IPAC2015 - List of Keywords (damping)

Paper	Title	Other Keywords	Page
MOYGB3	Commissioning of NSLS-II	insertion, insertion-device, emittance, lattice	11
	F.J. Willeke BNL, Upton, Long Island, New York, USA
	NSLS-II, the new 3rd generation light source at BNL was designed for a brightness of 10²² photons s^-1 mm^-2 mrad^-2 (0.1%BW)^-1. It was constructed between 2009 and 2014. The storage ring was commissioned in April 2014 which was followed by insertion device and beamline commissioning in the fall of 2014. All ambitious design parameters of the facility have already been achieved except for commissioning the full beam intensity of 500 mA which requires more RF installation. This paper reports on the results of commissioning.
	Slides MOYGB3 [3.884 MB]
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MOPWA001	Instability Thresholds and Tune Shift Estimation for Sirius	impedance, feedback, emittance, simulation	70
	F.H. de Sá, L. Liu, N. Milas, X.R. Resende LNLS, Campinas, Brazil
	In this work we present the evaluation of longitudinal and transverse instability thresholds as well as tune shifts for Sirius using time and frequency domain codes that are being developed in-house and take into account various effects on the beam instability, such as bunch by bunch feedback system, quadrupolar impedances from undulator chambers and tune spreads.
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MOPWA011	The Damping of Transverse Coherent Instabilities by Harmonic Cavities	synchrotron, betatron, simulation, electron	102
	F.J. Cullinan, R. Nagaoka SOLEIL, Gif-sur-Yvette, France G. Skripka, P.F. Tavares MAX-lab, Lund, Sweden
	At nonzero chromaticity, the threshold current due to transverse coupled bunch instabilities in an electron storage ring is defined by intrabunch head-tail motion of higher than zeroth order. Multibunch tracking simulations predict that this threshold can be increased to several times its original value through the introduction of bunch lengthening harmonic cavities. One previously suggested explanation is the narrower spectra of the elongated bunches but reliable estimates for the threshold currents are not obtainable for anything other than rigid beam motion since the usual Sacherer formulism is not directly applicable to beams in a non-harmonic potential. A new scheme has been developed in which the decay time of a higher than zeroth order transverse head-tail mode may be estimated by taking into account the synchrotron tune spread generated by the harmonic cavity potential. This scheme is presented along with the results of numerical simulations performed in order to confirm the analytical predictions and justify the assumptions made. The extension of the scheme to more complex scenarios is also discussed.
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MOPWA019	Status of the Robinson Wiggler Project at the Metrology Light Source	wiggler, dipole, radiation, dynamic-aperture	132
	T. Goetsch, J. Feikes, M. Ries, G. Wüstefeld HZB, Berlin, Germany
	The beam lifetime in electron storage rings concerns machines running in decay mode as well as machines doing top-up. A standard procedure to increase the lifetime is via bunch lengthening as the lifetime depends on the electron density in the bunch. Bunch lengthening is typically achieved with higher harmonic (Landau) cavities. As noted in , there are several advantages in using a different approach: it is possible to increase the bunch length by installing a Transverse Gradient (Robinson) Wiggler, which allows to transfer damping between the horizontal and the longitudinal plane. While increasing the bunch length, the horizontal emittance is being reduced yielding advantages regarding the source size depending on the magnet optics. At the Metrology Light Source, a primary source standard used by Germanys national metrology institute (Physikalisch-Technische Bundesanstalt), such a scheme is being investigated. The current state of the project including dynamic aperture effects and synchrotron radiation issues of the device is being presented in the following. T. Goetsch et al.,WEPRO028 in Proceedings of IPAC2014, Dresden (Germany), 2014 ** R. Klein et al., Phys. Rev. ST-AB 11, 110701, 2008
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MOPWA022	Influence of Transient Beam Loading on the Longitudinal Beam Dynamics at BESSY VSR	beam-loading, synchrotron, simulation, cavity	141
	M. Ruprecht, P. Goslawski, A. Jankowiak, A. Neumann, M. Ries, G. Wüstefeld HZB, Berlin, Germany T. Weis DELTA, Dortmund, Germany
	BESSY VSR, a scheme where 1.7 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring has recently been proposed . The strong longitudinal bunch focusing is achieved by superconducting high gradient RF cavities. If the bunch fill pattern exhibits a significant inhomogeneity, e.g. due to gaps, transient beam loading causes a distortion of the longitudinal phase space which is different for each bunch. The result are variations along the fill pattern in synchronous phase, synchrotron frequency and bunch shape. This paper presents investigations of transient beam loading and depicts the consequences on bunch length, phase stability and longitudinal multi-bunch oscillations for the projected setup of BESSY VSR. G. Wüstefeld, A. Jankowiak, J. Knobloch, M. Ries, Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proceedings of IPAC2011, San Sebastián, Spain
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MOPWA034	Coupled-Bunch Instability Suppression Using RF Phase Modulation at the DELTA Storage Ring	synchrotron, storage-ring, electron, feedback	179
	M. Sommer, M. Höner, B.D. Isbarn, S. Khan, B. Riemann, T. Weis DELTA, Dortmund, Germany
	Funding: Work supported by the BMBF under contract no. 05K13PEB The upcoming upgrade of BESSY II, called BESSY-VSR, involves the utilization of superconducting multicell RF-resonators with high accelerating gradients to provide short and long bunches in an electron storage ring simultaneously. Even under the assumption of strongest available damping of beam induced modes, the residual impedances of the cavities may cause collective multibunch instabilities at the frontier of stability available from current bunch-by-bunch feedback systems. At the DELTA electron storage ring, a phase modulation of the driving RF is used to suppress coupled-bunch instabilities and to increase the lifetime. The time dependent frequency variation in the order of the synchrotron frequency gives rise to additional damping of the bunch oscillators by decoherence and Landau damping. The behaviour and the additional damping of the bunch oscillators is investigated by the existing bunch-by-bunch feedback system e.g. the increase of the overall damping might support the capability of feedback systems under extreme operating conditions of BESSY-VSR. G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014
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MOPJE036	Longitudinal Impedance Characterization of the CERN SPS Vacuum Flanges	impedance, resonance, vacuum, simulation	363
	J.V. Campelo CERN, Geneva, Switzerland
	This contribution describes the thorough studies carried out to characterize the longitudinal impedance of the CERN SPS vacuum flanges, which are believed to be the main source of LHC beam instability. Around 500 high-impedance flanges of 8 different types have been identified. Three factors play an important role in the characterization of these flanges: the type of vacuum chambers that the flange interconnects, whether or not both sides are electrically isolated (by means of an enamel coating) and, finally, the presence of damping resistors which damp high-Q resonances. Not only, full-wave electromagnetic field simulations, but also RF measurements have been used to evaluate the impedance of these elements. The R/Q of the relevant resonances was measured using the well-known bead-pull technique. In particular, a subset of around 150 flanges has been found to be the source of a high-impedance resonance at 1.4 GHz, also observed in beam measurements. Guidelines on how to reduce the impedance of these elements are also presented.
