2011 Particle Accelerator Conference - List of Keywords (impedance)

Paper	Title	Other Keywords	Page
MOODS4	Dancing Bunches as van Kampen Modes	synchrotron, damping, injection, proton	94
	A.V. Burov Fermilab, Batavia, USA
	Theory of van Kampen modes is applied to bunch longitudinal motion. Case of inductive impedance domination is studied in more details. Threshold for loss of Landau damping is found to be very sensitive to fine structure of the distribution function. Good agreement with the Tevatron's "dancing bunches" is obtained.
	Slides MOODS4 [0.408 MB]

MOP115	Progress on Multipactor Studies in Dielectric-Loaded Accelerating Structures	multipactoring, electron, simulation, vacuum	310
	S.P. Antipov, C.-J. Jing, A. Kanareykin, P. Schoessow Euclid TechLabs, LLC, Solon, Ohio, USA D.S. Doran, W. Gai, J.G. Power ANL, Argonne, USA B. Feng IIT, Chicago, Illinois, USA
	Funding: DOE SBIR Significant progress has been made in the development of high gradient rf driven dielectric accelerating structures (DLA). One principal effect limiting further advances in this technology is the problem of multipactor. The fraction of the power absorbed at saturation in DLA experiments was found to increase with the incident power, with more than 30% of the incident power per unit length being absorbed. We studied a possibility of multipactor mitigation by introduction of surface grooves (transverse and longitudinal) to interrupt the resonant trajectories of electrons in the multipactor discharge. Four DLA structures based on quartz tubes with transverse and longitudinal grooves of various dimensions were designed. In this paper we report simulation results and plans for high-power tests of these structures.

MOP116	Development of an X-Band Dielectric-Based Wakefield Power Extractor for Potential CLIC Applications	wakefield, simulation, insertion, electron	313
	C.-J. Jing, S.P. Antipov, A. Kanareykin, P. Schoessow Euclid TechLabs, LLC, Solon, Ohio, USA M.E. Conde, W. Gai, J.G. Power ANL, Argonne, USA I. Syratchev CERN, Geneva, Switzerland
	Funding: Work is funded by DoE SBIR PhaseI. In the past decade, tremendous efforts have been put into the development of the CLIC Power Extraction and Transfer Structure (PETS), and significant progress has been made. However, one concern remains the manufacturing cost of the PETS, particularly considering the quantities needed for a TeV machine. A dielectric-based wakefield power extractor in principle is much cheaper to build. A low surface electric field to gradient ratio is another big advantage of the dielectric-loaded accelerating/decelerating structure. We are currently investigating the possibility of using a cost-effective dielectric-based wakefield power extractor as an alternative to the CLIC PETS. We designed a 12 GHz dielectric-based power extractor which has a similar performance to CLIC PETS with parameters 23 mm beam channel, 240 ns pulse duration, 135 MW output per structure using the CLIC drive beam. In order to study potential rf breakdown issues, as a first step we are building a 11.424 GHz dielectric-based power extractor scaled from the 12 GHz version, and plan to perform a high power rf test using the SLAC 11.424 GHz high power rf source.

MOP133	Fabrication and Measurements of a Silicon Woodpile Accelerator Structure	simulation, laser, lattice, electron	343
	C. McGuinness, E.R. Colby, R.J. England, R. Laouar, R.J. Noble, K. Soong, J.E. Spencer, Z. Wu, D. Xu SLAC, Menlo Park, California, USA R.L. Byer, E.A. Peralta Stanford University, Stanford, California, USA
	Funding: DOE grants: DE-AC02-76SF00515 and DE-FG03-97ER41043-II We present results for the fabrication of a silicon woodpile accelerator structure. The structure was designed to have an accelerating mode at 3.95 μm, with a high characteristic impedance and an accelerating gradient of 530 MeV/m. The fabrication process uses standard nanofabrication techniques in a layer-by-layer process to produce a three-dimensional photonic crystal with 400 nm features. Reflection spectroscopy measurements reveal a peak spanning from three to five microns, and are show good agreement with simulations. * Sears, PRST-AB, 11, 101301, (2008). Cowan, PRST-AB, 11, 011301, (2008). * McGuinness, J. Mod. Opt., vol. 56, is. 18, pp. 2142, (2009). **** Lin, Nature, 394, pp. 251 (1998).

MOP239	Commercially Available Transverse Profile Monitors, the IBIS	target, vacuum, optics, diagnostics	562
	M. Ruelas, R.B. Agustsson, I. Bacchus, A.Y. Murokh, R. Tikhoplav RadiaBeam, Santa Monica, USA
	With ever decreasing budgets, shorter delivery schedules and increased performance requirements for pending and future facilities, the need for cost effective yet high quality profile monitors is paramount to future advancement in the accelerator field. While individual facilities are capable of designing and fabricating these often custom devices, this is not always the most efficient or economical route. In response to the lack of commercially available profile monitors, RadiaBeam Technologies has been developing its line of Integrated Beam Imaging System (IBIS) over the past several years. Here, we report on these commercially available profile monitors.

MOP266	Stripline Kicker Design for NSLS2 Storage Ring	kicker, pick-up, damping, feedback	603
	W.X. Cheng, A. Blednykh, S. Krinsky, O. Singh BNL, Upton, Long Island, New York, USA
	In the NSLS2 storage ring, there are four stripline kickers/pickups. Two long striplines with electrode length of 30cm will be used as bunch-by-bunch transverse feedback actuators. Two short stripline kickers/pickups with 15cm length will mainly used for tune measurement excitation or signal pickup for the beam stability monitor. High shunt impedance of the long stripline kickers is demanded to produce 200μs damping time. Meanwhile the beam impedance should be minimized. The design work for these two types of stripline is discussed in this paper.

MOP269	Design of Longitudinal Feedback Kicker for HLS Storage Ring	kicker, cavity, storage-ring, vacuum	612
	W. Xu, D.H. He USTC/NSRL, Hefei, Anhui, People's Republic of China W. Wu, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA
	Hefei Light Source (HLS) is a dedicated synchrotron radiation research facility. It is now undergoing a major upgrade. To obtain a better performance of the light source, a longitudinal feedback system will be developed as part of the upgrade project to cure the coupled bunch mode instabilities. In this work, we present a design of the LFB kicker, a waveguide overloaded cavity with two input and two output ports. The cavity design specifications include a central frequency of 969 MHz (4.75 RF frequency), a bandwidth of more than 100 MHz, and a high shunt impedance of 1200 Ω. A study is carried out to find the dependence of the cavity performance on a few critical geometric parameters of the cavity. Since the shape of the vacuum chamber of the HLS storage ring is octagon, a transition from a circular vacuum chamber to an octagon one is built into the end pieces of the cavity to minimize the total cavity length. To lower the required amplifier power, the structure is optimized to obtain a high shunt impedance. The higher order modes of the kicker cavity are also considered during the design.

MOP281	ADC Clocking Formats and Matching Networks	coupling, HOM, power-supply	639
	A.J. Della Penna BNL, Upton, Long Island, New York, USA
	Clocking an ADC is the most critical point when resolution is a major concern. Any fluctuations on the input clock performance correlates to jitter. The many different formats used to clock ADCs on the market makes choosing the appropriate one no easy task. LVDS, PECL, LVPECL, CMOS and CML are just some of the different types. With each type a certain matching network will be required. This paper will discuss the advantages of each format as well as its associated matching network.

