IPAC2018 - List of Keywords (coupling)

Paper	Title	Other Keywords	Page
MOPMF010	Measurement and Simulation of Betatron Coupling Beam Transfer Function in RHIC	betatron, simulation, experiment, quadrupole	99
	Y. Luo, W. Fischer, A. Marusic, M.G. Minty 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. Transfer function measurements are important for characterizing betatron tunes, betatron coupling, and beam spectrum in the routine operation of the Relativistic Heavy Ion Collider (RHIC). To counteract the linear betatron coupling, we developed a technique to continuously measure the betatron coupling coefficient with a base band phase lock loop tune meter in 2006. Based on this technique, we demonstrated and built a robust tune/coupling feedback in RHIC. In this article, we revisit the BTF measurement with betatron coupling to benchmark our BTF simulation code. We also compared the values of eigenmode projection ratios from BTF with those calculated with the single particle model.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF010
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MOPMF020	Higher Order Mode Coupling Options for the eRHIC Crab Cavity	cavity, HOM, damping, impedance	121
	Q. Wu, I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: This work was supported by the US Department of Energy via Brookhaven Science Associates LLC under contract no. DE-SC0012704. The eRHIC crab cavity adopts the double quarter wave structure developed at Brookhaven National Lab for the LHC Hi-Lumi upgrade crab cavities. The cavity's fundamental mode is at 338 MHz with the first higher order mode more than 180 MHz above that. We looked into the higher order mode distribution up to 2 GHz, and considered various locations and geometries of the coupling scheme. The cylindrical outer shell of the cavity allowed various possibilities for coupler port openings on all the walls, which were difficult for the narrow waist of the LHC double quarter wave crab cavities. Beam pipe absorbers are also options for simpler high frequency modes damping. Some preliminary high pass filter design will also be discussed in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF020
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MOPMF023	Updates on the Optic Corrections of FCC-hh	quadrupole, injection, dipole, interaction-region	133
	D. Boutin, A. Chancé, B. Dalena CEA/IRFU, Gif-sur-Yvette, France B.J. Holzer, D. Schulte CERN, Geneva, Switzerland
	The FCC-hh (Future Hadron-Hadron Circular Collider) is one of the options considered for the next generation accelerator in high-energy physics as recommended by the European Strategy Group, and the natural evolution of existing LHC. The evaluation of the various magnets mechanical error and field error tolerances in the arc sections of FCC-hh, as well as an estimation of the correctors strengths necessary to perform the error corrections, are important aspects of the collider design. In this study recommended values for the mechanical errors, dipole and quadrupole field errors tolerances are proposed, with the possible consequences on the correctors technological choice and on the beam screen design. Advanced correction schemes of the linear coupling (with skew quadrupoles) and of the beam tunes (with normal quadrupoles) are discussed. Also a combined correction scheme including the interaction regions is tested.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF023
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MOPMF030	Broadband Impedance of Pumping Holes and Interconnects in the FCC-hh Beamscreen	impedance, wakefield, electronics, injection	153
	S. Arsenyev, D. Schulte CERN, Geneva, Switzerland
	In the proposed Future Circular Collider (FCC-hh) pumping holes and interconnects between sections of the beamscreen can be sources of unwanted broadband impedance, potentially leading to the transverse mode coupling instability (TMCI). The pumping holes pose a greater challenge to the impedance calculation due to their small contribution per hole. Unlike for the Large Hadron Collider (LHC), analytical methods cannot be applied due to the complex beamscreen geometry and the greater size of the holes. Instead, two computational methods are used and compared to each other. For the interconnects, the impedance due to a sophisticated system of tapers is also estimated using computational methods.
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MOPMF031	Modelling Wake Impedance of a Rough Surface in Application to the FCC-hh Beamscreen	impedance, electron, laser, vacuum	157
	S. Arsenyev, D. Schulte CERN, Geneva, Switzerland
	The inner surface of the future circular collider (FCC-hh) beamscreen is proposed to be laser-treated in order to mitigate the electron cloud build-up. However, the rough structure of the treated surface can result in unwanted impedance increase, potentially leading to the transverse mode coupling instability (TMCI). Three models have been adopted to estimate the wake impedance of a beamscreen with a rough surface. The models use the resistive wall formalism generalized for the case of an arbitrary surface impedance. The results apply to a beamscreen of a circular cross-section with the homogeneously rough inner surface for the case of ultrarelativistic particles. The free parameters of the models were fit into preliminary measurements of the surface resistivity, giving, as a result, a range of the real and the imaginary parts of the wake impedance.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF031
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MOPMF032	Nonlinear Correction Strategies for the LHC Using Resonance Driving Terms	resonance, dipole, optics, insertion	161
	F.S. Carlier, E.H. Maclean, T. Persson, R. Tomás CERN, Geneva, Switzerland
	The correction of nonlinearities in future colliders is critical to reach operational conditions and pose a significant challenge for commissioning schemes. Several approaches have been succesfully used in the LHC to correct sextupolar and octupolar sources in the LHC insertion regions. Measurements of resonance driving terms at top energy in the LHC have improved and now offer a new observable to calculate and validate nonlinear corrections. This paper reports on measurements of resonance driving terms in the LHC and the relevant strategies used for nonlinear corrections.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF032
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MOPMF046	Simulation of Hydrodynamic Tunneling Caused by High Energy Proton Beam in Copper through Coupling of FLUKA and Autodyn	target, simulation, proton, collider	204
	Y.C. Nie, A. Bertarelli, F. Carra, C. Fichera, L.K. Mettler, R. Schmidt, D. Wollmann CERN, Geneva, Switzerland
	For machine protection of high-energy colliders, it is important to assess potential damages caused to accelerator components in case large number of bunches are lost at the same place. The numerical assessment requires an iterative execution of an energy-deposition code and a hydrodynamic code, since the hydrodynamic tunneling effect will likely play an important role in the beam-matter interactions. For proton accelerators at CERN and for the Future Circular Collider (FCC), case studies were performed, coupling FLUKA and BIG2. To compare different hydrocodes and not to rely only on BIG2, FLUKA and a commercial tool, Autodyn, have been used to perform these simulations. This paper reports a benchmarking study against a beam test performed at the HiRadMat (High-Radiation to Materials) facility using beams at 440 GeV from the Super Proton Synchrotron. Good agreement has been found between the simulation results and the test as well as previous simulations with FLUKA and BIG2, particularly in terms of penetration depth of the beam in copper. This makes the coupling of FLUKA and Autodyn an alternative solution to simulating the hydrodynamic tunneling. More case studies are planned for FCC and other high-beam-power accelerators.
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MOPMF047	Transverse Coupling Measurements With High Intensity Beams Using Driven Oscillations	dipole, injection, controls, resonance	208
	T. Persson, G. Baud, X. Buffat, J.M. Coello de Portugal, E. Fol, K. Fuchsberger, M. Gabriel, M. Gąsior, M. Giovannozzi, G.H. Hemelsoet, M. Hostettler, M. Hruska, D. Jacquet, E.H. Maclean, L. Malina, J. Olexa, P.K. Skowroński, M. Solfaroli Camillocci, M.E. Söderén, R. Tomás, D. Valuch, A. Wegscheider, J. Wenninger CERN, Geneva, Switzerland
	Transverse coupling has been linked to instabilities and reduction in dynamic aperture and is hence a crucial parameter to control in the LHC. In this article we describe the development to use driven oscillations to measure the transverse coupling with high intensity beams. The method relies on the use of the transverse damper to drive an oscillation in a similar way as with an AC-dipole. The calculation of the coupling is based on the turn-by-turn data from all available BPMs gated for the excited bunch.
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MOPMF071	Polarization Studies for the eRHIC electron Storage Ring	polarization, storage-ring, electron, solenoid	292
	E. Gianfelice-Wendt Fermilab, Batavia, Illinois, USA S. Tepikian BNL, Upton, Long Island, New York, USA
	Funding: Manuscript authored by Fermi Res. All., LLC under Contr. No. DE-AC02-07CH11359 and Brookhaven Sc. Ass., LLC under Contr. No. DE-AC02-98CH10886 with the U.S. DOE, Office of Science, Office of HEP. A hadron/lepton collider with polarized beams has been under consideration by the scientific community since some years, in the U.S. and Europe. Among the various proposals, those by JLAB and BNL with polarized electron and proton beams are currently under closer study in the U.S. Experimenters call for the simultaneous storage of electron bunches with both spin helicity. In the BNL based Ring-Ring design, electrons are stored at top energy in a ring to be accommodated in the existing RHIC tunnel. The transversely polarized electron beam is injected into the storage ring at variable energies, between 5 and 18 GeV. Polarization is brought into the longitudinal direction at the IP by a couple of spin rotators. In this paper results of first studies of the attainable beam polarization level and lifetime in the storage ring at 18 GeV are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF071
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MOPML015	Simulations and Measurements of the CCL Modules of the LIGHT Accelerator	linac, proton, GUI, cavity	429
	V. F. Khan, G. De Michele, S. Fanella, S. H. Gibson, Ye. Ivanisenko, C. Mellace, J.L. Navarro Quirante, C. Zannini AVO-ADAM, Meyrin, Switzerland M. Esposito, P. Gradassi CERN, Geneva, Switzerland
	A 230 MeV proton LINAC system for medical applications is being developed and commissioned for the LIGHT (Linac Image Guided Hadron Therapy) project by AVO-ADAM. The LINAC system consists of a 750 MHz RFQ (Radio frequency quadrupole) for the low energy proton acceleration, 2998 MHz SCDTL (Side Coupled Drift Tube Linacs) for the medium energy and 2998 MHz CCL (Coupled Cavity Linacs) for the high energy. In particular, the CCL accelerating modules are used in the energy range from 37.5 - 230 MeV. In this paper we discuss the 3D EM (electro-magnetic) simulation results and measurements of the CCL modules.
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MOPML067	9/6 MeV European S-band Linac Structure for Container Inspection System at RTX and KAERI	electron, linac, bunching, gun	560
	P. Buaphad, H.D. Park, S. Song RTX, Daejeon, Republic of Korea P. Buaphad, Y. Joo University of Science and Technology of Korea (UST), Daejeon, Republic of Korea P. Buaphad, S.C. Cha, Y. Joo, Y. Kim, H.R. Lee KAERI, Jeongeup-si, Republic of Korea
	Recently, demands on low energy electron linear accelerators (linacs) for industrial applications are rapidly growing. Their beam energies are lower than 20 MeV, and they require a compact, cheap, and stable accelerator system. For the Container Inspection System (CIS), KAERI successfully developed a 9/6 MeV American S-band (= 2856 MHz) linac with a 5 MW klystron in 2013. To reduce the cost of the RF source, recently, KAERI and RTX also have been developing another 9/6 MeV European S-band (= 2998 MHz) linac by using a magnetron with a lower RF power of about 3.1 MW. Its accelerating structure is designed to be operated in π/2 mode by coupling 13 accelerating cells together through 12 side-coupling cells. The CST Microwave Studio is used for electromagnetic simulations and optimization of the accelerating structure. After various optimizations, a shunt impedance of 84 MΩ/m is obtained at π/2 mode frequency of 2998.31 MHz. In this paper, we describe design concept, optimization, and RF measurement of the new 9/6 MeV European S-band linac structure. Then, we compare it with our old American S-band linac structure.
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TUPAF024	Impedance and Instability Studies in LEIR with Xenon	impedance, space-charge, accumulation, injection	720
	N. Biancacci, H. Bartosik, M. Gąsior, S. Hirlaender, V. Kain, T.E. Levens, E. Métral CERN, Geneva, Switzerland M. Migliorati Rome University La Sapienza, Roma, Italy
	In 2017, the LEIR accelerator has been operated with Xe³⁹⁺ beam for fixed target experiments in the SPS North Area. The different ion species, with respect to the usually operated Pb⁵⁴⁺, allowed for additional comparative measurements of tune shift versus intensity at injection energy both in coasting and bunched beams. The fast transverse instability observed for high accumulated intensities has been as well characterized and additional observations relevant to impedance have been collected from longitudinal Schottky signal and BTF measurements. The results of these measurements are summarised and compared to the currently developed machine impedance model.
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TUPAL040	Ion Beam Studies in the FRIB Front End	ion-source, space-charge, ECR, optics	1094
	T. Yoshimoto, K. Fukushima, S.M. Lidia, T. Maruta, P.N. Ostroumov, G. Pozdeyev, H.T. Ren FRIB, East Lansing, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511. The commissioning of the FRIB Front End with 12 keV/u argon beam started in the spring of 2017. Beam profile monitors were used to evaluate RMS Twiss parameters in various locations along the beam line. Beam dynamics in the LEBT was simulated using full 3D model of beam optics elements in the tracking codes. We found a good consistency between measured and simulated data. A beam image viewer was used to measure the beam density distribution in the real space. A hollow beam structure was observed in the Ar⁹⁺ beam with the current of ~20 eμA. Extensive beam dynamics study with 3D tracking code suggests that the hollow density distribution can be generated by space charge effects of the multi-component, multi-charge state ion beam just after the ECR ion source. This paper reports studies of a mechanism that can produce a hollow beam structure. E. Pozdeyev, invited talk at this conference
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TUPAL050	Progress Work on a CW Deuteron RFQ with Magnetic Coupling Windows	rfq, cavity, experiment, Windows	1123
	Q. Fu, M.J. Easton, P.P. Gan, S.L. Gao, H.P. Li, Y.R. Lu, Q.Y. Tan, Z. Wang, K. Zhu PKU, Beijing, People's Republic of China W.P. Dou, Y. He IMP/CAS, Lanzhou, People's Republic of China
	Funding: This work was supported by the National Basic Research Program of China (Grant No. 2014CB845503). A new 162.5 MHz RFQ has been built for a joint 973 project between Peking University (PKU) and Institute of Modern Physics (IMP). It is designed to deliver 50-mA deuteron beams to 1 MeV in CW mode, with an inter-voltage of 60 kV and a length of 1.809 m. Due to its window-type structure, the RFQ has compact cross-section, sufficient mode separation and high specific shunt impedance. It consists of two segments fabricated and installed at IMP. The assembling error of the cavity is less than 0.05 mm. The RF measurements show good electrical properties of the resonant cavity with a measured unloaded quality factor equal to 96.4% of the simulated value. After tuning, we obtained the nominal frequency and field unbalance within 1.0%. Preparation of high-power test of this RFQ is underway. This paper will cover the fabrication details and RF measurements, as well as the progress of high-power test.
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TUPAL072	Dispersive Electron Cooling for JLEIC	electron, emittance, proton, scattering	1178
	H. Zhang, Y.S. Derbenev, Y. Zhang JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-06CH11357. JLEIC is the electron ion collider under design at Jefferson Lab, which will provide a luminosity up to 1034 cm^-2s⁻¹. To reach the high luminosity, short ion and electron bunches with high charge density colliding in high frequency are proposed in JLEIC design. The high charge density of the ion beam leads to strong intrabeam scattering effect, which enlarges the ion beam emittance and ruins the luminosity if not mitigated. Magnetized electron cooling is implemented to overcome the intrabeam scattering effect and to reduce or maintain the ion beam emittance. In this paper, we discuss the redistribution of the cooling effects in the longitudinal and the transverse directions by introducing the dispersion of the ion beam in the cooling section. When the charge density of the cooling electron beam varies, the dispersion of the ion beam leads to an increase of the transverse cooling rate and a reduction of the longitudinal cooling rate, while the total decrement of the Courant-Snyder invariant of the ion beam increases. Both theoretical analysis and numerical calculation are presented.
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TUZGBE4	Toward High-Power High-Gradient Testing of mm-Wave Standing-Wave Accelerating Structures	experiment, cavity, accelerating-gradient, diagnostics	1224
	E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA S. Jawla, R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA S. C. Schaub MIT, Cambridge, Massachusetts, USA B. Spataro INFN/LNF, Frascati (Roma), Italy
	Funding: This work is supported in part by Department of Energy contract DE-AC02-76SF00515 (SLAC) and DE-SC0015566 (MIT). We will preliminary testing results for single-cell accelerating structures intended for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.
	Slides TUZGBE4 [4.644 MB]
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TUPMF003	Dynamic Tuning of the APS-U Booster 5-cell Cavities	booster, cavity, resonance, extraction	1251
	G.J. Waldschmidt, M. Abliz, T.G. Berenc, D. Horan, U. Wienands ANL, Argonne, Illinois, USA
	The booster synchrotron for the APS-U is being upgraded to accommodate high-charge bunches, up to 20 nC, for extraction into the MBA lattice. The booster is required to operate at 85% efficiency in order to achieve bunch swap-out into the storage ring. In order to compensate for significant beam-loading effects as well as support a frequency ramp to achieve higher efficiency, a ferrite tuner is being considered to dynamically adjust the cavity frequency. A tuner design will be presented that spans 60 kHz and utilizes a low-loss YIG garnet similar to that used in the Recycler Ring at Fermilab.
