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| MOPC005 | Chromaticity and Impedance Effect on the Transverse Motion of Longitudinal Bunch Slices in the Tevatron | simulation, synchrotron, impedance, beam-losses | 455 | ||
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Funding: Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the U.S. Department of Energy. |
The Transverse turn-by-turn evolution of a bunch slice are examined considering chromatic and impedence effects. A quasi-analytical approximation is developed using perturbative expansion of Hills equation with a wake field. This approximation is compared to turn-by-turn measurements taken in the Tevatron and from this linear and second order chomaticity, and Impedence are calculated as well as beam stability thresholds. |
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| MOPC006 | Simulations and Experiments of Beam-Beam Effects in e+e- Storage Rings | simulation, luminosity, positron, electron | 520 | ||
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Funding: Work partially supported by the Department of Energy under Contract No. DE-AC02-76SF00515. |
Over the past decade, extensive simulations of beam-beam effects in positron-electron collliders, based on the particle-in-cell method, were developed to explain many complex experimental observations. Recently, such simulations were used to predict the future luminosity performance of e+e- colliders. Some predictions have been proven to be correct in the existing accelerators. In this paper, many effects such as dynamic beta, beam-beam limit, crossing angle, parasitic collisions, betatron spectrum, and beam-beam lifetime, will be reviewed from the viewpoints of both simulation and experiment. Whenever possible, direct comparisons between the predictions of the simulation and the corresponding experimental results will be provided. |
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| MPPE031 | Simulation of Resonance Streaming at the eRHIC Electron Storage Ring | electron, simulation, luminosity, background | 2215 | ||
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Funding: Work performed under the auspices of the U.S. Department of Energy. |
To estimate electron beam lifetime and detector background at the future electron-ion collider eRHIC, knowledge of the electron beam halo region is essential. Simulations have been performed to determine the deviation of the transverse beam profile from a Gaussian distribution. |
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| MPPE044 | Damping Wiggler Study at KEK-ATF | wiggler, emittance, power-supply, injection | 2809 | ||
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The effects by damping wiggler magnets have been studied at KEK-ATF. The damping ring of the KEK-ATF is a 1.3 GeV storage ring capable of producing ultra-low emittance electron beams. It is significant issue to realize fast damping in the damping ring. The tuning method with 4 sets of wiggler was investigated for the ultra-low emittance beam. The performance on the beam quality, which is related to the transverse (x and y) and the longitudinal (z and dp/p), has been measured by the SR monitor, the laser wire, the streak camera and the energy spread monitor at the extraction line. We report on the operation condition and the measurement results.
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| MPPP007 | Operating Performance of the Low Group Delay Woofer Channel in PEP-II | feedback, impedance, collider, controls | 1069 | ||
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Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515. |
In PEP-II collider a dedicated low group-delay processing channel has been developed in order to provide high damping rates necessary to control the fast-growing longitudinal eigenmodes driven by the fundamental impedances of the RF cavities. A description of the digital processing channel operating at 9.81 MHz and capable of supporting finite impulse response (FIR) controllers with up to 32 taps will be presented. A prototype system has been successfully commissioned in the High-Energy Ring (HER) in May 2004. Operating experiences with the prototype and the newly determined limits on achievable longitudinal damping will be discussed and illustrated with experimental data. |
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| MPPP008 | Equilibrium Beam Invariants of an Electron Storage Ring with Linear x-y Coupling | resonance, coupling, betatron, electron | 1111 | ||
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Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515. |
In accelerator systems, it is very common that the motion of the horizontal plane is coupled to that of the vertical plane. Such coupling will induce tune shifts and can cause instabilities. The damping and diffusion rates are also changed, which in turn will lead to a change in the equilibrium invariants. Following the perturbative approach which we developed for synchrobetatron coupling,* we study the x-y coupled case in this paper. Starting from the one turn map, we give explicit formulae for the tune shifts, damping and diffusion rates, and the equilibrium invariants. We focus on the cases where the system is near the integer or half integer, and sum or difference resonances where small coupling can cause a large change in the beam distribution. *B. Nash, J. Wu, and A. Chao, work in progress. |
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| MPPP010 | Feedback to Suppress Phase Noise at Aladdin | feedback, dipole, simulation, synchrotron | 1180 | ||
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The performance of the Aladdin infrared beamline is adversely affected by a Robinson mode in which all bunches move in unison with a frequency of 3 kHz. To decrease these oscillations, feedback has been installed in the radiofrequency system to damp longitudinal motion of the bunch centroids. Simulations indicate that at frequencies around 3 kHz, the phase noise generated by Robinson modes may be reduced 20 dB by feedback with a damping time of 0.3 ms. This agrees with the measured performance of feedback circuitry. Since the feedback greatly improves operation of the infrared beamline, it is now incorporated into the standard operation of Aladdin.
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| MPPP011 | Fermilab Recycler Damper Requirements and Design | impedance, kicker, betatron, feedback | 1239 | ||
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The design of transverse dampers for the Fermilab Recycler storage ring is described. An observed instability and analysis of subsequent measurements are used to identify the requirements. The digital approach being mplemented is presented.
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| MPPP012 | First-Principles Simulation and Comparison with Beam Tests for Transverse Instabilities and Damper Performance in the Fermilab Main Injector | simulation, dipole, injection, betatron | 1300 | ||
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An end-to-end performance calculation and comparison with beam tests was performed for the bunch-by-bunch digital transverse damper in the Fermilab Main Injector. Time dependent magnetic wakefields responsible for "Resistive Wall" transverse instabilities in the Main Injector were calculated with OPERA-2D using the actual beam pipe and dipole magnet lamination geometry. The leading order dipole component was parameterized and used as input to a bunch-by-bunch simulation which included the filling pattern and injection errors experienced in high-intensity operation of the Main Injector. The instability growth times, and the spreading of the disturbance due to newly mis-injected batches was compared between simulations and beam data collected by the damper system. Further simulation models the effects of the damper system on the beam.
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| MPPP013 | Stabilizing Low Frequency Beam Motion in the Tevatron | optics, quadrupole, feedback, resonance | 1353 | ||
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Funding: Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of Energy. |
A feed back orbit stabilization system has been developed using a set of BPMS and existing Tevatron corrector magnets to stabilize beam motion up to 50 microns below 25 Hz. The construction of this system is described and the stability limits and magnitude of beam motion reduction is explored. |
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| MPPP015 | Operational Performance of a Bunch by Bunch Digital Damper in the Fermilab Main Injector | antiproton, proton, injection, diagnostics | 1440 | ||
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We have implemented a transverse and longitudinal bunch by bunch digital damper system in the Fermilab Main Injector, using a single digital board for all 3 coordinates. The system has been commissioned over the last year, and is now operational in all MI cycles, damping beam bunched at both 53MHz and 2.5MHz. We describe the performance of this system both for collider operations and high-intensity running for the NuMI project.
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| MPPP017 | User Operation and Upgrades of the Fast Orbit Feedback at the SLS | feedback, photon, insertion, beam-losses | 1538 | ||
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A report on the performance of the fast orbit feedback (FOFB) in its 2nd year of user operation is given. Photon beam position monitors (XBPM) have been included by means of a slow feedback which changes the reference settings of the FOFB. Users are permitted to change the XBPM references within certain limits while the feedback is running. A fast synchronous readout of the XBPMs allows their integration into the FOFB loop. The FOFB will be extended by an additional beam position monitor (BPM) in order to satisfy the requirements of the upcoming FEMTO project.
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| MPPP024 | Recent Observations on a Horizontal Instability in the DAFNE Positron Ring | feedback, electron, positron, impedance | 1841 | ||
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A strong horizontal instability limits the maximum positron current storable in the DAFNE Phi-Factory. A powerful feedback system makes it possible to store and collide up to 1250 mA of positron current in 105 bunches. Nevertheless, a much higher current (> 2.4A) has been successfully stored in the twin electron ring. Measurements have been carried out to understand the positron current limit and to characterize the behavior of the horizontal instability at high current with different bunch patterns. Grow/damp turn-by-turn data obtained by turning off the horizontal feedback have been acquired and analyzed. Spectral analysis and grow rates of the instability are shown. In particular, the -1 mode has strong evidence and fast grow rate. Its grow rate behavior is analyzed at different beam currents and bunch patterns.