MOP292	Universal FMC-Compliant Module for xTCA Systems	controls, power-supply, monitoring, target	663
	D.R. Makowski, G.W. Jabłoński, T. Kozak, A. Mielczarek, A. Napieralski TUL-DMCS, Łódź, Poland
	Funding: The research leading to these results has received funding from Polish National Science Council Grant 642/N-TESLAXFEL/09/2010/0. The Advanced Telecommunications Computing Architecture (ATCA), MicroTCA (uTCA) and Advanced Mezzanine Card (AMC) standards, known as xTCA, provide unique features desired by various control systems of particle accelerators. The standards provide availability and operability as high as 99.999 %. A significant number of additional features must be implemented to take a full advantage of xTCA standards and gain the required availability. On the other hand, many control systems require various data acquisition and control modules with different number of input analogue and digital inputs or outputs as defined by their respective system specifications. The paper presents an universal base module, designed according to the AMC standard with an FPGA Mezzanine Card connector, that can be used for fast development of input-output subsystems. The module consists of two submodules. The digital part is designed according to the AMC standard while the main input-output functionality is realized by the FPGA Mezzanine Card part. The FMC submodule provides the functionality required by the specification of the LLRF system.

TUP097	Fundamental and HOM Coupler Design for the Superconducting Parallel-Bar Cavity	cavity, HOM, damping, coupling	1015
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA S.U. De Silva JLAB, Newport News, Virginia, USA
	The superconducting parallel-bar cavity is currently being considered as a deflecting system for the Jefferson Lab 12 GeV upgrade and as a crabbing cavity for a possible LHC luminosity upgrade. Currently the designs are optimized to achieve lower surface fields within the dimensional constraints for the above applications. A detailed analysis of the fundamental input power coupler design for the parallel-bar cavity is performed considering beam loading and the effects of microphonics. For higher beam loading the damping of the HOMs is vital to reduce beam instabilities generated due to the wake fields. An analysis of threshold impedances for each application and impedances of the modes that requires damping are presented in this paper with the design of HOM couplers.

TUP117	Solid State Direct Drive RF LINAC: High Power Experimental Program	cavity, controls, linac, high-voltage	1056
	T.J.S. Hughes, M. Back, R. Fleck, M. Hergt, R. Irsigler, T. Kluge, J. Sirtl Siemens AG, Erlangen, Germany O. Heid Siemens AG, Healthcare Technology and Concepts, Erlangen, Germany
	We report on a 150MHz λ/4 coaxial resonator driven by 32 integrated class F RF power modules according to our direct drive concept [1,2]. Electric fields of 60MV/m at the resonator gap have been reached, which correspond to 80kW RF power. This power level has been achieved at 160V DC supply voltage, significantly less than the component limits. The observed power and Q values can be explained by a simple equivalent circuit. The model predicts that 64 modules at 160V DC supply voltage may provide 170kW RF power, and that 250V DC supply voltage should yield 400kW. The corresponding 134MV/m gap E field may not be reachable due to vacuum flashover. * Heid O., Hughes T. THPD002, IPAC10, Kyoto, Japan Hergt M et al, 2010 IEEE International Power Modulator and High Voltage Conf., Atlanta GA, USA * Heid O., Hughes T. THP068, LINAC10, Tsukuba, Japan

TUP129	Simulation Results of RF Coupler Controllable by Dielectric Fluid	coupling, simulation, cavity, vacuum	1073
	P. Chen, D. Yu DULY Research Inc., Rancho Palos Verdes, California, USA
	Funding: Work supported by DOE SBIR Phase I grant No. DE-FG02-09ER85334. Tunable couplers for adjusting radiofrequency (RF) power coupling into accelerator cavities are useful devices for achieving optimal operation efficiency. Standard mechanical tuners currently used in large accelerator facilities are bulky and complicated. A novel tuner, based on the introduction of dielectric tubes or fluid-filled volumes adjacent to, but separated by window(s) from the coupler, is described. Simulations have shown that the tuner has a fairly large adjustment range and also demonstrated the viability of the tuning concept using fluid circuit.

TUP131	A New Main Injector Radio Frequency System For 2.3 MW Project X Operations	cavity, radio-frequency, cathode, feedback	1079
	J.E. Dey, I. Kourbanis Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. For Project X Fermilab Main Injector will be required to provide up to 2.3 MW to a neutrino production target at energies between 60 and 120 GeV. To accomplish the above power levels 3 times the current beam intensity will need to be accelerated. In addition the injection energy of Main Injector will need to be as low as 6 GeV. The current 30 year old Main Injector radio frequency system will not be able to provide the required power and a new system will be required. The specifications of the new system will be described.

TUP213	Research and Development toward the RHIC Injection Kicker Upgrade	kicker, injection, high-voltage, factory	1211
	W. Zhang, W. Fischer, H. Hahn, C. Pai, J. Sandberg, J.E. Tuozzolo BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A research and development work is on going toward the upgrade of the RHIC Injection Fast Kicker System. We report here the proposed nano-second pulse generator, the initial test result, the options of the deflector design, injection pattern, and the benefit to the future RHIC programs.

TUP259	A Solid-State Nanosecond Beam Kicker Modulator Based on the DSRD Switch	kicker, high-voltage, extraction, status	1310
	A.L. Benwell, R. Akre, C. Burkhart, A. Krasnykh, T. Tang SLAC, Menlo Park, California, USA A. Kardo-Sysoev IOFFE, St. Petersburg, Russia
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 A fast solid-state beam kicker modulator is under development at the SLAC National Accelerator Laboratory. The program goal is to develop a modulator that will deliver 4 ns, ±5 kV pulses to the ATF2 damping ring beam extraction kicker. The kicker is a 50 Ω, bipolar strip line, 60 cm long, fed at the downstream end and terminated at the upstream end. The bunch spacing in the ring is 5.6 ns, bunches are removed from the back end of the train, and there is a gap of 10³.6 ns before the next train. The modulator design is based on an opening switch topology that uses Drift Step Recovery Diodes as the opening switches. The design and results of the modulator development are discussed.

TUP277	RF Design of the Power Coupler for the Spiral2 Single Bunch Selector	vacuum, ion, simulation, kicker	1346
	F. Consoli, A.C. Caruso, G. Gallo, D. Rifuggiato, E. Zappalà INFN/LNS, Catania, Italy M. Di Giacomo GANIL, Caen, France
	Funding: Work supported by the European Community FP7 – Capacities – SPIRAL2 Preparatory Phase n° 212692. The single bunch selector of the Spiral2 driver uses high impedance travelling wave electrodes driven by fast pulse generators. The characteristic impedance of 100 Ω has been chosen to reduce the total power, but this non standard value requires the development of custom feed-through and transitions to connect the pulse generators and the matching load to the electrodes. The paper reviews the design of these devices.

TUP278	Tuning Method for the 2π/3 Traveling Wave Structures	coupling, controls, beam-loading, linac	1349
	A.S. Setty THALES, Colombes, France
	To build a constant gradient traveling wave structure, one must perform cold tests under a press in order to tune the different cells individually. For the tests to be valid, the test cells must be terminated by shorting planes located in planes of symmetry in which the electric field vector is normal in such a way that the standing wave "trapped" between them is an exact representation of the instantaneous traveling wave one wishes to study. For the TW structure, the cavities are put three by three under the press. We then try to reduce the contribution of "mixed cells" by adding to one wavelength at 2π/3 mode two-quarter wavelengths. This is possible when the end-cells mode at the same frequency is π/2 instead of 2π/3. These end cells are not included in the final assembly. The setting process will be analysed.

