| Paper | Title | Page |
|---|---|---|
| MOPLS001 | Large Scale Beam-beam Simulations for the CERN LHC using Distributed Computing | 526 |
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| We report on a large scale simulation of beam-beam effects for the CERN Large Hadron Collider (LHC). The stability of particles which experience head-on and long-range beam-beam effects was investigated for different optical configurations and machine imperfections. To cover the interesting parameter space required computing resources not available at CERN. The necessary resources were available in the LHC@home project, based on the BOINC platform. At present, this project makes more than 40000 hosts available for distributed computing. We shall discuss our experience using this system during a simulation campaign of more than six months and describe the tools and procedures necessary to ensure consistent results. The results from this extended study are presented and future plans are discussed. | ||
| MOPLS002 | The Study of the Machine-induced Background and its Applications at the LHC | 529 |
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| We present the recent advances in the analysis of the machine-induced background generation and formation at the LHC. Different aspects of the study of the machine background problem at the LHC are reviewed, including the background production at the different stages of the machine operation, the role and influence on the background from the collimators in the experimental insertions and the background shielding. The potential use of the machine background for the purposes of detector testing and alignment is also discussed. | ||
| MOPLS003 | Tertiary Halo and Tertiary Background in the Low Luminosity Experimental Insertion IR8 of the LHC | 532 |
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| In our report we present the results for numerical simulation of tertiary halo and tertiary background in the LHC. We study the case of the proton losses in the betatron cleaning insertion IR7 with the subsequent tertiary halo generation in the downstream experimental insertion IR8. We analyze the formation of tertiary background in the experimental area of the IR8 and evaluate the performance of the machine-detector interface shielding with respect to this source of the background. The results obtained are compared with the previous estimates of the machine-induced background in the low luminosity insertions of the LHC, and the balance between different sources of the background is discussed. | ||
| MOPLS004 | Estimation and Analysis of the Machine-induced Background at the TOTEM Roman Pot Detectors in the IR5 of the LHC | 535 |
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| The problem of background generation in the experimental insertion IR5 of the LHC during machine operation in the dedicated TOTEM mode with low intensity beams and the specially designed beta* = 1540 m optics is discussed. The sources of the machine-induced background in the IR5 forward physics areas are identified and their relative importance is evaluated. The results of the background simulation in the IR5 are presented, based on the most recent estimates of the residual gas density for TOTEM beam conditions. The methods for background analysis and rejection are explained. | ||
| MOPLS005 | A Staged Approach to LHC Commissioning | 538 |
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| After a brief reminder of the performance goals of the LHC, the overall strategy proposed for commissioning the machine with protons is presented. A thorough commissioning of the LHC hardware systems, presently ongoing, will lead into a staged approach for the first two years of operation with the beam, allowing both the complexity of the machine operation and the destructive power of the high intensity beams to be introduced in a controlled, incremental manner. The demands on the annual machine schedule are discussed, including the need to incorporate dedicated running for ions and proton-proton total cross section measurements. An important pre-commissioning milestone is the injection of the beam into a sector of the partially completed LHC; the motivation and tests planned are briefly summarised. | ||
| MOPLS006 | Adaptive RF Transient Reduction for High Intensity Beams with Gaps | 541 |
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| When a high-intensity beam with bunch-trains and gaps passes a cavity with a high-gain vector feedback enforcing a constant voltage, large transients appear, stressing the RF high power hardware and increasing the trip rate. By modulating the cavity voltage with a varying periodic waveform (set-function), the RF power can be made constant while still preserving the high feedback gain. The average cavity voltage is conserved but bunches have to settle at slightly shifted positions. A method is derived to obtain this set-function in practice while making no assumptions or measurements of the beam or RF parameters. Adiabatic iterations are made, including the whole machine as an analog computing device, using all parameters as they are. A computer simulation shows the success of the method. | ||
| MOPLS007 | Monitoring Heavy-ion Beam Losses in the LHC | 544 |
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| The LHC beam loss monitor (BLM) system, primarily designed for proton operation, will survey particle losses and dump the beam if the loss rate exceeds a threshold expected to induce magnet quenches. Simulations of beam losses in the full magnet geometry allow us to compare the response of the BLMs to ion and proton losses and establish preliminary loss thresholds for quenches. Further simulations of beam losses caused by collimation and electromagnetic interactions peculiar to heavy ion collisions determine the positions of extra BLMs needed for ion operation in the LHC. | ||
| MOPLS008 | Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets | 547 |
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| The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS collimator forms part of the TCDQ system. The requirement to place the TCDQ and TCS jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed. | ||
| MOPLS009 | The LHC as a Proton-nucleus Collider | 550 |
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| Following its initial operation as a proton-proton (p-p) and heavy-ion (208Pb82+ - 208Pb82+) collider, the LHC is expected to operate as a p-Pb collider. Later it may collide protons with other lighter nuclei such as 40Ar18+ or 16O8+. We show how the existing proton and lead-ion injector chains may be efficiently operated in tandem to provide these hybrid collisions. The two-in-one magnet design of the LHC main rings imposes different revolution frequencies for the two beams in part of the magnetic cycle. We discuss and evaluate the consequences for beam dynamics and estimate the potential performance of the LHC as a proton-nucleus collider. | ||
| MOPLS010 | Measurement of Ion Beam Losses Due to Bound-free Pair Production in RHIC | 553 |
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| When the LHC operates as a Pb82+ ion collider, losses of Pb81+ ions, created through Bound-free Pair Production (BFPP) at the collision point, and localized in cold magnets, are expected to be a major luminosity limit. With Au79+ ions at RHIC, this effect is not a limitation because the Au78+ production rate is low, and the Au78+ beam produced is inside the momentum aperture. When RHIC collided Cu29+ ions, secondary beam production rates were lower still but the Cu28+ ions produced were predicted to be lost at a well-defined location, creating the opportunity for the first direct observation of BFPP effects in an ion collider. We report on measurements of localized beam losses due to BFPP with copper beams in RHIC and comparisons to predictions from tracking and Monte Carlo simulation. | ||
| MOPLS011 | Investigations of the Parameter Space for the LHC Luminosity Upgrade | 556 |
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| Increasing the LHC luminosity by a factor of ten is a major challenge, not so much for the beam optics but certainly for the beam-beam long-range interactions and even more for the technology and layout: the quadrupole gradient, its physical aperture and tolerance to the energy deposition shall be significantly increased; its distance to the crossing point shall be reduced if the particle detectors can allow it. To help identifying consistent solutions in this multi-dimensional constrained space, a algorithmic model of an LHC insertion was prepared, based on the present LHC layout, i.e., "quadrupole first" and small crossing angle. The model deals with the layout, the beam optics, the beam-beam effect, the superconductor field margins and the peak heat deposition in the coils. The approach is simplified to allow a large gain in the design/computation time for optimization. First results have shown the need to use the Nb3Sn technology (or a material of equivalent performance) to reach the performance goal. In this paper, the model is refined to take into account the quench levels and temperature margins. The optimal insertions within the framework of this approach are identified. | ||
| MOPLS012 | The LHC Sector Test | 559 |
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| The proposal to inject beam into a sector of the partially completed LHC is presented. The test will provide an important milestone, force preparation of a number of key systems, and allow a number of critical measurements with beam. The motivation for the test is discussed, along with the proposed beam studies, the radiation issues and the potential impact on ongoing installation. The demands on the various accelerator systems implicated are presented along with the scheduling of the preparatory steps, the test itself and the recovery phase. | ||
| MOPLS013 | The Roman Pot for LHC | 562 |
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| The LHC machine will be equipped with Roman Pot stations by the TOTEM experiment to measure the pp total cross section and to study the elastic scattering and the diffraction physics processes. TOTEM needs to bring the pots, equipped with cold micro-strip silicon detectors, as a close as possible to the high intensity beam of LHC. Because of the special optics required by TOTEM, the beam has a transversal size of only 80 microns at the Roman pot locations. Safety considerations for the machine protection set the limit to 10 ?, i.e. 800 μm. Such unprecedented parameters, together with the issues of the Ultra High Vacuum and the RF compatibility, and the harsh radiation environment, have requested a design for the Roman Pot system, which is compliant with the LHC requirements and operations. To better meet also the challenging requirements of TOTEM, a technology development of a thin window has been pursued and a flatness of less than 50 μm has been obtained by brazing foil of 150 μm thicknesses. A prototype of the Roman Pot and of the thin window box have been manufactured and tested. We describe the main issues of the final design and the results of the preliminary tests. | ||
| MOPLS014 | Lifetime Limit from Nuclear Intra-bunch Scattering for High-energy Hadron Beams | 565 |
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| We derive an approximate expression for the nuclear scattering rate inside a bunched hadron beam. Application to the LHC suggests that the loss rate due to nuclear scattering can be significant in high-energy proton or ion storage rings. | ||
| MOPLS015 | Quality Control Techniques Applied to the Large Scale Production of Superconducting Dipole Magnets for LHC | 568 |
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| The LHC accelerator, under construction at CERN, is characterized by the use on a large scale of high field superconducting dipoles: the 27-km ring requires 1232 15-m long dipole magnets designed for a peak field of 9 T. The coils are wound with Rutherford-type cable based on copper-stabilized Nb-Ti superconductors and will be operated at 1.9 K in pressurized superfluid helium. The challenge that had to be faced has been an efficient, cost-effective and reproducible mass production to very tight tolerances: the field quality must be better than 10-4 and the geometry of the cold bore tube and magnet controlled to 0.1 mm over the whole length, any deviation being liable to induce delays and significant cost increase. This paper presents the main methods and tools chosen to face successfully this challenge: some methods were foreseen in the technical specification, others were implemented based on the experience gained in several years of fabrication. | ||
| MOPLS016 | LHC IR Upgrade: A Dipole First Option with Local Chromaticity Correction | 571 |
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| In the framework of the LHC Luminosity Upgrade, we develop a new layout of the interaction region (IR) with betastar equal to 25cm in which the combination-separation dipoles come first with respect to the triplet assembly (dipole first) in opposition of the nominal layout (quadrupole first). The new layout presents several advantages (separate channel for multipole errors, straightforward crossing angle scheme, early separation of the beam). The payoff is a large beta function in the triplet, which enhances the chromaticity and other non-linear effects. We investigate options for local chromaticity correction and their effects on long-term stability. | ||
| MOPLS017 | A Low Gradient Triplet Quadrupole Layout Compatible with NbTi Magnet Technology and Betastar=0.25m | 574 |
