chamber by photoemission or beam-induced multipacting and subsequent electron accumulation during a bunch or bunch-train passage. Both coupled and single bunch instabilities, pressure rise, malfunctioning of beam diagnostics and failures of multi-bunch feedback systems have all been attributed to the cloud of electrons. We compare observations from various laboratories with computer simulations and analytical estimates, and we address mechanisms by which the electrons may dilute the beam emittance. Possible cures and future research directions are also discussed. research-article

Damping rings for CLIC Jowett John M CERN Risselada Thys CERN Zimmermann Frank CERN Owen H Daresbury 2001 The Compact Linear Colider (CLIC) is designed to operate at 3 TeV centre-of-mass energy with a total luminosity of 10^35 cm^-2 s^-1. The overall system design leads to extremely demanding requirements on the bunch trains injected into the main libac at frequency of 100 Hz. In particular, the emittances of the intense bunches have to be about an order of magnitude smaller than presently achieved. We describe our approach to finding a damping ring design capable of meeting these requirements. Besides lattice design, emittance and damping rate considerations, a number of scattering and instability effects have to be incorporated into the optimisation of parameters. Among these, intra-bem scattering and the electron cloud effect are two of the most significant. CLINOT

The SPS Individual Bunch Measurement System Guerrero A Jakob H Jones R Savioz J J 2001 The Individual Bunch Measurement System (IBMS) allows the intensity of each bunch in an LHC batch to be the measured both in the PS to SPS transfer lines and in the SPS ring itself. The method is vased on measuring the peak and valley of the analogue signal supplied by a Fast Beam Current Transformer at a frequency of 40 MHz. A 12 bit acquisition system is required to obtain a 1% resolution for the intensity range of 5X10`9 to 1.7X10`11 protons per bunch, corresponding to the pilot and ultimate LHC bunch intensities. The acquisition selection and external trigger adjustment system is driven by the 200MHz RF, which is distributed using a single-mode fibre-optic link. A local oscilloscope, controlled via a GPIB interface, allows the remote adjustment of the timing signals. The low-level software consists of a real-time task and a communication server run on a VME Power PC, which is accessed using a graphical user interface. This paper describes the system as a whole and presents some recent uses and results from the SPS run in 2000. research-article

First Beam Tests for the Prototype LHC Orbit and Trajectory System in the CERN-SPS Cocq D Jensen L Jones R Savioz J J Bishop D Roberts B Waters G 2001 The first beam tests for the prototype LHC orbit and trajectory system were performed during the year 2000 in the CERN-SPS. The system is composed of a wide-bande time normaliser, which converts the analogue pick-up signals into a 10 bit position at 40 MHz, and a digital acquisition board, which is used to process and store the relevant data. This paper describes the hardware involved and presents the results of the first tests with beam. research-article

Possible Spin-Offs from LHC Physics Experiments for Beam Instrumentation Jones R 2001 This paper aims to introduce some of the new technology and materials used in the construction of the LHC physics experiments into the domain of the beam instrumentalist. The development of radiation hard fibre-optic technology, for example, can equally well be applied to beam instrumentation systems for the direct transmission of analogue or digital signals from high to low radiation environments. Many electronics techniques such as a system developed for the fast integration of photomultiplier signals could also prove very useful in the construction of new beam diagnostic instruments for bunch-to bunch measurements. Other topics covered will include a fast beam synchronous timing system based on laser technology and a look at pixel detectors as a possible replacement for CCD cameras in imaging applications. research-article

Control Modules for Scintillation Counters in the SPS Experimental Areas Baribaud Guy Beugnet C Cojan A Ferri G Fullerton J Manarin A Spanggaard J 2001 The hardware used in the SPS Experimental Areas to control the beam instrumentation electronics and mechanics of the particle detectors is based on CAMAC and NIM modules. The maintenance of this hardware now presents very serious problems. The modules used to operate the Experimental Areas are numerous and older than 20 years so many of them cannot be repaired any more and CAMAC is no longer well supported by industry. The fast evolution of technology and a better understanding of the detectors allow a new equipment-oriented approach, which is more favourable for maintenance purposes and presents fewer data handling problems. VME and IP Modules were selected as standard components to implement the new electronics to control and read out the particle detectors. The first application implemented in this way concerns the instrumentation for the Scintillation Counters (formerly referred to as triggers). The fundamental options and the design features will be presented. research-article