TUP283	Inductively Coupled, Compact HOM Damper for the Advanced Photon Source	HOM, coupling, diagnostics, damping	1358
	G.J. Waldschmidt, D. Horan, L.H. Morrison ANL, Argonne, USA
	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 requires damping of higher-order modes in the storage ring rf cavities in order to prevent beam instability at beam currents in excess of 100 mA proposed for the APS Upgrade. Due to constraints imposed by available space and by existing 35-mm pick-up ports on the cavity, a compact design has been analyzed with a quarter-wave rejection filter of the fundamental mode. Separate broadband, low-frequency and high-frequency dampers are utilized to span the frequency range from 500 MHz to 1500 MHz. The dampers have been designed to reject the fundamental cavity mode, couple strongly to HOM’s, utilize an external rf load, minimize the overall size, and incorporate rf diagnostics. In addition, the mechanical design has been optimized to simplify construction, improve mechanical stability, and reduce thermally induced stresses.

WEOBS5	Status of the Short-Pulse X-ray Project (SPX) at the Advanced Photon Source (APS)	cavity, feedback, cryomodule, emittance	1427
	R. Nassiri, N.D. Arnold, G. Berenc, M. Borland, D.J. Bromberek, Y.-C. Chae, G. Decker, L. Emery, J.D. Fuerst, A.E. Grelick, D. Horan, F. Lenkszus, R.M. Lill, V. Sajaev, T.L. Smith, G.J. Waldschmidt, G. Wu, B.X. Yang, A. Zholents ANL, Argonne, USA J.M. Byrd, L.R. Doolittle, G. Huang LBNL, Berkeley, California, USA G. Cheng, G. Ciovati, J. Henry, P. Kneisel, J.D. Mammosser, R.A. Rimmer, L. Turlington, H. Wang JLAB, Newport News, Virginia, USA
	Funding: Work at Argonne is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11354. The Advanced Photon Source Upgrade project (APS-U) at Argonne includes implementation of Zholents’* deflecting cavity scheme for production of short x-ray pulses. This is a joint project between Argonne National Laboratory, Thomas Jefferson National Laboratory, and Lawrence Berkeley National Laboratory. This paper describes performance characteristics of the proposed source and technical issues related to its realization. Ensuring stable APS storage ring operation requires reducing quality factors of these modes by many orders of magnitude. These challenges reduce to those of the design of a single-cell SC cavity that can achieve the desired operating deflecting fields while providing needed damping of all these modes. The project team is currently prototyping and testing several promising designs for single-cell cavities with the goal of deciding on a winning design in the near future. *A. Zholents et al., NIM A 425, 385 (1999).
	Slides WEOBS5 [1.730 MB]

WEODS1	Design and Optimization of Future X-ray FELs based on Advanced High Frequency Linacs	linac, klystron, FEL, acceleration	1491
	F. Wang SLAC, Menlo Park, California, USA
	To drive future XFELs, normal-conducting linacs at various rf freqencies are being considered. With optimized accelerator structures and rf systems, a higher rf frequency linac has several advantages, such as high acceleration gradient and high rf-to-beam efficiency. This paper presents a comparison of possible S-band, C-band and X-band linac designs for two cases, single bunch operation and multibunch operation, where the bunch train length is longer than the structure fill time and the beam loading is small. General scaling laws for the main linac parameters, which can be useful in the design such linacs, are derived.
	Slides WEODS1 [5.795 MB]

WEP084	Beam Dynamics and Instabilities in MEIC Design	ion, electron, feedback, positron	1630
	S. Ahmed, G.A. Krafft, B.C. Yunn JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In this paper, we report the first study of beam related instabilities in lepton ring of the proposed electron-ion collider beyond the 12 GeV upgrade of CEBAF at Jefferson lab. The design parameters are consistent with PEP-II. Present studies reveal that coupled bunch and two stream instabilities are important issues and we need feedback system.

WEP116	Bucket Shaking Stops Bunch Dancing in Tevatron	synchrotron, simulation, dipole, damping	1704
	A.V. Burov, C.-Y. Tan Fermilab, Batavia, USA
	Bunches in Tevatron are known to be longitudinally unstable: their collective oscillations stay without any sign of decay. Typically, a feedback damper is used to stop these oscillations. Recently, it was theoretically predicted that the oscillations can be stabilized by means of small bucket shaking. Detailed measurements in Tevatron have shown that this method does work. In this paper, an essential theory and specific observations of the related process are presented. A. Burov, “Dancing Bunches as van Kampen Modes”, this conference.

WEP119	Coherent Radiation in Whispering Gallery Modes	vacuum, resonance, radiation, synchrotron	1710
	R.L. Warnock SLAC, Menlo Park, California, USA J.C. Bergstrom CLS, Saskatoon, Saskatchewan, Canada
	Funding: Work at SLAC: U.S. Department of Energy Contract No. DE-AC03-76SF00515 Work at CLS: NSERC, NRC, Province of Saskatchewan, U. of Saskatchewan. Theory predicts that CSR in storage rings should appear in whispering gallery modes , which are resonances of the entire vacuum chamber and are characterized by their high frequencies and concentration of the field near the outer wall of the chamber. The theory assumes that the chamber is a smooth circular torus. We observe that a power spectrum from the NSLS-VUV ring , which has a vacuum chamber in bends like that of the model, shows a series of sharp peaks with frequencies close to those of the theory. Sharp peaks are also seen in highly resolved spectra at the Canadian Light Source*, and those are invariant in position under large changes in the machine setup (energy, fill pattern, bunch length, CSR bursting or steady, optical beam line, etc.). Invariance of the spectrum suggests that it is due to resonances like whispering gallery modes, but they must be strongly perturbed from the circular case because of large outer wall excursions at the two IR ports. R. L. Warnock and P. Morton, Part. Accel. 25, 113 (1990). G. L. Carr et al., Proc. PAC 2001, Chicago. * T. May et al., IEEE 33rd Intl. Conf. IR Millimeter and THz Waves, 2008.

WEP147	The Effect of Space-charge and Wake Fields in the Fermilab Booster	booster, wakefield, coupling, simulation	1758
	A. Macridin, J.F. Amundson, P. Spentzouris Fermilab, Batavia, USA D.O. McCarron IIT, Chicago, Illinois, USA L.K. Spentzouris Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: This work was supported by the DOE contracts DE-AC02-07CH11359, DE-AC02-05CH11231 and DE-AC02-06CH11357 and the ComPASS project funded through the SciDAC. We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements.

WEP176	Loss Factor of Tapered Structures for Short Bunches	vacuum, factory, simulation, electromagnetic-fields	1816
	A. Blednykh, S. Krinsky BNL, Upton, Long Island, New York, USA
	Funding: Work supported by DOE contract DE-AC02-98CH10886 Using the electromagnetic simulation code ECHO, we have found* a simple phenomenological formula that accurately describes the loss factor for short bunches traversing an axisymmetric tapered collimator. In this paper, we consider tapered collimators with elliptical cross-section and use the GdfidL code to calculate the loss factor dependence on the geometric parameters for short bunches. The results for both axisymmetric and elliptical collimators are discussed. * A. Blednykh and S. Krinsky, Phys. Rev. ST-AB 13, 064401 (2010).