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TUPMF032	RF Conceptual Design of Normal Conducting Cavity for an eRHIC Rapid Cycling Synchrotron	cavity, electron, GUI, vacuum	1316
	B. P. Xiao, M. Blaskiewicz, J.M. Brennan, D. Holmes, K.S. Smith, T. Xin, A. Zaltsman BNL, Upton, Long Island, New York, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. The Rapid Cycling Synchrotron (RCS) for the eRHIC Ring-Ring design will provide on energy injection (up to 18 GeV) of high charge, polarized electron bunches to the eRHIC electron storage ring. The RF system comprises a large number of 563MHz fundamental cavities, providing up to 45MV per turn. The cavities will operate in pulsed mode with <20% duty factor, at a repetition rate of 1 Hz. In this paper we report the conceptual RF design of the cavity.
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TUPMF053	Longitudinal Impedance Measurement of the Strip-Line Kicker for High Energy Photon Source (HEPS)	impedance, kicker, simulation, distributed	1379
	S.K. Tian, J. Chen, Y. Jiao, H. Shi, L. Wang, N. Wang IHEP, Beijing, People's Republic of China
	The High Energy Photon Source (HEPS) is a 6-GeV, kilometer-scale storage ring light source to be built in China. One of the main design challenges of the storage ring is to minimize collective instabilities associated with the impedance of small-aperture vacuum components. In this paper we present beam coupling impedance measurements obtained by the well known coaxial wire method, for the HEPS Strip-Line kicker. The frequency dependent real and imaginary parts of the distributed impedance are obtained from the measured S-parameters.
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TUPMF068	Beam Dynamics on a Coupling Resonance at PETRA III	resonance, optics, lattice, injection	1417
	I.V. Agapov, J. Keil, G. Kube, G.K. Sahoo, R. Wanzenberg DESY, Hamburg, Germany Y.-C. Chae ANL, Argonne, Illinois, USA A.I. Novokshonov TPU, Tomsk, Russia
	Working on a coupling resonance is a usual way of producing round beams in a synchrotron. The beam dynamics in this regime is however more complicated, and the emittance is sensitive to the working point, coupling correction, and bunch current drop with time, which complicates the operation. We present experience with optics setup for working on a coupling resonance in PETRA III, including linear and nonlinear beam optics characteristics, and the measurement of the horizontal and vertical beam emittances with a 2D interferometer. Beam dynamics on a coupling resonance for PETRA IV, the MBA upgrade of PETRA III currently under consideration, is also presented.
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TUPMK018	Round Beam Studies at NSLS-II	emittance, resonance, lattice, experiment	1529
	Y. Hidaka, W.X. Cheng, Y. Li, T.V. Shaftan, G.M. Wang BNL, Upton, Long Island, New York, USA
	Funding: The study is supported by U.S. DOE under Contract No. DE-AC02-98CH10886. Instead of typical flat beam, some synchrotron light us-ers prefer round beam, i.e., with equal horizontal and vertical emittance, for various reasons (e.g., simplified optics, smaller fraction of photons getting discarded, better phase space match between photon and e-beam). Several future upgrade storage rings such as APS-U, ALS-U, and SLS-2 currently plan to operate in round beam mode. We report our beam study results on round beam operating at NSLS-II by driving linear difference cou-pling resonance.
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TUPML003	Design of an L-band Accelerating Structure for the Argonne Wakefield Accelerator Facility Witness Beam Line Energy Upgrade	linac, impedance, acceleration, quadrupole	1533
	J.H. Shao, M.E. Conde, D.S. Doran, J.F. Power ANL, Argonne, Illinois, USA C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA
	The Argonne Wakefield Accelerator (AWA) facility has been devoting much effort to the fundamental R&D of two-beam acceleration (TBA) technology with two parallel L-band beam lines. Beginning from the 70 MeV drive beam line, the high frequency (C-band and above) rf power is extracted from the beam by a decelerating structure (a.k.a. power extractor), transferred to an accelerating structure in the witness beam line, and used to accelerate the 15 MeV main beam. These high frequency accelerating structures usually have a small aperture to obtain high gradient and high efficiency, making it difficult for the low energy main beam to pass. To address this issue, one proposal is to increase the main beam energy to above 30 MeV by replacing the current witness linac. A 9-cell 𝜋-mode L-band standing-wave accelerating structure has therefore been designed to meet the high shunt impedance and low cost requirements. In addition, the single-feed coupling cell has been optimized with additional symmetrical ports to eliminate field distortion. The detailed design of the new accelerating structure will be presented in this paper.
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TUPML060	Three-Dimentional Spiral Beam Injection for a Compact Storage Ring	injection, solenoid, experiment, electron	1673
	H. Iinuma Ibaraki University, Hitachi, Ibaraki, Japan M.R. Abdul Sokendai, Ibaraki, Japan Y. Fukao, K. Furukawa, H. Hisamatsu, T. Mibe, H. Nakayama, S. Ohsawa, K. Oide, K. Sasaki KEK, Tsukuba, Japan
	Funding: This work is supported by JSPS KAKENHI Grant Numbers JP26287055 and JP 23740216. A newly developed three-dimensional spiral injection scheme for beam insertion into a compact (medical MRI size) solenoidal storage ring is introduced. This is a one of key R&D items for a new planned muon g-2/EDM experiment at J-PARC, which aims to measure g-2 to a factor 5 better statistical precision and a factor of 100 better sensitivity for the electric dipole moment measurement (EDM) compared to the previous experiments. The new scheme provides a smooth injection utilizing a radial solenoidal fringe field, without causing any error field in the storage volume. Magnetic pulsed kicker will guide and set the beam in the storage field volume. The strongest point of this new scheme is that any source of the electric field is removed in this scheme to perform ideal EDM measurement. We have performed a test bench experimental work to demonstrate a feasibility of this new injection scheme. Instead of the muon beam, we inject electron beam, from an electron-gun, into the solenoid magnet, and detect three-dimensional spiral beam trajectory inside of the storage chamber by CCD camera. We will discuss outline of a new injection scheme and the latest results from the test bench works. *H. Iinuma et al.,Nuclear Instruments and Methods in Physics Research A, 832, 51-62 (2016)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML060
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WEPAF009	Optimising Response Matrix Measurements for LOCO Analysis	storage-ring, lattice, distributed, quadrupole	1826
	Y.E. Tan AS - ANSTO, Clayton, Australia
	The Linear Optics from Closed Orbit (LOCO) method is a common tool for determining storage ring lattice functions and requires a measured BPM to Corrector response matrix. For very large rings with many correctors, such measurements can be time consuming. The following study investigates how the number of correctors and the signal-to-noise ratio (SNR) affects the LOCO analysis results. For the Australian Synchrotron, the results show that four distributed correctors per plane with a SNR of >1000 is sufficient to fit the betatron functions to an accuracy of less than 0.2%.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF009
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WEPAF017	Correction of ID-Induced Transverse Linear Coupling at NSLS-II	emittance, operation, quadrupole, resonance	1856
	Y. Hidaka, Y. Li, T.V. Shaftan, T. Tanabe, Y. Tian, G.M. Wang BNL, Upton, Long Island, New York, USA
	Funding: The study is supported by U.S. DOE under Contract No. DE-AC02-98CH10886. Sizeable lifetime jumps have been observed sporadically since March 2016 at NSLS-II. These jumps were found to coincide with insertion device (ID) gap motions. Particularly, one of the in-vacuum undulators (IVUs) at Cell 17 was discovered to have large localized skew quadrupole component variation with gap. To allow the machine to operate stably in the low-emittance mode, a global coupling feedforward system has been recently implemented and successfully deployed. After installation of a new additional skew quadrupole, coupling compensation of this ID is now performed by a local coupling feedforward system. Furthermore, the maximum gap limit of all the existing IVUs has been decreased from 40 mm to 25 mm to limit the skew component variation during user operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF017
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WEPAF027	Low Q Cavity BPM Study for the Beam Position Measurement of Nanosecond Spaced Electron Bunches	cavity, FEL, dipole, electron	1881
	L. Yang, X. He, L.W. Zhang CAEP/IFP, Mainyang, Sichuan, People's Republic of China S.S. Cao, Y.B. Leng, L.Y. Yu, R.X. Yuan SINAP, Shanghai, People's Republic of China
	Funding: National natural science foundation of China, 11705184 Low Q cavity BPM is a key to distinguish closely spaced electron bunches allowing precise beam handling for XFEL facilities operating in a multi-bunch mode at high repetition rate up to hundreds MHz. The inter-bunch signal pollution issue becomes significant when bunch separation is down to nanosecond and causes the position detection to be increasingly overestimated. Solely relying on extreme low Q to achieve sufficient decay within bunch interval leads to appreciable interference from non-signal modes due to strong overcoupling of antenna design is required. The error imposed on measured position raises a challenge to meet the goal of high resolution. Alternatively, a concept is proposed to remove the dominant part of signal pollution at the moment of sampling by intentionally shifting the phase of the last bunch signal 90degree respect to that of current bunch signal, where signal sampling is normally taken for nanosecond spaced bunches. This quadrature phase shift is defined by properly choosing the operational frequency of dipole mode regarding to the bunch frequency. A low Q cavity BPM prototype to identify technical challenges and verify this concept is under development in the R&D plan for future XFEL with high repetition rate
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WEPAF042	Measurement of Beam yz Crabbing Tilt Due to Wake Fields Using Streak Camera at CESR	wakefield, storage-ring, positron, cavity	1905
	S. Wang, D. L. Rubin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This research was supported by NSF PHYS-1068662, PHYS-1416318 and DMR-1332208. Transverse vertical wake fields can increase the vertical emittance and distort the phase space of a bunch in a storage ring. Recently, we observed charge-dependent vertical beam size growth with a single scraper inserted through the top of the storage ring vacuum chamber. This apparent growth was due in large part to the yz coupling (vertical crabbing) induced by the wake field from the asymmetric scraper configuration. Here, we report a direct measurement of a small beam yz crabbing tilt using a streak camera. The recorded images (projected beam profiles in yz plane) are analyzed with three different methods, which yield consistent beam yz tilts. We found the directly-measured current-dependent beam tilts by the streak camera are consistent with the beam tilts calculated from a wake field model.
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WEPAF058	Detection of X-Rays and Charged Particles via Detuning of the Microwave Resonator	resonance, monitoring, network, experiment	1958
	S.P. Antipov Euclid TechLabs, LLC, Solon, Ohio, USA S.V. Kuzikov Euclid Beamlabs LLC, Bolingbrook, USA S. Stoupin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	Funding: DOE SBIR Critically coupled microwave resonator is a finely balanced system, reflection at the resonance is virtually zero. Small changes in dielectric properties of resonator parts destroy this balance, small reflection can be detected from the resonator. This measurement is used in electron paramagnetic resonance studies. In this paper we discuss two accelerator - related applications of this technology. First is related to beam halo measurement taking advantage of high sensitivity of the microwave measurement. High energy particles crossing the diamond inside of a tuned resonator induce a weak conductivity in the sensing material. This small change results in resonator decoupling providing a signal proportional to a number of particles crossing the diamond plate. Second application considered is the x-ray flux monitoring. In this case it is x-ray induced photoconductivity which alters resonator coupling and produces a signal. Interestingly, sensing dielectric material embedded in a resonator can be a diamond or kapton window, refractive lens or part of a silicon monochromator. Thus an inevitable x-ray absorption on optical elements of the beamline is used to monitor x-ray flux online.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF058
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WEPAG002	Tunable Q-Factor Gas-Filled RF Cavity	cavity, hadron, plasma, simulation	2064
	M.D. Balcazar, A. Moretti, A.V. Tollestrup, A.C. Watts, K. Yonehara, R.M. Zwaska Fermilab, Batavia, Illinois, USA M.A. Cummings, A. Dudas, R.P. Johnson, G.M. Kazakevich, M.L. Neubauer Muons, Inc, Illinois, USA
	Funding: Work supported by Fermilab Research Alliance, LLC under Contract No. DE-AC02-07CH11359 and DOE STTR Grant, No. DE-SC0013795. Fermilab is the main institution to produce the most powerful and wide-spectrum neutrino beam. From that respective, a radiation robust beam diagnostic system is a critical element in order to maintain the quality of the neutrino beam. Within this context, a novel radiation-resistive beam profile monitor based on a gas-filled RF cavity has been proposed. The goal of this measurement is to study a tunable Q-factor RF cavity to determine the accuracy of the RF signal as a function of the quality factor. Specifically, the measurement error of the Q-factor in the RF calibration is investigated. Then, the RF system will be improved to minimize signal error.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAG002
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WEPMF014	Fast Track Actively Shielded Nb3Sn IR Quadrupole R&D	quadrupole, site, hadron, collider	2398
	B. Parker, M. Anerella, J.P. Cozzolino, R.C. Gupta, R.B. Palmer, J. Schmalzle, H. Witte BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The Interaction Region (IR) magnets for future Electron Ion Colliders (EIC), such as eRHIC at BNL, JLEIC at JLab and LHeC at CERN, must satisfy strongly opposing requirements. EIC IR superconducting quadrupole coils must provide strong focusing gradients, leading to large peak fields, for the high momentum hadron beam while permitting the nearby electron beam to pass through a nearly field free region. An actively shielded coil geometry does this using nested, opposite polarity, quadrupoles where the combined external fields cancel while leaving a net gradient inside. In order to fabricate and test this concept in a timely and cost effective manner we propose to reuse the inner coils from an existing high gradient Nb3Sn LARP quadrupole inside a new structure with a new NbTi active shield coil. The main challenge is to design a compact structure for applying prestress to the Nb3Sn coil that fits the restricted space inside the shield coil. We first construct a 15 cm long mechanical model of this structure with coil strain gauges to verify the design concept before proceeding with the full coil. Mechanical modeling results and our preliminary design concept are reported here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF014
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WEPMF031	Development of a High-Power High-Directivity Directional Coupler and Four Power Dividers for S-Band	GUI, vacuum, MMI, simulation	2422
	X. He, J. Lei, J.R. Zhang IHEP, Beijing, People's Republic of China
	A novel Bethe-hole S band directional coupler has been designed based on some structural optimizations, the prototype has been tested with a Directivity of more than 30 dB. The new directional coupler can also hold higher power compared to the old type, which is more useful for the future accelerator applications. Four power dividers using different structures are studied and the best one is chosen for fabrication. The prototype with matching rod in the middle has got qualified microwave cold test results and has been used during the whole microwave commissioning of an accelerating structure, the performance is quite stable.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF031
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WEPMF033	RF Study And Cold Test of an S-band Spherical Cavity Pulse Compressor	cavity, simulation, vacuum, klystron	2429
	J. Lei, X. He, M. Hou, X.P. Li, G. Pei, H. Wang, J.B. Zhao IHEP, Beijing, People's Republic of China S. Shu Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
	An S-band (2856 MHz) spherical cavity pulse compressor has been designed, fabricated and tested in the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS). The pulse compressor consists of a special 3 dB coupler and only one spherical energy storage cavity, two TE114 modes are chosen to oscillate in which for fairly high unload Q factor. The prototype was made of aluminum for studying the performance of the pulse compressor and checking the validity of the simulations. The cold test results of the aluminum cavity are also presented. The copper coating on the whole internal surface of the aluminum spherical cavity is in progress and the test results will also be presented in the future.
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WEPMF034	Development of Superconducting RF Double Spoke Cavity at IHEP	cavity, target, electron, proton	2432
	Z.Q. Zhou, H.F.S. Feisi, W.M. Pan IHEP, Beijing, People's Republic of China
	Funding: State Key Development Program for Basic Research of China (Grant No.2014CB845500) The China Initiative Accelerator Driven System (CiADS) has been approved to transmute long-lived radi-oisotopes in used nuclear fuel into shorter-lived fission products. IHEP is developing a 325MHz double spoke cavity at β0 of 0.5 for the CiADS linac. The cavity shape was optimized to minimize Ep/Ea while keeping Bp/Ep reasonably low, while the multipacting was analyzed. Meanwhile, mechanical design was applied to check stress, Lorentz force detuning and microphonic effects, and to minimize pressure sensitivity. A new RF coupling scheme was proposed to avoid electrons hitting directly on ceramic window. The detailed design for the cavity is addressed in this paper.