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| The paper presents a triplet layout option with long (ca. 100 m total triplet length), low gradient (45 T/m to 70 T/m) quadrupole magnets. Assuming a maximum magnet diameter of 200mm, the peak coil field at the magnet coils still remains below 7 T which is still compatible with conventional NbTi magnet technology. The peak beta function inside the triplet magnets reaches 18 km and the configuration therefore requires an additional chromaticity correction scheme similar to a dipole first layout option. However, at the same time, the presented solution provides an interesting alternative to a high gradient triplet layout which requires the new Nb3Ti magnet technology. | ||
| MOPLS018 | High-order Effects and Modeling of the Tevatron | 577 |
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| The role and degree of nonlinear contributions to machine performance is a controversial topic in current collider operations and in the design of future colliders. A high-order model has been developed of the Tevatron in COSY, which includes the strongest sources of nonlinearities. Signatures of nonlinear behavior are studied and compared with performance data. The observed nonlinear effects are compared before and after implemention of nonlinear correction schemes. | ||
| MOPLS020 | Rad-hard Luminosity Monitoring for the LHC | 580 |
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| Luminosity measurements at the high luminosity points of the LHC are very challenging due to the extremely high radiation levels in excess of 1 GGy/yr. We have designed an ionization chamber that uses a flowing gas mixture and a combination of metals and ceramics. With such a choice, an additonal challenge is achieving the necessary speed to be able to resolve bunch-by-bunch luminosity data. We present the design, analysis and experimental results of the early demonstration tests of this device. | ||
| MOPLS021 | Beam Pipe Desorption Rate in RHIC | 583 |
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| Increase of beam intensity in RHIC has caused several decades of pressure rises in the warm sections during operation. This has been a major factor limiting the RHIC luminosity. About 250 meters of NEG coated beam pipes have been installed in many warm sections to ameliorate this problem. Beam ion induced desorption is one possible cause of pressure rises. A series beam studies in RHIC has been dedicated to estimate the desorption rate of various beam pipes (regular and NEG coated) at various warm sections. Correctors were used to generate local beam losses and consequently local pressure rises. The experiment results are presented and analyzed in this paper. | ||
| MOPLS022 | On the Feasibility of Polarized Heavy Ions in RHIC | 586 |
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| Heavy nonspherical ions such as uranium have been proposed for collisions in RHIC. When two such ions collide with their long axes aligned, then the plasma density might be as much as 60% higher. Since the collisions might have any orientation of the two nuclei, the alignment of the nuclei must be inferred from a complicated unfolding of multiplicity distributions. Instead, if it is possible to polarize the ions and control the orientation in RHIC, then a much better sensitivity could be obtained. This paper investigates the manipulation of such polarized ions with highly distorted shapes in RHIC. Several ion species are considered as possibilities with either full or partial Siberian snakes in RHIC. | ||
| MOPLS023 | Status of Fast IR Orbit Feedback at RHIC | 589 |
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| To compensate modulated beam-beam offsets caused by mechanical vibrations of IR triplet quadrupoles at frequencies around 10 Hz, a fast IR orbit feedback system has been developed. We report design considerations and recent status of the system. | ||
| MOPLS024 | RHIC Performance as Polarized Proton Collider in Run-6 | 592 |
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| The Relativistic Heavy Ion Collider in Run-6 was operating in polarized proton mode. With two Siberian Snakes per ring, the polarized protons were brought into collisions at 100 Gev and 31.2 Gev energies. The control of polarization orientation at STAR and PHENIX experiments was done using helical spin rotators. Physics studies were conducted with longitudinal, vertical and radial beam polarization at collision points. This paper presents the performance of RHIC as a polarized proton collider in the Run-6 with emphasis on beam polarization and luminosity issues. | ||
| MOPLS025 | Experience in Reducing Electron Cloud and Dynamic Pressure Rise in Warm and Cold Regions in RHIC | 595 |
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| Significant improvement has been achieved for reducing electron cloud and dynamic pressure rise at RHIC over several years; however, there remain to be factors limiting luminosity. The large scale application of non-evaporable getter (NEG) coating in RHIC has been proven effective in reducing electron multipacting and dynamic pressure rise. This will be reported together with the study of the saturated NEG coatings. Since beams with increased intensity and shorter bunch spacing became possible in operation, the electron cloud effects on beam, such as the emittance growth,are an increasing concern. Observations and studies are reported. We also report the study results relevant to the RHIC electron cloud and pressure rise improvement, such as the effect of anti-grazing ridges on electron cloud in warm sections, and the effect of pre-pumping in cryogenic regions. | ||
| MOPLS026 | Monitoring of Interaction-point Parameters using the 3-dimensional Luminosity Distribution Measured at PEP-II | 598 |
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| The 3-D luminosity distribution at the IP of the SLAC B-Factory is monitored using e+ e- -> e+ e-, mu+ mu- events reconstructed online in the BaBar detector. The transverse centroid and spatial orientation of the luminosity ellipsoid provide a reliable monitor of IP orbit drifts. The longitudinal centroid is sensitive to small variations in the average relative RF phase of the beams and provides a detailed measurement of the phase transient along the bunch train. Relative variations in horizontal luminous size are detectable at the micron level. The longitudinal luminosity distribution depends on the e± overlap bunch length and the vertical IP beta-function beta*y. In addition to continuous online monitoring of all the IP parameters above, we performed detailed studies of their variation along the bunch train to investigate a temporary luminosity degradation. We also used controlled variations in RF voltage and beam current to extract separate measurements of the e+ and e- bunch lengths. The time-history of the beta*y measurements, collected over a year of routine high-luminosity operation, are compared with HER & LER phase-advance data periodically recorded in single-bunch mode. | ||
| MOPLS027 | Beam-beam Simulations for a Single Pass SuperB-factory | 601 |
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A study of beam-beam collisions for an asymmetric single pass SuperB-Factory is presented*. In this scheme an electron and a positron beam are first stored and damped in two damping rings, then extracted, compressed and focused to the IP. After collision the two beams are re-injected in the DR to be damped and extracted for collision again. The explored beam parameters are similar to those used in the design of the International Linear Collider, except for the beam energies. Very flat beams and round beams were compared in the simulations, with the GuineaPig code**, in order to optimize both luminosity performances and beam blow-up after collision. With such approach, luminosities of the order of 1036 /(cm2 sec) can be achieved.
*http://arxiv.org/abs/physics/0512235.**D. Schulte. “Study of electromagnetic and hadronic background in the Interaction Region of the TESLA Collider”, PhD Thesis, Hamburg, 1996. |
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| MOPLS028 | DAFNE Status Report | 604 |
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| The operation of DAFNE, the 1.02 GeV c.m. e+e- collider of the Frascati National Laboratory with the KLOE detector, started in April 2004 has been concluded at the end of March 2006 with a total delivered luminosity of 2 fb-1 on the peak of the Phi resonance, 0.2 fb-1 off peak and a high statistics scan of the resonance. The best performances of the collider during this run have been a peak luminosity of 1.5 1032 cm-2s-1 and a daily delivered luminosity of 10 pb-1. The KLOE detector has been removed from one of the two interaction regions and its low beta section substituted with a standard magnetic structure, allowing for an easy vertical separation of the beams, while the FINUDA detector has been moved onto the second interaction point. Several improvements on the rings have also been implemented and are described together with the results of machine studies aimed at improving the collider efficiency and testing new operating conditions. | ||
| MOPLS029 | Preliminary Study of a Crab Crossing System for DAFNE | 607 |
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| The implementation of a crab crossing scheme at the Frascati Phi-factory DAFNE is under consideration, together with several other ideas and upgrades to increase the collider luminosity. The crab crossing is beneficial to the luminosity because it is expected to optimize the geometrical superposition of the colliding bunches and to weaken the synchro-betatron beam-beam resonances. The basic specifications of such a system, the expected luminosity increase, a preliminary design of the crab cavities and the architecture of the dedicated RF system are presented. | ||
| MOPLS030 | Recent Progress of KEKB | 610 |
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| We summarize the machine operation of KEKB during the past one year, focusing on progress for this period. | ||
| MOPLS031 | Beam Orbit Control System for the KEKB Crab Cavities | 613 |
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| KEKB is an electron-positron collider with an 8 GeV electron ring (HER) and a 3.5 GeV positron ring (LER). The two beams currently collide at one interaction point with a finite horizontal crossing angle of 11 mrad. The design luminosity of 10 /nb/sec was first reached in May 2003 and the peak luminosity exceeded 16 /nb/sec in December 2005. Simulations predict a luminosity boost if a crab crossing scheme is introduced. The installation of two superconducting crab cavities, one in each ring, is scheduled in March 2006 in order to implement the crab crossing scheme. For stable operation, the horizontal beam position in the crab cavity must be carefully controlled. This is needed to avoid loss of control of the crabbing mode field due to beam loading. A beam position feedback system at the crab cavity has been prepared and tested. Its performance will be discussed in this report. | ||
| MOPLS032 | Beam-beam Limit and the Degree of Freedom | 616 |
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| Beam-beam limit is caused by chaotic diffusion due to the strong nonlinear force of beam-beam interaction. Degree of freedom in the colliding system is essential for the diffusion. We discuss the diffusion using several models. | ||
| MOPLS033 | Beam-beam Limit and Feedback Noise | 619 |
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| Beam-beam interaction is strongly nonlinear, therefore particles in the beam experience chaotic motion. A small noise can be enhanced by the chaotic nature, with the result that unexpected emittance growth can be observed. We study the noise of transverse bunch by bunch feedback system and related luminosity degradation. Similar effects caused by crab cavity noise is also discussed. | ||
| MOPLS037 | Beams Injection System for e+e- Collider VEPP-2000 | 622 |
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| Electron-positron collider VEPP-2000 is under commissioning at the Budker Institute of Nuclear Physics. The paper presents the injection system of the collider delivering the beam from the booster storage ring BEP with maximum energy 900 MeV. A matching of the beam injection with the storage ring optics is done with respect to a nonlinear kicker field. Features of beam diagnostic and transfer line magnets including pulse septums (100 mksec; 30 kGs) and fast kickers (20 nsec; 70 kV) are described. Results of the magnetic measurements and their comparison to calculated data are given. | ||
| MOPLS038 | Beam Energy Calibration in Experiment on Precise Tau Lepton Mass Measurement at VEPP-4M with KEDR Detector | 625 |
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| Experiment on mass measurement of tau lepton requires an absolute energy calibration. The resonant depolarization technique is used for most accurate (1 keV) but once at a time energy calibration. The measured energy is used for calibration of the germanium detector for Compton backscattering energy monitoring. The developed Compton backscattering facility allows continuous energy monitoring with accuracy of 50 keV for 10 minutes of data acquisition. The tau lepton threshold is in the vicinity of integer spin resonance, which minimizes polarization lifetime in the presence of vertical orbit distortions. Therefore, spin matching of the VEPP-4M is required. The achieved lifetime is sufficient for absolute energy calibration. | ||
| MOPLS040 | Magnet Structure of the VEPP-2000 Electron-positron Collider | 628 |
