Benedikt, Michael 2003 2003 For the first commissioning phase of the LHC, a single proton bunch is required. The production of this so-called "LHC pilot bunch" will follow a different scheme than the one of the nominal LHC proton bunch train. Both the transverse and the longitudinal LHC bunch characteristics should already be established in the PS Booster. The parameter space for the LHC pilot bunch spans a factor 66 in beam brightness. To cover the whole parameter space, a mixture of several ingredients was required: intensity adjustment with low voltage rf-capture; definition of the transverse emittance with shavers; controlled blow-up followed by longitudinal shaving to define the longitudinal emittance. All beam variants were produced on harmonic two, with only one bunch being sent to the downstream accelerator chain. To cover also the lowest intensity side, the Linac beam was reduced by a factor 5 with a "sieve". The pilot bunches corresponding to the "corners" of the parameter space and a few selected inner reference points were successfully produced in the PS Booster. Baudrenghien, P Bohl, T Linnecar, Trevor Paul R Shaposhnikova, Elena Tückmantel, Joachim 2003 2003 A proton beam with the basic structure defined by the the LHC requirements, was first available for injection into the SPS in 1998. At the end of 2002, following a significant beam-studies and RF hardware upgrade programme, a beam having both the nominal LHC intensity and the correct longitudinal parameters was obtained at top energy for the first time. This beam, characterised by high local density, must satisfy strict requirements on bunch length, longitudinal emittance and bunch to bunch phase modulation for extraction to the LHC, where only very limited particle losses are acceptable. The problems to be solved came mainly from the high beam loading and microwave and coupled bunch instabilities which led both to beam losses and to unacceptably large longitudinal emittance on the flat top. In this paper the steps taken to arrive at these nominal beam parameters are presented. Garoby, R Grier, D G Haase, M Krusche, A Maesen, P Morvillo, M Paoluzzi, M Rossi, C 2003 2003 As part of the preparation of the PS as an injector for the LHC, a prototype 20 MHz rf system has been used, to demonstrate that the nominal longitudinal performance of the proton beam for LHC can be obtained using multiple bunch-splittings. Based on these successful results obtained during 2000, the development of the operational rf system began in 2001. To allow the preparation of bunch trains with a bunch spacing of 25 or 75 ns, this system must operate either at 20 or 13.3 MHz respectively. Two new ferrite cavities and their associated amplifiers have been designed and built. Each one can provide a maximum voltage of 20 kV peak during 200 ms with a 10% duty cycle. The cavities are equipped with fast (~20 ms) gap shorting relays, and rf feedback reduces their Q below 10 at both frequencies. A single system is sufficient to generate the nominal beam for LHC. The second one will then be both a "hot spare" and a very valuable performance enhancement providing the possibility of handling a larger than nominal emittance or generating bunch trains with different spacings in the same PS supercycle. The design and the results measured on the final device are described and discussed. Kroyer, Tom Caspers, Friedhelm Mahner, Edgar 2003 2003 Unexpected obstacle formation in the LHC beam-pipe during assembly, cool down and operation may lead to major disturbances. Thus a fast, precise, sensitive and reliable means to detect and characterize such a fault is highly desirable, preferably without the need to break the vacuum. Waveguide mode time domain reflectometry using the synthetic pulse technique has been selected for this purpose. The system will use a modern vector network analyzer operating using essentially the fundamental TM mode on the LHC beam-screen. The objective is to measure over a full arc with access from either side both in reflection and transmission mode. If the proposed system is implemented a total of 32 couplers will be permanently installed, which may be used in normal operation for beam diagnostics and other applications.<br> The attenuation of several short beam-screen sections has been measured both for TE and TM modes by means of a resonator method and these data are compared with theoretical results. Waveguide calibration on the beam-pipe and digital signal processing to compensate dispersion are studied. Finally, using a 44m test track the performance of the proposed methods is examined. Caspers, Friedhelm Mostacci, A Iriso-Ariz, U 2003 2003 The classical 2 wire method is not suitable for high precision transverse impedance measurements on a homogeneous copper beampipe with non-circular cross-section due to measurement noise limitations in case of narrow wire spacing. Thus we tackled the problem by simulating the 2D electrostatic field and image charge distribution of that setup and subsequently calculating the corresponding surface current for a TEM wave excitation. In this computer simulation the 2 wires can be assumed lossless, which is not possible in a practical bench setup. The theoretical justification for the method and certain limitations are discussed. The results obtained compare very well to several independent numerical and analytical results. Brunner, O C Frischholz, Hans Valuch, D 100 kV 300 kW klystrons 300 kW 40 A 400 MHz RF systems 400 MHz 7 TeV AC DC power converter LHC Large Hadron Collider RF power generation circulator counter rotating proton beams ferrite loaded waveguide absorber five gap thyratron crowbar group delay input coupler klystron output signal output power three port circulators waveguide line 2003 2003 The counter-rotating proton beams in the Large Hadron Collider (LHC) will be captured and then accelerated to their final energies of 2 x 7 TeV by two identical 