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MOPJE037	Study and Comparison of Mode Damping Strategies for the UA9 Cherenkov Detector Tank	cavity, vacuum, detector, resonance	366
	A. Danisi, F. Caspers, R. Losito, A. Masi, B. Salvant, C. Vollinger CERN, Geneva, Switzerland T. Demma, P. Lepercq LAL, Orsay, France
	In the framework of the UA9 experiment, the Cherenkov detector is useful to measure the amount of particles deflected by a bent crystal, proving the crystal collimation principle. The tank used to host this device is taken as a case study for an in-depth analysis of different damping strategies for electromagnetic modes which otherwise would give rise to important beam-coupling impedance contributions. Such strategies involve the use of ferrite, damping resistors and a mode-coupler, a solution which intercepts the modes inside the cavity but damps the related power outside the vacuum tank (potentially avoiding heating). Such solutions are discussed through experimental measurements and the relative quality factor is taken as a figure of merit.
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MOPJE065	Contribution of Optical Aberrations to Spot-size Increase with Bunch Intensity at ATF2	emittance, optics, extraction, simulation	455
	M. Patecki, R. Tomás, F. Zimmermann CERN, Geneva, Switzerland K. Kubo, S. Kuroda, T. Naito, T. Okugi, T. Tauchi, N. Terunuma KEK, Ibaraki, Japan M. Patecki Warsaw University of Technology, Warsaw, Poland G.R. White SLAC, Menlo Park, California, USA
	A primary goal of ATF2 (Accelerator Test Facility) is to demonstrate a low vertical beam size at the interaction point (IP) of about 37 nm. Measurements over the past years indicate that the ATF2 vertical beam size strongly rises with bunch intensity. Several different origins of this increase are considered, e.g. wakefields occurring between the ATF damping ring and the IP, and/or intrabeam scattering (IBS) causing the increase of transverse emittances and energy spread in the damping ring with the increase of the bunch intensity. In this paper we address the second possibility. Past measurements and simulations of the IBS effects in the ATF are used to model the intensity-dependent initial emittances and energy spread at the entrance of the final focus. Particle tracking simulations predict the IP vertical beam size growth expected from the known optical aberrations for initial beam parameters corresponding to varying bunch intensities. Comparing simulation results with emittance measurements at different locations allows us to draw some conclusions about the impact of IBS in the damping ring on the IP spot size, and about possible single-bunch wakefields in the ATF2.
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MOPMA017	Numerical simulations of transverse modes in Gaussian bunches with space charge	space-charge, simulation, lattice, synchrotron	575
	A. Macridin, J.F. Amundson, E.G. Stern Fermilab, Batavia, Illinois, USA
	The transverse modes and the intrinsic Landau damping in Gaussian bunched beams with space charge are numerically investigated. The evolution of the phase space density is calculated with the Synergia accelerator modeling package and analyzed with Dynamic Mode Decomposition (DMD) method. DMD is a relatively new technique used to calculate mode dynamics in both linear and nonlinear systems. The properties of the first three space charge modes, including their shape, damping rates and tune shifts are calculated over the entire range of the space charge interaction.
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MOPMA025	CSR Induced Microbunching Gain Estimation including Transient Effects in Transport and Recirculation Arcs	impedance, dipole, lattice, simulation	596
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA D. Douglas, R. Li, C. Tennant JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in the microbunching instability (μBI). To accurately quantify the direct consequence of this effect, we further extend our previously developed semi-analytical simulation [C. -Y. Tsai et al., FEL Conference 2014 (THP022)] to include more relevant coherent radiation models than the steady-state free-space CSR impedance, such as the entrance and exit transient effects, which derive from upstream beam entering to and exiting from individual dipoles and propagating across the elements to downstream straight sections. Then we semi-analytically solve the linearized Vlasov equation for the amplification factor. The resultant gain functions and spectra for our example lattices are presented and compared with particle tracking simulation. Some underlying physics with inclusion of these effects are also discussed.
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MOPMA060	Impedance Measurement for the SPEAR3 Storage Ring	impedance, lattice, storage-ring, vacuum	694
	X. Huang, J.J. Sebek SLAC, Menlo Park, California, USA
	We studied the transverse impedance of the SPEAR3 storage ring with tune shift vs. beam intensity, head-tail instability and transverse mode coupling instability measurements. By taking measurements under different machine conditions, we probed the frequency dependence of the impedance, from which an impedance model was built. This model is consistent with instability measurements and previous bunch lengthening results.
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MOPMN008	Space Charge Studies in FFAG Using the Tracking Code Zgoubi	space-charge, emittance, simulation, betatron	717
	M. Haj Tahar, F. Méot, N. Tsoupas 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 method is implemented in Zgoubi that allows the computation of space charge effects in 2D distributions and with some restrictions in 3D distributions. It relies on decomposiing field maps or analytical elements into slices and applying a space charge kick to the particles. The aim of this study is to investigate the accuracy of this technique, its limitations/advantages by comparisons with other linear/nonlinear computation methods and codes, and to apply it to high power fixed field ring design studies.
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MOPMN016	Decoherence due to Second Order Chromaticity in the NSLS-II Storage Ring	betatron, synchrotron, storage-ring, lattice	737
	G. Bassi, A. Blednykh, J. Choi, V.V. Smaluk BNL, Upton, Long Island, New York, USA
	We study decoherence effects due to second order chromaticity for small amplitude kicks, in order to estimate the energy spread from TbT data of the NSLS-II storage ring. The bare lattice case (no Damping Wigglers and Insertion devices) has been considered, due to the long transverse radiation damping time. To minimize the chromatic damping/antidamping from the slow-head tail effect, we used a short train of bunches distributed over consecutive rf-buckets with a high enough average current to obtain a good BPM signal. The vertical and horizontal betatron motion have been excited independently with pinger magnets. In this contribution we limit the discussion to the horizontal case.
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MOPMN025	Local Impedance Estimation of NSLS-II Storage Ring with Bumped Orbit	impedance, closed-orbit, wiggler, vacuum	754
	J. Choi, G. Bassi, A. Blednykh, Y. Hidaka BNL, Upton, Long Island, New York, USA
	Funding: DOE contract No: DE-AC02- 98CH10886 As the newly constructed 3rd generation light source, NSLS-II is expected to provide the synchrotron radiation of ultra high brightness and flux with advanced insertion devices. To minimize the beam emittance, damping wigglers are used and the small aperture is located at the straight section with the damping wiggler and the corresponding vacuum camber is NEG coated. We used the local bump method to find the effect on the beam from the narrow aperture and the paper shows the results.
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TUPJE065	Multi-Bunch Stability Analysis of the Advanced Photon Source Upgrade Including the Higher-Harmonic Cavity	HOM, impedance, simulation, radiation	1784
	L. Emery, T.G. Berenc, M. Borland, R.R. Lindberg ANL, Argonne, Ilinois, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be cured with more effective HOM damping or a longitudinal feedback system.