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| Electron-positron collider VEPP-2000 with beam energy up to 1 GeV is under commissioning at Budker Institute. This paper presents magnetic elements of the storage ring including 13T focusing superconducting solenoids in interaction regions. Features of magnet elements design and magnetic measurements results are given together with comparison to previously calculated data. | ||
| MOPLS041 | MAD-X/PTC Lattice Design for DAFNE at Frascati | 631 |
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| In absence of a program that takes as an input the desired or known location of the magnets in the tunnel, accelerator designers have been using MAD8/X that looks at a ring as a sequence of magnets without a connection to the tunnel. In many simple examples that is just fine, but once more complicated structures are treated one is bound to play tricks with MAD. Here PTC comes to the rescue. It is shown how pieces of this machine that exist in MAD-X format are used in PTC to create this double ring, as found in the tunnel, with a proper survey in the forward and backward direction. Special elements have been implemented in MAD-X to allow the full PTC description of the machine. It is discussed how this real PTC model differs from the 'fake' MAD-X model and how well PTC describes the real machine. | ||
| MOPLS042 | Longitudinal Beam Stability for CESR-c | 634 |
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| The Cornell Electron-Positron Storage Ring (CESR) operates at 1.9 GeV per beam for high energy physics collisions. To maintain high luminosity it is essential for the bunch trains to be longitudinally stable. Measurements of longitudinal stability with a single, multiple, and colliding trains have been performed using a dual sweep streak camera and are presented in this paper. | ||
| MOPLS043 | Studies of the Beam-beam Interaction at CESR | 637 |
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| The Cornell Electron Storage Ring facility operates 2-GeV multi-bunch electron and positron beams in a single beam-pipe. Electrostatic separators are used to separate the two counter-rotating beams at the parasitic crossings. When the beam energy was lowered from 5 GeV in 2003, the strength of the beam-beam interaction became a more important factor in beam-current limitations, resulting in extensive experimental and calculational studies of their characteristics. The CESR lattice design procedure has been modified recently to account explicitly for their dynamic consequences. We describe our modelling of the beam-beam interaction, experimental validation techniques, and investigations into compensation strategies. | ||
| MOPLS044 | Luminosity Variations along Bunch Trains in PEP-II | 640 |
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| In spring of 2005 after a long shut-down, the luminosity of the B-Factory PEP-II decreased along the bunch trains by about 25-30%. There were many reasons studied which could have caused this performance degradation, like a bigger phase transient due to an additional RF station in the Low-Energy-Ring (LER), bad initial vacuum, electron cloud, chromaticity, steering, dispersion in cavities, beam optics, etc. The initial specific luminosity of 4.2 sloped down to 3.2 and even 2.8 for a long train (typical: 130 of 144), later in the run with higher currents and shorter trains (65 of 72) the numbers were more like 3.2 down to 2.6. Finally after steering the interaction region for an unrelated reason (overheated BPM buttons) and the consequential lower luminosity for two weeks, the luminosity slope problem was mysteriously gone. Several parameters got changed and there is still some discussion about which one finally fixed the problem. Among others, likely candidates are: the LER betatron function in x at the interaction point got reduced, making the LER x stronger, dispersion reduction in the cavities, and finding and fixing a partially shorted magnet. | ||
| MOPLS045 | Achieving a Luminosity of 1034/cm2/s in the PEP-II B-factory | 643 |
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| For the PEP-II Operation Staff: PEP-II is an asymmetric e+e- collider operating at the Upsilon 4S and has recently set several performance records. The luminosity has exceeded 1x1034/cm2/s and has delivered an integrated luminosity of 728/pb in one day. PEP-II operates in continuous injection mode for both beams, boosting the integrated luminosity. The peak positron current has reached 2.94 A and 1.74 A of electrons in 1732 bunches. The total integrated luminosity since turn on in 1999 has reached over 333/fb. This paper reviews the present performance issues of PEP-II and also the planned increase of luminosity in the near future to over 2 x 1034/cm2/s. Upgrade details and plans are discussed. | ||
| MOPLS047 | Design of an Asymmetric Super-B Factory | 646 |
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| Submitted for the High Luminosity Study Group for an Asymmetric Single-pass Super-B Factory: Parameters are being studied for a high luminosity e+e- collider operating at the Upsilon 4S that would deliver a luminosity of over 1036/cm2/s. This collider would use a novel combination of linear collider and storage ring techniques. In this scheme an electron beam and a positron beam are first stored in fast-damping and low-emittance damping rings, then extracted, accelerated, compressed and focused to the interaction point. After collision the two beams are decelerated and re-injected in the damping rings to be damped and extracted for collision again. The explored beam parameters are similar to those used in the design of the International Linear Collider, except for the beam energies. Design parameters for very flat beams and round beams have been studied. | ||
| MOPLS048 | Doubling the PEP-II Luminosity in Simulations | 649 |
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| The PEP-II luminosity reached 1x1034cm-2s-1 in October 2005. The question of how to increase the luminosity using modest improvements in the PEP-II accelerator in the coming years is the subject of this paper. We found that the parasitic collisions significantly degrade the simulated luminosity as the beam currents are increased from 3A and 1.7A to 4A and 2.2A in the low and high energy rings, respectively. Using the beam-beam code BBI, we systematically optimized the luminosity and showed that a luminosity of over 2x1034cm-2s-1 is achievable within the limits of machine parameters. | ||
| MOPLS049 | Anomalous High Radiation Beam Aborts in the PEP-II B-factory | 652 |
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| The PEP-II B-factory at SLAC has recently experienced unexpected beam losses due to anomalously high radiation levels at the BaBar detector. The problem was finally traced to the occurrence of very high pressure (>100 nTorr) spikes that have a very short duration (few seconds). We describe the events and show analysis predicting where in the vacuum system the events originated and describe what was discovered in the vacuum system. | ||
| MOPLS050 | Combined Phase Space Characterization at the PEP-II IP using Single-beam and Luminous-region Measurements | 655 |
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| We present a novel method to characterize the e ± phase space at the IP of the SLAC B-factory, that combines single-beam measurements with a detailed mapping of luminous-region observables. Transverse spot sizes are determined in the two rings with synchrotron-light monitors & extrapolated to the IP using measured lattice functions. The 3-D luminosity distribution, as well as the spatial dependence of the transverse-boost distribution of the colliding beams, are measured using e+ e- –> mu+ mu- events reconstructed in the BaBar tracking detectors; they provide information on the luminous spot size, the e- angular divergence & the vertical emittance. The specific luminosity, which is proportional to the inverse product of the overlap IP beam sizes, is continuously monitored using Bhabha-scattering events. The combination of these measurements provide constraints on the horizontal & vertical spot sizes, angular divergences, emittances & beta functions of both beams at the IP during routine high-luminosity operation. Preliminary results of this combined-spot size analysis are confronted with measurements of IP beta-functions & overlap IP beam sizes at low beam current. | ||
| MOPLS051 | Tracking Down a Fast Instability in the PEP-II LER | 658 |
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| During Run 5, the beam in the PEP-II Low Energy Ring (LER) became affected by a predominantly vertical instability with very fast growth rate of 10…60/ms - much faster than seen in controlled grow-damp experiments - and varying threshold. The coherent amplitude of the oscillation was limited to approx. 1 mm pk-pk or less and would damp down over a few tens of turns; however, beam loss set in even as the measured amplitude damped, causing a beam abort. This led to the conclusion that the beam was actually blowing up. The presence of a 2 nu_s line in the spectrum suggested a possible head-tail nature of the instability, although chromaticity was not effective in raising the threshold. In this paper we will describe the measurements and data taken to isolate and locate the cause of the instability and, eventually, the discovery and fix of the root cause. | ||
| MOPLS052 | Luminosity Improvement at PEP-II Based on Optics Model and Beam-beam Simulation | 661 |
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| The model independent analysis (MIA) has been successfully used at PEP-II to understand machine optics and improve the luminosity. However, the rate of success was limited because the improvement of optics does not necessarily lead to increase of luminosity. Recently, we were able to reconstruct MIA model in a full optics code, LEGO, and used it to calculate complete lattice and beam parameters. These parameters were fed to the beam-beam code, BBI, to understand the luminosity histories at PEP-II over the past year. Using these tools, we optimized the luminosity by varying the beam parameters such as emittance. Finally, we implemented an optimized solution with a set of asymmetric horizontal orbit bumps into the machines during a delivery shift with a few percentage gain in luminosity. The solution was retained at PEP-II machines along with the luminosity. Later, these asymmetric bumps also played a vital role in reaching 1x1034cm-2s-1 as the beam currents increased. | ||
| MOPLS053 | Beta-beat Correction Using Strong Sextupole Bumps in PEP-II | 664 |
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| A method for correcting lattice beta mismatches has been developed for the PEP-II collider using orbit offsets in strong sextupoles. The solution is first predicted in the MAD program by modeling closed orbit bumps in the plane of correction at the sextupoles strongest in that plane. The derived solution is then tested in the machine to confirm the prediction and finally dialed into the machine under high-current conditions. | ||
| MOPLS054 | On Increasing the HERA Luminosity | 667 |
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| The luminosity of the HERA lepton proton collider is limited in part by the bunch length of the protons of 20cm. This limitation is expected to be removed by the installation of a new damper system which will control longitudinal coupled bunch instabilities of the proton beam and avoid the bunch lengthening of a factor of two. This opens the possibility for increasing the luminosity HERA since the beta functions at IP for both leptons and protons can be lowered by about 20% without noticeable reduction of the corresponding luminosity by the so-called hour-glass effect. The beam spot size can be further reduced if the beam-beam focusing of the leptons (dynamic beta) at IP is increased by softening the rigorous beam beam-beta beat compensation which is accomplished by proper phasing of the two IP's. Unfortunately the non-linear chromaticity compensation would be weakened as well, which will cause an enhancement of the synchro-betatron resonances and may lead to poor lifetime and poor background conditions. Therefore, the non-linear chromaticity needs to be reduced by means of a more complex scheme of chromaticity compensating sextupole magnets. | ||
| MOPLS055 | A Lepton-proton Collider with LHC | 670 |
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||
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The physics, and a design, of a Large Hadron Electron Collider (LHeC) are sketched. With high luminosity, 1033cm-2s-1, and high energy, ?s = 1.4TeV, such a collider can be built in which a 70GeV electron (positron) beam in the LHC tunnel is in collision with one of the LHC hadron beams and which operates simultaneously with the LHC. The LHeC makes possible deep-inelastic lepton-hadron (ep, eD and eA) scattering for momentum transfers Q2 beyond 106GeV2 and for Bjorken x down to the 10-6. New sensitivity to the existence of new states of matter, primarily in the lepton-quark sector and in dense partonic systems, is achieved. The precision possible with an electron-hadron experiment brings in addition crucial accuracy in the determination of hadron structure, as described in Quantum Chromodynamics, and of parton dynamics at the TeV energy scale. The LHeC thus complements the proton-proton and ion programmes, adds substantial new discovery potential to them, and is important for a full understanding of physics in the LHC energy range.
