| Paper | Title | Page |
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| MOPCH001 | Modeling Coherence Decay in Broad Band Triplet Interaction | 0 |
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In the present analysis we study the transition from coherent to incoherent dynamics in a nonlinear triplet of broad band combs of waves*. We first reduce the original set of equations into a set where all submodes within a comb interact with all pairs of submodes in the remaining combs. We then develop a spectral formalism that in a self-contained way enables: (i) to determine the point of the transition; (ii) to obtain a convenient set of low dimensional equations modeling the full dynamics**. As shall be discussed in connection with accelerator physics, the results can be applied to a variety of parametric or nonlinear wave devices like beat wave accelerators, FELs, etc.
*G. I. Oliveira et al. Physica D 164, 59 (2002).**M. Frichembruder et al. submitted to Physica. D (2005). |
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| MOPCH002 | Seeding the FEL of the SCSS Phase 1 Facility with the 13th Laser Harmonic of a Ti: Sa Laser Produced in Gas | 44 |
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| A seeding configuration, in which the 13th harmonic (60 nm) of a Ti: Sa laser (50 mJ, 10 Hz, 130 fs) generated in a gas cell is used as the external source, will be tested in 2006 on the SCSS test facility (SPring-8 Compact Sase Source, Japan). This facility is based on a thermionic cathode electron gun (1 nC of bunch charge), a C-band LINAC (5712 MHz, 35 MV/m) and two in-vacuum undulators (15 mm of period). The maximum electron beam energy is 250 MeV and the SASE emission from visible to 60 nm can be obtained. The High order Harmonic Generation (HHG) experiment was mounted off-line at the end of last December. A first chamber is dedicated to harmonic generation. A second one is used for spectral selection and adaptation of the harmonic waist in the modulator. The tests are performed in Saclay with the LUCA (Laser Ultra Court Accordable) laser (15 mJ, 10 Hz, 50 fs) from January to March at 266 nm, 160 nm and 60 nm and its results are presented here. Also, before performing the real tests in SPring-8 FEL presence, final theoretical estimations of the performances relying on 1D simulations using PERSEO code and 3D simulations using GENESIS and SRW codes are given. | ||
| MOPCH003 | Seeding SPARC Facility with Harmonic Generation in Gases: Preliminary Tests of the Harmonic Generation in Gas Chamber | 47 |
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| In High Gain Harmonic Generation Free Electron Laser configuration, an external light source is injected in the first part of an undulator. The electron-photon interaction leads to a coherent light emission in the second part of the undulator. We propose to use the High Order Harmonic Generation in gases process as the seed for SPARC project (Frascati, Italy). With this facility, the electron beam is accelerated to 200 MeV and passes through an undulator of 6 sections. The preliminary tests on the seeding chambers presented in this paper have been realised at the CEA (Saclay, France). The experiment is based on three vacuum chambers. In the first one, a Ti: Sa laser (800 nm, 2.5 mJ, 50 fs, 10 Hz) is focussed in a 10 Hz pulsed gas jet (Argon or Xenon), producing harmonics of the fundamental. Filters in the second chamber enable the selection of the harmonic (3rd or 5th). Finally, a telescope focuses the harmonic beam at a given position. The whole module is to be moved to the SPARC facility. Appropriate tuning of the undulator gaps will amplify the 3rd and 5th harmonics seeded, as well as non-linear harmonics of those wavelengths, allowing the perspective of producing a FEL at 53 nm | ||
| MOPCH004 | Coherent Harmonic Generation Experiment on UVSOR-II Storage Ring | 50 |
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| Harmonic Generation schemes on Free Electron Laser devices are very promising. The injection of a traditional laser source inside the first undulator leads to an efficient energy modulation of the electron bunch, and therefore, its spatial modulation, resulting in a more coherent light emission along the second undulator. Experiments have been performed on the UVSOR-II Storage Ring at Okazaki (Japan) with electrons stored at an energy of 600 MeV, and using a 2.5 mJ Ti:Sa laser at 800 nm wavelength, 1 kHz repetition rate, and 100 fs up to 2 ps pulse duration. The experimental setup is presented, including the transport alignment and synchronisation between the laser and the electron beam. The third harmonic at 266 nm has been characterised versus various parameters: current, RF cavity voltage, undulator gap, magnetic functions of the storage ring, and laser pulse duration. Those results are compared with theory via analytical models and simulations. | ||
| MOPCH005 | The ARC-EN-CIEL FEL Proposal | 53 |
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| ARC-EN-CIEL (Accelerator-Radiation Complex for Enhanced Coherent Intense Extended Light), the French project of a fourth generation light source aims at providing the user community with coherent femtosecond light pulses covering from UV to soft X ray. It is based on a CW 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches with a high repetition rate (1 kHz). Electron beam calculations will be presented. The FEL is based on the injection of High Harmonics Generated in Gases (HHG) in a High Gain Harmonic Generation scheme, leading to a rather compact solution. The produced radiation extending down to 0.8 nm with the Non Linear Harmonics reproduces the good longitudinal and transverse coherence of the harmonics in gas. Calculations are preformed with PERSEO, taking into account the proper transverse overlap between HHG and the electron beam, and with SRW. Optional beam loops are foreseen to increase the beam current or the energy. They will accommodate fs synchrotron infrared Coherent Synchrotron Radiation sources, VUV and X ray ranges and a FEL oscillator in the 10 nm range. An important synergy is expected between accelerat | ||
| MOPCH006 | Beam Adaptation at the Infrared FEL, CLIO | 56 |
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| The infrared free-electron laser CLIO is tunable from 3 to 150 5m by operating its driver RF linear accelerator between 50 and 12 MeV. This is the largest spectral range ever obtained with a single optical cavity. We have studied the electron beam transverse adaptation in the FEL undulator throughout the spectral and energy range. Each beam dimension is measured by a moving wire whose temperature dependant resistivity is monitored. The results are compared with simulations computed with the TRANSPORT code. | ||
| MOPCH007 | Undulators for a Seeded HGHG-FEL Test Bench at MAX-lab | 59 |
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| Undulators for a Seeded HGHG-FEL at MAX-lab Within the European FEL Design Study a seeded HGHG-FEL will be set up at MAX-lab. In the modulator, a planar pure permanent magnet undulator, the 3rd harmonic of a Ti:Sapphire laser (267nm) interacts with the electron beam. In the following dispersive section the energy modulation is converted into a spatial modulation. The radiator emits at the third harmonic (89nm). The radiator has an APPLE II type magnetic structure providing full polarization control. The undulators and the dispersive section are currently built at BESSY. The electron beam height at MAX-lab of 400mm requires a specific design of the undulator carriages. The magnetic and mechanical design of the HGHG stage will be presented. | ||
| MOPCH008 | Considerations for Double Pulse Lasing from the BESSY-FEL | 62 |
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| BESSY proposes a linac-based High-Gain Harmonic-Generation (HGHG) free electron laser (FEL) facility with three independent FEL lines. Two to four HGHG stages downconvert the initial seed wavelength (230nm to 460nm) to the desired radiation range (1.24nm to 51nm). High FEL gain is ensured as the seed radiation interacts only with unperturbed parts of the electron bunch in every HGHG-stage. This so-called fresh-bunch-technique relies on dipole chicanes that delay the electron bunches relative to the radiation. Fresh-bunch chicanes are incorporated prior to each modulator in the BESSY-FEL allowing the bunch to completely travel through all undulators. However, simulations show that bunch parts that have previously lased generate a noticeable radiation power level in the final amplifiers. This motivated simulation studies on the significance and applicability of such inherent additional pulses. It is revealed that the BESSY-FEL provides the opportunity to deliver double pulses at the FEL exit being of high interest to the user community. Temporal seperation and intensity levels can be controlled by carefully optimising the properties of the magnetic chicanes. | ||
| MOPCH009 | The BESSY 2nd Generation Soft X-ray FEL User Facility | 65 |
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| Future VUV-to-soft-X-ray FEL facilities promise to open fundamentally new frontiers for the synchrotron user community. So-called 2nd generation FELs, which use seeded schemes rather than SASE, can deliver reproducible ultra-short photon pulses at an energy level of mJ/pulse. BESSY has been designing a High-Gain-Harmonic-Generation (HGHG) based FEL with a 2.3 GeV superconducting driver linac that covers photon energies from 24 eV to 1 keV. The design provides full tuneability of photon energy, variable beam polarization and complete synchronization to external lasers—all essential for future femtosecond, time-resolved pump-probe experiments. Also, the CW linac offers great flexibility for the repetition rates and pulse patterns. BESSY-organized User Workshops helped identify the user requirements for such an FEL. This information provided the basis for the Technical Design Report that was submitted to the German Wissenschaftsrat in 2004, which then held an on-site review in 2005. Meanwhile, preparatory studies continue at BESSY. They include start-to-end simulations, tolerance studies, and the development of superconducting RF technology in the HoBiCaT test facility. | ||
| MOPCH010 | High Power Tests of a High Duty Cycle, High Repetition Rate RF Photoinjector Gun for the BESSY FEL | 68 |
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| The proposed BESSY Soft X-ray FEL uses a normal conducting 1.3 GHz photoinjector RF gun cavity at comissioning phase. Due to the challenging RF pulse pattern the cavity has to cope with an average power of 75 kW. A 1.5-cell RF gun prototype has been built with a dedicated cooling layout. Results of the first high power RF tests are detailed in this paper. | ||
| MOPCH011 | Jitter Measurement by Spatial Electro-optical Sampling at the Flash Free Electron Laser | 71 |
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| For pump-probe experiments carried out at the VUV-FEL at DESY, FEL laser pulses with 32 nm wavelength have to be synchronized with high precision to optical laser pulses generated by a TiSa oscillator. To measure the relative timing variations between the FEL and the optical laser, an electro-optical experiment to determine the electron beam arrival time at the undulator has been installed. Here, the electron beam profile is encoded spatially into the laser pulse and readout by an intensified camera. A similar experimental setup has been successfully used at the sub-picosecond pulsed source (SPPS) at higher charge and shorter rms bunch length. In this paper, we report about the achievements and difficulties of the Timing Electro-Optical (TEO) setup, that allows to post-order experimental user data with a precision of 100 fs rms and better. | ||
| MOPCH012 | FEL Disturbance by Ambient Magnetic Field Changes | 74 |
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| The VUV-FEL at DESY in Hamburg (Germany) is mostly located inside the circular accelerator PETRA which serves as an injector for the electron proton collider HERA. SASE was regularly lost in the VUV-FEL when protons were ramped to the injection energy in PETRA. This effect was mediated by magnetic field changes in the order of 1 microtesla, caused by time-dependent uncompensated magnet currents of more than 800 A which made PETRA act like a large current loop. The resulting beam displacements of several hundred micrometers in the undulators proved to be enough to make SASE fail. This serious disturbance of user runs was eliminated by introducing an improved compensation scheme which further limits residual currents in PETRA during proton injection. The consequences of this observation for the design of the XFEL are briefly discussed. | ||
| MOPCH013 | Slice Emittance Measurements at FLASH | 77 |
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| The SASE process in Free Electron Lasers mainly depends on time-sliced parameters of charge density, energy spread and transverse emittance. At the VUV-FEL at DESY, electron bunches are compressed longitudinally in two magnetic chicanes in order to achieve high peak currents. The compression causes considerabe variations in slice emittance along the bunches. The vertically deflecting rf-structure LOLA, which is in operation at the VUV-FEL since early 2005, allows to resolve longitudinal variations in horizontal slice width for single bunches. The horizontal slice emittances can be determined by additionally varying the strengths of the quadrupoles upstream of LOLA. Results of slice emittance measurements using different bunch compression schemes are presented. | ||
| MOPCH014 | Energy-time Correlation Measurements Using a Vertically Deflecting RF Structure | 80 |
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| To initiate the lasing process in SASE-based Free Electron Lasers, electron bunches with high peak currents are necessary. At the VUV-FEL at DESY, high peak currents are produced by bunch shortening in magnetic chicanes induced by a linear energy-time gradient. The residual uncorrelated time-sliced energy width after compression is a crucial parameter for the lasing process. The final energy-time correlation provides important information about the compression process. This paper presents a measurement of slice energy spread and energy-time correlation using a vertically deflecting rf-structure (LOLA). The structure allows to map the time delay of bunch slices to the vertical axis of a screen. After dispersing the bunches horizontally with a dipole, the energy-time correlation can be directly obtained in a single shot measurement. Results for different bunch compression schemes are presented. The measured bunch length in case of a non-compressed beam is compared to streak camera measurements. | ||
| MOPCH015 | Impact of Undulator Wakefileds and Tapering on European X-ray FEL Performance | 83 |
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| The European X-ray Free-Electron Laser (XFEL) based on self-amplified spontaneous emission (SASE) requires an electron beam with a few kA peak current and a small-gap undulator system up to 250 m in length. The interaction between the high-current electron bunch and the undulator vacuum chamber affects the FEL performance. In this paper we estimate the induced wakefields in elliptical pipe geometry, taking into account the main geometrical variations of the chamber. To study the expected performance in the presence of the calculated wakefields, we are doing start-to-end simulations with the tracking codes ASTRA, CSRtrack and GENESIS. To compensate the wakefield impact on the FEL performance, an adiabatic change of undulator parameters is considered. | ||
| MOPCH016 | Bunch Compression Monitor | 86 |
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| An accelerated bunch of electrons radiates coherently at wavelengths longer than or comparable to the bunch length. The first generation Bunch Compression Monitor (BCM) that is installed at the VUV-FEL applies this principle by measuring the total radiation intensity. For a better control on the degree of the compression, the radiated intensity in different bandwidth can be used. Dependent on the changes in the structure of the bunch, its radiation spectrum changes correspondingly. A new generation BCM uses wavelength dependent diffracting devices and multi-channel sensors to measure the signal in different wavelength channels simultaneously. This paper describes the construction of the first prototypes and experimental results in different short wavelength bands measured at the linac of the VUV-FEL at DESY, Hamburg. | ||
| MOPCH018 | Macro-Pulse Generation in a Storage-Ring Free-Electron Laser: A Single-Particle Plus FEL Numerical Approach | 89 |
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| In a storage-ring free-electron laser (FEL), the onset and growth of intra-cavity power at the fundamental resonant wavelength is naturally accompanied by coherent emission at higher harmonics. Contrary to what happens in single-pass linac-based devices, the electron beam is re-circulated in the storage ring and the microbunching becomes thermalized. As a consequence, a correct theoretical understanding of the process requires a proper modelling of the turn-by-turn evolution of the electron-beam phase space, both inside the undulators (where the FEL interaction takes place) and along the ring. To simulate this process we have coupled an ad hoc modified version of the 3D numerical code Ginger (which models the FEL interaction) together with a linear one-turn map (which propagates the electron beam along the ring). We present our results and draw a comparison with previous simplified approaches. We also present the first benchmarking of experiments carried out with the ELETTRA storage-ring FEL. | ||
| MOPCH019 | Baseline Design of the Linac Upgrade for Fermi | 92 |
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| The FERMI FEL requires a major upgrade of the existing linac, which needs to be transformed from being the injector for the ELETTRA light source, to becoming the source for the FERMI FEL. In this work, we present the baseline design, including the integration of the 7 additional systems from the LIL linac, and one X-band station as linearizers. We will present the new layout with the required modifications and additions to the existing infrastructure to meet the more demanding needs of the system. Such modifications include a new RF controller, improvements in the modulator stability and an upgrade to the average power capabilities of the system to operate at 50 Hz. Test results from the characterization of the existing systems will be included, as well as plans for future development. | ||
| MOPCH020 | Design and Optimization of the FERMI @ Elettra FEL Layout | 0 |
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| The FERMI @ ELETTRA project at Sincotrone Trieste will be comprised of two FEL's, each based on the principle of seeded harmonic generation. The first undulator line, FEL-1, will operate in the 40-100 nm wavelength range and will rely upon one stage of harmonic up-conversion. The second undulator line, FEL-2, extends the output spectral domain to the 10-40 nm wavelength range and will use two harmonic stages operating as a cascade. We review the FEL studies that have led to the final design and present results of numerical simulations with GENESIS and GINGER codes including those examining the effects of undulator errors and shot-to-shot fluctuations in multiple input parameters. | ||
| MOPCH021 | FERMI @ Elettra: Conceptual Design for a Seeded Harmonic Cascade FEL for EUV and Soft X-rays | 0 |
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| We present a summary of the conceptual design for the FERMI FEL project funded for construction at the Sincrotrone Trieste, Italy. The project will be the first user facility based on seeded harmonic cascade FEL's, providing controlled, high peak-power pulses, and complementing the storage ring light source at Sincrotrone Trieste. The facility is to be driven by electron beam from a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac. Designed for an initial complement of two FEL's, providing tunable output over a range from ~100 nm to ~10 nm, FERMI will allow control of pulse duration from less than 100 fs to approximately1 ps, and with polarization control from APPLE undulator radiators. Seeded by tunable UV lasers, FEL-1 is a single-stage of harmonic generation to operate over ~100 nm to ~40 nm, and FEL-2 a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelength. Photon output is spatially and temporally coherent, with peak power in the 100’s MW to GW range. We have designed FEL-2 to minimize the output radiation spectral bandwidth. Major systems and overal facility layout are described, and key performance parameters summarized. | ||
| MOPCH022 | Time-resolved "Start-to-end" FEL Simulation Results for the FERMI @ Elettra Project | 0 |
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The FERMI FEL project* is the first user facility based on seeded harmonic cascade FEL's, providing controlled, high peak-power pulses, and complementing the storage ring light source at Sincrotrone Trieste. FERMI will initial comprise two FEL's, providing tunable output over a wavelength range from ~100- to 40-nm (FEL-1) and ~40-to-10-nm (FEL-2) with control of both polarization and temporal pulse duration. We present results concerning the predicted FEL output based the expected 6D electron beam phase space at the undulator entrance as determined from detailed "start-to-end" simulations**. Both the GENESIS and GINGER codes were applied to this study. We discuss the expected transverse and longitudinal coherence, and also the predicted sensitivity to both undulator errors and accelerator jitter.
