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damping

Paper Title Other Keywords Page
MO4RAC02 Status of LHC Crab Cavity Simulations and Beam Studies cavity, luminosity, impedance, simulation 85
 
  • R. Calaga, R. De Maria
    BNL, Upton, Long Island, New York
  • R.W. Assmann, J. Barranco, F. Caspers, E. Ciapala, T.P.R. Linnecar, E. Métral, Y. Sun, R. Tomás, J. Tuckmantel, Th. Weiler, F. Zimmermann
    CERN, Geneva
  • G. Burt
    Lancaster University, Lancaster
  • Y. Funakoshi, A. Morita, Y. Morita, K. Nakanishi, Y. Ohnishi
    KEK, Ibaraki
  • Z. Li, A. Seryi, L. Xiao
    SLAC, Menlo Park, California
  • P.A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • J. Qiang
    LBNL, Berkeley, California
  • N. Solyak, V.P. Yakovlev
    Fermilab, Batavia
 
 

Funding: This work was partially performed under the auspices of the US DOE and the European Community-Research Infrastructure, FP6 programme (CARE, contract number RII3-CT-2003-506395)}


The LHC crab cavity program is advancing rapidly towards a first prototype which is anticipated to be tested during the early stages of the LHC phase I upgrade and commissioning. Some aspects related to crab optics, collimation, aperture constraints, impedances, noise effects, beam transparency and machine protection critical for a safe and robust operation of LHC beams with crab cavities are addressed here.

 

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MO6RFP064 Stacking Simulations for Compton Positron Sources of Future Linear Colliders positron, injection, septum, emittance 512
 
  • F. Zimmermann, Y. Papaphilippou, L. Rinolfi, A. Vivoli
    CERN, Geneva
  • F. Antoniou
    National Technical University of Athens, Zografou
  • R. Chehab
    IN2P3 IPNL, Villeurbanne
  • M. Kuriki
    HU/AdSM, Higashi-Hiroshima
  • T. Omori, J. Urakawa
    KEK, Ibaraki
  • A. Variola
    LAL, Orsay
  • V. Yakimenko
    BNL, Upton, Long Island, New York
 
 

The Compton positron source of a future linear collider must obtain the target bunch population by accumulating a large number of positron packets, arriving either in a number of bursts from a “Compton ring”, with intermediate damping of the scattering electron beam, or quasi-continually from a “Compton energy recovery linac”. We present simulation results for the longitudinal stacking of Compton positrons in the ILC damping ring and the CLIC pre-damping ring, reporting parameter optimization, stacking efficiency, possible further improvements, and outstanding questions.

 
TU3PBC04 Circularly Inclined Solenoid Channel for 6D Ionization Cooling of Muons solenoid, cavity, emittance, simulation 727
 
  • Y. Alexahin
    Fermilab, Batavia
 
 

Funding: Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy


Ionization cooling is essential for realization of Muon Collider, muons beam based neutrino factories and other experiments involving muons. The simplest structure - absorber(s) immersed in alternating solenoidal magnetic field - provides only transverse cooling since the longitudinal motion in the most suitable momentum range (2-300MeV/c) is naturally antidamped. To overcome this difficulty it is proposed to periodically tilt solenoids so that a rotating transverse magnetic field was created. By choosing the phase advance per period above a multiple of 2pi it is possible to ensure that muons with higher momentum make a longer path in the absorber (whether distributed or localized) thus providing longitudinal damping. Basic theory of such channel and results of tracking simulations are presented.

 

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TU5PFP006 Wakefield Damping for the CLIC Crab Cavity cavity, dipole, wakefield, HOM 815
 
  • P.K. Ambattu, G. Burt, R.G. Carter, A.C. Dexter
    Cockcroft Institute, Lancaster University, Lancaster
  • V.A. Dolgashev
    SLAC, Menlo Park, California
  • R.M. Jones, V.F. Khan
    UMAN, Manchester
 
 

Funding: The work is supported by STFC


A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency (X-band) for the crab cavity is preferred as the deflection voltage required and the RF phase tolerance are inversely proportional to the operating frequency. However, the strong inter-bunch wakefields deteriorate the quality of the colliding bunches. The short bunch spacing of the CLIC scheme and the crab cavity's high sensitivity to dipole kicks demands very high damping of the inter-bunch wakes. A crab cavity requires special attention to the damper design as its wakefield spectrum is entirely different from that of an accelerating cavity. In addition to the higher-order modes, the orthogonally polarised dipole mode (same order mode) and the fundamental monopole mode (lower order mode) also need to be damped, however their resonant frequencies make damping these modes complicated. The same order mode suppression requires the use of an azimuthally asymmetric damper. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using choke-mode damping and various types of waveguide damping to suppress them effectively.

 
TU5PFP007 Investigation of an Alternate Means of Wakefield Suppression in the Main Linacs of CLIC wakefield, dipole, coupling, linac 818
 
  • V.F. Khan, R.M. Jones
    UMAN, Manchester
 
 

Here we present initial results on an alternate design for CLIC main accelerating linacs which is moderately damped and detuned structure. In order to suppress the wake-fields, we detune the lowest dipole modes as they have significant impact on the beam emittance compared to the other multipoles. In order to mitigate the reappearance of the wake-field of a detuned accelerator structure, we provide moderate damping by coupling cells to manifolds which run parallel to each accelerator structure. The manifolds are designed such that they are non-propagating at the acceleration mode frequency. The cell parameters are optimised by considering the r.f. breakdown, pulse surface heating and beam dynamics constraints.

 
TU5PFP040 Novel Geometries for the LHC Crab Cavity cavity, dipole, HOM, radio-frequency 909
 
  • B.D.S. Hall, G. Burt
    Cockcroft Institute, Lancaster University, Lancaster
  • R. Calaga
    BNL, Upton, Long Island, New York
  • J.R. Delayen, R.A. Rimmer, H. Wang
    JLAB, Newport News, Virginia
  • J.D.A. Smith
    Lancaster University, Lancaster
 
 

In 2017 the LHC is envisioned to increase is luminosity via an upgrade. This upgrade is likely to require a large crossing angle hence a crab cavity is required to align the bunches prior to collision. There are two possible schemes for crab cavity implementation, global and local. In a global crab cavity the crab cavity is far from the IP and the bunch rotates back and forward as it traverses around the accelerator in a closed orbit. For this scheme a two cell elliptical squashed cavity at 800 MHz is preferred. To avoid any potential beam instabilities all the modes of the cavities must be damped strongly, however crab cavities have lower order and same order modes in addition to the usual higher order modes and hence a novel damping scheme must be used to provide sufficient damping of these modes. In the local scheme two crab cavities are placed at each side of the IP two start and stop rotation of the bunches. This would require crab cavities much smaller transversely than in the global scheme but the frequency cannot be increased any higher due to the long bunch length of the LHC beam. This will require a novel compact crab cavity design.

 
TU5PFP048 Robustness of the Superconducting Multicell Cavity Design for the Cornell Energy Recovery Linac cavity, HOM, linac, dipole 933
 
  • M. Liepe, G.Q. Stedman, N.R.A. Valles
    Cornell University, Ithaca, New York
 
 

Funding: This work is supported by the National Science Foundation.


Cornell University is developing an Energy-Recovery-Linac driven x-ray light source. One of the major components of this accelerator will be its 5 GeV superconducting main linac. The design of the superconducting RF cavities in this main linac has been optimized primarily for two objectives: (1) low RF losses from the accelerating mode to minimize refrigeration cost and (2) strong Higher-Order-Mode damping to preserve low emittance and prevent beam break-up at high beam current (100 mA). In this paper we study the robustness of this optimized cavity design with respect to small cell shape fluctuations from fabrication errors.

 
TU5PFP051 Superconducting Multicell Cavity Design for the Energy Recovery Linac at Cornell cavity, HOM, linac, dipole 939
 
  • V.D. Shemelin, M. Liepe
    CLASSE, Ithaca, New York
 
 

Funding: DOE


The first phase of the Cornell Energy Recovery Linac was the high current, low emittance injector. At present the injector is under commissioning. The next phase calls for the development of multicell cavity for the main linac. The cavities need to have low RF losses to minimize refrigeration and strong HOM damping to preserve low emittance and prevent beam break-up at high current (100 mA). Here we present the RF design of the cavity meeting these requirements.

 
TU5PFP053 Cryogenic Test of a Coaxial Coupling Scheme for Fundamental and Higher Order Modes in Superconducting Cavities cavity, coupling, HOM, vacuum 945
 
  • J.K. Sekutowicz
    DESY, Hamburg
  • P. Kneisel
    JLAB, Newport News, Virginia
 
 

A coaxial coupling device located in the beam pipe of the TESLA type superconducting cavities provides for better propagation of Higher Order Modes (HOMs) and their strong damping in appropriate HOM couplers. Additionally, it also provides efficient coupling for fundamental mode RF power into the superconducting cavity. The whole coupling device can be designed as a detachable system. If appropriately dimensioned, the magnetic field can be minimized to a negligible level at the flange position. This scheme, presented previously*, provides for several advantages: strong HOM damping, flangeable solution, exchangeability of the HOM damping device on a cavity, less complexity of the superconducting cavity, possible cost advantages. This contribution will describe the results of the first cryogenic test.


*J. Sekutowicz et al., Proceedings LINAC08, Victoria, Canada, 2008.

 
TU5PFP064 SC Crab Cavity with Reduced Transverse Size for the LHC Upgrade cavity, dipole, HOM, impedance 975
 
  • V.P. Yakovlev, I.G. Gonin, T.N. Khabiboulline, N. Solyak
    Fermilab, Batavia
 
 

In the paper the Crab Cavity is described for local Crab schemes for LHC that demand reduced transverse cavity dimensions small enough to fit limited space necessary for the beams separation. The results of the configuration cavity optimization are presented that include (a) the surface field minimization; (b) parasitic monopole and dipole spectrum optimization and dumping, (c) the input and the parasitic mode damping couplers design. The results of multipacting simulations, which were performed in order to understand the possible gradient limitations, are discussed also.

 
TU5RFP003 Superconducting Multi-Cell Deflecting Cavity for Short-Pulse X-Ray Generation at the Advanced Photon Source cavity, impedance, dipole, photon 1087
 
  • G.J. Waldschmidt, L.H. Morrison, R. Nassiri
    ANL, Argonne
  • R.A. Rimmer, K. Tian, H. Wang
    JLAB, Newport News, Virginia
 
 

Funding: * Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.


