| Paper | Title | Page |
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| MOPS001 | Electron-cloud Pinch Dynamics in Presence of Lattice Magnet Fields | 586 |
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| The pinch of the electron cloud due to a passing proton bunch was extensively studied in a field free region and in a dipolar magnetic field. For the latter study, a strong field approximation helped to formulate the equations of motion and to understand the complex electron pinch dynamics, which exhibited some similarities with the field-free situation. Here we extend the analysis to the case of electron pinch in quadrupoles and in sextupoles. We discuss the limits of validity for the strong field approximation and we evaluate the relative magnitude of the peak tune shift along the bunch expected for the different fields. | ||
| MOPS002 | Mitigation of Space Charge and Nonlinear Resonance Induced Beam Loss in SIS100 | 589 |
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| The control of beam loss in SIS100 is essential for avoiding vacuum instability and guarantee the delivery of the foreseen beam intensity. On the other hand simulations show that the simultaneous presence of space charge and lattice resonances creates during 1 second cycle a progressive beam loss exceeding the limit of 5%. Until now the mechanism of periodic resonance crossing were suspected to be, in conjunction with pure dynamic aperture effects, at the base of the beam loss. In this proceeding we present the state of the art in the beam loss prediction and we prove that the periodic resonance crossing is the deteriorating mechanism, and show that the compensation of a relevant resonance intercepting the space charge tune spread sensibly mitigate the beam loss. A short discussion on beam loss during acceleration is addressed as well. | ||
| MOPS003 | Coherent Beam-beam Resonances in SuperB with Asymmetric Rings | 592 |
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| One of the latest options of SuperB foresees exploiting rings with unequal circumferences. In such a configuration additional coherent beam-beam resonances can arise. In this paper we discuss the possible impact of the resonances on beam dynamics in SuperB, maximum achievable tune shifts and working point choice. | ||
| MOPS004 | Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC | 595 |
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| In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability. | ||
| MOPS005 | Beam Dynamics Simulations of J-PARC Main Ring for Upgrade Plan of Fast Extraction Operation | 598 |
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| Beam loss simulations under space charge effects are necessary to seek higher intensity proton beams. This paper presents simulations for fast extraction operation of Japan Proton Accelerator Research Complex (J-PARC) Main Ring. For upgrade plan, increasing protons per bunch and making higher repetition pattern are considered. Their optimal balance is discussed to minimize beam losses for aimed beam power considering space charge effects. We found that to optimize RF voltage pattern is a strong key to reduce beam losses for higher repetition. As benchmark works, we compare our simulations with the measured beam loss in our past operation. | ||
| MOPS006 | Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB | 601 |
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| When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB. | ||
| MOPS007 | Interference of CSR Fields in a Curved Waveguide | 604 |
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| CSR fields generated by a bunched beam passing through a series of bending magnets may interfere with each other due the reflections of outer chamber wall. This kind of multi-bend interference causes sharp peaks and long-range tail in the CSR impedance and wake potentials, respectively. Using a dedicated computer code, CSRZ, we calculated the longitudinal CSR impedance in the SuperKEKB positron damping ring for purpose of demonstration. It was found that multi-bend interference may enhance the CSR fields within a distance comparable to the bunch length, which is typically in the order of several millimeters. A simple instability analysis was performed and it suggested that multi-bend interference might play a role in the single-bunch instabilities of small electron/positron rings. | ||
| MOPS008 | Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection | 607 |
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| The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS. | ||
| MOPS009 | Probing Intensity Limits of LHC-type Bunches in the CERN SPS with Nominal Optics | 610 |
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| Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4·1011 p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6·1011 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.3·1011 p/b LHC type bunches with satisfying parameters at extraction of the SPS. | ||
| MOPS010 | Experimental Studies with Low Transition Energy Optics in the SPS | 613 |
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| The optics of the SPS can be tuned to lower transition energy such that the slippage factor at injection is raised by a factor of almost 3. From theory, an increase of the intensity thresholds for transverse mode coupling, longitudinal coupled bunch and longitudinal instabilities due to the loss of Landau damping can be expected. In this paper, experimental studies in the SPS with single bunches of protons with intensities of up to 3.5·1011 p/b on the flat bottom and at 450 GeV/c are presented. Longitudinal instabilities were studied with LHC-type beams with 50~ns spacing and injected intensities up to 1.8·1011 p/b. The measurements address the increase of intensity thresholds and the achievable transverse emittances in the new low gamma transition optics with respect to the nominal SPS optics. The obtained results are compared with numerical simulations. | ||
| MOPS011 | Impact of Low Transition Energy Optics to the Electron Cloud Instability of LHC Beams in the SPS | 616 |
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| One of the main limitations for high intensity multi-bunch LHC proton beams in the SPS is imposed by electron cloud instabilities. A new optics of the SPS with lower transition energy was implemented and successfully tested in machine studies. The significant increase of the slippage factor that it provides at injection energy results in the expected increase of the single bunch instability thresholds. In this paper, the impact of this new optics on the electron cloud instability threshold is estimated by using numerical simulations, taking into account the change of the optics functions and the faster synchrotron motion due to the reduced transition energy. | ||
| MOPS012 | Optics Considerations for Lowering Transition Energy in the SPS | 619 |
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| Beam stability for high intensity LHC beams in the SPS can be improved by increasing the slippage factor, i.e. reducing the transition energy. In this paper, possible ways of modifying the optics of the SPS for lower transition energy are reviewed. In particular, a threefold increase of the slippage factor at injection can be achieved by decreasing the integer part of the tunes by 6 units. The properties of this new low-transition optics are compared with the nominal SPS optics, including working point and resonance behavior. Possible limitations are discussed. | ||
| MOPS013 | Transverse Low Frequency Broad-band Impedance Measurements in the CERN PS | 622 |
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| The base-line scenario for the High-Luminosity LHC upgrade foresees an intensity increase delivered by the injectors. With its 53 years, the CERN PS would have to operate beyond the limit of its performances to match the future requirements. Beam instabilities driven by transverse impedance are an important issue for the operation of high intensity beams as for the high-brightness LHC beams. Measurements of transverse tune dependence with beam intensity were performed at injection kinetic energy 1.4~GeV and at LHC beam extraction momentum 26~GeV/c. This allows deducing the low frequency inductive broad-band impedance of the machine. Then an estimation of the real part of the impedance is made by the rise time measurement of a fast transverse instability believed to be a TMCI type. Those are the first step towards a global machine impedance characterization in order to push forward the performances of the accelerator. | ||
| MOPS014 | Tune and Space Charge Studies for High-brightness and High-intensity Beams at CERN PS | 625 |
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| The current 1.4 GeV CERN PS injection energy limits the maximum intensity required by the future High-Luminosity LHC. The bare-machine large chromaticity combined with the non-linear space charge forces make high-brightness and high-intensity beams crossing betatron resonances along the injection flat bottom, inducing transverse emittance blow-up and beam losses. A scan of the working point plane {Qx,Qy} was done in order to identify beam destructive resonances, in the framework of a possible 2 GeV injection energy upgrade which would reduce the space charge effect on the tune. Experiments were carried out in order to review the maximum space charge tune shift for which no transverse emittance blow-up is observed. The results of measurements and simulations will be presented in this paper. | ||
| MOPS015 | 40-80 MHz Muon Front-End for the Neutrino Factory Design Study | 628 |