*C. J. Bocchetta et al. “FERMI @ Elettra – Conceptual Design for a Seeded Harmonic Cascade FEL for EUV and Soft X-rays”, this conference. **S. DiMitri et al. “Start to End Simulations of FERMI@ELETTRA”, this conference. |
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| MOPCH024 | Future Seeding Experiments at SPARC | 95 |
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| Sources based on High order Harmonics Generated in gases (HHG) with high power Ti:Sa lasers pulses represent promising candidates as seed for FEL amplifiers for several reasons, as spatial and temporal coherence, wavelength tunability and spectral range, which extends down to the nm wavelength scale. This communication describes the research work plan that is under implementation at the SPARC FEL facility in the framework of the EUROFEL programme. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in crystals (400 nm and 266 nm) and in gases (266 nm, 160 nm, 114 nm). The SPARC FEL can be configured to test several cascaded FEL layouts that will be analysed in this contribution. | ||
| MOPCH025 | Laser Comb: Simulations of Pre-modulated E- Beams at the Photocathode of a High Brightness RF Photoinjector | 98 |
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A density modulated beam at the photocathode though the proper modulation of the laser beam pulse does not change substantially emittance and energy spread, properties directly related to FEL. It has been found that bunch density modulation is transformed into energy modulation along the propagation through the injector*. There are some physical arguments that suggest a possibility to use this modulation for the enhancement of the FEL process, or for the production of plasma wakes. Preliminary beam dynamics studies have been carried on to explore the use of electron beam pre-modulation at the cathode to adjust their longitudinal structure at the end of the beamline. Energy modulation at the end of the beamline could eventually be turned into current modulation through a magnetic compressor with R56<0. The feasibility of this experiment has to be investigated carefully, preliminary studies are discussed here. This paper focuses on simulations that explore the properties of the energy modulation at the end of the beamline correlated to the initial characteristics of the train of electron pulses.
*M. Biagini et al. “Beam Dynamics Studies for the SPARC Project”, Proc. of PAC03. |
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| MOPCH026 | A Biperiodic X-band RF Cavity for SPARC | 101 |
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| The Frascati photo-injector SPARC (Pulsed Self Amplified Coherent Radiation Source) will be equipped with an X-band RF cavity for linearizing emittance to enhance bunch compression and for reducing bunch longitudinal energy spread. A biperiodic cavity working on the pi/2-mode offers some advantages in comparison to a conventional (periodic) cavity despite the need of accurate machining. A copper prototype made of 17 separated cells has been built following numerical simulation. In this paper we report on preliminary measurements of its RF properties. The main characteristics of the cooling system for the final device are also addressed. | ||
| MOPCH027 | Metal Film Photocathodes for High Brightness Electron Injectors | 104 |
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| Advanced high brightness injectors require photocathodes with fast response,high quantum efficiency and good surface uniformity. Both Mg films deposited by laser ablation and Pb films deposited by vacuum arc could satisfy these requirements. Their emission and morphology are compared. | ||
| MOPCH028 | Status of the SPARX FEL Project | 107 |
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| The SPARX project consists in an X-ray-FEL facility jointly supported by MIUR (Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and Rome University Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1 and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5-6 nm and 6-1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC high brightness photoinjector presently under commissioning at Frascati INFN-LNF Laboratories. The use of superconducting and exotic undulator sections will be also exploited. In this paper we report the progress of the collaboration together with start to end simulation results based on a combined scheme of RF compression techniques. | ||
| MOPCH029 | Status of the SPARC Project | 110 |
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| The SPARC Project is starting the commissioning of its photo-injector. RF gun, RF sources, RF network and control, power supplies, emittance meter, beam diagnostics and control to measure the RF gun beam are installed. The photocathode drive laser has been characterized in terms of pulse shape and quality. We expect to conduct beam measurements at RF gun exit in the next future and consequently to start the installation of accelerating sections. The design of the 12 m undulator for the FEL experiment has been completed and the first undulator section out of 6 is under construction: we expect to characterize it at Frascati ENEA laboratory within the next months. SPARC as a facility will host FEL experiments using SASE, seeding and non-linear resonant harmonics. Additional R&D on X-band and S-band structures for velocity bunching are in progress, as well as studies on new photocathode materials and exotic undulator designs. We also present studies on solenoid field defects, beam based alignments, exotic electron bunch production (blow-out of short laser pulses or intensity modulated laser pulses). The possible use of segmented superconducting micro-undulators will be discussed too. | ||
| MOPCH030 | Production of Coherent X-rays with a Free Electron Laser Based on an Optical Wiggler | 113 |
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| The interaction between high-brightness electron beams and counter-propagating laser pulses produces X rays via Thomson scattering. If the laser source is long enough, the electrons bunch on the scale of the emitted X-ray wavelength and a regime of collective effects establishes. In this case, the FEL instability develops and the system behaves like a FEL based on an optical undulator. Coherent X-rays are irradiated, with a bandwidth thinner than that of the incoherent emission. The emittance of the beam and gradients or irregularities in the laser energy distribution are the principal factors that limit the growth of the X-ray signal. We analyse with a 3-D code the transverse effects in the emission produced by a relativistic electron beam when it is under the action of an optical laser pulse and the X-ray spectra obtained. The scalings typical of the optical wiggler, with very short gain lengths and overall time durations of the process make possible considerable emission also in violation of the Pellegrini criterion for static wigglers. A generalized form of this criterion is validated on the basis of the numerical evidence. | ||
| MOPCH031 | Progress on the Pi-mode X-band RF Cavity for SPARC | 116 |
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The Frascati photo-injector SPARC (Pulsed Self Amplified Coherent Radiation Source) will be equipped with an x-band RF cavity for linearizing emittance to enhance bunch compression and for reducing bunch longitudinal energy spread. The nine cell standing wave cavity prototype made of separated cells has been already built and measured*. In this paper we report on characterization of the first brazed prototype. Heat load studies have been performed as well to design the cooling system for the final device.
*D. Alesini et al. Nucl. Instr. and Meth. A 554 (2005) 1. |
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| MOPCH034 | On a Skeleton CASSINI Ovals Current Undulator | 119 |
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A new undulator structure for free electron lasers was presented. Current skeleton CASSINI ovals produced magnetic fields which are spatially periodic. The current structure was in the shape of stacks of modified CASSINI ovals. The current has alternating directions. The magnetic field components for each wire present C2 symmetry. CASSINI undulator transverse cross-section* was approximated by polygons. In cartesian coordinates the Biot-Savart law was analytically evaluated. The magnetic field was mainly transversal and easily adjusted with the current. The versatility of this structure introduces a new type of two beams longitudinal undulator or wiggler design for transverse moments.
*Cassini curve; C. Mihu, I.P. Iambor-1989. |
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| MOPCH036 | Photocathode Roughness Impact on Photogun Beam Characteristics | 121 |
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| Photocathode surface roughness has an impact on photoelectron yield, bunch duration, beam emittance at the exit of femtosecond photogun with an accelerating field that is considered in assumption of quasi-stationary one in the paper. The main problem in investigating the impact is determination of the field near the surface, statistical properties of which are defined through rms values of deviation and slope in profile line of the surface roughness. Developed and created code allows determining the field with relative rms error not worse than 0.001%. The results of the investigation for rms values of roughness and its slope within respectively 500…0 nm and 20…0 degrees are presented and discussed. | ||
| MOPCH038 | Predicted Parameters of the Second Stage of High Power Novosibirsk FEL | 124 |
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The first stage of Novosibirsk high power terahertz FEL was successfully put into operation in 2003*. The measured parameters of the FEL turned out to be in a good agreement with calculations [2]. The second and the third stages of the FEL are under construction now. The beam energy at the second stage will be about 20 MeV and the wavelength will change in the range 40-80 μm. In this paper we present the design parameters for the second stage FEL. The simulations were carried out with the help of 1-D code based on macroparticles. This code was previously used for the first stage simulations**.
*E. A. Antokhin et al. NIM A528 (2004) p.15-18.**A. V. Kuzmin et al. NIM A543 (2005) p.114-117. |
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| MOPCH040 | Simulations for the FEL Test Facility at MAX-lab within EUROFEL | 127 |
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| Within the EUROFEL project a High Gain Harmonic Generation Free Electron Laser will be constructed at MAX-lab in collaboration with BESSY. The electron bunches will be created in the existing MAX-lab injector and transported to the inside of the MAX II ring where the FEL undulators will be located. To predict FEL performance and stability, simulations of the photo injector, linac, recirculator, transport and undulator sections as well as start to end simulations have been carried out. | ||
| MOPCH041 | Design of a New Preinjector for the MAX Recirculator to be Used in EUROFEL | 130 |
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| The MAX-lab recirculator injector will be equipped with a new preinjector system. The aim is to reduce the emittance, increase the charge and achieve a proper timing between accelerator and laser systems. All is aimed at the MAX-lab test facility for HG built in collaboration with BESSY in the EUROFEL program. The preinjector system consists of a photo cathode RF-gun with an emittance compensating solenoid. Special issues regard the injection of the new beam into the beam path of the MAX recirculator and the conservation of beam parameters. | ||
| MOPCH042 | Progress in the Design of a Two-Frequency RF Cavity for an Ultra-Low Emittance Pre-Accelerated Beam | 133 |
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| Today most of the X-rays Free-Electron Laser projects are based on state of the art RF guns, which aim at a normalized electron beam emittance close to 1 mm$·$mrad. In this paper we report on the progress made at PSI towards a hybrid DC + RF Low Emittance Gun (LEG) capable of producing a beam with an emittance below 0.1 mm.mrad. To reduce the intrinsic thermal emittance at the LEG cathode the electrons are extracted from nano-structured field-emitters. A gun test facility is under construction wherein after emission the beam is accelerated up to 500 keV in a diode before being injected and accelerated in a two-frequency 1.5-cell RF cavity. The fast acceleration in the diode configuration allows to minimize the emittance dilution due to the strong space charge forces. The two-frequency RF structure is optimized to limit the emittance blow-up due to the non-linearity of the RF field. | ||
| MOPCH043 | An Optimization Study for an FEL Oscillator at TAC Test Facility | 136 |
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| Recently, conceptual design of the Turkic Accelerator Center (TAC) proposal was completed. The main goal of this proposal is a charm factory that consists of a linac-ring type electron-positron collider. In addition, synchrotron radiation from the positron ring and free electron laser from the electron linac are proposed. The project related with this proposal has been accepted by the Turkish government. It is planned that the Technical Design Report of TAC will have been written in the next three years. In this period, an infrared oscillator free electron laser (IR FEL) will be constructed as a test facility for TAC. 20 and 50 MeV electron energies will be used to obtain infrared FEL. The main parameters of the electron linacs, the optical cavities and the FEL were determined. The possible use of obtained laser beam in basic and applied research areas such as biotechnology, nanotechnology, semiconductors and photo chemistry were discussed. | ||
| MOPCH044 | Peculiarities of the Doppler Effect for Moving Radiative Particles in Dispersive Medium at Extreme Conditions | 139 |
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| The features of Doppler effect for fast moving radiating particles with discrete energy levels spectrum (e.g. radiation at channeling) at parameters close or equal to extreme condition of Cherenkov effect are studied. The formal usage of Cherenkov condition leads in this case to incorrect and unphysical results. The main task of this work was to find maximal radiation frequency and its dependence from the system parameters. This finite frequency was found. It was shown that at correct use of conservation laws the dependence of radiation and absorption frequencies on deviation from exact Cherenkov condition contains one discontinuity. The value of these frequencies on two sides of this discontinuity is different by 2.5 times. It was shown that the positions of these discontinuities depend on deviation value and corresponds to the condition of normal Doppler effect transformation into abnormal. Conditions that correspond to maximal radiation and absorption frequencies are different and are shifted in different directions form the exact Cherenkov condition (in relation to the velocity and dielectric permittivity). | ||
| MOPCH045 | A Source of Coherent Soft X-ray Radiation Based on High-order Harmonic Generation and Free Electron Lasers | 142 |
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| We examine a scheme for a Free Electron Laser (FEL) harmonic amplifier seeded by a ~30-nm wavelength signal produced using a process of High-order Harmonic Generation (HHG). The seed is first amplified in an optical klystron from ~100 kW to ~30 MW using a 1 GeV electron beam and then is used for an energy modulation of electrons in the downstream undulator. Subsequently, a 100-MW level of radiation at shorter wavelengths down to 4 nm is obtained by bunching the energy modulated electrons and passing the bunched beam through an undulator tuned to the desired harmonic of 30 nm. We also compare this scheme to a more familiar harmonic cascade FEL by replacing the HHG with an additional stage of harmonic generation. | ||
| MOPCH047 | Study of the Electron Beam Dynamics in the FERMI @ ELETTRA Linac | 145 |
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A study of the electron beam dynamics in the linac is made within the framework of the design of a free electron laser (FEL) at the Syncrotrone Trieste*. A scope of the work includes analysis of two operational scenarios, one with relatively long electron bunches of the order of 1.5 ps and a moderate peak current of 500 A and one with shorter bunches of the order of 0.7 ps and higher peak current of the order of 800 A. In both cases, care has been taken to preserve the slice and projected emittances formed in the photocathode gun injector and to minimize the slice energy spread. The latter goal is accomplished by balancing the onset of the microbunching instability driven by the longitudinal space charge forces and the emission of coherent synchrotron radiation using Landau damping produced by a so-called laser heater. Various analytical techniques and tracking codes have been employed to obtain the reported results.
*C. Bocchetta, et al., this conference. |
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| MOPCH048 | Linac Coherent Light Source Electron Beam Collimation | 148 |
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| This paper describes the design and preliminary simulations of the electron beam collimation system in the Linac Coherent Light Source (LCLS) linac. Dark current is expected from the gun and some of the accelerating cavities. Particle tracking of the expected dark current through the entire LCLS linac, from L0-linac exit to FEL undulator entrance, is used to estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction. A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an estimate of average continuous beam power lost on each individual collimator. In addition, the transverse wakefield alignment tolerances are calculated for each collimator. | ||
| MOPCH049 | Trajectory Stability Modeling and Tolerances in the LCLS | 151 |
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| To maintain stable performance of the Linac Coherent Light Source X-ray Free-electron laser, one has to control undulator trajectory stability to a small fraction of the rms beam size. BPM based feedback loops running at 120 Hz will be effective in controlling jitter at low frequencies less than a few Hz. On the other hand, linac and injector stability tolerances must control jitter at higher frequencies. In this paper, we study the possible sources of such high frequency jitter, including: 1) steering coil current regulation; 2) quadrupole (and solenoid) transverse vibrations; 3) quadrupole (and solenoid) current regulation in presence of typical 200-micron misalignments; 4) charge jitter coupling to RF cavity transverse wakefield due to alignment errors; and 5) bunch length jitter coupling to Coherent Synchrotron Radiation in Chicane. Based on this study, we then set tolerances on each item. | ||
| MOPCH051 | Operation of the First Undulator-based Femtoslicing Source | 154 |
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At the BESSY II storage ring, a source of sub-100-fs x-ray pulses with tunable polarization and excellent signal-to-background ratio has been constructed in 2004, based on laser-induced energy modulation ("femtoslicing"*) and subsequent angular separation of the short-pulse x-rays from an elliptical undulator. After commissioning and characterizing the source, short-pulse radiation is now routinely delivered for pump-probe applications. The paper summarizes the results from commissioning and operational experience as well as possible upgrade options.