LHC Beam Loss Monitors Arauzo-Garcia A Dehning Bernd CERN Ferioli G Gschwendtner E 2001 At the Large Hadron Collider (LHC) a beam loss system will be installed for a continuous surveillance of particle losses. These beam particles deposit their energy in the super-conducting coils leading to temperature increase, possible magnet quenches and damages. Detailed simulations have shown that a set of six detectors outside the cryostats of the quadrupole magnets in the regular arc cells are needed to completely diagnose the expected beam losses and hence protect the magnets. To characterize the quench levels different loss rates are identified. In order to cover all possible quench scenarios the dynamic range of the beam loss monitors has to be matched to the simulated loss rates. For that purpose different detector systems (PIN-diodes and ionization chambers) are compared. research-article

Sensitivity Studies with the SPS Rest Gas Profile Monitor Ferioli G Fischer C Koopman J Sillanoli M 2001 During the SPS run in the year 2000 further test measurements were performed with the rest gas monitor. First, profiles of single circulating proton bunches were measured and the bunch charge progressively reduced, in order to determine the smallest bunch intensity which can be scanned under the present operating conditions. The image detector in this case was a CMOS camera. Using a multi-anode strip photo-multiplier with fast read-out electronics, the possibility to record profiles on a single beam passage and on consecutive turns was also investigated. This paper presents the results of these tests and discusses the expected improvements for the operation in 2001. Moreover, the issue of micro channel plate ageing effects was tackled and a calibration system based on electron emission from a heating wire is proposed. The gained experience will be used for the specification of a new monitor with optimised design, to be operated both in the SPS and in the LHC. research-article

Results with LHC Beam Instrumentation Prototypes Fischer C 2001 The beam instrumentation foreseen to provide the necessary diagnostics in the transfer lines and in the main rings of the LHC was conceived in the past years. The requirements expected from the different systems are now being closely analyzed and specified. In a few cases, tests of prototypes have already been performed, profiting from the facilities offered by existing machines. The beam position measurement system had to be tackled first, as the pick-ups had to be integrated into the cryogenic part of the machine. Over the last two years other topics started to be experimentally investigated in order to define the best way to meet the requirements for the LHC era. Amongst these different studies are luminosity monitoring devices, various instruments for the measurement of the transverse beam distributions, the use of head-tail sampling to measure the beam chromaticity and quadrupole gradient modulation to derive the local amplitude of the lattice function. The paper discusses the results of these tests. research-article

New development of a Radiation-Hard Polycrystalline CdTe Detector for LHC Luminosity Monitoring Rossa E Schmickler Hermann Brambilla A Mongellaz F Verger L 2001 Detectors presently considered for monitoring and control of the LHC luminosity will sample the hadronic/electromagnetic showers produced by neutrons and photons in copper absorbers designed to protect the superconducting magnets from quenching. At this location the detectors will have to withstand extreme radiation levels and their long term operation will have to be assured without requiring human intervention. For this application we have successfully tested thick polycrystalline-CdTe detectors. The paper summarizes the results obtained on rise-times, sensitivity and resistance to neutron irradiation up to a dose of 10 ^15/cm 2. research-article

A logarithmic processor for Beam Position Measurements applied to a Transfer Line at CERN Schmickler Hermann Vismara Giuseppe 2001 The transfer line from the CERN proton synchrotron (PS) to the super proton synchrotron (SPS) requires a new beam position measurement system in view of the LHC. In this line, the single passage of various beam types (up to 7), induces signals with a global signal dynamics of more than 100 dB and with a wide frequency spectral distribution. Logarithmic amplifiers, have been chosen as technical solution for the challenges described above. The paper describes the details of the adopted solutions to make beam position measurements, with a resolution down to few 10-4 of the full pickup aperture over more than 50 dB of the total signal dynamics. The reported performances has been measured on the series production cards, already installed into the machine and on one pickup in the transfer line. research-article