A superconducting multi-cell cavity for the production of short x-ray pulses at the Advanced Photon Source (APS) has been explored as an alternative to a single-cell cavity design in order to improve the packing factor and potentially reduce the number of high-power RF systems and low-level RF controls required. The cavity will operate at 2815 MHz in the APS storage ring and will require heavy damping of parasitic modes to maintain stable beam operation. Novel on-cell dampers, attached directly to the cavity body, have been utilized by taking advantage of the magnetic field null on the equatorial plane in order to enhance damping. Design issues and simulation results will be discussed.

 
TU5RFP008 NSLS-II Lattice Optimization with Damping Wigglers sextupole, quadrupole, lattice, dynamic-aperture 1102
 
  • W. Guo, S.L. Kramer, S. Krinsky, Y. Li, B. Nash, T. Tanabe
    BNL, Upton, Long Island, New York
 
 

Funding: NSLS-II, Brookhaven National Laboratory


NSLS-II, the third-generation light source which will be built at BNL is designed and optimized for 3 GeV energy, ultra-small emittance and high intensity of 500 mA. It will provide very bright synchrotron radiation over a large spectral range from IR to hard X-rays. Damping wigglers (DWs) are deployed to reduce the emittance of 2 nm by factors of 2-4, as well as for intense radiation sources for users. The linear and nonlinear effects induced by the DWs are integrated into the lattice design. In this paper, we discuss the linear and nonlinear optimization with DWs, and present a solution satisfying the injection and lifetime requirements. Our approach could be applied to the other light sources with strong insertion devices.

 
TU5RFP063 Laser Heater and Coherent Synchrotron Radiation: Analytical and Numerical Results FEL, laser, electron, synchrotron 1229
 
  • G. Dattoli
    ENEA C.R. Frascati, Frascati (Roma)
  • M. Migliorati
    INFN/LNF, Frascati (Roma)
  • A. Schiavi
    Rome University La Sapienza, Roma
 
 

We develop some considerations allowing the possibility of deriving the conditions under which laser heater devices may suppress the Coherent Synchrotron Instability (CSRI) without creating any prejudice to the use of the beam for FEL SASE or FEL oscillator operation. We discuss the problem using either numerical and analytical methods. The analytical part is aimed at evaluating the amount of laser power, necessary to suppress the instability. We use methods already developed within the context of FEL-storage rings beam dynamics, with particular reference to the interplay between FEL and Saw Tooth Instability. The numerical method employs a procedure based on the integration of the Liouville equation, describing the coupled interaction between e-beam and wake-fields, producing the instability, and the laser producing the heating. Particular attention is devoted to the competition between instability and heating. The comparison between numerical and analytical results is discussed too and the agreement is found to be satisfactory.

 
TU6RFP036 Beam Extraction Using Strip-Line Kicker at KEK-ATF kicker, septum, extraction, collider 1620
 
  • T. Naito, H. Hayano, K. Kubo, S. Kuroda, T. Okugi, N. Terunuma, J. Urakawa
    KEK, Ibaraki
 
 

The kicker of the damping ring for the International linear collider(ILC) requires fast rise/fall times(3 or 6ns) and high repetition rate(3 MHz). A multiple strip-line kicker system is developing to realize the specification*. We present results of the beam test at KEK-ATF by the strip-line kicker**. The multi-bunch beam, which has 5.6ns bunch spacing in the damping ring, is extracted with 308ns duration. Two units of the strip-line electrodes are used to extract the beam. The scheme of the beam extraction is same as the kicker of the ILC. A bump orbit and an auxiliary septum magnet are used with the kicker to clear the geometrical restriction.


*T. Naito et. al., Proc. of PAC07, pp2772-2274
**T. Naito et. al., Proc. of EPAC08, pp601-603

 
TU6RFP079 A High Voltage, High Rep-Rate, High Duty Factor Stacked Transformer Modulator gun, electron, proton, cathode 1733
 
  • G.W. Saewert, H. Pfeffer
    Fermilab, Batavia
 
 

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.


A high voltage modulator has been built and installed at Fermi National Accelerator Laboratory for the purpose of driving the gun anode of the Tevatron Electron Lens (TEL). It produces a defined voltage for each of the 36 (anti)proton bunches. This modulator employs five transformers to produce high voltage at a high repetition rate and high duty factor. It is capable of outputting sustained complex waveforms having peak voltages over 6 kV and average periodic rates up to 450 kHz with voltage transitions occurring at 395 ns intervals. This paper describes key aspects of the hardware design and performance.

 
TU6RFP082 Tests and Operational Experience with the DAΦNE Stripline Injection Kicker kicker, impedance, injection, simulation 1739
 
  • F. Marcellini, D. Alesini, S. Guiducci, P. Raimondi
    INFN/LNF, Frascati (Roma)
 
 

New injection stripline kickers are operating since December 2007 at the DAΦNE collider. They are designed to operate with very short pulse generators to perturb only the injected bunch and the two stored adjacent ones at 2.7 ns and are a test for the design of the fast kickers of the damping ring of the International Linear Collider (ILC). Stripline frequency response and impedance measurements have been performed to characterize the structure and are compared to the simulation results. Operational performances are also described, pointing out the problems occured and the flexibility of the stripline structure that worked with both the short and the old pulse generators and has been used as an additional damping kicker to improve the efficiency of the horizontal multibunch feedback system.

 
TU6RFP091 Development of an Adder-Topology ILC Damping Ring Kicker Modulator kicker, high-voltage, extraction, injection 1760
 
  • T. Tang, C. Burkhart
    SLAC, Menlo Park, California
 
 

Funding: Work supported by the Department of Energy under contract No. DE-AC02-76SF00515


The injection and extraction kickers (50 Ω) for the ILC damping rings will require highly reliable modulators to deliver ±5 kV, 2 ns flattop (~1 ns rise and fall time) electrical pulses at up to 6 MHz*. An effort is underway at SLAC National Accelerator Laboratory to meet these requirements using a transmission line adder topology to combine the output of an array of ~1 kV modules. The modules employ an ultra-fast hybrid driver/MOSFET that can switch 33 A in 1.2 ns. Experimental results for a scale adder structure will be presented.


*ILC Reference Design Report, http://www.linearcollider.org/cms/?pid=1000437

 
WE1PBC04 The New RF Deflectors for the CTF3 Combiner Ring simulation, electron, multipactoring, cavity 1812
 
  • D. Alesini, A. Ghigo, F. Marcellini
    INFN/LNF, Frascati (Roma)
  • J.F. DeFord
    STAAR/AWR Corporation, Mequon
  • V.A. Dolgashev
    SLAC, Menlo Park, California
  • G. McMonagle
    CERN, Geneva
 
 

To suppress the vertical beam instability in the CTF3 Combiner Ring caused by vertical trapped modes in the rf deflectors, two new devices have been constructed. In the new structures special antennas absorb the power released by the beam to the modes. They have been realized in aluminium to reduce the costs and delivery time and have been successfully installed in the ring. In the paper we illustrate the electromagnetic design, the realization procedures, the rf measurement and high power test results.

 

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WE3RAI01 Progress in High Gradient Accelerator Structure Research for Future Linear Colliders linear-collider, collider, wakefield, vacuum 1872
 
  • S.G. Tantawi
    SLAC, Menlo Park, California
 
 

This talk will summarize progress towards high-gradient accelerator structures for a future multi-TeV linear collider. The research summarized will include the US high gradient research collaboration and the CLIC research program, and will include recent experimental results of testing a variety of accelerator structures with different frequencies, geometries and materials, and features that allow for wake field damping. The talk also presents the results of specialized material studies geared towards the understanding of surface fatigue limits due to high magnetic fields, and progress on the theory of rf breakdown in high vacuum structures and multipactoring in dielectric loaded structures.

 

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WE3PBI01 Head-Tail Modes for Strong Space Charge space-charge, synchrotron, lattice, emittance 1889
 
  • A.V. Burov
    Fermilab, Batavia
 
 

Head-tail modes are described when the space charge tune shift significantly exceeds the synchrotron tune. Spatial shape of the modes, their frequencies, coherent growth rates and Landau damping rates are found.

 

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WE3PBI02 Study of Beam Dynamics during the Crossing of the Third-Order Resonance at VEPP-4M resonance, octupole, betatron, collider 1894
 
  • P.A. Piminov, S.A. Glukhov, E.B. Levichev, O.I. Meshkov, S.A. Nikitin, I.B. Nikolaev, A.N. Zhuravlev
    BINP SB RAS, Novosibirsk
 
 

The influence of resonances on the beam dynamics in storage rings is of substantial interest to accelerator physics. For example, a fast crossing of resonances occurs in the damping rings of future linear colliders during the beam damping (due to the incoherent shift) can result in a loss of particles. We have studied experimentally the crossing of resonances of different power near the working point of the VEPP-4M storage ring. Observation of the beam sizes and particle losses was performed with a single-turn time resolution. Comparison with the numerical simulation has been made and will be presented alongside the experimental results.

 

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WE5PFP018 Results from the CLIC X-Band Structure Test Program at NLCTA HOM, linear-collider, collider, linac 2027
 
  • C. Adolphsen, G.B. Bowden, V.A. Dolgashev, L. Laurent, S.G. Tantawi, F. Wang, J.W. Wang
    SLAC, Menlo Park, California
  • S. Döbert, A. Grudiev, G. Riddone, W. Wuensch, R. Zennaro
    CERN, Geneva
  • Y. Higashi, T. Higo
    KEK, Ibaraki
 
 

Funding: Work supported by the DOE under contract DE-AC02-76SF00515


As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their manufacturing (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives which could bring even higher efficiency. This paper summarizes the high gradient test results from the NLCTA in support of this effort.

 
WE5PFP024 Optimal Timing for Spark Recovery in the TRIUMF Cyclotron cyclotron, TRIUMF, cavity, resonance 2045
 
  • K. Fong, M.P. Laverty, Q. Zheng
    TRIUMF, Vancouver
 
 

In the TRIUMF cyclotron when a spark occurs it is necessary to shut off the RF drive and to initiate a RF restart procedure. It is also desirable to restore the full operational dee voltage as soon as possible in order to prevent thermal detuning of the resonant cavity. However, when the RF drive is shut off, the disappearance of Lorentz force on the resonator hot-arms causes the hot-arms to vibrate at their mechanical resonant frequency. When the RF field is being restored, the electromagnetic resonance is coupled to the mechanical resonance through the Lorentz force, and the amplitudes of both the mechanical vibration and the RF field depend on the timing when RF drive is re-applied. Computer simulations and experimental results will be presented to demonstrate that an optimum exists as to when to initiate the RF restart. With this optimal timing, the Lorentz force is used to damp the mechanical vibrations of the hot-arms. The reduction in hot-arm vibrations increases the probability of successful restarts as well as reduces the stress on the RF components.