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Funding: EU FP7 EUROnu WP3. CERN summer student programme. To understand better the neutrino properties, machines able to produce an order of 1021 neutrinos per year have to be built. One of the proposed machine is called a neutrino factory. In this scenario, muons produced by the decay of pions coming from the interaction of a proton beam onto a target are accelerated to energies of several GeV and injected in a storage ring where they will decay in neutrinos. The so-called front-end section of the neutrino factory is conceived to reduce the transverse divergence of the muon beam and to adapt its temporal structure to the acceptance of the downstream accelerators to minimize losses. We present a re-evaluation of the muon front-end scenario which used 40-80 MHz radio-frequency cavities capturing one sign at a time in a single-bunch to bucket mode. The standard software environment of the International Study for the Neutrino Factory (IDS-NF) has been used, for comparison of its performance with the IDS-NF baseline front-end design which operates with higher frequency (330-200 MHz) capturing in a train of alternated sign the muons bunches. |
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| MOPS016 | First Observations of Intensity-dependent Effects for Transversally Split Beams | 631 |
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| During the commissioning of the CERN PS Multi-Turn Extraction (MTE) tests with different beam intensities were performed. The beam current before transverse splitting was varied and the properties of the five beamlets obtained by crossing the fourth-order horizontal resonance were studied. A clear dependence of the beamlets’ parameters on the total intensity was found, which is a first observation of intensity-dependent effects for such a peculiar beam type. The experimental results are presented and discussed in this paper. | ||
| MOPS017 | Simulation Studies of Macro-particles Falling into the LHC Proton Beam | 634 |
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| We report updated simulations on the interaction of macro-particles falling from the top of the vacuum chamber into the circulating LHC proton beam. The path and charge state of micron size micro-particles are computed together with the resulting beam losses, which – if high enough - can lead to the local quench of SC magnets. The simulated time evolution of the beam loss is compared with observations in order to constrain some macro-particle parameters. We also discuss the possibility of a "multiple crossing" by the same macro-particle, the effect of a strong dipole field, and the dependence of peak loss rate and loss duration on beam current and on beam size. | ||
| MOPS018 | Simulation and Measurement of Half Integer Resonance in Coasting Beams on the ISIS Ring | 637 |
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| ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on an 800 MeV rapid cycling synchrotron (RCS), which provides 3·1013 protons per pulse at 50 Hz, corresponding to a beam power of 0.2 MW. In common with many lower energy, high intensity proton rings, a key loss mechanism on ISIS is half integer resonance under space charge. This paper summarises experimental and simulation work studying half integer resonance in a “2D” coasting beam in the ISIS ring: understanding this is an essential prerequisite for explaining the more complicated case of RCS operation. For coasting beam experiments, the ring is reconfigured to storage ring mode with RF off and main magnets powered on DC current only. A 70 MeV beam is injected, painted appropriately, and manipulated so as to approach resonance. Understanding how the resonant condition develops is central to explaining observations, so realistic simulations of resonance, including injection, ramping of intensity and tunes are being developed. Results from the ORBIT code are presented and compared with experimental and theoretical results. Finally, future plans are summarized. | ||
| MOPS019 | High Intensity Longitudinal Dynamics Studies for Higher Energy Injection into the ISIS Synchrotron | 640 |
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| ISIS is the world’s most productive pulsed neutron and muon source, at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates 3·1013 protons per pulse from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies on ISIS upgrades are focussed on a new linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge and optimized injection. Studies assume injection of a chopped beam at 180 MeV and offer the possibility of beam powers in the 0.5 MW regime. A critical aspect of such an upgrade is the longitudinal dynamics, associated RF parameters, space charge levels and stringent requirements on beam loss. This paper outlines studies optimizing longitudinal parameters including key design requirements such as bunching factor and satisfying the Keil-Schnell-Boussard stability criterion throughout acceleration. Work developing and benchmarking the in-house longitudinal dynamics code used for these studies is also summarized. | ||
| MOPS021 | Beam Dynamics of a Compact SC Isochronous Cyclotron - Preliminary Study of Central Region* | 643 |
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Funding: Pennsylvania State University ARL S11-07 and N00024-02-D-6604 US Defense Threat Reduction Agency A compact high field superconducting isochronous cyclotron, Megatron (K250), is designed as a proof-of-principle for a single stage high power proton accelerator. This cyclotron is to accelerate proton to a final energy of 250 MeV with two 45° Dees with a radius ~40 cm. By employing a 20 mA external ECR proton source, the injected proton beam currents at high brightness are foreseen. Using phase selection in the center, a fully magnetized elliptical pole, low energy gain per turn, a precise relation between momentum and radius at large radius are expected. Two goals, a) to use this relationship to develop multi-turn extraction with passive elements only, to achieve a high external proton beam intensity (~1 mA); and b) to see if it is possible to achieve a high extraction efficiency (> 99%) without single turn extraction, with an energy spread |DE/E| ~0.1%. The RF acceleration is on the first harmonic with ωrf=ω0~64 MHz. Superconductor coils will provide a central field of B0 = 4.3 T and a peak hill field of 6.6 T. The general beam dynamics studies will be performed. Precise central field design including space charge effect will be shown in the presentation. |
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| MOPS023 | An Analytical Lagrangian Model for Analyzing Temperature Effects in Intense Non-neutral Beams* | 646 |
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| High-intensity charged-particle beams are used in several areas of physics. We can mention as an illustration, high-energy colliders, particle accelerators and vacuum electron devices. In all cases quoted above, the beam lose particles in the acceleration process, between its production to its fi nal destination. These ejected particles, generally, produce a surrounding structure around the beam core, called halo. This undesirable structure is seen in simulation as well as in actual linacs, and its formation has been one of the main sources of energy loss in the acceleration devices. For this reason, the need for an advance in understand the mechanism that produce the halo becomes necessary. In view of the whole problem, we contruct a 1D Lagrangian warm-fluid model for describe the behavior of inhomogeneous charged-particle beam in solenoidal focusing magnetic field. The equations of motion are derived for an adiabatic process with a state equation originated from the ideal gas law. In the end, the model is compared with self-consistent simulation and is used to explain emittance growth and jets of particle, even when the system is out of equilibrium. | ||
| MOPS024 | Bunch Dynamics through Accelerator Column | 649 |
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Funding: TRIUMF research is supported by the National Research Council of Canada. The differential equations for the bunched beam envelope through an axially symmetric DC accelerator are derived. In the case of no space charge, a particle's total energy is conserved, so the longitudinal evolution is simple: particles of same energy are a fixed time increment apart and this implies in first order that their separation is proportional to their speed. However, with space charge, the longitudinal force depends upon the bunch length, so we need equations that track this parameter. The full 6-dimensional and relativistically correct envelope equations are derived. |
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| MOPS025 | Studies of Emittance Measurement by Quadrupole Variation for the IFMIF-EVEDA High Space Charge Beam | 652 |
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| For the high-power (1 MW) beam of the IFMIF-EVEDA prototype accelerator, emittance measurements at nearly full power are only possible in a non-interceptive way. The method of quadrupole variation is explored here. Due to the high space charge regime, beam transport is strongly non-linear, and the classical matrix inversion is no more relevant. Inverse calculations using a multiparticle code is mandatory. In this paper, such emittance measurements are studied, aiming at checking its feasibility and evaluating its precision, taking into account the constraints of losses and quadrupole limitations. | ||
| MOPS026 | Start-to-end Beam Dynamics Simulations for the Prototype Accelerator of the IFMIF/EVEDA Project | 655 |
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| The EVEDA (Engineering Validation and Engineering Design Activities) phase of the IFMIF (International Fusion Materials Irradiation Facility) project consists in building, testing and operating a 125 mA/9 MeV prototype accelerator in Rokkasho-Mura (Japan). Because of high beam intensity and power, the different sections of the accelerator (injector, RFQ, MEBT, Superconducting Radio-Frequency linac and HEBT) have been optimized with the twofold objective of minimizing losses along the machine and keeping a good beam quality. Extensive start-to-end multi-particles simulations have been performed to validate the prototype accelerator design. A Monte Carlo error analysis has been carried out to study the effects of misalignments and field variations. In this paper, the results of theses beam dynamics simulations, in terms of beam emittance, halo formation and beam losses, are presented. | ||