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| MPPP027 | Suppression of the Longitudinal Coupled-Bunch Instabilities by the RF Phase Modulation in the Pohang Light Source | synchrotron, simulation, higher-order-mode, storage-ring | 1970 | ||
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In the 2.5 GeV Pohang Light Source, we have investigated the suppression of the longitudinal coupled instabilities (CBI) caused by higher order modes (HOMs) of RF cavities. At higher beam current than 170 mA the 758 MHz or 1300 MHz HOMs occurred and the beam could be unstable. The longitudinal CBI could be suppressed by modulating the phase of an RF accelerating voltage at a frequency of 2 times the synchrotron oscillation frequency and by adjusting the water temperatures of the RF cavities. The longitudinal beam oscillations measured by streak camera in synchro-scan mode were shown. The experiment results were compared with the macro particle tracking simulation.
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| MPPP029 | The Code MBIM2 for the Calculation of the Arbitrary Multibunch Beams Longitudinal Coherent Oscillations Stability (in the Case of Long Bunches) | synchrotron, multipole, impedance, single-bunch | 2110 | ||
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The presented code is an advanced version of the code MBIM1 also presented at this conference and dealing with short bunches. The code MBIM2 analyses the stability of longitudinal coherent motion for arbitrary multibunch beams in storage rings without limitations on the bunch length or RF cavities wavelength, which is especially important for higher types of multipole synchrotron oscillations. The code implies also the possibility to consider coupling between different types of multipole synchrotron oscillations and Landau damping. In considered approach, the problem reduces to the eigenvalue problem for the linear algebraic equation system. The order of this system is equal to the number of bunches times number of multipole types times approximation order wich appears to be small (a few units) in most cases.
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| MPPP033 | Beam Transfer Functions and Beam Stabilisation in a Double RF System | synchrotron, injection, beam-loading, space-charge | 2300 | ||
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The high intensity proton beam for LHC accelerated in the CERN SPS is stabilised against coupled-bunch instabilities by a 4th harmonic RF system in bunch-shortening mode. Bunch-lengthening mode, which could also be useful to reduce peak line density and alleviate problems from e-cloud and kicker heating does not give desirable results for beam stability. In this paper an analysis of the limitations of these two different modes of operation is presented together with measurements of the Beam Transfer Function for the double RF system. As predicted by theory, for sufficiently long bunches with the same noise excitation, the measured amplitude of the beam response in bunch-lengthening mode is an order of magnitude higher than that for bunch-shortening mode or for a single RF system.
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| MPPP037 | A Model Study of Transverse Mode Coupling Instability at NSLS-II. | impedance, vacuum, resonance, undulator | 2500 | ||
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The vertical impedances of the preliminary designs of NSLS-II MGUs are calculated by means of GdfidL code. The TMCI thresholds corresponding to these impedances are estimated using an analytically solvable model.
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| MPPP038 | Harmonic Cavity Performance for NSLS-II | undulator, synchrotron, emittance, brightness | 2544 | ||
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NSLS-II is a 3 GeV ultra-high brightness storage ring that is planned to succeed the present NSLS rings at Brookhaven. Ultra-low emittance bunch combined with a short bunch length results in the Touschek lifetime of only a few hours, which strongly advocates including harmonic RF in the baseline design of NSLS-II. This paper describes the required harmonic RF parameters, trade-offs between the possible choices and the expected system performance, including the implications on lifetime and instabilities.
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| MPPP041 | Transverse Instability of a Rectangular Bunch | impedance, synchrotron, space-charge, emittance | 2657 | ||
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Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-76CH03000. |
Some results of theoretical investigations of transverse dipole instability of a rectangular bunch are reported in this paper. Such a form is characteristic of the bunch in a rectangular potential wall which is created by a barrier-shaped acceleration field. Similar regime is a major one for accumulating and cooling of antiproton beams in the Fermilab Recycler Ring. In this case, the known theory of transverse instability of a bunched beam is inapplicable directly both because of "unusual" form of phase trajectories and strong dependence of synchrotron frequency on energy. A series of equations, adequately describing the instability is derived in the paper. Exact analytical solution is obtained for space charge dominated impedance, and some approximate methods are proposed for arbitrary impedance. The theory is applied to the Fermilab Recycler Ring including a numerical simulation. |
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| MPPP042 | Landau Damping of the Weak Head-Tail Instability at Tevatron | octupole, betatron, proton, injection | 2714 | ||
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Landau damping of the head-tail modes in Tevatron beam with the help of octupole-generated betatron tune spreads permits to reduce chromaticity from 15-20 units to zero thus significantly improving the beam lifetime. The octupole strengths have been experimentally optimized at different stages of the Tevatron operation, from proton injection to collision. Predictions of the analytical Landau damping model are compared with the experimental results.
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| MPPT034 | Field Modelling for the CESR-c Superconducting Wiggler Magnets | wiggler, quadrupole, emittance, linear-collider | 2336 | ||
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Funding: National Science Foundation. |
Superconducting wiggler magnets for operation of the CESR electron-storage ring at energies as low as 1.5 \gev have been designed, built and installed in the years 2000 to 2004. Finite-element models of field quality have been developed, various sources of field errors investigated and compared to field measurements. Minimization algorithms providing accurate analytic representations of the wiggler fields have been established. We present quantitative descriptions of field modelling, of measured field quality and of the accuracy achieved in the analytic functions of the field. |
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| TOAC001 | Overview of Impedance and Single-Beam Instability Mechanisms | impedance, coupling, synchrotron, octupole | 14 | ||
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Single-bunch and coupled-bunch instability mechanisms will be reviewed in both longitudinal and transverse planes. The resistive-wall impedance will be discussed in the particular case of the LHC collimators, which reveal a new physical regime. Stabilization by Landau damping, feedbacks, or linear coupling between the transverse planes will also be treated. Benchmarking of analytical predictions with some instability codes will be shown as well as several experimental results.
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| TOAC004 | Experimental Investigation of Beam Breakup in the Jefferson Laboratory 10 kW FEL Upgrade Driver | optics, simulation, recirculation, quadrupole | 369 | ||
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Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, Cornell University and by DOE Contract DE-AC05-84ER40150. |
In recirculating accelerators, and in particular energy recovery linacs (ERLs), the maximum current has been limited by multipass, multibunch beam breakup (BBU), which occurs when the electron beam interacts with the higher-order modes (HOMs) of an accelerating cavity on the accelerating pass and again on the energy recovered pass. This effect is of particular concern in the design of modern high average current energy recovery accelerators utilizing superconducting technology. Experimental observations of the instability at the Jefferson Laboratory 10 kW Free-Electron Laser (FEL) are presented. Measurements of the threshold current for the instability are presented and compared to the predictions of several BBU simulation codes. To further characterize the instability, beam based measurements were made to determine the orientation of the dangerous HOMs. With BBU posing a threat to high current beam operation in the FEL, several suppression schemes were developed. These include direct damping of the dangerous HOMs and appropriately modifying the electron beam optics. Preliminary results of their effectiveness in raising the threshold current for stability are presented. |
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| TPAE026 | Wakefields in a Dielectric Tube with Frequency Dependent Dielectric Constant | resonance, impedance, plasma, laser | 1916 | ||
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Funding: U.S. Department of Energy. |
Dielectric laser driven accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effect on the short range wakefield is calculated. |
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| TPAT011 | Impedance Analysis of Longitudinal Bunch Shape Measurements at PLS | impedance, undulator, single-bunch, insertion | |||
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We measured the longitudinal bunch shape by streak camera at 2.5 GeV Pohang Light Source. The impedances estimated by a series R+L model indicate a resistance R= 960 ohm, an inductance L= 80 nH and a longitudinal impedance Z/n= 0.53 ohm. The scaling law for the bunch lengthenig is expressed as I0.22. The effects of insertion device in the ring on the ring impedance, particularly the vertical height of in-vacuum undulator are also presented.