 
WE5PFP035 Prototyping PEFP Low-Beta Copper Cavity and HOM Coupler cavity, HOM, controls, SRF 2070
 
  • S. An, Y.-S. Cho, B.H. Choi, Y.M. Li, Y.Z. Tang, L. Zhang
    KAERI, Daejon
 
 

Funding: This work is supported by the Ministry of Education, Science and Technology of Korea.


A superconducting radio frequency (SRF) cavity with a geometrical beta of 0.42 has been designed to accelerate a proton beam after 100 MeV at 700 MHz for an extended project of Proton Engineering Frontier Project (PEFP). In order to confirm the RF and mechanical properties of the cavity, and to produce documentation for a procurement and quality control for an industrial manufacture of the cavities, two prototype copper cavities have been produced, tuned and tested. In this paper, the copper cavity’s production, tuning and testing are introduced. The testing results show that the low-beta cavity and its tuning system can work as we design.

 
WE5PFP041 1500 MHz Passive SRF Cavity for Bunch Lengthening in the NSLS-II Storage Ring cavity, HOM, SRF, coupling 2086
 
  • J. Rose
    BNL, Upton, Long Island, New York
  • A.E. Bogle, T.L. Grimm
    Niowave, Inc., Lansing, Michigan
  • T. Yanagisawa
    MHI, Kobe
 
 

NSLS-II is a new ultra-bright 3GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. Ion clearing gaps are required to suppress ion effects on the beam. The natural bunch length of 3mm is planned to be lengthened by means of a third harmonic cavity in order increase the Touschek limited lifetime. After an extensive investigation of different cavity geometries a passive, superconducting 2-cell cavity has been selected for prototyping. The cavity is HOM damped with ferrite absorbers on the beam-pipes. The 2-cell cavity simplifies the tuner design as compared to two independent cells. Tradeoffs between the damping of the higher order modes, thermal isolation associated with the large beam tubes and overall cavity length are described. A copper prototype has been constructed and measurements of fundamental and higher order modes will be compared to calculated values.

 
WE5PFP047 A Compact Alternative Crab Cavity Design at 400-MHz for the LHC Upgrade cavity, HOM, simulation, electron 2104
 
  • Z. Li, L. Xiao
    SLAC, Menlo Park, California
 
 

Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.


Crab cavities are proposed for the LHC upgrade to improve the luminosity. In the local crabbing scheme, the crab cavities are located close to the interaction region and the transverse separation between the two beam lines at the crab cavity location can only accommodate an 800-MHz cavity of the conventional elliptical shape. Thus the baseline crab cavity design for the LHC upgrade is focused on the 800-MHz elliptical cavity shape although a lower frequency cavity is preferable due to the long bunch length. In this paper, we present a compact 400-MHz design as an alternative to the 800-MHz baseline design. The compact design is of a half-wave resonator (HWR) shape that has a small transverse dimension and can fit into the available space in the local crabbing scheme. The optimization of the HWR cavity shape and the couplers for the HOM, LOM, and SOM damping will be presented.

 
WE5PFP048 800MHz Crab Cavity Conceptual Design for the LHC Upgrade cavity, HOM, coupling, simulation 2107
 
  • L. Xiao, Z. Li, C.-K. Ng, A. Seryi
    SLAC, Menlo Park, California
 
 

Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.


In this paper, we present a 800MHz crab cavity conceptual design for LHC upgrade, including the cell shape optimization, and LOM, SOM, HOM and input coupler design. The compact coax-to-coax coupler scheme is proposed to couple to the LOM and SOM modes which can provide strong coupling to the LOM and SOM modes. HOM coupler design uses a two-stub antenna with a notch filter to couple to the HOM modes in the horizontal plane and reject the operating mode at 800MHz. All the damping results for the LOM/SOM/HOM modes satisfy their damping requirements. The multipacting in cell and couplers is simulated as well. And the issue of the cross-coupling between the input coupler and LOM/SOM couplers due to cavity asymmetry is addressed. The power coming out of the LOM/SOM/HOM couplers are estimated. All the simulations are carried out using SLAC developed parallel EM simulation codes Omega3P, S3P and Track3P.

 
WE5PFP053 Design of Superconducting Parallel Bar Deflecting and Crabbing RF Structures cavity, HOM, simulation, RF-structure 2120
 
  • J.R. Delayen, H. Wang
    JLAB, Newport News, Virginia
  • J.R. Delayen
    ODU, Norfolk, Virginia
 
 

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177


A new concept for a deflecting and crabbing rf structure based on half-wave resonant lines was introduced recently*. It offers significant advantages to existing designs and, because of it compactness, allows low frequency operation. This concept has been further refined and optimized for superconducting implementation. Results of this optimization and application to a 400 MHz crabbing cavity and a 499 MHz deflecting cavity are presented.


*A New TEM-Type Deflecting and Crabbing RF Structure, J. R. Delayen and H. Wang, Proc. LINAC08

 
WE5PFP056 A Family of L-Band SRF Cavities for High Power Proton Driver Applications cavity, HOM, cryomodule, impedance 2129
 
  • R.A. Rimmer, F. Marhauser
    JLAB, Newport News, Virginia
 
 

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.


Recent global interest in high duty factor or CW superconducting linacs with high average beam power highlights the need for robust and reliable SRF structures capable of delivering high average RF power to the beam with moderate HOM damping, low interception of halo and good efficiency. Potential applications include proton or H- drivers for spallation neutron sources, neutrino physics, waste transmutation, subcritical reactors, and high-intensity high-energy physics experiments. We describe a family of SRF cavities with a range of Betas capable of transporting beam currents in excess of 10 mA CW with large irises for minimal interception of halo and HOM and power couplers capable of supporting high average power operation. Goals include an efficient cell shape, high packing factor for efficient real-estate gradient and strong HOM damping to ensure stable beam operation. Designs are being developed for low-frequency (e.g. 650-975 MHz), but can easily be scaled to high-frequency (e.g. 1.3-1.5 GHz), depending on the application. We present the results of conceptual design studies, simulations and prototype measurements.

 
WE5PFP059 Design, Prototype and Measurement of a Single-Cell Deflecting Cavity for the Advanced Photon Source cavity, impedance, cryomodule, simulation 2138
 
  • H. Wang, G. Cheng, G. Ciovati, P. Kneisel, R.A. Rimmer, K. Tian, L. Turlington
    JLAB, Newport News, Virginia
  • R. Nassiri, G.J. Waldschmidt
    ANL, Argonne
 
 

Funding: This manuscript has been authored by Jefferson Science Associates, LLC and by UChicago Argonne, LLC under U.S. DOE Contract numbers DE-AC05-06OR23177 and DE-AC02-06CH11357.


After design optimization of a squashed elliptical single-cell crab cavity at 2.8 GHz, a copper prototype has been bench measured in order to determine its rf properties and the effectiveness of waveguide damping of parasitic modes, especially the low-order mode (LOM)*. We also present detailed results of the RF cold test at 2K on niobium single-cell and two-cell prototype cavities operating either in the zero or pi mode. Further progress will be discussed on the design of high-order mode (HOM) waveguide damping, the analysis of the Lorenz force detuning simulations by ANSYS, and the prototype of on-cell damping in which a waveguide port is attached directly on the cavity’s long equator. Details of LOM/HOM impedance calculations and experimental bench measurements will be reported and compared to strict requirements for satisfying the APS impedance budget.


*J. Shi et. al., “Superconducting RF Deflecting Cavity Design and Prototype for Short X-ray Pulse Generation”, EPAC 2008, paper MOPP155.

 
WE5PFP075 The New CERN PS Transverse Damper betatron, kicker, injection, pick-up 2183
 
  • A. Blas, J.M. Belleman, E. Benedetto, F. Caspers, D.C. Glenat, R. Louwerse, M. Martini, E. Métral, V. Rossi, J.P.H. Sladen
    CERN, Geneva
 
 

Since 1999 the PS has been operated without active transverse damping thanks to an increase of the coupling between the transverse planes and the reduction of injection steering errors. Although the LHC requirements are met by these means, a new transverse feedback system has been commissioned to reinforce the robustness of operation and avoid the blow-up generated by residual injection steering errors. This system could also allow the reduction of the chromaticity and reduce the slow incoherent losses during the long PS injection plateau. It could also stabilize the high energy instabilities that appear occasionally with the LHC nominal beam and may be a limiting factor for ultimate LHC beam. Highlights include a signal processing with an automatic delay adapting itself to the varying revolution frequency, a programmable betatron phase adjustment along the cycle, pick-ups that have been re-furbished with electronics covering the very low frequency of the first betatron line and a compact wideband high-power solid state amplifier that drives the strip-line kicker via an impedance matching transformer. The overall system is described together with experimental results.

 
WE5PFP078 Development of SCRF Cavity Resonance Control Algorithms at Fermilab cavity, resonance, controls, feedback 2192
 
  • Y.M. Pischalnikov, R.H. Carcagno, A. Makulski, D.F. Orris, W. Schappert
    Fermilab, Batavia
 
 

Funding: Work supported by U.S. Department of Energy under contract DE-AC02-76CH03000


Progress has been made at Fermilab on the development of feed-forward and feed-back algorithms used to compensate SCRF cavity detuning, which is caused by Lorentz Forces and microphonics. Algorithms that have been developed and tested for the 1.3GHz (ILC-style) SCRF cavities (Capture Cavity II) will be reported.

 
WE5PFP079 The Damping of Longitudinal Quadrupole Oscillations at GSI quadrupole, controls, cavity, dipole 2195
 
  • M. Mehler, H. Klingbeil, M. Kumm, U. Laier, K.-P. Ningel
    GSI, Darmstadt
 
 

Funding: Project funded by the European Community under the FP6 "Structuring the European Research Area" program (SIS1002, contract number 515873)


SIS100 is a synchrotron that will be built in the scope of the FAIR (Facility for Antiproton and Ion Research) project. High intensity ion beams are required, making it necessary to damp longitudinal coupled and uncoupled bunch oscillations. For this purpose, a closed-loop control system was designed. Its processing part is based on digital signal processors (DSP) and field programmable gate arrays (FPGA) whose advantage is their adaptability to different problems by software changes. Experiments with a prototype were performed at the existing synchrotron SIS12/18 at GSI concentrating on the damping of longitudinal coupled bunch quadrupole oscillations of the lowest order. The configuration of the electronic system is described and results of the machine development experiments are reported. Finally, an outlook to the application in SIS100 is given.