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WEPMF062	Simulation of Cavity Conditioning for the Diamond SCRF Cavity	cavity, GUI, simulation, operation	2509
	S.A. Pande, C. Christou, P. Gu DLS, Oxfordshire, United Kingdom
	Diamond SCRF cavities are pulse conditioned every week in order to keep them operating reliably. During conditioning, the cavities are detuned in order to sweep the standing wave through the waveguide. To match these cavities at lower voltage (typically < 1.4 MV) and at higher power, 3 stub tuners are used in the waveguide feed. Simulations with CST studio show that a strong SW field exists between the RF window and the matching posts. As the cavity is detuned the electric field maximum passes through the window causing heating of the ceramic. Temperature measurements with thermal camera reveal that the temperature of the window increases to maximum when the cavity is detuned towards higher frequency. Based on the simulation results and the measurements, it was decided to reduce the conditioning voltage. These results are summarised.
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WEPMF065	High Efficiency, High Power, Resonant Cavity Amplifier For PIP-II	cavity, impedance, network, operation	2518
	M.P.J. Gaudreau, N. Butler, D.B. Cope, P. H. Gordon, E.G. Johnson, M.K. Kempkes, R.E. Simpson Diversified Technologies, Inc., Bedford, Massachusetts, USA
	Funding: Funded under US DOE grant no. DE-SC0015780 Diversified Technologies, Inc. (DTI) is developing an integrated resonant-cavity combined solid-state amplifier for the Proton Improvement Plan-II (PIP-II) at Fermilab. The prototype has demonstrated multiple-transistor combining at 71% efficiency, at 675 watts per transistor at 650 MHz. The design simplifies solid-state transmitters to create straightforward scaling to high power levels. A crucial innovation is the reliable "soft-failure" mode of operation; a failure in one or more of these myriad combined transistors has negligible performance impact. The design couples the transistor drains directly to the cavity without first transforming to 50 Ohms, avoiding the otherwise-necessary multitude of circulators, cables, and connectors. DTI's design increases the power level at which it is cost-effective to employ a solid-state transmitter. DTI is upgrading the system to accommodate more transistors in each cavity module, and then will design and build a complete 100 kW-class transmitter which will consist of four such cavity modules and a combiner.
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WEPMF066	Fabrication of Split-Section X-band Structure Using Elastic Averaging	vacuum, alignment, electron, gun	2521
	P. Borchard, S.A. Appert, J.S. Hoh Dymenso LLC, San Francisco, USA
	Conventional accelerator structures are manufactured using axial stacks of cylindrical components which, when brazed together, form the accelerator cell structure. Splitting the accelerator structure into two sections along the beam axis allows for a significant reduction in part count and vacuum joint length. The resultant single and coplanar vacuum joint between the two split sections allows for joining techniques such as electron beam welding or brazing of the parts to form the accelerator vacuum envelope. High precision alignment of the two sections is achieved through an elastic averaging interface coupling where improved accuracy is derived from the averaging of errors over a large number of relatively compliant contacting members. The monoblock split sections allow for highly optimized cooling configurations with enhanced heat removal in high heat flux regions, reducing vacuum wall thermal stresses and enabling higher power operation. This paper describes the engineering and manufacturing of four generations of brazed and electron beam welded X-band accelerator structures at both 9.3 GHz and 11.4 GHz frequencies.
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WEPMF069	High Shunt Impedance Accelerating Structure with Distributed Microwave Coupling	cavity, GUI, distributed, impedance	2531
	S.P. Antipov, R.A. Kostin, S.V. Kuzikov Euclid TechLabs, LLC, Solon, Ohio, USA V.A. Dolgashev SLAC, Menlo Park, California, USA
	Funding: DOE SBIR Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. In this paper we present results from an accelerating structure prototype with distributed microwave coupling, an approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. Thus there is no microwave power flow through the accelerating cavity, making this geometry favorable for high gradient operation and maximizing the shunt impedance.
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WEPMF089	Measurements of Electromagnetic Properties of Ferrites as a Function of Frequency and Temperature	kicker, impedance, injection, simulation	2592
	A. Chmielinska, M.J. Barnes, F. Caspers, B.K. Popovic, C. Vollinger CERN, Geneva, Switzerland
	Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.
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WEPMK005	Preliminary Results from Validation Measurements of the Longitudinal Power Deposition Model for the LHC Injection Kicker Magnet	impedance, kicker, injection, operation	2636
	V. Vlachodimitropoulos, M.J. Barnes, A. Chmielinska CERN, Geneva, Switzerland A. Chmielinska EPFL, Lausanne, Switzerland
	During Run 1 of the LHC, one of the injection kicker magnets (MKIs) exhibited an excessively high ferrite temperature, caused by coupling of the high intensity beam to the real impedance of the magnet. Beam-screen upgrades, implemented during Long Shutdown 1 (LS1), have been very effective in reducing beam coupling impedance and since then the MKIs have not limited LHC's availability. However, temperature measurements during operation have shown that one end of the MKI's ferrite yoke is consistently hotter than the other. Detailed simulation models and data post-processing algorithms have been developed to understand and mitigate the observed behaviour. In the present paper, the model used to obtain the power loss distribution along the magnet is presented. The model is subsequently applied to two MKI design configurations under study: (i) the one currently in operation and (ii) an upgraded magnet that was installed in the LHC tunnel during the Year End Technical Stop (YETS) 2017/18. In order to validate the expected behaviour a novel measurement technique was developed, applied in both configurations and compared to predictions. The results obtained are reported and conclusions regarding the effectiveness of the design are drawn.
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WEPMK007	INFN-LASA Design and Prototyping Activity for PIP-II	cavity, HOM, operation, linac	2640
	A. Bignami, M. Bertucci, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy S. Pirani ESS, Lund, Sweden
	The design of the PIP-II medium-β, 5-cell, 650 MHz SRF elliptical cavity and the first steps of its prototyping activity are here presented. A design based on a three dies fabrication model has been chosen and fully characterized in terms of electromagnetic and mechanical parameters. Goal of the optimization has been to realize a highly performant cavity for CW operation with reasonably good performances when pulsed. A prototyping phase started with the production of three single-cell cavities used to validate the LASA model and to develop an optimal recipe for RF surface treatment according to the state-of-the-art of the high-Q frontier.
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WEPML003	Precision Q0 Measurement of an SRF Cavity with a Digital RF Techniques	cavity, SRF, impedance, GUI	2674
	J.P. Holzbauer, B.M. Hanna, Y.M. Pischalnikov, W. Schappert, D.A. Sergatskov, A.I. Sukhanov Fermilab, Batavia, Illinois, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. Direct measurement of the quality factor of SRF cavity using traditional RF techniques is essential for cavity production and development. Systematic effects of the measurement can contribute significant amounts of error to these measurements if not accounted for. This paper will present measurements taken at Fermilab using a digital RF system to characterize and correct for these systematic effects and directly measure the quality factor versus gradient curve for a single spoke resonator in the Spoke Test Cryostat at Fermilab. These measurements will be compared to traditional calorimetric measurements, and a discussion of improving/extending these techniques to other testing situations will be included.
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WEPML032	The FAIR-SIS100 Bunch Compressor RF Station	cavity, power-supply, controls, electronics	2759
	H.G. König, R. Balß, P. Hülsmann, H. Klingbeil, P.J. Spiller GSI, Darmstadt, Germany R. Gesche, J.H. Scherer Aurion Anlagentechnik GmbH, Seligenstadt, Germany A. Morato, C. Morri, G.T. Taddia OCEM, Valsamoggia, Italy
	In the frame of the Facility for Antiproton and Ion Research (FAIR) 9 bunch compressor RF stations were ordered for the first stage of realization of the SIS100 synchrotron. For RF gymnastics referred to as bunch rotation, one RF station has to provide a sudden rise in gap voltage of up to 40 kVp within less than 30 μs. The system is designed for a maximum RF burst of 3 ms per second. The RF frequency will be pre-selectable between 310 kHz and 560 kHz at a harmonic number of h=2 with respect to the beam. Compressed bunches with a peak current > 150 A and a width < 50 ns are the goal. For this purpose, a 1.218 m long cavity was designed using iron-based magnetic alloy cores. Variable vacuum capacitors are attached for tuning. The cavity is driven by a cross-coupled push-pull tetrode amplifier. This scheme minimizes the influence of the tetrode's DC current at the working point to the cores. The energy for the pulsed system is stored in a relatively small capacitor bank which will be charged semi-continuously and a voltage-stabilizing device is added. Cavity and power amplifier were realized by AURION Anlagentechnik GmbH ' the power supply unit is designed and built by OCEM Power Electronics.
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WEPML055	Simulation Study of Parasitic-Mode Damping Methods for a 1.5-GHz TM020-Mode Harmonic Cavity	cavity, impedance, damping, radiation	2822
	N. Yamamoto, S. Sakanaka, T. Takahashi KEK, Ibaraki, Japan
	Design study of parasitic-mode (PM) damped structures has been conducted for the purpose to realize a normal conducting 1.5 GHz harmonic cavity which is based on the TM020 resonant mode. We have investigated the performances of two PM-damping mechanisms, that are, rod-type antennas* and annular slots. The rod-type antennas locate at the node of electric field of the TM020 mode while the annular slots locate at the node of magnetic field. As a result of 3D electromagnetic simulations, suitable performances of PMs were confirmed by employing either of the PM-damping mechanisms. It was also shown that the slot-type structure is superior in PM-damping performance and in the unloaded Q of the TM020 mode. * N. Yamamoto et al., IPAC'17, paper THOPIK037; N. Yamamoto Phys. Rev. Accel. Beams, 21, 1, 012001. ** T. Takahashi et al., IPAC'17, paper THPIK036.
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WEPML075	Test of Magnet Girder Prototypes for HEPS-TF	alignment, HOM, photon, site	2863
	H. Wang, C. H. Li, S.J. Li, J. Liu, H. Qu, Z. Wang, L. Wu IHEP, Beijing, People's Republic of China H.Y. Zhu Institute of High Energy Physics (IHEP), People's Republic of China
	Auto-tuning magnet girder is one of the key technolo-gies to be solved for HEPS-TF (Test Facility of High Ener-gy Photon Source). The girder should have high adjusting accuracy, high stability and can be beam-based aligned, to obtain the stability requirements of beam orbit. There are two girders developed, and the tests have been done. The accuracy of girder motion is within 10 microns while the adjusting range is 1 mm and the resolution is better than 1 microns, the natural frequency is higher than 24 Hz.
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THPAF036	Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions	impedance, vacuum, factory, electromagnetic-fields	3040
	M. Migliorati, L. Palumbo Sapienza University of Rome, Rome, Italy N. Biancacci CERN, Geneva, Switzerland M. Migliorati, L. Palumbo INFN-Roma1, Rome, Italy V.G. Vaccaro Naples University Federico II and INFN, Napoli, Italy
	Funding: Work supported by the CERN PS-LIU project The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultra-relativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultra-relativistic particles. Even if some of the results, in particular in the ultra-relativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multi-layer vacuum chamber with different conductivities and of elliptic cross section.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF036
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THPAF048	Destabilising Effect of the LHC Transverse Damper	damping, impedance, feedback, synchrotron	3076
	E. Métral, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, K.S.B. Li CERN, Geneva, Switzerland
	Three questions motivated this study for the CERN Large Hadron Collider in terms of beam stability: (i) why a chromaticity close to zero seemed more critical than predicted during Run 1 (in 2011 and 2012) and during Run 2 (in 2015)?; (ii) why some past simulations with a chromaticity close to zero revealed a more critical situation with the transverse damper than without?; (iii) what should be the minimum operational chromaticity in the future in the LHC and High-Luminosity LHC? A new Vlasov solver (called GALACTIC) was developed to shed light on the destabilising mechanism of the transverse damper, which is a potential contributor to explain the LHC observation. Due to the features, which are discussed in this paper, the name 'ISR (for Imaginary tune Split and Repulsion) instability' is suggested for this new kind of single-bunch instability with zero chromaticity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF048
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THPAF051	Beam Impedance Evaluation for CERN PS Gate Valves by Simulation and Benchmark Measurement	impedance, simulation, wakefield, resonance	3080
	B.K. Popovic, C. Vollinger CERN, Geneva, Switzerland
	The CERN High Luminosity LHC project calls for a doubling of beam intensity which requires a clear identification of possible longitudinal instability sources in the injector chain. This requirement yields the need to further improve the longitudinal impedance model for the Proton Synchrotron (PS). In this impedance model it is necessary to include not only obvious impedance sources, such as RF cavities and kickers but also seemingly innocuous elements like certain vacuum components. Individually these vacuum elements would give only a small impedance contribution, however, due to the large number of these elements in the machine, their resultant combined impedances impact the overall impedance budget. This paper presents the electromagnetic simulation analysis of the PS sector gate valves along with EM measurements confirming the simulation model. These measurements are especially crucial in this case since no complete mechanical model or drawings are available and assumptions had to be made regarding its interior mechanical structure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF051
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THPAF052	Impedance Analysis of New PS Internal Dump Design	impedance, HOM, resonance, vacuum	3083
	B.K. Popovic, L. Teofili, C. Vollinger CERN, Geneva, Switzerland
	The High Luminosity Large Hadron Collider (HL-LHC) project at CERN calls for increasing beam intensity in the injector chain. In the Proton Synchrotron (PS), a pre-injector of the LHC, these intensities can result in beam instabilities and potential RF heating of machine components, such that impedance mitigation measures are required. To study these intensity effects, the PS impedance model has been developed and is continuously updated. Each new machine element that is to be added into the accelerator requires an impedance study to minimize its contribution with respect to the machine's overall impedance budget. In such a context, this paper presents the impedance analysis of the new design of the internal beam dump for the PS, showing the design process required to reduce the impedance contribution of this element. Furthermore, the impedance analysis of the currently installed beam dump is analysed in order to compare the impedance contributions of the two designs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF052
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THPAF057	Instability Observations in the Large Hadron Collider During Run 2	operation, simulation, electron, hadron	3099
	L.R. Carver, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, G. Iadarola, K.S.B. Li, E.H. Maclean, L. Mether, E. Métral, B. Salvant, M. Schenk CERN, Geneva, Switzerland L. Mether, M. Schenk EPFL, Lausanne, Switzerland
	Instabilities of many different types and characteristics have been observed in the LHC during Run 2. The origin of these instabilities come from a variety of stabilising and destabilising mechanisms. Efforts to understand these instabilities and prevent their occurrence has improved the performance of the LHC in all stages of the machine cycle. This paper aims to give an overview into some of the instability observations and details the operational steps to prevent them.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF057
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THPAF063	Identification of Imperfections in Impedance Shields on the SPS-QF Flanges via Non-Intrusive Measurements	resonance, impedance, shielding, cavity	3119
	A. Farricker, P. Kramer, B.K. Popovic, E. Sunar, C. Vollinger, M. Wendt CERN, Geneva, Switzerland
	In order to achieve the highest beam intensities possible in the LHC the highest quality beam possible has to be supplied by the injector chain. The Super Proton Synchrotron (SPS) at CERN is the last accelerator in the injector chain of the LHC. One factor that is currently known to limit the intensity of the beam for injection to the LHC, is the longitudinal beam-coupling impedance in the SPS. One known source of multi-bunch instability is the vacuum flanges and campaigns to mechanically shield this source were completed in the year 2000. However, today it cannot be excluded that some of these shields may have partial or indeed full failures. Since these flanges are next to a QF magnet and are in most cases connected to a BPH (Beam Position Monitor Horizontal), it is possible to carry out via the BPH an in-situ measurement of the effectiveness of the shields. In this paper we present a methodology as well as measurement results taken with this non-intrusive in-situ method. From measurements, it is possible to identify if the flanges are without any impedance shield, equipped with either a fully functioning shield or a shield exhibiting non-ideal properties.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF063
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THPAF067	Effects of Synchrotron Motion on Nonlinear Integrable Optics	synchrotron, optics, betatron, lattice	3131