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| TPAT065 | Damping Transverse Instabilities in the Tevatron Using AC Chromaticity | simulation, proton, synchrotron, sextupole | 3665 | ||
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Funding: Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the U.S. Department of Energy. |
Several papers*,** have suggested possibility of using varying chromaticity to damp the head-tail instability. We test this by cycling the chromaticity sextupole magnets in the Tevatron near the synchrotron frequency to see if the head-tail stability threshold is increased. Further we compare the turn-by-turn evolution of a bunch slice in the presence of varying chromaticity to a model previously developed. *W.-H. Cheng, A. M. Sessler, and J. S. Wurtele, Phys. Rev. Lett. 78, 4565 (1997). **T. Nakamura in Proceedings of the 1995 IEEE Particle Accelerator Conference (IEEE, Dallas, 1995), Vol. 5, p. 3100. |
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| TPAT078 | Coherent Beam-Beam Modes in the CERN Large Hadron Collider (LHC) for Multiple Bunches, Different Collisions Schemes and Machine Symmetries | simulation, coupling, emittance, dipole | 4030 | ||
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In the LHC almost 3000 bunches in each beam will collide near several experimental regions and experience head-on as well as long range beam-beam interactions. In addition to single bunch phenomena, coherent bunch oscillations can be excited. Due to the irregular filling pattern and the unsymmetric collision scheme, a large number of possible modes must be expected, with possible consequences for beam measurements. To study these effects, a simulation program was developped which allows to evaluate the interaction of many bunches. It is flexible enough to easily implement any possible bunch configuration and collision schedule and also to study the effect of machine imperfections such as optical asymmetries. First results will be presented and future developments are discussed.
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| TPPP001 | Design of Damping Ring for SuperKEKB | emittance, dynamic-aperture, linac, positron | 773 | ||
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In the SuperKEKB, a plan upgrading the KEKB to higher luminosity of (2.5-5) x1035 cm2/sec, the beam currents are 9.4 A for the LER (3.5 GeV-electrons) and 4.1 A for the HER (8 GeV-positrons). In order to supply the HER with the positron beam, which is currently injected to the LER, the field gradient of the injector linac has to be increased. To meet this requirement, the S-band accelerating structures placed at the beam energy greater than 1 GeV, after the positron target, are replaced with C-band structures. A damping ring (DR) is indispensable since the aperture of the C-band structure is much smaller than the beam emittance. In this paper, we describe on the design of DR. We adopt a new cell structure for DR; FODO cell with alternating bends, where one of two bends in a cell is reversed. One of advantages of the proposed ring is that very small, even negative, momentum compaction factor is easily achieved by properly choosing the bend-angle ratio of the reverse bend to the main bend. Tracking simulation for the proposed DR has shown that it has very large dynamic aperture in both transverse and longitudinal phase space, for very wide tune space.
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| TPPP004 | Study of the Beam-Beam Effect for Crab Crossing in KEKB and Super KEKB | luminosity, coupling, radiation, simulation | 925 | ||
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Luminosity upgrade using crab cavities is planned at KEK-B factory (KEKB)in 2006. The crab crossing is expected to increase the beam-beam parameter >0.1, which is twice of present value, for KEKB. We discuss torelances of crab cavities and lattice to get the high beam-beam parameter.
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| TPPP006 | Beam-Beam Simulation Study with Parasitic Crossing Effect at KEKB | luminosity, simulation, target, beam-beam-effects | 1033 | ||
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KEKB is an asymmetric-energy, two-ring, electron-positron collider for B physics. Two beams collide at one interaction point with a finite crossing angle of 22 mrad. The bunch spacing has chosen to be 4 buckets (8 nsec) in most physics run of KEKB. While the shorter bunch spacing is necessary for a higher luminosity, the degradation of the specific luminosity by unknown reason is observed in 4 or 6 nsec spacing. In order to investigate whether parasitic crossing effect degrades a beam-beam performance, we have performed strong-strong beam-beam simulation with parasitic long-range beam-beam force. In this paper we present and discuss our simulation results.
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| TPPP016 | Beam Physics for the 12 GeV CEBAF Upgrade Project | linac, polarization, recirculation, optics | 1482 | ||
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Funding: Work supported by DOE Contract DE-AC05-84ER40150. |
Beam physics aspects of the 12 GeV Upgrade of CEBAF are presented. The CEBAF Upgrade to 12 GeV is achieved via 5.5 recirculations through the linacs, and the installation of 10 new high-gradient cryomodules. A new experimental hall, Hall D, is envisioned at the end of North Linac. Simulation results for straight-through and recirculated injectors are summarized and compared. Beam transport designs are discussed and evaluated with respect to matching and beam breakup (BBU) optimization. Effects of synchrotron radiation excitation on the beam properties are calculated. BBU simulations and derived specifications for the damping of higher order modes of the new 7-cell cavities are presented. The energies that provide longitudinal polarization in multiple experimental halls simultaneously are calculated. Finally, a detailed optics design for the Hall D transport line has been obtained. |
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| TPPP028 | Simulation of HOM Leakage in the PEP-II Bellows | vacuum, simulation, coupling, higher-order-mode | 2050 | ||
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Funding: Work supported by U.S. DOE contract, DE-AC02-76SF00515. |
An important factor that limits the PEP-II from operating at higher currents is higher-order-mode (HOM) heating of the bellows. One source of HOM heating is the formation of trapped modes at the bellows as a result of geometry variation in the vacuum chamber, for example, the masking near the central vertex chamber. Another source comes from HOMs generated upstream that leak through the gaps between the bellows fingers. Modeling the fine details of the bellows and the surrounding geometry requires the resolution and accuracy only possible with a large number of mesh points on an unstructured grid. We use the parallel finite element eigensolver Omega3P for trapped mode calculations, and the S-matrix solver S3P for transmission analysis. The damping of the HOMs by the use of absorbers inside the bellows will be investigated. |
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| TPPP030 | Damping Higher Order Modes in the PEP-II B-Factory Vertex Bellows | positron, vacuum, higher-order-mode, impedance | 2131 | ||
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Funding: Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515. |
Higher stored currents and shorter bunch lengths are requirements for increasing luminosity in colliding storage rings. As a result, more HOM power is generated in the IP region. This HOM power propagates to sensitive components causing undesirable heating, thus becoming a limiting issue for the PEP-II B-factory. HOM field penetration through RF shielding fingers has been shown to cause heating in bellows structures. To overcome these limitations, a proposal to incorporate ceramic absorbers within the bellows cavity to damp these modes is presented. Results show that the majority of modes of interest are damped, the effectiveness depending on geometrical considerations. An optimal configuration is presented for the PEP-II B-factory IR bellows component utilizing commercial grade ceramics with consideration for heat transfer requirements. |
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| TPPP031 | A Proposal for a New HOM Absorber in a Straight Section of the PEP-II Low Energy Ring | impedance, quadrupole, dipole, scattering | 2173 | ||
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Funding: Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515. |
Attainment of high luminosity in storage ring colliders necessitates increasing stored currents and reducing bunch lengths. Consequently, intense beam fields will scatter more power into higher order modes from beam line sources such as collimators, masks and tapers. This power penetrates into sensitive components such as a bellows, causing undesirable heating and limits machine performance. To overcome this limitation we propose incorporating ceramic absorbers in the vicinity of the bellows to damp beam induced modes while preserving a matched impedance to the beam. This is accomplished with an absorber configuration which damps TE dipole and quadrupole traveling waves while preserving TM monopole propagation. A scattering parameter analysis is presented utilizing properties of commercial grade ceramics and indicates a feasible solution. |
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| TPPT008 | New Design of Crab Cavity for SuperKEKB | coupling, impedance, polarization, feedback | 1129 | ||
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Crab-crossing scheme has been adopted as a baseline design for SuperKEKB, which is planned as an upgrade of KEKB. For the design of crab cavities for SuperKEKB, a very high beam current of 10A with a short bunch length of 3mm must be taken into account. Much heavier damping of any parasitic mode as well as smaller loss factor are required, compared with those of KEKB crab cavities. We propose new design of crab cavities for SuperKEKB. It has a high kick voltage, sufficiently low coupling impedance to any parasitic modes including the fundamental mode, and a considerably low loss factor. The new crab cavity meets the requirements for SuperKEKB.
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| TPPT010 | HOM Damping of ARES Cavity System for SuperKEKB | coupling, klystron, dipole, luminosity | 1186 | ||
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The ARES cavity scheme is a decisive edge for KEKB to stably accelerate high-current electron and positron beams. The RF structure is a coupled-cavity system where a HOM-damped accelerating cavity is coupled with a large cylindrical energy storage cavity via a coupling cavity between. The HOM-damped structure is designed to be smoothly embedded into the whole coupled-cavity scheme without any structural or electromagnetic incompatibility. Currently, the total HOM power dissipated in the RF absorbers per cavity is about 5 kW according to calorimetric measurements in the KEKB LER with a beam current of 1.6 A. On the other hand, for SuperKEKB aiming at luminosity frontiers over 1035 cm-2 s-1, the total HOM power per cavity is estimated about 100 kW for the LER with the design beam current of 9.4 A. In this article, a new HOM-damped structure of the ARES cavity system designed for the SuperKEKB LER is reported together with the recent activities and future plans for upgrading the HOM absorbers.