Contributed to the Open Symposium on European Strategy for Particle Physics Research, LAL Orsay, France, January 30th to February 1st , 2006. hep-ex/0603016 DESY 06-00Cockcroft-06-05 |
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| MOPLS056 | QCD Explorer Proposal: E-linac versus E-ring | 673 |
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| TeV center of mass energy lepton-hadron collider is necessary both to clarify fundamental aspects of strong interactions and for adequate interpretation of the LHC data. Recently proposed QCD Explorer utilizes the energy advantage of the LHC proton and ion beams, which allows the usage of relatively low energy electron beam. Two options for the LHC based ep collider are possible: construction of a new electron ring in the LHC tunnel or construction of an e-linac tangentially to the LHC. In the latter case, which seems more acceptable for a number of reasons, two options are under consideration for electron linac: the CLIC technology allows shorter linac length, whereas TESLA technology gives higher luminosity. | ||
| MOPLS058 | eRHIC - Future Machine for Experiments on Electron-ion Collisions | 676 |
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| The paper presents recent developments for the design of the high luminosity electron-ion collider, eRHIC, proposed on the basis of the existing RHIC machine. The goal of eRHIC is to provide collisions of electrons and positrons on ions and protons in the center-of-mass energy range from 30 to 100 GeV. Lepton beams as well as the beam of protons (and, possibly, light ions) should be polarized. Two independent designs are under development, the so-called 'ring-ring' and 'linac-ring' options. The 'ring-ring' option is based on a 10 GeV electron storage ring. The design issues for the 'ring-ring' option are similar to those at existing B-factories. In the 'linac-ring' option, the electron beam is accelerated in a 10 GeV recirculating energy recovery linac. This option may provide higher luminosities (> 1·1033 cm-2s-1 for e-p collisions), but requires considerable R&D studies for a high current electron polarized source. In order to maximize the collider luminosity, ion ring upgrades, such as electron cooling and ion beam intensity increase, are considered. | ||
| MOPLS059 | The Probe Beam Linac in CTF3 | 679 |
|
||
| The test facility CTF3, presently under construction at CERN within an international collaboration, is aimed at demonstrating the key feasibility issues of the multi-TeV linear collider CLIC. The objective of the probe beam linac is to "mimic" the main beam of CLIC in order to measure precisely the performances of the 30 GHz CLIC accelerating structures. In order to meet the required parameters of this 200 MeV probe beam, in terms of emittance, energy spread and bunch-length, the most advanced techniques have been considered: laser triggered photo-injector, velocity bunching, beam-loading compensation, RF pulse compression … The final layout is described, and the selection criteria and the beam dynamics results are reviewed. | ||
| MOPLS060 | Design of an Interaction Region with Head-on Collisions for the ILC | 682 |
|
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| An interaction region with head-on collisions is considered an alternative to the baseline configuration of the International Linear Collider, including two interaction regions with finite crossing-angles (2 and 20 mrad). Although more challenging from the point of view of the beam extraction, the head-on scheme is favoured by the experiments because it allows a more convenient detector configuration, particularly in the forward region. The optics of the head-on extraction is revisited by separating the e+ and e- beams horizontally, first by electrostatic separators operated at their LEP nominal field and then using a defocusing quadrupole of the final focus beam line. In this way the septum magnet is protected from the beamstrahlung power. Newly optimized final focus and extraction optics are presented, including a first look at post-collision diagnostics. The influence of parasitic collisions is shown to lead to a region of stable collision parameters. Beam and beamstrahlung photon losses are calculated along the extraction elements. Issues concerning the design of the large bore superconducting final focus magnets, common to both incoming and outgoing beams, are considered. | ||
| MOPLS061 | Optimization of the e-e- Option for the ILC | 685 |
|
||
| The e-e- running mode is one of the interesting physics options for the International Linear Collider. The luminosity for e-e- collisions is reduced by mutual defocusing due to the strong electromagnetic fields that the bunches experience during collisions. The resulting beamstrahlung energy loss and beam-beam deflection angles as function of the vertical transverse offset are different compared to the e+e- collisions. In this paper, the dependence of these observables with the offset for different beam sizes has been analysed to optimize performances for the e-e- mode, taking into account the requirements of the beam-beam deflection based intra-train feedback system. A first study of the implications for the final focus and extraction line optics is also presented for the cases of the 2mrad and 20mrad ILC base line crossing angle geometries. | ||
| MOPLS063 | Accelerator Component Vibration Studies and Tools | 688 |
|
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| This talk will cover a research program on accelerator component vibrations. Ground motion and technical noise, such as vacuum and refrigeration systems, couple to the beam, mainly via quadrupoles, making the design of their supports, especially, in the case of the superconducting magnets, critical. This program includes investigation of cold mass vibration of the superconducting quadrupoles inside an accelerating module and sensor performance in the main or fringe field of a linear collider detector. Seismometer accuracy limitations in correlated ground motion measurements are also being investigated. | ||
| MOPLS064 | Measurement of Ground Motion in Various Sites | 691 |
|
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| This presentation will be an overview of a study program, initiated in DESY, to measure ground vibration of various sites which can be used for site characterization for the International Linear Collider (ILC) design. Commercial broadband seismometers have been used to measure ground motion, correlation and surface wave velocity. The database of measured ground vibrations is available to the scientific community. A parameterization of the spectra will also be presented. | ||
| MOPLS065 | An ILC Main Linac Simulation Package Based on Merlin | 694 |
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The preservation of the ultra-small vertical emittance in the International Linear Collider (ILC) will require the use of beam-based alignment techniques, the expected performance of which relies heavily on the use of simulation tools. In this report, we present the newest release of a purpose-built ILC main linac simulation tool, based on the Merlin* C++ class library. Examples of results from Dispersion Free Steering (DFS) simulations are also be presented.