400 MHz RF systems. The RF power source required for each beam comprises eight 300 kW klystrons. The output power of each klystron is fed via a circulator and a waveguide line to the input coupler of a single-cell super-conducting (SC) cavity. Four klystrons are powered by a 100 kV, 40A AC/DC power converter, previously used for the operation of the LEP klystrons. A five-gap thyratron crowbar protects the four klystrons in each of these units. The technical specification and measured performance of the various high-power elements are discussed. These include the 400MHz/300kW klystrons with emphasis on their group delay and the three-port circulators, which have to cope with peak reflected power levels up to twice the simultaneously applied incident power of 300 kW. In addition, a novel ferrite loaded waveguide absorber, used as termination for port No 3 of the circulator is described, including its advantages with respect to a water-load. A system to measure the harmonic content in the klystron output signal is also presented. Bravin, Enrico Lefèvre, T Vermare, C 2003 2003 The CTF3 (CLIC Test Facility 3) will produce 1.56µs long intense electron pulses. The unbunched 5.4A beam of the injector will have a transverse beam size ~1mm. After the buncher the current is reduced to 3.5A and the transverse size varies between a few hundred micrometers and one millimetre along the length of the linac. Calculations indicate that these beam parameters will impose an unbearable thermal load for the intercepting screens currently in use (scintillators and aluminium OTR foils). Graphite and SiC have been investigated as possible alternative materials for the OTR radiators. The possibility of replacing scintillating screens with OTR targets at the low energies of the injector has also been considered. A possible limitation in the use of such high temperature radiators has been identified; ions released from the heated target could focus further the beam with the risk of damaging the target itself and/or blowing up the beam. This would also affect the emittance measurement and would hinder any effort to detect head-tail phenomena. This paper gives the results of the theoretical estimations, and of the beam-based experiments. Verdier, A Wittmer, W Zimmermann, Frank 2003 2003 To correct the beta* at the main collision points (IP1 and IP5) simultaneously for the two counterrotating proton beams in the Large Hadron Collider (LHC), a set of specific quadrupoles in the non-common part of the machine is used. Due to the antisymmetric optics, several quadrupoles on each side of the insertion have to be employed. The change of beta* is accomplished by incrementing the quadrupole gradients. This set of increments is referred to as beta* tuning knob. The increments were calculated by rematching beta* in a range of + 20 % about the nominal value. Linear curves were fitted to the variation of increments to construct a linear tuning knob. This was done for each plane using MAD 8 [1] and repeated with MAD X [2]. The linear behaviour and the orthogonality of the knobs were investigated for the LHC lattices V6.2 and V6.4. Different field errors were introduced in the lattice and the correction efficiency of the knobs was studied. Kashikhin, V V Brüning, Oliver Sim Mokhov, N V Rakhno, I L Ruggiero, F Strait, J B Yadav, S Zlobin, A V 2003 2003 Interaction region inner triplets are among the systems which may limit the LHC performance. An option for a new higher luminosity IR is a double-bore inner triplet with separation dipoles placed in front of the first quadrupole. The radiation load on the first dipole, resulting from pp-interactions, is a key parameter to determine the feasibility of this approach. Detailed energy deposition calculations were performed with the MARS14 code for two Nb_3Sn dipole designs with no superconductor on the mid-plane. Comparison of peak power densities with those in the baseline LHC IR suggests that it may be possible to develop workable magnets for luminosities up to 10^35 cm^_2 s^_1. Arduini, Gianluigi Baglin, V Benedetto, Elena Cimino, R Collier, Paul Collins, I R Cornelis, K Henrist, Bernard Hilleret, Noël Jenninger, B Jiménez, M Rossi, A Ruggiero, F Rumolo, Giovanni Schulte, Daniel Zimmermann, Frank 2003 2003 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. Catalan-Lasheras, N Fartoukh, Stéphane David Koutchouk, Jean-Pierre 2003 2003 Before correction, the difference coupling coefficient in LHC is expected to reach 0.2 at injection and vary by 30 to 40% from injection to top energy. These high values arise mostly from the field imperfections in the super-conducting dipoles, the feed-down from the parasitic sextupoles and the strongly-focused low-beta insertions. A measurement method which lends itself to continuous monitoring and active feedback is therefore investigated. Our approach is based on the beam response to an excitation in the other plane (coupling BTF). The analytical approach [1] shows that a proper measurement protocol allows extracting the global and local complex coefficients of both the difference and sum coupling resonances. In order to prevent any emittance blow-up, the beam is excited at small amplitude outside its eigen-frequencies with smooth transitions (AC-dipole principle). A first experiment in the SPS [2] confirms the approach and its robustness. Strait, J Lamm, M Limon, P Mokhov, N V Sen, T Zlobin, A V Brüning, Oliver Sim Ostojic, R Rossi, L Ruggiero, F Taylor, T ten Kate, H Devred, A Gupta, R Harrison, M Peggs, S Pilat, F Caspi, S Gourlay, S Sabbi, G LHC interaction region design advanced superconducting magnets baseline insertions field quality higher performance design luminosity upgrade second generation designs triplet errors 2003 2003 After the LHC operates for several years at nominal parameters, it will be necessary to upgrade it for higher luminosity. Replacing the low-beta insertions with a higher performance