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| TPPT049 | Design and Cold Model Test of 500MHz Damped Cavity for ASP Storage Ring RF System | impedance, coupling, synchrotron, storage-ring | 3076 | ||
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TOSHIBA is constructing the storage ring RF system for the Australian Synchrotron Project(ASP). Two pairs of the 500MHz Higher Order Mode(HOM) damped cavities will be applied for this system. The cavities are modified KEK-PF type with silicon-carbide(SiC) microwave absorber and added three HOM anttenas for damping the longitudinal HOM impedance less than 20kOhm/GHz to meet requirement of ASP specification. The shunt impedance has been improved more than 5% in comparison with the original design by reducing the beam bore diameter without degrading HOM damping capability. The design of the cavity and the test results of an Al cold model are described.
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| TPPT056 | Design of a Low Loss SRF Cavity for the ILC | dipole, linac, linear-collider, collider | 3342 | ||
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An international team comprising DESY, KEK, JLAB, FNAL and SLAC is collaborating on the design, fabrication and test of a low loss, 1.3 GHz 9-cell SRF structure as a potential improvement for the ILC main linac. The advantages of this structure over the TTF structure include lower cryogenic loss, shorter rise time, and less stored energy. Among the issues to be addressed in this design are HOM damping, Lorentz force detuning and multipacting. We will report on HOM damping calculations using the parallel finite element eigenmode solver Omega3P and the progress made towards an optimized design. Studies on multipacting and estimates of the Lorentz force detuning will also be presented.
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| TPPT063 | Higher-Order-Mode Damping of L-Band Superconducting Cavity using a Radial-Line HOM Damper | simulation, linac, dipole, quadrupole | 3606 | ||
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For the energy recovery linacs, strong damping of higher-order-modes (HOMs) is indispensable to avoid beam breakup instabilities. We studied a new HOM damping scheme using a radial-line HOM damper with a choke structure. Both models of the radial-line damper and the TESLA-type 9-cell cavity were prepared and the HOM characteristics of this scheme were experimentally investigated. Measurement results showed a promising performance of the radial-line HOM damper.
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| TPPT069 | Design Considerations for the Mechanical Tuner of the RHIC Electron Cooler SRF Cavity | vacuum, controls, resonance, cryogenics | 3786 | ||
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Funding: Work is supported by the DOD Joint Technology Office and by the U.S. Department of Energy. |
The ECX Project, Brookhaven Lab's predecessor to the RHIC e-Cooler, includes a prototype RF tuner mechanism capable of both coarse and fine tuning of the superconducting RF cavity. This tuner is adapted originally from a DESY design concept but with a longer stroke and significantly higher loads due to our very stiff cavity shape. Structural design, kinematics, controls, thermal and RF issues are discussed and certain improvements are proposed. |
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| TPPT070 | Development of the Superconducting 3.9 GHz Accelerating Cavity at Fermilab | higher-order-mode, simulation, vacuum, resonance | 3825 | ||
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Funding: U.S. Department of Energy. |
A superconducting third harmonic accelerating cavity (3.9 GHz) was proposed to improve beam quality in the TTF-like photoinjector. Fermilab has developed, built and tested several prototypes, including two copper 9-cell cavities, and niobium 3-cell and 9-cell cavities. The helium vessel and frequency tuner for the 9-cell cavity was built and tested as well. In cold tests, we achieved a peak surface magnetic field of ~120mT, well above the 70mT specification. The accelerating gradient was limited by thermal breakdown. Studies of the higher order modes in the cavity revealed that the existing cavity design with two HOM couplers will provide sufficient damping of these modes. In this paper we discuss the cavity design, results of the studies and plans for further development. |
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| TPPT074 | Simulation Study of Electronic Damping of Microphonic Vibrations in Superconducting Cavities | feedback, simulation, coupling, resonance | 3916 | ||
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Funding: This work was supported by the Department of Energy under contract DE-AC05-84ER-40150. |
Electronic damping of microphonic vibrations in superconducting rf cavities involves an active modulation of the cavity field amplitude in order to induce ponderomotive forces that counteract the effect of ambient vibrations on the cavity frequency. In lightly beam loaded cavities, a reduction of the microphonics-induced frequency excursions leads directly to a reduction of the rf power required for phase and amplitude stabilization. Jefferson Lab is investigating such an electronic damping scheme that could be applied to the JLab 12 GeV upgrade, the RIA driver, and possibly to energy-recovering superconducting linacs. This paper discusses a model and presents simulation results for electronic damping of microphonic vibrations. |
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| TPPT081 | Fabrication and Testing of the SRF Cavities for the CEBAF 12 GeV Upgrade Prototype Cryomodule Renascence | coupling, dipole, simulation, impedance | 4081 | ||
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Funding: This manuscript has been authorized by SURA, Inc. under Contract No. DE-AC05-84ER-40150 with the U.S. Department of Energy. |
Twelve seven-cell niobium cavities for the CEBAF 12 GeV upgrade prototype cryomodule Renascence have been fabricated at JLab and tested individually. This set includes four of the "Low Loss" (LL) design and eight of the "High Gradient" (HG) design. The fabrication strategy was an efficient mix of batch job-shop component machining and in-house EBW, chemistry, and final-step machining to meet mechanical tolerances. Process highlights will be presented. The cavities have been tested at 2.07 K, the intended CEBAF operating temperature. Performance exceeded the tentative design requirement of 19.2 MV/m cw with less than 31 W dynamic heat dissipation. These results, as well as the HOM damping performance will be presented. |
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| TPPT082 | High Thermal Conductivity Cryogenic RF Feedthroughs for Higher Order Mode Couplers | pick-up, higher-order-mode, simulation, SNS | 4108 | ||
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Funding: This manuscript has been authorized by SURA, Inc. under Contract No. DE-AC05-84ER-40150 with the U.S. Department of Energy. |
The use of higher-order-mode (HOM) pickup probes in the presence of significant fundamental rf fields can present a thermal challenge for cw or high average power SRF cavity applications. The electric field probes on the HOM-damping couplers on the JLab "High Gradient" and "Low Loss" seven-cell cavities for the CEBAF upgrade are exposed to approximately 10% of the peak magnetic field in the cavity. To avoid significant dissipative losses, these probes must remain superconducting during operation. Typical cryogenic rf feedthroughs provide a poor thermal conduction path for the probes, and provide inadequate stabilization. We have developed solutions that meet the requirements, providing a direct thermal path from the niobium probe, thorough single-crystal sapphire, to bulk copper which can be thermally stationed (or heat sunk). Designs, electromagnetic and thermal analyses, and performance data will be presented. |
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| TPPT086 | Elliptical Cavity Shape Optimization for Acceleration and HOM Damping | laser, resonance, single-bunch, impedance | 4191 | ||
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Funding: Supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, and by DOE Contract DE-AC05-84ER40150. |
A normal design process for a superconducting cavity shape is to maximize the R/Q (shunt impedance/intrinsic quality factor) and geometry factor G for a given RF field limit of Bpeak/Eacc or Epeak/Eacc. For the application of an Ampere-class, high current energy recovery linac or storage ring, heavy HOM damping is required. This paper reports on a survey of single cell shapes developed for multi-cell cavities for different projects. Using a set of normalized parameters, we compare the designs for different frequencies and ß structures for the fundamental mode. Using dispersion curve (frequency verse phase advance) calculated by MAFIA for a single cell, we explore further how to optimize the cavity shape to avoid a light cone line crossing at the dangerous resonance frequencies determined by the beam bunch structure or the dangerous (trapped or high R/Q) modes with a low group velocity. We expect such a formulation to inform our development of a 5-cell, optimized cavity shape, with good real estate accelerating gradient and strong HOM damping waveguide structure for the JLab 1MW ERL-FEL project. |
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| TPPT094 | Design of the CW Cornell ERL Injector Cryomodule | emittance, linac, higher-order-mode, alignment | 4290 | ||
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Funding: This work is supported by Cornell University. |
The Cornell ERL Prototype injector will accelerate bunches from an electron source to an energy of several MeV, while preserving the ultra-low emittance of the beam. The injector linac will be based on superconducting RF technology with five 2-cell RF cavities operated in cw mode. The beam tubes on one side of the cavities have been enlarged to propagate Higher-Order-Mode power from the cavities to broadband RF ring-absorbers located at 80 K between the cavities. The axial symmetry of these ferrite based absorbers, together with two symmetrically placed input couplers per cavity, avoids transverse on-axis fields, which would cause emittance growth. Each cavity is surrounded by a LHe vessel and equipped with a frequency tuner. The cryomodule provides the support and alignment for the cavity string, the LN cooling of the ferrite loads, and the 2K LHe cryogenic system for the high cw heat load of the cavities. In this paper we give an overview of the ERL injector cryomodule design. |
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| TOPA011 | Self Consistent Scheme for Obtaining Electron-Positron Collisions with Multi-TeV Energy | laser, acceleration, radiation, photon | 740 | ||
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We describe here a self-consistent scheme for arrangement of multi-TeV collisions of electrons and positrons by using laser burst swept along microstructures with stable rate of acceleration ~10GeV/m. Shown that all component of the scheme are within present day technology. For energy ~1TeV luminosity could reach 1035 /cm2/s with wall-plug power of few tens of kW only.