*http://www.desy.de/~merlin |
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| MOPLS066 | Direct Measurement of Geometric and Resistive Wakefields in Tapered Collimators for the International Linear Collider | 697 |
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| Precise collimation of the beam halo is required in the ILC to prevent beam losses near the interaction region that could cause unacceptable backgrounds for the physics detector. The necessarily small apertures of the collimators lead to transverse wakefields that may result in beam deflections and increased emittance. A set of collimator wakefield measurements has previously been performed in the ASSET region of the SLAC LINAC. We report on the next phase of this programme, which is carried out at the recently commissioned End Station A test facility at SLAC. Measurements of resistive and geometric wakefields using tapered collimators are compared with model predictions from MAFIA and GdfidL and with analytic calculations. | ||
| MOPLS067 | Test Beam Studies at SLAC's End Station A, for the International Linear Collider | 700 |
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| The SLAC Linac can deliver to End Station A a high-energy test beam with similar beam parameters as for the International Linear Collider for bunch charge, bunch length and bunch energy spread. ESA beam tests run parasitically with PEP-II with single damped bunches at 10Hz, beam energy of 28.5 GeV and bunch charge of (1.5-2.0)·1010 electrons. A 5-day commissioning run was performed in January 2006, followed by a 2-week run in April. We describe the beamline configuration and beam setup for these runs, and give an overview of the tests being carried out. These tests include studies of collimator wakefields, prototype energy spectrometers, prototype beam position monitors for the ILC Linac, and characterization of beam-induced electro-magnetic interference along the ESA beamline. | ||
| MOPLS068 | Beam Impact of the ILC Collimators | 703 |
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| Spoilers in the ILC Beam Delivery System are required to survive a minimum of 1-2 direct impacts from each energetic electron or positron bunch of charged particles without failure, in addition to maintaining low geometric and resistive wall wakefields. The transient shock wave resulting from rapid localised beam heating and its implications for spoiler design are studied using ANSYS. The realistic patterns of energy deposition are taken from FLUKA.The results presented quantify uncertainties in the predictions and consider possible options for spoiler jaws for the ILC. | ||
| MOPLS069 | Development of a Superconducting Helical Undulator for the ILC Positron Source | 706 |
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| An undulator positron source has been recently selected by the International Linear Collider (ILC) community as a baseline. For the ILC a helical undulator capable of producing 10 MeV photons and with a period as close as possible to 10 mm is required. The HeliCal collaboration in the UK is looking at the merits of both permanent magnet and superconducting technologies for the design of a helical undulator. For the superconducting option, several prototypes have been built and tested. This paper details the design, construction and test results of the first superconducting prototypes. | ||
| MOPLS070 | Numerical Calculations of Collimator Insertions | 709 |
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| A series of collimator spoilers have been designed and manufactured for testing in the ESA wakefield tests. The purpose of the tests is a benchmarking exercise to assist with the understanding into the causes of wakefields due to spoiler profile and materials. Simulations of the spoiler designs have been used to understand the likely effects that would be observed with the beam tests. Simulations of these collimator insertions have been carried out in MAFIA and GDFIDL, and a comparison of the results completed. The wake potential has been measured, and the corresponding loss factor and kick factors have been calculated. The results from the simulations are discussed in this report. | ||
| MOPLS071 | TDR Measurements in support of ILC Collimator Studies | 712 |
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| In this report the outcome of the "wire method" cold test, experimental results and their relevance toward the ILC set-up is considered. A wire is stretched through the centre of a vessel along the axis that the electron beam would take, and a voltage pulse representing the electron bunch is passed along the wire. The parasitic mode loss parameter from this voltage can then be measured. The bunch length for the ILC is 0.3mm, requiring a pulse rise time of ~1ps. The fastest rise time available for a time domain reflectrometry (TDR) scope is ~10ps. Reference vessels have been examined to evaluate the suitability of the test gear at comparable bunch structures to the ILC. | ||
| MOPLS072 | Status of the HeLiCal Contribution to the Polarised Positron Source for the International Linear Collider | 715 |
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| The baseline positron source for the International Linear Collider is a helical undulator-based design, which can generate unprecedented quantities of polarised positrons. A major thrust of the global design in this area is led by the UK-based HeLiCal collaboration. The collaboration takes responsibility for the design and prototyping of the helical undulator itself, which is a highly demanding short period device with very small aperture, and also leads the start to end simulations of the polarised particles to ensure that the high polarisation levels generated are maintained from the source, right through the beam transport systems and up to the interaction point itself. This paper will provide an update on the work of the collaboration, focusing on these two topic areas, and will also discuss future plans. | ||
| MOPLS073 | Shower Simulations, Comparison of Fluka, Geant4 and EGS4 | 718 |
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| Computer simulations with different packages (Fluka, Geant4 and EGS4) were run in order to determine the energy deposition of an ILC bunch in a spoiler of specified geometry at various depths. The uncertainty in these predictions is estimated by comparison of their results. Various candidate spoiler designs (geometry, material) are studied. These shower simulations can be used as inputs to thermal and mechanical studies using programs such as ANSYS. | ||
| MOPLS074 | Collimation Optimisation in the Beam Delivery System of the International Linear Collider | 721 |
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| The collimation systems of the International Linear Collider (ILC) beam delivery system (BDS) must perform efficient removal of halo particles which lie outside the acceptable ranges of energy and spatial spread. An optimisation strategy is developed to improve the performance of the BDS collimation system. Primary considerations are the phase relationships between collimation systems and the final focus, and the overall bandwidth of the system. | ||
| MOPLS075 | Progress towards Crab Cavity Solutions for the ILC | 724 |
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|
In order to achieve acceptable luminosity for ILC crossing angles greater than a few mrad, RF deflection cavities must be used to rotate electron and position bunches leading up to the IP. A bunch that passes through a deflection cavity at a phase where the deflection averages to zero receives a crab kick leading to a finite rotation at the IP. For a beam energy of 500GeV and a crossing angle of 20mrad, the required crab kick is about 19.5MV at 1.3GHz and 6.5MV at 3.9GHz. Cavities are needed on both beams and are likely to be positioned about 12m before the IP. Any RF phase error between the bunch and the cavity leads to a deflection of the bunch in addition to a rotation of the bunch. Any differential phase error between the cavities leads to differing deflections and consequential loss in luminosity. Collaborative work with FNAL, being undertaken to develop a variant of their 3.9GHz CKM cavity optimised for an ILC solution, is described. Current analysis favours a solution with four nine-cell cavities on each beam. It is anticipated that the cavities will be run CW and driven from small Klystron/s (< 5kW) or solid state amplifiers.*
*We would like to thank Chris Adolphsen, SLAC, for his help in technical discussions, which were greatly appreciated. |
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| MOPLS076 | The Stimulated Breit-Wheeler Process as a Source of Background e+e- Pairs at the ILC | 727 |
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| Passage of beamstrahlung photons through the bunch fields at the interaction point of the ILC determines background pair production. The number of background pairs per bunch crossing due to the Breit-Wheeler, Bethe-Heitler and Landau-Lifshitz processes is well known. However the Breit-Wheeler process also takes place in and is modified by the bunch fields. A full QED calculation of this Stimulated Breit-Wheeler process reveals cross section resonances due to the virtual particle reaching the mass shell. The one loop Electron Self energy in the bunch field is also calculated and included as a radiative correction. The bunch field is considered to be a contant crossed electromagnetic field with associated bunch field photons. Resonance is found to occur whenever the energy of contributed bunch field photons is equal to the beamstrahlung photon energy. The Stimulated Breit-Wheeler cross section exceeds the ordinary Breit-Wheeler cross section by several orders of magnitude and a significantly different pair background may result. | ||
| MOPLS077 | The 2mrad Crossing Angle Interaction Region and Extraction Line | 730 |
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| A complete optics design for the 2mrad crossing angle interaction region and extraction line was presented at Snowmass 2005. Since this time, the design task force has been working on developing and improving the performance of the extraction line. The work has focused on optimising the final doublet parameters and on reducing the power losses resulting from the disrupted beam transport. In this paper, the most recent status of the 2mrad layout and the corresponding performance are presented. | ||
| MOPLS078 | Benchmarking of Tracking Codes (BDSIM/DIMAD) using the ILC Extraction Lines | 733 |
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| The study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this work, we benchmark two contemporary codes - DIMAD and BDSIM, the latter being a relatively new tracking code and built within the framework of GEANT4. We consider both the 20mrad and 2mrad extraction lines of the International Linear Collider and perform disrupted beam tracking studies of heavily disrupted post-collision electron beams. We find that the two codes in most cases give an equivalent description of the beam transport. | ||
| MOPLS079 | The Charged Beam Dumps for the International Linear Collider | 736 |
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| The baseline configuration of the International Linear Collider requires 2 beam dumps per interaction region, each rated to 18MW of beam power, together with additional beam dumps for tuning purposes and machine protection. The baseline design uses high pressure moving water dumps, first developed for the SLC and used in the TESLA design, although a gas based dump is also being considered. In this paper we discuss the progress made by the international community on both physics and engineering studies for the beam dumps. | ||
| MOPLS080 | A Laser-wire System at the ATF Extraction Line | 738 |
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| A new laser-wire system has been installed at the ATF extraction line at KEK, Tsukuba. The system aims at a micron-scale laser spot size and employs a mode-locked laser system. The purpose-built interaction chamber, light delivery optics, and lens systems are described, and the first results are presented. | ||
| MOPLS081 | A Study of Laser System Requirements for Application in Beam Diagnostics and Polarimetry at the ILC | 741 |
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| Advanced laser systems will be essential for a range of diagnostics devices at the ILC. High average power, excellent stability and reliability will be crucial in order to deliver the information required to attain the necessary ILC luminosity. The key parameters are listed together with the R&D required to achieve the necessary laser system performance. | ||
| MOPLS082 | Simulation of the ILC Collimation System Using BDSIM, MARS15 and STRUCT | 744 |
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| The simulation codes STRUCT, MARS15 and BDSIM are used to simulate in detail the collimation section of the ILC. A comparative study of the collimation system performance is performed, and the key radiation loads are calculated. Results for the latest ILC designs are presented together with their implications for future design iterations. | ||
| MOPLS083 | Higher Order Mode Study of Superconducting Cavity for ILC Baseline | 747 |