 
WE5PFP096 Damping Effect Studies for X-Band Normal Conducting High Gradient Standing Wave Structures dipole, acceleration, coupling, impedance 2237
 
  • S. Pei, V.A. Dolgashev, Z. Li, S.G. Tantawi, J.W. Wang
    SLAC, Menlo Park, California
 
 

Funding: Work supported by the DOE under contract DE-AC02-76SF00515.


The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, π-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (RT/Q)T. The effect of damping on the acceleration mode is also discussed.

 
WE5RFP018 Reduction of Beam Emittance of PEP-X Using Quadruple Bend Achromat Cell emittance, dipole, brightness, undulator 2306
 
  • M.-H. Wang, Y. Cai, R.O. Hettel, Y. Nosochkov
    SLAC, Menlo Park, California
 
 

Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515


SLAC National Accelerator Laboratory is studying an option of building a high brightness synchrotron light source machine, PEP-X, in the existing PEP-II tunnel*,**. By replacing 6 arcs of FODO cells of PEPII High Energy Ring (HER) with two arcs of DBA and four arcs of TME and installation of 89.3 m long damping wiggler an ultra low beam emittance of 0.14 nm-rad (including intra-beam scattering) at 4.5 GeV is achieved. In this paper we study the possibility to further reduce the beam emittance by releasing the constraint of the dispersion free in the DBA straight. The QBA (Quadruple Bend Achromat) cell is used to replace the DBA. The ratio of outer and inner bending angle is optimized. The dispersion function in the non-dispersion straight is controlled to compromise with lower emittance and beam size at the dispersion straight. An undulator of period length 23 mm, maximum magnetic field of 1.053 T, and total periods of 150 is used to put in the 30 straights to simulate the effects of these IDs on the beam emittance and energy spread. The brightness including all the ID effects is calculated and compared to the original PEP-X design.


*R. Hettel et al., “Ideas for a Future PEP-X Light Source”, EPAC08, p.2031(2008).
**M-H Wang et al., “Lattice Design of PEP-X as a Light Source Machine at SLAC”, EPAC08, p.2127(2008).

 
WE5RFP024 HALS: Our Future Light Source at NSRL emittance, lattice, wiggler, radiation 2321
 
  • L. Wang, Z. Bai, G. Feng, W. Li, L. Liu, C.-F. Wu, S.C. Zhang
    USTC/NSRL, Hefei, Anhui
 
 

Hefei Light Source is a second generation VUV light source, whose performance cannot meet the requirements of synchrotron radiation users at the present time. One year ago, the concept of the Hefei Advanced Light Source, whose main features are ultra low beam emittance and high brilliance in VUV and soft X-ray range, was brought forward. In the preliminary design study, a medium scale storage ring and multi bend achromat focusing structure were adopted to achieve beam emittance lower than 0.2 nm.rad. Linear and nonlinear parameter optimizations were performed to obtain large on-momentum and off-momentum dynamic aperture. The design status will be introduced briefly in the presentation.

 
WE5RFP086 New Materials and Designs for Superconductive Insertion Devices undulator, wiggler, electron, radiation 2471
 
  • P. Peiffer, T. Baumbach, A. Bernhard, G. Fuchert, D. Wollmann
    KIT, Karlsruhe
  • R. Maccaferri, Y. Papaphilippou
    CERN, Geneva
  • R. Rossmanith
    FZ Karlsruhe, Karlsruhe
 
 

NbTi wires are relatively easy to handle and are therefore up to now the preferred material for superconductive insertion devices. Yet other materials, like Nb3Sn, MgB2 or high temperature superconductors, are less sensitive to beam heat load and/or are able to produce higher magnetic fields. In this paper the different superconducting materials and their advantages and challenges are discussed. Additionally this paper describes new designs for special insertion devices like damping wigglers and undulators for laser wakefield accelerators.

 
WE6PFP060 eRHIC Ring-Ring Design with Head-on Beam-Beam Compensation electron, proton, luminosity, emittance 2637
 
  • C. Montag, M. Blaskiewicz, W. Fischer, W.W. MacKay, E. Pozdeyev
    BNL, Upton, Long Island, New York
 
 

The luminosity of the eRHIC ring-ring design is limited by the beam-beam effect exerted on the electron beam. Recent simulation studies have shown that the beam-beam limit can be increased by means of an electron lens that compensates the beam-beam effect experienced by the electron beam. This scheme requires proper design of the electron ring, providing the correct betatron phase advance between interaction point and electron lens. We review the performance of the eRHIC ring-ring version and discuss various parameter sets, based on different cooling schemes for the proton/ion beam.

 
WE6PFP068 Emittance Evolution of the Drive Electron Beam in a Helical Undulator for ILC Positron Source undulator, emittance, simulation, electron 2656
 
  • W. Gai, M. Borland, K.-J. Kim, W. Liu, A. Xiao
    ANL, Argonne
  • J. Sheppard
    SLAC, Menlo Park, California
 
 

Funding: This work was supported by the US Department of Energy Office of Science under Contract No. DE-AC02-06CH11357.


The effect of ILC positron source’s helical undulator to the drive electron beam is of great interest. People have been looking into the effect of wakefield, quad misalignment and also the effect of radiation. In this paper we’ll report an emittance damping effect of the ILC positron source undulator to the drive electron beam and our QUAD-BPM error simulation results. For 100m RDR undulator, the emittance of drive electron beam will be damped down by about 1% instead of growing as the damping is stronger than quantum excitation for this RDR undulator with the RDR drive electron beam. Quad-BPM misalignment simulations show that a 20um rms misalignment error in a 250m long undulator beamline can cause about 5% emittance growth in drive electron beam. Taking into consider the damping effect of undulator, the net emittance growth will be smaller.

 
WE6PFP103 CesrTA Layout and Optics emittance, wiggler, optics, quadrupole 2751
 
  • D. L. Rubin, D. Sagan, J.P. Shanks
    CLASSE, Ithaca, New York
 
 

Funding: Work supported by the National Science Foundation and the US Department of Energy


The Cornell Electron Storage Ring has been reconfigured as a test accelerator (CesrTA) for the investigation of the beam physics of a linear collider damping ring. The low beta interaction region optics have been replaced with simple FOFO lattice structures. Superconducting damping wigglers are located in straights where horizontal dispersion can be constrained to be zero to minimize horizontal emittance. The flexibility of the CESR optics allows for an energy reach of 1.5 GeV /beam→ 6.0GeV/beam and a wide range of emittances and radiation damping times. We exploit that flexibility for measurements of the dependencies of various phenomena, on energy, emittance, and damping rate. At 2GeV beam energy, with no damping wigglers, the minimum horizontal emittance is 10nm. With 16 meters of wiggler magnets operating at 1.9 T, the horizontal emittance is reduced by a factor of four to 2.5 nm and the radiation damping time to 56ms. With tuning and alignment we expect to reach a vertical emittance approaching that of the International Linear Collider (ILC) damping rings. We report on the details of the CesrTA optics and the measurements of optical parameters.

 
WE6PFP105 Lattice Options for the CLIC Damping Rings emittance, wiggler, lattice, quadrupole 2757
 
  • Y. Papaphilippou, F. Antoniou
    CERN, Geneva
  • E.B. Levichev, S.V. Sinyatkin, P. Vobly, K. Zolotarev
    BINP SB RAS, Novosibirsk
  • P. Raimondi
    INFN/LNF, Frascati (Roma)
 
 

Optics design optimisation studies have been undertaken for the CLIC damping ring lattice. Main parameters such as the ring energy and output longitudinal emittance were reconsidered in order to reduce the detrimental effect of collective instabilities. In this respect, the low emittance arc cell length was rationalized taking into account space and magnet design requirements. The straight section cell filled with super-conducting wigglers was modified to accommodate a robust absorption scheme. Several low emittance rings were considered and compared with respect to their dynamic aperture and the IBS-dominated output emittances.

 
WE6PFP107 Design Considerations for the CLIC Pre-Damping Rings emittance, wiggler, dipole, lattice 2760
 
  • F. Antoniou
    National Technical University of Athens, Zografou
  • Y. Papaphilippou, F. Zimmermann
    CERN, Geneva
 
 

The CLIC pre-damping rings have to accommodate a large emittance beam, coming in particular from the positron target and reduce its size to low enough values for injection into the main damping rings. In particular, polarized positron stacking imposes stringent requirements with respect to longitudinal acceptance and damping times. Linear lattice design options based on low-emittance cells, multiple bend cells and the inclusion of damping wigglers are compared with respect to linear optics functions, tunability, chromatic properties and acceptance. The optics of special regions for the placement of injection, extraction and RF elements are also presented. Non-linear dynamics simulations are finally undertaken for evaluating and maximizing the rings dynamic aperture, especially for large momentum spreads.

 
WE6RFP006 Cryogenic Considerations on SRF Operation at 2K for a Light Source Using a Standard 4.5K Cryo-Plant SRF, cryogenics, cavity, linac 2793
 
  • M.H. Chang, M.-C. Lin, C.H. Lo, M.H. Tsai, Ch. Wang
    NSRRC, Hsinchu
 
 

The feasibility of SRF operation at 2K using the remaining refrigeration capacity of an operating 4.5K cryogenic plant at NSRRC is examined. A refrigeration configuration with warm compression is proposed under an assumption that a reasonable amount of cryogenic heat load is required at 2K. The expectation of the efficacy of the cold and warm heat exchangers (HEX) is evaluated in terms of the corresponding equivalent cryogenic heat load on the 4.5K cold box. A factor approximately 9.5 or 6.0 is required to convert the cryogenic loss, 12 W at 2K, into our 4.5K cold box operated in a refrigeration mode without or with the cold heat exchanger (efficiency 85 %), respectively. An additional benefit is that the required volumetric pumping speed of the warm compressor can be greatly decreased. Moreover, a considerable cold capacity from the sub-atmospheric cold return helium gas can be ultimately converted by combining the cold HEX working together with a highly effective warm HEX, to a conversion factor 3.8 with an efficiency 95 %. Special attention must be devoted to minimize the risk of contamination or impurity for a turbine refrigerator.