	S.D. Webb, N.M. Cook RadiaSoft LLC, Boulder, Colorado, USA J.S. Eldred Fermilab, Batavia, Illinois, USA
	Funding: This work was supported in part by the Department of Energy, Office of Science, Office of High Energy Physics under contract number DE-SC0011340. An integrable Rapid-Cycling Synchrotron (iRCS) has been proposed as a replacement for the Fermilab Booster to achieve multi-MW beam power for the Fermilab high-energy neutrino program.* The successful application of nonlinear integrable optics to proton synchrotrons requires careful examination of single-particle longitudinal effects, especially synchrotron motion. For example, synchrobetatron coupling may excite transverse resonances in the ring. We will use the Synergia code to simulate the effects of this synchrobetatron coupling on the iRCS design with nonlinear inserts. Our goal will be to identify new invariants in the presence of this coupling. Assuming the synchrotron tune is sufficiently small, we have identified one or more adiabatic invariants of the motion. These invariants suggest that integrable optics with synchrobetatron coupling retains integrability when averaged over a synchrotron period. * J. Eldred and A. Valishev, "Design Considerations for Proposed Fermilab Integrable RCS," arXiv 1703.00952 (2017).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF067
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THPAF069	Particle Tracking Simulation of Collective Modes - Parametric Landau Damping Off Coupling Resonance	damping, simulation, resonance, synchrotron	3137
	A. Macridin, J.F. Amundson, A.V. Burov, P. Spentzouris, E.G. Stern Fermilab, Batavia, Illinois, USA
	Employing Synergia simulations with the DMD method we investigate the Landau damping of space charge modes in bunched beams. The simulations reveal two instances of the parametric damping mechanism in bunched beams. The first example occurs in the proximity of coupling resonance and is due to the oscillation of particles' amplitudes in the transverse plane. This oscillation modulates the mode-particle coupling with particle dependent trapping frequency. The second example is due to the modulation of the mode-particle coupling in one transverse plane by the oscillatory motion in the other plane.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF069
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THPAF070	Design of a One-Dimensional Sextupole Using Semi-Analytic Methods	sextupole, lattice, quadrupole, focusing	3140
	L. Gupta Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA S. Baturin Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA Y.K. Kim University of Chicago, Chicago, Illinois, USA S. Nagaitsev Fermilab, Batavia, Illinois, USA
	Funding: Work supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams Sextupole magnets provide position-dependent momentum kicks and are tuned to provide the correct kicks to particles within a small acceptance region in phase space. Sextupoles are useful and even necessary in circular accelerators for chromaticity corrections. They are routinely used in most rings, i.e. CESR. Although sextupole magnets are necessary for particle energy corrections, they also have undesirable effects on dynamic aperture, especially because of their non-linear coupling term in the momentum kick. Studies of integrable systems suggest that there is an analytic way to create transport lattices with specific transfer matrices that limit the momentum kick to one dimension. A one-dimension sextupole is needed for chromaticity corrections: a horizontal sextupole for horizontal bending magnets. We know how to make a "composite" horizontal sextupole using regular 2D sextupoles and linear transfer matrices in an ideal thin-lens approximation. Thus, one could create an accelerator lattice using linear elements, in series with sextupole magnets to create a '1d sextupole'. This paper describes progress towards realizing a realistic focusing lattice resulting in a 1d sextupole.* *S.A. Antipov, et. al., Single-particle dynamics in a nonlinear accelerator lattice: attaining a large tune spread with octupoles in IOTA, Journal of Instrumentation, Volume 12, April 2017.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF070
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THPAF073	Beam Phase Space Tomography at Fast Electron Linac at Fermilab	experiment, lattice, MMI, linac	3146
	A.L. Romanov Fermilab, Batavia, Illinois, USA
	FAST linear accelerator has been commissioned in 2017. Experimental program of the facility requires high quality beams with well-defined properties. Solenoidal fields at photoinjector, laser spot shape, space charge forces and other effects can distort beam distribution and introduce coupling. This work presents results of a beam phase space tomography for a coupled 4D case. Beam was rotated in two planes with seven quads by 180 degrees and images from YaG screen were used to perform SVD based reconstruction of the beam distribution.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF073
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THPAF089	Mode Coupling Theory in Collisions With a Large Crossing Angle	dipole, synchrotron, collider, positron	3197
	N. Kuroo UTTAC, Tsukuba, Ibaraki, Japan K. Hirosawa, K. Ohmi, D. Zhou KEK, Ibaraki, Japan K. Oide, F. Zimmermann CERN, Geneva, Switzerland
	We discuss a novel coherent beam-beam instability in collisions with a large crossing angle. The instability appears in the correlated head-tail motion of the two colliding beams. Cross wake force is introduced to represent the head-tail correlation between colliding beams. The cross wake force is localized at the collision point. Mode coupling theory based on the cross wake force is developed. Collision scheme with a large crossing angle is being very popular in design of electron positron collider. In SuperKEKB project, a collision with a large crossing angle is performed to boost the luminosity ~ 10³⁶ cm^-2s⁻¹. Future circular collider, FCC is also designed with a large crossing angle. Strong-strong simulations have shown a strong coherent head-tail instability, which can limit the performance of proposed future colliders. The mode coupling theory using the cross wake force explains the instability. The instability may affect all colliders designs based on the crab waist scheme.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF089
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THPAK005	Measuring the Coupling Impedance of Vacuum Components for the Advanced Photon Source Upgrade Using a Goubau Line	impedance, cavity, simulation, vacuum	3211
	M.P. Sangroula IIT, Chicago, Illinois, USA R.M. Lill, R.R. Lindberg, R.B. Zabel ANL, Argonne, Illinois, USA
	The Planned upgrade of the Advanced Photon Source to a multi-bend achromat (MBA) will increase the x-ray brightness by two to three orders of magnitude. Storing such an intense beam stably inside the narrow gap vacuum chambers requires sophisticated and appropriately designed rf-components that helps to minimize rf heating and collective instabilities associated with the impedance of these small-aperture vacuum components. As part of this effort, my research focuses on impedance measurement and simulation of various MBA vacuum components. In this paper, we briefly introduce the novel Goubau line (G-line) test fixture for the impedance measurement, at first, and then present our measurements data along with simulations with simulations for various vacuum components designed for the APS Upgrade.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK005
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THPAK010	Optimization on the Optical Resonator of CTFEL	FEL, GUI, radiation, electron	3228
	X.J. Shu, Y.H. Dou Institute of Applied Physics and Computational Mathematics, People's Republic of China M. Li, Z. Xu, Y. Xu, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	Funding: Program for the National Science Foundation of China (Grant No. 11105019) and the National Science Device Exploitation Foundation of China (Grant No. 2011YQ130018). A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CTFEL) since October, 2011. The radiation frequency of the FEL facility will be tuned in range of 1~3 THz and the average output power is about 10 W. The system mainly consists of a GaAs photoemission DC gun, superconductor accelerator, the hybrid wiggler, optical cavity. The first lasing is obtained on Aug. 29, 2017. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and round-trip loss. The optical resonator consists of metal-coated reflect mirror, the center-hole output mirror, waveguide. The influence of waveguide and Rayleigh length on the quality of optical cavity is evaluated by the 3D-OSIFEL code. The waveguide size, mirror curvature radius, output hole radius is optimized to different frequencies between 1 THz to 3 THz.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK010
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THPAK015	Impedance and Heat Load Analysis of the Stripline Kicker in HEPS	kicker, impedance, simulation, injection	3234
	N. Wang, J. Chen, Z. Duan, H. Shi, S.K. Tian, L. Wang, H.S. Xu IHEP, Beijing, People's Republic of China
	In the High Energy Photon Source (HEPS), strip-line kickers are adopted for beam injection and extraction. Beam coupling impedance contribution from the strip-line kicker is calculated. Detailed studies on the heat load dissipation have been performed. The peak electric field on the blade and the induced voltage on the feedthroughs due to the beam passage are also calculated.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK015
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THPAK054	Optics Calibration and Measurement for Low Alpha Lattices in TPS Storage Ring	lattice, emittance, optics, operation	3343
	F.H. Tseng, C.H. Chen, J.Y. Chen, P.C. Chiu, C.H. Huang, C.-C. Kuo, C.C. Liang, C.Y. Liao, Y.-C. Liu, H.-J. Tsai NSRRC, Hsinchu, Taiwan
	In order to provide short-pulse radiation for pump-probe experiments and coherent radiation for THz/IR measurements, we develop low alpha lattices to reduce the momentum compaction factor from nominal operation values 2.410^-4 to 2.610-5 or lower. The corresponding bunch length at 2.8 MV RF voltage and zero current are from 10.78 ps to 3.55 ps or less. In the low alpha operations, the bunch lengthening as a function of bunch current, the orbit drift and noise enhancements as well as rf stability effect are observed. In this report we will present our studies on the lattice design, optics correction, beam parameters measurements and alpha measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK054
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THPAK099	The Influence of Higher Order Multipoles of IR Magnets on Luminosity for SuperKEKB	sextupole, luminosity, multipole, octupole	3463
	K. Hirosawa, T. Okada Sokendai, Ibaraki, Japan N. Kuroo UTTAC, Tsukuba, Ibaraki, Japan K. Ohmi, N. Ohuchi, D. Zhou KEK, Ibaraki, Japan
	SuperKEKB is an electron-positron circular collider upgraded from KEKB. To reach higher luminosity, values of beta are extremely small at Interaction Point. Although magnets in interaction region have a very strong focusing effect, they make a large disturbance to beams. Higher order multipoles and their skew components of magnetic fields of IR magnets are located at a very high beta section with pi/2 phase difference from IP. These multipoles can give critical effect to beam dynamics at interaction point and reduce luminosity on SuperKEKB design. In this study, we calculated beam dynamics for effect of skew components for multipole magnet, and estimated the influence on luminosity by them.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK099
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THPAK110	Correction of ν_r-ν_z=1 Resonance in TRIUMF Cyclotron	resonance, cyclotron, TRIUMF, simulation	3492
	Y.-N. Rao, R.A. Baartman, T. Planche TRIUMF, Vancouver, Canada
	Funding: TRIUMF receives federal funding via a contribution agreement through the National Research Council of Canada The second order linear coupling resonance nu_r-nu_z=1 is driven by an asymmetry in the median plane of the cyclotron due to presence of the first harmonic in B_r component. In TRIUMF cyclotron, this resonance is encountered at about 166 MeV and 291 MeV, where nu_r=1.2 and nu_z=0.2. When the beam is off-centered radially to pass through this resonance, the radial oscillation gets converted into vertical oscillation, which can cause beam loss to occur, though these loss modes do not reduce the machine transmission under normal operation. In this paper, we present the results of simulations and measurements that we have performed to correct this resonance by using the existing harmonic coils.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK110
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THPAK113	Cavity Characterization Studies With the Latest Revision of YACS	cavity, storage-ring, superconducting-cavity, higher-order-mode	3503
	B.D. Isbarn, S. Koetter, B. Riemann, M. Sommer, T. Weis DELTA, Dortmund, Germany
	Funding: Work supported by the BMBF under contract no. 05K13PEB. YACS is a 2.5D finite element method solver capable of solving for the full 3D eigenfrequency spectra of resonant axisymmetric structures while reducing the computational problem to a 2D rotation plane. The most recent revision of YACS now supports arbitrary order basis functions for the geometry and field discretization. In earlier revisions of YACS spurious modes were introduced by increasing the order of either the geometry or field basis functions. To prevent the emergence of spurious modes, YACS now matches the function spaces of the in-plane and out-plane function basis, and thus yields spurious free solutions. To demonstrate the capabilities of YACS, extensive cavity characterization studies on curved multicell microwave cavities are presented. Due to the combined utilization of the rotation symmetry, higher order basis functions and curved elements, eigenfrequency spectra above 10 GHz for L-band multicell structures can be easily obtained.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK113
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THPAL002	RF System Operation of High Current RFQ in ADS Project	rfq, cavity, operation, LLRF	3613
	L.P. Sun, R. Huang, C.X. Li, L. Lu, A. Shi, L.B. Shi, W.B. Wang, X.B. Xu, H.W. Zhao IMP/CAS, Lanzhou, People's Republic of China Y. Hu TUB, Beijing, People's Republic of China
	Funding: Work supported by Natural Science Foundation of China， No.11505253 New RF system has been upgraded several times for high-current operation, especially for extra beam power and detuning angle. The current was increased gradually resulting in more and more frequency detuning, and an effective method is to tune the temperature of cavity to compromise detuning. Of course, the power dissipated in cavity and high intensity beam are approximately 120kW resulting in too many power modules operated in the high risk of failure. The specific analysis and simulation were introduced in detail.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL002
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THPAL037	Nano-engineering of Nb3Sn Thin Films to Improve Wire Performance and Reduce Cost	collider, lattice, electron, dipole	3720
	S.A. Kahn, M.A. Cummings Muons, Inc, Illinois, USA E.Z. Barzi Fermilab, Batavia, Illinois, USA
	State-of-the-art Nb3Sn wires have plateaued in the performance of the critical current density Jc. Chemical and geometrical optimization of the wire layout have produced Nb3Sn wires with average Jc(4.2K, 16T) ~ 1,300 A/mm2. A future high energy hadron collider that is being considered to follow the LHC would need larger Jc and be cost effective. The approach to improving the performance of Nb3Sn conductor would be to introduce enhanced flux pinning mechanisms with nano-engineering techniques.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL037
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THPAL041	Power Coupler Design for the LUCRECE Project	cavity, simulation, SRF, linac	3732
	H. Guler, D. Auguste, J. Bonis, O. Bouras, M. El Khaldi, W. Kaabi, P. Lepercq LAL, Orsay, France
	The LUCRECE project aims at developing an elementary RF system (cavity, power source, LLRF and controls) suitable for continuous (CW) operation at 1.3 GHz. This effort is made in the framework of the advanced and compact FEL project LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation), using superconducting linac technology for high repetition rate and multi-user operation (www.lunex5.com). In this context, based on its large experience on coupler design and RF conditioning, LAL Laboratory is in charge of the design and the fabrication of RF couplers that could operate at up to 15-20 kW in CW mode. For this purpose, geometry based on CORNELL 65kW CW couplers will me modified to fulfil the LCLS2 type cavity with the high necessary coupling level. Electromagnetic simulations and optimisation and associated thermal heating will be discussed. Methods to decrease the thermal impact, and strategy for RF conditioning will be considered.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL041
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THPAL049	Power Supply Decoupling Design	controls, power-supply, simulation, electron	3751
	Y.T. Li, F.Y. Chang NSRRC, Hsinchu, Taiwan
	After an actual operation of the phase-shifted magnet's power supply was conducted, it was found that the currents in the two modules of magnets would be coupled each other. In order to solve this mutual coupling current, a decoupling controller is designed. From the experiment results indicate that it does not only solve the issue of coupling current but also shorten the rising time of the power supply current. This helps to increase the power supply bandwidth.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL049
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THPAL061	Simulation of Pulsed Temperature Rise in Cryogenic Copper RF Cavity Achieving a Very High Accelerating Field	cavity, simulation, accelerating-gradient, cryogenics	3788
	T. Tanaka, K. Hayakawa, Y. Hayakawa, K. Nogami, T. Sakai, Y. Sumitomo LEBRA, Funabashi, Japan
	A cryogenic C-band photocathode RF electron gun cavity has been studied at Nihon University LEBRA in cooperation with KEK. The RF properties of a cold model measured at 20 K have shown good agreement with those expected from computer simulations using the cavity surface resistance predicted by the theory of the anomalous skin effect. Recent studies on the vacuum RF breakdown at high electric fields suggest that the temperature in the cavity surface during the high power RF pulse has a significant effect on the behavior of the breakdown rate. In order to investigate the breakdown property of the cryogenic cavity aiming at a very high accelerating field with as low breakdown rate as possible, one-dimensional simulations of the temperature rise in the cavity surface have been done for various combinations of the RF pulse width and the peak input RF power. The evaluation will be taken into consideration in the design of a new high power cryogenic cavity that has basically the same configuration with the cold model.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL061