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| The superconducting cavity of ILC baseline shape is being developed at KEK-STF (Superconducting RF Test Facility). The Higher Order Mode (HOM) of the cavity is one study item for the development. The purpose of the HOM study is further optimization of TTF HOM coupler and measurement of the HOM field distribution and the polarization of the main dipole modes. The result will be applied to HOM readings of beam induced signal for the purpose of cavity offset position and angle of axis measurement relative to the beam. We tried to improve of TESLA-type HOM coupler for more small size and relaxation of second stop-band. The cold-model coupler was made, and the RF characteristic was measured. After HOM couplers welded to the KEK Baseline nine-cell SC cavity, Qext of fundamental mode and each HOM, field pattern of each HOM and polarization of dipole modes were measured by the network analyzer. The results of the improved HOM coupler are presented. | ||
| MOPLS084 | Experimental Comparison at KEK of High Gradient Performance of Different Single Cell Superconducting Cavity Designs | 750 |
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| We have performed a series of vertical tests of three different designs of single cell Niobium superconducting cavities at 2 degrees Kelvin. These tests aimed at establishing that an accelerating gradient of 45 MV/m could be reached in any of the designs, while using the standard KEK surface preparation. The designs tested were the Cornell re-entrant shape (RE), the DESY/KEK low loss shape (LL), and the KEK ICHIRO series. The cavities underwent surface preparation consisting of centrifugal barrel polishing, light chemical polishing, electropolishing, and finally a high pressure water rinse. All three kinds of cavities were used in a series of vertical tests to investigate details of the surface treatment. When using ultra-pure water for the high pressure rinse, the LL cavity reproducibly exceeded a gradient of 45 MV/m, the RE design reproducibly reached a gradient of between 50 MV/m and 52 MV/m, and three of the six ICHIRO cavities reached a gradient of between 45 MV/m and 49 MV/m. | ||
| MOPLS085 | Experience with a Zero Impedance Vacuum Flange at He Super-Leak Temperature for the ILC | 753 |
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| Several tens of thousands of vacuum flanges will be used in the construction of the ILC. So the reliability and large scale reproducibility of these elements are important issue. To arrive at a standardized vacuum flange, a new design of a unisex flange has been developed. This important component has to serve in two roles at He-super-leak temperature; both as an rf seal and as a vacuum seal. We chose the unisex type with a 90-degree sharp edge forming the seal. The design is a modification of the DESY S-band rectangular waveguide flange. The variation in flatness between the flange and gasket along the inside wall is within 50 micrometer. This should present zero impedance for a bunched beam and for rf power. The He-super-leak performance was measured using the "build up method", i.e.the test was carried out for three hours at 2 degrees Kelvin. The measured He leak rate was below 1·10-13 Atm*cc/sec for a test flange after three successive tests. We describe the design concept and the operational experience at various rf frequencies. These span the frequency range corresponding to warm and cold accelerators. | ||
| MOPLS087 | Series Test of High-gradient Single-cell Superconducting Cavity for the Establishment of KEK Recipe | 756 |
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| We have performed a series of vertical tests of single cell Niobium superconducting cavities at 2 degrees Kelvin. These tests aimed at establishing the feasibility of reaching an accelerating gradient of 45 MV/m on a routine basis. The cavity profiles were all of the KEK low loss design and were fabricated from deep drawn Niobium half shells using electron beam welding. The cavity surface preparation followed an established KEK procedure of centrifugal barrel polishing, light chemical polishing, high temperature annealing, electropolishing, and finally a high pressure water rinse. Of the six cavities tested, three exceeded 45 MV/m on the first test. This clearly establishes the feasibility of this gradient. In this paper we describe these tests and our future program for optimising the surface preparation. | ||
| MOPLS088 | Resonant Kicker System for Head-on-collision Option of Linear Collider | 759 |
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| The separation of incoming and outgoing (electron and positron) beams at the interaction point of a linear collider is investigated using a resonant kicker system. It should enable head-on-collisions at the interaction point with the use of staggered passing times for each bunch at certain locations. Magnetic core materials for such a resonant kicker with a frequency of 6MHz are under investigation. Such a kicker system should minimize the perturbation of the incoming bunch with a finite bunch length, while it kicks the outgoing bunch by more than 1 millirad. Various arrangements of such kickers along the beamlines are discussed. | ||
| MOPLS090 | Design of a Strip-line Extraction Kicker for CTF3 Combiner Ring | 762 |
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| The new CLIC test facility (CTF3) is the latest stage to prove the technical feasibility of the CLIC project. An extraction kicker is necessary for the combiner ring, and it will be a strip-line type device due to lower coupling impedances and straightforward fabrication. The field uniformity together with a correct beam dynamics are the most challenging issues of this design. The main parameters of the kicker are analytically calculated using standard analytic formulae. The numeric modelling and simulation of several possible straight sections are reported, and the characteristic impedance is matched with the 50 Ω load. The field homogeneity, the kick angle and the scattering parameters are calculated in a 3D finite element model. Several manufacturing issues for the first prototype are also outlined. | ||
| MOPLS091 | First Design of a Post Collision Line for CLIC at 3 TeV | 765 |
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| As part of the Post collision diagnostic task of the ILPS work-package of EuroTeV we discuss a design of the beam line between the interaction point and the beam dump for CLIC with a center-of-mass energy of 3 TeV. The design is driven by the requirement to transport the beam and all secondaries such as beamstrahlung and coherent pairs to the beam dump with minimal losses. Moreover, we discuss the integration of novel diagnostic methods into the post collision beam line based on the detection of coherent pairs and monitoring the beam profile of the primary beam. | ||
| MOPLS092 | Efficient Collimation and Machine Protection for the Compact Linear Collider | 768 |
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| We present a new approach to machine protection and collimation in CLIC, separating these two functions: If emergency dumps in the linac protect the downstream beam line against drive-beam failures, the energy collimation only needs to clean the beam tails and can be compact. Overall, the length of the beam delivery system is significantly reduced. | ||
| MOPLS093 | Commissioning Status of the CTF3 Delay Loop | 771 |
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| The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme by 2010. In particular, one of the main goals is to study the generation of high-current electron pulses by interleaving bunch trains in delay lines and rings using transverse RF deflectors. This will be done in the 42 m long delay loop, built under the responsibility of INFN/LNF, and in the 84 m long combiner ring that will be installed in 2006. The delay loop installation was completed, and its commissioning started at the end of 2005. In this paper the commissioning results are presented, including the first tests of beam recombination. | ||
| MOPLS094 | Luminosity Tuning at the Interaction Point | 774 |
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| Minimisation of the emittance in a linear collider is not enough to achieve optimal performance. For optimisation of the luminosity, tuning of collision parameters such as angle, offset, waist, etc. is needed, and a fast and reliable tuning signal is required. In this paper tuning knobs are presented, and their optimisation using beamstrahlung as a tuning signal is studied. | ||
| MOPLS095 | Investigations of DC Breakdown Fields | 777 |
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| The need for high accelerating gradients for the future 30 GHz multi-TeV e+e- Compact Linear Collider (CLIC) at CERN has triggered a comprehensive study of DC breakdown fields of metals in UHV. The experimental setup is based on a capacitor discharge across a gap junction. The simple design and fully automated computer control enable breakdown fields and dark current of numerous materials to be measured. The study shows that Mo, W and Ti reach high breakdown fields, and are thus good candidates for the iris material of CLIC structures. For untreated Mo the breakdown field is higher than Cu but the conditioning speed is slower. Ti, on the other hand, shows acceptable conditioning speeds, but material erosion makes this solution problematic. Feasible solutions to increase the spark conditioning speed for the case of Mo are presented together with attempts to prevent Ti erosion. For some of the materials studied a significant reduction in the saturated breakdown field was observed upon gas exposure during intensive spark conditioning. As an example, a 50% decrease of the breakdown field of Mo is recorded when spark conditioning is carried out in an environment of 10-5 mbar air. | ||
| MOPLS096 | Effects of Wake Fields in the CLIC BDS | 780 |
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| The wake fields due to collimators in the Beam Delivery System of CLIC are modeled using a conventional approach. According to the chosen ranges of parameters, differences in the transverse kicks due to both the geometric and resistive wall components for different regimes are highlighted (inductive or diffractive for the geometric wake fields, short- or long-range, ac or dc for the resistive wall wake fields). A module for particle tracking along the BDS including the effect of wake fields has been introduced in PLACET, and the first tracking results are shown. | ||
| MOPLS097 | Progress on the CTF3 Test Beam Line | 783 |
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| In CLIC, the RF power to accelerate the main beam is produced by decelerating a drive beam. The test beamline (TBL) of the CLIC test facility (CTF3) is designed to study and validate the stability of the drive beam during deceleration. This is one of the R&D items required from the International Linear Collider Technical Review Committee to demonstrate feasibility of CLIC. It will produce 30 GHz rf power in the GW range and allow to benchmark computer codes used for the CLIC decelerator design. Different options of this experimental beam line are discussed. | ||
| MOPLS098 | Study of an ILC Main Linac that Follows the Earth Curvature | 786 |
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| In the base line configuration, the tunnel of the ILC will follow the earth curvature. The emittance growth in a curved main linac has been studied, including static and dynamic imperfections. These include effects due to current ripples in the power supplies of the steering coils, the impact of the beam position monitor scale errors. | ||
| MOPLS099 | A Study of Failure Modes in the ILC Main Linac | 789 |
|
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| Failures in the ILC can lead to beam loss or even damage the machine. Also failures that do not lead to beam loss can affect the luminosity performance, in particular since some time is required to recover from them. In the paper a number of different failures is being investigated and the impact on the machine performance is being studied. | ||
| MOPLS100 | CLIC Final Focus Studies | 792 |
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| The design of the CLIC final focus system is based on the local compensation scheme proposed by P. Raimondi and A. Seryi. However, there exist important chromatic aberrations that deteriorate the performance of the system. This paper studies the optimization of the final focus based on the computation of the high orders of these aberrations using MAD-X and PTC. The use of octupole doublets to reduce the size of the halo in the locations with aperture limitations is also discussed. | ||
| MOPLS101 | Beam Dynamics and First Operation of the Sub-harmonic Bunching System in the CTF3 Injector | 795 |
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| The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme by 2010. The CTF3 drive beam generation scheme relies on the use of a fast phase switch of a sub-harmonic bunching system in order to phase-code the bunches. The amount of charge in unwanted satellite bunches is an important quantity, which must be minimized. Beam dynamics simulations have been used to study the problem, showing the limitation of the present CTF3 design and the gain of potential upgrades. In this paper the results are discussed and compared with beam measurements taken during the first operation of the system. | ||
| MOPLS102 | Beam Dynamic Studies and Emittance Optimization in the CTF3 Linac at CERN | 798 |
|