 
WE6RFP061 A Transverse Mode Damped DLA Structure vacuum, simulation, wakefield, controls 2933
 
  • C.-J. Jing, F. Gao, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio
  • M.E. Conde, W. Gai, R. Konecny, J.G. Power
    ANL, Argonne
 
 

Funding: DoE SBIR Phase I 2008


As the dimensions of accelerating structures become smaller and beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis. These deflection modes can cause inter-bunch beam breakup and intra-bunch head-tail instabilities along the beam path, and thus BBU control becomes a critical issue. All new metal based accelerating structures, like the accelerating structures developed at SLAC or power extractors at CLIC, have designs in which the transverse modes are heavily damped. Similarly, minimizing the transverse wakefield modes (here the HEMmn hybrid modes in Dielectric-Loaded Accelerating (DLA) structures) is also very critical for developing dielectric based high energy accelerators. We have developed a 7.8GHz transverse mode damped DLA structure. The design and bench test results are presented in the article.

 
WE6RFP081 Design of Advanced Photonic Bandgap (PBG) Structures for High Gradient Accelerator Applications simulation, dipole, HOM, wakefield 2986
 
  • R.A. Marsh, B.J. Munroe, M.A. Shapiro, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts
 
 

Funding: Work supported by DOE HEP, under contract DE-FG02-91ER40648


The design of advanced photonic bandgap (PBG) accelerator structures is examined. PBG structures are chosen for their wakefield damping. A potential disadvantage of PBG structures, as well as damped detuned structures, is the increased wall currents at the structure surface due to the reduced surface area, leading to higher pulsed wall heating. Research is carried out to improve the pulsed heating performance of PBG structure concepts while maintaining higher order mode damping. Wakefield damping parameters are discussed and a quantitative figure of merit is expressed to evaluate and compare PBG concepts. Pulsed heating performance in PBG structures is improved by breaking perfect symmetry and allowing deformation of both rod and lattice geometry. A final design for an improved pulsed heating performance PBG structure for breakdown testing at 11.424 GHz is presented and discussed.

 
WE6RFP082 Design of Photonic Bandgap (PBG) Accelerator Structures with Reduced Symmetry dipole, simulation, HOM, wakefield 2989
 
  • B.J. Munroe, R.A. Marsh, M.A. Shapiro, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts
 
 

Funding: Work supported by DOE HEP, under contract DE-FG02-91ER40648


The design of a new photonic bandgap (PBG) accelerator structure based on a pentagonal array of rods is presented. The goal of this structure is to damp the higher order modes (HOMs) present in the structure. By removing the bilateral symmetry present in the four and six rod PBG structures the five rod photonic quasi-crystal (PQC) structure is able to damp the symmetric dipole mode. The field pattern and mode Q factors for the fundamental and dipole modes are presented for various values of the ratio of rod radius to rod spacing. These results are compared to the equivalent results for the six rod structure. The ratio of the Q factors is also calculated, and found to show an optimal value near a rod radius to rod spacing ratio of 0.17 in both cases.

 
WE6RFP103 Development of X-band Photonic Band Gap Accelerating Structure cavity, coupling, simulation, HOM 3041
 
  • Z.P. Li
    USTC, Hefei, Anhui
  • S. Dong, X.D. He, C.-F. Wu
    USTC/NSRL, Hefei, Anhui
 
 

Funding: National Nature Science Foundation of China, Grant No. 10675116 and 10375060


We present the new experimental results for an X-band (11.42GHz) metallic PBG accelerating cavity. A coupler of a single cavity was fabricated and cold tested. An X-band traveling-wave PBG accelerator was designed based on CST MWS transient analysis. The X-band PBG accelerator is now under construction, future work will focus on the structure to be cold tested and tuned.

 
TH4GBC06 X-Band Photonic Bandgap (PBG) Structure Breakdown Experiment klystron, HOM, accelerating-gradient, wakefield 3163
 
  • R.A. Marsh, M.A. Shapiro, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts
  • V.A. Dolgashev, S.G. Tantawi
    SLAC, Menlo Park, California
 
 

Funding: Work supported by DoE HEP, under contracts DE-FG02-91ER40648 and DE-AC02-76-SF00515


In order to understand the performance of photonic bandgap (PBG) structures under realistic high gradient operation, an X-band (11.424 GHz) PBG structure was designed for high power testing in a standing wave breakdown experiment at SLAC. The PBG structure was hot tested to gather breakdown statistics, and achieved an accelerating gradient of 65 MV/m at a breakdown rate of two breakdowns per hour at 60 Hz, and accelerating gradients above 110 MV/m at higher breakdown rates, for a total pulse length of 320 ns. High pulsed heating occurred in the PBG structure, with many shots above 270K, and an average of 170K for 35 x 106 shots. Damage was observed in scanning electron microscope imaging. No breakdown damage was observed on the iris surface, the location of peak electric field, but pulsed heating damage was observed on the inner rods, the location of magnetic fields as high as 1 MA/m. Breakdown in accelerator structures is generally understood in terms of electric field effects. PBG structure results highlight the unexpected role of magnetic fields on breakdown. We think that relatively low electric field in combination with high magnetic field on the rod surface may trigger breakdowns.

 

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Slides

 
TH5PFP055 Mathematica Application for Methodical Ionization Cooling Channel Design emittance, solenoid, optics, scattering 3330
 
  • Y. Alexahin
    Fermilab, Batavia
 
 

Funding: Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy


Existing codes for accelerator design (e.g. MAD) are not well suited for ionization cooling channels where particles exhibit strongly dissipative and nonlinear motion. A system of Mathematica programs was developed which allows to: 1) find periodic orbit and eigenvectors of the transfer matrix around it with account of (regular part of) ionization losses and feeddown effect from nonlinear fields; 2) compute emittance growth due to scattering and straggling, find equilibrium values (if exist); 3) analyze nonlinear effects such as dependence of tunes and damping rates on the amplitudes, resonance excitation; 4) perform tracking with account of stochastic processes. Underlying theory and application to helical cooling channel are presented.

 
TH5PFP073 Ion Effect Issues in PETRA III ion, feedback, electron, simulation 3371
 
  • G.X. Xia
    MPI-P, München
  • M. Ivanyan
    CANDLE, Yerevan
  • K. Manukyan, K.A. Sargsyan
    YSU, Yerevan
  • R. Wanzenberg
    DESY, Hamburg
 
 

At DESY the PETRA accelerator has been converted into a new 3rd generation high-brilliance synchrotron radiation facility called PETRA III. For the first commissioning in spring 2009 a positron beam is used. In the future it is also foreseen to operate the synchrotron light source with an electron beam. Ion effects pose a potential problem to the electron beam operation of PETRA III. In this paper, a weak-strong simulation code is employed to study the ion effect issues in detail for different operation scenarios.

 
TH5PFP089 Trapped Mode Study for a Rotatable Collimator Design for the LHC Upgrade vacuum, simulation, HOM, collimation 3416
 
  • L. Xiao, C.-K. Ng, J.C. Smith
    SLAC, Menlo Park, California
  • F. Caspers
    CERN, Geneva
 
 

Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.


A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosses the collimator, trapped modes will be excited that result in beam energy loss and collimator power dissipation. Some of the trapped modes can also generate transverse kick on the beam and affect the beam operation. In this paper the parallel eigensolver code Omega3P is used to search for all the trapped modes below 2GHz in the collimator, including longitudinal modes and transverse modes. The loss factors and kick factors of the trapped modes are calculated as function of the jaw positions. The amplitude ratio between transverse and longitudinal trapped mode intensity can be used as a direct measure of the position of the beam. We present simulation results and discuss the results.

 
TH5RFP007 Tune Measurement System Upgrade with FPGA-Based Technology at the APS booster, storage-ring, synchrotron, controls 3450
 
  • C. Yao, W.E. Norum, H. Shang, J. Wang
    ANL, Argonne
 
 

Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.


The Advanced Photon Source (APS) has three circular machines: a 7-GeV electron storage ring (SR), a booster synchrotron (booster) of beam energy 325 MeV to 7 GeV, and a particle accumulator ring (PAR). Their tune measurement systems are based on HP 4396 network and spectrum analyzers (NASA) and HP 89400 vector spectrum analyzers (VSA). The instruments are no longer supported by the vendor and will need replacement in the future. An upgrade of these systems with FPGA-based processors has been implemented. The new systems provided faster tune history and bunch-by-bunch tune reading in addition to the original systems. We present a brief description of the implementation and performance of the new systems.

 
TH5RFP009 The LNLS Experience with Libera Brilliance feedback, power-supply, controls, storage-ring 3456
 
  • L. Sanfelici, S.R. Marques, X.R. Resende
    LNLS, Campinas
  • K. Raizer
    UNICAMP, Campinas, São Paulo
 
 

This paper reports on the LNLS experience with the digital electron beam position monitor Libera Brilliance through the realization of several standard accelerator physics experiments, taking advantage mainly of the equipment’s turn-by-turn capabilities.

 
TH5RFP013 RHIC BPM System Average Orbit Calculations feedback, closed-orbit, collider, heavy-ion 3468
 
  • R.J. Michnoff, P. Cerniglia, C. Degen, R.L. Hulsart, M.G. Minty, R.H. Olsen, T. Roser, T. Satogata
    BNL, Upton, Long Island, New York
 
 

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.


RHIC BPM system average orbit was originally calculated by averaging positions of 10000 consecutive turns for a single selected bunch. Known perturbations in RHIC particle trajectories, with multiple frequencies around 10 Hz, contribute to observed average orbit fluctuations. In 2006, the number of turns for average orbit calculations was made programmable; this was used to explore averaging over single periods near 10 Hz. Although this has provided an average orbit signal quality improvement, an average over many periods would further improve the accuracy of the measured closed orbit. A new continuous average orbit calculation is currently under development and planned for use in the 2009 RHIC run. This paper will discuss the algorithm, performance with a simulated beam signal, and beam measurements.

 
TH5RFP015 Preliminary Design of Pinhole Camera for NSLS-II Project wiggler, photon, electron, vacuum 3473
 
  • I. Pinayev, B.N. Kosciuk, O. Singh
    BNL, Upton, Long Island, New York
 
 

Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-98CH10886.


The NSLS-II Light Source being built at Brookhaven National Laboratory is expected to provide very small emittances and electron beam sizes. High resolution imaging systems are required in order to provide robust measurements. The pinhole cameras will utilize 5-fold magnification with a pinhole placed inside a crotch absorber. The pinhole is protected from high power synchrotron radiation with a filter made of refractory metal. In this paper we provide resolution analyses, heat load calculations, and optimization of NSLS-II pinhole cameras including beamline design.