WEP177	Radial Transmission Line Analysis of Multi-layer Circular Structures	damping, cavity, simulation, gun	1819
	H. Hahn, L.R. Hammons BNL, Upton, Long Island, New York, USA
	Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The analysis of multi-layer beam tubes is a frequent problem and is usually solved with axially propagating waves. This treatment is ill suited to a short multi-layer structure such as the present example of a ferrite covered ceramic break in the beam tube at the ERL photo-cathode electron gun. This paper demonstrates that such structures can better be treated by radial wave propagation. The theoretical method is presented and numerical results are compared with measured network analyser data and Microwave Studio generated simulations. The results confirm the concept of radial transmission lines as a valid analytical method.

WEP178	Electromagnetic Field Measurement of Fundamental and Higher-order Modes for 7-cell Cavity of PETRA-II	cavity, electromagnetic-fields, HOM, acceleration	1822
	Y. Kawashima, A. Blednykh, J. Cupolo, M.A. Davidsaver, B. Holub, H. Ma, J. Oliva, J. Rose, R. Sikora, M. Yeddulla BNL, Upton, Long Island, New York, USA
	The booster synchrotron for NSLS-II will include a 7-cell PETRA cavity, which was manufactured for the PETRA-II project at DESY. The cavity fundamental frequency operates at 500 MHz. In order to verify the impedances of the fundamental and higher-order modes (HOM) which were calculated by computer code, we measured the magnitude of the electromagnetic field of the fundamental acceleration mode and HOM’s, using the bead-pull method. To keep the cavity body temperature constant, we used a chiller system to supply cooling water at 20 degrees C. The bead-pull measurement was automated with a computer. We encountered some issues during the measurement process due to the difficulty in measuring the electromagnetic field magnitude in a multi-cell cavity as compared to a single-cell cavity. We describe the apparatus for the field measurement and the obtained results.

WEP179	Calculating Point-Charge Wakefields from Finite Length Bunch Wake-Potentials	cavity, wakefield, vacuum	1825
	B. Podobedov BNL, Upton, Long Island, New York, USA G.V. Stupakov SLAC, Menlo Park, California, USA
	Starting from analytical properties of high frequency geometric impedance we show how one can accurately calculate short bunch wake-potentials (and even point-charge wakefields) from time domain calculations performed with a much longer bunch. In many practical instances this drastically reduces the need for computer resources, speeds up the calculations, and improves their accuracy. To illustrate this method we give examples for 2D accelerator structures of various complexities.

WEP187	Simulation and Optimization of Project-X Main Injector Cavity	cavity, HOM, simulation, dipole	1840
	L. Xiao, C.-K. Ng SLAC, Menlo Park, California, USA J.E. Dey, I. Kourbanis, Z. Qian Fermilab, Batavia, USA
	Project-X, a proposed high intensity proton facility to support a world-leading program in neutrino and flavor physics at Fermilab, plans to use the existing FNAL recycler and main injector (MI) complex, but requires upgrading the MI RF system. Currently there are two proposed 53MHz RF cavity designs for 6GeV to 120GeV operation. One design is a straight-line quarter wave resonant cavity, and the other a tapered quarter wave resonant cavity. The electromagnetic (EM) simulations of the two cavity designs are carried out by using SLAC finite element parallel code suit ACE3P. The EM simulation results for the RF parameters and higher-order-mode (HOM) properties have shown that the tapered cavity design has better RF performance than the straight one. The tapered cavity shape will then be optimized for the final design to meet the specified performance requirements for the Project-X. Possible multipacting zones in the cavity will be identified and the use of HOM dampers investigated for the optimized design.

WEP220	Development of the Dual-Slot Resonance Linac	cavity, coupling, linac, resonance	1897
	D.J. Newsham, N. Barov, R.H. Miller Far-Tech, Inc., San Diego, California, USA
	Funding: Work supported by DOE Office of High Energy Physics, DOE-SBIR #DE-FG02-08ER85034. We present the development of a novel electron accelerating structure with strong cell-to-cell coupling. The coupling is provided by a pair of resonant slots, separated by a non-resonant void region, located within the wall between adjacent cells. The 10+2/2 cell standing-wave structure, operating in a phase and amplitude stabilized pi/2 mode, will provide an energy gain of 10 MeV.

WEP274	Broadband Antenna Matching Network Design and Application for RF Plasma Ion Source	ion, ion-source, plasma, simulation	1990
	K.R. Shin ORNL RAD, Oak Ridge, Tennessee, USA A.E. Fathy University of Tennessee, Knoxville, Tennessee, USA Y.W. Kang, M.F. Piller ORNL, Oak Ridge, Tennessee, USA
	Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. The RF ion source at Spallation Neutron Source has been upgraded to meet higher beam power requirement. One important subsystem for efficient operation of the ion source is the 2MHz RF impedance matching network. The real part of the antenna impedance is very small and is affected by plasma density for 2MHz operating frequency. Previous impedance matching network for the antenna has limited tuning capability to cover this potential variation of the antenna impedance since it employed a single tuning element and an impedance transformer. A new matching network with two tunable capacitors has been built and tested. This network can allow precision matching and increase the tunable range without using a transformer. A 5-element broadband matching network also has been designed, built and tested. The 5-element network allows wide band matching up to 50 kHz bandwidth from the resonance center of 2 MHz. The design procedure, simulation and test results are presented.

THP001	Hybrid Electron Linac Based on Magnetic Coupled Accelerating Structure	linac, coupling, electron, simulation	2136
	S.V. Kutsaev, K.I. Nikolskiy, N.P. Sobenin MEPhI, Moscow, Russia
	This paper presents the design of a hybrid linac which consists of a standing wave buncher and a travelling wave accelerating part. Both electric and magnetic-coupled disk-loaded waveguide (DLW) could be used as accelerating structure. The last one has better electrodynamical parameters comparing to classical DLW. Such an accelerator possesses the advantages of both standing wave and travelling wave linacs and has better output beam parameters.

THP109	Dielectric Collimators for Linear Collider Beam Delivery System	wakefield, collimation, collider, linear-collider	2330
	A. Kanareykin, P. Schoessow Euclid TechLabs, LLC, Solon, Ohio, USA S. Baturin LETI, Saint-Petersburg, Russia R. Tomás CERN, Geneva, Switzerland
	Funding: US Department of Energy The current status of ILC and CLIC concepts require additional research on wakefield reduction in the collimator sections. New materials and new geometries have been considered recently. Dielectric collimators for the CLIC Beam Delivery System have been discussed with a view to minimize the BDS collimation wakefields. Dielectric collimator concepts for the linear collider are presented in this paper; cylindrical and planar collimators for the CLIC parameters have been considered, and simulations to minimize the beam impedance have been performed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLAC. J.R.Lopez. ILC-CLIC Beam Dynamics Workshop. CERN, Geneva, 23-25 June, 2009. **R. Tomas. ILC-CLIC Beam Dynamics Workshop. CERN, Geneva, 23-25 June, 2009.