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THPAL080	Parallel-Feed SRF Accelerator Structures	cavity, SRF, simulation, impedance	3835
	P.B. Welander, Z. Li, M.H. Nasr, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This work is supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. Development of SRF accelerator technology that enables both higher gradient and higher efficiency is crucial for future machines. While much of the recent R&D focus has been on materials and surface science, our aim is to optimize the cavity geometry to maximize performance with current materials. The recent demonstration of a highly efficient parallel-feed NCRF structure at SLAC has served as a proof-of-concept. Applied to SRF, such a structure could dramatically reduce power consumption while boosting the achievable gradient. Instead of coupled elliptical cells, our structure employs isolated reentrant cells. To feed RF power to the cavities, each cell is directly coupled to an integrated manifold. The structure is made in two parts, split along the beam axis, which are then joined. Such a structure has been fabricated from bulk Cu and tested at SLAC - designed for X-band, it operates at a record gradient of 150 MV/m. Adapting to SRF at 1.3 GHz and fabricating from Nb, such a cavity could achieve more than 50% lower RF loss and 40% higher gradient compared to the TESLA cavity. We will describe our simulations and propose an experimental roadmap for demonstrating this technology.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL080
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THPAL109	The New 118 MHz Cavity for RF Development Activities of the RF for Accelerator Laboratory at SLRI	cavity, simulation, HOM, impedance	3895
	N. Juntong, K. Kittimanapun, P. Sunwong SLRI, Nakhon Ratchasima, Thailand A. Sutchada Walailak University, Nakhon Si Thammarat, Thailand
	The RF for accelerator laboratory is established at SLRI to perform RF related development activities of the current light source and the future synchrotron light facility in Thailand. One of activities is to build an in-house RF cavity. It will be used for testing of RF amplifier unit and the developed LLRF system. The cavity is a nose-cone pill-box cavity operating at 118 MHz and aiming at 100 kV gap voltage. Details of designing in particular the inner surface profile, the RF properties, the higher order modes properties, the RF power coupler, and the tuning mechanism will be presented with the manufacturing timeline.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL109
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THPAL110	High-Power RF Test of Coaxial Couplers for the Injection Linac of XiPAF	cavity, vacuum, multipactoring, linac	3899
	Y. Lei, X. Guan, R. Tang, X.W. Wang, Q.Z. Xing, H.Y. Zhang, S.X. Zheng TUB, Beijing, People's Republic of China J. Jiang, H. Li, C. Yu Beijing Aerospace Guagntong Technology Co., Beijing, People's Republic of China
	For the high-power RF test of the coaxial couplers which will be employed on the linac injector of the XiPAF (Xi'an Proton Application Facility) project, a high-power conditioning cavity was designed and manufactured [1]. There are some optimized aspects on the cavity and couplers to obtain better RF performance during the high-power testing process. The traveling-wave test and full-power-reflection test were executed to check whether the coupler can afford the enough power level for the linac operation, and whether only one coupler can afford the total power for the RFQ. The construction of the testing stand, optimization of RF parameters and results of high-power RF test are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL110
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THPAL152	Study of X-Band Phase Shifter Using Ferrite Material	cavity, GUI, simulation, insertion	4005
	Y.L. Jiang, D.Z. Cao, H.B. Chen, J. Shi, P. Wang, H. Zha TUB, Beijing, People's Republic of China
	Ferrite has the feature of the permeability depended on the external static magnetic field, thus could be used to shift the phase of the propagating radio frequency (RF) signal. In this paper, we introduce a novel design of ferrite-based RF phase shifter. The design changes the resonant frequency of a ferrite-filled pill-box cavity to implement the phase changing. This design has a lower local RF field and a higher sensitivity on the phase changing than those of waveguide phase shifter, which may bring advantages such as higher power capacity, fast changing speed and lower insertion loss. Theory and simulation results are also presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL152
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THPAL153	High Power Test of the S-Band Spherical Pulse Compressor at Tsinghua University	cavity, FEL, polarization, klystron	4008
	P. Wang, D.Z. Cao, H.B. Chen, C. Cheng, J. Shi, Z.H. Wang, H. Zha TUB, Beijing, People's Republic of China
	We designed, fabricated and high power tested an S-band spherical pulse compressor for the high-power test facility at Tsinghua University. The pulse compressor comprises a spherical resonant cavity with an unloaded quality factor of 100, 000 and an RF polarizer with two rectangular ports and a circular port. To achieve high efficiency and large power gain, the coupling coefficient was optimized to 8 with input pulse length of 3.6 us and compression ratio of 12. After conditioning the RF system, the pulse compressor generated RF pulses with peak power of more than 400MW. And during the operation, the pulse compressor has very low breakdown rate and was extremely stable.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL153
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THPMF028	Coherent Stacking Scheme for Inverse-Compton Scattering at MHz Repetition Rates	laser, cavity, simulation, feedback	4103
	P. Piot, D. Mihalcea Northern Illinois University, DeKalb, Illinois, USA T.J. Campese, A.Y. Murokh RadiaBeam Systems, Santa Monica, California, USA D. Mihalcea, P. Piot, J. Ruan Fermilab, Batavia, Illinois, USA
	Funding: Work sponsored by the DNDO award 2015-DN-077-ARI094 to Northern Illinois University and US DOE contract DE-AC02-07CH11359 to Fermilab. An experiment to produce 1-MeV gamma rays via Compton back-scattering of infrared photons on 250-MeV electron bunches is currently in preparation at the Fermilab Accelerator Science & Technology (FAST) facility. To increase the gamma-ray flux the energy of the infrared laser pulses are planned to be amplified within the interaction region using a resonant cavity. This passive amplifier composed of a Fabry-Perot cavity will allow the laser pulse bunches to coherently and constructively stack. Our estimates, based on theoretical models, show that the laser pulse energy can be increased from approximately 1-2 mJ at the exit of the last active amplifier to 5 -10 mJ at the interaction point when the laser repetition rate is set at the nominal value of 3 MHz. This paper details the cavity design option(s) and associated wave-optic simulations.
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THPMF050	High-Efficient XFELO Based on Optical Resonator with Self-Modulated Q-Factor	undulator, FEL, laser, electron	4172
	S.V. Kuzikov, A.V. Savilov, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia S.P. Antipov, S.V. Kuzikov Euclid TechLabs, LLC, Solon, Ohio, USA
	In this paper we describe an efficient XFELO having a new non-stationary out-coupling scheme. It consists of two undulator sections placed inside optical cavity. The first section is a conventional uniform undulator and the second one is a tapered undulator. At start time point X-ray radiation is mostly produced by the uniform section. Mirrors of XFELO's optical resonator are designed so that diffraction Q-factor reaches the highest value, i.e losses are near zero. As X-ray power increases the tapered undulator begins to contribute more to radiation power. However a portion of that power misses mirrors of the optical cavity, because those are tuned to confine radiation produced by the first undulator. This process establishes a steady state operation of the XFELO.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF050
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THPMF060	Touschek Beam Loss Simulation for Light Source Storage Rings	electron, scattering, storage-ring, simulation	4206
	M. Takao, K. Soutome JASRI/SPring-8, Hyogo-ken, Japan Y. Shimosaki JASRI, Hyogo, Japan K. Soutome, H. Tanaka RIKEN SPring-8 Center, Hyogo, Japan
	In light source storage rings, it is important to know the distribution of lost electrons due to the Touschek scattering for protecting insertion devices (IDs) from radiation damage. This will become crucial especially in future light sources where narrow gap in-vacuum IDs are normally used. While the Touschek scattered electron begins to oscillate in the horizontal direction with the amplitude proportional to the dispersion at the scattering point and to the momentum deviation after scattering, the motion is converted into the vertical direction due to the betatron coupling and some of the scattered electrons are lost at the narrow gaps of in-vacuum IDs. The momentum deviation by the Touschek scattering reaches 5% more, and according to which the vertical oscillation is more excited. Hence electrons even scattered at small horizontal dispersion are also lost at narrow gap IDs. We carried out computer simulations by taking the present SPring-8 storage ring and a planned 3GeV low-emittance ring as examples. The results and possible measures for ID protection will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF060
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THPMK018	Design of a rotationally symmetric S-band photocathode RF gun	gun, cathode, impedance, emittance	4336
	Zh. X. Tang USTC, Hefei, Anhui, People's Republic of China Z.G. He, W.W. Li, Y.J. Pei, L. Wang USTC/NSRL, Hefei, Anhui, People's Republic of China
	The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell with a symmetrical distribution of four grooves is concatenated to the first 0.6 cell at the photocathode end to form a new resonant cell (NRC) to mantain the symmetric multi-pole field in 1.6 cell. Our simulations indicate that 3D multi-pole fields of NRC are with the perfect symmetry. After that, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Our simulations demonstrate promising outlook of using coaxial cell for photocathode RF guns with various applications.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK018
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THPMK130	Study of Beam Instabilities with a Higher-Harmonic Cavity for the HALS	cavity, storage-ring, HOM, quadrupole	4623
	Y.G. Tang, W. Li, Z.B. Sun, L. Wang, C.-F. Wu USTC/NSRL, Hefei, Anhui, People's Republic of China
	Hefei Advanced Light Source (HALS), a diffrac-tion-limited storage ring is on the design. In HALS project, a passive higher-harmonic cavity may be added in order to increase the beam lifetime of the storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the high-er-harmonic cavity. In this paper, we run an algorithm (analytic modeling) to consider the Robinson instabilities for normal and superconducting cavity respectively. The Robinson instabilities are predicted with and without mode coupling. Coupled-bunch instability induced by resonant interaction with parasitic longitudinal mode is also considered. The analytic modeling may be used to give rf-cavity parameters that are more conducive to stability. The results show that the storage ring can oper-ate at a higher beam current and the parasitic high-er-order mode of the fundamental cavity has less impact on the beam by using superconducting harmonic cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK130
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THPMK139	Design of 9/6 MeV S-band Electron Linac Structure with 1.5 Bunching Cells	linac, bunching, electron, simulation	4635
	Y. Joo, P. Buaphad, H.R. Lee University of Science and Technology of Korea (UST), Daejeon, Republic of Korea S.C. Cha, Y. Kim KAERI, Daejon, Republic of Korea
	Funding: University of Science and Technology of Korea The Korea Atomic Energy Research Institute (KAERI) has been developing several 9/6 MeV dual energy S-band RF electron linear accelerators (linacs) for non-destructive testing such as container inspection system. Until now the bunching cell of the linac has a full-cell geometry. However, to maximize the acceleration of electrons after emission from the electron gun, the geometry of the first bunching cell is modified from a full-cell to a half-cell. The optimization of Q-factor and flatness of electric field along the linac structure can be obtained by adjusting diameters of bunching and power coupling cells. By adjusting gap of the first side-coupling cell, we can optimize the field ratio between the bunching cells and normal accelerating cells. In this paper, we describe design concepts of a 9/6 MeV linac with 1.5 bunching cells as well as optimization of RF parameters such as the quality factor, resonance frequency, and electric field distribution.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK139
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THPML047	Design and Measurement of the X-Band Pulse Compressor for TTX	cavity, GUI, vacuum, ISOL	4745
	Y.L. Jiang, H.B. Chen, C. Cheng, W. Gai, J. Shi, P. Wang, Z.H. Wang, X.W. Wu, H. Zha TUB, Beijing, People's Republic of China
	A radio frequency (RF) pulse compressor had been designed for the X-band (11.424 GHz) high power test stands at the Accelerator Laboratory of Tsinghua University. It is the SLED-I type pulse compressor, which uses a high quality factor corrugated circular cavity to store the RF power. An RF polarizer couples two quadrature modes into the cavity so that the pulse compressor needs only one cavity. The cavity implements HE1-1-14 mode, with the Q0 of 115, 000 and the coupling factor (β) of 3.23. The design and the microwave measurement before brazing of this pulse compressor are presented in this paper.
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THPML095	Improvement of Wire-Stretching Technique to the RF Measurements of E-Center and Multipole Field for the Dipole Cavities	cavity, kicker, simulation, electron	4885
	G.-T. Park, J. Guo, H. Wang JLab, Newport News, Virginia, USA A. Overstreet ODU, Norfolk, Virginia, USA B. P. Xiao, T. Xin BNL, Upton, Long Island, New York, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. After the first publication* of wire-stretching technique from its principle to measure the electrical center of a deflecting cavity, more refinements of this techniques including the review of its analytical and simulation results, RF circuit improvement to improve the signal to noise ratio and its application to other cavities have been developed. These applications include the electrical center measurements for the LHC RFD and DQW crabbing cavity prototypes, multi-frequency harmonic kicker cavity for JLEIC electron cooler, TE011 cavity developed for the beam magnetization measurement, and a separator cavity at BNL**. Further development of measurement calibration, error reduction, alignment of cavity installation to the machine beam line, and multipole field analysis for the beam dynamics will be presented. H. Wang, Proceedings of NAPAC2016, pp225-228 S. A. Overstreet, BS Thesis 2017, Guilford College, Greensboro, NC J. Guo et al. these proceedings ***T. Xin et al, these proceedings
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THPML096	A Non-Invasive Magnetic Momentum Monitor Using a TE011 Cavity	cavity, impedance, electron, GUI	4889
	J. Guo, J. Henry, M. Poelker, R.A. Rimmer, R. Suleiman, H. Wang JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC with Laboratory Directed Research and Development funding, under U.S. DOE Contract No. DE-AC05-06OR23177. The Jefferson Lab Electron-Ion Collider (JLEIC) design relies on cooling of the ion beam with bunched electron beam. The bunched beam cooler complex consists of a high current magnetized electron source, an energy recovery linac, a circulating ring, and a pair of long solenoids where the cooling takes place. A non-invasive real time monitoring system is highly desired to quantify electron beam magnetization. The authors propose to use a passive copper RF cavity in TE011 mode as such a monitor. In this paper, we will show the mechanism and scaling law of this device, as well as the design and testing results of the prototype cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML096
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THPML113	Design and Simulation of the Waveguide Coupler for the Cavity Beam Monitor	GUI, cavity, simulation, electromagnetic-fields	4932
	Q. Wang, Q. Luo, B.G. Sun, F.F. Wu, Y.L. Yang, Z.R. Zhou USTC/NSRL, Hefei, Anhui, People's Republic of China Y.W. Wu USTC, Hefei, Anhui, People's Republic of China
	Funding: Supported by The National Key Research and Development Program of China (2016YFA0401900), NSFC (11375178, 11575181) and the Fundamental Research Funds for the Central Universities (WK2310000046) The waveguide coupling is an important way to extract the signals of the specific eigenmodes required. The design of the waveguide coupler, including the waveguide-to-coaxial adapter behind it for the cavity bunch length monitor is presented. The influence of the dimension parameters is analyzed, which offers the theoretical support for the design and application of cavity bunch length monitor or cavity beam position monitor (CBPM). A series simulation based on CST is performed to verify the feasibility, and the simulation results show good performance.
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THPML117	Study of the Impact of Linear Coupling on Off-Axis Injection	resonance, injection, dynamic-aperture, quadrupole	4943
	X. Huang SLAC, Menlo Park, California, USA T. Zhang USTC/NSRL, Hefei, Anhui, People's Republic of China
	The next generation of storage ring light sources will likely operate with high linear coupling, which could potentially prevent the use of off-axis injection as large horizontal oscillation of the injected beam is coupled to the vertical plane. We did experiments on the SPEAR3 storage ring to study how linear coupling impact the dynamic aperture and the off-axis injection efficiency. The results show that the dynamic aperture is significantly reduced and injection efficiency can drop to zero when operated on the coupling resonance. However, with large nonlinear detuning, the dynamic aperture and high injection efficiency can survive with the stored beam at full coupling because the injected beam is shifted away from the coupling resonance.
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THPML125	Efficiency Analysis of High Average Power Linacs for Environmental and Industrial Applications	linac, impedance, beam-loading, higher-order-mode	4970