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TUPMA012	Developing an Improved Pulsed Mode Operation for Duke Storage Ring Based FEL	FEL, operation, wiggler, storage-ring	1860
	S.F. Mikhailov, H. Hao, V. Popov, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA
	Funding: This work is supported in part by the US DoE grant # DE-FG02-97ER41033 The Duke FEL and High Intensity Gamma-ray Source (HIGS) facility is operated with an e-beam from 0.24 to 1.2 GeV and a photon beam from 190 to 1060 nm. Currently, the energy range of the gamma-ray beam is from 1 MeV to about 100 MeV, with the maximum total gamma-ray flux about 3·10¹⁰ gammas per second around 10 MeV. The FEL is typically operated in quasi-CW mode. Some HIGS user experiments can benefit tremendously from a pulsed mode of FEL operation. For that purpose, a fast steering magnet was developed years ago to modulate the FEL gain. This FEL gain modulator decouples the e-beam from the FEL beam in the interaction region for most of time, but periodically allows a brief overlap of the electron and FEL beams. This allows us to build up a high peak power FEL pulse from a well-damped electron beam. However, the use of this gain modulator at low e-beam energies can dramatically limit e-beam current due to beam instability and poor injection. To overcome these shortcomings, we have successfully tested an RF frequency modulation technique to pulse the FEL beam. In this paper, we will describe this development, and report our preliminary results of this improved pulsed FEL operation.
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TUPTY022	Alternative Optics Design of the CLIC Damping Rings with Variable Dipole Bends and High-field Wigglers	emittance, wiggler, dipole, optics	2046
	P.S. Papadopoulou, F. Antoniou, Y. Papaphilippou CERN, Geneva, Switzerland
	The CLIC Damping Rings baseline design aims to reach an ultra-low horizontal normalised emittance of 500nm-rad at 2.86GeV, based on the combined effect of TME arc cells and high-field super-conducting damping wigglers, while keeping the ring as compact as possible. In this paper, an alternative design is described, based on TME cells with longitudinally variable bends and an optimized Nb3Sn high-field wiggler. The impact of these changes on ring optics parameters and the associated optimisation steps are detailed taking account the dominant effect of intrabeam scattering.
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TUPTY043	Analysis of Intensity-dependent Effects on LHC Transverse Tunes at Injection Energy	injection, operation, database, quadrupole	2108
	R. De Maria, M. Giovannozzi, T. Persson, R. Tomás CERN, Geneva, Switzerland Y. Wei IHEP, Beijing, People's Republic of China
	The LHC Run I has provided a huge amount of data that can be used to deepen the understanding of the beam behaviour. In this paper the focus is on the analysis of transverse tunes at injection energy to detect signs of intensity-dependent effects. BPM data, recording the injection oscillations of the operational beams during the ring-filling phase, have been analysed in detail to enable extracting useful information about the tune shift vs. injected beam intensity. The data processing and the results are discussed in detail, including also possible implications for future operation.
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TUPTY062	FCC-hh Hadron Collider - Parameter Scenarios and Staging Options	luminosity, operation, proton, radiation	2173
	M. Benedikt, B. Goddard, D. Schulte, F. Zimmermann CERN, Geneva, Switzerland M.J. Syphers NSCL, East Lansing, Michigan, USA M.J. Syphers Fermilab, Batavia, Illinois, USA
	FCC-hh is a proposed future energy-frontier hadron collider, based on dipole magnets with a field around 16 T installed in a new tunnel with a circumference of about 100 km, which would provide proton collisions at a centre-of-mass energy of 100 TeV, as well as heavy-ion collisions at the equivalent energy. The FCC-hh should deliver a high integrated proton-proton luminosity at the level of several 100 fb^-1 per year, or more. The challenges for operating FCC-hh with high beam current and at high luminosity include the heat load from synchrotron radiation in a cold environment, the radiation from collision debris around the interaction region, and machine protection. In this paper, starting from the FCC-hh design baseline parameters we explore different approaches for increasing the integrated luminosity, and discuss the impact of key individual parameters, such as the turnaround time. We also present some injector considerations and options for early hadron-collider operation.
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WEPMA004	A 250 Hz AC Scan Magnet for High-Power Radioisotope Production and BNCT Applications	target, power-supply, proton, insertion	2747
	M.P. Dehnel, J. Chu, C. Hollinger, A. Kilbourne-Quirk, D.E. Potkins, T.M. Stewart, S. Tranfo D-Pace, Nelson, British Columbia, Canada C. Philpott BSL, Auckland, New Zealand
	Funding: D-Pace acknowledges Canadian Government funding through SRED-CRA & NSERC-USRA, and through regional funding provided by KAST. This paper describes the proto-type magnet measurement results for a compact (212 mm, effective length) yet large gap (97 mm) ambient air-cooled laminated AC scan magnet. A large aperture is essential for machine safety in radioisotope production, and Boron Neutron Capture Therapy (BNCT) applications with steady-state beam power up to 50 kW . Rose shim and Purcell filter techniques are examined for improved transverse field flatness. The measured magnetic field and frequency response curves through a range from (250 Gauss, 70 Hertz) to (25 Gauss, 250 Hertz) are given for the case of an air-gap, SS316 beampipe, and SS316 bellows. Measured transverse and longitudinal magnetic field curves are also given. A model of the frequency response of the magnet was created and validated. The model simplifies power supply selection and maps the effects of system natural frequency on the magnetic field. Tests were conducted with and without a capacitor in parallel with the magnet coils. Lastly, algorithms for flat-topped square, and circular scanned beam intensity distributions are given. M.P. Dehnel et al, "A Specialized High-Power (50 kW) Proton Beamline for BNCT", Proc. of NA-PAC13, pp.116-118, Pasadena, CA, USA, Oct 2013.
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WEPMA013	Hom Damping Optimization Design Studies for BESSY VSR Cavities	HOM, cavity, impedance, SRF	2774
	A.V. Vélez, H.-W. Glock, J. Knobloch, A. Neumann HZB, Berlin, Germany
	The BESSY VSR project is a future upgrade of the 3rd generation BESSY II light source. By using the same "standard" user optics, simultaneously long (ca. 15ps) and short (ca. 1.5ps) bunches will be stored. Thus, superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. This work describes the optimizations studies for the Waveguide-based HOM dampers and the adjustable fundamental power coupler for the 1.5 GHz first SRF cavity prototype.
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WEPMA021	Efficient Pulsed Quadrupole	quadrupole, simulation, pulsed-power, operation	2799
	I.J. Petzenhauser, U. Blell, P.J. Spiller GSI, Darmstadt, Germany C. Tenholt IAP, Frankfurt am Main, Germany
	Funding: Work supported by EuCARD-2-WP03-EnEfficient. EuCARD-2 is co-funded by the partners and the European Commission under Capacities 7th Framework Programme, Grant Agreement 312453 In order to raise the focusing gradient in case of bunched beam lines, an alternative, iron free, pulsed quadrupole was designed. The transfer channels between synchrotrons as well as the final focusing for the production of secondary beams are possible applications. The quadrupole is running in a pulsed mode, which means an immense saving of energy by avoiding standby operation. Still the high gradients demand high currents. Hence a circuit had to be developed which is able to recover a significant amount of the pulsing energy for following shots. The basic design of the electrical circuit of the pulsed quadrupole is introduced. Furthermore more energy efficient circuits are presented and the limits of adaptability are considered.