 
TH5RFP026 CESRTA X-Ray Beam Size Monitor Design vacuum, emittance, photon, controls 3503
 
  • J.P. Alexander, C.J. Conolly, E. Fontes, W.H. Hopkins, B. Kreis, H. Liu, A. Lyndaker, M.A. Palmer, D.P. Peterson, P. Revesz, J.J. Savino, R.D. Seeley
    CLASSE, Ithaca, New York
  • J.W. Flanagan
    KEK, Ibaraki
 
 

Funding: NSF


We report on the performance goals and design of the CESRTA x-ray beam size monitor (xBSM). The xBSM resolution must be sufficient to measure vertical beam sizes under 20um. The xBSM images 2–4keV synchrotron radiation photons onto one-dimensional photodiode array. Instrumentation in the dedicated x-ray beam line includes upstream interchangeable optics elements (slits, coded apertures, and Fresnel zone plates), a monochrometer and the InGaAs photodiode detector. To provide sufficient x-ray flux in 2 GeV operation, the beam line is evacuated, with only a thin diamond window isolating the detector vacuum from the damping ring. The readout is a beam-synchronized FADC that is sufficient to measure consecutive bunches independently in a 4ns bunch spacing configuration.

 
TH5RFP027 First Results from the CESRTA X-Ray Beam Size Monitor photon, emittance, optics, positron 3505
 
  • J.P. Alexander, W.H. Hopkins, B. Kreis, H. Liu, D.P. Peterson
    CLASSE, Ithaca, New York
  • J.W. Flanagan
    KEK, Ibaraki
 
 

Funding: NSF


Engineering data sets were collected with the CESRTA x-ray beam size monitor (xBSM) during November 2008 and January 2009 runs. We report on the performance of the InGaAs photodiode array detector, including time response and signal-to-noise. We report on the observed measurement resolution for changes in the damping ring vertical beam size using the interchangeable optics elements: slits, coded apertures, and a Fresnel zone plates. Observed resolutions are compared to predictions based on characteristics of the optics elements.

 
TH5RFP029 Design and Implementation of CESRTA Superconducting Wiggler Beampipes with Thin Retarding Field Analyzers wiggler, vacuum, electron, diagnostics 3507
 
  • Y. Li, M.G. Billing, S. Greenwald, T.I. O'Connell, M.A. Palmer, J.P. Sikora, E.N. Smith, K.W. Smolenski
    CLASSE, Ithaca, New York
  • J.N. Corlett, R. Kraft, D.V. Munson, D.W. Plate, A.W. Rawlins
    LBNL, Berkeley, California
  • K. Kanazawa, Y. Suetsugu
    KEK, Ibaraki
  • M.T.F. Pivi
    SLAC, Menlo Park, California
 
 

Funding: Work supported by the National Science Foundation, the US Department of Energy, and the Japan/US Cooperation Program


Wiggler magnets are one of the key components in the ILC Damping Ring. It is critical to the ILCDR GDE to understand electron cloud (EC) growth and patterns, and to develop EC suppression techniques in the wiggler beampipes. The CESR-c superconducting wigglers, closely matching the parameters of the ILCDR wigglers, serve as unique testing vehicles. As part of the CesrTA project, we replaced the copper beampipes of two SCWs with EC diagnostic beampipes, where one of the beampipes is uncoated and the second is coated with a thin TiN film. Each of the EC diagnostic beampipes is equipped with three retarding field analyzers (RFAs) at strategic longitudinal locations in the wiggler field. Each of the RFAs has 12-fold segmentation to measure the horizontal EC density distribution. To maintain sufficient vertical beam aperture and to fit within the SCW warm bore, a thin style of RFA (with a thickness of 2.5 mm) has been developed and deployed. These SCWs with RFA-equipped beampipe have been installed and successfully operated in the re-configured CesrTA vacuum system. This paper describes the design and the construction of the RFA-equipped SCW beampipes and operational experience.

 
TH5RFP071 The TE Wave Transmission Method for Electron Cloud Measurements at Cesr-TA electron, positron, vacuum, coupling 3606
 
  • S. De Santis, J.M. Byrd
    LBNL, Berkeley, California
  • M.G. Billing, J.P. Sikora
    CLASSE, Ithaca, New York
 
 

Funding: Supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.


We report on the optimization of TE Wave measurements at the Cesr-TA ring at Cornell University. The CESR storage ring is currently used as a testbed for technologies to be used in the damping rings of the International Linear Collider. The TE Wave measurement method utilizes capacitive buttons (BPMs) in the ring to excite and detect a propagating electromagnetic wave corresponding to the beampipe's fundamental TE mode. The presence of low-energy electrons along the wave path changes its propagation characteristics, which can be detected by analyzing the received signal. By choosing the machine fill pattern (gaps and bunch trains length) it is possible to modulate the density of the electron cloud and derive information on its rise and fall times by observing the detected signal spectrum. The possibility of circulating both electron and positron beams in the ring enabled us to separate the contribution of primary photoelectrons, which are independent on the circulating particle nature, from the transverse resonant mechanism, which can increase the primary electron density many times over and which only takes place with a circulating positron beam.

 
TH5RFP075 Tune Measurements in the Los Alamos Proton Storage Ring betatron, linac, storage-ring, proton 3618
 
  • R.C. McCrady
    LANL, Los Alamos, New Mexico
 
 

Funding: This work is supported by the United States Department of Energy under contract DE-AC52-06NA25396


Precise measurement of the tunes in the Los Alamos Proton Storage Ring (PSR) is difficult because the beam is normally extracted immediately after accumulation, preventing the use of continuous-wave radio frequency measurements. Presented here is a method that takes advantage of the phase information in the response of the beam to a transverse oscillatory driving voltage. This technique offers much greater precision than using the amplitude spectrum alone.

 
TH5RFP087 Linear Collider Final Doublet Considerations: ATF2 Vibration Measurements ground-motion, resonance, site, coupling 3654
 
  • B. Bolzon, N. Geffroy, A. Jeremie
    IN2P3-LAPP, Annecy-le-Vieux
  • Y. Kamiya
    ICEPP, Tokyo
  • T. Kume
    KEK, Ibaraki
  • M. Oroku, T. Yamanaka
    University of Tokyo, Tokyo
 
 

Funding: Work supported by the Agence Nationale de la Recherche of the French Ministry of Research (Programme Blanc, Project ATF2-IN2P3-KEK, contract ANR-06-BLAN-0027).


Future linear collider projects like ILC and CLIC will have beam sizes of a few nm. Vibration sources like ground motion can hamper the beam collisions. Relative jitter tolerance between the final focus magnets and the Interaction point (IP) is a fraction of the beam size. The ATF2 project proposes a test facility with a projected beam of 37nm. To measure the beam size with only 2% of error, vertical relative jitter tolerance (above 0.1Hz) between the final doublet magnets (FD) and the IP (with a Shintake beam Size Monitor: BSM) is of the order of 7nm while ground motion is of about 150nm. Thanks to determined adequate instrumentations, investigations were done to design supports for FD. Since ground motion measurements showed that this one is coherent up to 4m, more than the distance between FD and BSM, we chose a stiff support for FD fixed to the ground on its entire surface. Thus, FD and BSM should move in a coherent way. Vibration measurements show that relative motion between FD and BSM is only of 4.8nm and that flowing water in FD does not add any significant jitter. The FD support has been consequently validated on site at ATF2 to be within the vibration specifications.

 
TH6PFP020 ILC RTML Extraction Line for Single Stage Bunch Compressor extraction, sextupole, kicker, collimation 3738
 
  • S. Seletskiy
    BNL, Upton, Long Island, New York
  • N. Solyak
    Fermilab, Batavia
 
 

The use of single stage bunch compressor (BC) in the International Linear Collider (ILC)* Damping Ring to the Main Linac beamline (RTML) requires new design for the extraction line (EL). The EL located downstream of the BC will be used for both an emergency abort dumping of the beam and the tune-up continuous train-by-train extraction. It must accept both compressed and uncompressed beam with energy spread of 3.54% and 0.15% respectively. In this paper we report design that allowed minimizing the length of such extraction line while offsetting the beam dumps from the main line by 5m distance required for acceptable radiation level in the service tunnel. Proposed extraction line can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum ball dump window.


*N. Phinney et al., “International Linear Collider Reference Design Report: Accelerator”, SLAC-R-857C

 
TH6PFP064 Touschek Lifetime Calculations for NSLS-II lattice, scattering, multipole, closed-orbit 3853
 
  • B. Nash, S.L. Kramer
    BNL, Upton, Long Island, New York
 
 

The Touschek effect limits the lifetime for NSLS-II. The basic mechanism is Coulomb scattering resulting in a longitudinal momentum outside the momentum aperture. The momentum aperture results from a combination of the initial betatron oscillations after the scatter and the non-linear properties determining the resultant stability. We find that higher order multipole errors may reduce the momentum aperture, particularly for scattered particles with energy loss. The resultant drop in Touschek lifetime is minimized, however, due to less scattering in the dispersive regions. We describe these mechanisms, and present calculations for NSLS-II using a realistic lattice model including damping wigglers and engineering tolerances.

 
TH6PFP084 Experimental Frequency Map Analysis Using Multiple BPMs closed-orbit, lattice, storage-ring, simulation 3898
 
  • C. Steier, L. Yang
    LBNL, Berkeley, California
 
 

Funding: This work was supported by the Director, Office of Science, U. S. Department of Energy under Contract No. DE-AC02-05CH11231.


Frequency map analysis is being widely used, nowadays, both in simulations to design or improve accelerator lattices, as well as in experiments to study the transverse nonlinear dynamics in accelerators. A significant challenge to the use of frequency map analysis in experiments is the usually very fast decoherence of transverse oscillations, caused by the large nonlinearities of state-of-the-art lattices. Due to the decoherence, the center of mass oscillations of bunches often disappear in less than 100 turns. A potential way to get around this limitation is the use of multiple BPMs distributed (symetrically) around the storage ring. The presentation will describe the challenges multi-BPM frequency map analysis poses as well as initial results using the ALS.

 
TH6PFP088 Integrable Accelerator Lattices with Periodic and Exponential Invariants lattice, SRF, betatron, resonance 3910
 
  • V.V. Danilov
    ORNL, Oak Ridge, Tennessee
 
 

Funding: SNS is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.


The paper presents a new variety of one-dimensional nonlinear integrable accelerator lattices with periodic and exponential invariants in coordinates and momenta. Extension to two-dimensional transverse motion, based on a recently published approach*, is discussed.