| MOPS027 | Stability Charts for the IFMIF SRF-Linac | 658 |
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| Among the most recent projects, the IFMIF-EVEDA accelerators break the record of high intensity, leading to a multi-MW beam power at relatively low energy. The concern for such accelerated beams is the predominance of the self-field energy upon the beam energy. In these conditions, the space charge effect is at its maximum, which triggers different nonlinear mechanisms implying emittance growth, halo formation and sudden particle lost. In this proceeding we show the stability charts constructed for the IFMIF SRF-Linac, with which are identified the collective space charge resonances responsible of transverse-longitudinal emittance exchange and emittance growth. | ||
| MOPS028 | An Ion Beam Matching to a Linac Accelerating-focusing Channel | 661 |
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Funding: Work supported by HIC for FAIR A modern linear accelerator of ions is a long chain of different accelerating-focusing structures. The design of new linacs, as well as an upgrade and optimization of operating facilities, requires precise and reliable beam matching with the subsequent sections. Proper matching of the beam to the channel allows to improve the performance of the whole linac and to reduce the specific costs. Additionally it helps to avoide particle loss in high energy high intensity linacs. Generally a matching algorithm combines precisely measured or calculated accelerating-focusing external fields and experimentally obtained details of the beam parameters with an advanced code for beam dynamics simulations including space charge effects. Experimental results are introduced into a code as input data. The described algorithm has already been successfully implemented for several GSI projects: an upgrade of the GSI heavy ion linac UNILAC, an ion linac for the cancer therapy, the proton linac for the FAIR facility, a facility for laser acceleration of ions and others. Measured data and results of beam dynamics simulations leading to an achieved improvement of the linac performance are presented. |
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| MOPS029 | Experiments with a Fast Chopper System for Intense Ion Beams | 664 |
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| Chopper systems are used to pulse charged particle beams. In most cases, electric deflection systems are used to generate beam pulses of defined lengths and appropriate repetition rates. At high beam intensities, the field distribution of the chopper system needs to be adapted precisely to the beam dynamics in order to avoid aberrations. An additional challenge is a robust design which guarantees reliable operation. For the Frankfurt Neutron Source FRANZ, an E×B chopper system is being developed which combines static magnetic deflection with a pulsed electric field in a Wien filter configuration. It will generate proton pulses with a flat top of 50 ns at a repetition rate of 250 kHz for 120 keV, 200 mA beams. For the electric deflection, pre-experiments with static and pulsed fields were performed using a helium ion beam. In pulsed mode operation, ion beams of different energies were deflected with voltages of up to ±6 kV and the resulting response was measured using a beam current transformer. A comparison between experiments and theoretical calculations as well as numerical simulations are presented. | ||
| MOPS030 | Beam Dynamics of the FRANZ Bunch Compressor using Realistic Fields with a Focus on the Rebuncher Cavities | 667 |
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Funding: Work supported by HIC for FAIR. The ARMADILLO bunch compressor currently being designed at IAP is capable of reaching a longitudinal pulse compression ratio of 45 for proton beams of 150 mA at 2 MeV. It will provide one nanosecond proton pulses with a peak current of 7.7 A. The system guides nine linacμbunches deflected by a 5 MHz rf kicker and uses four dipole magnets - two homogeneous and two with field gradients - to merge them on the target. For longitudinal focusing and an energy variation of ±200 keV two multitrack rf cavities are included. ARMADILLO will be installed at the end of the Frankfurt Neutron Source FRANZ making use of the unique 250 kHz time structure. This contribution will provide an overview of the layout of the system as well as recent advances in component design and beam dynamics of the compressor. |
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| MOPS031 | Beam Dynamics Redesign of IFMIF-EVEDA RFQ for a Larger Input Beam Acceptance | 670 |
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| For the IFMIF-EVEDA RFQ, a very challenging project of a deuteron CW RFQ at 175 MHz from 0.1 MeV to 5 MeV with 125 mA of current, the input beam characteristics are very important. A lower focusing force in the first part of the RFQ as beam implemented in order to reduce the requirements of the input beam. In the article a full description of the new design will be reported with the changes in the RFQ performances. | ||
| MOPS033 | Beam Dynamics Studies on the 100 MeV/100 kW Electron Linear Accelerator for NSC KIPT Neutron Source | 673 |
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| We designed one 100MeV/100kW electron linear accelerator for NSC KIPT, which will be used to drive a neutron source on the base of subcritical assembly. Beam dynamics studies has been conducted to reach the design requirement (E=100MeV, P=100kW, dE/E<1% for 99% particles). In this paper, we will present the progress of the design and dynamics simulation results. For high intensity and long beam pulse linear accelerators, BBU effect is one big issue; special care has been taken in the accelerating structure design. To satisfy the energy spread requirement at the linac exit, the particles with large energy difference from the synchronous particle should be eliminated at low energy stage to ease the design of the collimation system and radiation shielding. A dispersion free chicane with 4 bending magnets is introduced at the downstream of the 1st accelerating section; the unwanted particles will be collimated there. | ||
| MOPS034 | Progress on Space Charge Compensation Study in Low Energy High Intense H+ Beam* | 676 |
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| This article lays emphasis on the relationship between the Space Charge Compensation (SCC) and the beam quality in different conditions. Ar and Kr are used to compensate a 35keV/90mA H+ beam with the gas pressure from 3.7×10-4 Pa to 6×10-3 Pa. Experiments are conducted in different compensation states with three approaches. With an energy spectrometer, we have got the energy spectra of Extra Compensation Gas Ions (ECGI). By a beam profile meter, the beam profiles are obtained when the injection of compensation gas is gradually rising. In the meantime, the beam emittance is measured under different compensation conditions. After measurements of the above data, the potential and the rest charge distributions in the beam are calculated by analyzing the ECGI energy spectra and beam profiles. All experiments performed aimed to seek out the best circumstance for SCC dominated low energy high intensity ion beams.together to calculate the potential distribution are calculated by analyzing the energy spectra and beam profiles. All experiments performed aimed to seeking for the best circumstances in SCC dominated low energy high intensity ion beams. | ||
| MOPS035 | Energy Spreads by Transient Beam Loading Effect in Pulsed RF Linac | 679 |
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Funding: Work partly supported by KAPRA and POSTECH Physics BK21 Program RF linacs for high power beams are operated in the fully beam-loaded condition for the power efficiency. In this condition, temporal energy spreads are induced by the transient beam loading effect. Irradiation sources require the beam energy of less than 10 MeV to prevent undesirable neutron production. In order to maximize the beam power and maintain the beam energy in a safe value, we need to suppress the temporal energy spreads. In an L-band traveling-wave linac for irradiation sources, the high energy electrons are suppressed by the beam current modulation with the RF power modulation. As a result, the average beam energy and the corresponding beam power are improved by nearly 60% compared to the case without any modulations. |
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| MOPS037 | High Intensity Transient Beam Dynamic Study in Travelling Wave Electron Accelerators with Accounting of Beam Loading Effect | 682 |
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The beam loading effect is one of main problems limiting the beam current. The methods of beam dynamic simulation taking into account the beam loading effect were discussed previously. Simulation methods and the especial code version BEAMDULAD-BL was described in the paper*. The beam loading effect was considered only for traveling wave linacs and for stationary beam only. Now it is important to study the beam dynamics of short current pulses, i.e. for transient process. We can consider only one beam bunch (or a packet of bunches) in a long external RF field pulse in stationary case. The beam radiation and wave fields can be calculated in the quasi-statically approximation. This approximation can not be used for transient mode. The methods of beam dynamics simulation will be discussed in this paper for transient mode. New code version BEAMDULAC-BLNS will be described. The simple test simulations will be carried out.