Accuracy of the LEP Spectrometer Beam Orbit Monitors Barbero E Dehning Bernd CERN Prochnow J Bergoz J Unser K Matheson J Torrence E 2001 At the LEP e+/e- collider, a spectrometer is used to determine the beam energy with a target accuracy of 10-4. The spectrometer measures the lattice dipole bending angle of the beam using six beam position monitors (BPMs). The required calibration error imposes a BPM accuracy of a 10-6 m corresponding to a relative electrical signal variation of 2. 10-5. The operating parameters have been compared with beam simulator results and non-linearBPM response simulations. The relative beam current variations between 0.02 and 0.03 and position changes of 0.1 mm during the fills of last year lead to uncertainties in the orbit measurements of well below 10-6 m. For accuracy tests absolute beam currents were varied by a factor of three. The environment magnetical field is introduced to correct orbit readings. The BPM linearity and calibration was checked using moveable supports and wire position sensors. The BPM triplet quantity is used to determine the orbit position monitors accuracy. The BPM triplet changed during the fills between 1 and 2 10-6 m RMS, which indicates a single BPM orbit determination accuracy between 1 and 1.5 10-6 m. research-article

Measuring Beta-Functions with K-Modulation Berrig O E Fischer C Schmickler Hermann 2001 The precise measurement of the local value of the beta-function at the place of a beam size monitor is necessary for the precise determination of the beam emittance. We developed a new method for the measurement of the beta-function by using of continuous square-wave modulation of the force of the quadrupole and by continuous tune tracking. Measurements were performed at LEP in order to evaluate the precision that can be achieved with this method in the LHC. The paper describes the method and discusses in details the results obtained at LEP for colliding and non-colliding beams. research-article

Excitation of Large Transverse Beam Oscillations without Emittance Blow-up using the AC-Dipole Principle Berrig O E Höfle Wolfgang Jones R Koopman J Koutchouk Jean-Pierre Schmickler Hermann Schmidt F 2001 The so-called "AC-Dipole" principle allows the excitation of transverse oscillations to large (several sigma) excursions without emittance blow-up. The idea was originally proposed and tested at BNL for resonance crossing with polarized beams, using an orbit corrector dipole with an excitation frequency close to the betatron tune, hence "AC-Dipole". This method of beam excitation has several potential applications in teh LHC, such as phase advance and beta-measurements, dynamic aperture studies and the investigation of resonance strengths. The technique was recently tested in the CERN SPS using the transverse damper as an "AC-Dipole" providing the fixed frequency excitation. Results from this experiment are presented, along with an explanation of the underlying principle. research-article

Increasing the Proton Intensity of PS and SPS Cappi R Cornelis Karel Comelis K Delahaye J P Garoby R Haseroth H Hübner K Linnecar Trevor Paul R Myers S Schindl Karlheinz Wyss C 2001 Recently, a series of meetings were organised with PS and SPS participants, to discuss the possibilities of increasing the proton intensity on the SPS targets (with particular emphasis to CNGS) as well as ISOLDE and nTOF. Increasing the brilliance of the LHC beam, as required for ultimate LHC performance, was also discussed. Several schemes were proposed, as a staged approach, i.e. starting from the most simple and cheap, though difficult, to the more advanced and expensive. After comparing the advantages and disadvantages of the various methods, three basic schemes were retained as candidates for further investigations and as good / necessary starting points for further improvements. Chapter 1 is devoted to PSB and PS issues and contains essentially a description of the three selected schemes. Chapter 2 deals with limitations in the SPS. Chapter 3 is a synthesis of basic conclusions. In the Appendix, a work-plan is presented for PSB and PS theoretical and experimental studies with a time estimate for preliminary results. technical-report

Ultimate Performance of the LEP RF System Brown P Brunner O C Butterworth A Ciapala Edmond Frischholz Hans Geschonke Günther Peschardt E Sladen Jonathan P H 2001 The LEP Superconducting RF system reached its maximum configuration of 288 four-cell cavities powered by 36 klystrons in 1999. In 2000, this system, together with 56 cavities of the original copper RF system, routinely provided more than 3630 MV, allowing the beam energy to be raised up to 104.5 GeV. This not only required operating the cavities more than 15% above their design gradient, but has also demanded a very high operational reliability from the entire system. This paper will describe the operation of the LEP RF system during 2000, including new features, operational procedures and limitations. research-article