design based on advanced superconducting magnets is one of the most straightforward steps in this direction. Preliminary studies show that, with magnet technology that is expected to be developed by early in the next decade, a factor of 2 to 5 reduction in beta* could be achieved with new insertions, as part of an upgrade aimed at a factor of 10 luminosity increase. In this paper we survey several possible second generation LHC interaction regions designs, which address the expected limitations on LHC performance imposed by the baseline insertions. Jeanneret, J B Schindl, K Jowett, John M 2003 2003 In addition to protons, the LHC will collide beams of heavy ions. The beam intensity in the LHC ring is tightly constrained from below by beam instrumentation (visibility on the beam position monitors in partiuclar) and from above by magnet quench limits, the capabilities of the injectros and beam lifetime. We summarise current plans for beams of lead ions with emphasis on beam dynamics issues, commissioning strategy and the differences from operation with protons. Burkhardt, H Goddard, G Mertens, V 2003 2003 Beams will be transferred from SPS to LHC through two transfer lines, each of over 2.5 km length, equipped with conventional resistive magnets with relatively small apertures. Beam energy densities will be roughly 4 orders of magnitude above the LHC quench limit and about one order above damage level. Possible failures of the various elements in the transfer lines and the SPS machine are discussed, together with results from tracking studies. The benefit from installing protection devices in the transfer lines is discussed, along with related layout aspects and the required protection performance. Assmann, R W Aberle, O Baishev, I S Bruno, L Brugger, M Chiaveri, Enrico Dehning, Bernd Ferrari, A Goddard, B Jeanneret, J B Jiménez, M Kain, V Kaltchev, D I Lamont, M Ruggiero, F Schmidt, R Sievers, P Uythoven, J Vlachoudis, V Vos, L Wenninger, J 2003 2003 The Large Hadron Collider (LHC) will collide proton beams at 14 TeV c.m. with unprecedented stored intensities. The transverse energy density in the beam will be about three orders of magnitude larger than previously handled in the Tevatron or in HERA, if compared at the locations of the betatron collimators. In particular, the population in the beam halo is much above the quench level of the superconducting magnets. Two LHC insertions are dedicated to collimation with the design goals of preventing magnet quenches in regular operation and preventing damage to accelerator components in case of irregular beam loss. We discuss the challenges for designing and building a collimation system that withstands the high power LHC beam and provides the required high cleaning efficiency. Plans for future work are outlined. Braun, Hans Heinrich Döbert, Steffen Syratchev, I V Taborelli, M Wilson, Ian H Wuensch, Walter Achard, Claude 2003 2003 One priority of the CLIC (Compact Linear Collider) accelerating-structure development program has been to investigate ways to achieve accelerating gradients above 150 MV/m. Two main concepts to achieve such high gradients have emerged: reduced surface field geometries and the use of alternative materials. An experimental demonstration of these two concepts has been made in CTFII (CLIC Test Facility) using three 30 GHz accelerating structures: one made entirely from copper, one with copper cavity walls and tungsten irises and one with copper cavity walls and molybdenum irises. A peak accelerating gradient of over 190 MV/m was achieved using the molybdenum-iris structure. The effect of pulse length on achievable gradient was investigated using a novel 'pulse stretcher'. Braun, H Carron, G Döbert, Steffen Gai, W Konecny, R Liu, W Smirnov, A Yu Thorndahl, L Wilson, Ian H Wuensch, Walter Yu, D Newsham, D 2003 2003 A ceramic based power extractor [1] operating at 21 GHz was built by DULY Research Inc. and tested at CTF2, the CERN Linear Collider (CLIC) Test Facility. The structure includes a ceramic extractor section, a 2-output-port, circular-to-rectangular waveguide coupler, and a 3-port rectangular waveguide combiner that provides for a single output waveguide. Results of cold tests and full beam tests are presented and compared with theoretical and numerical models. Rohlev, A Serrano, J Garoby, R 2003 2003 A new VME based system has been developed and built at CERN for the servo loops regulating the field in the linac accelerating structure. It makes use of high speed digital In-phase/Quadrature (IQ) detection, digital processing, and digital IQ modulation. The digital processing and IQ modulation is done in a single PLD. The system incorporates continually variable set points, iterative learning, feed forward as well as extensive diagnostics and other features well suited for digital implementations. Built on a single VME card, it will be first used in the energy ramping RF chain of the CERN Heavy Ion Linac (linac 3) and later for upgrading the present proton linac (linac 2). This system serves also as a prototype for the future Superconducting Proton Linac (SPL). The design principle and the experimental results are described. Wilson, Ian H Wuensch, Walter Raguin, J Y 2003 2003 Two of the main requirements for CLIC 30 GHz accelerating structures are an average accelerating gradient of 150 MV/m and features which suppress long-range transverse and longitudinal wakefields. The main effects that constrain the design of a copper structure are a surface electric field limit of about 300 MV/m, from evidence produced by the CLIC high-gradient testing program, and a pulsed surface heating temperature rise limit estimated to be of the order of 100 K. The interplay between maximum surface electric field, maximum surface magnetic field, transverse-wakefield suppression and RF-to-beam efficiency has been studied in detail. Several structures with a 110° phase advance and rather constant peak surface field distributions have been designed. Different damping-waveguide geometries and waveguide-to-cavity couplings are compared. 