* A.V. Voronkov et al., "Beam Loading Effect of High Current Trawling Wave Accelerator Dynamic Study", Proc. of IPAC’10, Kyoto, Japan, TUPEA012, p. 1348 (2010). |
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| MOPS038 | 3D Beam Dynamic Simulation in Heavy Ion Superconducting Drift Tube Linac | 685 |
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| The superconducting (SC) linac conventionally consists of some different classes of the identical cavities. Each cavity is based on a SC structure with a high accelerating gradient. The low charge state beams require stronger transverse focusing. This focusing can be reached with the help of SC solenoid lenses. In this paper beam dynamics simulation obtain by smooth approximation and full field. Traditionally only the Coulomb field is taken into account for low energy beams. In this paper the computer simulation of heavy ion beam dynamics in superconducting (SC) linac will carried out by means of the "particle-in-cell" method. Simulation results will present. | ||
| MOPS039 | High Power Proton Linac Front-End: Beam Dynamics Investigation and Plans for the ESS | 688 |
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| Beam availibility is one of the major concerns for the designer of high power proton linacs. Since the Radio-Frequency Quadrupole (RFQ) will shape and accelerate the beam in the early stage of its propagation it will have a significant impact on the particle dynamics throughout the rest of the linac. The key role of the RFQ is consequently to deliver high quality beams with optimal transmission. Furthermore understanding the space charge compensation mechanism in the Low Energy Beam Transport line (LEBT) is mandatory if one wants to perform calculations with realistic beams. The European Spallation Source (ESS) has put important R&D efforts in designing the linac front-end and deep beam dynamics studies have been undertaken. Results of the investigation work will be presented. We will then deal with the future plans for the ESS and we will finally give a full description of the RFQ and LEBT scheme. | ||
| MOPS040 | Intra-Bunch Energy Spread of Electrons in Powerful RF Linacs for Nuclear Physics Research* | 691 |
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Funding: Ukrainian State program of fundamental and applied studies on the use of nuclear materials, nuclear and radiation technologies in the fields of economics (YaMRT project No. 826/35) There are some particles in RF electron linacs with energy that may be significantly different from that of particles within a core of the bunch. Loss of these particles at average beam power of tens of kilowatts can cause radiation and thermal problems. Filtration of such particles during the initial stage of acceleration, at energies below the threshold of photonuclear reactions, is important. The paper analyzes several ways to perform such type of filtration in the injector part of a powerful electron linac using a RF chopper or magnetic systems. |
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| MOPS042 | One-Dimensional Adiabatic Child-Langmuir Flow | 694 |
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Funding: Research supported in part by US Department of Energy, Grant No. DE-FG02-95ER40919, CNPq, FAPERGS, INCTFCx of Brazil, and US Air Force Office of Scientific Research, Grant No. FA9550-09-1-0283. A theory is presented that describes steady-state one-dimensional Child-Langmuir flow at a self-consistent finite temperature distribution. In particular, warm-fluid equations and adiabatic equation of state are used to derive the self-consistent Poisson equation. The profiles of the charged-particle density, the velocity, the electrostatic potential, the pressure and the temperature are computed. Results are compared with self-consistent simulations. |
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| MOPS043 | Beam Performance in H− Injector of LANSCE | 697 |
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During beam development time in 2010 we performed a series of beam emittance and beam profile scans along 750-keV H− beam transport and 800-MeV linac. The purpose of the measurements was to determine the effects of space charge, slow-wave intensity modulation or chopping, RF buncher fields, and vacuum conditions on beam performance. As previously reported*, from our observation and analysis we concluded that the 750 keV H− beam transport is space-charge uncompensated. This presentation will look at the relative importance of space-charge, chopping, and RF-buncher on the observed emittance growth for beam in the short and long pulse regime as well as the effects of beam line vacuum degradation on beam size and emittance at the end of the linac.