Report on the Working Group set up to Study the Requirements for Operating the SPS within the INB Framework (INBOPS) Ball A Billen R Charavay R Elsener K Faugier A Jacot C Jirdén L Menzel Hans Gregor Pajunen J Poole John Roy G Silari Marco Spinks Alan Tsesmelis E Wahl H 2001 The convention signed with the French authorities for the LHC defines a new Installation Nucléaire de Base (INB). The LHC machine tunnel, the experiments, some buildings which cover access shafts to the machine and the SPS with its extraction lines up to the targets are all inside the new perimeter. The new convention came into effect in September 2000 and therefore the SPS fell within the new context from that time. As a consequence, SL has to operate the SPS within this new regulatory framework and a small working group was set up to look at the requirements and to estimate the resources required. The conclusions of the working group are reported in this paper. PREPRINT

Status of CERN Hübner K CERN 2001 An overview of the present CERN facilities is given and their planned development is outlined as required by the approved physics programme. Although the main task of CERN in the next years will be the construction of LHC, a small but significant programme for accelerator R&D has been defined. It comprises a multi-TeV linear collider, advanced neutrino beams and the upgrading of LHC. research-article

Summary Notes of the GLM held on 20.08.2001 BAILEY R. 2001 DSLLIB

CNGS Ball A E Guglielmi A M Pietropaolo F Sala P R Vassilopoulos N Vincke H H 2001 Simulations of the CNGS neutrino beam from CERN to the Gran Sasso Laboratory (LNGS)assume that the proton beam and all secondary beam elements are perfectly aligned on an axis between the two laboratories. This study examines the effects on the neutrino flux at Gran Sasso of deviations from the axis of the primary proton beam and misalignment of secondary beam elements. It also examines how such deviation or misalignment can be detected at monitors placed along the secondary beam line at CERN and at Gran Sasso. Calculations are based on the CNGS neutrino beam, optimized for nu_mu ->nu_tau appearance experiments as described in the Addendum to the Conceptual Technical Design Report of CNGS. It is shown that the number of neutrino charged current events predicted at Gran Sasso is insensitive to all but the most extreme misalignments. PREPRINT

Interplay of Ionization and Sputtering with the Electron Cloud Rumolo Giovanni Zimmermann Frank 2001 The electron cloud enhances the generation and accumulation of ions, which in turn might increase both electron density and electron decay time. We report analytical considerations and simulations of ion motion under the combined influence of beam, electron cloud, and various external magnetic fields. From these, we infer ion survival times, ion impact energies and the equilibrium ion density. All of these are shown to be small. Only in a dipole field whose ion cyclotron frequency is resonant with the bunch spacing (2.62 T for hydrogen ions in the LHC) some ions may acquire kinetic energies of several keV. We argue that additional contributions from ion reflection and sputtering are insignificant. PREPRINT

A Z Factory in the VLLC Injector Keil Eberhard 2001 A Z factory in the VLLC injector with polarized beams is presented. Its circumference is about two Tevatron circumferences. Wigglers make the bunches longer at injection, and reduce the risk of collective instabilities and the polarization time at collision energy. However, they are powerful sources of synchrotron radiation, and associated damage. The vertical amplitude function beta_y^* at the interaction point is assumed to be 40 mm. At this value, reaching a peak luminosity 10^33cm^-2s^-1 implies about 50 MW of RF power for the two beams. A lower value of beta_y^* could be exploited by using any intermediate method between two extremes: (i) At constant L and RF power, the circumference and the polarization time could be reduced. (ii) At constant circumference, RF power, and polarization time, L could be increased. Apertures and separation schemes have only been designed at the collision energy. In the discussion of polarization time, peak polarization and figure of merit, all depolarizing mechanisms, due to the momentum spread in the beam and orbit errors, are ignored. PREPRINT