*A. Zholents and M. Zoloterev, PRL 76 (1996), 912. |
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| MOPCH053 | Towards Sub-picoseconds Electron Bunches: Upgrading Ideas for BESSY II | 157 |
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Sub-picoseconds bunches were achieved with the BESSY low alpha optics, and their lengths were measured using Fourier Transform spectroscopy*. To avoid the coherent synchrotron radiation instability, the current in these short bunches has to be limited to theμampere level. An upgrade of the BESSY II rf gradient to much larger values is suggested to overcome this low current limitation by two orders of magnitude. Intense, picoseconds long bunches could then be achieved already at the regular user optics. The resulting short and very intense electron bunches are useful for generation of short x-ray pulses and powerful THz-radiation. Expected parameters of bunch length and current are discussed.
*J. Feikes et al. "Sub-Picoseconds Electron Bunches in the BESSY Storage Ring", EPAC'04, Luzerne (Switzerland), July 2004. |
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| MOPCH054 | Plans for the Generation of Short Radiation Pulses at the Diamond Storage Ring | 160 |
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| Diamond is a third generation light source under commissioning in Oxfordshire UK. In view of the increasing interest in the production of short radiation pulses, we have investigated the possibility to operate with a low-alpha optics, the use of a third harmonic cavity for bunch shortening and the implementation of a crab cavity scheme in the Diamond storage ring. The results of the initial accelerator studies will be described, including the modification of the beam optics, non-linear beam dynamics optimisation and choice of RF parameters for the crab cavity operation. The expected performance of these schemes will be summarised. | ||
| MOPCH055 | Circulation of a Short, Intense Electron Bunch in the NewSUBARU Storage Ring | 163 |
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| One new method is proposed which supplies synchrotron radiation light from a short and intense electron bunch. This method supplies a short and intense x-ray pulse and extremely strong coherent radiation in a long wavelength region to beam lines of a storage ring. SPring-8 linac supplied a short and intense 1.0 GeV electron beam to NewSUBARU storage ring. The electron bunch was compressed to 10ps (full width) from the normal condition (20ps full width) using ECS system. The pulse charge was 0.10nC/bunch and the energy spread was (±) 0.2 % (full width) at the injection point. The ring lattice was adjusted at a quasi-isochronous condition to keep the short bunch for many revolutions. The estimated linear and non-linear momentum compaction factors were -6·10-5 (the linear factor), 0.0 (the second order factor) and +0.9 (the third order factor). The bunch length was measured by a streak camera, and the coherent radiation was detected by a Shottky diode detector. The short bunch was successfully circulated for about 50 turns. | ||
| MOPCH056 | Development of High Brightness Soft X-ray Source Based on Inverse Compton Scattering | 166 |
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| Compact soft X-ray source based on inverse compton scattering have been developed at Waseda University. Using 1047nm laser light from Nd:YLF laser scattered off 4.2MeV electron beam generated from a photo-cathode rf-gun, we have already suceeded to generate the soft X-ray. The energy of this x-ray is included in the part of water window, in which absorption of water is much less than that of moleculars that organize a living body. Furthermore, this x-ray source has other features such as short pulse, proportional mono-energy and energy variableness. Because of these tures, the application to the biological microscope have been expected. However, the flux of x-ray is not satisfied for the biological microscope application. Therefore, to multiply a soft X-ray flux, we utilized multi-pass amplifier for the laser light and improved a collision chamber. In this conference, we will report the experimental results and future plans. | ||
| MOPCH057 | The Design of a 1.8 keV Compton X-ray Generator for a SC RF Linac at KAERI | 169 |
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| A quasi-monochromatic X-ray source based on the KAERI SC linac system has been designed and is being manufactured now. A 10 MeV 10 mA electron beam together with a 20 W 1.06 ?m laser beam will be used for 1.8 keV Compton X-ray generation with a few percentage of energy spread and 107 photons per second. A simple straight beamline was designed to deliver the electron beam with no degradation of its emittance and energy spread and to focus it to a proper size to produce the desired X-rays. We expect the first demonstration of 1.8 keV Compton X-ray generation in autumn 2006. | ||
| MOPCH058 | RF Photogun as Ultra Bright Terahertz Source | 0 |
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| Recently research into new terahertz (0.3 to 30 THz) light sources has gained a lot of interest. Especially compact sources capable of delivering high peak fields (~ 1 MV/cm), in a short pulse. To achieve this, we will use short relativistic electron bunches, created by photoemission and accelerated in an rf-photogun, to create THz light by means of coherent transition radiation. Because wavelengths smaller and comparable to the bunch length add up coherently, the intensity scales with N2, with N the number of electrons in the bunch. In the first experiments we expect to create THz light pulses with a bandwidth of 1 THz and 1 μJ per pulse. If such a light pulse is focused on a spot of radius 250 μm, this corresponds to peak electrical fields of 1 MV/cm. The eventual goal is to increase the bandwidth of the source, by creating shorter electron bunches. This will be accomplished by choosing a suitable radial laser profile, leading to ellipsoidal electron bunches, which can be focused and compressed very effectively. Eventually this will lead to THz pulses with a bandwidth of 10 THz and energy of 100 μJ. This corresponds to peak electrical fields of 10 MV/cm and higher. | ||
| MOPCH059 | From Pancake to Waterbag: Creation of High-brightness Electron Bunches | 0 |
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| Our recent insight is that, when creating high-brightness electron bunches, the major problem is not space charge density itself, but its distribution. Non-linear space charge effects lead to a decrease of brightness. We have a novel recipe of creating waterbag bunches (uniformly charged 3D ellipsoids), which have linear space charge fields. Because of these linear fields we have control of the Coulomb explosion of the bunches. Furthermore, using linear charged particle optics, waterbags can be compressed and focussed with conservation of brightness. Our recent simulations prove that it is possible to create such ideal waterbag bunches in practice. The recipe is to create at the cathode a pancake-like electron bunch with a "hemisphere" charge density distribution. During acceleration this pancake will evolve into a waterbag by its own space charge forces, if two conditions on the acceleration field and the surface charge density are fulfilled. These two conditions are leading to a parameter space, which is explored by simulations. We will present numerical simulations and the present status of the experimental realization. | ||
| MOPCH062 | Centroid, Size, and Emittance of a Slice in a Kicked Bunch | 172 |
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| A transversely kicked bunch will decohere due to, among other things, chromatic and amplitude-dependent tune shifts. The chromatic tune shift leads to correlation between transverse and longitudinal phase space. Such a correlation can be used for compressing synchrotron radiation of the bunch with adequate optics. In this report, we revise the decoherence calculation to derive the centroid and second moments of a beam slice in a kicked bunch, taking into account chromatic and nonlinear decoherence, but neglecting wakefield and radiation damping, etc. A simple formula for estimating slice bunch length (and potential pulse compression ratio) is given for the ideal situation. | ||
| MOPCH064 | The Specification, Design and Measurement of Magnets for the Energy Recovery Linac Prototype (ERLP) at Daresbury Laboratory | 175 |
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| The Energy Recovery Linac Prototype (ERLP) is currently under construction at Daresbury Laboratory in the UK and will serve as a test bed for the investigation of technologies and beam physics issues necessary for the development of Daresbury Laboratory's Fourth Generation Light Source (4GLS) proposal. A number of new ERLP beam transport system magnets have been procured for the project. The magnets have been designed, manufactured and measured by Danfysik following a stringent magnetic field specification produced by Daresbury Laboratory. In this paper we summarise the magnet specification. We then present details of the magnetic and mechanical design of the magnets and finally discuss the measurement techniques used to demonstrate that the field quality of the magnets satisfied the specification. | ||
| MOPCH065 | Fabrication and Installation of Superconducting Accelerator Modules for the ERL Prototype (ERLP) at Daresbury | 178 |
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| Installation and commissioning of the superconducting energy recovery linac(ERL) prototype is under way at Daresbury Laboratory. ACCEL have manufactured two superconducting accelerator modules for the injector and the linac, operating at 2K with 1.3 GHz TESLA type cavities. Each module contains two cavities and is designed to provide an accelerating voltage of 25 MV in cw mode. This paper presents details of the module fabrication, cavity preparation and performance results. An overview of the cryogenic installations for the modules is given and status results of the commissioning are discussed. | ||
| MOPCH066 | The Conceptual Design of 4GLS at Daresbury Laboratory | 181 |
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| 4GLS is a novel next generation proposal for a UK national light source to be sited at Daresbury Laboratory, based on a superconducting energy recovery linac (ERL) with both high average current photon sources (undulators and bending magnets) and three high peak current free electron lasers. Key features are a high gain, seeded FEL amplifier to generate XUV radiation and the prospect of advanced research arising from unique combinations of sources with femtosecond pulse structure. The conceptual design is now completed and a CDR recently published. The 4GLS concept is summarised, highlighting how the significant design challenges have been addressed, and the project status and plans explained. | ||
| MOPCH069 | Lattice Design for the Fourth Generation Light Source at Daresbury Laboratory | 184 |
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| The proposed Fourth Generation Light Source (4GLS) has three electron transport paths, an energy recovery loop containing the main linac, IDs and a VUV-FEL, a separate branch after the main linac for an XUV-FEL and a transport path for an IR-FEL. The first two present major challenges in lattice design. The energy recovery loop will be fed by a high average current gun, with bunches of charge of about 80 pC. High charge (1nC) bunches from a high brightness gun will be accelerated prior to the main linac and split into the XUV-FEL branch using energy separation after the main linac. We present a lattice design and results from numerical modelling of the electron bunch transport. The requirements of the machine are short bunches, a small emittance for both branches and an overall topology which gives a reasonable dimension for the building. Different transport and compression schemes were assessed to meet these requirements whilst balancing the disruptive effects of longitudinal and transverse space charge, CSR, wakefields and BBU. Investigations into all of these instabilities are summarized together with other transport issues and the resulting requirements on all IDs. | ||
| MOPCH070 | The Status of the Daresbury Energy Recovery Prototype Project | 187 |
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| The major component of the UK's R&D programme towards an advanced energy recovery linac-based light source facility is a 35 MeV technology demonstrator called the energy recovery linac prototype (ERLP). This is based on a combination of a DC photocathode electron gun, a superconducting linac operated in energy recovery mode and an IR FEL. The current status of the of this project is presented, including the construction and commissioning progress and plans for the future exploitation of this scientific and technical R&D facility. | ||
| MOPCH071 | Optimization of Optics at 200 MeV KEK-ERL Test Facility for Suppression of Emittance Growth Induced by CSR | 190 |
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| Energy Recovery Linac (ERL) gets a lot of attention as a next period light source instrument. To produce high-brightness and short pulse synchrotoron lights, it is necessary to pass through high current and short bunch electron beams to the insertion part of ERL with keeping the low emittance and the low energy spread. However, it is challenging because Coherent Synchrotorn Radiation (CSR) generated at bending magnets is potential sources of the emittance growth which is enomous especially for high current, short bunch and a low energy beam. Therefore, it is benefit to a gradual bunch compression in the arc after accelerating the beam up to the full energy. The beam optics and lattice design of 200MeV ERL Test Facility is optimized to suppress the emittance growth caused by CSR at the arc section on two conditions, high-current mode (100mA, 1psec) and short bunch mode (0.1psec) similar to 5GeV ERL facility proposed by Cornell University. | ||
| MOPCH072 | Adjustable Input Coupler Development for Superconducting Accelerating Cavity | 193 |
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| The waveguide and coaxial-type input couplers for Energy Recovery Linac type injector cavity electrodynamical and thermal simulation results are presented. The devices are designed to feed the superconducting cavity with up to 500 kW RF power in continuous wave regime at 1.3 GHz operating frequency. The cavity external quality factor adjustment is provided. The heat load to the cryogenic system was lowered to a tolerable level by coupler design optimization. | ||
| MOPCH073 | A Project of a High-power FEL Driven by an SC ERL at KAERI | 196 |
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| A project of a high-power FEL at Korea Atomic Energy Research Institute is described. The FEL is driven by a superconducting energy recovery linac. The future ERL will be connected to the existing machine without any modification. It consists of two 180-degree bents and two straight sections: one is for the FEL, another for a Compton X-rays source. One can choose the regime controlling the lenses. The total ERL is isochronous to avoid any problems with longitudinal beam instability. The total relative emittance degradation through the whole machine is ? 1.5. The FEL will be based on a 2 m helical in-vacuum undulator made of permanent magnets. One mirror of the optical cavity is blind and made of copper; the other one, the outcoupler, is semi-transparent and made of CVD diamond. The expected average power is a few kW and the tuning range 35…70 ?m. | ||
| MOPCH074 | Layout of an Accumulator and Decelerator Ring for FAIR | 199 |
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| Antiproton physics and experiments with rare isotope beams are major research fields at FAIR. Antiproton physics requires the accumulation of high intensity antiproton beams. The accumulation of up to 1011 antiprotons at 3 GeV is foreseen. This will be accomplished by the combination of the collector ring CR for stochastic precooling and the specialized accumulator ring RESR. The accumulation scheme in the RESR is based on the usage of a stochastic cooling system. The requirements of this cooling system strongly affect the magnetic structure of the RESR. For experiments with short-lived rare isotope beams the RESR serves the task of fast deceleration. Precooled rare isotope beams will be injected at 740 MeV/u and then decelerated to energies between 100 and 400 MeV/u in less than 1 s. This contribution presents the ring design and lattice studies relevant for both tasks of the ring as well as a description of the antiproton accumulation scheme. | ||
| MOPCH075 | Internal Target Effects in the ESR Storage Ring with Cooling | 202 |
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| The accurate description of beam-target effects is important for the prediction of operation conditions in terms of high luminosity and beam quality in the FAIR facility at GSI. Numerical models have been developed to evaluate beam dynamics in ion storage rings, where strong cooling in combination with a dense target is applied. First systematic benchmarking experiments were carried out at the existing ESR storage ring at GSI. The influence of the internal target on the beam parameters is demonstrated. Comparison of experimental results with simple models describing the energy loss of the beam particles in the target as well as with more sophisticated simulations with the BETACOOL code will be given. | ||
| MOPCH076 | Baseline Design for the Facility for Antiproton and Ion Research (FAIR) Finalized | 205 |
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| The baseline design for the future international facility FAIR has been worked out. The unique accelerator complex will provide high intensity ion beams ranging from antiprotons to uranium for nuclear matter and hadron physics studies. Radioactive beams are generated for nuclear structure and astrophysics experiments. Phase space compression utilizing stochastic and electron cooling allow for fundamental tests at highest precision. Centered around two fast ramping superconducting synchrotrons, ions are accelerated to a beam rigidity of up to 100 Tm and 300 Tm, respectively. Two dedicated storage rings serve for beam accumulation and cooling, providing unprecedented beam quality for experiments in the NESR and HESR storage rings. An overview of the layout of the accelerator complex and beam delivery systems is given. Ongoing R&D activities are reported; project status and international participation will be presented. | ||
| MOPCH077 | The Collector Ring CR of the FAIR Project | 208 |
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| The Collector Ring is a storage ring in the framework of the FAIR project. It has the purpose of stochastic precooling of both rare isotope and antiproton beams and of measurung nuclear masses in an isochronous setting. The paper discusses progress in the development of magnet systems, rf systems, injection/extraction strategies and stochastic cooling systems. Finally it is discussed how to confirm the predicted performance of the slotline electrodes developed recently for stochastic cooling. | ||
| MOPCH078 | Simulation of Dynamic Vacuum Induced Beam Loss | 211 |
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| In synchrotrons, operated with intermediate charge state, heavy ion beams, intensity dependent beam losses have been observed. The origin of these losses is the change in charge state of the beam ions at collisions with residual gas atoms or molecules. The resulting A/Z deviation from the reference beam ion leads to modified trajectories in dispersive elements, which finally results in beam loss. At the impact positions, secondary particles are produced by ion stimulated desorption and increase the vacuum pressure locally. In turn, this pressure rise will enhance the charge change- and particle loss process and finally cause significant beam loss within a very short time (a few turns). A program package has been developed, which links the described beam loss mechanisms to the residual gas status and determines the vacuum dynamics. Core of the program is an ion optics tracking routine, in which the atomic physics and vacuum effects are embedded. | ||
| MOPCH079 | Ion Optical Design of the Heavy Ion Synchrotron SIS100 | 214 |
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| We present the ion optical design of SIS100, which is the main synchrotron of the FAIR project. The purpose of SIS100 is the acceleration of high intensity heavy ion and proton beams and the generation of short compressed single bunches for the production of secondary beams. Since ionization in the residual gas is the main loss mechanism, a new lattice design concept had to be developed, especially for the operation with intermediate charge state heavy ions. The lattice was optimized to generate a peaked loss distribution in charge separator like lattice cells. Thereby it enables the control of generated desorption gases in special catchers. For bunch compression, the lattice provides dispersion free straight sections and a low dispersion in the arcs. A special difficulty is the optical design for fast and slow extraction, and the emergency dumping of the high rigidity ions within the same short straight section. | ||
| MOPCH080 | Design of the NESR Storage Ring for Operation with Ions and Antiprotons | 217 |
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| The New Experimental Storage Ring (NESR) of the FAIR project has two major modes of operation. These are storage of heavy ion beams for internal experiments and deceleration of highly charged ions and antiprotons before transfer into a low energy experimental area. The heavy ion beams can be either stable highly charged ions or rare isotope beams at an energy of 740 MeV/u selected in a magnetic separator. The antiprotons come with an energy of 3 GeV from the production target, they are pre-cooled and accumulated in a storage ring complex. The magnetic structure of the NESR has been optimized for large transverse and longitudinal acceptance by detailed dynamic aperture calculations. This will allow storage of multi-component beams with a large spread of charge to mass ratio, corresponding to a large spread in magnetic rigidity. Highest phase space density of the stored beams is provided by an electron cooling system, which for ions covers the full energy range and for antiprotons allows intermediate cooling during the deceleration process. For experiments with short-lived isotopes the cooling time and the time of deceleration will be optimized to a few seconds. | ||
| MOPCH081 | FLAIR: a Facility for Low-energy Antiproton and Ion Research | 220 |
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| To exploit the unique possibilities that will become available at the Facility for Antiproton and Ion Research (FAIR), a collaboration of about 50 institutes from 15 countries was formed to efficiently enable an innovative research program towards low-energy antimatter-physics. In the Facility for Low-energy Antiproton and Ion Research (FLAIR) antiprotons and heavy ions are slowed down from 30 MeV to energies as low as 20 keV by a magnetic and an electrostatic storage ring. In this contribution, the facility and the research program covered are described with an emphasis on the accelerator chain and the expected particle numbers. An overview of the novel beam handling, cooling and imaging techniques as they will be required across the facility is given. | ||
| MOPCH083 | Design Study for an Antiproton Polarizer Ring (APR) | 223 |
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In the framework of the FAIR* project, the PAX collaboration has suggested a new experiments using polarized antiprotons**, in particular the study of the transverse spin structure of the proton. To polarize antiprotons the spin filtering method is proposed. The PAX collaboration is going to design the Antiproton Polarizer Ring (APR). In this contribution the design of this storage ring is described. The basic parameters of the APR are antiproton beam energy of 250 MeV and emittance in both planes of 250 pi mm mrad. The APR consists of two 180 degree arcs and two straight sections. One straight section houses the injection/extraction and the polarized internal target cell, in the other straight section, the electron cooler and a Siberian snake are located. Different optical conditions have to be fulfilled in the straight sections: (1) The target cell requires a beta function of less than 0.3 m. (2) The beam has to be circular and upright in the phase space ellipse at the target, the electron cooler, and the snake. (3) The antiproton beam should have a size of 10 mm for an emittance of 250 pi mm mrad. (4) The momentum dispersion has to be zero in both straight sections.