* Y. Batygin et al., “Space-charge effects in H− Low-Energy Beam Transport of LANSCE,” to be published in Proc. of the 2011 Particle Accelerator Conference, March 28-April 1, 2011, New York, NY. |
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| MOPS045 | Coupling Impedance of Rough Resistive Pipe* | 700 |
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| A new version of modelling of the surface roughness impact by thin dielectric layer in the round resistive beam pipe is suggested. The calculation method of coupled resistive-roughness impedance is developed. | ||
| MOPS046 | Impedances and Wakes in Round Three-layer Ceramic Waveguide | 703 |
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| The round ceramic waveguide with inner and outer thin metal coating is considered. Using the exact methods the longitudinal impedances and potentials are calculated. Identification of the main patterns of changes in their properties by varying the electrodynamic and geometric parameters of the waveguide is performed as well. The possibility of optimizing the parameters of the waveguide for the effective implementation of two-beam acceleration is discussed. | ||
| MOPS047 | Studies of Transverse Single-pass Beam Breakup in E-Linac | 706 |
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| Time-domain simulations of single-pass transverse beam-breakup (BBU) effects in E-linac are described. We use dipole-HOM parameters for the 9-cell cavity obtained with Particle Studio to evaluate the rms bunch orbit offsets at linac exit. Finding the multi-bunch orbit contribution to machine emittance as a function of the average beam current allows to evaluate the performance of two cavity models for two different modes of machine operation. | ||
| MOPS048 | Microbunching Instability Studies at SOLEIL | 709 |
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| Microbunching instability arises in storage rings when the number of electrons in a bunch exceeds a threshold value. Its signature, i.e. a strong and irregular emission of Coherent Synchrotron Radiation (CSR) in the Terahertz (THz) domain, is studied at SOLEIL on the AILES infrared beamline, with the storage ring tuned in a low-alpha configuration (used to get shorter electron bunch). The comparison of this observed THz CSR with numerical simulations of the longitudinal electron bunch dynamics, permits to put in evidence that during the instability a modulation appears and drifts in the longitudinal profile of the electron bunch. The understanding of this instability is important as it limits some operation of the storage rings. Indeed the induced fluctuations prevent the use of THz on the far IR beamline at high current per bunch. And in normal alpha operation this instability may spoil the electron/laser interaction effects used to get femtosecond and/or coherent pulse in storage rings (with slicing, Coherent Harmonic Generation or EEHG schemes on storage ring). | ||
| MOPS049 | Study of Ion-induced Instabilities and Transverse Feedback Performance at SOLEIL | 712 |
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| Experimental studies indicate that the SOLEIL storage ring at its maximum designed current of 500 mA is under a large influence of ions, potentially capable of inducing the so called fast beam-ion instability. To avoid it, the following three conditions have been empirically found effective: A reduced RF voltage, uniform filling and a large vertical chromaticity. While the choice of uniform filling appears contradictory to raising the ion instability threshold, it goes well with lowering of the RF voltage if outgassing due to beam-induced heating of the vacuum components is the primary source of ions. Additional difficulties associated are frequent occurrence of sudden beam blowups despite the presence of transverse feedback, which are large enough to trigger machine interlocks leading to complete beam losses. These blow ups may even take place horizontally inside in-vacuum insertion devices. The present paper reports on the results and findings obtained through experimental and simulation studies carried out on the collective beam dynamics and the transverse feedback performance, which are deeply interlinked, in order to clarify the mechanism of the encountered phenomena. | ||
| MOPS050 | Electron Beam Dynamics in the 50 MeV ThomX Compact Storage Ring | 715 |
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| ThomX is a high flux compact X-ray source based on Compton back scattering between a relativistic electron beam and an intense laser pulse. To increase the repetition rate, the electron beam is stored in a ring. The main drawback of such a scheme is the low energy of the electrons regarding collective effects and intrabeam scattering. These effects tend to enlarge or even disrupt the stored bunch and they limit its charge, especially in a system where damping plays a negligible role. Thus such collective effects reduce the maximum X-ray flux and it is important to investigate them to predict the performance of this type of X-ray source. In addition, the Compton back scattering acts on the electron beam by increasing its energy spread. This presentation will show firstly the impact of collective effects on the electron beam, essentially during the first turns when they are the most harmful. Then, the reduction of the X-ray flux due to Compton back scattering and intrabeam scattering will be investigated on a longer time scale. | ||
| MOPS051 | Modeling of the Beam Break Up Instability for BERLinPro* | 718 |
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| Following funding approval late 2010, Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current low emittance beam. In this work the threshold current of the Beam Break Up (BBU) instability was calculated for the BERLinPro. The comparison of two 100 MeV linacs based on different type of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold). | ||
| MOPS052 | Analytical and Numerical Calculations of Beam Pipe Impedances at Low Frequencies with Application to Thin SIS100 Pipe | 721 |
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| The projected fast ramped synchrotron SIS100 for FAIR uses an elliptical stainless steel beam pipe of 0.3 mm thickness. The lowest coherent betatron sidebands reach down to 100 kHz which demands accurate impedance calculations in the low frequency (LF) regime. For these frequencies, i.e. skin depth greater than wall thickness, structures behind the pipe may contribute to the impedance. Due to the extremely large wake length numerical methods in the time domain are not applicable. The longitudinal and transverse impedance of the thin SIS100 beam pipe including structures behind the pipe are obtained numerically by a method using power loss in the frequency domain. We compare different analytical models for simplified pipe structures to the numerical results. The dc and ultra-relativistic limits are investigated. The interpretation of bench measurements in the LF regime is discussed. | ||
| MOPS053 | Electron Cloud Effects in Coasting Heavy-ion Beams* | 724 |
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Funding: Work supported by BMBF under contract 06DA9022I. During slow extraction of intense ion beams electron clouds (EC) can accumulate in the circulating coasting beam and reduce the extraction efficiency. This is a concern for the existing SIS-18 heavy ion synchrotron at GSI and for the projected SIS-100 as part of the FAIR project. For medium energy heavy-ion beams the production of electrons from residual gas ionization is very effective. The electron density is limited due to Coulomb scattering by the beam ions. Above a threshold beam intensity the two-stream instability and the resulting coherent beam oscillations limit the electron density. Below this threshold the electron cloud can lead to observable deformations of the Schottky side-bands. To avoid EC build-up one can introduce a gap in the beam using barrier rf bucket. The reduction of the build-up efficiency caused by the gap is studied in details based on the solution of the Hill's equation for electrons. Finally we estimate the saturation level for the electron cloud density. |
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| MOPS054 | Impedance of the Pulse Power Converter for the SIS100 Bipolar Extraction Kicker System | 727 |
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| SIS100 will be operated with high intensity heavy-ion and proton beams. The reduction of ring impedances is therefore of great importance in order to avoid coherent beam instabilities. The kicker system is one of the main contributors to the overall ring impedance in SIS100. This paper will focus on the contribution of the external network to the kicker impedance. Calculations as well as experimental impedance measurements of the network contribution have already been carried out for the SIS18 and ESR kickers. The SIS100 will be equipped with a bipolar kicker system, which uses a Pulse Forming Network (PFN) as energy storage. For potential detachment purposes an insulation transformer will be installed. Since this setup is new in several ways it is important to know its contribution to the coupling impedance of the kicker system. In this contribution the corresponding numerical calculation is presented. | ||