Realistic RF system and Beam Simulation in Real Time for a Synchrotron Tückmantel Joachim CERN 2001 Due to heavy beam loading with gaps in the LHC beams, RF and beam are intimately linked to a complex system with fast transients where the RF loops and their limitations play a decisive role. Such a system is difficult to assess with analytical methods. To learn about overall system stability and for the definition of RF components to be built it is essential to understand the complete system long before the machine really exists. Therefore the author has written a general purpose real time simulation program and applied it to model the LHC machine with its beam pattern and complete double RF system. The latter is equipped with fast RF vector feedback loops having loop delay, transmitter power limitation and limited amplifier bandwidth as well as including one-turn-delay feedback and longitudinal batch injection damping. The development of all RF and beam quantities can be displayed graphically turn by turn. These frames can be assembled to a realistic multi-trace scope movie. research-article

Heat deposition by transient beam passage in spoilers Fartoukh Stéphane David Jeanneret J B Pancin J 2001 Future electron-positron linear colliders must produce bunches of tiny emittance grouped in short bunch trains in order to provide adequately large luminosities. A collimation system must be installed between the end of the main linac and the optical elements of the final focus to protect the detectors from errant beams. With ordinary values of the betatron functions, the transverse beam size is of a few microns. With such sizes, the local deposition of heat of even a single bunch train is so high that no material can survive such an event.The problem is solved by increasing the beam sizes at the location of the collimators. But the use of large betatron functions is costly and can induce strong optical errors. It is therefore important to compute precisely safe beam sizes which allow the survival of the collimators, in order to limit their increase to the minimum needed. The deposition of heat occurs both by ionisation along the path of the particles which traverse the material and by ohmic image current heating at the surface of the collimator, for that fraction of the beam which flies outside the collimator.With small bunches, heat diffusion is substantial even with short bunch trains and helps to reduce the excursion of temperature. The rise of temperature is computed by solving analytically the time-dependent heat equation in two spatial dimensions near an interface with vacuum. Numerical results are given for the CLIC study. PREPRINT

Wake field and transverse mode coupling instability caused by electron cloud Ohmi K KEK, Tsukuba Zimmermann Frank CERN Perevedentsev E A Novosibirsk, IYF 2001 In positron and proton storage rings, electrons produced by photo-emission, ionization and secondary emission accumulate in the vacuum chamber during multi-bunch operation with close spacing. A positron or proton bunch passing through this `electron cloud' experiences a force similar to a short-range wake field. This effective wake field can cause a transverse mode coupling instability, if the electron-cloud density exceeds a threshold value. In this report, we compute the electron-cloud induced wake both analytically and and via computer simulation, for the low-energy positron ring of KEKB and the LHC proton beam in the CERN SPS, and evaluate the instability threshold using the two approaches of transverse mode coupling and fast transverse blow up including its dependence on chromaticity. research-article

Final-Focus Schemes for CLIC at 3 TeV Zimmermann Frank CERN Burkhardt H CERN Risselada Thys CERN Schmidt F CERN Schreiber H J DESY 2001 We discuss benefits and drawbacks of two different final-focus schemes for CLIC at 3 TeV centre-of-mass (c.m.) energy, by examining tolerances, tunability and potential background for a 3.3-km long baseline final-focus system and a shorter advanced design. CLINOT

Luminosity Limitations at Hadron Colliders Zimmermann Frank CERN 2001 I discuss fundamental luminosity limitations at hadron colliders, addressing head-on and long-range beam-beam interaction, empirical scaling, synchrotron radiation, intrabeam scattering, dynamic evolution during the store, flat beams, heat load, power consumption, and electron cloud. Parameters of past or operating colliders - ISR, SPS, Tevatron, RHIC -, are compared with the LHC and further extrapolated to an LHC upgrade and to the VLHC. research-article

Beam-Loading Compensation in the Recirculating Linacs of the CERN Neutrino Factory Zimmermann Frank 2001 We evaluate the multi-bunch beam loading in the recirculating linacs (RLAs) of the CERN neutrino factory, and show that the resulting energy variation along the bunch train can be reduced to an acceptable level, while maintaining a high average acceleration, by a proper choice of the rf phase and a bunch spacing slightly different from an integer multiple of the rf wavelength. NEUFACNOT