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MOODS4

Dancing Bunches as van Kampen Modes

synchrotron, damping, injection, proton

94

A.V. Burov
Fermilab, Batavia, USA

Theory of van Kampen modes is applied to bunch longitudinal motion. Case of inductive impedance domination is studied in more details. Threshold for loss of Landau damping is found to be very sensitive to fine structure of the distribution function. Good agreement with the Tevatron's "dancing bunches" is obtained.

Slides MOODS4 [0.408 MB]

MOP115

Progress on Multipactor Studies in Dielectric-Loaded Accelerating Structures

multipactoring, electron, simulation, vacuum

310

S.P. Antipov, C.-J. Jing, A. Kanareykin, P. Schoessow
Euclid TechLabs, LLC, Solon, Ohio, USA
D.S. Doran, W. Gai, J.G. Power
ANL, Argonne, USA
B. Feng
IIT, Chicago, Illinois, USA

Funding: DOE SBIR
Significant progress has been made in the development of high gradient rf driven dielectric accelerating structures (DLA). One principal effect limiting further advances in this technology is the problem of multipactor. The fraction of the power absorbed at saturation in DLA experiments was found to increase with the incident power, with more than 30% of the incident power per unit length being absorbed. We studied a possibility of multipactor mitigation by introduction of surface grooves (transverse and longitudinal) to interrupt the resonant trajectories of electrons in the multipactor discharge. Four DLA structures based on quartz tubes with transverse and longitudinal grooves of various dimensions were designed. In this paper we report simulation results and plans for high-power tests of these structures.

MOP116

Development of an X-Band Dielectric-Based Wakefield Power Extractor for Potential CLIC Applications

wakefield, simulation, insertion, electron

313

C.-J. Jing, S.P. Antipov, A. Kanareykin, P. Schoessow
Euclid TechLabs, LLC, Solon, Ohio, USA
M.E. Conde, W. Gai, J.G. Power
ANL, Argonne, USA
I. Syratchev
CERN, Geneva, Switzerland

Funding: Work is funded by DoE SBIR PhaseI.
In the past decade, tremendous efforts have been put into the development of the CLIC Power Extraction and Transfer Structure (PETS), and significant progress has been made. However, one concern remains the manufacturing cost of the PETS, particularly considering the quantities needed for a TeV machine. A dielectric-based wakefield power extractor in principle is much cheaper to build. A low surface electric field to gradient ratio is another big advantage of the dielectric-loaded accelerating/decelerating structure. We are currently investigating the possibility of using a cost-effective dielectric-based wakefield power extractor as an alternative to the CLIC PETS. We designed a 12 GHz dielectric-based power extractor which has a similar performance to CLIC PETS with parameters 23 mm beam channel, 240 ns pulse duration, 135 MW output per structure using the CLIC drive beam. In order to study potential rf breakdown issues, as a first step we are building a 11.424 GHz dielectric-based power extractor scaled from the 12 GHz version, and plan to perform a high power rf test using the SLAC 11.424 GHz high power rf source.

MOP133

Fabrication and Measurements of a Silicon Woodpile Accelerator Structure

simulation, laser, lattice, electron

343

C. McGuinness, E.R. Colby, R.J. England, R. Laouar, R.J. Noble, K. Soong, J.E. Spencer, Z. Wu, D. Xu
SLAC, Menlo Park, California, USA
R.L. Byer, E.A. Peralta
Stanford University, Stanford, California, USA

Funding: DOE grants: DE-AC02-76SF00515 and DE-FG03-97ER41043-II
We present results for the fabrication of a silicon woodpile accelerator structure. The structure was designed to have an accelerating mode at 3.95 μm, with a high characteristic impedance and an accelerating gradient of 530 MeV/m. The fabrication process uses standard nanofabrication techniques in a layer-by-layer process to produce a three-dimensional photonic crystal with 400 nm features. Reflection spectroscopy measurements reveal a peak spanning from three to five microns, and are show good agreement with simulations.
* Sears, PRST-AB, 11, 101301, (2008).
** Cowan, PRST-AB, 11, 011301, (2008).
*** McGuinness, J. Mod. Opt., vol. 56, is. 18, pp. 2142, (2009).
**** Lin, Nature, 394, pp. 251 (1998).

MOP239

Commercially Available Transverse Profile Monitors, the IBIS

target, vacuum, optics, diagnostics

562

M. Ruelas, R.B. Agustsson, I. Bacchus, A.Y. Murokh, R. Tikhoplav
RadiaBeam, Santa Monica, USA

With ever decreasing budgets, shorter delivery schedules and increased performance requirements for pending and future facilities, the need for cost effective yet high quality profile monitors is paramount to future advancement in the accelerator field. While individual facilities are capable of designing and fabricating these often custom devices, this is not always the most efficient or economical route. In response to the lack of commercially available profile monitors, RadiaBeam Technologies has been developing its line of Integrated Beam Imaging System (IBIS) over the past several years. Here, we report on these commercially available profile monitors.

MOP266

Stripline Kicker Design for NSLS2 Storage Ring

kicker, pick-up, damping, feedback

603

W.X. Cheng, A. Blednykh, S. Krinsky, O. Singh
BNL, Upton, Long Island, New York, USA

In the NSLS2 storage ring, there are four stripline kickers/pickups. Two long striplines with electrode length of 30cm will be used as bunch-by-bunch transverse feedback actuators. Two short stripline kickers/pickups with 15cm length will mainly used for tune measurement excitation or signal pickup for the beam stability monitor. High shunt impedance of the long stripline kickers is demanded to produce 200μs damping time. Meanwhile the beam impedance should be minimized. The design work for these two types of stripline is discussed in this paper.

MOP269

Design of Longitudinal Feedback Kicker for HLS Storage Ring

kicker, cavity, storage-ring, vacuum

612

W. Xu, D.H. He
USTC/NSRL, Hefei, Anhui, People's Republic of China
W. Wu, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA

Hefei Light Source (HLS) is a dedicated synchrotron radiation research facility. It is now undergoing a major upgrade. To obtain a better performance of the light source, a longitudinal feedback system will be developed as part of the upgrade project to cure the coupled bunch mode instabilities. In this work, we present a design of the LFB kicker, a waveguide overloaded cavity with two input and two output ports. The cavity design specifications include a central frequency of 969 MHz (4.75 RF frequency), a bandwidth of more than 100 MHz, and a high shunt impedance of 1200 Ω. A study is carried out to find the dependence of the cavity performance on a few critical geometric parameters of the cavity. Since the shape of the vacuum chamber of the HLS storage ring is octagon, a transition from a circular vacuum chamber to an octagon one is built into the end pieces of the cavity to minimize the total cavity length. To lower the required amplifier power, the structure is optimized to obtain a high shunt impedance. The higher order modes of the kicker cavity are also considered during the design.

MOP281

ADC Clocking Formats and Matching Networks

coupling, HOM, power-supply

639

A.J. Della Penna
BNL, Upton, Long Island, New York, USA

Clocking an ADC is the most critical point when resolution is a major concern. Any fluctuations on the input clock performance correlates to jitter. The many different formats used to clock ADCs on the market makes choosing the appropriate one no easy task. LVDS, PECL, LVPECL, CMOS and CML are just some of the different types. With each type a certain matching network will be required. This paper will discuss the advantages of each format as well as its associated matching network.