2003 2003 The aim of the CLIC Test Facility CTF3 at CERN is to prove the feasibility of key issues of the two-beam based Compact Linear Collider (CLIC) study. In particular, it addresses the generation of a drive beam with the appropriate time structure to produce high power RF pulses at a frequency of 30 GHz. The first major goal of CTF3 was to demonstrate at low charge the combination of successive bunch trains by RF deflectors in an isochronous ring. This bunch frequency multiplication has been successfully performed for various combination factors up to five and will be presented. Assmann, R W Baishev, I S Brugger, M Hayes, M Jeanneret, J B Kain, V Kaltchev, D I Schmidt, F 2003 2003 The computer codes SIXTRACK and DIMAD have been upgraded to include realistic models of proton scattering in collimator jaws, mechanical aperture restrictions, and time-dependent fields. These new tools complement long-existing simplified linear tracking programs used up to now for tracking with collimators. Scattering routines from STRUCT and K2 have been compared with one another and the results have been cross-checked to the FLUKA Monte Carlo package. A systematic error is assigned to the predictions of cleaning efficiency. Now, predictions of the cleaning efficiency are possible with a full LHC model, including chromatic effects, linear and nonlinear errors, beam-beam kicks and associated diffusion, and time-dependent fields. The beam loss can be predicted around the ring, both for regular and irregular beam losses. Examples are presented. Arduini, Gianluigi Baudrenghien, P Bohl, T Collier, Paul Cornelis, K Höfle, Wolfgang Linnecar, Trevor Paul R Shaposhnikova, Elena Tückmantel, Joachim Wenninger, J brightness electron cloud emittance multipacting 2003 2003 During the 2001 run the beam-induced electron-cloud, generating dramatic vacuum pressure increases and fast transverse instabilities, was the main limitation in the achievement of the nominal LHC beam intensity in the SPS. Nominal longitudinal and transverse parameters at the extraction energy (450 GeV) could be achieved only with a single batch and with a maximum bunch population of 0.5×10^11 p. In 2002 the threshold for the onset of the electron cloud in the arcs could be increased from 0.4×10^11 p/bunch to 0.9×10^11 p/bunch by means of a dedicated 10-day 'scrubbing' run with the LHC beam. At the end of this period four LHC batches with design bunch population (1.1×10^11 p) could be injected for each SPS cycle, as foreseen for the nominal filling scenario, without provoking vacuum interlocks. After a series of machine development sessions the LHC beam with nominal intensity could be accelerated to 450 GeV with nominal longitudinal emittance and with transverse emittances close to the design values for the first three batches. The problems encountered with this high brilliance beam and the solutions developed are presented. Arduini, Gianluigi Cornelis, K Höfle, Wolfgang Rumolo, Giovanni Zimmermann, Frank 2003 2003 The electron cloud induced by the LHC beam in the SPS occurs mainly in the dipoles and it is responsible for strong transverse instabilities. In the horizontal plane a coupled bunch mode instability develops in a few tens of turns at injection. Tune shift measurements, mode number and phase space analyses have been performed at different energies and provide information about the electron cloud distribution and its dynamics. In the vertical plane a single bunch head-tail-like instability occurs. The equivalent 'electron-cloud wake field' is inferred from the analysis of the head-tail motion of the bunches of the LHC beam train. Borburgh, Jan Balhan, Bruno Bobbio, Piero Carlier, Etienne Hourican, Michael Masson, Thierry Müller, Tania Prost, Antoine Crescenti, Massimo 2003 2003 The CERN PS electrostatic septum consolidation program is coming to completion after almost 4 years of development. The program was started to fulfil the increased requirements on vacuum performance and the need to reduce the time necessary for maintenance interventions. The new design of septum 31, used for the so-called 'continuous transfer' 5-turn extraction, and the related construction issues will be presented together with the operational experience gained during the PS 2002 run. In addition, the experience of two years of operation with the new generation septum 23, used for a resonant slow extraction, will be briefly discussed. The continued development undertaken since its installation in the PS ring in 2001 will also be described. Angoletta, Maria Elena Belohrad, D Bojtar, L Findlay, A Ludwig, M Marqversen, O Pedersen, F 2003 2003 The CERN AD Low-Intensity Beam Multi-Diagnostics (LIMD) has been upgraded as planned since 2001 by adding tune measurements during ramps and plateaus, based on the Beam Transfer Function (BTF) method. This relies on transversally exciting the beam by a deflector and deriving the BTF and coherence function from FFTs of excitation and beam response recorded by digital receivers (DRX). These, continuously tuned to a betatron sideband, pass data to a digital signal processor (DSP) on the DRX board for data processing. The upgrades discussed also include increased longitudinal frequency range, noise reduction measures and digital flags for setup of Data Acquisition (DAQ) and processing parameters. Roncarolo, Federico Dehning, Bernd 2003 2003 During the SPS high intensity run 2002 with LHC type beam, the breaking of several of the carbon wires in the wire scanners has been observed in their parking position. The observation of large changes in the wire resistivity and thermionic electron emission clearly indicated strong RF heating that was depending on the bunch length. A subsequent analysis in the laboratory, simulating the beam by two probe antennas