*Conceptual Design Report for an International Accelerator Facility for Research with Ions and Antiprotons, available from www.gsi.de/GSI-Future/cdr.**PAX Technical Proposal, available from www.fz-juelich.de/IKP/pax. |
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| MOPCH084 | From COSY to HESR | 226 |
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| The High Energy Storage Ring (HESR) at the proposed Facility for Antiproton and Ion Research (FAIR) puts strong demands on quality and intensity of the stored antiproton beam in the presence of thick internal targets. The existing synchrotron and storage ring COSY in Juelich can be seen as a smaller model of the HESR. In this paper we will discuss possible benchmarking experiments at COSY, involving effects like beam cooling, target heating, intra-beam scattering, etc. The aim of these experiments is to support the design work for the HESR and ensure that the specified beam conditions can be achieved. | ||
| MOPCH085 | Pickup Structures for the HESR Stochastic Cooling System | 228 |
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| The design of the High-Energy Storage Ring (HESR) of the future International Facility for Antiproton and Ion Research (FAIR) at the GSI in Darmstadt includes electron and stochastic cooling. Simulations have shown that the bandwidth of a 2-4 GHz stochastic cooling system is sufficient to achieve the requested beam parameter at the internal target. New 2-4 GHz pickup structures have been developed and tested. First results of the low impedance, printed loop structures will be presented. | ||
| MOPCH086 | Stochastic Cooling for the HESR at the GSI-FAIR Complex | 231 |
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| The High-Energy Storage Ring (HESR) of the future International Facility for Antiproton and Ion Research (FAIR) at the GSI in Darmstadt is planned as an anti-proton cooler ring in the momentum range from 1.5 to 15 GeV/c. An important and challenging feature of the new facility is the combi-nation of phase space cooled beams with internal targets. The required beam parameters and intensities are prepared in two operation modes: the high luminosity mode with beam intensities up to 1011 and the high reso-lution mode with 1010 anti-protons cooled down to a relative momentum spread of only a few 10-5. In addition to electron cooling, transverse and longitudinal stochastic cooling are envisaged to accomplish these goals. It is shown how the great benefit of the stochastic cooling system to adjust the cooling force in all phase planes independently is utilized to achieve the requested beam spot and the high momentum resolution at the internal target within reasonable cooling down times for both HESR modes even in the presence of intra-beam scattering. A numerical and analytical approach to the Fokker-Planck equation for longitudinal filter cooling has been carried out. | ||
| MOPCH087 | Quasi-adiabatic Transition Crossing in the Hybrid Synchrotron | 234 |
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Non-adiabatic features around the transition energy are well-known to be one of most important beam physics issues in most of circular hadron accelerators. A novel technique to avoid them by the adiabatic motion, a quasi-adiabatic focusing-free transition crossing (QAFFTC), was proposed. In a longitudinally separated function-type accelerator*, in which particles are confined by an rf voltage or burrier voltages and accelerated by a step voltage, the confinement voltage can be arbitrarily manipulated as long as the particles do not diffuse, while a strict acceleration voltage is necessary for the orbit of a charged particle to be balanced in the radial direction. The introduction of QAFFTC is most suitable for the longitudinally separated function-type accelerator. This new method was examined in this type of accelerator**, both theoretically and experimentally. This was a first and significant application of the hybrid synchrotron. The results will be presented.
*K. Takayama and J. Kishiro, Nucl. Inst. Meth. A 451, 304 (2000).**K. Takayama et al. Phys. Rev. Lett. 94, 144801 (2005). |
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| MOPCH088 | Ion Cooler Storage Ring, S-LSR | 237 |
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Ion cooler and storage ring, S-LSR has been constructed. Its beam commissioning has been successfully performed since October, 2005 and electron beam cooling for 7 MeV proton beam has been performed with both flat and hollow spatial distributions. Effect of relative velocity sweep between electron and ion beams on the cooling time* has been confirmed. Based on the success to create the peaks in the energy spectrum of laser-produced ions, injection of laser-produced ions into S-LSR after rotation in the longitudinal phase space by an RF cavity synchronized to the pulse laser is under planning in order to apply electron cooling for such real laser produced hot ions. Three dimensional laser cooling satisfying the condition of 'tapered cooling' is also under investigation. 24Mg+ ions are to be laser-cooled only in the 'Wien Filter' in order to be cooled down to the appropriate energy according to their horizontal positions**. In parallel with the computer simulation, construction of the laser cooling system with use of ring dye laser accompanied with the second harmonics generator is now underway.
*H. Fadil et al. Nucl. Instr. & Meth. in Phys. Res. A517, 1-8 (2004).**A. Noda and M. Grieser, Beam Science and Technology, 9, 12-15 (2005). |
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| MOPCH089 | Basic Aspects of the SIS100 Correction System Design | 240 |
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| The basic concept and the main design features of the superconducting SIS100 correction system are presented. The system comprises 84 steerer magnets consisting of two orthogonal dipole windings each for correction of the beam close orbit in vertical and horizontal planes, 48 normal sextupole windings connected in two families with opposite polarities for chromaticity correction and 12 units containing skew quadrupoles, normal and skew sextupoles and octupoles as well. The correction system should operate in a pulse mode corresponding to the accelerator cycle, i.e., up to 1 Hz. The main magnetic, geometrical and electrical parameters of the corrector magnets were specified. They are based on the beam dynamic analysis within the frames of the DF-type SIS100 lattice at different betatron tune numbers and tolerable alignment and manufacturing errors of the main lattice dipole and quadrupole magnets. The problem of reasonable unification of the corrector modules is discussed also, including their geometrical sizes, maximum supply current and cooling at 4.5 K. The concept of the SIS100 corrector magnets is based on the pulsed correctors designed for the Nuclotron. | ||
| MOPCH090 | ITEP-TWAC Status Report | 243 |
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Three years of successful operation the ITEP-TWAC facility delivers proton and ion beams in several modes of acceleration and accumulation of by using the multiple charge exchange injection technique*. Substantial progress is achieved in output ion beam current intensity of the linear injector I3, in intensity of the buster synchrotron UK, in efficiency increasing of ion beam stacking and longitudinal compression in the storage ring U10. The machine status analysis and current results of activities aiming at subsequent improvement of beam parameters for extending beam technology applications are presented.
*N. Alexeev et al. Laser and Particle Beams (2002) V 20, N3, 385-392. |
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| MOPCH091 | An Alternative Nonlinear Collimation System for the LHC | 246 |
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| The optics design of an alternative nonlinear collimation system for the LHC is presented. We discuss an optics scheme based on a single spoiler located in between a pair of skew sextupoles for betatron collimation. The nonlinear system allows opening up the collimator gaps and, thereby reduces the collimator impedance, which presently limits the LHC beam intensity. After placing secondary absorbers at optimum locations behind the spoiler, we analyze the beam losses and calculate the cleaning efficiency from tracking studies. The results are compared with those of the conventional linear collimation system. | ||
| MOPCH092 | CRYRING Machine Studies for FLAIR | 249 |
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| At the FLAIR facility (Facility for Low-energy Antiproton and Ion Research) at FAIR, antiprotons and heavy ions will be decelerated to very low energies and ultimately to rest. One step in this deceleration is made in the magnetic storage ring LSR (Low-Energy Storage Ring). CRYRING at the Manne Siegbahn Laboratory in Stockholm will be closed down within the next few years, and since CRYRING has an energy range quite similar to the proposed LSR, is equipped with beam cooling, and has several other features required for a deceleration ring, plans are being made for the transfer of CRYRING to FAIR and for its use as the LSR ring. This paper describes some of the characteristics of CRYRING relevant for its new role, modifications that need to be made, and test that have been performed at CRYRING with, e.g., deceleration of protons from 30 MeV to 300 keV kinetic energy, which is the proposed energy range for antiprotons at LSR. | ||
| MOPCH093 | Design of the Double Electrostatic Storage Ring DESIREE | 252 |
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| A double electrostatic storage ring named DESIREE is under construction at the Manne Siegbahn Laboratory and Stockholm University. The two rings will have the same circumference, 9.2 m, and a common straight section where merged beam experiments with ions of opposite signs will be performed. The whole structure will be contained in a single vacuum vessel resulting in a very compact design. In addition to its unique double ring structure it will be possible to cool DESIREE down to 10-20K using cryogenerators. This will reduce the internal vibrational and rotational excitations of stored molecules. A cold system will also result in excellent vacuum conditions where longer lifetimes of the stored beams can be expected. While the ion optical calculations have entered a final phase much of the work is now devoted to solve many of the mechanical and cryogenic challenges of DESIREE. In order to test the mechanical and cryogenic properties of for example insulators, vacuum seals, and laser viewports a small test system has been built. The test system is expected to provide valuable information for the final design of DESIREE. | ||
| MOPCH094 | Low-intensity Beams for LHC Commissioning from the CERN PS-booster | 255 |
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| A variety of low-intensity beams will be required for LHC commissioning. In contrast to the nominal LHC physics beam, these single-bunch beams are produced without longitudinal bunch splitting in the injector chain. Consequently, not only the transverse but also the longitudinal beam characteristics have already to be established in the CERN PS-Booster. The required intensities extend down to four orders of magnitude below the typical PS-Booster working range and the transverse emittances must be adjustable to vary the beam brightness over a large range. The different beam variants are briefly summarized and the specific techniques developed for their production, like low-voltage rf capture, and transverse and longitudinal shaving, are described. In particular, the choice of harmonic number and its consequences for operation and beam reproducibility are discussed. Finally, the performance achieved for the different beams is summarized. | ||
| MOPCH095 | Performance of Nominal and Ultimate LHC Beams in the CERN PS-booster | 258 |
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| The requirements for nominal and ultimate LHC beams in the CERN PS-Booster were specified in 1993 and served as input for the definition of the "PS conversion for LHC" project. Already during the upgrade project and also after its completion in 2000, the beam intensities to be provided from the PS Booster were increased in order to compensate for changes on the LHC machine, the beam production scheme in the PS and for non-anticipated beam losses along the injector chain. In order to improve the beam brightness, to be compatible with the increased requirements, extensive machine studies have taken place on the PS-Booster. The working point was changed to reduce the influence of systematic resonances and the injection line optics was re-matched to improve the injection efficiency. The paper summarizes briefly the evolution of the performance requirements. The various measures undertaken to improve the LHC beam quality are outlined and the present performance achieved in the PS-Booster is presented. | ||
| MOPCH096 | LEIR Lattice | 261 |
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| The Low Energy Ion Ring (LEIR) is a low energy ion cooling and accumulation ring and serves to compress long ion pulses from Linac 3 into high density bunches suitable for LHC ion operation. Issues of the LEIR lattice are to fulfil all constraints with a small number of quadrupoles and compensations of perturbations due to an electron cooler and gradients seen by the beam in the bending magnets during the ramp. Furthermore, experimental investigations via orbit reponse measurements will be reported. | ||
| MOPCH097 | CERN Proton Synchrotron Working Point Control Using an Improved Version of the Pole-face-windings and Figure-of-eight Loop Powering | 264 |
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| The working point of the CERN Proton Synchrotron, which is equipped with combined function magnets, is controlled using pole-face-windings. Each main magnet consists of one focusing and one de-focusing half-unit on which four pole-face-winding plates are mounted containing two separate coils each, called narrow and wide. At present they are connected in series, but can be powered independently. In addition, a winding called the figure-of-eight loop, contours the pole faces and crosses between the two half units, generating opposite fields in each half-unit. The four optical parameters, horizontal and vertical tune and chromaticity, are adjusted by acting on the pole-face-winding currents in both half units and in the figure-of-eight loop, leaving one physical quantity free. The power supply consolidation project opened the opportunity to use five independent power supplies, to adjust the four parameters plus an additional degree of freedom. This paper presents the results of the measurements that have been made in the five-current mode together with the influence of the magnetic nonlinearities, due to the unbalance in the narrow and wide winding currents, on the beam dynamics. | ||
| MOPCH098 | LHC@FNAL: A Remote Access Center for the LHC at Fermilab | 267 |
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| A facility is being designed at Fermilab to help people contribute to the Large Hadron Collider (LHC) effort at CERN. This facility is called LHC@FNAL. The purpose of LHC@FNAL is to permit members of the LHC community in North America contribute their expertise to LHC activities at CERN, and to assist CERN with the commissioning and operation of the LHC accelerator and CMS experiment. As a facility, LHC@FNAL has three primary functions: 1) To provide access to information in a manner that is similar to what is available in control rooms at CERN, and to enable members of the LHC community to participate remotely in LHC and CMS activities. 2) To serve as a (bidirectional) communications conduit between CERN and members of the LHC community located in North America. 3. To allow visitors to Fermilab to see firsthand how research is progressing at the LHC. Visitors will be able to see current LHC activities, and will be able to see how future international projects in particle physics can benefit from active participation in projects at remote locations. LHC@FNAL is expected to contribute to a wide range of activities for the CMS experiment and for the LHC accelerator. | ||
| MOPCH099 | Performance and Capabilities of the NASA Space Radiation Laboratory at BNL | 270 |
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| The NASA Space Radiation Laboratory (NSRL) at BNL has been in operation since 2003. The first commissioning of the facility took place beginning in October 2002 and the facility became operational in July 2003. The facility was constructed in collaboration with NASA for the purpose of performing radiation effect studies for the NASA space program. The NSRL is capable of making use of protons and heavy ions in the range of 0.05 to 3 GeV/n slow extracted from BNL's AGS Booster. It is also capable of making use of protons and heavy ions fast extracted from the AGS Booster. Many different beam conditions have been produced for experiments at NSRL, including very low intensity In this report we will describe the facility and its' performance over the eight experimental run periods that have taken place since it became operational. We will also describe the current and future capabilities of the NSRL. | ||
| MOPCH100 | Polarized Proton Acceleration in the AGS with Two Helical Partial Snakes | 273 |