Focusing in Recirculating Muon Accelerators Keil Eberhard 2001 This report discusses the focusing in the FODO cells along the linear accelerators in a recirculating muon accelerator that is part of the ongoing study of a neutrino factory in Europe. The quadrupoles for the focusing in the FODO cells alternate with RF cavities that accelerate the muon beam. The report derives the parameters of the FODO cells that accommodate the muon beam with the assumed emittance. Two different styles of focusing are considered, constant betatron wavelength and constant quadrupole gradient. NEUFACNOT

Transverse Behaviour of the LHC Proton Beam in the SPS Arduini Gianluigi Cornelis Karel Höfle Wolfgang Rumolo Giovanni Zimmermann Frank 2001 During the 1999 SPS run, strong transverse instabilities were observed with the LHC beam [1]. Both the instability characteristics and the identical threshold current as for beam-induced electron multipacting led to consider the interaction of the beam with the electron cloud as a likely source. In 2000, we have measured the dependence of beam motion, beam loss, and emittance growth on bunch intensity, number of bunches, octupole strength, chromaticity, and gaps in the bunch train. We report on these recent studies and compare the beam observations with simulations of electron cloud build up and electron-induced single-bunch instabilities. research-article

High power semiconductor switches in the 12 kV, 50 kA pulse generator of the SPS beam dump kicker system Bonthond J Ducimetière L Faure P Vossenberg Eugène B 2001 Horizontal deflection of the beam in the dump kicker system of the CERN SPS accelerator is obtained with a series of fast pulsed magnets. The high current pulses of 50 kA per magnet are generated with capacitor discharge type generators which, combined with a resistive free-wheel diode circuit, deliver a critically damped half-sine current with a rise-time of 25 ms. Each generator consists of two 25 kA units, connected in parallel to a magnet via a low inductance transmission line. PREPRINT

IEE proceedings - Generation, transmission and distribution PERI

IEE proceedings - Electric power applications PERI

The decay of a lambda particle in the 32 cm hydrogen bubble chamber 1960 This image from 1960 is of real particle tracks formed in CERN's first liquid hydrogen bubble chamber to be used in experiments. It was a tiny detector by today's standards at only 32 cm in diameter. Negatively charged pions with an energy of 16 GeV enter from the left. One of them interacts with a proton in the liquid hydrogen and creates sprays of new particles, including a neutral particle (a lambda) that decays to produce the "V" of two charged particle tracks at the centre. Lower-energy charged particles produced in the interactions spiral in the magnetic field of the chamber. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real particle tracks to be seen and photographed, after releasing the pressure that had kept a liquid above its normal boiling point. PHOTOLAB

Bubble chamber: antiproton annihilation 1971 These images show real particle tracks from the annihilation of an antiproton in the 80 cm Saclay liquid hydrogen bubble chamber. A negative kaon and a neutral kaon are produced in this process, as well as a positive pion. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real tracks left by particles to be seen and photographed by expanding liquid that had been heated to boiling point. PHOTOLAB

Bubble chamber: Omega production and decay 1973 This image is taken from one of CERN's bubble chambers and shows the decay of a positive kaon in flight. The decay products of this kaon can be seen spiraling in the magnetic field of the chamber. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real tracks left by particles to be seen and photographed by expanding liquid that has been heated to boiling point. PHOTOLAB

Gargamelle: neutral current event 1973 This event shows real tracks of particles from the 1200 litre Gargamelle bubble chamber that ran on the PS from 1970 to 1976 and on the SPS from 1976 to 1979. In this image a neutrino passes close to a nucleon and reemerges as a neutrino. Such events are called neutral curent, as they are mediated by the Z0 boson which has no electric charge. PHOTOLAB

NA35: sulphur-gold collision 1991 In this image the real particles produced by the collision of a 6400 GeV sulphur ion with a gold target can be seen as they pass through a streamer chamber. Streamer chambers consist of a gas chamber through which a strong pulsed electric field is passed, creating sparks as a charged particle passes through it. The NA35 experiment, which was in operation in the 1980s, was part of CERN's ongoing heavy ion project. PHOTOLAB