or by a powered stretched wire, showed two main problems: i) the housing of the wire scanner acts as a cavity with a mode spectrum starting around 350MHz and high impedance values around 700 MHz; ii) the carbon wire used so far appears to be an excellent RF absorber and thus dissipates a significant part of the beam-induced power. Different wire materials are compared with the classical cavity mode technique for the determination of the complex permittivity in the range of 2-4 GHz. As a resonator a rectangular TE01n type device is utilized. Walker, N Kozanecki, Witold Napoly, O Schulte, Daniel Zimmermann, Frank Drozhdin, A I Mokhov, N V Keller, L Markiewicz, T W Maruyama, T Raubenheimer, T O Seryi, Andrei Tenenbaum, P G Woodley, M Blair, G A AIP Conf. Proc. 200-204 693 2004 2004 This report describes studies performed in the framework of the Collimation Task Force organized to support the work of the second International Linear Collider Technical Review Committee. The post-linac beam-collimation systems in the TESLA, JLC/NLC and CLIC linear-collider designs are compared using the same computer code under the same assumptions. Their performance is quantified in terms of beam-halo and synchrotron-radiation collimation efficiency. The performance of the current designs varies across projects, and does not always meet the original design goals. But these comparisons suggest that achieving the required performance in a future linear collider is feasible. Ruggiero, F Zimmermann, Frank Rumolo, Giovanni Papaphilippou, Y LHC luminosity beam beam interaction beam beam tune shift crossing schemes electron cloud flat longitudinal profile intrabeam scattering luminosity proton super bunches tune footprints 2003 2003 Super-bunches are long bunches with a flat longitudinal profile, which could potentially increase the LHC luminosity in a future upgrade. We present example parameters and discuss a variety of issues related to such superbunches, including beam-beam tune shift, tune footprints, crossing schemes, luminosity, intrabeam scattering, and electron cloud. We highlight the benefits, disadvantages and open questions. 2003 2003 We simulate the interaction of a bunch train with either an external wake field, (semi-)trapped ions in a field-free region or in a dipole field, or an electron cloud, on successive turns, using a simplified algorithm with only a small number of macro-particles. We present simulated mode spectra and rise times for the ensuing coupled-bunch instabilities, and show that observations at the KEKB HER are consistent with a horizontal instability driven by carbon monoxide ions in a region without magnetic field. Zimmermann, Frank Oide, K 2003 2003 We compute the longitudinal and transverse wake fields for velocities smaller than c, and examine under which conditions the non-relativistic terms become important. Meot, Francois Rees, Grahame Lemuet, Franck 2003 2003 One important issue in a neutrino factory is the target system for pion production. The A.G. funneling system addressed here consists of four horns, with 1 MW target per horn, followed by a recombination A.G. channel and a FODO decay channel. The transmission of this scheme is analyzed in detail. It is compared with that of a simple solenoid for several sets of optics parameters. This study makes it possible to gain in transmission efficiency in comparison with earlier proposals. Fischer, W Schmidt, F Tomás, R 2003 2003 Theory predicts that resonance driving terms can be determined by harmonic analysis of BPM data recorded after applying single kicks. In recent experiments at the CERN SPS this technique has been succesfully applied to measure coupling and sextupolar resonance terms around the ring. A similar experiment has been carried out in RHIC, BNL, to proove the feasibility of this measurement in this more complex machine. Results of the experiment are presented, including a direct measurement of sextupolar resonances and a comparison to the model. Schmidt, F Hayes, M Tomás, R 2003 2003 This paper represents the completion of the series of sextupole driving terms measurements in the SPS which started in June 1998. The following two items have been missing from earlier reports on these studies: measuring two dimensional resonances and the resonance phase. The possible dependence of these terms on collective effects was studied. Lastly, the experiment was performed at two different energies of 26 and 80 GeV, to suppress energy dependencies. Comparisons to the tracking model show excellent agreement, proving that this technique is ready for other machines. Faus-Golfe, Angeles Tomas, Rogelio Arduini, Gianluigi Zimmermann, Frank 2003 2003 In 2002, nonlinear chromaticity, coupling, amplitude-dependent detuning, chromatic phase advance, resonance driving terms, and off-energy orbits were measured in the CERN SPS at 26 GeV/c. The optics model has been updated by adjusting the strengths of nonlinear field errors in the dipoles and quadrupoles, so as to reproduce the measured nonlinear chromaticity. We compare the field errors deduced in 2002, measuring over a larger momentum range, with those found in 2001 and 2000. The resolution is improved by averaging over all turn-by-turn position monitors in the ring instead of using a single dedicated pick up ('tune meter'). Computations using two different optics codes, MAD and SAD, indicate the sensitivity to matching algorithm and magnet representation. To validate the nonlinear optics model, the predicted tune shifts with transverse amplitude, driving terms of low-order resonance, etc., are compared with direct measurements. Schulte, Daniel Walker, N White, G 2003 2003 The tolerances on the beams as they collide at the interaction point of the TESLA linear collider are very tight due to the nano-metre scale final vertical bunch spot sizes. Ground motion causes the beams to increase in emittance and drift out of collision leading to dramatic