Paper

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MOPMF010

Measurement and Simulation of Betatron Coupling Beam Transfer Function in RHIC

betatron, simulation, experiment, quadrupole

99

Y. Luo, W. Fischer, A. Marusic, M.G. Minty
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.
Transfer function measurements are important for characterizing betatron tunes, betatron coupling, and beam spectrum in the routine operation of the Relativistic Heavy Ion Collider (RHIC). To counteract the linear betatron coupling, we developed a technique to continuously measure the betatron coupling coefficient with a base band phase lock loop tune meter in 2006. Based on this technique, we demonstrated and built a robust tune/coupling feedback in RHIC. In this article, we revisit the BTF measurement with betatron coupling to benchmark our BTF simulation code. We also compared the values of eigenmode projection ratios from BTF with those calculated with the single particle model.

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MOPMF020

Higher Order Mode Coupling Options for the eRHIC Crab Cavity

cavity, HOM, damping, impedance

121

Q. Wu, I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: This work was supported by the US Department of Energy via Brookhaven Science Associates LLC under contract no. DE-SC0012704.
The eRHIC crab cavity adopts the double quarter wave structure developed at Brookhaven National Lab for the LHC Hi-Lumi upgrade crab cavities. The cavity's fundamental mode is at 338 MHz with the first higher order mode more than 180 MHz above that. We looked into the higher order mode distribution up to 2 GHz, and considered various locations and geometries of the coupling scheme. The cylindrical outer shell of the cavity allowed various possibilities for coupler port openings on all the walls, which were difficult for the narrow waist of the LHC double quarter wave crab cavities. Beam pipe absorbers are also options for simpler high frequency modes damping. Some preliminary high pass filter design will also be discussed in this paper.

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MOPMF023

Updates on the Optic Corrections of FCC-hh

quadrupole, injection, dipole, interaction-region

133

D. Boutin, A. Chancé, B. Dalena
CEA/IRFU, Gif-sur-Yvette, France
B.J. Holzer, D. Schulte
CERN, Geneva, Switzerland

The FCC-hh (Future Hadron-Hadron Circular Collider) is one of the options considered for the next generation accelerator in high-energy physics as recommended by the European Strategy Group, and the natural evolution of existing LHC. The evaluation of the various magnets mechanical error and field error tolerances in the arc sections of FCC-hh, as well as an estimation of the correctors strengths necessary to perform the error corrections, are important aspects of the collider design. In this study recommended values for the mechanical errors, dipole and quadrupole field errors tolerances are proposed, with the possible consequences on the correctors technological choice and on the beam screen design. Advanced correction schemes of the linear coupling (with skew quadrupoles) and of the beam tunes (with normal quadrupoles) are discussed. Also a combined correction scheme including the interaction regions is tested.