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WEPMA026	Higher Order Mode Propagation and Damping Studies on Axisymmetric Superconducting Multicell RF-Resonators	cavity, factory, higher-order-mode, coupling	2812
	B.D. Isbarn, B. Riemann, M. Sommer, T. Weis DELTA, Dortmund, Germany
	Funding: Work supported by the BMBF under contract no. 05K13PEB Higher order mode (HOM) propagation and damping is a major concern in feasibility studies regarding the upcoming upgrade of BESSY II, named BESSY-VSR, which involves the utilization of superconducting multicell RF-resonators in a storage ring while maintaining a reasonably high beam current typical for third generation synchrotron radiation facilities. In addition to the computation of the typical figures of merit, we focus on studies of the mode propagation in axisymmetric structures. Due to the focus on axisymmetric studies we are able to use 2D codes to investigate in eigenmodes with substantial higher frequencies than usually considered with full 3D codes in parametric studies. In this work we present preliminary studies involving mode propagation in superconducting elliptical multicell cavities. G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014
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WEPMN046	Compassion of Higher Order Modes Damping Techniques for Superconducting 9-Cell Structure	HOM, quadrupole, cavity, dipole	3030
	Ya.V. Shashkov, A.A. Mitrofanov, N.P. Sobenin MEPhI, Moscow, Russia V. Zvyagintsev TRIUMF, Vancouver, Canada
	Funding: Work supported by Ministry of Education and Science grant 3.245.2014/r Modern types of accelerators, such as Energy recovery linacs, require low values of higher order modes (HOM) Qext. In accelerators with high current HOM could lead to high losses for the modes excitation, beam instability and beam break up. HOM couplers and waveguides are often used in such structures for HOM damping. Unfortunately they could lead to a violation of the axial symmetry of the accelerating field and negatively affect the beam emittance. Also these devices are subject for multipactor discharge and could be difficult in maintaining and fabrication. In this paper we examine several ways of HOM damping with ridged, fluted and corrugated drift tubes which are devoid of the above-mentioned drawbacks. The influence of the parameters of the drift tube on the HOM damping and on the parameters of the fundamental wave were analyzed. Higher order modes, ERL, SRF
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WEPMN047	Suppression of Higher Order Modes in an Array of Cavities Using Waveguides	HOM, impedance, cavity, wakefield	3033
	Ya.V. Shashkov, N.P. Sobenin MEPhI, Moscow, Russia M. Zobov INFN/LNF, Frascati (Roma), Italy
	Funding: Work is supported by Ministry of Education and Science grant 3.245.2014/r и and by the EU FP7 HiLumi LHC - Grant Agreement 284404 In the frameworks of the High Luminosity LHC upgrade program an application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussion. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between “warm” and “cold” parts of the collider vacuum chamber. Unfortunately it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. In this paper we describe the results obtained for arrays of 2, 4 and 8 cavities.
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WEPHA002	Electromagnetic Characterization of NEG Properties Above 200 GHz for the CLIC Damping Rings	simulation, impedance, network, electron	3097
	E. Koukovini-Platia, G. Iadarola, G. Rumolo, C. Zannini CERN, Geneva, Switzerland
	Non-Evaporable Getter (NEG) will be used in the CLIC electron damping rings (EDR) to suppress fast beam ion instabilities due to its effective pumping ability. The electromagnetic (EM) characterization of the NEG properties up to high frequencies is required for the correct impedance modeling of the DR components. The properties are determined using WR-3.4 and WR-1.5 rectangular waveguides, based on a combination of experimental measurements of the complex transmission coefficient S21 with a Vector Network Analyzer (VNA) and CST 3D EM simulations, for the frequency range of 220-330 GHz and 500-750 GHz. The results obtained using NEG-coated Aluminum (Al) waveguides are presented in this paper.
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WEPTY083	Five-cell Superconducting RF Module with a PBG Coupler Cell: Design and Cold Testing of the Copper Prototype	HOM, cavity, factory, impedance	3475
	S. Arsenyev, D.Y. Shchegolkov, E.I. Simakov LANL, Los Alamos, New Mexico, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA
	We report the design and experimental data for a copper prototype of a superconducting radio-frequency (SRF) accelerator module. The five-cell module has an incorporated photonic band gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better higher order mode (HOM) damping which is vital for preserving the quality of highcurrent electron beams. Better HOM damping raises the current threshold for beam instabilities in novel SRF accelerators. The PBG design also increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of on the beam pipe via complicated end assemblies. First, we will discuss the design and accelerating properties of the structure. The five-cell module was optimized to provide good HOM damping while maintaining the same accelerating properties as conventional elliptical-cell modules. We will then discuss the process of tuning the structure to obtain the desired accelerating gradient profile. Finally, we will list measured quality factors for the accelerating mode and the most dangerous HOMs.
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WEPWI004	FPC and Hi-Pass Filter HOM Coupler Design for the RF Dipole Crab Cavity for the LHC HiLumi Upgrade	HOM, cavity, dipole, coupling	3492
	Z. Li SLAC, Menlo Park, California, USA S.U. De Silva, J.R. Delayen, R.G. Olave, H. Park ODU, Norfolk, Virginia, USA
	Funding: Work partially supported by the US DOE through the US LHC Accelerator Research Program (LARP), and by US DOE under contract number DE-AC02-76SF00515. A 400-MHz compact RF dipole (RFD) crab cavity design was jointly developed by Old Dominion University and SLAC under the support of US LARP program for the LHC HiLumi upgrade. The RFD cavity design is consisted of a rounded-square tank and two ridged deflecting poles, operating with a TE11-like dipole mode, which is the lowest mode of the cavity. A prototype RFD cavity is being manufactured and will be tested on the SPS beam line at CERN. The coaxial fundamental Power Coupler (FPC) of the prototype cavity was re-optimized to minimizing the power heating on the coupler internal antenna. A hi-pass filter HOM damping coupler was developed to achieve the required wakefield damping while maintaining a compact size to fit into the beam line space. In this paper, we will discuss the details of the RF optimization and tolerance analyses of the FPC and HOM couplers.
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WEPWI039	Engineering Study of Crab Cavity HOM Couplers for LHC High Luminosity Upgrade	HOM, niobium, cavity, luminosity	3578
	H. Park, S.U. De Silva, J.R. Delayen, R.G. Olave ODU, Norfolk, Virginia, USA T. Capelli CERN, Geneva, Switzerland S.U. De Silva, J.R. Delayen, H. Park JLab, Newport News, Virginia, USA Z. Li SLAC, Menlo Park, California, USA T.H. Nicol Fermilab, Batavia, Illinois, USA N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	The LHC is planning to employ crab cavities for the high luminosity upgrade. Old Dominion University and SLAC National Laboratory are developing the crab cavity completed with the HOM damping couplers. The HOM couplers are coaxial type and perform over broad band up to 2 GHz. The amount of extracted power requires active cooling using liquid helium. The electromagnetic study has provided expected power dissipation on the coupler. Correlations between the fabrication tolerance and its damping performance have been studied and the results are providing guidelines on how to manufacture the HOM couplers. This paper summarizes the engineering studies; mechanical strength as a part of pressure system, thermal stability, and fabrication method to ensure the required tolerance.
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Paper