MOP292

Universal FMC-Compliant Module for xTCA Systems

controls, power-supply, monitoring, target

663

D.R. Makowski, G.W. Jabłoński, T. Kozak, A. Mielczarek, A. Napieralski
TUL-DMCS, Łódź, Poland

Funding: The research leading to these results has received funding from Polish National Science Council Grant 642/N-TESLAXFEL/09/2010/0.
The Advanced Telecommunications Computing Architecture (ATCA), MicroTCA (uTCA) and Advanced Mezzanine Card (AMC) standards, known as xTCA, provide unique features desired by various control systems of particle accelerators. The standards provide availability and operability as high as 99.999 %. A significant number of additional features must be implemented to take a full advantage of xTCA standards and gain the required availability. On the other hand, many control systems require various data acquisition and control modules with different number of input analogue and digital inputs or outputs as defined by their respective system specifications. The paper presents an universal base module, designed according to the AMC standard with an FPGA Mezzanine Card connector, that can be used for fast development of input-output subsystems. The module consists of two submodules. The digital part is designed according to the AMC standard while the main input-output functionality is realized by the FPGA Mezzanine Card part. The FMC submodule provides the functionality required by the specification of the LLRF system.

TUP097

Fundamental and HOM Coupler Design for the Superconducting Parallel-Bar Cavity

cavity, HOM, damping, coupling

1015

S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
S.U. De Silva
JLAB, Newport News, Virginia, USA

The superconducting parallel-bar cavity is currently being considered as a deflecting system for the Jefferson Lab 12 GeV upgrade and as a crabbing cavity for a possible LHC luminosity upgrade. Currently the designs are optimized to achieve lower surface fields within the dimensional constraints for the above applications. A detailed analysis of the fundamental input power coupler design for the parallel-bar cavity is performed considering beam loading and the effects of microphonics. For higher beam loading the damping of the HOMs is vital to reduce beam instabilities generated due to the wake fields. An analysis of threshold impedances for each application and impedances of the modes that requires damping are presented in this paper with the design of HOM couplers.

TUP117

Solid State Direct Drive RF LINAC: High Power Experimental Program

cavity, controls, linac, high-voltage

1056

T.J.S. Hughes, M. Back, R. Fleck, M. Hergt, R. Irsigler, T. Kluge, J. Sirtl
Siemens AG, Erlangen, Germany
O. Heid
Siemens AG, Healthcare Technology and Concepts, Erlangen, Germany

We report on a 150MHz λ/4 coaxial resonator driven by 32 integrated class F RF power modules according to our direct drive concept [1,2]. Electric fields of 60MV/m at the resonator gap have been reached, which correspond to 80kW RF power. This power level has been achieved at 160V DC supply voltage, significantly less than the component limits. The observed power and Q values can be explained by a simple equivalent circuit. The model predicts that 64 modules at 160V DC supply voltage may provide 170kW RF power, and that 250V DC supply voltage should yield 400kW. The corresponding 134MV/m gap E field may not be reachable due to vacuum flashover.
* Heid O., Hughes T. THPD002, IPAC10, Kyoto, Japan
** Hergt M et al, 2010 IEEE International Power Modulator and High Voltage Conf., Atlanta GA, USA
*** Heid O., Hughes T. THP068, LINAC10, Tsukuba, Japan

TUP129

Simulation Results of RF Coupler Controllable by Dielectric Fluid

coupling, simulation, cavity, vacuum

1073

P. Chen, D. Yu
DULY Research Inc., Rancho Palos Verdes, California, USA

Funding: Work supported by DOE SBIR Phase I grant No. DE-FG02-09ER85334.
Tunable couplers for adjusting radiofrequency (RF) power coupling into accelerator cavities are useful devices for achieving optimal operation efficiency. Standard mechanical tuners currently used in large accelerator facilities are bulky and complicated. A novel tuner, based on the introduction of dielectric tubes or fluid-filled volumes adjacent to, but separated by window(s) from the coupler, is described. Simulations have shown that the tuner has a fairly large adjustment range and also demonstrated the viability of the tuning concept using fluid circuit.

TUP131

A New Main Injector Radio Frequency System For 2.3 MW Project X Operations

cavity, radio-frequency, cathode, feedback

1079

J.E. Dey, I. Kourbanis
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
For Project X Fermilab Main Injector will be required to provide up to 2.3 MW to a neutrino production target at energies between 60 and 120 GeV. To accomplish the above power levels 3 times the current beam intensity will need to be accelerated. In addition the injection energy of Main Injector will need to be as low as 6 GeV. The current 30 year old Main Injector radio frequency system will not be able to provide the required power and a new system will be required. The specifications of the new system will be described.

TUP213

Research and Development toward the RHIC Injection Kicker Upgrade

kicker, injection, high-voltage, factory

1211

W. Zhang, W. Fischer, H. Hahn, C. Pai, J. Sandberg, J.E. Tuozzolo
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A research and development work is on going toward the upgrade of the RHIC Injection Fast Kicker System. We report here the proposed nano-second pulse generator, the initial test result, the options of the deflector design, injection pattern, and the benefit to the future RHIC programs.

TUP259

A Solid-State Nanosecond Beam Kicker Modulator Based on the DSRD Switch

kicker, high-voltage, extraction, status

1310

A.L. Benwell, R. Akre, C. Burkhart, A. Krasnykh, T. Tang
SLAC, Menlo Park, California, USA
A. Kardo-Sysoev
IOFFE, St. Petersburg, Russia

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
A fast solid-state beam kicker modulator is under development at the SLAC National Accelerator Laboratory. The program goal is to develop a modulator that will deliver 4 ns, ±5 kV pulses to the ATF2 damping ring beam extraction kicker. The kicker is a 50 Ω, bipolar strip line, 60 cm long, fed at the downstream end and terminated at the upstream end. The bunch spacing in the ring is 5.6 ns, bunches are removed from the back end of the train, and there is a gap of 10³.6 ns before the next train. The modulator design is based on an opening switch topology that uses Drift Step Recovery Diodes as the opening switches. The design and results of the modulator development are discussed.

TUP277

RF Design of the Power Coupler for the Spiral2 Single Bunch Selector

vacuum, ion, simulation, kicker

1346

F. Consoli, A.C. Caruso, G. Gallo, D. Rifuggiato, E. Zappalà
INFN/LNS, Catania, Italy
M. Di Giacomo
GANIL, Caen, France

Funding: Work supported by the European Community FP7 – Capacities – SPIRAL2 Preparatory Phase n° 212692.
The single bunch selector of the Spiral2 driver uses high impedance travelling wave electrodes driven by fast pulse generators. The characteristic impedance of 100 Ω has been chosen to reduce the total power, but this non standard value requires the development of custom feed-through and transitions to connect the pulse generators and the matching load to the electrodes. The paper reviews the design of these devices.

TUP278

Tuning Method for the 2π/3 Traveling Wave Structures

coupling, controls, beam-loading, linac

1349

A.S. Setty
THALES, Colombes, France

To build a constant gradient traveling wave structure, one must perform cold tests under a press in order to tune the different cells individually. For the tests to be valid, the test cells must be terminated by shorting planes located in planes of symmetry in which the electric field vector is normal in such a way that the standing wave "trapped" between them is an exact representation of the instantaneous traveling wave one wishes to study. For the TW structure, the cavities are put three by three under the press. We then try to reduce the contribution of "mixed cells" by adding to one wavelength at 2π/3 mode two-quarter wavelengths. This is possible when the end-cells mode at the same frequency is π/2 instead of 2π/3. These end cells are not included in the final assembly. The setting process will be analysed.