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MOPMF030

Broadband Impedance of Pumping Holes and Interconnects in the FCC-hh Beamscreen

impedance, wakefield, electronics, injection

153

S. Arsenyev, D. Schulte
CERN, Geneva, Switzerland

In the proposed Future Circular Collider (FCC-hh) pumping holes and interconnects between sections of the beamscreen can be sources of unwanted broadband impedance, potentially leading to the transverse mode coupling instability (TMCI). The pumping holes pose a greater challenge to the impedance calculation due to their small contribution per hole. Unlike for the Large Hadron Collider (LHC), analytical methods cannot be applied due to the complex beamscreen geometry and the greater size of the holes. Instead, two computational methods are used and compared to each other. For the interconnects, the impedance due to a sophisticated system of tapers is also estimated using computational methods.

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MOPMF031

Modelling Wake Impedance of a Rough Surface in Application to the FCC-hh Beamscreen

impedance, electron, laser, vacuum

157

S. Arsenyev, D. Schulte
CERN, Geneva, Switzerland

The inner surface of the future circular collider (FCC-hh) beamscreen is proposed to be laser-treated in order to mitigate the electron cloud build-up. However, the rough structure of the treated surface can result in unwanted impedance increase, potentially leading to the transverse mode coupling instability (TMCI). Three models have been adopted to estimate the wake impedance of a beamscreen with a rough surface. The models use the resistive wall formalism generalized for the case of an arbitrary surface impedance. The results apply to a beamscreen of a circular cross-section with the homogeneously rough inner surface for the case of ultrarelativistic particles. The free parameters of the models were fit into preliminary measurements of the surface resistivity, giving, as a result, a range of the real and the imaginary parts of the wake impedance.

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MOPMF032

Nonlinear Correction Strategies for the LHC Using Resonance Driving Terms

resonance, dipole, optics, insertion

161

F.S. Carlier, E.H. Maclean, T. Persson, R. Tomás
CERN, Geneva, Switzerland

The correction of nonlinearities in future colliders is critical to reach operational conditions and pose a significant challenge for commissioning schemes. Several approaches have been succesfully used in the LHC to correct sextupolar and octupolar sources in the LHC insertion regions. Measurements of resonance driving terms at top energy in the LHC have improved and now offer a new observable to calculate and validate nonlinear corrections. This paper reports on measurements of resonance driving terms in the LHC and the relevant strategies used for nonlinear corrections.

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MOPMF046

Simulation of Hydrodynamic Tunneling Caused by High Energy Proton Beam in Copper through Coupling of FLUKA and Autodyn

target, simulation, proton, collider

204

Y.C. Nie, A. Bertarelli, F. Carra, C. Fichera, L.K. Mettler, R. Schmidt, D. Wollmann
CERN, Geneva, Switzerland

For machine protection of high-energy colliders, it is important to assess potential damages caused to accelerator components in case large number of bunches are lost at the same place. The numerical assessment requires an iterative execution of an energy-deposition code and a hydrodynamic code, since the hydrodynamic tunneling effect will likely play an important role in the beam-matter interactions. For proton accelerators at CERN and for the Future Circular Collider (FCC), case studies were performed, coupling FLUKA and BIG2. To compare different hydrocodes and not to rely only on BIG2, FLUKA and a commercial tool, Autodyn, have been used to perform these simulations. This paper reports a benchmarking study against a beam test performed at the HiRadMat (High-Radiation to Materials) facility using beams at 440 GeV from the Super Proton Synchrotron. Good agreement has been found between the simulation results and the test as well as previous simulations with FLUKA and BIG2, particularly in terms of penetration depth of the beam in copper. This makes the coupling of FLUKA and Autodyn an alternative solution to simulating the hydrodynamic tunneling. More case studies are planned for FCC and other high-beam-power accelerators.

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MOPMF047

Transverse Coupling Measurements With High Intensity Beams Using Driven Oscillations

dipole, injection, controls, resonance

208

T. Persson, G. Baud, X. Buffat, J.M. Coello de Portugal, E. Fol, K. Fuchsberger, M. Gabriel, M. Gąsior, M. Giovannozzi, G.H. Hemelsoet, M. Hostettler, M. Hruska, D. Jacquet, E.H. Maclean, L. Malina, J. Olexa, P.K. Skowroński, M. Solfaroli Camillocci, M.E. Söderén, R. Tomás, D. Valuch, A. Wegscheider, J. Wenninger
CERN, Geneva, Switzerland

Transverse coupling has been linked to instabilities and reduction in dynamic aperture and is hence a crucial parameter to control in the LHC. In this article we describe the development to use driven oscillations to measure the transverse coupling with high intensity beams. The method relies on the use of the transverse damper to drive an oscillation in a similar way as with an AC-dipole. The calculation of the coupling is based on the turn-by-turn data from all available BPMs gated for the excited bunch.

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MOPMF071

Polarization Studies for the eRHIC electron Storage Ring

polarization, storage-ring, electron, solenoid

292

E. Gianfelice-Wendt
Fermilab, Batavia, Illinois, USA
S. Tepikian
BNL, Upton, Long Island, New York, USA

Funding: Manuscript authored by Fermi Res. All., LLC under Contr. No. DE-AC02-07CH11359 and Brookhaven Sc. Ass., LLC under Contr. No. DE-AC02-98CH10886 with the U.S. DOE, Office of Science, Office of HEP.
A hadron/lepton collider with polarized beams has been under consideration by the scientific community since some years, in the U.S. and Europe. Among the various proposals, those by JLAB and BNL with polarized electron and proton beams are currently under closer study in the U.S. Experimenters call for the simultaneous storage of electron bunches with both spin helicity. In the BNL based Ring-Ring design, electrons are stored at top energy in a ring to be accommodated in the existing RHIC tunnel. The transversely polarized electron beam is injected into the storage ring at variable energies, between 5 and 18 GeV. Polarization is brought into the longitudinal direction at the IP by a couple of spin rotators. In this paper results of first studies of the attainable beam polarization level and lifetime in the storage ring at 18 GeV are presented.

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MOPML015

Simulations and Measurements of the CCL Modules of the LIGHT Accelerator

linac, proton, GUI, cavity

429

V. F. Khan, G. De Michele, S. Fanella, S. H. Gibson, Ye. Ivanisenko, C. Mellace, J.L. Navarro Quirante, C. Zannini
AVO-ADAM, Meyrin, Switzerland
M. Esposito, P. Gradassi
CERN, Geneva, Switzerland

A 230 MeV proton LINAC system for medical applications is being developed and commissioned for the LIGHT (Linac Image Guided Hadron Therapy) project by AVO-ADAM. The LINAC system consists of a 750 MHz RFQ (Radio frequency quadrupole) for the low energy proton acceleration, 2998 MHz SCDTL (Side Coupled Drift Tube Linacs) for the medium energy and 2998 MHz CCL (Coupled Cavity Linacs) for the high energy. In particular, the CCL accelerating modules are used in the energy range from 37.5 - 230 MeV. In this paper we discuss the 3D EM (electro-magnetic) simulation results and measurements of the CCL modules.

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MOPML067

9/6 MeV European S-band Linac Structure for Container Inspection System at RTX and KAERI

electron, linac, bunching, gun

560

P. Buaphad, H.D. Park, S. Song
RTX, Daejeon, Republic of Korea
P. Buaphad, Y. Joo
University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
P. Buaphad, S.C. Cha, Y. Joo, Y. Kim, H.R. Lee
KAERI, Jeongeup-si, Republic of Korea

Recently, demands on low energy electron linear accelerators (linacs) for industrial applications are rapidly growing. Their beam energies are lower than 20 MeV, and they require a compact, cheap, and stable accelerator system. For the Container Inspection System (CIS), KAERI successfully developed a 9/6 MeV American S-band (= 2856 MHz) linac with a 5 MW klystron in 2013. To reduce the cost of the RF source, recently, KAERI and RTX also have been developing another 9/6 MeV European S-band (= 2998 MHz) linac by using a magnetron with a lower RF power of about 3.1 MW. Its accelerating structure is designed to be operated in π/2 mode by coupling 13 accelerating cells together through 12 side-coupling cells. The CST Microwave Studio is used for electromagnetic simulations and optimization of the accelerating structure. After various optimizations, a shunt impedance of 84 MΩ/m is obtained at π/2 mode frequency of 2998.31 MHz. In this paper, we describe design concept, optimization, and RF measurement of the new 9/6 MeV European S-band linac structure. Then, we compare it with our old American S-band linac structure.

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TUPAF024

Impedance and Instability Studies in LEIR with Xenon

impedance, space-charge, accumulation, injection

720

N. Biancacci, H. Bartosik, M. Gąsior, S. Hirlaender, V. Kain, T.E. Levens, E. Métral
CERN, Geneva, Switzerland
M. Migliorati
Rome University La Sapienza, Roma, Italy

In 2017, the LEIR accelerator has been operated with Xe³⁹⁺ beam for fixed target experiments in the SPS North Area. The different ion species, with respect to the usually operated Pb⁵⁴⁺, allowed for additional comparative measurements of tune shift versus intensity at injection energy both in coasting and bunched beams. The fast transverse instability observed for high accumulated intensities has been as well characterized and additional observations relevant to impedance have been collected from longitudinal Schottky signal and BTF measurements. The results of these measurements are summarised and compared to the currently developed machine impedance model.

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TUPAL040

Ion Beam Studies in the FRIB Front End

ion-source, space-charge, ECR, optics

1094

T. Yoshimoto, K. Fukushima, S.M. Lidia, T. Maruta, P.N. Ostroumov, G. Pozdeyev, H.T. Ren
FRIB, East Lansing, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511.
The commissioning of the FRIB Front End with 12 keV/u argon beam started in the spring of 2017*. Beam profile monitors were used to evaluate RMS Twiss parameters in various locations along the beam line. Beam dynamics in the LEBT was simulated using full 3D model of beam optics elements in the tracking codes. We found a good consistency between measured and simulated data. A beam image viewer was used to measure the beam density distribution in the real space. A hollow beam structure was observed in the Ar⁹⁺ beam with the current of ~20 eμA. Extensive beam dynamics study with 3D tracking code suggests that the hollow density distribution can be generated by space charge effects of the multi-component, multi-charge state ion beam just after the ECR ion source. This paper reports studies of a mechanism that can produce a hollow beam structure.
*E. Pozdeyev, invited talk at this conference

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TUPAL050

Progress Work on a CW Deuteron RFQ with Magnetic Coupling Windows

rfq, cavity, experiment, Windows

1123

Q. Fu, M.J. Easton, P.P. Gan, S.L. Gao, H.P. Li, Y.R. Lu, Q.Y. Tan, Z. Wang, K. Zhu
PKU, Beijing, People's Republic of China
W.P. Dou, Y. He
IMP/CAS, Lanzhou, People's Republic of China

Funding: This work was supported by the National Basic Research Program of China (Grant No. 2014CB845503).
A new 162.5 MHz RFQ has been built for a joint 973 project between Peking University (PKU) and Institute of Modern Physics (IMP). It is designed to deliver 50-mA deuteron beams to 1 MeV in CW mode, with an inter-voltage of 60 kV and a length of 1.809 m. Due to its window-type structure, the RFQ has compact cross-section, sufficient mode separation and high specific shunt impedance. It consists of two segments fabricated and installed at IMP. The assembling error of the cavity is less than 0.05 mm. The RF measurements show good electrical properties of the resonant cavity with a measured unloaded quality factor equal to 96.4% of the simulated value. After tuning, we obtained the nominal frequency and field unbalance within 1.0%. Preparation of high-power test of this RFQ is underway. This paper will cover the fabrication details and RF measurements, as well as the progress of high-power test.

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TUPAL072

Dispersive Electron Cooling for JLEIC

electron, emittance, proton, scattering

1178

H. Zhang, Y.S. Derbenev, Y. Zhang
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-06CH11357.
JLEIC is the electron ion collider under design at Jefferson Lab, which will provide a luminosity up to 1034 cm^-2s⁻¹. To reach the high luminosity, short ion and electron bunches with high charge density colliding in high frequency are proposed in JLEIC design. The high charge density of the ion beam leads to strong intrabeam scattering effect, which enlarges the ion beam emittance and ruins the luminosity if not mitigated. Magnetized electron cooling is implemented to overcome the intrabeam scattering effect and to reduce or maintain the ion beam emittance. In this paper, we discuss the redistribution of the cooling effects in the longitudinal and the transverse directions by introducing the dispersion of the ion beam in the cooling section. When the charge density of the cooling electron beam varies, the dispersion of the ion beam leads to an increase of the transverse cooling rate and a reduction of the longitudinal cooling rate, while the total decrement of the Courant-Snyder invariant of the ion beam increases. Both theoretical analysis and numerical calculation are presented.

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TUZGBE4

Toward High-Power High-Gradient Testing of mm-Wave Standing-Wave Accelerating Structures

experiment, cavity, accelerating-gradient, diagnostics

1224

E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi
SLAC, Menlo Park, California, USA
S. Jawla, R.J. Temkin
MIT/PSFC, Cambridge, Massachusetts, USA
S. C. Schaub
MIT, Cambridge, Massachusetts, USA
B. Spataro
INFN/LNF, Frascati (Roma), Italy

Funding: This work is supported in part by Department of Energy contract DE-AC02-76SF00515 (SLAC) and DE-SC0015566 (MIT).
We will preliminary testing results for single-cell accelerating structures intended for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.

Slides TUZGBE4 [4.644 MB]

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TUPMF003

Dynamic Tuning of the APS-U Booster 5-cell Cavities

booster, cavity, resonance, extraction

1251

G.J. Waldschmidt, M. Abliz, T.G. Berenc, D. Horan, U. Wienands
ANL, Argonne, Illinois, USA

The booster synchrotron for the APS-U is being upgraded to accommodate high-charge bunches, up to 20 nC, for extraction into the MBA lattice. The booster is required to operate at 85% efficiency in order to achieve bunch swap-out into the storage ring. In order to compensate for significant beam-loading effects as well as support a frequency ramp to achieve higher efficiency, a ferrite tuner is being considered to dynamically adjust the cavity frequency. A tuner design will be presented that spans 60 kHz and utilizes a low-loss YIG garnet similar to that used in the Recycler Ring at Fermilab.