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| Acceleration of polarized protons in the energy range of 5 to 25 GeV is particularly difficult: the depolarizing resonances are strong enough to cause significant depolarization but full Siberian snakes cause intolerably large orbit excursions and it is not feasible in the AGS since straight sections are too short. Recently, two helical partial snakes with double pitch design have been built and installed in the AGS. With careful setup of optics at injection and along the ramp, this combination can eliminate intrinsic and imperfection depolarizing resonances encountered during acceleration. This paper presents the accelerator setup and preliminary results. The effect of horizontal intrinsic resonances in the presence of two partial snakes are also discussed. | ||
| MOPCH101 | On the Feasibility of a Spin Decoherence Measurement | 276 |
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| In this paper, we study the feasibility of making a turn-by-turn spin measurement to extract the spin tune of a synchrotron from a polarized beam injected perpendicular to the stable spin direction. For the ideal case of a zero-emittance beam with no spin-tune spread, there would be no spin decoherence and a measurement of the spin tune could easily be made by collecting turn-indexed polarization data of several million turns. However, in a real beam there is a momentum spread which provides a tune spread. With a coasting beam the tune spread will cause decoherence of the spins resulting in a fast depolarization of the beam in a thousand turns. With synchrotron oscillations the decoherence time can be greatly increased, so that a measurement becomes feasible with summation of the turn-by-turn data from a reasonable number of bunches (100 or fewer). Both the cases of a single Siberian snake and a pair of Siberian snakes are considered. | ||
| MOPCH102 | A Straight Section Design in RHIC to Allow Heavy Ion Electron Cooling | 279 |
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| The Relativistic Heavy Ion Collider (RHIC) has been continuously producing exciting results. One of the major luminosity limitations of the present collider is the intra beam scattering. A path towards the higher luminosities requires cooling of the heavy ion beams. Two projects in parallel electron and stochastic cooling are progressing very well. To allow interaction between electrons and the RHIC beams it is necessary to redesign one of the existing interaction regions in RHIC to allow for the longer straight section with fixed and large values of the betatron functions. We present a new design of the interaction region for the electron cooling in RHIC. | ||
| MOPCH103 | SPIRAL2 RFQ Prototype – First Results | 282 |
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| The SPIRAL2 RFQ has been designed to accelerate a 5 mA deuteron beam (Q/A=1/2) or a 1 mA particle beam with q/A=1/3 up to 0.75 MeV/A at 88MHz. It is a CW machine which has to show stable operation, provide the required availability and reduce losses to a minimum in order to minimize the activation constraints. Extensive modelisation was done to ensure a good vane position under RF. The prototype of this 4-vane RFQ has been built and tested in INFN-LNS Catania and then in IN2P3-LPSC Grenoble. It allowed us to measure the vacuum quality, the RF field by X-ray measurements, the cavity displacement and the real vane displacement during the RF injection. Different techniques were used, including an innovative and effective CCD measurement with a 0.6 μm precision. This paper outlines the different results. | ||
| MOPCH105 | A New RF Tuning Method for the End Regions of the IPHI 4-vane RFQ | 285 |
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| The 3-MeV High Intensity Proton Injector (IPHI) RFQ is constituted by the assembly of three 2-m-long segments. The tuning of the end regions of such an accelerator with respect to the quadrupole mode is generally made by machining the thickness of the end plates. The dipole modes are moved away from the accelerator mode frequency by adding dipole rods and adjusting their length. In the case of the last IPHI RFQ segment, the tuning range given by possible plate thickness was not sufficient to adjust the frequency at 352 Mhz without modifying the notch depth, leading to serious engineering problems for the cooling, new thermo-mechanical simulations and drawings. To avoid these difficulties, a new way has been investigated by replacing the end plate thickness adjustment by a "quadrupole rod" length adjustment. These rods are situated between the beam axis and the dipole rods, and the tuning range is largely increased. The paper will describe this method applied to the IPHI RFQ and some experimental results obtained on the cold model. | ||
| MOPCH106 | An Innovative Method to Observe RFQ Vanes Motion with Full-scale RF Power and Water Cooling | 288 |
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| The design of high current RFQs is heavily strained by thermo-mechanical considerations, which eventually have an impact on machining costs, cooling systems, etc. A 1-meter long copper prototype of the SPIRAL2 RFQ has been specifically built to corroborate design options. An innovative method has been developed, allowing real-time observation of mechanical deformations of RFQ vanes, with full-scale RF power and water cooling. Digital images are acquired by a CCD camera, and processed by a dedicated software. Processing includes contrast stretching, low-pass filtering, and block-correlation followed by interpolation. Sub-pixel relative motions of RFQ electrode ends are clearly detected and measured, with RMS errors of the order of 0.6 microns. | ||
| MOPCH107 | Tuning Procedure of the 6 Meter IPHI RFQ | 291 |
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| In the framework of the IPHI project (High Intensity Proton Injector), the RFQ cavity is divided into 6 sections of 1 meter each, and assembled in 3 segments separated by coupling plates. We will present the tuning procedure of the aluminium RFQ cold model to set the accelerating mode frequency, a flat voltage profile and to minimize the dipole components of the accelerating voltage. This tuning procedure can be divided in three steps. First, dipole mode frequencies are adjusted with rods for the 3 separated segments. Second, RFQ end cells and coupling cells are tuned by mechanical machining of tuning plates. Third, using a fully automated bead-pull for the measurement of the field distribution inside every RFQ quadrants, the RFQ is tuned with 96 plungers in a small number of iterations. Tuning this 6-meter long cold model is a comprehensive training in view of the future tuning of the copper RFQ with the variable voltage profile. | ||
| MOPCH108 | Error Study of LINAC 4 | 294 |
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| Within the framework of the Joint Research Activity HIPPI (High Intensity Pulsed Proton Injector) of the CARE program, the conception study of the LINAC 4 accelerator which aims to intensify the proton flux available for the CERN injection line is pursued. The linac, operating in pulsed mode at 352 MHz, is designed to accelerate a 65 mA beam of H- ions up to an energy of 160 MeV. The requirements on acceptable beam emittance growth and particle loss are extremely tight. In order to determine the Drift Tube Linac tolerances, we examined the sensitivity of the LINAC 4 DTL to errors on the accelerating field and the focusing quadrupoles. Simulations were performed with the transport code TRACEWIN (CEA-Saclay, France). We will present results on individual sensitivities to a single error as well as the global impact of alignment and RF errors on the beam quality. Similarly, accelerating structures following the DTL in the LINAC4 design (CCDTL, SCL) have been studied. | ||
| MOPCH109 | Design Studies on a Novel Stellarator Type High Current Ion Storage Ring | 297 |
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| A high current storage ring for the accumulation of ion beams provided by a new 150 kV terminal is under consideration at the Frankfurt University. The configuration based on a toroidal magnetic field seems promising for the storage of intense low energy ion beams, especially when concerning the various potential concepts for space charge compensation. The theory of plasma confinement on magnetic surface is transformed to numerical simulations on circulating ion beams. The space charge effects and stability conditions are studied and will be presented. Various injection techniques based on crossed field-drifts are investigated. Accordingly test experiments are prepared based on two 30 degree toroidal sectors at a major radius of 1.3m with a maximum toroidal magnetic field of 0.6T on axis. | ||
| MOPCH111 | A Fast Beam Chopper for the RAL Front End Test Stand | 300 |
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| The FETS project at RAL will test a fast beam chopper, designed to address the requirements of high power proton drivers for next generation pulsed spallation sources and neutrino factories. A description is given of the novel RAL 'Fast - Slow' chopping scheme, and of candidate optical designs for the 3.0 MeV, 60 mA, H- Medium Energy Beam Transport (MEBT) line. | ||
| MOPCH112 | The RAL Front End Test Stand | 303 |
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| High power proton accelerators (HPPAs) with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. These applications typically propose beam powers of 5 MW or more compared to the highest beam power achieved from a pulsed proton accelerator in routine operation of 0.16 MW at ISIS. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London and the University of Warwick. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational regimes. This paper describes the status of the RAL Front End Test Stand which consists of five main components: a 60 mA H- ion source, a low energy beam transport, a 324 MHz Radio Frequency Quadrupole accelerator, a high speed beam chopper and a comprehensive suite of diagnostics. The aim is to demonstrate production of a 60 mA, 2 ms, 50 pps, chopped H- beam at 3 MeV. | ||
| MOPCH113 | Re-bunching RF Cavities and Hybrid Quadrupoles for the RAL Front-end Test Stand (FETS) | 306 |
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| The proposed FETS project at RAL will test a fast beam chopper in a 3.0 MeV H- Medium Energy Beam Transport (MEBT) line. Space restrictions in the MEBT line place constraints on component length and drive the requirement to identify compact component configurations. A description is given of candidate re-bunching RF cavities and hybrid quadrupole designs. The cavity options considered are the space efficient Drift Tube Linac type cavity (DTL) with integrated quadrupoles, and the high shunt impedance Coupled Cavity Linac type cavity (CCL) with external quadrupoles. The advantages and disadvantages of both structures are discussed and a comprehensive comparison between the two is made enabling the best cavity geometry choice. The compact hybrid quadrupole configurations considered are the 'tandem' combination of permanent magnet (PMQ) and electro-magnetic (EMQ) types, and the concentric combination of PMQ and laminar conductor (Lambertson) EMQ types. | ||
| MOPCH114 | Progress on Dual Harmonic Acceleration on the ISIS Synchrotron | 309 |
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| The ISIS facility at the Rutherford Appleton Laboratory in the UK is currently the most intense pulsed, spallation, neutron source. The accelerator consists of a 70 MeV H- Linac and an 800 MeV, 50 Hz, rapid cycling, proton Synchrotron. The synchrotron beam intensity is 2.5·1013 protons per pulse, corresponding to a mean current of 200 μA. The synchrotron beam is accelerated using six, ferrite loaded, RF cavities with harmonic number 2. Four additional, harmonic number 4, cavities have been installed to increase the beam bunching factor with the potential of raising the operating current to 300 μA. As ISIS has a busy user schedule the time available for dual harmonic work has been limited. However, much progress has been made in the last year and encouraging results have been obtained. This paper reports on the hardware commissioning and beam tests with dual harmonic acceleration. | ||
| MOPCH115 | Transverse Space Charge Studies for the ISIS Synchrotron | 312 |
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| The ISIS Facility at the Rutherford Appleton Laboratory in the UK produces intense neutron and muon beams for condensed matter research. It is based on a 50 Hz proton synchrotron which, once the commissioning of a new dual harmonic RF system is complete, will accelerate about 3.5·1013 protons per pulse from 70 to 800 MeV, corresponding to mean beam powers of 0.2 MW. Following this upgrade, transverse space charge is expected to be one of the main intensity limitations, and is also a key factor for further machine upgrades. A programme of R&D on transverse space charge is now under way, aiming not only to improve the ISIS ring but also to exploit it as an experimental tool for testing theory and codes. This paper summarises work so far, outlining calculations for coherent envelope modes on ISIS, using numerical solutions of the envelope equation to show the expected behaviour near half integer resonance. Progress on work linking these predictions with more realistic beam models in space charge codes, and extending calculations to images, coupling and non linear resonances will be described. Plans and preparations for experiments, along with initial results, will also be presented. | ||
| MOPCH116 | Electromagnetic Design of a Radio Frequency Quadrupole for the Front End Test Stand at RAL | 315 |
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| The goal of the RAL front end test stand is to demonstrate cleanly chopped bunches of a 60mA H- ion beam at 3MeV. The acceleration of the H- ions from 65keV to 3MeV will be done using a radio frequency quadrupole (RFQ) operating at a resonant frequency of 324MHz. The two types of RFQ considered were a 4-vane and a 4-rod. The 4-vane has a higher Q-value but the post-production adjustment is limited. The 4-rod design is easier to manufacture but requires complicated cooling at 324MHz. The results of electromagnetic simulations using CST Microwave Studio are presented for the 4-vane type and 4-rod type RFQ. | ||
| MOPCH117 | Mechanical Design and RF Measurement on RFQ for Front-end Test Stand at RAL | 318 |
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| This paper will present the mechanical design and preliminary results of a RF measurement system for the cold model of a 324MHz 4-vane RFQ, which is part of the development of a proton driver front end test stand at the Rutherford Appleton Laboratory (RAL) in the UK. The design concepts will be discussed and some issues in manufacturing of the RFQ will be pointed out, and specific modifications will be explained. Furthermore, results of thermal simulations of the RFQ will be presented together with RF simulations of the resonant frequency, the Q-value and the longitudinal field distribution. | ||
| MOPCH118 | Wideband Low-output-impedance RF System for the Second Harmonic Cavity in the ISIS Synchrotron | 321 |
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| Wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron has been developed by the collaboration between Argonne National Laboratory, US, KEK, Japan and Rutherford Appleton Laboratory, UK. Low output impedance is realized by the feedback from plate output to grid input of the final triode amplifier, resulting in less than 30 ohms over the frequency range of 2.7 - 6.2 MHz which is required for the second harmonic cavity. The vacuum tubes in the driver and final stages are both operated in class A, and a grid bias switching system is used on each tube to avoid unnecessary plate dissipations during a non-acceleration cycle. High power test was performed with a ferrite-loaded second harmonic cavity, where the bias current was swept at 50 Hz repetition rate. The maximum voltage of 12kV peak per accelerating gap was obtained stably at earlier period of an acceleration cycle. A beam test with this system is planned at the ISIS synchrotron in order to investigate how the low impedance system works under heavy beam loading conditions, and is capable of mitigating the space charge detuning at the RF trapping stage. | ||
| MOPCH119 | Present Status of the Induction Synchrotron Experiment in the KEK PS | 324 |
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A concept of the induction synchrotron, which was proposed by Takayama and Kishiro in 2000, has been demonstrated by using the KEK PS since 2004. A proton bunch trapped in the RF bucket was accelerated with the induction acceleration devices from 500 MeV to 8 GeV*, which was energized with the newly developed switching power supply. This form of the KEK PS is something like a hybrid synchrotron. In addition, the injected proton bunch was confined by the step barrier-voltages at the injection energy of 500MeV**, which were generated with the same induction acceleration device. Then a concept of the induction synchrotron that a proton bunch was captured by the barrier bucket and accelerated with the induction voltage is to be fully demonstrated.