Title

Other Keywords

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MOYGB3

Commissioning of NSLS-II

insertion, insertion-device, emittance, lattice

11

F.J. Willeke
BNL, Upton, Long Island, New York, USA

NSLS-II, the new 3rd generation light source at BNL was designed for a brightness of 10²² photons s^-1 mm^-2 mrad^-2 (0.1%BW)^-1. It was constructed between 2009 and 2014. The storage ring was commissioned in April 2014 which was followed by insertion device and beamline commissioning in the fall of 2014. All ambitious design parameters of the facility have already been achieved except for commissioning the full beam intensity of 500 mA which requires more RF installation. This paper reports on the results of commissioning.

Slides MOYGB3 [3.884 MB]

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MOPWA001

Instability Thresholds and Tune Shift Estimation for Sirius

impedance, feedback, emittance, simulation

70

F.H. de Sá, L. Liu, N. Milas, X.R. Resende
LNLS, Campinas, Brazil

In this work we present the evaluation of longitudinal and transverse instability thresholds as well as tune shifts for Sirius using time and frequency domain codes that are being developed in-house and take into account various effects on the beam instability, such as bunch by bunch feedback system, quadrupolar impedances from undulator chambers and tune spreads.

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MOPWA011

The Damping of Transverse Coherent Instabilities by Harmonic Cavities

synchrotron, betatron, simulation, electron

102

F.J. Cullinan, R. Nagaoka
SOLEIL, Gif-sur-Yvette, France
G. Skripka, P.F. Tavares
MAX-lab, Lund, Sweden

At nonzero chromaticity, the threshold current due to transverse coupled bunch instabilities in an electron storage ring is defined by intrabunch head-tail motion of higher than zeroth order. Multibunch tracking simulations predict that this threshold can be increased to several times its original value through the introduction of bunch lengthening harmonic cavities. One previously suggested explanation is the narrower spectra of the elongated bunches but reliable estimates for the threshold currents are not obtainable for anything other than rigid beam motion since the usual Sacherer formulism is not directly applicable to beams in a non-harmonic potential. A new scheme has been developed in which the decay time of a higher than zeroth order transverse head-tail mode may be estimated by taking into account the synchrotron tune spread generated by the harmonic cavity potential. This scheme is presented along with the results of numerical simulations performed in order to confirm the analytical predictions and justify the assumptions made. The extension of the scheme to more complex scenarios is also discussed.

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MOPWA019

Status of the Robinson Wiggler Project at the Metrology Light Source

wiggler, dipole, radiation, dynamic-aperture

132

T. Goetsch, J. Feikes, M. Ries, G. Wüstefeld
HZB, Berlin, Germany

The beam lifetime in electron storage rings concerns machines running in decay mode as well as machines doing top-up. A standard procedure to increase the lifetime is via bunch lengthening as the lifetime depends on the electron density in the bunch. Bunch lengthening is typically achieved with higher harmonic (Landau) cavities. As noted in *, there are several advantages in using a different approach: it is possible to increase the bunch length by installing a Transverse Gradient (Robinson) Wiggler, which allows to transfer damping between the horizontal and the longitudinal plane. While increasing the bunch length, the horizontal emittance is being reduced yielding advantages regarding the source size depending on the magnet optics. At the Metrology Light Source, a primary source standard used by Germanys national metrology institute (Physikalisch-Technische Bundesanstalt)**, such a scheme is being investigated. The current state of the project including dynamic aperture effects and synchrotron radiation issues of the device is being presented in the following.
* T. Goetsch et al.,WEPRO028 in Proceedings of IPAC2014, Dresden (Germany), 2014
** R. Klein et al., Phys. Rev. ST-AB 11, 110701, 2008

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MOPWA022

Influence of Transient Beam Loading on the Longitudinal Beam Dynamics at BESSY VSR

beam-loading, synchrotron, simulation, cavity

141

M. Ruprecht, P. Goslawski, A. Jankowiak, A. Neumann, M. Ries, G. Wüstefeld
HZB, Berlin, Germany
T. Weis
DELTA, Dortmund, Germany

BESSY VSR, a scheme where 1.7 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring has recently been proposed *. The strong longitudinal bunch focusing is achieved by superconducting high gradient RF cavities. If the bunch fill pattern exhibits a significant inhomogeneity, e.g. due to gaps, transient beam loading causes a distortion of the longitudinal phase space which is different for each bunch. The result are variations along the fill pattern in synchronous phase, synchrotron frequency and bunch shape. This paper presents investigations of transient beam loading and depicts the consequences on bunch length, phase stability and longitudinal multi-bunch oscillations for the projected setup of BESSY VSR.
* G. Wüstefeld, A. Jankowiak, J. Knobloch, M. Ries, Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proceedings of IPAC2011, San Sebastián, Spain

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MOPWA034

Coupled-Bunch Instability Suppression Using RF Phase Modulation at the DELTA Storage Ring

synchrotron, storage-ring, electron, feedback

179

M. Sommer, M. Höner, B.D. Isbarn, S. Khan, B. Riemann, T. Weis
DELTA, Dortmund, Germany

Funding: Work supported by the BMBF under contract no. 05K13PEB
The upcoming upgrade of BESSY II, called BESSY-VSR*, involves the utilization of superconducting multicell RF-resonators with high accelerating gradients to provide short and long bunches in an electron storage ring simultaneously. Even under the assumption of strongest available damping of beam induced modes, the residual impedances of the cavities may cause collective multibunch instabilities at the frontier of stability available from current bunch-by-bunch feedback systems. At the DELTA electron storage ring, a phase modulation of the driving RF is used to suppress coupled-bunch instabilities and to increase the lifetime. The time dependent frequency variation in the order of the synchrotron frequency gives rise to additional damping of the bunch oscillators by decoherence and Landau damping. The behaviour and the additional damping of the bunch oscillators is investigated by the existing bunch-by-bunch feedback system e.g. the increase of the overall damping might support the capability of feedback systems under extreme operating conditions of BESSY-VSR.
* G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014

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MOPJE036

Longitudinal Impedance Characterization of the CERN SPS Vacuum Flanges

impedance, resonance, vacuum, simulation

363

J.V. Campelo
CERN, Geneva, Switzerland

This contribution describes the thorough studies carried out to characterize the longitudinal impedance of the CERN SPS vacuum flanges, which are believed to be the main source of LHC beam instability. Around 500 high-impedance flanges of 8 different types have been identified. Three factors play an important role in the characterization of these flanges: the type of vacuum chambers that the flange interconnects, whether or not both sides are electrically isolated (by means of an enamel coating) and, finally, the presence of damping resistors which damp high-Q resonances. Not only, full-wave electromagnetic field simulations, but also RF measurements have been used to evaluate the impedance of these elements. The R/Q of the relevant resonances was measured using the well-known bead-pull technique. In particular, a subset of around 150 flanges has been found to be the source of a high-impedance resonance at 1.4 GHz, also observed in beam measurements. Guidelines on how to reduce the impedance of these elements are also presented.