*V. Danilov, “Practical Solutions for Nonlinear Accelerator Lattice with Stable Nearly Regular Motion”, Phys. Rev. ST AB 11, 114001 (2008)

 
TH6PFP093 Nonlinear Beam Dynamics with Strong Damping and Space Charge in the CLIC Damping Ring space-charge, resonance, simulation, emittance 3925
 
  • P.A. Piminov, E.B. Levichev, D.N. Shatilov
    BINP SB RAS, Novosibirsk
 
 

The beam is injected into the CLIC damping ring with the relatively large emittance and energy spread and then is damped to the extremely low phase volume. During the damping process the betatron frequency of each particle changes due to the space charge tune shift and nonlinear detuning produced by the chromatic sextupoles, wiggler nonlinear field components and by the space charge force. During the damping, the particle cross resonances, which can trap some fraction of the beam, cause the loss of intensity, the beam blow up and degrade the beam quality. In this paper we study the evolution of the beam distribution in time during the damping.

 
TH6PFP100 Computation of Transfer Maps from Surface Data with Applications to LHC Quadrupoles and ILC Damping Ring Wigglers quadrupole, wiggler, multipole 3946
 
  • C.E. Mitchell
    UMD, College Park, Maryland
 
 

Funding: DOE grant DEFG02-96ER40949


Transfer maps for magnetic elements in storage and damping rings can depend sensitively on nonlinear fringe-field and high-order-multipole effects. The inclusion of these effects requires a detailed and realistic model of the interior and fringe magnetic fields, including their high spatial derivatives. A collection of surface fitting methods has been developed for extracting this information accurately from 3-dimensional magnetic field data on a grid, as provided by various 3-dimensional finite element field codes. The virtue of surface methods is that they exactly satisfy the Maxwell equations and are relatively insensitive to numerical noise in the data. These techniques can be used to compute, in Lie-algebraic form, realistic transfer maps for LHC final-focus quadrupoles and for the proposed ILC Damping Ring wigglers. An exactly-soluble but numerically challenging model field is used to provide a rigorous collection of performance benchmarks.

 
TH6REP064 Measuring Betatron Tunes with Driven Oscillations betatron, radiation, pick-up, storage-ring 4099
 
  • R.A. Bosch
    UW-Madison/SRC, Madison, Wisconsin
 
 

The betatron tunes of an electron storage ring may be measured by driving transverse oscillations with an excitation electrode and measuring the resonant beam response with a pickup electrode. We model the damping of coherent betatron oscillations from the tune spread and radiation damping, finding that the tune signal is proportional to the square root of the product of the betatron functions at the excitation and pickup locations. The signal is independent of the betatron phase advance between the two locations. Our results are applied to the Aladdin 800-MeV electron storage ring.

 
TH6REP066 Growth/Damp Measurements and Bunch-by-Bunch Diagnostics on the Australian Synchrotron Storage Ring feedback, storage-ring, synchrotron, diagnostics 4105
 
  • D.J. Peake, R.P. Rassool
    Melbourne
  • M.J. Boland, G. LeBlanc
    ASCo, Clayton, Victoria
 
 

Recently a transverse bunch-by-bunch feedback system was commissioned to combat the resistive-wall instability in the storage ring. The system successfully controls the vertical beam motion so 200 mA can be stored with all in-vacuum undulators at minimum gap and a slightly positive chromaticity setting. The FPGA that comes with the feedback system also provides powerful possibilities for diagnostic measurements. Results will be presented for a) growth/damp measurements to quantitatively characterise the resistive-wall instability, b) bunch-by-bunch diagnostics such as tune chromaticity and c) initial bunch-cleaning attempts in conjunction with a APD bunch purity measurement system.

 
TH6REP069 Measurements of Coupled-Bunch Instabilities in BEPC-II feedback, kicker, positron, electron 4114
 
  • D. Teytelman
    Dimtel, San Jose
  • J.M. Byrd
    LBNL, Berkeley, California
  • J. Cao, J. Yue
    IHEP Beijing, Beijing
 
 

BEPC-II is a two ring electron-positron collider designed to operate at 1 A beam currents. Longitudinal and transverse coupled-bunch instabilities have been observed in both electron and positron rings. In this paper we present measurements of both transverse and longitudinal instabilities with the identification of active eigenmodes, measurements of growth and damping rates, as well as of the residual beam motion levels. The measurements will then be used to estimate the growth rates at the design beam currents (yet to be achieved). We will also demonstrate how such data is used for specifying power amplifier and kicker parameters.

 
TH6REP071 SuperB Fast Feedback Systems feedback, emittance, diagnostics, luminosity 4120
 
  • A. Drago
    INFN/LNF, Frascati (Roma)
 
 

The SuperB project consists of an asymmetric (4x7 GeV), very high luminosity, B-Factory to be built at Roma-II University campus in Italy, with the ambitious luminosity goal of 1036 cm-2 s-1. To achieve the very challenging performances, robust and powerful bunch-by-bunch feedback systems are necessary to cope with fast coupled bunch instabilities in rings with high beam currents and very low emittances. The SuperB bunch by bunch feedback should consider the rich legacy of previous systems, the longitudinal (DSP-based) feedback built in 1993-97 and the recent “iGp” feedback system designed in 2002-06. Both were designed by large collaborations between Research Institute (SLAC, DAΦNE@LNF/INFN, ALS@LBNL, KEK). The core of the new system will be the digital processing module, based on powerful FPGA components, to be used in longitudinal and transverse planes. Off-line analysis programs, as well real-time diagnostic tools, will be included. The feedback impact on very low emittance beams have to be carefully considered. A MATLAB simulator based on a beam/feedback model is also foreseen for performance checks and fast downloads of firmware/gateware code and parameters.

 
TH6REP072 DAΦNE Horizontal Feedback Upgrade feedback, kicker, injection, positron 4123
 
  • A. Drago
    INFN/LNF, Frascati (Roma)
 
 

In this paper the horizontal feedback upgrade for the positron DAΦNE ring is presented. After having completed the analysis of the e+ current limit behavior, a feedback upgrade has been turned out necessary. For the success of the crab waist experiment in the 2008 year, a fast solution to implement the upgrade has been necessary. It has been considered if a simple power increase would be the best solution. The lack of power combiners and of space for other two power amplifiers has brought to a different approach, doubling the entire feedback system. The advantages of this implementation respect to a more traditional power amplifier doubling are evident: two feedback kicks every revolution turns, better use of the power amplifiers, greater reliability, and less coherent noise in the system. Measurements of the two feedbacks have shown a perfect equivalence of the new and the old system: in fact the resulting damping rate is exactly the double of each system taken individually. A description of the implementation is presented together with the performance of the system.

 
TH6REP082 Experiment of Transverse Feedback System at HLS feedback, injection, octupole, controls 4147
 
  • J.H. Wang, Y.B. Chen, W. Li, L. Liu, M. Meng, B. Sun, L. Wang, Y.L. Yang, Z.R. Zhou
    USTC/NSRL, Hefei, Anhui
  • J. Cao, J. Yue
    IHEP Beiing, Beijing
  • D.K. Liu
    SINAP, Shanghai
  • L. Ma
    IHEP Beijing, Beijing
  • K.R. Ye
    SSRF, Shanghai
 
 

In this paper, we introduce the BxB transverse feedback systems at Hefei Light Source (HLS), which employ an analog system and a digital system. The construction and commissioning for two feedback systems, as well as the instability analysis of beam and the experiment result of the feedback system in HLS are also presented in this paper.

 
TH6REP083 Commissioning of the HLS Analog TFB System feedback, injection, status, controls 4150
 
  • Y.L. Yang, Y.B. Chen, W. Li, L. Liu, M. Meng, B. Sun, J.H. Wang, L. Wang, Z.R. Zhou
    USTC/NSRL, Hefei, Anhui
 
 

As low injection energy and multi-turn injection at HLS, the task of diagnosing and curing coupled-bunch instabilities becomes ever harder. The transverse analog feedback system has been redeveloped to improve effect, recently. In this paper, the new improved designs are described and new system's commissioning results are discussed. The transverse coupled bunch instability at 200MeV injection status is also experimentally studied.

 
TH6REP084 Commissioning of the Digital Transverse Bunch-by-Bunch Feedback System for the HLS feedback, injection, octupole, storage-ring 4153
 
  • Z.R. Zhou, Y.B. Chen, M. Meng, B. Sun, J.H. Wang, L. Wang, Y.L. Yang
    USTC/NSRL, Hefei, Anhui
  • K. Kobayashi, T. Nakamura
    JASRI/SPring-8, Hyogo-ken
 
 

Hefei Light Source (HLS) is an 800MeV storage ring with bunch rate of 204 MHz, the harmonics of 45, and circumference of 66 meters. HLS injection works at 200MeV, where the multi-bunch instabilities limit the maximum stored current. A digital transverse bunch-by-bunch feedback system has recently been commissioned at HLS to suppress the multi-bunch instabilities during injection. We employ the SPring-8 FPGA based feedback processor and modified it at NSRL to process horizontal and vertical oscillation signals, independently and simultaneously by one single processor. The design of the digital transverse feedback system and the experiment results are presented in this paper.

 
TH6REP085 Design and Analysis of a Mixed-Signal Feedback Damper System for Controlling Electron-Proton Instabilities feedback, pick-up, kicker, proton 4156
 
  • Z.P. Xie, M.J. Schulte
    UW-Madison, Madison, Wisconsin
  • C. Deibele
    ORNL, Oak Ridge, Tennessee
 
 

Funding: *Work performed under the auspices of ORNL/SNS, ORNL/SNS is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725


An electron-proton (e-p) instability is observed with increased beam intensity at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory (ORNL). This paper presents a wide-band, mixed-signal system for active damping of the e-p instability. It describes techniques used for feedback damping, data acquisition, and analysis. The paper also describes analysis strategies to monitor system performance. The mixed-signal feedback damper system includes anti-aliasing low-pass filters, power amplifiers (PAs), analog-to-digital converters (ADCs), reconfigurable field programmable gate array (FPGA) hardware and digital-to-analog converters (DACs). The system will provide feedback damping, system monitoring, and offline analysis capabilities. The digital portion of the system features programmable gains and delays, and equalizers that are implemented using parallel comb filters and finite impulse response (FIR) filters. These components perform timing adjustments, compensate for gain mismatches, correct for ring harmonics, and equalize magnitude and phase dispersions from cables and amplifiers.

 
FR1RAI01 CLIC Overview linac, emittance, collider, linear-collider 4195
 
  • R. Tomás
    CERN, Geneva
 
 

The CLIC study is exploring the scheme for an electron-positron collider with a centre-of-mass energy of 3 TeV in order to make the multi-TeV range accessible for physics. The current goal of the project is to demonstrate the feasibility of the technology by the year 2010. Recently, important progress has has been made concerning the high-gradient accelerating structure tests and the experiments with beam in the CLIC test facility, CTF3. On the organizational side, the CLIC international collaborations have significantly gained momentum considerably boosting the CLIC study.