*K. Takayama et al. "Observation of the Acceleration of a Single Bunch by Using the Induction Device in the KEK Proton Synchrotron", Phys. Rev. Lett., 94, 144801 (2005).**K. Torikai et al. "Acceleration and Confinement of a Proton Bunch with the Induction Acceleration System in the KEK Proton Synchrotron", submitted to Phys. Rev. ST-AB (2005), KEK-Preprint 2005-80 A, December 2005. |
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| MOPCH120 | Ground Motion Study and the Related Effects on the J-PARC | 327 |
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| The power spectrum density, coherence and cross-spectrum density of the ground motion in the J-PARC site are studied to get the guideline of the beam control systems. J-PARC consists of a 600 MeV linac, a 3 GeV Rapid-cycling synchrotron (RCS) and a 50 GeV synchrotron (MR). MR provides a beam current of 15 micro-A with a period of 3 sec to either the nuclear physics experimental area or the neutrino production target. MR is a very high beam power machine, so its optimum beam loss must be kept fewer than 0.01% of an accelerated beam in order to decrease the radiation damage of accelerator components and to get easy accessibilty to them. From the point of view of beam loss, we give some detailed discussion about the relation between the MR operation and the ground motion using the observed data. | ||
| MOPCH121 | Ground Motion Measurement at J-PARC | 330 |
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| In the next generation accelerator, construction of the machine on the stable ground is preferable for accelerator beam operation. We have measured ground motion at the J-PARC site under construction, where the ground is very close to the Pacific Ocean. In this paper, some of the observed results are shown, comparing the results of the previous observation at some accelerator facilities and next generation accelerator candidate sites in Japan. | ||
| MOPCH122 | Realistic Beam Loss Estimation from the Nuclear Scattering at the RCS Charge-exchange Foil | 333 |
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| We have developed simulation tools for the realistic beam loss estimation at the RCS(rapid cycling synchrotron) of J-PARC(Japan Proton Accelerator Research Complex). The present simulation concerns an accurate estimation of the beam loss caused by the nuclear scattering at the charge-exchange foil during the multi turn injection period. It can also figure out the loss point in the ring, so would become very useful for the maintenance and optimization as well. The simulation code GEANT together with the SAD(Strategic Accelerator Design) have been used for the present purpose. In this paper, detail simulation method including the result will be discussed. | ||
| MOPCH124 | Energy Deposition in Adjacent LHC Superconducting Magnets from Beam Loss at LHC Transfer Line Collimators | 336 |
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| Injection intensities for the LHC are over an order of magnitude above the damage threshold. The collimation system in the two transfer lines is designed to dilute the beam sufficiently to avoid damage in case of accidental beam loss or mis-steered beam. To maximise the protection for the LHC most of the collimators are located in the last 300 m upstream of the injection point where the transfer lines approach the LHC machine. To study the issue of possible quenches following beam loss at the collimators the entire collimation section in one of the lines, TI 8, together with the adjacent part of the LHC has been modeled in FLUKA. The simulated energy deposition in the LHC for worst-case accidental losses as well as for losses expected during a normal filling is presented. The operational implications are discussed. | ||
| MOPCH126 | Accelerator Research on the Rapid Cycling Synchrotron at IPNS | 339 |
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| The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory is a national user facility for neutron scattering. Neutrons are produced by 70 ns pulses of protons (~3x 1012 protons per pulse) impacting a depleted-uranium target at a pulse repetition rate of 30 Hz. Three accelerators in series (a 750 keV Cockcroft-Walton, 50 MeV Alvarez linac accelerating H- ions, and a 450 MeV rapid-cycling proton synchrotron) provide the beam that is directed to the target. New diagnostics and a third rf cavity that can be operated at either the fundamental or second harmonic of the ring frequency have recently been installed and an experimental program established to try to gain understanding of an instability that limits the charge-per-bunch in the RCS. This program will be described, and preliminary results presented. | ||
| MOPCH127 | SNS Warm Linac Commissioning Results | 342 |
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| The Spallation Neutron Source accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of an H- injector, capable of producing one-ms-long pulses at 60Hz repetition rate with 38 mA peak current, a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The 2.5MeV beam from the Front End is accelerated to 86 MeV in the Drift Tube Linac, then to 185 MeV in a Coupled-Cavity Linac and finally to 1 GeV in the Superconducting Linac. The staged beam commissioning of the accelerator complex is proceeding as component installation progresses. Current results of the beam commissioning program of the warm linac will be presented including transverse emittance evolution along the linac, longitudinal bunch profile measurements at the beginning and end of the linac, and beam loss study. | ||
| MOPCH129 | Status of the SNS Beam Power Upgrade Project | 345 |
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| The baseline Spallation Neutron Source (SNS) accelerator complex, consisting of an H- injector, a 1 GeV linear accelerator, an accumulator ring and associated transport lines, will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. Upgrades to the SNS accelerator and target systems to increase the beam power to at least 2 MW, with a design goal of 3 MW, are in the planning stages. The increased SNS beam power can be achieved primarily by increasing the peak H- ion source current from 38 mA to 59 mA, installing additional superconducting cryomodules to increase the final linac beam energy to 1.3 GeV, and modifying injection and extraction hardware in the ring to handle the increased beam energy. The mercury target power handling capability will be increased to 2 MW or greater by i) mitigating cavitation damage to the target container through improved materials/surface treatments, and introducing a fine dispersion of gas bubbles in the mercury, and ii) upgrading the proton beam window, inner reflector plug and moderators. The upgrade beam parameters will be presented and the required hardware modifications will be described. | ||
| MOPCH130 | Simulations for SNS Ring Commissioning | 348 |
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| In preparation for SNS ring commissioning, a number of operational issues have been studied using ORBIT Code simulations. These include beam injection without the use of time-dependent painting, beam accumulation and transport to the extraction dump and to the target, optimal painting schemes for various beam intensities, detailed tracking through the extraction septum with fully correct geometry, quadrupole current constraints in the ring-to-target transfer line (RTBT), and detailed modeling of H minus carbon foil stripping at injection. All these studies incorporated detailed physics including beam-foil interactions, symplectic single particle tracking, space charge and impedances, and losses due to apertures and collimation. | ||
| MOPCH131 | SNS Ring Commissioning Results | 351 |
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| The Spallation Neutron Source (SNS) comprises a 1.5-MW, 60-Hz, 1-GeV linac, an accumulator ring, associated beam lines, and a spallation neutron target. Construction began in 1999 and the project is on track to be completed in June 2006. By September 2005 the facility was commissioned up through the end of the superconducting linac, and in January 2006 commissioning began on the High Energy Beam Transport beam line, the accumulator ring, and the Ring to Target Beam Transport beam line up to the Extraction Beam Dump. In this paper we will discuss early results from ring commissioning including a comparison of achieved vs. design beam machine parameters and the maximum beam intensity achieved to date. | ||
| MOPCH132 | Coupled Maps for Electron and Ion Clouds | 354 |
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| Contemporary electron cloud models and simulations reproduce second order phase transitions, in which electron clouds grow smoothly beyond a threshold from "off" to "on". In contrast, some locations in the Relativistic Heavy Ion Collider (RHIC) exhibit first order phase transition behaviour, in which electron cloud related outgassing rates turn "on" or "off" precipitously. This paper presents a global framework with a high level of abstraction in which additional physics can be introduced in order to reproduce first (and second) order phase transitions. It does so by introducing maps that model the bunch-to-bunch evolution of coupled electron and ion clouds. This results in simulations that run several orders of magnitude faster, reproduce first order phase transitions, and show hysteresis effects. Coupled maps also suggest that additional dynamical phases (like period doubling, or chaos) could be observed. | ||
| MOPCH133 | An Analytic Calculation of the Electron Cloud Linear Map Coefficient | 357 |
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| The evolution of the electron density during multibunch electron cloud formation can often be reproduced using a bunch-to-bunch iterative map formalism. The coefficients that parameterize the map function are readily obtained by fitting to results from compute-intensive electron cloud simulations. This paper derives an analytic expression for the linear map coefficient that governs weak cloud behaviour from first principles. Good agreement is found when analytical results are compared with linear coefficient values obtained from numerical simulations. This analysis is useful in predicting thresholds beyond which electron cloud formation occurs, and thus in determining safety regions in parameter space where an accelerator can be operated without creating electron clouds. The formalism explicitly shows that the multipacting resonance condition is not a sine qua non for electron cloud formation. | ||
| MOPCH134 | Electron-impact Desorption at the RHIC Beam Pipes | 360 |
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| The electron induced molecular desorption coefficient of a material provides the number of molecules released when an electron hits its surface. This coefficient changes as a function of the material, energy of the electrons, surface status, etc. In this paper, this coefficient is inferred analyzing electron detector and pressure gauge signals during electron clouds at the Relativistic Heavy Ion Collider (RHIC) beam pipes. The evolution of the electron-impact desorption coefficient after weeks of electron bombardment is followed for both baked and unbaked stainless steel chambers, evaluating the feasibility of the scrubbing effect. Measurements of an energy spectrum during multipacting conditions are shown, and the final results are compared with laboratory simulations. | ||
| MOPCH135 | Benchmarking Electron Cloud Data with Computer Simulation Codes | 363 |
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| Saturated electron flux and time decay of the electron cloud are experimentally inferred using many electron detector datasets at the Relativistic Heavy Ion Collider (RHIC). These results are compared with simulation results using two independent electron cloud computer codes, CSEC and ECLOUD. Simulation results are obtained over a range of different values for 1) the maximum Secondary Electron Yield (SEY), and 2) the electron reflection probability at zero energy. These results are used to validate parameterization models of the SEY as a function of the electron energy. | ||
| MOPCH136 | China Spallation Neutron Source Accelerators: Design, Research, and Development | 366 |
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| The Beijing Spallation Neutron Source (BSNS) is a newly approved high power accelerator project based on a H- linear accelerator and a rapid cycling synchrotron. During the past year, several major revisions were made to the design including the type of the front end, linac frequency, transport layout, ring lattice, and type of ring components. Possible upgrade paths were also laid out: based on an extension of the warm linac, the ring injection energy and the beam current could be raised doubling the beam power on target to reach 200 kW; an extension with a superconducting RF linac of similar length could raise the beam power near 0.5 MW. Based on these considerations, research and development activities are started. In this paper, we discuss the rationale of design revisions and summarize the recent work. | ||
| MOPCH137 | An Anti-symmetric Lattice for High Intensity Rapid-cycling Synchrotrons | 369 |
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| Rapid cycling synchrotrons are used in many high power facilities like spallation neutron sources and proton drivers. In such accelerators, beam collimation plays a crucial role in reducing the uncontrolled beam loss. Furthermore, the injection and extraction section needs to reside in dispersion-free region to avoid couplings; a significant amount of drift space is needed to house the RF accelerating cavities; orbit, tune, and chromatic corrections are needed; long, uninterrupted straights are desired to ease injection tuning and to raise collimation efficiency. Finally, the machine circumference needs to be small to reduce construction costs. In this paper, we present a lattice designed to satisfy these needs. The lattice contains a drift created by a missing dipole near the peak dispersion to facilitate longitudinal collimation. The compact FODO arc allows easy orbit, tune, coupling, and chromatic correction. The doublet straight provides long uninterrupted straights. The four-fold lattice symmetry separates injection, extraction, and collimation to different straights. This lattice is chosen for the Beijing Spallation Neutron Source synchrotron. | ||
| MOPCH138 | Choice of Proton Driver Parameters for a Neutrino Factory | 372 |
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| A Neutrino Factory typically comprises the following subsystems: proton driver; target; muon collection and conditioning( bunching, phase rotation, and cooling); muon acceleration; and muon decay ring. It takes great effort to design each subsystem properly, such that it can mesh with all other subsystems to optimize the overall facility performance. This optimization is presently being studied as part of the International Scoping Study of a Future Neutrino Factory and Superbeam Facility. This paper will evaluate the implications of other subsystems on the parameters of a proton driver for a Neutrino Factory. At the desired power of 4 MW, the impacts of the choice of the proton energy, bunch length, bunch intensity, and repetition rate on other subsystems are assessed to identify a proper range of operation for each parameter. A suitable "design phase space" of proton driver parameters is defined. Given possible choices of design parameters for proton driver, we compare the performance of a linac, a synchrotron, and an FFAG accelerator. The relative merits of existing proton driver proposals will also be examined. | ||
| MOPCH139 | Results and Experience with Single Cavity Tests of Medium Beta Superconducting Quarter Wave Resonators at TRIUMF | 375 |
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| A heavy ion superconducting linac is being installed at ISAC/TRIUMF. A first stage of the ISAC-II upgrade will see the installation of 20 quarter wave bulk niobium cavities (Beta0=0.057,0.071). The cavities operate CW at 106MHz with design peak fields of Ep=30MV/m, Bp=60mT while delivering an accelerating voltage of 1.08MV at <7W power consumption. All cavities have been tested in a single cavity test stand with twenty of twenty-one meeting ISAC-II specifications. The cavity test results will be presented. In particular we will discuss our experience with BCP vs. EP surface treatments and with Q-disease. In addition the tuning plates of two of the cavities were modified to provide a unique compensation to the resonant frequency. | ||
| MOPCH140 | Compensation of Lorentz Force Detuning of a TTF 9-cell Cavity with a New Integrated Piezo Tuner | 378 |
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| The high gradient operation of superconducting elliptical multicells in pulsed mode is required for linear colliders or free-electron lasers based on the superconducting technology. Such an operation is limited by dynamic Lorentz force detuning if no compensation for this effect is attempted. The RF power headroom required for accelerating field amplitude and phase stabilisation by low-level RF control techniques solely would be too costly. A new active tuner with integrated piezo actuators has been developped in the framework of the european CARE/SRF program solve this issue. The design is based on the lever-arm concept of the Saclay tuner already installed on running TTF cavities. We have carried out integrated tests of the 9-cell cavity equipped with the piezo tuner and power coupler in the CryHoLab horizontal test cryostat. Characterisation of the electromechanical system consisting of the cavity and piezo-tuner assembly and full power pulsed tests will be presented. | ||
| MOPCH141 | Fast Argon-Baking Process for Mass Production of Niobium Superconducting RF Cavities | 381 |
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Baking is a necessary stage to reach high gradients with niobium superconducting cavities. In the standard process, so called "in-situ UHV baking", Nb cavity is baked at 110°C, during 2 days. During this treatment the inner part of the cavity is pumped out under Ultra High Vacuum conditions. In order to save time, "fast UHV baking" at 145 °C during 3 hours, under UHV pumping, has been successfully demonstrated* with similar improvements for cavity performances compare to the standard treatment. With the same simplification concern, we report here about an alternative method to avoid restrictive UHV requirements. Experiments have been carried out to perform "fast baking" in oxygen-free atmosphere, because bad performances have been observed with "fast baking" in air. These degradations are closely connected with a strong oxygen penetration in bulk analysed by Secondary Ion Mass Spectroscopyon on Nb samples .