degradation of luminosity performance. To combat this, both slow orbit and fast intra-train feedback systems will be used. The design of these feedback systems depends critically on how component misalignment effects the beam throughout the whole accelerator. A simulation has been set up to study in detail the accelerator performance under such conditions by merging the codes of PLACET, MERLIN and GUINEA-PIG together with Simulink code to model feedback systems, all under a Matlab environment. Schulte, Daniel Wolski, A Tenenbaum, P G Seryi, Andrei Woodley, M Walker, N 2003 2003 One of the major challenges facing the proposed high-energy linear e^+e^ colliders is the preservation of the extremely small vertical emittance from the damping rings to the interaction point (IP). This emittance must be transported through bunch compression sections, the main linac and finally through the beam delivery system to the IP. Historically, the beam dynamics issues of each subsystem have been studied quasi-independently, with the beam conditions and tolerances being specified at the boundaries. As part of the recent International Linear Collider Technical Review Committee, new simulation tools have been developed to simulate the beam transport through the integrated system, including static and dynamic errors, stabilization systems, and tuning algorithms. Seryi, Andrei Hendrickson, L Raubenheimer, T O Tenenbaum, P G Woodley, M Schulte, Daniel 2003 2003 The performance of high energy linear colliders depends critically on the stability with which they can maintain the collisions of nanometer-size beams. Ground motion and vibration, among other effects, will produce dynamic misalignments which can offset the beams at the collision point. A system of train-to-train and intra-train beam-beam feedbacks, possibly combined with additional beam-independent active systems, is planned to compensate for these effects. Extensive simulation studies of ground motion and luminosity stabilization have been performed as part of the work of the International Linear Collider Technical Review Committee [1]. This paper presents a comparison of the expected performance for TESLA, JLC/NLC and CLIC under various assumptions about feedbacks and the level of ground motion. Schulte, Daniel Walker, N 2003 2003 At the heart of the TESLA linear collider are the two 10 km long superconducting linacs. A linac is constructed from 858 cryomodules each containing 12 nine-cell 1.3 GHz superconducting cavities. 355 quadrupoles provide the necessary beam focusing. The advantages of low-frequency superconducting RF in terms of wakefield behaviour are well known, and the TESLA alignment tolerances are relatively loose. However, the effects of cavity tilts and their impact of the linac beam-based alignment algorithms have until recently not been fully investigated. In addition, the strong sensitivity to correlated emittance growth due to the high beam-beam disruption parameter makes it desirable to control the linac emittance down to a few percent. In this report we discuss various static tuning algorithms and present new simulation results. Discussions of the relative merits and applicability of the methods is also discussed. Schulte, Daniel 2003 2003 Wakefield and dispersive effects in the main linac of a future linear collider can strongly affect the beam-beam interaction at the collision point [1]. For a static situation, this paper investigates the luminosity for realistic bunches in the case of the TESLA, NLC and CLIC projects assuming different degrees of collision optimisation. A part of this work was performed for the International Linear Collider Technical Review Committee [2]. Grote, H Schmidt, F 2003 2003 The development of MAD8 has been suspended for many years. At the start of 2001 it was decided to revive it and put it into a more maintainable form since it is needed for the LHC during design and operation. In particular, the home grown dynamic data management in Fortran77 limits further extensions, and is not guaranteed to survive for another ten years. In fact, MAD-X has been originally planned to be a copy of MAD8 with a more modern data management. The data structures that hold the information about the accelerator, and the interfaces to the modules are written in C which provides the dynamic data structures needed. Contrary to MAD8, the MAD-X modules are designed as truly independent entities; they are much simpler and therefore better maintainable. It was also thought important to spread the responsibility for the various MAD-X modules among several accelerator physicists. Lastly, an upgrade of MAD-X is being planned to improve the physics models and to include map related tools using Etienne Forest's PTC (Polymorphic Tracking Code) code. A fully operational and documented version is available via the MAD-X web site. Hofmann, I Franchetti, Giuliano Giovannozzi, Massimo Martini, M Métral, Elias 2003 2003 As a first step of a space charge - nonlinear resonance benchmarking experiment over a large number of turns, beam loss and emittance evolution were measured over 1 s on a 1.4 GeV kinetic energy flat-bottom in the presence of a single octupole. By lowering the working point towards the resonance a gradual transition from a loss-free core emittance blow-up to a regime dominated by continuous loss was found. Our 3D simulations with analytical space charge show that trapping on the resonance due to synchrotron oscillation causes the observed core emittance growth as well as halo formation, where the latter is explained as the source of the observed loss. Giovannozzi, Massimo Martini, M Métral, Elias Métral, G Steerenberg, R 2003 2003 Several beam dynamics codes are used in the design of the next generation of high beam power accelerators. They are all capable of simulating the full six-dimensional motion through a machine lattice in the presence of strong space-charge effect and