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MOPJE037

Study and Comparison of Mode Damping Strategies for the UA9 Cherenkov Detector Tank

cavity, vacuum, detector, resonance

366

A. Danisi, F. Caspers, R. Losito, A. Masi, B. Salvant, C. Vollinger
CERN, Geneva, Switzerland
T. Demma, P. Lepercq
LAL, Orsay, France

In the framework of the UA9 experiment, the Cherenkov detector is useful to measure the amount of particles deflected by a bent crystal, proving the crystal collimation principle. The tank used to host this device is taken as a case study for an in-depth analysis of different damping strategies for electromagnetic modes which otherwise would give rise to important beam-coupling impedance contributions. Such strategies involve the use of ferrite, damping resistors and a mode-coupler, a solution which intercepts the modes inside the cavity but damps the related power outside the vacuum tank (potentially avoiding heating). Such solutions are discussed through experimental measurements and the relative quality factor is taken as a figure of merit.

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MOPJE065

Contribution of Optical Aberrations to Spot-size Increase with Bunch Intensity at ATF2

emittance, optics, extraction, simulation

455

M. Patecki, R. Tomás, F. Zimmermann
CERN, Geneva, Switzerland
K. Kubo, S. Kuroda, T. Naito, T. Okugi, T. Tauchi, N. Terunuma
KEK, Ibaraki, Japan
M. Patecki
Warsaw University of Technology, Warsaw, Poland
G.R. White
SLAC, Menlo Park, California, USA

A primary goal of ATF2 (Accelerator Test Facility) is to demonstrate a low vertical beam size at the interaction point (IP) of about 37 nm. Measurements over the past years indicate that the ATF2 vertical beam size strongly rises with bunch intensity. Several different origins of this increase are considered, e.g. wakefields occurring between the ATF damping ring and the IP, and/or intrabeam scattering (IBS) causing the increase of transverse emittances and energy spread in the damping ring with the increase of the bunch intensity. In this paper we address the second possibility. Past measurements and simulations of the IBS effects in the ATF are used to model the intensity-dependent initial emittances and energy spread at the entrance of the final focus. Particle tracking simulations predict the IP vertical beam size growth expected from the known optical aberrations for initial beam parameters corresponding to varying bunch intensities. Comparing simulation results with emittance measurements at different locations allows us to draw some conclusions about the impact of IBS in the damping ring on the IP spot size, and about possible single-bunch wakefields in the ATF2.

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MOPMA017

Numerical simulations of transverse modes in Gaussian bunches with space charge

space-charge, simulation, lattice, synchrotron

575

A. Macridin, J.F. Amundson, E.G. Stern
Fermilab, Batavia, Illinois, USA

The transverse modes and the intrinsic Landau damping in Gaussian bunched beams with space charge are numerically investigated. The evolution of the phase space density is calculated with the Synergia accelerator modeling package and analyzed with Dynamic Mode Decomposition (DMD) method. DMD is a relatively new technique used to calculate mode dynamics in both linear and nonlinear systems. The properties of the first three space charge modes, including their shape, damping rates and tune shifts are calculated over the entire range of the space charge interaction.

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MOPMA025

CSR Induced Microbunching Gain Estimation including Transient Effects in Transport and Recirculation Arcs

impedance, dipole, lattice, simulation

596

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
D. Douglas, R. Li, C. Tennant
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in the microbunching instability (μBI). To accurately quantify the direct consequence of this effect, we further extend our previously developed semi-analytical simulation [C. -Y. Tsai et al., FEL Conference 2014 (THP022)] to include more relevant coherent radiation models than the steady-state free-space CSR impedance, such as the entrance and exit transient effects, which derive from upstream beam entering to and exiting from individual dipoles and propagating across the elements to downstream straight sections. Then we semi-analytically solve the linearized Vlasov equation for the amplification factor. The resultant gain functions and spectra for our example lattices are presented and compared with particle tracking simulation. Some underlying physics with inclusion of these effects are also discussed.

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MOPMA060

Impedance Measurement for the SPEAR3 Storage Ring

impedance, lattice, storage-ring, vacuum

694

X. Huang, J.J. Sebek
SLAC, Menlo Park, California, USA

We studied the transverse impedance of the SPEAR3 storage ring with tune shift vs. beam intensity, head-tail instability and transverse mode coupling instability measurements. By taking measurements under different machine conditions, we probed the frequency dependence of the impedance, from which an impedance model was built. This model is consistent with instability measurements and previous bunch lengthening results.

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MOPMN008

Space Charge Studies in FFAG Using the Tracking Code Zgoubi

space-charge, emittance, simulation, betatron

717

M. Haj Tahar, F. Méot, N. Tsoupas
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 method is implemented in Zgoubi that allows the computation of space charge effects in 2D distributions and with some restrictions in 3D distributions. It relies on decomposiing field maps or analytical elements into slices and applying a space charge kick to the particles. The aim of this study is to investigate the accuracy of this technique, its limitations/advantages by comparisons with other linear/nonlinear computation methods and codes, and to apply it to high power fixed field ring design studies.

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MOPMN016

Decoherence due to Second Order Chromaticity in the NSLS-II Storage Ring

betatron, synchrotron, storage-ring, lattice

737

G. Bassi, A. Blednykh, J. Choi, V.V. Smaluk
BNL, Upton, Long Island, New York, USA

We study decoherence effects due to second order chromaticity for small amplitude kicks, in order to estimate the energy spread from TbT data of the NSLS-II storage ring. The bare lattice case (no Damping Wigglers and Insertion devices) has been considered, due to the long transverse radiation damping time. To minimize the chromatic damping/antidamping from the slow-head tail effect, we used a short train of bunches distributed over consecutive rf-buckets with a high enough average current to obtain a good BPM signal. The vertical and horizontal betatron motion have been excited independently with pinger magnets. In this contribution we limit the discussion to the horizontal case.

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MOPMN025

Local Impedance Estimation of NSLS-II Storage Ring with Bumped Orbit

impedance, closed-orbit, wiggler, vacuum

754

J. Choi, G. Bassi, A. Blednykh, Y. Hidaka
BNL, Upton, Long Island, New York, USA

Funding: DOE contract No: DE-AC02- 98CH10886
As the newly constructed 3rd generation light source, NSLS-II is expected to provide the synchrotron radiation of ultra high brightness and flux with advanced insertion devices. To minimize the beam emittance, damping wigglers are used and the small aperture is located at the straight section with the damping wiggler and the corresponding vacuum camber is NEG coated. We used the local bump method to find the effect on the beam from the narrow aperture and the paper shows the results.

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TUPJE065

Multi-Bunch Stability Analysis of the Advanced Photon Source Upgrade Including the Higher-Harmonic Cavity

HOM, impedance, simulation, radiation

1784

L. Emery, T.G. Berenc, M. Borland, R.R. Lindberg
ANL, Argonne, Ilinois, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be cured with more effective HOM damping or a longitudinal feedback system.