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| TOPE003 | Results from DR and Instrumentation Test Facilities | emittance, laser, coupling, quadrupole | 305 | ||
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The KEK Accelerator Test Facility (ATF) is a 1.3GeV storage ring capable of producing ultra-low emittance electron beams and has a beam extraction line for ILC R&D. The ATF has proven to be an ideal place for researches with small, stable beams. 2x1010 single bunch and low current 20 bunch-train with 2.8nsec bunch spacing have been extracted to develop Nano-Cavity BPM’s, FONT, Nano Beam Orbit handling (FEATHER), Optical Diffraction Radiation (ODR) monitor, a precision multi-bunch laser-based beam profile monitor and polarized positron beam generation via backward-Compton scattering by the international collaboration. A set of three cavity BPM's is installed in the ATF extraction line on a set of extremely stiff supports. The KEK group installed another set of three BPM's, with their own support mechanism. The full set of 6 will prove extremely useful. In the DR (Damping Ring), we are researching the fast ion instability, micro-wave instability with four sets of damping wiggler and developing pulsed laser wire monitor, X-ray SR monitor, very fast kicker with about 1nsec rise/fall time to make ILC beam. I will report the recent results on above R&D’s.
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| TOPE004 | CLIC Progress Towards Multi-TeV Linear Colliders | linac, luminosity, collider, emittance | 353 | ||
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Novel parameters of an e+/e- Linear Collider based on CLIC technology with a broad colliding energy range from 0.5 to 5 TeV are presented for an optimised luminosity of 8x1034 cm-2s-1 at the nominal energy of 3 TeV. They are derived in part from the very successful tests and experience accumulated in the CLIC Test facility, CTF2. A new and ambitious test facility, CTF3, presently under construction at CERN within an international collaboration of laboratories and institutes, and aimed at demonstrating the key feasibility issues of the CLIC scheme, is described.
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| WOAA001 | The International Linear Collider (ILC) Organization and Plans | collider, linear-collider, linac, positron | 94 | ||
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A discussion of the current organization and Central Team functions will be given. A plan for evolution of the organization towards governance by the funding agencies will be presented. The work plan for the first year will be described and today’s ideas of a possible timeline laid out.
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| WOAA003 | Progress and Plans for R&D and the Conceptual Design of the ILC Injector Systems | positron, emittance, electron, undulator | 315 | ||
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The International Linear Collider Injector is a complex of different subsystems that are strictly correlated: positron source, polarized electron source, damping rings, bunch compressor and spin rotator. The choice of parameters of each subsystem has a strong influence on the others. A description of the critical items requiring further R&D in order to finalize the choice of the parameters needed for the Conceptual Design is given. The status and plans of the R&D in progress on these items at a global level are reported.
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| WPAE061 | LC Filter for High Accuracy and Stability Digital MPS at PLS | power-supply, simulation, feedback, alignment | 3550 | ||
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Funding: Work supported by the Ministry of Science and Technology, Korea. |
High accuracy and stability digital power supply for magnet is developed at PLS. This power supply has three sections. The first section is digital controller including DSP&FPGA and precision ADC, the second consists of IGBT driver and four quad IGBT switch, and the third is LC output section. AC input voltage of power supply is 3-phase 21V, output current is 0 ~ 150 A dc. Switching frequency of IGBT is 25 kHz. The output current of power supply has very high accuracy of 100 mA step resolution at full range and the stability of ± 1.5 ppm for short term and ± 5 ppm for long term. This paper describes characteristics of filter and output current performance improvement after LC output filter at four quad digital power supplies. |
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| WPAP034 | Positron Emulator for Commissioning ILC Positron Source | positron, electron, target, linac | 2321 | ||
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Funding: U.S. DOE. |
It is apparent that the gamma-ray based positron source components including positron linac and damping rings for ILC can not be easily commissioned until the electron beam is fully conditioned at high energies (> 150 GeV). In this paper, we discuss a scheme that could use a short and energetic electron beam scattered through a set of carefully selected targets to simulate certain behaviors of the positron beam, such as beam emittance and energy spread. The basic idea is to make the phase space distribution of the scattered electron beam to reflect certain aspects of the positron beam distributions. Subsequently, the positron source elements such as capture optics, linacs and even damping ring could be effectively commissioned before ILC colliding electron beam is ready. The simulation results using EGS4 for beam scattering and PARMELA for beam dynamics are presented. |
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| WPAT007 | Control Loops for the J-PARC RCS Digital Low-Level RF Control | synchrotron, acceleration, feedback, controls | 1063 | ||
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The low-level radiofrequency control for the Rapic Cycling Syncrotron of J-PARC is based on digital signal processing. This system controls the acceleration voltages of 12 magnetic alloy loaded cavities. To achive a short overall delay, mandatory for stable loop operation, the data-processing is based on distributed arithmetics in FPGA. Due to the broadband characteristic of the acceleration cavities, no tuning loop is needed. To handle the large beam current, the RF system operates simultaneously with dual harmonics (h=2) and (h=4). The stability of the amplitude loops is limited by the delay of the FIR filters used after downconversion. The phase loop offers several operation modes to define the phase relation of (h=2) and (h=4) between the longitudinal beam signal and the vector-sum of the cavity voltages. Besides the FIR filters, we provide cascaded CIC filters with smoothly varying coefficients. Such a filter tracks the revolution frequency and has a substantially shorter delay, thereby increasing the stable operating region of the phase loops. The adaptive radial loop accumulates the orbit variation over several machine cycles to reduce the effects of measurement errors on the effective acceleration frequency program.
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| WPAT017 | Commissioning of the New RF System with the HOM Damped RF Cavity | storage-ring, vacuum, impedance, higher-order-mode | 1555 | ||
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A new 178 MHz RF system has been commissioned at Duke Storage Ring. It consists of a 140 kW tetrode transmitter, a high order modes (HOM) damped RF cavity and the necessary frequency and voltage control electronics. The cavity walls are made of copper-on-stainless steel bimetal (8 mm Cu, 7 mm SS). The cavity has a larger beam pipe opening (700 mm in diameter) in the down-stream side, which allows the HOM propagating out of the cavity and being absorbed by the ceramic loads. The design details and the commissioning results are presented in this paper.