beam-to-wall interaction. A key issue is the validation of these codes. This is usually accomplished by comparing simulation results against available theories, and more importantly, against experimental observations. To this aim, a number of well-defined test cases, obtained by accurate measurements made in existing machines, are of high interest. This paper reports and discusses precise measurements of transverse emittance blow-up due to space-charge-induced crossing of the integer or half-integer stop band. Métral, Elias 2003 2003 The stability criterion for the longitudinal microwave instability in bunched lepton beams is derived using the mode-coupling formalism and taking into account the potential-well distortion. The new formula yields an intensity threshold which can be higher than the one given by the Keil-Schnell-Boussard approximation by a large factor. This result may explain why the classical instability threshold has been exceeded in some lepton machines. Zimmermann, Frank Korostelev, Maxim S 2003 2003 The CLIC damping ring design is optimized to produce a beam with ultra low emittances. The lattice for such a machine requires a small value of the optical functions, a large number of compact arc cells and, for the chromatic correction, strong sextupoles, that introduce significant nonlinearities, decreasing the dynamic aperture. In this paper, the nonlinear optimization of the damping ring lattice is described. Herr, Werner Jones, F W 2003 2003 In beam-beam macroparticle simulations for collider rings, the accurate determination of the incoherent spectrum and potentially unstable coherent modes requires (1) large numbers of collisions, and (2) accurate electric field solutions at each collision. On single processor, a self consistent simulation typically uses a 2D model of the beam-beam interaction in order to achieve a reasonable computation time, however for the long (~0.3m) bunches in the LHC we wish to include the 3rd dimension in order to account for effects such as longitudinal motion, crossing angle, and the beam size and density variations. We describe here a parallel algorithm, developed with MPI on a small commodity Linux cluster, to extend our simulation code BeamX from 2D to 3D using longitudinal subdivision (slicing) of the bunches. In addition to an overview of the computational framework, we present performance results and initial test cases. Gruber, P Torun, Y 2003 2003 Dark currents are unwanted electron currents that stem from surface electrons that are emitted in rf cavities and accelerated in their electric field. This paper describes a novel technique to produce a 2D-image of dark currents and presents some results. Ordinary black and white photographic paper has been exposed to dark current electrons stemming from an 805Mhz cavity in the Lab G facility at Fermilab. This cavity is a closed-cell cavity in a 2.5 T solenoidal field parallel to the electrical field. Thin rf and vacuum windows allow the electrons to exit the cavity. Due to the focusing effect of the magnetic field, a sharp picture of the sources of the dark currents is obtained. Single emitters, surrounded by regions of virtually no dark current, can be clearly identified. Cappi, R Giovannozzi, Massimo Martini, M Métral, Elias Métral, G Steerenberg, R Müller, A S 2003 2003 The CERN Proton Synchrotron machine is built using combined function magnets. The control of the linear tune as well as the chromaticity in both planes is achieved by means of special coils added to the main magnets, namely two pole-face-windings and one figure-of-eight loop. As a result, the overall magnetic field configuration is rather complex not to mention the saturation effects induced at top-energy. For these reasons a linear model of the PS main magnet does not provide sufficient precision to model particle dynamics. On the other hand, a sophisticated optical model is the key element for the foreseen intensity upgrade and, in particular, for the novel extraction mode based on adiabatic capture of beam particles inside stable islands in transverse phase space. A solution was found by performing accurate measurement of the nonlinear tune as a function of both amplitude and momentum offset so to extract both linear and nonlinear properties of the lattice. In this paper the measurement results are presented and the derived optical model is discussed in detail. Burkhardt, H Koschik, A Rumolo, Giovanni Zimmermann, Frank Zotter, Bruno W 2003 2003 Coherent tune shifts with current have been measured in the SPS with single bunches and two bunches at varying distances between them. The measurements showed the usual negative slope with intensity in the vertical plane and a small positive one in the horizontal direction. The results are compared with theoretical predictions which include estimates of tune shifts due to the impedance of resistive vacuum chambers with non-circular geometry and finite wall thickness. Burkhardt, H Rumolo, Giovanni Zimmermann, Frank 2003 2003 Space charge effects generally play a rather minor role in high energy machines like the SPS. Rather high space charge tune shifts may however become unavoidable in the SPS for the heavy ion beams required by the LHC. We describe recent measurements performed with intense proton beams in the SPS. The space charge effects were enhanced by a reduction of the injection energy from 26 to 14 GeV. Braun, Hans Heinrich Schulte, Daniel 2003 2003 Recent experimental results on normal conducting RF structures indicate that the scaling of the gradient limit with frequency is less favourable than what was believed. We therefore reconsider the optimum choice of RF frequency and iris aperture for a normal conducting, two-beam linear collider with E_CMS=3 TeV, a loaded accelerating gradient of 150 MV/m and a luminosity of 8 10^34 cm-^2 s^-1. The optimisation criterion is minimizing overall RF costs for investment and operation with