*Proceedings of SRF Workshop – Ithaca (July 2005) – TuP05. |
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| MOPCH142 | Commissioning of the SOLEIL RF Systems | 384 |
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| The 352 MHz RF accelerating systems for the SOLEIL Booster (BO) and Storage Ring (SR) are being commissioned. In the BO a 5-cell copper cavity of the CERN-LEP type is powered with a 35kW solid state amplifier. In the SR the required RF accelerating voltage (up to 4.4MV) will be provided by two cryomodules, each containing a pair of superconducting cavities, specifically designed for SOLEIL. The parasitic impedances of the high order modes are strongly attenuated by means of four coaxial couplers, located on the tube connecting the two cavities. The first cryomodule is already installed in the SR tunnel, while the second one is being constructed by ACCEL (Germany). These cryomodules are supplied in liquid helium from a single 350W liquefier and each cavity is powered with a 190kW solid state amplifier. The RF system commissioning and first operation results are reported. | ||
| MOPCH143 | Electromechanical Characterization of Piezoelectric Actuators Subjected to a Variable Preloading Force at Cryogenic Temperature | 387 |
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| Piezoelectric actuators are actually used in Fast Active Cold Tuning Systems (FACTS) for SRF cavities. The characteristics, performances and lifetime of these actuators depend on the preloading force applied by the cavity and the FACTS to the piezostacks. Experimental data are needed for reliable and optimum operation of piezostacks in superconducting protons or electrons linacs. In the frame of the CARE project supported by EU, we designed and constructed a dedicated apparatus for studying the electromechanical behavior of prototype piezoelectric actuators subjected to variable preloading force at cryogenic temperatures. This device was successfully used for testing piezoelectric actuators prototypes for T in the range 2K-300K. The dielectric properties as well as dynamic properties were measured including the actuator characteristics when used as force sensor. The corresponding data are reported and discussed. | ||
| MOPCH144 | Low Temperature Properties of Piezoelectric Actuators Used in SRF Cavities Cold Tuning Systems | 390 |
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| High accelerating gradients (10 MV/m for SNS, 33 MV/m for ILC) at which SRF cavities will be operated in pulsed machines induce frequency shift much higher than the resonator bandwidth. This so-called Lorentz detuning should be compensated dynamically by means of an active piezo-tuning system. In the frame of the CARE project activities supported by EU, IPN Orsay participates to the development of a fast cold tuning system based and piezoelectric technology for SRF cavities operating at temperature T=2K. The aim of this study is the full characterization of piezoelectric actuators at low temperature including dielectric properties (capacitance, impedance, dielectric losses), radiation hardness tests (fast neutron tolerance), mechanical measurements (maximum displacement, maximum stroke) and thermal properties (heating, heat capacity). Results obtained in the temperature range from 2K up to 300K will be presented and discussed. | ||
| MOPCH145 | Tests Results of the Beta 0.07 and Beta 0.12 Quarter Wave Resonators for the SPIRAL2 Superconducting Linac | 393 |
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| New developments and tests have been carried out on low beta (0.07) and high beta (0.12) 88 MHz superconducting Quarter Wave Resonators. These resonators will be installed in the LINAC driver, respectively in the low beta section, composed of cryomodules A (developed at CEA-Saclay) and the high beta section composed of cryomodules B (developed at IPN-Orsay). Both resonators' types will be equipped with the same power coupler (developed at LPSC-Grenoble) and designed for a maximum power of 20 kW. RF tests results of the prototype cavities and power couplers are reported. The fabrication of the two cryomodules prototypes, fully equipped, is in progress in order to be ready for high power RF tests at 4.2 K at the beginning of 2007. | ||
| MOPCH146 | Status of the Beta 0.12 Superconducting Cryomodule Development for the Spiral2 Project | 396 |
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| SPIRAL2 is a radioactive beams facility, composed of a superconducting linac driver, delivering deuterons with an energy up to 40 MeV (5 mA) and heavy ions with an energy of 14.5 MeV/u (1 mA). This facility is now fully approved by the French government. IPN Orsay is in charge of the study and manufacture of the beta 0.12 cryomodule of the superconducting LINAC. These cryomodule, designed for an overall cryogenic power of 30 W at 4.2 K, is composed of two quarter wave type 88 MHz rf resonator providing a minimum of 6.5 MV/m with a quality factor of 1 10 9, two tuning mechanisms controlling the resonator frequency and an alignment system allowing to adjust the cavity position with a ± 1 mm accuracy. Several tests performed on a first resonator prototype fabricated by the "Ettore Zanon SpA" Company, have validated the cavity and its auxiliary components design. A first cryomodule fully equipped (cavities, cryostat, tuning and alignment systems), planned to be tested at the beginning of 2007, is under manufacturing. The details of the cryomodule design and the resonator tests results are discussed in the paper. | ||
| MOPCH147 | Developments in Conditioning Procedures for the TTF-III Power Couplers | 399 |
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| Despite extensive experience in many laboratories on power conditioning of couplers for RF superconducting accelerators, it is still not a well understood procedure and can produce many unpredictable phenomena. There remains considerable interest in reducing the power coupler conditioning time necessary for superconducting linear accelerators. This paper presents studies of optimisation of the conditioning procedure for the couplers intended for use on the European XFEL project. | ||
| MOPCH148 | First RF Tests in the HoBiCaT Superconducting Test Facility at BESSY | 402 |
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| In preparation for the construction of the BESSY-FEL User Facility, BESSY recently completed the installation of the HoBiCaT cryogenic test facility for superconducting RF (SRF) TESLA cavity units, including all ancillary devices (helium tank, input coupler, tuner, magnetic shielding). It is designed to house two such units in a configuration similar to that envisaged for the superconducting CW linac of the BESSY FEL. Commissioning of the facility is now complete and the first TTF-III RF coupler and cavity unit have been tested. In particular, the complete production, cleaning and assembly of the cavity unit was carried out by industry. These tests thus serve as a first step at qualifying industrial partners for series production of such systems, which will be essential for the future construction of SRF based light sources. Results will be presented. | ||
| MOPCH149 | Microphonics Measurements in a CW-driven TESLA-type Cavity | 405 |
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| Superconducting cavities with a high quality factor exhibit a very low bandwidth in their resonant frequency, which makes their operation very sensitive to mechanical oscillations. In CW mode of operation, as is intended for the BESSY-FEL Linac, microphonics are therefore the dominant error source for field stability. In order to compensate the detuning, it is necessary to properly characterize amplitude and frequency with respect to all involved mechanical and electrical components. Such measurements have been performed at the HoBiCaT test facility at BESSY and will be described in detail. | ||
| MOPCH150 | Characterization of a Piezo-based Microphonics Compensation System at HoBiCaT | 408 |
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| In the superconducting driver linac for the BESSY FEL, piezo actuators will be utilized to rapidly counteract the detuning of the cavity resonance caused by nm mechanical oscillations (microphonics). This is of importance to guarantee field stability and lower the power consumption of the RF system for the superconducting cavities. To design a suitable compensator, mechanical and electro-mechanical transfer functions, as well as the tuning range of the system under operating conditions have been measured and will be presented. | ||
| MOPCH151 | Pulsed RF System for the ELBE Superconducting Accelerator | 411 |
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| The RF system for the ELBE accelerator was originally designed for CW mode. Although this works problem-free tests have shown that it is possible to reach higher gradients in the TESLA cavities with a pulsed RF system. The new RF system will be presented together with measurements of the achievable gradients. Roughly 30% higher gradients could now be used in pulsed mode. As positive side effects the radiation by field emission is reduced by the duty cycle and an easy in situ RF conditioning of cavities and coupler windows is possible. | ||
| MOPCH152 | A Pulsed-RF High-power Processing Effect of Superconducting Niobium Cavities observed at the ELBE Linear Accelerator | 413 |
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| The driver LINAC of the ELBE radiation source is built for cw operation. However, in some cases a pulsed-mode operation was desired to extend the otherwise stringent gradient limits. The main restriction results from field emission that decreases the Q of the cavities which was evaluated from measurements of the liquid helium consumption. After pulsed-mode operation with gradients exceeding the maximum cw accelerating gradients by 30–40\% a significant reduction in the field emission was observed. This in turn allows higher accelerating gradients to be used in cw as well. We attribute this behaviour to an rf-processing of the cavity surface which burns off field emitters. | ||
| MOPCH153 | Peak Field Optimization for the Superconducting CH Structure | 415 |
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| The Cross-Bar H-type (CH) cavity is a multi-gap drift tube structure operated in the H-210 mode which has been developed at the IAP Frankfurt and in collaboration with GSI. Based on detailed numerical simulations a 19 cell prototype cavity from massive Nb was realised. For optimization of the magnetic and electric peak fields, detailed numerical simulations with CST MicroWave Studio have been performed. After successful experiments on the superconducting prototype cavity calculations about improved drift tube geometries with respect to field emission took place. Additionally, the stem geometry was further improved by simulations. | ||
| MOPCH154 | Dry-ice Cleaning on SRF Cavities | 418 |
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| High pressure rinsing with ultra-pure water is the well-proven standard cleaning step after chemical or electrochemical surface treatment of SRF cavities. Dry-ice cleaning (DIC) is a powerful additional cleaning option which depends on the sublimation-impulse method. Particles and film contaminations, especially hydro-carbons, are removed without residues. Furthermore DIC offers the possibility of a final horizontal cleaning of a fully equipped cavity because water is not present in the cleaning process. Horizontal cleaning tests on single-cell cavities showed promising high gradient, high Q-value performances, but field emission is still the limiting effect. On the basis of these tests a new IR-heater module is installed to keep a high temperature gradient between the CO2 jet and the cavity surface. New test results for this optimized cleaning set-up will be presented. | ||
| MOPCH155 | Performance Limitations of Tesla Cavities in the Flash Accelerator and their Relation to the Assembly Process | 421 |
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| Several accelerator modules with superconducting cavities have been assembled for TTF. The paper reviews the performance of these structures and will try to correlate their performance to information about the assembly process. In some cases a performace degradation could be attributed to problems in this process. The introduction of additional quality control steps improved accelerator module performance. For example, the more recently assembled modules have shown the expected acceleration gradients and no vacuum leaks. | ||
| MOPCH157 | Structural Analysis for a Half-reentrant Superconducting Cavity | 424 |
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| A half-reentrant cavity (1300 MHz, beta=1.0) is being developed at Michigan State University for use in a superconducting linear collider and other applications. The electromagnetic performance of a half-reentrant cell shape is similar to that of a fully reentrant cavity, but a multi-cell half-reentrant cavity can be cleaned using traditional techniques. We present the results of structural analyses of the half-reentrant cavity for the mid-cell, single-cell, and multi-cell cases. The analysis includes the static and dynamic response of the cavity. Stiffening options to minimize the resonant RF frequency shift due to pressure and the Lorentz force are explored. | ||
| MOPCH158 | HIPPI Triple-spoke Cavity Design | 427 |
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| In the frames of the European project of High Intensity Pulsed Proton Injector (HIPPI) the 352 MHz, beta=0.48 triple-spoke cavity is under development and will be built at the research center FZJ in Juelich. The criteria and results of the cavity RF and structural analyses are presented. | ||
| MOPCH159 | Coupler Design Considerations for the ILC Crab Cavity | 430 |
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| Transverse deflecting cavities, such as the ILC crab cavity, commonly operate in the TM110 dipole mode. This means that in addition to the higher order modes (HOMs), that need to be controlled for every cavity, the fundamental TM010 mode and the other polarisation of the dipole mode also need to be damped. As the resonant frequency of the fundamental mode is much lower than the cut-off frequency of the beampipe, this mode becomes trapped in the cavity and difficult to extract using conventional HOM couplers, hence a dedicated coupler is likely to be required. The ILC crab cavities will require excellent damping of all undesirable modes in order to maintain maximum luminosity at the IP. | ||
| MOPCH160 | A Beam-based High Resolution Phase Imbalance Measurement Method for the ILC Crab Cavities | 433 |
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| A high resolution method of RF phase adjustment and test is proposed for the Crab Cavity system of the ILC. The method is based on beam as ultimate test instrument. To measure phase imbalance in the pair of crab cavities (<0.02deg at 1.3GHz is required), a low energy (~1GeV) beam is used. A bunch center-of-mass trajectory through the cavities spaced (n+1/2) RF wavelengths and excited as in the case of the ILC, is a straight line for phase-balanced cavities and gets a kick when unbalanced. The kick is measured by two spaced BPMs with reference to the initial trajectory angle measured by two other BPMs. The method is insensitive to a bunch arrival time jitter and RF phase Common Mode jitter. A prototype of the test bench based on the method, is proposed. Using a 10MeV beam, two simple dipole cavities and low RF power, the prototype can be utilized for mastering high resolution measurements, for adjustment and tests of low level electronics of the Crab Cavity system and RF systems of XFEL ERLs as well. The phase resolution of the prototype is estimated as 0.01deg and the amplitude resolution as 0.01%. | ||
| MOPCH161 | Development of a Prototype Superconducting CW Cavity and Cryomodule for Energy Recovery | 436 |
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| Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when the electron bunch repetition rate is as high as possible, making CW-mode operation at high average current a fundamental requirement for these light sources. Challenges arise in controlling the substantial HOM power and in minimizing the power dissipated at cryogenic temperatures during acceleration and energy recovery, requiring novel techniques to be employed. This paper details a collaborative development for an advanced high-Qo cavity and cryomodule system, based on a modified TESLA cavity, housed in a Stanford/Rossendorf cryomodule. The cavity incorporates a Cornell developed resistive-wall HOM damping scheme, capable of providing the improved level of HOM damping and reduced thermal load required. | ||
| MOPCH162 | RF Requirements for the 4GLS Linac Systems | 439 |
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| The 4GLS facility at Daresbury will combine energy recovery linac (ERL) and free electron laser (FEL) technologies to deliver a suite of naturally synchronised state-of-the-art sources of synchrotron radiation and FEL radiation covering the terahertz (THz) to soft X-ray regimes. CW-mode operation at high acceleration gradients are needed for the various 4GLS accelerator systems and here is where Superconducting Radio Frequency (SRF) cavities excel. Since resistive losses in the cavity walls increase as the square of the accelerating voltage, conventional copper cavities become uneconomical when the demand for high CW voltage grows with particle energy requirements. After accounting for the refrigeration power needed to provide the liquid helium operating temperature, a net power gain of several hundred remains for SRF over conventional copper cavities. This paper details the RF requirements for each of the SRF accelerating stages of the 4GLS facility, outlining techniques necessary to cope with CW-mode operation and HOM power generation. | ||
| MOPCH163 | Analysis of Wakefields in the ILC Crab Cavity | 442 |
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| The large crossing angle schemes of the ILC need a correction of bunch orientation at the IP in order to recover a luminosity loss of up to 80%. The orientation of bunches can be changed using a transverse deflecting cavity. The location of the crab cavity would be close to the final focus, and small deflections caused by wakefields in the cavities could cause misalignments of the bunches at the IP. Wakefields in the FNAL CKM cavities have been analysed and their effects studied in view of use as the ILC crab cavity. Numerical simulations have been performed to analyse the transverse wakepotentials of up to quadrupole order modes in this cavity and the effect upon bunches passing through this cavity. Trapped modes within the CKM cavity have been investigated. Perturbation tests of normal conducting models of this cavity have been launched to verify these results. The effect of the final focus quadrupole magnets on the deflection given to the bunch have also been calculated and used to calculate luminosity loss due to wakefields. | ||
| MOPCH164 | Status of the Diamond Storage Ring Radio Frequency System | 445 |
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| The installation and commissioning of the Diamond Storage Ring RF system is nearing completion. Diamond will initially operate with two RF high power amplifiers and two cavities. The key components in each RF system are a 300 kW amplifier implemented through the combination of four 80 kW IOTs, a 500 MHz superconducting cavity providing up to 2 MV of accelerating voltage and an advanced analogue IQ Low Level RF (LLRF) system to control the cavity frequency, voltage and phase. We present here an update on the recent installation and early commissioning results of the RF systems. | ||
| MOPCH165 | Low- and Intermediate-beta, 352 MHz Superconducting Half-wave Resonators for High Power Hadron Acceleration | 448 |
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| A beta=0.17, 352 MHz superconducting Half-Wave resonator was designed and constructed at INFN-LNL in the framework of the SPES and EURISOL projects. This cavity, together with the beta=0.31 HWR of similar design that was previously built in the framework of the SPES project, allows acceleration of high power hadron beams in the 5?100 MeV/u energy range, as required in the SPES primary linac and in the first part of the EURISOL proton driver. Main features of this structure, compared to other ones developed elsewhere with different geometries for similar applications, are compactness and mechanical stability. Characteristics and test results will be presented. | ||
| MOPCH166 | Construction, Tuning and Assembly of the Beta=0.12 SC Ladder Resonator at LNL | 451 |
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| The Ladder resonator is a 4-gap full Nb cavity suitable for the 0.1< beta <0.2 range of high current proton linacs. A beta=0.12 Nb prototype of this cavity has been built by ZANON (Schio, Italy) on the basis of LNL design. In this paper we describe the construction procedure of such cavity, as well as the tuning steps, aimed at the achievement of the target frequency of 352.2 MHz and the desired field uniformity along the four gaps. Related results of RF simulations and room temperature tests are presented. The preparation of the SC test at LNL is at an advanced stage. | ||
| MOPCH167 | PBG Superconducting Resonant Structures | 454 |
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| We have realized normal conducting and superconducting “open resonators” based on the Photonic Band Gap (PBG) concept. We present the study, the optimisation and the measurements (from room temperature to 1.5 K) of Copper and Niobium PBG accelerating cavities operating at two different frequencies, 6 GHz and 16 GHz. All the structures are realised by extruding a single bulk piece of material, using a new machining method that minimizes the surface losses caused by the contact between different conducting parts. Measurements on the compact (54 mm external diameter) 16 GHz Nb structure are very good, showing in the superconducting state a quality factor Q =1.2x105 at the lowest temperature (1.5 K), limited by radiation losses only. The shunt impedance measured for the 16 GHz prototype is 70 MOhm/m, underlining the applicability of such resonant structures as accelerating cavities. | ||