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TUPMA012

Developing an Improved Pulsed Mode Operation for Duke Storage Ring Based FEL

FEL, operation, wiggler, storage-ring

1860

S.F. Mikhailov, H. Hao, V. Popov, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA

Funding: This work is supported in part by the US DoE grant # DE-FG02-97ER41033
The Duke FEL and High Intensity Gamma-ray Source (HIGS) facility is operated with an e-beam from 0.24 to 1.2 GeV and a photon beam from 190 to 1060 nm. Currently, the energy range of the gamma-ray beam is from 1 MeV to about 100 MeV, with the maximum total gamma-ray flux about 3·10¹⁰ gammas per second around 10 MeV. The FEL is typically operated in quasi-CW mode. Some HIGS user experiments can benefit tremendously from a pulsed mode of FEL operation. For that purpose, a fast steering magnet was developed years ago to modulate the FEL gain. This FEL gain modulator decouples the e-beam from the FEL beam in the interaction region for most of time, but periodically allows a brief overlap of the electron and FEL beams. This allows us to build up a high peak power FEL pulse from a well-damped electron beam. However, the use of this gain modulator at low e-beam energies can dramatically limit e-beam current due to beam instability and poor injection. To overcome these shortcomings, we have successfully tested an RF frequency modulation technique to pulse the FEL beam. In this paper, we will describe this development, and report our preliminary results of this improved pulsed FEL operation.

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TUPTY022

Alternative Optics Design of the CLIC Damping Rings with Variable Dipole Bends and High-field Wigglers

emittance, wiggler, dipole, optics

2046

P.S. Papadopoulou, F. Antoniou, Y. Papaphilippou
CERN, Geneva, Switzerland

The CLIC Damping Rings baseline design aims to reach an ultra-low horizontal normalised emittance of 500nm-rad at 2.86GeV, based on the combined effect of TME arc cells and high-field super-conducting damping wigglers, while keeping the ring as compact as possible. In this paper, an alternative design is described, based on TME cells with longitudinally variable bends and an optimized Nb3Sn high-field wiggler. The impact of these changes on ring optics parameters and the associated optimisation steps are detailed taking account the dominant effect of intrabeam scattering.

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TUPTY043

Analysis of Intensity-dependent Effects on LHC Transverse Tunes at Injection Energy

injection, operation, database, quadrupole

2108

R. De Maria, M. Giovannozzi, T. Persson, R. Tomás
CERN, Geneva, Switzerland
Y. Wei
IHEP, Beijing, People's Republic of China

The LHC Run I has provided a huge amount of data that can be used to deepen the understanding of the beam behaviour. In this paper the focus is on the analysis of transverse tunes at injection energy to detect signs of intensity-dependent effects. BPM data, recording the injection oscillations of the operational beams during the ring-filling phase, have been analysed in detail to enable extracting useful information about the tune shift vs. injected beam intensity. The data processing and the results are discussed in detail, including also possible implications for future operation.

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TUPTY062

FCC-hh Hadron Collider - Parameter Scenarios and Staging Options

luminosity, operation, proton, radiation

2173

M. Benedikt, B. Goddard, D. Schulte, F. Zimmermann
CERN, Geneva, Switzerland
M.J. Syphers
NSCL, East Lansing, Michigan, USA
M.J. Syphers
Fermilab, Batavia, Illinois, USA

FCC-hh is a proposed future energy-frontier hadron collider, based on dipole magnets with a field around 16 T installed in a new tunnel with a circumference of about 100 km, which would provide proton collisions at a centre-of-mass energy of 100 TeV, as well as heavy-ion collisions at the equivalent energy. The FCC-hh should deliver a high integrated proton-proton luminosity at the level of several 100 fb^-1 per year, or more. The challenges for operating FCC-hh with high beam current and at high luminosity include the heat load from synchrotron radiation in a cold environment, the radiation from collision debris around the interaction region, and machine protection. In this paper, starting from the FCC-hh design baseline parameters we explore different approaches for increasing the integrated luminosity, and discuss the impact of key individual parameters, such as the turnaround time. We also present some injector considerations and options for early hadron-collider operation.

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WEPMA004

A 250 Hz AC Scan Magnet for High-Power Radioisotope Production and BNCT Applications

target, power-supply, proton, insertion

2747

M.P. Dehnel, J. Chu, C. Hollinger, A. Kilbourne-Quirk, D.E. Potkins, T.M. Stewart, S. Tranfo
D-Pace, Nelson, British Columbia, Canada
C. Philpott
BSL, Auckland, New Zealand

Funding: D-Pace acknowledges Canadian Government funding through SRED-CRA & NSERC-USRA, and through regional funding provided by KAST.
This paper describes the proto-type magnet measurement results for a compact (212 mm, effective length) yet large gap (97 mm) ambient air-cooled laminated AC scan magnet. A large aperture is essential for machine safety in radioisotope production, and Boron Neutron Capture Therapy (BNCT) applications with steady-state beam power up to 50 kW *. Rose shim and Purcell filter techniques are examined for improved transverse field flatness. The measured magnetic field and frequency response curves through a range from (250 Gauss, 70 Hertz) to (25 Gauss, 250 Hertz) are given for the case of an air-gap, SS316 beampipe, and SS316 bellows. Measured transverse and longitudinal magnetic field curves are also given. A model of the frequency response of the magnet was created and validated. The model simplifies power supply selection and maps the effects of system natural frequency on the magnetic field. Tests were conducted with and without a capacitor in parallel with the magnet coils. Lastly, algorithms for flat-topped square, and circular scanned beam intensity distributions are given.
* M.P. Dehnel et al, "A Specialized High-Power (50 kW) Proton Beamline for BNCT", Proc. of NA-PAC13, pp.116-118, Pasadena, CA, USA, Oct 2013.

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WEPMA013

Hom Damping Optimization Design Studies for BESSY VSR Cavities

HOM, cavity, impedance, SRF

2774

A.V. Vélez, H.-W. Glock, J. Knobloch, A. Neumann
HZB, Berlin, Germany

The BESSY VSR project is a future upgrade of the 3rd generation BESSY II light source. By using the same "standard" user optics, simultaneously long (ca. 15ps) and short (ca. 1.5ps) bunches will be stored. Thus, superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. This work describes the optimizations studies for the Waveguide-based HOM dampers and the adjustable fundamental power coupler for the 1.5 GHz first SRF cavity prototype.

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WEPMA021

Efficient Pulsed Quadrupole

quadrupole, simulation, pulsed-power, operation

2799

I.J. Petzenhauser, U. Blell, P.J. Spiller
GSI, Darmstadt, Germany
C. Tenholt
IAP, Frankfurt am Main, Germany

Funding: Work supported by EuCARD-2-WP03-EnEfficient. EuCARD-2 is co-funded by the partners and the European Commission under Capacities 7th Framework Programme, Grant Agreement 312453
In order to raise the focusing gradient in case of bunched beam lines, an alternative, iron free, pulsed quadrupole was designed. The transfer channels between synchrotrons as well as the final focusing for the production of secondary beams are possible applications. The quadrupole is running in a pulsed mode, which means an immense saving of energy by avoiding standby operation. Still the high gradients demand high currents. Hence a circuit had to be developed which is able to recover a significant amount of the pulsing energy for following shots. The basic design of the electrical circuit of the pulsed quadrupole is introduced. Furthermore more energy efficient circuits are presented and the limits of adaptability are considered.