| MOPS055 | Observation of Intensity Dependent Single Bunch Effects at the Synchrotron Light Source PETRA III | 730 |
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| At DESY the PETRA ring is operated as a synchrotron radiation facility with a very low emittance of 1 nm. Regular user operation has started in summer 2010. A summary of observations and measurements of intensity dependent single bunch effects is presented in this report. The longitudinal impedance of the ring is estimated from the measured bunch length versus beam intensity. The results are compared with predictions from the impedance model. Furthermore measurements of the single bunch intensity limit due to the transverse mode coupling instability (TMCI) are reported. The tune and phase shift around the ring has been measured as a function of the beam intensity. At PETRA III tune spectra have been observed with some characteristics which have been observed at other storage rings in connection with electron cloud effects. The present status of the observations of potential electron cloud effects is also discussed. | ||
| MOPS056 | An Analytical Formula of the Electron Cloud Linear Map Coefficient in a Strong Dipole | 733 |
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| Electron cloud effects have been indentified as one of the most serious bottleneck for reaching design performances in presently running and proposed future storage rings. The analysis of these effects is usually performed with very time consuming simulation codes. An alternative analytic approach, based on a cubic map model for the bunch-to-bunch evolution of the electron cloud density, could be useful to determine regions in parameters space compatible with safe machine operations. In this communication we derive a simple approximate formula relating the quadratic coefficient in the electron cloud density map to the parameters relevant for the electron cloud evolution in a strong vertical magnetic field. Results are compared with simulations with particular reference to the LHC dipoles. | ||
| MOPS057 | Beam-beam Interaction under External Force Oscillation | 736 |
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| Beam-ion interaction is strongly nonlinear. Response for external oscillation applied to beam shows characteristic feature. Simulations for external frequency scan becomes feasible for the recent computer power. We show the frequency response for beam-ion system in KEK-PF and recent low emittance rings. | ||
| MOPS058 | KEKB Linac Wakefield Studies of Comparing Theoretical Calculation, Simulation and Experimental Measurement* | 739 |
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| For superKEKB, in order to achieve aiming luminosity machine need to run with a nano-beam scheme so that a small beam emittance is critical important. During the beam propagation, the short-range wake field in the accelerating structure will cause the beam instability and emittance growth. In practical, injecting beam with certain offset could compensate wakfield. And beam emittance could be measured by tuning the quadruple known as quadscan method. In this paper, wakefield theoretical calculation, simulation results will be presented. And then the wakefield impact to beam emittance and wakefield compensation will be discussed. Finally, we will show the comparison of the results getting from theoretical calculation and experimental measurement. | ||
| MOPS059 | Transverse Impedance Calculation for Simplified Model of Ferrite Kicker Magnet with Beta < 1 | 742 |
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| In high intensity rings, kicker magnet is usually considered as a main source to the total impedance. Transverse coupling impedance of a simplified kicker model has been derived analytically in the ultrarelativistic limit. We extend the result to the general case of v < c, and present the analytical formulae of both horizontal and vertical transverse impedances. Numerical results are given for the CSNS extraction kicker magnets. | ||
| MOPS060 | Study on Resistive Wall Instability in CSNS/RCS | 745 |
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| Rapid Cycling Synchrotron of the China Spallation Neutron Source is a high intensity proton accelerator, with average beam power of 100kW. The collective effects caused by the coupling impedance may be the limit to beam power. The impedance estimation for components on beam line shows that the resistive wall impedance and its instability are more serious than any others. Based on the impedance budget, the instability is theoretically estimated. And a simple resistive wall wake field model is used to simulate the bunch oscillation and the growth rate instability. In this model, the continuous resistive wall wake field is equivalent to a point wake field and long bunch is sliced into many micro-bunches. By tracking the dynamics of the macro-bunches, the transverse growth rate are obtained and the result are analyzed. | ||
| MOPS064 | Longitudinal Beam Stability and Related Effects at the ALBA Storage Ring | 748 |
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| The risk of longitudinal instabilities excited by narrowband and broadband resonator impedance was studied. A campaign for the search of modes trapped in vacuum chamber elements of the ALBA storage ring via electromagnetic simulation was initiated. Several critical vacuum elements in the ring like the vertical scraper, the injection and feedback kickers were identified. The outlets of the injection kicker had to be protected with RF-fingers whereas the scraper only produces dangerous modes in the withdrawn state, both do not pose a real problem. However, the calculated power distribution generated in the feedback kickers could be an obstacle for reaching the nominal current of 400mA. Furthermore, the budget of Z(n)/n of the storage ring was computed and checked on the risk of microwave instability using the Boussard criterion. | ||
| MOPS065 | Transverse Instability Studies at the ALBA Storage Ring | 751 |
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In the first phase of the ALBA storage ring operation 3 NEG-coated aluminum chambers, 2 in-vacuum undulators and one wiggler chamber will be installed. Under particular consideration of the multilayer character of these chambers and the injection kickers the thresholds of the transverse mode coupled instability(TMCI) were calculated using MOSES*. The thresholds 17.5mA/40.5mA vertical/horizontal leave a rather large operative margin. The detrimental effect of the NEG-coating on the TMCI is relatively limited and on the resistive wall instability is even negligible. As well the thresholds of the head-tail instability were computed as function of chromaticity. Also the incoherent tune shifts generated by the quadrupolar resistive wall wake fields due to the flatness of the vacuum chambers were calculated. The computed results have been compared to first measurements of the storage ring commissioning.
* Y.H.Chin, MOSES 2.0, CERN/LEP-TH/88-05 |
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| MOPS066 | Collective Effects in the MAX IV 3 GeV Ring | 754 |
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| We present calculations of collective instability effects in the 3 GeV electron storage ring of the MAX IV facility currently under construction in Lund, Sweden. The storage ring is designed to deliver ultra-low emittance down to 0.24 nm rad so as to provide high brightness synchrotron radiation from undulators. This is achieved in a comparatively small machine (528 m circumference) through the use of a multi-bend achromat lattice and a compact magnet design featuring multi-purpose narrow gap magnet blocks. This design features small dispersion leading to low momentum compaction, which, together with the small circular (11 mm radius) chambers, poses a challenge to reach the design current (500 mA in 176 bunches) without exciting instabilities and degrading beam parameters due to the interaction with the machine impedance. Particularly important are multi-bunch resistive wall effects in the NEG coated copper chamber as well single-bunch instabilities driven by the broad-band impedance. A low RF frequency (100 MHz) and harmonic cavities are foreseen to lengthen the bunches and increase instability thresholds. | ||
| MOPS068 | Localization of Transverse Impedance Sources in the SPS using HEADTAIL Macroparticle Simulations | 757 |