 

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Slides

 
FR2PBI02 Gravitational Instability of a Nonrotating Galaxy impedance, simulation, collective-effects, wakefield 4275
 
  • A. Chao
    SLAC, Menlo Park, California
 
 

Funding: This work was supported by Department of Energy contract DE-AC02-76SF00515.


Gravitational instability of a star distribution in a galaxy is a well-known phenomenon in astrophysics. This problem can be analyzed using the standard tools developed in accelerator physics for analyzing the onset of beam instability and loss of Landau damping. An attempt is made here for a nonrotating galaxy. Predictions for the maximum stable galaxy size are in remarkable agreement with observations.

 

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Slides

 
FR3RBI05 Progress Towards the International Linear Collider cavity, cryomodule, linac, klystron 4297
 
  • N.J. Walker
    DESY, Hamburg
  • M.C. Ross
    Fermilab, Batavia
  • A. Yamamoto
    KEK, Ibaraki
 
 

With a now extended plan to 2012, the ILC Global Design Effort Technical Design Phase focuses on key R&D to verify performance goals and to reduce both technical risk and cost. This talk will review the progress during the last two years, and plans for the future.

 

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Slides

 
FR5PFP068 Wakefield Simulation of CLIC PETS Structure Using Parallel 3D Finite Element Time-Domain Solver T3P wakefield, simulation, impedance, radio-frequency 4467
 
  • A.E. Candel, A.C. Kabel, K. Ko, L. Lee, Z. Li, C.-K. Ng, G.L. Schussman
    SLAC, Menlo Park, California
  • I. Syratchev
    CERN, Geneva
 
 

Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.


In recent years, SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic time-domain code T3P. Higher-order Finite Element methods on conformal unstructured meshes and massively parallel processing allow unprecedented simulation accuracy for wakefield computations and simulations of transient effects in realistic accelerator structures. Applications include simulation of wakefield damping in the Compact Linear Collider (CLIC) Power Extraction and Transfer Structure (PETS).

 
FR5RFP023 Design of Photonic Bandgap Fiber Accelerating Structure lattice, accelerating-gradient, wakefield, background 4582
 
  • H.Z. Zhang, S. Dong, C.-F. Wu
    USTC/NSRL, Hefei, Anhui
  • Z.P. Li
    USTC, Hefei, Anhui
 
 

Photonic crystals have been suggested for use as laser driven particle accelerator structures with higher accelerating gradients and effective damping of unwanted higher order modes. Here we selected Photonic band gap (PBG) fibers with hollow core defects to design such an accelerating structure. To achieve this design, Out-plane-wave mode in photonic crystal fiber was selected for longitudinal electric field. The out-plane-wave plane wave expansion method was deduced for confinement and the dispersive curve versus variation of kz and speed of line for synchronization. Then super cell approximation was also introduced for calculating the defected photonic crystal structure. After the design of appropriate geometry and the dimensions of photonic crystal fiber accelerating structure, the field distribution was simulated with RSOFT Bandsolve software for this structure.

 
FR5RFP030 Landau Damping with High Frequency Impedance impedance, simulation, synchrotron, cavity 4592
 
  • M. Blaskiewicz
    BNL, Upton, Long Island, New York
 
 

Funding: Work supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the U.S. Department of Energy


Couples bunch longitudinal instability in the presence of high frequency impedance is considered. A frequency domain technique is developed and compared with simulations. The frequency domain technique allows for absolute stability tests and is applied to the problem of longitudinal stability in RHIC with the proposed 56 MHz rf system.

 
FR5RFP033 Microwave Instability Simulations for NSLS-II vacuum, simulation, cavity, undulator 4601
 
  • A. Blednykh, S. Krinsky, B. Nash, L.-H. Yu
    BNL, Upton, Long Island, New York
 
 

For the NSLS-II storage ring with damping wigglers but without a Landau cavity, the low-current bunch length is 4.5mm. We have studied bunch lengthening and estimated the microwave instability threshold using the multi-particle tracking code TRANFT. An estimate of the pseudo-Green’s function for a 0.5mm driving bunch was obtained for most components of the vacuum system by using the 3D code GdfidL. With our present computer resources, certain components were too large and had too complex geometry to allow the wake for such a short bunch to be computed using GdFidL. In these cases, the actual 3D geometry was approximated by a structure having circular cross-section, and the pseudo-Green’s function was computed using the 2D code ABCI. It was found that the dominant geometric wake is due to the tapers for the in-vacuum undulators. The resistive wall wake is also important. The effect of pseudo-Green’s functions corresponding to an even shorter driving bunch (0.05mm) was investigated using the program ECHO to compute the wake of tapers with circular cross-section. Our results suggest that the microwave threshold will occur at an average single-bunch current greater than 5mA.

 
FR5RFP035 Equilibrium Tail Distribution due to Touschek Scattering scattering, radiation, electron, synchrotron 4607
 
  • B. Nash, S. Krinsky
    BNL, Upton, Long Island, New York
 
 

Single large angle Coulomb scattering is referred to as Touschek scattering. In addition to causing particle loss when the scattered particles are outside the momentum aperture, the process also results in a non-Gaussian tail, which is an equilibrium between the Touschek scattering and radiation damping. Here we present an analytical calculation for this equilibrium distribution.

 
FR5RFP040 Wake Field Simulations for the Vacuum Chamber Transitions of the ILC Damping Ring wakefield, impedance, vacuum, simulation 4619
 
  • M. Korostelev, A. Wolski
    Cockcroft Institute, Warrington, Cheshire
  • N.A. Collomb, J.M. Lucas
    STFC/DL, Daresbury, Warrington, Cheshire
  • O.B. Malyshev
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
 

Vacuum chamber transitions of the ILC damping rings associated with BPM insertions, vacuum ports, antechamber tapers etc, may make a significant contribution to the overall machine impedance. Since most transitions are not azimuthally symmetric, commercial 3D codes based on the finite element method have been used to compute their wake fields. The results for selected vacuum chamber components are presented in this paper, together with some estimates of the impact of the wake fields on the beam dynamics in the damping rings.

 
FR5RFP052 Impedance Studies for the Phase 2 LHC Collimators impedance, feedback, vacuum, octupole 4655
 
  • E. Métral, F. Caspers, A. Grudiev, T. Kroyer
    CERN, Geneva
  • F. Roncarolo
    UMAN, Manchester
  • B. Salvant
    EPFL, Lausanne
  • B. Zotter
    Honorary CERN Staff Member, Grand-Saconnex
 
 

The LHC phase 2 collimation project aims at gaining a factor ten in cleaning efficiency, robustness and impedance reduction. From the impedance point of view, several ideas emerged during the last year, such as using dielectric collimators, slots or rods in copper plates, or Litz wires. The purpose of this paper is to discuss the possible choices, showing analytical estimates, electro-magnetic simulations performed using Maxwell, HFSS and GdFidL, and preliminary bench measurements. The corresponding complex tune shifts are computed for the different cases and compared on the stability diagram defined by the settings of the Landau octupoles available in the LHC at 7 TeV.

 
FR5RFP061 Stability of Flat Bunches in the Recycler Barrier Bucket proton, space-charge, dipole, electron 4679
 
  • T. Sen, C.M. Bhat, J.-F. Ostiguy
    Fermilab, Batavia
 
 

We examine the stability of intense flat bunches in barrier buckets. We consider a class of stationary distributions and derive analytical expressions for the threshold intensity at which Landau damping is lost against rigid dipole oscillations in the presence of impedances and space charge forces. Particle simulations are used to follow the dynamics in a barrier bucket and compare with the analytic expressions. These studies are related to experimental observations in the Recycler ring at Fermilab.

 
FR5RFP066 Higher Order Modes in a String of Multi-Cell Accelerating Structures higher-order-mode, linac, linear-collider, simulation 4685
 
  • Y. Morozumi
    KEK, Ibaraki
 
 

The International Linear Collider will employ tens of thousands of superconducting 9-cell accelerating structures for its main linacs. Damping of higher order modes is crucial to beam stability. Study of higher order modes, however, tends to focus on trapped modes in a single 9-cell structure model alone both in simulation and measurement. Propagating modes above cut-off frequencies are left untouched because of difficulty of a realistic model of multiple 9-cell structures. We have simulated a full spectrum of higher order modes in a long string of 9-cell structures.

 
FR5RFP067 Fast Head Tail Instability due to Electron Cloud under the Presence of the Dispersion electron, wakefield, simulation, synchrotron 4686
 
  • K. Ohmi
    KEK, Ibaraki
  • J. Hyunchang
    POSTECH, Pohang, Kyungbuk
 
 

Electron cloud causes a transverse single bunch instability above a threshold of the cloud density. The threshold is determeined by the strength of the beam-electron cloud interaction and Landau damping due to the synchrotron oscillation and/or momentum compaction. We discuss that the threshold is remarkably degraded due to the dispersion, one of the parameter of the circular accelerator optics. The single bunch instability is more serious than previous predictions without considering the dispersion, especially in the case that the horizontal beam size due to the dispersion dominates compare than that due to the emittance.

 
FR5RFP087 The Effect of an Oxide Layer on Resistive-Wall Wake Fields wakefield, dipole, FEL, electron 4743
 
  • A. Novokhatski
    SLAC, Menlo Park, California
 
 

Funding: work supported by the Department of Energy under contract number DE-AC03-76SF00515


Shorter and shorter electron bunches are now used in the FEL designs. The fine structure of the wall of a beam vacuum pipe plays more noticeable role in the wake field generation. Additionally to the resistance and roughness, the wall may have an oxide layer, which is usually a dielectric. It is important for aluminum pipe, which have Al2O3 layer. The thickness of this layer may vary in a large range: 1-100 nm. We study this effect for the very short (20-1000 nm) ultra relativistic bunches in an infinite round pipe. We solved numerically the Maxwell equations for the fields in the metal and ceramics. Results showed that the oxide layer may considerably increase the wavelength and the decay time of the resistive-wall wake fields, however the loss factor of the very short bunches does not change much.

 
FR5RFP097 Four Regimes of the IFR Ion Hose Instability ion, electron, betatron, synchrotron 4767
 
  • R.A. Bosch
    UW-Madison/SRC, Madison, Wisconsin
 
 

An electron beam focused by an ion channel without a magnetic field, in the so-called ion focus regime (IFR), may be disrupted by the transverse ion hose instability. We describe the growth in four regimes.