Streamer chamber: pion decay 1992 The real particles produced in the decay of a positive pion can be seen in this image from a streamer chamber. Streamer chambers consist of a gas chamber through which a strong pulsed electric field is passed, creating sparks as a charged particle passes through it. A magnetic field is added to cause the decay products to follow curved paths so that their charge and momentum can be measured. PHOTOLAB

Bubble chamber with colour enhanced tracks 2004 This artistically-enhanced image shows the tracks of real particles produced when a neutrino interacted in a liquid mixture of neon and hydrogen inside the Big European Bubble Chamber (BEBC) during the 1960s. The tracks become visible when bubbles form along the paths of the particles as a piston expands the liquid. A magnetic field is produced in the detector causing the particles to travel in spirals, allowing charge and momentum to be measured. PHOTOLAB

Compilation of radiation damage test data Tavlet Marc CERN Fontaine Anne CERN Schönbacher Helmut CERN 1998 BOOK

Phys. Rev. D Phys. Rev. D High Energy Colliders as Black Hole Factories Giddings Steven B Thomas S 2002 65 056010 12 If the fundamental Planck scale is of order a TeV, as the case in some extra-dimensions scenarios, future hadron colliders such as the Large Hadron Collider will be black hole factories. The non-perturbative process of black hole formation and decay by Hawking evaporation gives rise to spectacular events with up to many dozens of relatively hard jets and leptons, with a characteristic ratio of hadronic to leptonic activity of roughly 5:1. The total transverse energy of such events is typically a sizeable fraction of the beam energy. Perturbative hard scattering processes at energies well above the Planck scale are cloaked behind a horizon, thus limiting the ability to probe short distances. The high energy black hole cross section grows with energy at a rate determined by the dimensionality and geometry of the extra dimensions and therefore probes distances larger than the Planck scale. research-article

Phys. Lett. B Phys. Lett. B Semiclassical suppression of black hole production in particle collisions Voloshin M B 2001 518 137 142 It is argued that the cross section for production of large black holes, for which a semiclassical description is applicable, cannot be given by the geometric area of the black hole horizon, as claimed recently in the literature. Rather the production cross section in a few-particle collision is suppressed by at least a factor exp(-I_E) with I_E being the Gibbons-Hawking (Euclidean) action for the black hole. Thus only essentially non-classical small black holes with mass of the order of the Planck mass can possibly be produced in few-particle collisions at trans-Planckian energies. research-article

High Energy Scattering in the Brane-World and Black Hole Production Aref'eva I Ya 1999 Black hole production in the collision of ultra-relativistic particles in the brane-world approach is considered. In particular, stability of the brane under collision with ultra-relativistic particles is discussed. As a toy model we consider the 3 dimensional version of the Randall and Sundrum solution and show that stability of the brane depends on a choice of continuation of the solution across the horizon. In the unstable case black holes can be produced in the collision of a particle with the brane. PREPRINT

A Model for High Energy Scattering in Quantum Gravity Banks T Fischler Willy 1999 We present a model for high energy two body scattering in a quantum theory of gravity. The model is applicable for center of mass energies higher than the relevant Planck scale. At impact parameters smaller than the Schwarzchild radius appropriate to the center of mass energy and total charge of the initial state, the cross section is dominated by an inelastic process in which a single large black hole is formed. The black hole then decays by Hawking radiation. The elastic cross section is highly suppressed at these impact parameters because of the small phase space for thermal decay into a high energy two body state. For very large impact parameter the amplitude is dominated by eikonalized single graviton exchange. At intermediate impact parameters the scattering is more complicated, but since the Schwarzchild radius grows with energy, we speculate that a more sophisticated eikonal calculation which uses the nonlinear classical solutions of the field equations may provide a good approximation at all larger impact parameters. We discuss the extent to which black hole production will be observable in theories with low scale quantum gravity and large dimensions. PREPRINT

Radiation tests on selected electrical insulating materials for high-power and high-voltage application Lipták G Brown Boveri, Baden Haberthur B Maier P Müller Hubert Schuler Roland Schönbacher Helmut Zeier Z 1985 BOOK

Opportunities for the study of beta-delayed fission at ISOLDE Köster U CERN 2000 research-article

Wagemans C Serot Olivier D'Hondt P 2000 PROCEEDINGS