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| WPAT060 | SNS Low-Level RF Control System: Design and Performance | SNS, linac, controls, feedback | 3479 | ||
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Funding: ORNL managed by UT-Battelle for US DOE. |
A full digital Low-Level RF controller has been developed for SNS LINAC. Its design is a good example of a modern digital implementation of the classic control theory. The digital hardware for all the control and DSP functionalities, including the final vector modulation, is implemented on a single high-density FPGA. Two models for the digital hardware have been written in VHDL and Verilog respectively, based on a very low latency control algorithm, and both have been being used for supporting the testing and commissioning the LINAC to the date. During the commissioning, the flexibility and ability for precise controls that only digital design on a larger FPGA can offer has proved to be a necessity for meeting the great challenge of a high-power pulsed SCL. |
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| WPAT093 | A Three-Cell Superconducting Deflecting Cavity Design for the ALS at LBNL | impedance, simulation, dipole, coupling | 4287 | ||
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Deflecting RF cavities can be used to generate sub-pico-second x-rays by creating correlations between longitudinal and transverse phase space of electron bunches in radiation devices. Up to 2-MV defecting voltage at 1.5-GHz is required for 1.9-GeV electron beam at the Advanced Light Source (ALS) at LBNL. We present a conceptual design for a 1.5-GHz three-cell superconducting RF cavity and its coupler. The cavity geometry and deflecting shunt impedance are optimized using MAFIA code. The cavity impedance from lower and higher order modes (LOM and HOM) are computed. Possible schemes for damping most harmful LOM and HOM modes are discussed and simulated.
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| WOAC010 | Measurement of Linear Lattice Functions in the ESRF Storage Ring Using Turn-by-Turn Data | optics, storage-ring, kicker, synchrotron | 698 | ||
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A model-independent method to measure linear optics functions has been tested in turn-by-turn data from the ESRF storage ring. This method does not necessitate neither the knowledge of the model nor magnetic element manipulation. It uses only the positions measured in consecutive BPMs of betatron oscillations issued by small transverse kicks. The phase advances and tunes necessary to construct the transfer matrices are issued by refined Fourier analysis. The method's precision is compared with classical methods such as response matrix analysis and beam matrix construction.
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| ROAA001 | DAFNE Operation and Plans for DAFNE2 | luminosity, injection, factory, coupling | 112 | ||
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The e+e- collider DAFNE, a 1.02 Gev c.m. Phi-factory, has exceeded 1.2 1032 cm-2s-1 peak luminosity with 7.5 pb-1 maximum daily integrated luminosity. At the present performance the physics program of the three main experiments DEAR, FINUDA and KLOE will be completed by mid 2007. In this paper we describe the steps which have led to the luminosity improvement and present proposals for the upgrade of the collider towards higher energy and/or luminosity. The main accelerator issues on which we are planning to rely for this purpose, such as lattices with negative momentum compaction, strong RF focusing, design of high field magnets and Linac upgrade, are discussed in detail.
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| RPAE029 | Analytical Considerations for Reducing the Effective Emittance with Variable Dipole Field Strengths | emittance, optics, dipole, betatron | 2086 | ||
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The basic optics design scope in lepton rings is to match the sections in either side of the bending magnets in order to minimise the equilibrium emittance. A further important emittance reduction can be achieved by incorporating dipoles for which the deflecting field varies along the electron beam path in the magnet. The figure of merit for such lattices when used in a synchrotron light source is the minimization of the so-called effective emittance. The effective emittance is computed in the middle of the undulator straight section as the product of the rms size and divergence and therefore includes contributions from the betatron emittance and from the electron energy spread. In this paper, analytical formulas are obtained for the minimum betatron and effective emittance in arbitrary dipole fields and the associated optics function at the dipole entrance. Examples are given for specific dipole field functions and their properties with respect to the effective emittance minimisation. Finally, the effective emittance is parameterised with respect to standard cell optics properties, such as the phase advance, the maximum beta and dispersion functions and the focusing element strengths.
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| RPAE036 | Damping Wigglers for the PETRA III Light Source | wiggler, emittance, radiation, synchrotron | 2446 | ||
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Within the reconstruction of the PETRA booster ring at DESY towards a third generation light source after 2007, damping wigglers will be installed to reduce the emittance to a value of 1 nmrad. Two damping sections in the long straights of PETRA have been assigned to accommodate 20 wigglers in total. The wigglers will be permanent magnet devices with a fixed gap which are surrounded by an iron enclosure to reduce the leakage flux. Each wiggler will provide a damping integral of 4 T2m per segment and generate a synchrotron radiation power of 42 kW. A short one period long prototype has recently been built to prove the magnetic design and study the correction scheme for tuning the pole strength. The wiggler segments will be followed by an SR absorber shading the downstream quadrupole and successive wiggler segment, the accumulated on-axis power of about 200 kW will be taken up by the final absorber at the damping section end.
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| RPAE045 | Production of Short Electron Bunches by Slow and Fast Excitations of Longitudinal Bunch-Shape Oscillations | synchrotron, simulation, radiation, storage-ring | 2887 | ||
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In the Brookhaven Alternating Gradient Synchrotron (AGS), adiabatic excitation of longitudinal bunch-shape oscillations has been successfully used for extracting shortened proton bunches.* We applied this technique to the electron storage ring. In case of electron machines, growth time of bunch-shape oscillations should be shorter than the radiation damping time for preventing radiation excitation. We demonstrated in the 2.5-GeV Photon Factory storage ring that electron bunches could be shortened by a factor of about two from its natural length using this technique. We show that non-adiabatic excitation of oscillations is also very useful for obtaining shorter bunches.
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*M. Bai et al., Phys. Rev. ST Accel. Beams 3, 064001 (2000). |
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| ROPB001 | Suppressing Electron Cloud in Future Linear Colliders | electron, simulation, vacuum, collider | 24 | ||
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Funding: Work supported by the U.S. DOE under contract DE-AC02- 76SF00515. |
Any accelerator circulating positively charged beams can suffer from a build-up of an electron cloud in the beam pipe. The cloud develops through ionization of residual gases, synchrotron radiation and secondary electron emission and, when severe, can cause instability, emittance blow-up or loss of the circulating beam. The electron cloud is potentially a limiting effect for both the Large Hadron Collider (LHC) and the International Linear Collider (ILC). For the ILC positron damping ring, the development of the electron cloud must be suppressed. This paper presents the various effects of the electron cloud and evaluates their significance. It also discusses the state-of-the-art of the ongoing international R&D program to study potential remedies to reduce the secondary electron yield to acceptably low levels. |
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| ROPB005 | Recent Experiment Results on Fast Ion Instability at 2.5 GeV PLS | vacuum, ion, simulation, storage-ring | 466 | ||
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We present recent experiment results on the fast ion instability that were performed at the PLS storage ring. With higher vacuum pressures of three orders of magnitude than nominal one by He gas injection into the ring, increases of a factor of around three in the vertical beam size were observed by interferometer system. From the various measurement results, we estimated growth times for the instability as a funcion of vacuum pressure and beam current. We also compared the results with those of the computer simulations and analytical calculations.
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| ROPB008 | Halo Mitigation Using Nonlinear Lattices | focusing, collimation, simulation, space-charge | 620 | ||
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This work shows that halos in beams with space charge effects can be controlled by combining nonlinear focusing and collimation. The study relies on Particle-in-Cell (PIC) simulations for a one dimensional, continuous focusing model. The PIC simulation results show that nonlinear focusing leads to damping of the beam oscillations thereby reducing the mismatch. It is well established that reduced mismatch leads to reduced halo formation. However, the nonlinear damping is accompanied by emittance growth causing the beam to spread in phase space. As a result, inducing nonlinear damping alone cannot help mitigate the halo. To compensate for this expansion in phase space, the beam is collimated in the simulation and further evolution of the beam shows that the halo is not regenerated. The focusing model used in the PIC is analysed using the Lie Transform perturbation theory showing that by averaging over a lattice period, one can reuduce the focusing force to a form that is identical to that used in the PIC simulation.
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| RPPE008 | Water Induced Vibration in the NSRRC | quadrupole, storage-ring, vacuum, coupling | 1102 | ||
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Water flow related vibrations were found on the spectrum of electron beam position monitor in the NSRRC. They were associated with the vibrations of quadrupole magnets. One major vibration source was from a pump in the cooling water system. Most amount of vibration coupled through water pipe and water flow and propagated to the magnets. A small water flow station was set up to study the effect about coupling, propagating and excitation. Some damping schemes tested in the ring to improve the vibration are also included..