constraints put on peak surface electric fields and pulsed heating of accelerating structures. Analytical models are employed where applicable, while interpolation on simulation program results is used for the calculation of luminosity and RF structure properties. Guignard, G Assmann, R W Schulte, D Coosemans, W Wilson, I Zimmermann, F Redaelli, Stefano 2003 2003 The Compact Linear Collider (CLIC) aims at colliding e^+e^- beams at 1:5 TeV with effective transverse spot sizes of 60nm (horizontal) times 0:7nm (vertical). Strict stability tolerances must be respected in order to achieve a sufficient overlap of the two colliding beams. A stability test stand has been set up at CERN, bringing latest stabilization technology to the accelerator field. Using this technology, a CLIC prototype magnet was stabilized in a normal CERN working environment to less than 1-nm vertical RMS motion above 4 Hz. Detailed simulations of the time-dependent luminosity performance of CLIC are discussed. They include the beam-beam interaction, the beam-based feedbacks and the measured data on magnet stability Frischholz, Hans Valuch, D 2003 2003 For possible future accelerator projects, as, e. g., the Super-Conducting Proton Linac, SPL, at CERN, it would be desirable to reuse as much of the LEP/RF equipment as possible. In the SPL, as in other proposed proton linacs, pulsed operation is required with RF pulse-lengths varying between 1 and 3 ms and a pulse repetition rate of 50 Hz. The LEP klystrons are equipped with a modulation anode by means of which their beam current and hence the output power can be controlled. In LEP the klystron output power had to be varied very slowly when the energy was ramped. In order to keep a high efficiency also in pulsed mode the rise- and fall-time of the beam pulse in the klystron should be considerably less than 100µs. This goal was achieved by modifying the tetrode modulator, the HV line between modulator and klystron, and the filter network of the HV power supply. SPICE simulations were performed to evaluate the optimum values of capacitors and inductors in the HV filtering network of the LEP 100kV, 40A power converter when a specified DC pulse shape is required and up to eight klystrons are to be powered by one HV supply. These simulations are presented, together with the experimental results obtained on a modified LEP klystron/power converter assembly. Caspers, Friedhelm Iriso-Ariz, U Mostacci, A 2003 2003 For frequencies below 10 MHz the classical two wire transmission line method is subject to difficulties in sensitivity and measurement uncertainties. Thus for evaluation of the low frequency transverse impedance properties of the LHC dump kicker a modified version of the two wire transmission line has been used. It consists, in the present case, of a 10 turn loop of approximately 1 meter length and 2 cm width. The change of input impedance of the loop is measured as a function of the surroundings and by using a proper reference (metallic beampipe) these changes are converted into a meaningful transverse beam coupling impedance. Measurements of several calibration objects have shown close agreement with theoretical results. Gyr, M Uythoven, J Veness, R Weterings, W Goddard, B 2003 2003 The LHC beam dumping system must safely abort the LHC beams under all conditions, including those resulting from abnormal behaviour of machine elements or subsystems of the beam dumping system itself. The extraction channels must provide sufficient aperture both for the circulating and extracted beams, over the whole energy range and under various beam parameters. These requirements impose tight constraints on the tolerances of various extraction channel components, and also on the allowed range of beam positions in the region of these components. Operation of the beam dumping system under various fault states has been considered, and the resulting apertures calculated. After describing briefly the beam dumping system and the extraction channel geometry, the various assumptions made in the analysis are presented, before deriving tolerance limits for the relevant equipment and beam parameters. Cappi, R Giovannozzi, Massimo Martini, M Métral, M Métral, G Steerenberg, R Müller, A S CERN PS adiabatic beam trapping adiabatic capture multi turn extraction octupoles sextupoles stable islands transverse phase space 2003 2003 Recently a novel approach to the problem of multi-turn extraction was proposed. It consists of splitting the beam by adiabatic capture inside stable islands created in the transverse phase space by sextupoles and octupoles. Numerical simulations indicate that such a technique should be feasible and potentially superior to the method presently used at the CERN Proton Synchrotron. During 2002, intense efforts were devoted to the experimental verification of this newly proposed extraction mode. Finally, beam capture into the islands was observed. In this paper, the extraction principle is briefly reviewed and the experimental results are presented and discussed in detail. Cappi, R Giovannozzi, Massimo 2003 2003 Recently a novel approach has been proposed aimed at performing multi-turn extraction from a circular machine. Such an approach consists of splitting the beam by means of stable islands created in transverse phase space by nonlinear magnetic elements such as sextupoles and octupoles. Provided a slow time-variation of the linear tune is applied, adiabatic with respect to the betatron motion, the islands can be moved in phase space and eventually charged particles may be trapped inside the stable structures. This generates a certain number of well-separated beamlets. Originally, this principle was successfully tested using a fourth-order resonance. In this paper the approach is generalised to other type of resonances and some examples of adiabatic capture performed by using various low-order resonances are presented and described in detail.