TUP283

Inductively Coupled, Compact HOM Damper for the Advanced Photon Source

HOM, coupling, diagnostics, damping

1358

G.J. Waldschmidt, D. Horan, L.H. Morrison
ANL, Argonne, USA

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 requires damping of higher-order modes in the storage ring rf cavities in order to prevent beam instability at beam currents in excess of 100 mA proposed for the APS Upgrade. Due to constraints imposed by available space and by existing 35-mm pick-up ports on the cavity, a compact design has been analyzed with a quarter-wave rejection filter of the fundamental mode. Separate broadband, low-frequency and high-frequency dampers are utilized to span the frequency range from 500 MHz to 1500 MHz. The dampers have been designed to reject the fundamental cavity mode, couple strongly to HOM’s, utilize an external rf load, minimize the overall size, and incorporate rf diagnostics. In addition, the mechanical design has been optimized to simplify construction, improve mechanical stability, and reduce thermally induced stresses.

WEOBS5

Status of the Short-Pulse X-ray Project (SPX) at the Advanced Photon Source (APS)

cavity, feedback, cryomodule, emittance

1427

R. Nassiri, N.D. Arnold, G. Berenc, M. Borland, D.J. Bromberek, Y.-C. Chae, G. Decker, L. Emery, J.D. Fuerst, A.E. Grelick, D. Horan, F. Lenkszus, R.M. Lill, V. Sajaev, T.L. Smith, G.J. Waldschmidt, G. Wu, B.X. Yang, A. Zholents
ANL, Argonne, USA
J.M. Byrd, L.R. Doolittle, G. Huang
LBNL, Berkeley, California, USA
G. Cheng, G. Ciovati, J. Henry, P. Kneisel, J.D. Mammosser, R.A. Rimmer, L. Turlington, H. Wang
JLAB, Newport News, Virginia, USA

Funding: Work at Argonne is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11354.
The Advanced Photon Source Upgrade project (APS-U) at Argonne includes implementation of Zholents’* deflecting cavity scheme for production of short x-ray pulses. This is a joint project between Argonne National Laboratory, Thomas Jefferson National Laboratory, and Lawrence Berkeley National Laboratory. This paper describes performance characteristics of the proposed source and technical issues related to its realization. Ensuring stable APS storage ring operation requires reducing quality factors of these modes by many orders of magnitude. These challenges reduce to those of the design of a single-cell SC cavity that can achieve the desired operating deflecting fields while providing needed damping of all these modes. The project team is currently prototyping and testing several promising designs for single-cell cavities with the goal of deciding on a winning design in the near future.
*A. Zholents et al., NIM A 425, 385 (1999).

Slides WEOBS5 [1.730 MB]

WEODS1

Design and Optimization of Future X-ray FELs based on Advanced High Frequency Linacs

linac, klystron, FEL, acceleration

1491

F. Wang
SLAC, Menlo Park, California, USA

To drive future XFELs, normal-conducting linacs at various rf freqencies are being considered. With optimized accelerator structures and rf systems, a higher rf frequency linac has several advantages, such as high acceleration gradient and high rf-to-beam efficiency. This paper presents a comparison of possible S-band, C-band and X-band linac designs for two cases, single bunch operation and multibunch operation, where the bunch train length is longer than the structure fill time and the beam loading is small. General scaling laws for the main linac parameters, which can be useful in the design such linacs, are derived.

Slides WEODS1 [5.795 MB]

WEP084

Beam Dynamics and Instabilities in MEIC Design

ion, electron, feedback, positron

1630

S. Ahmed, G.A. Krafft, B.C. Yunn
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In this paper, we report the first study of beam related instabilities in lepton ring of the proposed electron-ion collider beyond the 12 GeV upgrade of CEBAF at Jefferson lab. The design parameters are consistent with PEP-II. Present studies reveal that coupled bunch and two stream instabilities are important issues and we need feedback system.

WEP116

Bucket Shaking Stops Bunch Dancing in Tevatron

synchrotron, simulation, dipole, damping

1704

A.V. Burov, C.-Y. Tan
Fermilab, Batavia, USA

Bunches in Tevatron are known to be longitudinally unstable: their collective oscillations stay without any sign of decay. Typically, a feedback damper is used to stop these oscillations. Recently, it was theoretically predicted that the oscillations can be stabilized by means of small bucket shaking*. Detailed measurements in Tevatron have shown that this method does work. In this paper, an essential theory and specific observations of the related process are presented.
* A. Burov, “Dancing Bunches as van Kampen Modes”, this conference.

WEP119

Coherent Radiation in Whispering Gallery Modes

vacuum, resonance, radiation, synchrotron

1710

R.L. Warnock
SLAC, Menlo Park, California, USA
J.C. Bergstrom
CLS, Saskatoon, Saskatchewan, Canada

Funding: Work at SLAC: U.S. Department of Energy Contract No. DE-AC03-76SF00515 Work at CLS: NSERC, NRC, Province of Saskatchewan, U. of Saskatchewan.
Theory predicts that CSR in storage rings should appear in whispering gallery modes *, which are resonances of the entire vacuum chamber and are characterized by their high frequencies and concentration of the field near the outer wall of the chamber. The theory assumes that the chamber is a smooth circular torus. We observe that a power spectrum from the NSLS-VUV ring **, which has a vacuum chamber in bends like that of the model, shows a series of sharp peaks with frequencies close to those of the theory. Sharp peaks are also seen in highly resolved spectra at the Canadian Light Source***, and those are invariant in position under large changes in the machine setup (energy, fill pattern, bunch length, CSR bursting or steady, optical beam line, etc.). Invariance of the spectrum suggests that it is due to resonances like whispering gallery modes, but they must be strongly perturbed from the circular case because of large outer wall excursions at the two IR ports.
* R. L. Warnock and P. Morton, Part. Accel. 25, 113 (1990).
** G. L. Carr et al., Proc. PAC 2001, Chicago.
*** T. May et al., IEEE 33rd Intl. Conf. IR Millimeter and THz Waves, 2008.

WEP147

The Effect of Space-charge and Wake Fields in the Fermilab Booster

booster, wakefield, coupling, simulation

1758

A. Macridin, J.F. Amundson, P. Spentzouris
Fermilab, Batavia, USA
D.O. McCarron
IIT, Chicago, Illinois, USA
L.K. Spentzouris
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: This work was supported by the DOE contracts DE-AC02-07CH11359, DE-AC02-05CH11231 and DE-AC02-06CH11357 and the ComPASS project funded through the SciDAC.
We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements.

WEP176

Loss Factor of Tapered Structures for Short Bunches

vacuum, factory, simulation, electromagnetic-fields

1816

A. Blednykh, S. Krinsky
BNL, Upton, Long Island, New York, USA

Funding: Work supported by DOE contract DE-AC02-98CH10886
Using the electromagnetic simulation code ECHO, we have found* a simple phenomenological formula that accurately describes the loss factor for short bunches traversing an axisymmetric tapered collimator. In this paper, we consider tapered collimators with elliptical cross-section and use the GdfidL code to calculate the loss factor dependence on the geometric parameters for short bunches. The results for both axisymmetric and elliptical collimators are discussed.
* A. Blednykh and S. Krinsky, Phys. Rev. ST-AB 13, 064401 (2010).