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| Small transverse beam emittances and well-known lattice functions are crucial for the 30 GHz power production in the Power Extraction and Transfer Structure (PETS), and for the commissioning of the delay loop of the CLIC Test Facility 3 (CTF3). Following beam-dynamics-simulation results, two additional solenoids were installed in the CTF3 injector in order to improve the emittance. During the runs in 2005 and 2006, an intensive measurement campaign to determine Twiss parameters and beam sizes was launched. The results obtained by means of quadrupole scans for different modes of operation suggest rms emittances well below the nominal (100 pi mm mrad) and a convincing agreement with PARMELA simulations. | ||
| MOPLS103 | A High-gradient Test of a 30 GHz Molybdenum-iris Structure | 801 |
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| The CLIC study is investigating a number of different materials as part of an effort to find ways to increase achievable accelerating gradient. So far, a series of rf tests have been made with a set of identical-geometry structures: a tungsten-iris 30 GHz structure, a molybdenum-iris 30 GHz structure and a scaled molybdenum-iris X-band structure. A second molybdenum-iris 30 GHz structure of the same geometry has now been tested in CTF3 with pulse lengths up to 350 ns. The new results are presented and compared to those of the previous structures to determine dependencies of quantities such as accelerating gradient, material, frequency, pulse length, power flow, conditioning rate and breakdown rate. | ||
| MOPLS104 | The Progress in Developing Superconducting Third Harmonic Cavity | 804 |
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| XFEL and TTF facilities are planning to use section with a few third harmonic cavities (3.9GHz) upstream of the bunch compressor to improve beam performances [1-2]. Fermilab is developing superconducting third harmonic section for TTFII upgrade. This section will include four cavities equiped with couplers and blade tuners, installed in cryostat. Up to now, two cavities are complete and one of them is under test. The status of the cavity development and preliminary test results are presented in the paper. | ||
| MOPLS105 | Collimators for ILC | 807 |
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| We considered two types of collimators for usage in undulator conversion system of ILC. In the first, the Pyrolytic graphite is used and it is installed in front of a target; the second one uses InGa alloy in rotating cylinder. The last one installed in front of undulator. Collimators allow absorption single train on bunches in ILC and enhace the photon polarization. | ||
| MOPLS106 | Independent Operation of Electron/Positron Wings of ILC | 810 |
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| We represent a concept of fast feedback system allowing independent operation of electron-positron wings of ILC. | ||
| MOPLS107 | Test of SC Undulator for ILC | 813 |
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| We represent details of design and results of test SC 40cm-long undulator having period 10mm and aperture ~8 mm allowing K=0.7. This undulator can be used in ILC positron conversion system. | ||
| MOPLS108 | Liquid Metal Target for ILC | 816 |
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| We considered the Hg target for gamma/positron conversion suitable for usage in ILC project. Positron scheme generation with undulator allows usage thin Hg jet confined in profiled duct with rectangular cross-section. | ||
| MOPLS109 | Operational Experience with Undulator for E-166 | 819 |
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| We represent results of operation of 2.54 mm period, K=0.2, up to 30 Hz undulator used in E-166 experiment for polarized positron production. One peculiarity is in usage of Ferrofluid for cooling. | ||
| MOPLS110 | ILC Linac R&D at SLAC | 822 |
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| Since the ITRP recommendation in 2004 to use superconducting rf technology for a next generation linear collider, the former NLC group at SLAC has been actively pursuing a broad range of R&D for this collider (the ILC). In this paper, we review the progress of those programs relating to linac technology. These include the development of a Marx-style modulator (120 kV, 120 A, 1.5 ms, 5 Hz) and a 10 MW sheet-beam klystron, construction of an L-band (1.3 GHz) rf source using a SNS HVCM modulator and commercial klystrons, fabrication and testing of a five-cell L-band cavity prototype for the ILC positron capture accelerator, high power tests of cavity coupler components, beam tests of prototype S-band linac beam position monitors and measurements of the magnetic center stability of an ILC prototype superconducting quadrupole magnet built by the CIEMAT group in Spain. | ||
| MOPLS113 | Commissioning of the ALTO 50 MeV Electron Linac | 825 |
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| The ALTO 50 MeV electron linac is dedicated to the production of neutron-rich radioactive nuclei using the photo-fission process and the optimisation of the target-ion source system for SPIRAL 2 and Eurisol projects. A description of the accelerator consisting in 3 Mev injector (old test station of LAL), LIL accelerating structure, RF power plant, beam line, control system and diagnostics will be given. Specified and measured beam parameters will be compared to show the performance for the photo-fission and eventually other applications. | ||
| MOPLS114 | Construction of the Probe Beam Photo-injector of CTF3 | 828 |
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| The paper describes the HF and dynamic beam modelling performed onto the 3 GHz / 2,5 cells photo-injector of the future CTF3 (CLIC Test Facility 3) probe beam linac, whose goal is to demonstrate the feasibility of the 30 GHz accelerating sections in the framework of the CLIC project. The Probe Beam Photo-Injector (PBPI) conception is inspired from the drive beam photo-injector already designed by LAL (Orsay, France) and actually tested in our laboratory. However, the design of PBPI has been simplified with respect to the previous because the charge per bunch is 4 times lower and the number of bunches several orders of magnitude smaller. The internal geometry and the coupling system of the PBPI have been designed with 2D (SUPERFISH) and 3D (HFSS, ANSYS) codes. A detailed analysis of the dissymmetry (induced by the coupling system) of the accelerating field component has been performed. Based on the modified design, PARMELA simulations showed that the technical specifications are fulfilled. The vacuum issue has been also carefully investigated, and NEG (Non Evaporated Getter) technology has been adopted in order to reach the 10-10 mbar pressure inside the structure. | ||
| MOPLS115 | A Spin Rotator for the ILC | 831 |
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| A spin rotator featuring an optic axis with straight vision is presented. This rotator utilizes three bends, two solenoid pairs and two correction devices. These correctors, named reflectors, are mandatory for removing the cross plane coupling introduced by the solenoids. It is shown how the solenoids have to be set up to achieve longitudinal IP polarization taking into account non-zero crossing angles at the interaction region and a linac following the curvature of the earth. Furthermore, the stability requirements for mechanical and electrical imperfections are analyzed. | ||
| MOPLS116 | Status Report on the Harmonic Double-sided Microtron of MAMI C | 834 |
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The Mainz Mikrotron MAMI is a cascade of three racetrack microtrons, delivering since 1991 a high quality 855MeV, 100muA cw electron beam for nuclear and radiation physics experiments. An energy upgrade of this machine to 1.5GeV by adding a Harmonic Double-Sided Microtron (HDSM)* as a fourth stage is well under way. Here we give a review of the experiences gained during fabrication and testing of the main components of the HDSM and report the status of its construction. Initial operation of the machine is expected for the first half of 2006. After a period of commissioning in diagnostic pulse mode with low beam power (10ns, high intensity bunch trains with a repetition rate of max. 10kHz), soon the first nuclear physics experiments will be started.
*A. Jankowiak et al. "Design and Status of the 1.5 GeV-Harmonic Double Sided Microtron for MAMI", Proceedings EPAC2002, Paris, p. 1085. |
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| MOPLS117 | Tuning Algorithms for the ILC Beam Delivery System | 837 |
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| Emittance preservation is an important aspect in the design and running of the International Linear Collider (ILC) with a direct consequence on the luminosity of the machine. The Beam Delivery System represents a major problem in this respect as it produces emittance dilution effects that are difficult to correct and that have a direct effect on the emittance as seen at the interaction point, and thus upon the luminosity of the machine. Tuning algorithms for this section of the machine rely on the correction of aberrations through the use of linear and higher order knobs, using corrections magnets distributed throughout the system. Alternative systems are also discussed. The design and implementation of these tuning algorithms, and their effectiveness in a variety of cases, are investigated and estimates made for tolerances on a variety of error sources. Simulations results are also presented for models of the ATF-2 accelerator under development at KEK, with comparisons made to the ILC design. | ||
| MOPLS118 | Magnetic Modelling of a Short-period Superconducting Helical Undulator for the ILC Positron Source | 840 |
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| A positron source utilising undulators is now defined as the baseline option for the International Linear Collider (ILC). The ILC requires a short period undulator, as close to 10mm as possible, that is capable of producing 10 MeV photons. The HeliCal collaboration in the UK has undertaken a programme to design, develop and produce a prototype undulator. As part of the programme, the group has used the OPERA software package to perform the magnetic design of the undulator. The design has addressed several issues, including the effect of magnetic material for the undulator former, optimal winding geometry, the magnetic flux inside the superconductor and its variation with undulator period and the winding bore. This paper summarizes the results of both the 2d and the 3d magnetic simulations. | ||
| MOPLS120 | Mitigation of Emittance Dilution due to Transverse Mode Coupling in the L-band Linacs of the ILC | 843 |
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| The main L-band linacs of the ILC accelerate 2820 bunches from a center of mass of 10 GeV to 500 GeV (and in the proposed later upgrade, to 1 TeV). The emittance of the vertical plane is approximately 400 times less than that of the horizontal plane. Provided the vertical and horizontal mode dipole frequencies are degenerate, then the motion in each plane is not coupled. However, in reality the degeneracy will more than likely be removed with the eigen modes lying in planes rotated from the x and y planes due to inevitable manufacturing errors introduced in fabricating 20,000 cavities. This gives rise to a transverse coupling in the horizontal-vertical motion and can readily lead to a dilution in the emittance in the vertical plane. We investigate means to ameliorate this emittance dilution by splitting the horizontal-vertical tune of the lattice. | ||
| MOPLS121 | The DAFNE Beam Test Facility: from 1 to 10 Milliards of Particles | 846 |
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| The DAFNE Beam Test Facility is operating since 2002, providing electrons, positrons and photons from the single particle up to 1010 particleS per spill and from 20 to 750 MeV. During these years, the facility has hosted tens of high energy test and experiments coming from all Europe, operating in a wide spread of multiplicity and energy. Operation performance and parameters, tools and diagnostics, as well as the main results obtained, are presented. | ||
| MOPLS122 | Design of the ILC Prototype FONT4 Digital Intra-train Beam-based Feedback System | 849 |
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| We report on the design and initial testing of the 4th generation Feedback on Nanosecond Timescales (FONT) prototype intra-train beam-based feedback system for beam control and luminosity optimisation at the International Linear Collider (ILC). FONT4 comprises a fast-analogue front-end BPM signal processor, with an FPGA-based digital feedback processor and a fast-risetime kicker-driver amplifier. The system is being designed with a total latency budget (including signal propagation delays) of about 140ns. FONT4 will be deployed at the Accelerator Test Facility (ATF) at KEK, where it will be tested with the electron bunchtrain extracted from the ATF damping ring. The bunches will have a spacing of c. 150ns, chosen to match the ILC design. We report the results of initial beam tests of the system components. We aim to demonstrate feedback, with delay-loop operation, on this ILC-like bunchtrain. | ||
| MOPLS123 | Performance of the FONT3 Fast Analogue Intra-train Beam-based Feedback System at ATF | 852 |
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| We report on the design and testing of the 3rd generation Feedback On Nanosecond Timescales (FONT) prototype intra-train beam-based feedback system for beam control and luminosity optimisation at the International Linear Collider (ILC). The all-analogue FONT3 electronics was designed to have an ultra-short latency of c. 10ns. We describe the design of the BPM signal processor, feedback circuit and kicker-driver amplifier. We report on deployment of FONT3 at the Accelerator Test Facility (ATF) at KEK, where it was tested with the 56ns-long electron bunchtrain extracted from the ATF damping ring. Feedback, with delay-loop operation, on the beam was demonstrated with a latency close to design. We comment on the applicability of this technology to ILC, as well as future warm-RF based linear colliders, such as CLIC. | ||