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| RPPE059 | Measurements of Epsilon and Mu of Lossy Materials for the Cryogenic HOM Load | resonance, coupling, insertion, superconductivity | 3462 | ||
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Funding: Supported by Cornell University |
In high current storage rings with superconducting cavities strong broadband HOM damping has been achieved by using beam-pipe ferrite loads, located at room temperature. Adopting the same damping concept for the ERL with RF absorbers between the cavities in a cavity string will require operating the absorbers at a temperature of about 80 K. This temperature is high enough to intercept HOM power with good cryogenic efficiency, and is low enough to simplify the thermal transition to the cavities at 2 K. However the electromagetic properties of possible absorber materials were not well known at cryogenic temperatures. We performed a measurement program at Cornell to find possible absorbers for HOMs in the ERL. Measurements were done for 10 different materials in the range from 1 to 40 GHz. |
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| RPPE063 | Concepts for the JLab Ampere-Class CW Cryomodule | SNS, vacuum, dipole, linac | 3588 | ||
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Funding: This manuscript has been authored by SURA, Inc. under Contract No. DE-AC05-84ER-40150 with the U.S. Department of Energy, and by The Office of Naval Research under contract to the Dept. of Energy. |
We describe the concepts and developments underway at JLab as part of the program to develop a new CW cryomodule capable of transporting ampere-level beam currents in a compact FEL. Requirements include real-estate gradient of at least 10 MV/m and very strong HOM damping to push BBU thresholds up by two or more orders of magnitude compared to existing designs. Cavity shape, HOM damping, power couplers, tuners etc. are being designed and optimized for this application. Cavity considerations include a large iris for beam halo, low-RF losses, HOM frequencies and Q’s, low peak surface fields, field flatness and microphonics. Module considerations include high packing factor, low static heat leak, image current heating of beam-line components, cost and maintainability. This module is being developed for the next generation ERL based high power FELs but may be useful for other applications such as electron cooling, electron-ion colliders, industrial processing etc. |
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| RPPP003 | Proposal of the Next Incarnation of Accelerator Test Facility at KEK for the International Linear Collider | optics, linear-collider, collider, extraction | 874 | ||
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The realization of the International Linear Collider (ILC) will require the ability to create and reliably maintain nanometer size beams. The ATF damping ring is the unique facility where ILC emittancies are possible. In this paper we present and evaluate the proposal to create a final focus facility at the ATF which, using compact final focus optics and an ILC-like bunch train, would be capable of achieving 35nm beam size. Such a facility would enable the development of beam diagnostics and tuning methods, as well as the training of young accelerator physicists.
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| RPPP005 | Simulation Study of a Dogbone Damping Ring | wiggler, space-charge, emittance, simulation | 928 | ||
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Damping ring is one of the major issues in the future linear collider (ILC). We discuss the design of the dogbone damping ring and the performance that includes dynamic apertures, space charge effects, and optics corrections.
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| RPPP007 | CLIC Damping Ring Optics Design Studies | wiggler, emittance, dynamic-aperture, sextupole | 1060 | ||
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In this paper the nonlinearities induced by the short period NbFeB permanent wiggler optimized for the CLIC damping ring and their influence to the beam dynamics are studied.
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| RPPP008 | The Short Circumference Damping Ring Design for the ILC | wiggler, emittance, scattering, dynamic-aperture | 1126 | ||
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The ILC damping ring tentative design is driven by the operational scenario of the main linac, the beam-dynamics demand of producing a stable and high-quality beam, the injection/extraction scheme and the kicker performance. In this paper, a short circumference damping ring design based on TME cells is described. The ring accommodates injection kickers which provide a flat top of 280 nsec and a 60 nsec rise and fall time and very fast strip-line kickers for beam extraction with a 2 nsec rise and fall time for 3-MHz operation. The potential impact of collective effects and the possible degradation of the dynamic aperture by nonlinear-wiggler fields are estimated.
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| RPPP010 | Considerations on the Design of the Decelerator of the CLIC Test Facility (CTF3) | simulation, linac, beam-losses, quadrupole | 1177 | ||
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Funding: We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT-2003-506395). |
One of the main aims of the CLIC Test Facility (CTF3) is to study the beam stability in the drive beam decelerator and to bench mark the performance against beam simulation codes. Particular challenges come from the large drive beam energy spread, the strong wakefields and potential beam losses. The development towards a decelerator design and the required instrumentation is described in this paper. |
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| RPPP012 | Collective Effects in the CLIC Damping Rings | wiggler, ion, emittance, radiation | 1312 | ||
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The small emittance, short bunch length, and high current in the CLIC damping ring could give rise to collective effects which degrade the quality of the extracted beam. In this paper, we survey a number of possible instabilities and estimate their impact on the ring performance. The effects considered include fast beam-ion instability, coherent synchrotron radiation, and electron cloud, in addition to conventional single and multi-bunch instabilities.
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| RPPP019 | Revisiting the Cold ILC Parameters | linac, collider, luminosity, feedback | 1661 | ||
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At the first ILC Workshop, discussions were underway to re-examine the parameters of the cold ILC. Using the TESLA parameters MathCad program developed in 1991, I examined several variations to explore consequences to the capital and operating costs of the linac (cryomodules, RF, & refrigerator). The cost coefficients were chosen to match the distribution of the above items in the TESLA TDR at 25 MV/m. One parameter varied is the gradient from 25 to 50 MV/m coupled with a realistic Q as well as an optimistic Q (1010). Other parameters varied are: number of bunches, spacing, and rep rate to decrease the damping ring size. Keeping all other TDR parameters the same, the optimal gradient for the realistic Q curve is about 35 MV/m, yielding a capital cost savings of 16% and a total cost savings of 9% over the nominal gradient of 25 MV/m. If however the Q remains at 1010, the optimum gradient moves to 50 MV/m where the total cost savings rise to 17.5%, and capital cost savings rise to 35%. Of course, gradients higher than 35 MV/m are extremely challenging, demanding major development efforts, such as control of Lorentz force detuning which increases as the square of the gradient.
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| RPPP020 | Linear Damping Systems for the International Linear Collider | wiggler, emittance, positron, radiation | 1689 | ||
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Funding: Supported by the National Science Foundation |
The International Linear Collider requires very low transverse emittance beams in order to realize the specified high luminosity. These beams are conventionally produced using radiation damping in specially designed damping rings. A linear damping system, consisting of alternating wigglers and accelerating structures arranged in a straight line, can be considered to replace, or to augment, conventional damping rings. In this paper, the basic features, feasibility, advantages, and disadvantages, of such systems, as applied to the International Linear Collider, will be discussed. |
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| RPPP023 | A Compact Damping Ring Using RF Deflectors for the International Linear Collider | kicker, dynamic-aperture, quadrupole, extraction | 1811 | ||
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Funding: NSF |
Current specifications for the International Linear Collider call for bunch trains hundreds of kilometers in length. We describe a scheme for manipulating a compressed bunch train in the damping ring using RF deflectors and multiple transfer lines. The concept is demonstrated in the design of a 4 km damping ring that circulates 2800 bunches spaced 4 ns apart, and we show that injection and extraction of individual bunches is possible with conventional kickers requiring rise/fall times of only 16 ns. The performance and stability of the 4 km damping ring is evaluated and compared with existing machines. |
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| RPPP025 | CESR-c Wiggler Studies in the Context of the International Linear Collider Damping Rings | wiggler, dynamic-aperture, emittance, linear-collider | 1880 | ||
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Funding: Work supported by the NSF. |
We present a picture of the International Linear Collider (ILC) damping ring wiggler dynamics using the experience gained from the experimental and simulation-based research studying the wigglers used in the current configuration of the Cornell Electron Storage Ring (CESR). CESR is currently running at 1.8 GeV with 12 superconducting wigglers that have been designed, fabricated, tested, and simulated on-site. We will present results which include frequency map analyses and conventional dynamic aperture studies of CESR-c and the ILC damping rings. We will also provide results from an initial look at physical limitations in the design of the ILC damping ring wigglers. |
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| RPPP029 | Analysis of Positron Collection in Linear Collider | positron, target, electron, emittance | 2101 | ||
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Funding: Work is supported by Department of Energy Contract No. DE-AC02-76SF00515 |
In the Linear Collider, the positron capture system includes a positron production target, a flux concentrator, and a linac to accelerate positrons up to the injection energy of the positron damping ring. Two schemes for positron production have been studied: (i) a conventional approach with an electron beam interacting with a high-Z target and (ii) polarized positron production using polarized photons generated in a helical undulator by electron beam which then interact with a positron production target. Efficiency of positron collector is defined by positron yield which is a ratio of positrons accepted into damping ring to the number of incident electrons or photons. The capture system has been optimized to insure high positron yield into the 6-dimensional acceptance of the damping ring keeping the high value of positron polarization. Various parameters affecting the positron capture are analyzed. |
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| RPPP034 | Multi-Stage Bunch Compressors for the International Linear Collider | emittance, linac, extraction, injection | 2357 | ||
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We present bunch compressor designs for the International Linear Collider (ILC) which achieve a reduction in RMS bunch length from 6 mm to 0.3 mm via multiple stages of compression, with stages of acceleration inserted between the stages of compression. The key advantage of multi-stage compression is that the maximum RMS energy spread is reduced to approximately 1%, compared to over 3% for a single-stage design. Analytic and simulation studies of the multi-stage bunch compressors are presented, along with performance comparisons to a single-stage system. Parameters for extending the systems to a larger total compression factor are discussed.