WEP177

Radial Transmission Line Analysis of Multi-layer Circular Structures

damping, cavity, simulation, gun

1819

H. Hahn, L.R. Hammons
BNL, Upton, Long Island, New York, USA

Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
The analysis of multi-layer beam tubes is a frequent problem and is usually solved with axially propagating waves. This treatment is ill suited to a short multi-layer structure such as the present example of a ferrite covered ceramic break in the beam tube at the ERL photo-cathode electron gun. This paper demonstrates that such structures can better be treated by radial wave propagation. The theoretical method is presented and numerical results are compared with measured network analyser data and Microwave Studio generated simulations. The results confirm the concept of radial transmission lines as a valid analytical method.

WEP178

Electromagnetic Field Measurement of Fundamental and Higher-order Modes for 7-cell Cavity of PETRA-II

cavity, electromagnetic-fields, HOM, acceleration

1822

Y. Kawashima, A. Blednykh, J. Cupolo, M.A. Davidsaver, B. Holub, H. Ma, J. Oliva, J. Rose, R. Sikora, M. Yeddulla
BNL, Upton, Long Island, New York, USA

The booster synchrotron for NSLS-II will include a 7-cell PETRA cavity, which was manufactured for the PETRA-II project at DESY. The cavity fundamental frequency operates at 500 MHz. In order to verify the impedances of the fundamental and higher-order modes (HOM) which were calculated by computer code, we measured the magnitude of the electromagnetic field of the fundamental acceleration mode and HOM’s, using the bead-pull method. To keep the cavity body temperature constant, we used a chiller system to supply cooling water at 20 degrees C. The bead-pull measurement was automated with a computer. We encountered some issues during the measurement process due to the difficulty in measuring the electromagnetic field magnitude in a multi-cell cavity as compared to a single-cell cavity. We describe the apparatus for the field measurement and the obtained results.

WEP179

Calculating Point-Charge Wakefields from Finite Length Bunch Wake-Potentials

cavity, wakefield, vacuum

1825

B. Podobedov
BNL, Upton, Long Island, New York, USA
G.V. Stupakov
SLAC, Menlo Park, California, USA

Starting from analytical properties of high frequency geometric impedance we show how one can accurately calculate short bunch wake-potentials (and even point-charge wakefields) from time domain calculations performed with a much longer bunch. In many practical instances this drastically reduces the need for computer resources, speeds up the calculations, and improves their accuracy. To illustrate this method we give examples for 2D accelerator structures of various complexities.

WEP187

Simulation and Optimization of Project-X Main Injector Cavity

cavity, HOM, simulation, dipole

1840

L. Xiao, C.-K. Ng
SLAC, Menlo Park, California, USA
J.E. Dey, I. Kourbanis, Z. Qian
Fermilab, Batavia, USA

Project-X, a proposed high intensity proton facility to support a world-leading program in neutrino and flavor physics at Fermilab, plans to use the existing FNAL recycler and main injector (MI) complex, but requires upgrading the MI RF system. Currently there are two proposed 53MHz RF cavity designs for 6GeV to 120GeV operation. One design is a straight-line quarter wave resonant cavity, and the other a tapered quarter wave resonant cavity. The electromagnetic (EM) simulations of the two cavity designs are carried out by using SLAC finite element parallel code suit ACE3P. The EM simulation results for the RF parameters and higher-order-mode (HOM) properties have shown that the tapered cavity design has better RF performance than the straight one. The tapered cavity shape will then be optimized for the final design to meet the specified performance requirements for the Project-X. Possible multipacting zones in the cavity will be identified and the use of HOM dampers investigated for the optimized design.

WEP220

Development of the Dual-Slot Resonance Linac

cavity, coupling, linac, resonance

1897

D.J. Newsham, N. Barov, R.H. Miller
Far-Tech, Inc., San Diego, California, USA

Funding: Work supported by DOE Office of High Energy Physics, DOE-SBIR #DE-FG02-08ER85034.
We present the development of a novel electron accelerating structure with strong cell-to-cell coupling. The coupling is provided by a pair of resonant slots, separated by a non-resonant void region, located within the wall between adjacent cells. The 10+2/2 cell standing-wave structure, operating in a phase and amplitude stabilized pi/2 mode, will provide an energy gain of 10 MeV.

WEP274

Broadband Antenna Matching Network Design and Application for RF Plasma Ion Source

ion, ion-source, plasma, simulation

1990

K.R. Shin
ORNL RAD, Oak Ridge, Tennessee, USA
A.E. Fathy
University of Tennessee, Knoxville, Tennessee, USA
Y.W. Kang, M.F. Piller
ORNL, Oak Ridge, Tennessee, USA

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
The RF ion source at Spallation Neutron Source has been upgraded to meet higher beam power requirement. One important subsystem for efficient operation of the ion source is the 2MHz RF impedance matching network. The real part of the antenna impedance is very small and is affected by plasma density for 2MHz operating frequency. Previous impedance matching network for the antenna has limited tuning capability to cover this potential variation of the antenna impedance since it employed a single tuning element and an impedance transformer. A new matching network with two tunable capacitors has been built and tested. This network can allow precision matching and increase the tunable range without using a transformer. A 5-element broadband matching network also has been designed, built and tested. The 5-element network allows wide band matching up to 50 kHz bandwidth from the resonance center of 2 MHz. The design procedure, simulation and test results are presented.

THP001

Hybrid Electron Linac Based on Magnetic Coupled Accelerating Structure

linac, coupling, electron, simulation

2136

S.V. Kutsaev, K.I. Nikolskiy, N.P. Sobenin
MEPhI, Moscow, Russia

This paper presents the design of a hybrid linac which consists of a standing wave buncher and a travelling wave accelerating part. Both electric and magnetic-coupled disk-loaded waveguide (DLW) could be used as accelerating structure. The last one has better electrodynamical parameters comparing to classical DLW. Such an accelerator possesses the advantages of both standing wave and travelling wave linacs and has better output beam parameters.

THP109

Dielectric Collimators for Linear Collider Beam Delivery System

wakefield, collimation, collider, linear-collider

2330

A. Kanareykin, P. Schoessow
Euclid TechLabs, LLC, Solon, Ohio, USA
S. Baturin
LETI, Saint-Petersburg, Russia
R. Tomás
CERN, Geneva, Switzerland

Funding: US Department of Energy
The current status of ILC and CLIC concepts require additional research on wakefield reduction in the collimator sections. New materials and new geometries have been considered recently*. Dielectric collimators for the CLIC Beam Delivery System have been discussed with a view to minimize the BDS collimation wakefields**. Dielectric collimator concepts for the linear collider are presented in this paper; cylindrical and planar collimators for the CLIC parameters have been considered, and simulations to minimize the beam impedance have been performed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLAC.
*J.R.Lopez. ILC-CLIC Beam Dynamics Workshop. CERN, Geneva, 23-25 June, 2009.
**R. Tomas. ILC-CLIC Beam Dynamics Workshop. CERN, Geneva, 23-25 June, 2009.