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| In particle accelerators, beam coupling impedance is one of the main contributors to instability phenomena that lead to particle losses and beam quality deterioration. For this reason these machines are continuously monitored and the global and local amount of impedance needs to be evaluated. In this work we present our studies on the local transverse impedance detection algorithm. The main assumptions behind the algorithm are described in order to understand limits in reconstructing the impedance location. The phase advance response matrix is analyzed in particular for the SPS lattice, studying the different response from 90,180,270 degrees phase advance sections. The thin lenses scheme is also implemented and new analytical formulas for phase advance beating were derived. This avails us to put reconstructing lenses everywhere in the lattice, and to study their positioning scheme. Limits in linear response are analyzed. This sets the upper and lower limits in reconstruction to the phase advance measurement accuracy and the linear response regime limit. | ||
| MOPS069 | Review of Beam Instabilities in the Presence of Electron Clouds in the LHC | 760 |
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| Recent observations at the LHC indicate the build-up of electron clouds when 50 ns spaced beams are injected into the machine at nominal intensity. These electron clouds are a source of coherent beam instabilities and incoherent emittance growth and limit the achievable luminosity. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to study both the coherent and the incoherent effects on the beam. The simulations are performed with the HeadTail tracking code; the usage of new post-processing software allows determining not only the beam intensity thresholds in terms of the central electron cloud density but also the footprint of the beam in tune space. In this paper we review instability thresholds and tune footprints for beams with different emittances and interacting with an electron cloud in field-free or dipole regions. | ||
| MOPS070 | Electromagnetic Modeling of C Shape Ferrite Loaded Kickers | 763 |
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| The kickers are major contributors to the CERN SPS beam coupling impedance. As such, they may represent a limitation to increasing the SPS bunch current in the frame of an intensity upgrade of the LHC. In this paper, analytical approach and CST Particle Studio time domain electromagnetic simulations are performed to obtain the longitudinal and transverse impedances/wake potentials of models of ferrite loaded kickers. It turns out that the existing models are not sufficient to characterize correctly these components from the coupling impedance point of view. In particular the results show that below few hundred MHz the real C-structure of the magnet cannot be neglected. Therefore an analytical model was developed and benchmarked with EM simulations to take into account the C-shape of the magnet. | ||
| MOPS071 | Simulations of the Impedance of the New PS Wire Scanner Tank | 766 |
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| The CERN PS is equipped with 4 wire scanners. It was identified that the small aperture of the current wire scanner tank causes beam losses and a new tank design was needed. The interaction of the PS bunches with the beam coupling impedance of this new tank may lead to beam degradation and wire damage. This contribution presents impedance studies of the current PS tank as well as the new design in order to assess the need to modify the design and/or install lossy materials plates dedicated to damp higher order cavity modes and reduce the total power deposited by the beam in the tank. | ||
| MOPS072 | Broadband Electromagnetic Characterization of Materials for Accelerator Components | 769 |
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| Electromagnetic (EM) characterization of materials up to high frequencies is a major requirement for the correct modeling of many accelerator components: collimators, kickers, high order modes damping devices for accelerating cavities. In this scenario, the coaxial line method has gained much importance compared to other methods because of its applicability in a wide range of frequencies. In this paper we describe a new coaxial line method that allows using only one measurement setup to characterize the material in a range of frequency from few MHz up to several GHz. A coaxial cable fed at one side is filled with the material under test and closed on a known load on the other side. The properties of the material are obtained from the measured reflection coefficient by using it as input for a transmission line (TL) model or for 3D EM simulations, which describe the measurements setup. We have applied this method to characterize samples of SiC (Silicon Carbide) which could be used for LHC collimators and for CLIC accelerating structures and NiZn ferrite used for kicker magnets. | ||
| MOPS073 | Impedance Calculation for Simple Models of Kickers in the Non-ultrarelativistic Regime | 772 |
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| Kicker magnets are usually significant contributors to the beam coupling impedance of particle accelerators. An accurate understanding of their impedance is required in order to correctly assess the machine intensity limitations. The field matching method derived by H. Tsutsui for the longitudinal and transverse dipolar (driving) impedance of simple models of kickers in the ultrarelativistic regime was already extended to the non-ultrarelativistic case, and to the quadrupolar (detuning) impedance in the ultrarelativistic case. This contribution presents the extension to the quadrupolar impedance in the non-ultrarelativistic case, as well as benchmarks with other available methods to compute the impedance. In particular, all the components of the impedances are benchmarked with Tsutsui's model, i.e. in the ultrarelativistic limit, with the model for a flat chamber impedance recently computed by N. Mounet and E. Métral, in the case of finite relativistic gamma, and with CST Particle Studio simulations. | ||
| MOPS074 | Stabilization of the LHC Single-bunch Transverse Instability at High-energy by Landau Octupoles | 775 |
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| When the first ramp was tried on Saturday 15/05/2010 with a single bunch of about nominal intensity (i.e. ~ 1011 p/b), the bunch became unstable in the horizontal plane at ~ 2 TeV. The three main observations were: (i) a “Christmas tree” in the transverse tune measurement application (with many synchrotron sidebands excited), (ii) beam losses (few tens of percents) in IR7, and (iii) an increase of the bunch length. This transverse coherent instability has been stabilized successfully with Landau octupoles. Comparing all the measurements performed during this first year of LHC commissioning with the theoretical and simulation predictions reveals a good agreement. | ||
| MOPS075 | Simulation of Multibunch Motion with the HEADTAIL Code and Application to the CERN SPS and LHC | 778 |
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| Multibunch instabilities due to beam-coupling impedance can be a critical limitation for synchrotrons operating with many bunches. It is particularly true for the LHC under nominal conditions, where according to theoretical predictions the 2808 bunches rely entirely on the performance of the transverse feedback system to remain stable. To study these instabilities, the HEADTAIL code has been extended to simulate the motion of many bunches under the action of wake fields. All the features already present in the single-bunch version of the code, such as synchrotron motion, chromaticity, amplitude detuning due to octupoles and the ability to load any kind of wake fields through tables, have remained available. This new code has been then parallelized in order to track thousands of bunches in a reasonable amount of time. The code was benchmarked against theory and exhibited a good agreement. We also show results for bunch trains in the LHC and compare them with beam-based measurements. | ||
| MOPS076 | Long Range Wakefields in the SwissFEL C-band Linac | 781 |
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The SwissFEL main linac consists of more than hundred constant gradient C-band accelerating structures which boost the beam energy from 410 MeV at the injector to the final nominal energy of 5.8 GeV. With a repetition rate of 100 Hz, two bunches per pulse can be accelerated with a spacing of 28 ns to feed simultaneously two different FEL arms*. Rising of the long range wakefields, both longitudinal and transverse, could affect this multibunch operation, causing degenerative effects on the quality of the second bunch. A direct computation of the longitudinal and transverse wakes by means of time domain simulations is compared with a model based on the computation of the dispersion curves of the wake modes by frequency domain simulations. A good agreement is obtained for both the synchronous frequency and impedance of all the main modes contributing to the wakefields. Moreover, the total longitudinal wake at 28 ns is below the thighter tolerances required by the beam dynamics, so that neither Higher Order Modes (HOMs) either beam loading require compensation. The effects on the beam of the long range transverse wakefields are also negligeable.