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| RPPP045 | Single-Bunch Instability Driven by the Electron Cloud Effect in the Positron Damping Ring of the International Linear Collider | electron, dipole, single-bunch, simulation | 2884 | ||
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Funding: Work supported by the U.S. DOE under contracts DE-AC02-76SF00515. |
With the recommendation that the future International Linear Collider (ILC) should be based on superconducting technology, there is considerable interest in exploring alternate designs for the damping rings (DR). The TESLA design was 17 km in circumference with a "dog-bone" configuration. Two other smaller designs have been proposed that are 6 km and 3 km in length. In the smaller rings, collective effects may impose the main limitations. In particular for the positron damping ring, an electron cloud may be produced by ionization of residual gas or photoelectrons and increase through the secondary emission process. The build-up and development of an electron cloud is more severe with the higher average beam current in the shorter designs. In this paper, we present recent computer simulation results for the electron cloud build-up and instability thresholds for the various DR configurations. |
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| RPPP047 | Global Optimization of Damping Ring Designs Using a Multi-Objective Evolutionary Algorithm | wiggler, sextupole, lattice, optics | 2962 | ||
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Funding: This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. |
Several damping ring designs for the International Linear Collider have been proposed recently. Some of the specifications, such as circumference and bunch train, are not fixed yet. Designers must make a choice anyway, select a geometry type (dog-bone or circular), an arc cell type (TME or FODO), and optimize linear and nonlinear part of the optics. The design process include straightforward steps (usually the linear optics), and some steps not so straightforward (when nonlinear optics optimization is affected by the linear optics). A first attempt at automating this process for the linear optics is reported. We first recognize that the optics is defined by just a few primary parameters (e.g., phase advance per cell) that determine the rest (e.g., quadrupole strength). In addition to the exact specification of circumference, equilibrium emittance and damping time there are some other quantities which could be optimized that may conflict with each other. A multiobjective genetic optimizer solves this problem by producing a population of best-ranked solutions on a multi-dimensional surface from which one solution can be chosen by the designer. The application of the NSGA-II optimizer to a damping ring of FODO cells is presented. |
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| RPPP049 | Bunching for Shorter Damping Rings for the ILC | extraction, kicker, linac, positron | 3052 | ||
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A variant rearrangement of the bunch trains for the ILC that enables much shorter damping rings is presented. In a particular example the ~2280 bunches are regrouped into ~450 subtrains of five adjacent bunches. These subtrains are extracted from the damping rings at ~2.2 ms intervals, obtaining the 1ms macrobunch length of the baseline TESLA collider scenario. If the baseline damping rf frequency is 325 MHz and the kicker rise and fall times are ~20 ns, a ring circumference of ~4.5km is required. Variations of the scheme could easily reduce the circumference to ~3km, and faster kickers could reduce it even further.
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| RPPP051 | Characterization of a 6-km Damping Ring for the International Linear Collider | lattice, dynamic-aperture, emittance, wiggler | 3147 | ||
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Several damping ring designs for the International Linear Collider have been proposed recently. One particular design has a circumference of 6 km (hoping to take advantage of future kicker technology advances), TME arc cells, and 77 m of 2 T wigglers. Several beam dynamics characterizations and optimizations are reported. We used the accelerator code elegant for matching and tracking, and a 100-CPU linux cluster to provide high throughput.
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| RPPP053 | Simulations of Resistive-Wall Instability in the ILC Damping Rings | feedback, simulation, pick-up, radiation | 3241 | ||
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Funding: Work supported by U.S. Department of Energy, Director, Office of Science, Contract No. DE-AC03-76SF00098. |
Options being considered for the ILC Damping Rings include lattices with circumferences up to 17 km. The circumference, beam current and beam energy place the damping rings in a regime where resistive-wall instability is a concern, particularly as there are very demanding tolerances on the bunch-to-bunch jitter. Generally, it is possible to make good analytical estimates of the coupled-bunch growth rates in a storage ring, but particular features of the damping rings (including the fill pattern, large variations of the lattice functions and beam-pipe cross-section in different parts of the ring, and transverse beam coupling in the long straight sections) make it desirable to study the coupled-bunch instabilities using simulations. Here, we present the results of simulations of the transverse instabilities using a detailed lattice model. A bunch-by-bunch feedback system will be needed to suppress the instabilities, and a model for an appropriate feedback system is included in the simulations. |
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| RPPP054 | Achieving Large Dynamic Aperture in the ILC Damping Rings | lattice, dynamic-aperture, sextupole, emittance | 3277 | ||
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Funding: Work supported by US Department of Energy, Director, Office of Science - Contract Nos. DE-AC03-76SF00098 and DE-AC03-76SF00515. |
The Damping Rings for the International Linear Collider have challenging requirements for the acceptance, because of the high average injected beam power and the large beam produced from the positron source. At the same time, the luminosity goals of the collider mean that the natural emittance must be very small, and this makes it particularly difficult to achieve a good dynamic aperture. We describe a design approach and present a lattice design that meets the emittance specification and has a very promising dynamic aperture. We also discuss the potential impact of the damping wiggler and of magnet errors. |
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| RPPT046 | Development and Application of Bunch-by-Bunch Measurement System of HLS | synchrotron, betatron, single-bunch, pick-up | 2932 | ||
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This paper is intended to present the newly implemented wideband (100MHz) bunch oscillation measurement system, which is in nature a different method from the narrow-band (<5MHz) facilities employed before. Basic formalism and implementation details of the system is introduced to illustrate the function of observing coupled bunch instabilities in time and frequency domain. The designed function includes detecting of transverse oscillation, synchrotron phase oscillation, as well as bunch filling pattern. Some diagnostics results of machine instabilities and application of this system are also discussed.
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| FPAT022 | Performance of the CERN SPS Fast Extraction for the CNGS Facility | extraction, kicker, feedback, betatron | 1757 | ||
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The SPS LSS4 fast extraction system will serve both the anti-clockwise ring of the LHC and the long baseline neutrino (CNGS) facility. For the latter two extractions spaced by 50 ms, each affecting half of the ring, are foreseen. During the shutdown 2003-2004 the performance of the fast extraction kickers was improved in order to match more closely the specifications for the kicker pulse shape required for the CNGS and LHC extractions. The rise and fall times were significantly reduced, as well as the post-pulse kick ripple. However, the latter remains outside specifications and oscillations are induced in the leading bunches of the batch remaining in the machine at the moment of the first extraction. While further improving the characteristics of the kicker pulse shape, the possibility of damping the beam oscillations using the transverse feedback system has been explored. We report on the recent pulse form improvements and results of beam tests.
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| FPAT085 | The TAO Accelerator Simulation Program | quadrupole, linac, simulation, lattice | 4159 | ||
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Funding: NSF and DOE. |
A new accelerator design and analysis simulation environment based on the BMAD relativistic charged particle dynamics library is in development at Cornell University. Called TAO (Tool for Accelerator Optimization), it is a machine independent program that implements the essential ingredients needed to solve simulation problems. This includes the ability to: 1. Design lattices subject to constraints, 2. Simulate errors and changes in machine parameters, and 3. Simulate machine commissioning including simulating data measurement and correction. TAO is designed to be easily customizable so that extending it to solve new and different problems is straight forward. The capability to simultaneously model multiple accelerator lattices, both linacs and storage rings, and injection from one lattice to another allows for the design and commissioning of large multi stage accelerators. It can also simultaneously model multiple configurations of a single lattice. Single particle, particle beam and macroparticle tracking is implemented. Use of TAO with both the International Linear Collider and the Cornell Energy Recovery Linac are provided as examples. |
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