| MOPCH168 | Novel Development on Superconducting Niobium Film Deposition for RF Applications | 457 |
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| A new deposition technology has been developed, based on a cathodic arc system working under UHV conditions, to produce metallic thin films. The technique presents several advantages compared to standard sputtering, mainly: ionized state of the evaporated material, absence of gases to sustain the discharge, higher energy of atoms reaching the substrate surface, possibility to apply bias to the substrate and to guide the arc plasma using magnetic fields. Recent results on superconducting Niobium films deposited under several conditions and on sapphire substrate are reported. A cavity deposition system has been developed and the plasma transport to the cavity cell studied | ||
| MOPCH169 | High Pressure Rinsing Water Jet Characterization | 460 |
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| High pressure rinsing is widely used as the final wet step in the high field superconducting cavities production. The interaction of an high speed ultra pure water jet with the niobium surface depends on various parameters such as water pressure, water throughput, treatment duration, cavity rotation speed, etc. In this paper we illustrate a simple technique for the characterization of water jet parameters based on the momentum transfer between the water jet and a load cell. The jet profile and its dependence on water pressure as well as the force exerted by the jet on the surface are easily measured. Moreover a portable apparatus has been set up and the information gathered in different laboratories will be used for a quantitative comparison of the different HPR systems. These measurements allow to study the correlation of the jet parameters with the effects (surface status, oxide formation, corrosion, etc) of the water interaction with the niobium surface. Furthermore a new analysis, based on the luminescence induced on transparent dielectric samples, is used for confirmation of the water jet structure. | ||
| MOPCH170 | Experimental and Theoretical Analysis of the Tesla-like SRF Cavity Flanges | 463 |
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| In view of the future large SC accelerator, an improvement of the reliability and a cost reduction of the SRF cavities cold flanges is required. In this paper, a critical analysis of the TESLA-like cold connection flanges at room and at cryogenic temperature is presented. This analysis is based on experimental characterization of the mechanical properties of the joint and of the leak rates during the sealing process. A FEM model, that agrees with the experimental data, is also presented. This model is being used for the optimization of the present SRF flanges and the development of new cold connections. | ||
| MOPCH171 | ILC Coaxial Blade Tuner | 466 |
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| A coaxial (blade) tuner solution has been developed for the compensation of the Lorentz force detuning of the superconducting cavities under the high gradient pulsed operation foreseen for ILC operation. The device is based on prototypes successfully tested at DESY in 2002 both on CHECHIA and on the superstructures inserted in the TTF string. During both tests the blade tuner performed as expected in terms of stiffness, frequency sensitivity and tuning capabilities. An improvement of the tuner characteristics has been designed by the integration of fast tuning capabilities by means of piezo-ceramic element. Two prototipes of the new INFN coaxial piezo blade tuner have just been manufactured and they will be tested at DESY and BESSY after the cavity integration. In this paper the blade tuner design and main characteristics are presented, together with the early interpretation of the cold test results. | ||
| MOPCH174 | Optimization of the BCP Processing of Elliptical Nb SRF Cavities | 469 |
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| Bulk niobium (Nb) electropolished SRF cavities performing at or above 35 MV/m is an aggressive goal recently put forth by the International Linear Collider (ILC) collaboration. Buffered chemical polishing (BCP) is still the most cost effective and least complex processing technique known today to optimize the surface properties of high gradient single crystal and relatively low gradient polycrystalline SRF cavities. BCP will be the preferred chemical process in the production of the nine-cell third harmonic 3.9 GHz cavities at Fermilab. The internal shape of these cavities will result in uneven material removal rates between iris and equator of the cells. We will describe a thermal-fluid finite element model adopted to simulate the etching process, and thus revealing the issues at hand. Experimental work, such as flow visualization tests performed to verify the simulation, will also be discussed. Finally we are presenting results obtained with a novel device, which allows to homogenize the flow pattern and to resolve the problem. | ||
| MOPCH175 | High Power Testing RF System Components for the Cornell ERL Injector | 472 |
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| There are two high power 1300 MHz RF systms under development for the Cornell University ERL Injector. The first system, based on a 16 kWCW IOT transmitter, will provide RF power to a buncher cavity. The second system employs five 120 kWCW klystrons to feed 2-cell superconducting cavities of the injector cryomodule. All components of these systems were ordered and some have already been delivered, including the IOT transmitter (manufactured by Thales-BM), 20 kWCW AFT circulator, 170 kWCW circulators (Ferrite Co.) and two prototype input couplers for superconducting cavities. A special LN2 cryostat has been designed and built for testing/processing the input couplers. The results of the first high-power tests are presented. | ||
| MOPCH176 | A Comparison of Large Grain and Fine Grain Cavities Using Thermometry | 475 |
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| An important limitation for SRF niobium cavities is the ”high field Q-slope.” To investigate this phenomenon we compare the behavior of large grain and fine grain cavities using thermometry. Thermometry allows us to distinguish between different problems which occur in cavities, and to distinguish between different areas showing high field Q-slope. We looked for the difference in heating between grain boundaries and inside grains. We have found interesting differences between the heating of high field slope regions and the heating of point-like defects. | ||
| MOPCH177 | Status of HOM Load for the Cornell ERL Injector | 478 |
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| The HOM load for the injector of the Energy Recovery Linac at Cornell University is proposed to work at a temperature of 80 K. The anticipated absorbed power of the load is up to 200 W. Versions with inner diameter of 78 and 106 mm are under development. Two different kinds of ferrites and a lossy ceramic are chosen as RF absorbers for the load to cover a wide frequency range. Measurements of electromagnetic properties of absorbing materials have been performed in a frequency range from 1 to 40 GHz. The engineering design of the load is ready and technological issues of brazing the absorbing tiles and cooling have been solved. Brazing quality is controlled by IR thermograms. First warm measurements of a prototype load are expected this summer. | ||
| MOPCH178 | Tests on MgB2 for Application to SRF Cavities | 481 |
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| Magnesium diboride (MgB2) has a transition temperature (Tc) of ~40 K, i.e., about four times higher than niobium (Nb). The studies in the last three years have shown that it could have about one order of magnitude less RF surface resistance (Rs) than Nb and seems much less power dependent compared to high-Tc materials such as YBCO. In this paper we will present results on the dependence of Rs on surface magnetic fields and possibly the critical RF surface magnetic field. | ||
| MOPCH179 | Design of a New Electropolishing System for SRF Cavities | 484 |
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| Electropolishing (EP) is considered the baseline surface treatment for Superconducting RF (SRF) cavities to achieve >35 MV/m accelerating gradient for the International Linear Collider (ILC). Based on the lessons learned at the forerunners such as KEK/Nomura, DESY and JLAB and on the recent studies, we have started a new design of the next EP system that will be installed in the US. This paper presents requirements, specifications, and the detail of the system design as well as the path forward towards the future industrialization. | ||
| MOPCH181 | 1.3 GHz Electrically-controlled Fast Ferroelectric Tuner | 487 |
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| A fast, electrically-controlled tuner is described with parameters suitable for operation with the 9-cell SC accelerator structure of ILC. The tuner is based on a magic tee and two phase shifters that contain ferroelectric rings. The dielectric constant of the ferroelectric ring is altered by applying a 4.2 kV DC pulse that provides an RF phase shift from 0 deg to 180 deg. This, in turn allows a change of the input signal amplitude from zero to its maximum value, or a change in phase from 0 deg to 360 deg during the RF pulse. It is shown that the possibility of changing the cavity coupling to the input line during the RF pulse allows significant RF power savings, up to 12.5 MW for the 800 GeV ILC option. In addition, fast electrically-tuned amplitude and phase control with a feed-back system should be useful to compensate for possible phase deviations of the input RF fields in each cavity of ILC to match the cavity with the feeding transmission line as the beam load varies. | ||
| MOPCH182 | The JLAB Ampere-class Cryomodule Conceptual Design | 490 |
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| For the next generation of compact high-power FELs a new cryomodule is required that is capable of accelerating up to Ampere levels of beam current. Challenges include strong HOM damping, high HOM power and high fundamental-mode power (in operating scenarios without full energy recovery). For efficient use of space a high real-estate gradient is desirable and for economic operation good fundamental-mode efficiency is important. The technology must also be robust and should be based on well-proven and reliable technologies. For Ampere-class levels of beam current both halo interception and beam break-up (BBU) are important considerations. These factors tend to drive the designs to lower frequencies where the apertures are larger and the transverse impedances are lower. To achieve these goals we propose to use a compact waveguide-damped multi-cell cavity packaged in an SNS-style cryomodule. | ||
| MOPCH184 | Plasma Treatment of Bulk Niobium Surfaces for SRF Cavities | 493 |
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| Cavity surface preparation has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface. The primary objective of our work is to explore the effects of various types of electric discharge plasmas to minimize surface roughness and eliminate or minimize deterioration of cavity properties by oxygen, hydrogen and other chemical contaminants. To optimize the plasma etching process, samples of bulk Nb are being exposed to three types of electrical discharge in various experimental set-ups. The surface quality obtained by the three methods was compared with samples treated with buffer chemical polishing techniques. Surface comparisons are made using digital imaging (optical) microscopy, scanning electron microscopy, and atomic force microscopy. In preliminary tests, samples compared with those treated conventionally have shown comparable or superior properties. Tests have also shown that surface quality varies with plasma conditions and their optimization to obtain the best SRF cavity surface is a major goal of the ongoing work. | ||
| MOPCH186 | First Cool Down of the Juelich Accelerator Module Based on Superconducting Half-Wave Resonators | 496 |
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| In the context of upgrading the existing proton and deuteron accelerator facility COSY at the Forschungszentrum Juelich, an accelerator module based on superconducting half wave resonators is prototyped. Due to beam dynamics, the requirements of cavity operation and a top-loading design for mounting, the cryostat had to be designed very compact and with a separate vacuum system for beam and insulation vacuum. These restricted requirements lead to very short cold-warm transitions in beam port region and to an unconventional design regarding to the shape of the cryostat vessel. This paper will review the design constraints, gives an overview of the ancillary parts of the module (cavities, tuner, etc.) and will present the results of the first cool-down experiments. Furthermore the future work will be presented. | ||
| MOPCH187 | Key Cryogenics Challenges in the Development of the 4GLS | 499 |
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| The fourth generation light source (4GLS) is a uniquely flexible source of ultra-high brightness continuous and pulsed radiation covering the IR to XUV range of the spectrum. It is the first light source in the world that is planned from the outset to be a multi-user, multi-source facility combining ERL (energy recovery LINAC) and FEL (free electron laser) technology. 4GLS will require six different sets of superconducting LINACs. Each of the LINAC modules consists of 2 to 7, 1.3 GHz superconducting RF cavities of the TESLA design operating at 1.8 K. The overall cooling power necessary to cool the cavities is estimated to be around 2.5KW demanding the superfluid liquid helium flow rates in excess of 200g/s. Even though the technology of the superconducting RF cavities is somewhat well understood, the design and subsequent operation of the cryogenic system / Cryo modules is an extremely complex task. In this paper we describe the key cryogenic challenges of the 4GLS project and our approach in identifying solutions to meet them. | ||
| MOPCH189 | Calculating the Muon Cooling within a MICE Liquid Absorber | 502 |
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| The key elements of the Muon Ionization Cooling Experiment (MICE) cooling channel are the absorbers that are a part of the MICE absorber focus coil modules (AFC modules). The boundaries of room temperature solid absorbers are well defined. The density of most solid absorber materials is also well understood. The properties of solid absorber are most certainly understood to 0.3 percent. The MICE liquid absorbers are different in that their dimensions are a function of the absorber temperature and the fluid pressure within the absorber. The second element in the liquid absorber is the variability of the liquid density with temperature and pressure. While one can determine the absorber boundary within 0.3 percent, the determination of the liquid density within 0.3 percent is more difficult (particularly with liquid helium in the absorber). This report presents a method of calculating absorber boundary and the cooling performance of the MICE absorbers as a function of fluid temperature and pressure. | ||
| MOPCH190 | Cryomodule Development for Superconducting RF Test Facility (STF) at KEK | 505 |
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| Current status of the cryomodule development for superconducting RF test facility, STF, at KEK is presented. The objective of the STF construction is to have an experience of 5-m long cryomodule fabrications and to learn an operational method of superconducting RF cavities. The STF consists of two 5-m long cryomodules, each housing four 9-cell cavities (one for 35 MV/m and the other for 45 MV/m). In addition to the cavity type, each cavity has variations in its appendices. Thus, two cryomodules must have different structures for the cavity support and for the port of the RF input coupler. This paper describes the details of the cryomodule design, the development of the bimetallic joint for connecting the titanium helium vessel to the stainless steel cooling pipe, and the studies of the magnetic shielding for high quality cavities. | ||
| MOPCH191 | Copper Heat Exchanger for the External Auxiliary Bus-bars Routing Line in the LHC Insertion Regions | 508 |
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| The corrector magnets and the main quadrupoles of the LHC dispersion suppressors are powered by a special superconducting line (called auxiliary bus-bars line N), external to the cold mass and housed in a 50 mm diameter stainless steel tube fixed to the cold mass. As the line is periodically connected to the cold mass, the same gaseous and liquid helium is used for cooling the magnets and the line. The final sub-cooling process (from 4.5 K down to 1.9 K) consists of the phase transformation from liquid to superfluid helium. It is slightly delayed with respect to the magnets. To accelerate the process, a special heat exchanger has been designed. Located in the middle of the dispersion suppressor portion of the line it consists in creating a local sink of heat extraction, providing two additional λ fronts that propagate in opposite directions towards the line extremities. Both the numerical model and the sub-cooling analysis are presented in the paper for different configurations of the line. Design, manufacturing and integration aspects of the heat exchanger are described. Finally, the results of the qualification tests and the expected performance of the line are given. | ||
| MOPCH192 | Operation of a Helium Cryogenic System for a Superconducting Cavity in an Electron Storage Ring | 511 |
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| A 500 MHz superconducting cavity maintaining the energy of electrons in the storage ring of TLS light source started from the year 2005. A helium system dedicated to keep the niobium cavity at 4.5 K has begun its operation since the year 2003. The cryogenic system provides maximum refrigeration of 469 W or liquefaction rate of 134 l/hr. The constraint from the superconducting cavity leads to specific features of the cryogenic system. This paper presents the operation of the cryogenic system as the superconducting cavity at different conditions. The interaction in between the cryogenic system and the superconducting cavity and the constraints on the starting and shutdown of the cryogenic system are indicated. | ||
| MOPCH193 | SNS 2.1K Cold Box Turn-down Studies | 514 |
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| The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is nearing completion. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 watt cryogenic refrigeration system. The 2.1K cold box consists of four stages of centrifugal compressors with LN2-cooled variable speed electric motors and magnetic bearings. The cryogenic system successfully supported the Linac beam commissioning at both 4.2K and 2.1K and has been fully operational since June 2005. This paper describes the control principles utilized and the experimental results obtained for the SNS cold compressors turn-down capability to about 30% of the design flow, and possible limitation of the frequency dependent power factor of the cold compressor electric motors, which was measured for the first time during commissioning. These results helped to support the operation of the Linac over a very broad and stable cold compressor operating flow range (refrigeration capacity) and pressure. This in turn helped to optimise the cryogenic system operating parameters, minimizing the utilities and improving the system reliability and availability. | ||
| MOPCH194 | Studies of the Alignment Tolerance for the Injector System of the IFUSP Microtron | 517 |
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| The Instituto de Fmsica da Universidade de Sco Paulo (IFUSP) is building a two-stage 38 MeV continuous-wave racetrack microtron. In this work, we describe the determination of alignment tolerances for the injector system of the IFUSP Microtron. This system consists of a linear accelerator with input energy of 100 keV and output energy of 1.8 MeV. The work presented ere involves analysis of our possibilities of alignment, the beam specifications for the acceleration structures and the strength of the correcting coils. Simulations were made using a method based on rotation matrices that allows for misalignments in the optical elements. It uses a tolerance parameter, given by the user, which is interpreted as a standard deviation of the normal misalignment distribution used to shuffle a configuration. A 5% loss of particles is achieved at a tolerance of 0.25-mm, without the inclusion of correcting coils (steerings) in the simulations. | ||
| MOPCH195 | The LiCAS-RTRS – A Survey System for the ILC | 520 |
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| The ILC requires an unprecedented accuracy and speed for the survey and alignment of its components. The Rapid Tunnel Reference Surveyor (RTRS) is a self-propelled train intended to automatically survey a reference network in the ILC tunnels with a design accuracy of 200 microns over distances of 600 m. A prototype RTRS has been built by the LiCAS collaboration. It will shortly commence operation at DESY. The operation principle of the RTRS will be explained. The status of the project's hardware, software and calibrations as well as the principles and performance of the underlying measurement techniques will be described. | ||
| MOPCH196 | Diamond Storage Ring Remote Alignment System | 523 |
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| The 24 cell Diamond Storage Ring is 561.6m in circumference and is mounted on 72 support girders, the largest of which are 6m long and weigh 17 Tonnes. Each girder can be remotely positioned in 5 axes using a system of motorised cams. This system has been designed to enable the future remote realignment of the Storage Ring using beam based alignment techniques. The system is described in detail including the mechanical and electrical components of the system as well as a description of the alignment algorithms employed and how these have been incorporated into the control system. |