| MOPLS124 | The KEK Injector Upgrade for the Fast Beam-Mode Switch | 855 |
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| The KEK linac is a 600-m-long linear accelerator with maximum energy 8-GeV electron and 3.5-GeV positron, and it is used as an injector for 4-rings (KEKB e-/ e+, PF, PF-AR). To increase the operation efficiency, we have an injector upgrade plan for the quasi-simultaneous injection. In this paper, we will present the operation scheme and the construction of a new beam transport line in detail. | ||
| MOPLS128 | Status of the Fatigue Studies of the CLIC Accelerating Structures | 858 |
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| The need for high accelerating gradients for the future Compact Linear Collider imposes considerable constraints on the materials of the accelerating structures. The surfaces exposed to high pulsed RF currents are subjected to cyclic thermal stresses possibly resulting in surface break up by fatigue. Since no fatigue data exists in the literature up to very large numbers of cycles, a comprehensive study has been initiated. Low cycle fatigue data (up to 108 cycles) has been collected by means of a pulsed laser surface heating apparatus. The surface damage has been characterized by SEM observations and roughness measurements. High cycle fatigue data (up to 1011 cycles) at various stress ratios have been collected in high frequency bulk fatigue tests using an ultrasonic apparatus. It is found that the appearance of surface fatigue damage in the laser experiments, and of fatigue cracks in the bulk specimen, happen at similar stress levels for similar numbers of cycles. This allows the two experimental techniques to be connected and to predict the surface damage at a high number of cycles. Up-to-date fatigue data for selected high conductivity, high strength Cu alloys are presented. | ||
| MOPLS129 | Integration of the PHIN RF Gun into the CLIC Test Facility | 861 |
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| CERN is a collaborator within the European PHIN project, a joint research activity for Photo injectors within the CARE program. The scope of this project is to build an RF Gun equipped with high quantum efficiency Cs2Te cathodes and a laser to produce the nominal beam for the CLIC Test Facility (CTF3). The nominal beam for CTF3 has an average current of 3.5 A, 1.5 GHz bunch repetition frequency and a pulse length of 1.5 us (2310 bunches) with quite tight stability requirements. In addition a phase shift of 90 deg is needed after each train of 140 ns for the special CLIC combination scheme. This RF Gun will be tested at CERN in fall 2006 and should be integrated as a new injector into the CTF3 linac, replacing the existing injector consisting of a thermionic gun and a subharmonic bunching system. The paper studies the optimal integration into the machine trying to optimize transverse and longitudinal phase space of the beam while respecting the numerous constraints of the existing accelerator. The presented scheme uses emittance compensation and velocity bunching to fulfill the requirements. | ||
| MOPLS130 | Implications of a Curved Tunnel for the Main Linac of CLIC | 864 |
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| Preliminary studies of a linac that follows the earth's curvature are presented for the CLIC main linac. The curvature of the tunnel is modeled in a realistic way by use of geometry changing elements. The emittance preservation is studied for a perfect machine as well as taking into account imperfections. Results for a curved linac are compared with those for a laser-straight machine. | ||
| MOPLS133 | Preliminary Studies of Ion Effects in ILC Damping Rings | 867 |
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| Ion effects are potentially detrimental to the performance of the damping rings for the International Linear Collider (ILC). In this paper, the ion effects in the damping rings of ILC are briefly reviewed. Fast beam-ion instability (FBII) is studied in the linear regime. The growth rates and the beam blowups due to FBII are analytically calculated and compared for two variants of the ILC damping ring designs (OCS and TESLA) and discussed as a function of the vacuum pressure. Finally, some detailed simulation results are also presented. | ||
| MOPLS134 | Minimizing Emittance for the CLIC Damping Ring | 870 |
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| The CLIC damping rings aim at unprecedented small normalized equilibrium emittances of 3.3 nm vertical and 550 nm horizontal, for a bunch charge of 2.6 109 particles and an energy of 2.4 GeV. In this parameter regime the dominant emittance growth mechanism is intra-beam scattering. Intense synchrotron radiation damping from wigglers is required to counteract its effect. Here the overall optimization of the wiggler parameters is described, taking into account state-of-the-art wiggler technologies, wiggler effects on dynamic aperture, and problems of wiggler radiation absorption. Two technical solutions, one based on superconducting magnet technology and the other on permanent magnets, are presented. Although dynamic aperture and tolerances of this ring design remain challenging, benefits are obtained from the strong damping. Only bunches for a single machine pulse need to be stored, making injection/extraction particularly simple and limiting the synchrotron-radiation power. With a 360 m circumference, the ring remains comparatively small. | ||
| MOPLS135 | Correction of Vertical Dispersion and Betatron Coupling for the CLIC Damping Ring | 873 |
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| The sensitivity of the CLIC damping ring to various kinds of alignment errors have been studied. Without any correction, fairly small vertical misalignments of the quadrupoles and, in particular, the sextupoles, introduce unacceptable distortions of the closed orbit as well as intolerable spurious vertical dispersion and coupling due to the strong focusing optics of the damping ring. A sophisticated beam-based correction scheme has been developed to bring the design target emittances and the dynamic aperture back to the ideal value. The correction using dipolar correctors and several skew quadrupole correctors allows a minimization of the closed-orbit distortion, the cross-talk between vertical and horizontal closed orbits, the residual vertical dispersion and the betatron coupling. | ||
| MOPLS136 | Ion Effects in the Damping Rings of ILC and CLIC | 876 |
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| We discuss ion trapping, rise time of the fast beam-ion instability, and ion-induced incoherent tune shift for various incarnations of the ILC damping rings and for CLIC, taking into account the different regions of each ring. Analytical calculations for ion trapping are compared with results from a new simulation code. | ||
| MOPLS137 | Tracking Studies to Determine the Required Wiggler Aperture for the ILC Damping Rings | 879 |
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| The injection efficiency of an ILC damping ring is closely tied to its acceptance. To maximize both, one wants a physical aperture as large as possible in the wiggler magnets, as these are the limiting physical apertures in the ring. On the other hand, a small aperture in the wiggler magnets is needed to achieve the required field profile, a high magnetic field that is very linear over the whole physical aperture of the magnet. Tracking studies were done for all proposed ILC damping ring lattices to determine their required apertures. Although a half-aperture of 8 or 10 mm had been proposed, our studies showed that, for most lattices, a 16 mm half-aperture is required. (For some lattices a 12 mm half aperture might suffice.) We present here the results of our studies, which led to adopting a 16 mm half-aperture in the current ILC damping ring baseline design. | ||
| MOPLS138 | Space Charge and Equilibrium Emittances in Damping Rings | 882 |
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| The unusual combination of small beam size and long ring circumference may cause space charge to have noticeable effects on the beam dynamics of the ILC (International Linear Collider) damping rings. One possible consequence is a modification of the vertical equilibrium emittance resulting from a non-ideal lattice. One simple way to account for this effect is to model space charge in the linear approximation within the framework of Oide's envelope (or Chao's matrix) formalism, whis is commonly used to calculate equilibrium emittances in lepton storage rings. However, this model would likely overestimate the effect as a linear approximation for space charge is accurate only in a small neighborhood of a bunch center. For a more accurate modelling, we propose to make use of Sacherer's envelope equations consisting of a closed set of equations for the second moments of a beam distribution that account for the nonlinear dependence of the space-charge force. Here we will illustrate how Sacherer's equations can be combined with Oide's formalism and apply the result to the ILC damping rings. | ||
| MOPLS139 | Choosing a Baseline Configuration for the ILC Damping Rings | 885 |
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| The damping rings for the International Linear Collider must be capable of accepting large beams from the electron and positron sources, and producing highly damped beams meeting demanding stability specifications, at the machine repetition rate of 5 Hz. Between March and November 2005, a program of studies was undertaken by an international collaboration of 50 researchers to compare a number of configuration options, including ring circumferences between 3 and 17 km. Here, we outline the studies and discuss the principal considerations in the choices of the baseline and alternative damping ring configurations. | ||
| MOPLS140 | Tuning Algorithms for the ILC Damping Rings | 888 |
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| Emittance preservation is an important aspect in the design and running of the International Linear Collider with a direct consequence on the luminosity of the machine. One major area of concern is in the damping rings, where the extracted emittances set the effective lower limits for the rest of the machine. Algorithms for tuning this system have been investigated, and simulations have been performed to understand the design and implementation issues. The different algorithms have been applied to the various damping ring designs, and the effectiveness of each algorithm has been assessed. A preliminary recommendation of tuning algorithm, and its effectiveness under various conditions, is given. | ||
| MOPLS141 | The Proposed Conversion of CESR to an ILC Damping Ring Test Facility | 891 |
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| In 2008 the Cornell Electron Storage Ring (CESR) will end nearly three decades of providing electron-positron collisions for the CLEO experiment. At that time it will be possible to reconfigure CESR as a damping ring test facility, CesrTF, for the International Linear Collider (ILC) project. With its complement of 12 damping wigglers, CesrTF will offer horizontal emittances in the few nanometer range and, ideally, vertical emittances approaching those specified for the ILC damping rings. An important feature of the CesrTF concept is the ability to operate with positrons or electrons. Positron operation will allow detailed testing of electron cloud issues critical for the operation of the ILC positron damping rings. Other key features include operation with wigglers that meet or exceed all ILC damping ring requirements, the ability to operate from 1.5 to 5.5 GeV beam energies, and the provision of a large insertion region for testing damping ring hardware. We discuss in detail the CesrTF machine parameters, critical conversion issues, and experimental reach for damping ring studies. | ||
| MOPLS142 | Optimization of CESR-c Superferric Wiggler for the International Linear Collider Damping Rings | 894 |
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| We present the results of an optimization of the Cornell Electron Storage Ring (CESR) superferric wiggler for the International Linear Collider (ILC) damping ring. The superferric CESR wiggler has been shown to have excellent beam dynamics properties in the ILC damping ring. We reduced the physical size, and hence cost, of the CESR wiggler with minimal degradation of ILC damping ring beam dynamics. We will provide a description of the optimized superferric wiggler and show the performance of this wiggler in the ILC baseline damping ring. | ||
| MOPLS143 | Suppression of Secondary Emission in a Magnetic Field using Sawtooth Surface | 897 |
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| The effect of surface roughness on the secondary electron emission from a sawtooth surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. Some of the secondary electrons emitted from the sawtooth surface return to the surface within their first few gyrations, resulting in low effective secondary electron yield. A sawtooth surface in magnetic field can significantly reduce the secondary emission yield below the multipacting threshold. |