*R. Ganter et al, SwissFEL CDR, PSI report n. 10-04; http://www.psi.ch/swissfel/CurrentSwissFELPublicationsEN/SwissFELCDR_v1903.03.11-small.pdf |
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| MOPS078 | Coaxial Wire Measurements of Ferrite Kicker Magnets | 784 |
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| Fast kicker magnets are used to inject beam into and eject beam out of the CERN accelerator rings. These kickers are generally transmission line type magnets with a rectangular shaped aperture through which the beam passes. Unless special precautions are taken the impedance of the yoke can provoke significant beam induced heating, especially for high intensities. In addition the impedance may contribute to beam instabilities. The results of longitudinal and transverse impedance measurements, for various kicker magnets, are presented and compared with analytical calculations: in addition predictions from a numerical analysis are discussed. | ||
| MOPS079 | Simulations of Coaxial Wire Measurements of the Impedance of Asymmetric Structures | 787 |
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| Coaxial wire measurements have provided a simple and effective way to measure the beam coupling impedance of accelerator structures for a number of years. It has been known how to measure the longitudinal and dipolar transverse impedance using one and two wires for some time. Recently the ability to measure the quadrupolar impedance of structures exhibiting top/bottom and left/right symmetry has been demonstrated. A method for measuring the beam coupling impedance of asymmetric structures using displaced single wires and two wire measurements is proposed. Simulations of the measurement system are presented with further work proposed. | ||
| MOPS080 | Comparison of the Current LHC Collimators and the SLAC Phase 2 Collimator Impedances | 790 |
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| One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design. | ||
| MOPS082 | Some Considerations on the Choice of Frequency and Geometrical Beta in High Power Proton Linacs in the Context of Higher Order Modes | 793 |
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| Several high power superconducting (SC) proton linear accelerators are currently in the design stage around the world, such as for example the European Spallation Source (ESS) in Lund, Project X at Fermilab, the European ADS demonstrator MYRRAH in Mol and the Superconducting Proton linac (SPL) at CERN. In this contribution, the influence of Higher Order Modes (HOMs) in elliptical SC cavities is discussed as a function of the operation frequency, the number of cells and the geometrical beta of the cavity. Based on cavity design data beam dynamics simulations are executed for different linac layouts to quantify the influence of HOMs. | ||
| MOPS083 | Update on Electron Cloud Mitigation Studies at Cesr-TA* | 796 |
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Funding: Work supported by the US National Science Foundation (PHY-0734867) and Department of Energy (DE-FC02-08ER41538) Over the course of the past three years, the Cornell Electron Storage Ring (CESR) has been reconfigured to serve as a test facility for next generation particle accelerators. A significant part of this program has been the installation of several diagnostic devices to measure and quantify the electron cloud effect, a potential limiting factor in these machines. In particular, more than 30 Retarding Field Analyzers (RFAs) have been installed in CESR. These devices measure the local electron cloud density and energy distribution, and can be used to evaluate the efficacy of different cloud mitigation techniques. This paper will provide an overview of RFA results obtained at CesrTA over the past year, including measurements taken as function of bunch spacing and wiggler magnetic field. Understanding these results provides a great deal of insight into the behavior of the electron cloud. |
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| MOPS084 | Status of Electron Cloud Dynamics Measurements at CESRTA* | 799 |
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Funding: Supported by US National Science Foundation (PHY-0734867) & Dept. of Energy (DE-FC02-08ER41538) The study of electron cloud-related instabilities for the CESR-TA project permits the observation of the interaction of the electron cloud with the stored beam under a variety of accelerator conditions. These measurements are undertaken utilizing automatic and semi-automatic techniques for three basic observations: the measurement of tune shifts of individual bunches along a train, the detection of the coherent self-excited spectrum for each bunch within a train and the pulsed excitation of either the betatron dipole or head-tail mode for each individual bunch within the train, followed by the observation of the damping of its coherent motion. These techniques are employed to study the electron cloud-related interactions in a number of conditions, such as trains of bunches with low emittance and spaced by as little as 4 nsec between bunches. We report on the most recent observations and results. |
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| MOPS085 | Wakefield Calculations for the LCLS in Multibunch Operation* | 802 |
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Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515. Normally the Linac Coherent Light Source (LCLS) operates in single-bunch mode, sending a bunch of up to 250 pC charge at 120 Hz through the linac and the undulator, and the resulting FEL radiation into one of the experimental hutches. With two bunches per rf pulse, each pulse could feed either two experiments or one experiment in a pump-probe type configuration. Two-bunch FEL operation has already been briefly tested at the LCLS, and works reasonably well*, although not yet routinely. In this report we study the longitudinal and transverse long-range (bunch-to-bunch) wakefields of the linacs and their effects on LCLS performance in two-bunch mode. The longitudinal wake changes the average energy and chirp at the second bunch, and the transverse wake misaligns the second bunch (in transverse phase space) in the presence of e.g. transverse injection jitter or quad misalignments. Finally, we extend the study to consider the LCLS with trains of up to 20 bunches per rf pulse. * F.-J. Decker et al, "A demonstration of multi-bunch operation in the LCLS," Proceedings of FEL2010, Malmoe, Sweden, p. 467. |
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| MOPS086 | Beam Breakup Simulation for the PEP-X ERL | 805 |
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Funding: The work is supported by the U.S. Department of Energy under contract No. DE-AC02-76SF00515. The transverse beam breakup (BBU) is one of the dominant factors in ERL for the available beam current. A tracking code built in Matlab is developed and benchmarked by comparing with the analytical solutions with the simple model. Study on the threshold current and emittance growth due to the transverse BBU for PEP-X ERL are presented in this paper. |
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| MOPS088 | Simulation of Electron Cloud Beam Dynamics for CesrTA | 808 |
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This presentation provides a comprehensive set of results obtained using the simulation program CMAD. CMAD is being used for studying electron cloud induced beam dynamics issues for CesrTA, which is a test facility for studying physics associated with electron and positron damping rings. In particular, we take a closer look at electron cloud induced effects on positron beams, including head-tail motion, emittance growth and incoherent tune shifts for parameters specific to ongoing experimental studies at CesrTA. The correspondence between simulation and experimental results will also be discussed.
Work supported by US Department of Energy grant number DE-FC02-08ER41538 and the National Science Foundation grant number PHY-0734867 |
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| MOPS089 | Identification of Bunch Dynamics in the Presence of E-cloud and TMCI for the CERN SPS Ring | 811 |
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Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP). Measurements and multi-particle simulation codes (i.e. HEAD-TAIL, WARP, CMAD) indicate that bunched particle beams show unstable motions induced by electron-clouds and strong head-tail interactions. The bunch dynamics exhibits highly non-linear, complex and unstable behavior under certain operating conditions. Feedback control systems have been proposed to mitigate these instabilities in the CERN SPS ring. The design of feedback systems requires the knowledge of a reduced dynamic model of the bunch. It allows to include and quantify the effect of noise and signal perturbations, as well as system robustness to parameter variation. Identification techniques are used to estimate those models based on bunch motion measurements. In this work we present reduced mathematical models representing the transverse bunch dynamics and identification techniques to extract the model parameters based on measurements. These techniques are validated using time domain simulations of the bunch motion conducted using multi-particle simulation codes. For that, different sections of the bunch are driven by random signals, and the vertical motion of those areas is used to estimate the reduced model. |
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| MOPS090 | Observation of Beam Ion Instability in SPEAR3 | 814 |
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| Weak vertical coupled bunch instability with oscillation amplitude at μm level has been observed in SPEAR3. The instability becomes stronger when there is a vacuum pressure rise by partially turning off vacuum pumps and it becomes weaker when the vertical beam emittance is increased by turning off the skew quadrupole magnets. These confirmed that the instability was driven by ions in the vacuum. The threshold of the beam ion instability when running with a single bunch train is just under 200 mA. This paper presents the comprehensive observations of the beam ion instability in SPEAR3. The effects of vacuum pressure, beam current, beam filling pattern, chromaticity, beam emittance and bunch-by-bunch feedback are investigated in great detail.pattern, chromaticity, beam emittance and bunch-by-bunch feedback are investigated in great detail. | ||
| MOPS091 | Study of Electron Cloud for MEIC | 817 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The Medium Energy Electron Ion Collider (MEIC) at Jefferson Lab has been envisioned as a future high energy particle accelerator beyond the 12 GeV upgrade of the existing Continuous Electron Beam Accelerator Facility (CEBAF). Synchrotron radiation from the closely spaced proton bunches in MEIC can generate photoelectrons inside the vacuum chamber and cause secondary emission due to multipacting in the presence of beam's electric field. This phenomenon can lead to fast build up of electron density, known as electron cloud effect – resulting into beam instability coupled to multi-bunches in addition to a single bunch. For MEIC, the estimated threshold value of the electron-cloud density is approximately 5 x 1012 m-3. In this paper, we would like to report the self-consistent simulation studies of electron cloud formation for MEIC. The code has been benchmarked against the published data of electron cloud effects observed in LHC. Our first simulations predict increase of electron clouds with the increase of repetition rate. The detailed simulations are under progress and will be reported. |
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