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WEPMA026

Higher Order Mode Propagation and Damping Studies on Axisymmetric Superconducting Multicell RF-Resonators

cavity, factory, higher-order-mode, coupling

2812

B.D. Isbarn, B. Riemann, M. Sommer, T. Weis
DELTA, Dortmund, Germany

Funding: Work supported by the BMBF under contract no. 05K13PEB
Higher order mode (HOM) propagation and damping is a major concern in feasibility studies regarding the upcoming upgrade of BESSY II, named BESSY-VSR*, which involves the utilization of superconducting multicell RF-resonators in a storage ring while maintaining a reasonably high beam current typical for third generation synchrotron radiation facilities. In addition to the computation of the typical figures of merit, we focus on studies of the mode propagation in axisymmetric structures. Due to the focus on axisymmetric studies we are able to use 2D codes to investigate in eigenmodes with substantial higher frequencies than usually considered with full 3D codes in parametric studies. In this work we present preliminary studies involving mode propagation in superconducting elliptical multicell cavities.
* G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014

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WEPMN046

Compassion of Higher Order Modes Damping Techniques for Superconducting 9-Cell Structure

HOM, quadrupole, cavity, dipole

3030

Ya.V. Shashkov, A.A. Mitrofanov, N.P. Sobenin
MEPhI, Moscow, Russia
V. Zvyagintsev
TRIUMF, Vancouver, Canada

Funding: Work supported by Ministry of Education and Science grant 3.245.2014/r
Modern types of accelerators, such as Energy recovery linacs, require low values of higher order modes (HOM) Qext. In accelerators with high current HOM could lead to high losses for the modes excitation, beam instability and beam break up. HOM couplers and waveguides are often used in such structures for HOM damping. Unfortunately they could lead to a violation of the axial symmetry of the accelerating field and negatively affect the beam emittance. Also these devices are subject for multipactor discharge and could be difficult in maintaining and fabrication. In this paper we examine several ways of HOM damping with ridged, fluted and corrugated drift tubes which are devoid of the above-mentioned drawbacks. The influence of the parameters of the drift tube on the HOM damping and on the parameters of the fundamental wave were analyzed.
Higher order modes, ERL, SRF

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WEPMN047

Suppression of Higher Order Modes in an Array of Cavities Using Waveguides

HOM, impedance, cavity, wakefield

3033

Ya.V. Shashkov, N.P. Sobenin
MEPhI, Moscow, Russia
M. Zobov
INFN/LNF, Frascati (Roma), Italy

Funding: Work is supported by Ministry of Education and Science grant 3.245.2014/r и and by the EU FP7 HiLumi LHC - Grant Agreement 284404
In the frameworks of the High Luminosity LHC upgrade program an application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussion. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between “warm” and “cold” parts of the collider vacuum chamber. Unfortunately it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. In this paper we describe the results obtained for arrays of 2, 4 and 8 cavities.

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WEPHA002

Electromagnetic Characterization of NEG Properties Above 200 GHz for the CLIC Damping Rings

simulation, impedance, network, electron

3097

E. Koukovini-Platia, G. Iadarola, G. Rumolo, C. Zannini
CERN, Geneva, Switzerland

Non-Evaporable Getter (NEG) will be used in the CLIC electron damping rings (EDR) to suppress fast beam ion instabilities due to its effective pumping ability. The electromagnetic (EM) characterization of the NEG properties up to high frequencies is required for the correct impedance modeling of the DR components. The properties are determined using WR-3.4 and WR-1.5 rectangular waveguides, based on a combination of experimental measurements of the complex transmission coefficient S21 with a Vector Network Analyzer (VNA) and CST 3D EM simulations, for the frequency range of 220-330 GHz and 500-750 GHz. The results obtained using NEG-coated Aluminum (Al) waveguides are presented in this paper.

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WEPTY083

Five-cell Superconducting RF Module with a PBG Coupler Cell: Design and Cold Testing of the Copper Prototype

HOM, cavity, factory, impedance

3475

S. Arsenyev, D.Y. Shchegolkov, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA

We report the design and experimental data for a copper prototype of a superconducting radio-frequency (SRF) accelerator module. The five-cell module has an incorporated photonic band gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better higher order mode (HOM) damping which is vital for preserving the quality of highcurrent electron beams. Better HOM damping raises the current threshold for beam instabilities in novel SRF accelerators. The PBG design also increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of on the beam pipe via complicated end assemblies. First, we will discuss the design and accelerating properties of the structure. The five-cell module was optimized to provide good HOM damping while maintaining the same accelerating properties as conventional elliptical-cell modules. We will then discuss the process of tuning the structure to obtain the desired accelerating gradient profile. Finally, we will list measured quality factors for the accelerating mode and the most dangerous HOMs.

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WEPWI004

FPC and Hi-Pass Filter HOM Coupler Design for the RF Dipole Crab Cavity for the LHC HiLumi Upgrade

HOM, cavity, dipole, coupling

3492

Z. Li
SLAC, Menlo Park, California, USA
S.U. De Silva, J.R. Delayen, R.G. Olave, H. Park
ODU, Norfolk, Virginia, USA

Funding: Work partially supported by the US DOE through the US LHC Accelerator Research Program (LARP), and by US DOE under contract number DE-AC02-76SF00515.
A 400-MHz compact RF dipole (RFD) crab cavity design was jointly developed by Old Dominion University and SLAC under the support of US LARP program for the LHC HiLumi upgrade. The RFD cavity design is consisted of a rounded-square tank and two ridged deflecting poles, operating with a TE11-like dipole mode, which is the lowest mode of the cavity. A prototype RFD cavity is being manufactured and will be tested on the SPS beam line at CERN. The coaxial fundamental Power Coupler (FPC) of the prototype cavity was re-optimized to minimizing the power heating on the coupler internal antenna. A hi-pass filter HOM damping coupler was developed to achieve the required wakefield damping while maintaining a compact size to fit into the beam line space. In this paper, we will discuss the details of the RF optimization and tolerance analyses of the FPC and HOM couplers.

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WEPWI039

Engineering Study of Crab Cavity HOM Couplers for LHC High Luminosity Upgrade

HOM, niobium, cavity, luminosity

3578

H. Park, S.U. De Silva, J.R. Delayen, R.G. Olave
ODU, Norfolk, Virginia, USA
T. Capelli
CERN, Geneva, Switzerland
S.U. De Silva, J.R. Delayen, H. Park
JLab, Newport News, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
T.H. Nicol
Fermilab, Batavia, Illinois, USA
N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

The LHC is planning to employ crab cavities for the high luminosity upgrade. Old Dominion University and SLAC National Laboratory are developing the crab cavity completed with the HOM damping couplers. The HOM couplers are coaxial type and perform over broad band up to 2 GHz. The amount of extracted power requires active cooling using liquid helium. The electromagnetic study has provided expected power dissipation on the coupler. Correlations between the fabrication tolerance and its damping performance have been studied and the results are providing guidelines on how to manufacture the HOM couplers. This paper summarizes the engineering studies; mechanical strength as a part of pressure system, thermal stability, and fabrication method to ensure the required tolerance.

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