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TUPMF032

RF Conceptual Design of Normal Conducting Cavity for an eRHIC Rapid Cycling Synchrotron

cavity, electron, GUI, vacuum

1316

B. P. Xiao, M. Blaskiewicz, J.M. Brennan, D. Holmes, K.S. Smith, T. Xin, A. Zaltsman
BNL, Upton, Long Island, New York, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
The Rapid Cycling Synchrotron (RCS) for the eRHIC Ring-Ring design will provide on energy injection (up to 18 GeV) of high charge, polarized electron bunches to the eRHIC electron storage ring. The RF system comprises a large number of 563MHz fundamental cavities, providing up to 45MV per turn. The cavities will operate in pulsed mode with <20% duty factor, at a repetition rate of 1 Hz. In this paper we report the conceptual RF design of the cavity.

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TUPMF053

Longitudinal Impedance Measurement of the Strip-Line Kicker for High Energy Photon Source (HEPS)

impedance, kicker, simulation, distributed

1379

S.K. Tian, J. Chen, Y. Jiao, H. Shi, L. Wang, N. Wang
IHEP, Beijing, People's Republic of China

The High Energy Photon Source (HEPS) is a 6-GeV, kilometer-scale storage ring light source to be built in China. One of the main design challenges of the storage ring is to minimize collective instabilities associated with the impedance of small-aperture vacuum components. In this paper we present beam coupling impedance measurements obtained by the well known coaxial wire method, for the HEPS Strip-Line kicker. The frequency dependent real and imaginary parts of the distributed impedance are obtained from the measured S-parameters.

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TUPMF068

Beam Dynamics on a Coupling Resonance at PETRA III

resonance, optics, lattice, injection

1417

I.V. Agapov, J. Keil, G. Kube, G.K. Sahoo, R. Wanzenberg
DESY, Hamburg, Germany
Y.-C. Chae
ANL, Argonne, Illinois, USA
A.I. Novokshonov
TPU, Tomsk, Russia

Working on a coupling resonance is a usual way of producing round beams in a synchrotron. The beam dynamics in this regime is however more complicated, and the emittance is sensitive to the working point, coupling correction, and bunch current drop with time, which complicates the operation. We present experience with optics setup for working on a coupling resonance in PETRA III, including linear and nonlinear beam optics characteristics, and the measurement of the horizontal and vertical beam emittances with a 2D interferometer. Beam dynamics on a coupling resonance for PETRA IV, the MBA upgrade of PETRA III currently under consideration, is also presented.

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TUPMK018

Round Beam Studies at NSLS-II

emittance, resonance, lattice, experiment

1529

Y. Hidaka, W.X. Cheng, Y. Li, T.V. Shaftan, G.M. Wang
BNL, Upton, Long Island, New York, USA

Funding: The study is supported by U.S. DOE under Contract No. DE-AC02-98CH10886.
Instead of typical flat beam, some synchrotron light us-ers prefer round beam, i.e., with equal horizontal and vertical emittance, for various reasons (e.g., simplified optics, smaller fraction of photons getting discarded, better phase space match between photon and e-beam). Several future upgrade storage rings such as APS-U, ALS-U, and SLS-2 currently plan to operate in round beam mode. We report our beam study results on round beam operating at NSLS-II by driving linear difference cou-pling resonance.

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TUPML003

Design of an L-band Accelerating Structure for the Argonne Wakefield Accelerator Facility Witness Beam Line Energy Upgrade

linac, impedance, acceleration, quadrupole

1533

J.H. Shao, M.E. Conde, D.S. Doran, J.F. Power
ANL, Argonne, Illinois, USA
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA

The Argonne Wakefield Accelerator (AWA) facility has been devoting much effort to the fundamental R&D of two-beam acceleration (TBA) technology with two parallel L-band beam lines. Beginning from the 70 MeV drive beam line, the high frequency (C-band and above) rf power is extracted from the beam by a decelerating structure (a.k.a. power extractor), transferred to an accelerating structure in the witness beam line, and used to accelerate the 15 MeV main beam. These high frequency accelerating structures usually have a small aperture to obtain high gradient and high efficiency, making it difficult for the low energy main beam to pass. To address this issue, one proposal is to increase the main beam energy to above 30 MeV by replacing the current witness linac. A 9-cell 𝜋-mode L-band standing-wave accelerating structure has therefore been designed to meet the high shunt impedance and low cost requirements. In addition, the single-feed coupling cell has been optimized with additional symmetrical ports to eliminate field distortion. The detailed design of the new accelerating structure will be presented in this paper.

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TUPML060

Three-Dimentional Spiral Beam Injection for a Compact Storage Ring

injection, solenoid, experiment, electron

1673

H. Iinuma
Ibaraki University, Hitachi, Ibaraki, Japan
M.R. Abdul
Sokendai, Ibaraki, Japan
Y. Fukao, K. Furukawa, H. Hisamatsu, T. Mibe, H. Nakayama, S. Ohsawa, K. Oide, K. Sasaki
KEK, Tsukuba, Japan

Funding: This work is supported by JSPS KAKENHI Grant Numbers JP26287055 and JP 23740216.
A newly developed three-dimensional spiral injection scheme for beam insertion into a compact (medical MRI size) solenoidal storage ring is introduced. This is a one of key R&D items for a new planned muon g-2/EDM experiment at J-PARC, which aims to measure g-2 to a factor 5 better statistical precision and a factor of 100 better sensitivity for the electric dipole moment measurement (EDM) compared to the previous experiments. The new scheme provides a smooth injection utilizing a radial solenoidal fringe field, without causing any error field in the storage volume. Magnetic pulsed kicker will guide and set the beam in the storage field volume. The strongest point of this new scheme is that any source of the electric field is removed in this scheme to perform ideal EDM measurement. We have performed a test bench experimental work to demonstrate a feasibility of this new injection scheme. Instead of the muon beam, we inject electron beam, from an electron-gun, into the solenoid magnet, and detect three-dimensional spiral beam trajectory inside of the storage chamber by CCD camera. We will discuss outline of a new injection scheme and the latest results from the test bench works.
*H. Iinuma et al.,Nuclear Instruments and Methods in Physics Research A, 832, 51-62 (2016)

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WEPAF009

Optimising Response Matrix Measurements for LOCO Analysis

storage-ring, lattice, distributed, quadrupole

1826

Y.E. Tan
AS - ANSTO, Clayton, Australia

The Linear Optics from Closed Orbit (LOCO) method is a common tool for determining storage ring lattice functions and requires a measured BPM to Corrector response matrix. For very large rings with many correctors, such measurements can be time consuming. The following study investigates how the number of correctors and the signal-to-noise ratio (SNR) affects the LOCO analysis results. For the Australian Synchrotron, the results show that four distributed correctors per plane with a SNR of >1000 is sufficient to fit the betatron functions to an accuracy of less than 0.2%.

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WEPAF017

Correction of ID-Induced Transverse Linear Coupling at NSLS-II

emittance, operation, quadrupole, resonance

1856

Y. Hidaka, Y. Li, T.V. Shaftan, T. Tanabe, Y. Tian, G.M. Wang
BNL, Upton, Long Island, New York, USA

Funding: The study is supported by U.S. DOE under Contract No. DE-AC02-98CH10886.
Sizeable lifetime jumps have been observed sporadically since March 2016 at NSLS-II. These jumps were found to coincide with insertion device (ID) gap motions. Particularly, one of the in-vacuum undulators (IVUs) at Cell 17 was discovered to have large localized skew quadrupole component variation with gap. To allow the machine to operate stably in the low-emittance mode, a global coupling feedforward system has been recently implemented and successfully deployed. After installation of a new additional skew quadrupole, coupling compensation of this ID is now performed by a local coupling feedforward system. Furthermore, the maximum gap limit of all the existing IVUs has been decreased from 40 mm to 25 mm to limit the skew component variation during user operation.

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WEPAF027

Low Q Cavity BPM Study for the Beam Position Measurement of Nanosecond Spaced Electron Bunches

cavity, FEL, dipole, electron

1881

L. Yang, X. He, L.W. Zhang
CAEP/IFP, Mainyang, Sichuan, People's Republic of China
S.S. Cao, Y.B. Leng, L.Y. Yu, R.X. Yuan
SINAP, Shanghai, People's Republic of China

Funding: National natural science foundation of China, 11705184
Low Q cavity BPM is a key to distinguish closely spaced electron bunches allowing precise beam handling for XFEL facilities operating in a multi-bunch mode at high repetition rate up to hundreds MHz. The inter-bunch signal pollution issue becomes significant when bunch separation is down to nanosecond and causes the position detection to be increasingly overestimated. Solely relying on extreme low Q to achieve sufficient decay within bunch interval leads to appreciable interference from non-signal modes due to strong overcoupling of antenna design is required. The error imposed on measured position raises a challenge to meet the goal of high resolution. Alternatively, a concept is proposed to remove the dominant part of signal pollution at the moment of sampling by intentionally shifting the phase of the last bunch signal 90degree respect to that of current bunch signal, where signal sampling is normally taken for nanosecond spaced bunches. This quadrature phase shift is defined by properly choosing the operational frequency of dipole mode regarding to the bunch frequency. A low Q cavity BPM prototype to identify technical challenges and verify this concept is under development in the R&D plan for future XFEL with high repetition rate

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WEPAF042

Measurement of Beam yz Crabbing Tilt Due to Wake Fields Using Streak Camera at CESR

wakefield, storage-ring, positron, cavity

1905

S. Wang, D. L. Rubin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This research was supported by NSF PHYS-1068662, PHYS-1416318 and DMR-1332208.
Transverse vertical wake fields can increase the vertical emittance and distort the phase space of a bunch in a storage ring. Recently, we observed charge-dependent vertical beam size growth with a single scraper inserted through the top of the storage ring vacuum chamber. This apparent growth was due in large part to the yz coupling (vertical crabbing) induced by the wake field from the asymmetric scraper configuration. Here, we report a direct measurement of a small beam yz crabbing tilt using a streak camera. The recorded images (projected beam profiles in yz plane) are analyzed with three different methods, which yield consistent beam yz tilts. We found the directly-measured current-dependent beam tilts by the streak camera are consistent with the beam tilts calculated from a wake field model.

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WEPAF058

Detection of X-Rays and Charged Particles via Detuning of the Microwave Resonator

resonance, monitoring, network, experiment

1958

S.P. Antipov
Euclid TechLabs, LLC, Solon, Ohio, USA
S.V. Kuzikov
Euclid Beamlabs LLC, Bolingbrook, USA
S. Stoupin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

Funding: DOE SBIR
Critically coupled microwave resonator is a finely balanced system, reflection at the resonance is virtually zero. Small changes in dielectric properties of resonator parts destroy this balance, small reflection can be detected from the resonator. This measurement is used in electron paramagnetic resonance studies. In this paper we discuss two accelerator - related applications of this technology. First is related to beam halo measurement taking advantage of high sensitivity of the microwave measurement. High energy particles crossing the diamond inside of a tuned resonator induce a weak conductivity in the sensing material. This small change results in resonator decoupling providing a signal proportional to a number of particles crossing the diamond plate. Second application considered is the x-ray flux monitoring. In this case it is x-ray induced photoconductivity which alters resonator coupling and produces a signal. Interestingly, sensing dielectric material embedded in a resonator can be a diamond or kapton window, refractive lens or part of a silicon monochromator. Thus an inevitable x-ray absorption on optical elements of the beamline is used to monitor x-ray flux online.

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WEPAG002

Tunable Q-Factor Gas-Filled RF Cavity

cavity, hadron, plasma, simulation

2064

M.D. Balcazar, A. Moretti, A.V. Tollestrup, A.C. Watts, K. Yonehara, R.M. Zwaska
Fermilab, Batavia, Illinois, USA
M.A. Cummings, A. Dudas, R.P. Johnson, G.M. Kazakevich, M.L. Neubauer
Muons, Inc, Illinois, USA

Funding: Work supported by Fermilab Research Alliance, LLC under Contract No. DE-AC02-07CH11359 and DOE STTR Grant, No. DE-SC0013795.
Fermilab is the main institution to produce the most powerful and wide-spectrum neutrino beam. From that respective, a radiation robust beam diagnostic system is a critical element in order to maintain the quality of the neutrino beam. Within this context, a novel radiation-resistive beam profile monitor based on a gas-filled RF cavity has been proposed. The goal of this measurement is to study a tunable Q-factor RF cavity to determine the accuracy of the RF signal as a function of the quality factor. Specifically, the measurement error of the Q-factor in the RF calibration is investigated. Then, the RF system will be improved to minimize signal error.

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WEPMF014

Fast Track Actively Shielded Nb3Sn IR Quadrupole R&D

quadrupole, site, hadron, collider

2398

B. Parker, M. Anerella, J.P. Cozzolino, R.C. Gupta, R.B. Palmer, J. Schmalzle, H. Witte
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The Interaction Region (IR) magnets for future Electron Ion Colliders (EIC), such as eRHIC at BNL, JLEIC at JLab and LHeC at CERN, must satisfy strongly opposing requirements. EIC IR superconducting quadrupole coils must provide strong focusing gradients, leading to large peak fields, for the high momentum hadron beam while permitting the nearby electron beam to pass through a nearly field free region. An actively shielded coil geometry does this using nested, opposite polarity, quadrupoles where the combined external fields cancel while leaving a net gradient inside. In order to fabricate and test this concept in a timely and cost effective manner we propose to reuse the inner coils from an existing high gradient Nb3Sn LARP quadrupole inside a new structure with a new NbTi active shield coil. The main challenge is to design a compact structure for applying prestress to the Nb3Sn coil that fits the restricted space inside the shield coil. We first construct a 15 cm long mechanical model of this structure with coil strain gauges to verify the design concept before proceeding with the full coil. Mechanical modeling results and our preliminary design concept are reported here.

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WEPMF031

Development of a High-Power High-Directivity Directional Coupler and Four Power Dividers for S-Band

GUI, vacuum, MMI, simulation

2422

X. He, J. Lei, J.R. Zhang
IHEP, Beijing, People's Republic of China

A novel Bethe-hole S band directional coupler has been designed based on some structural optimizations, the prototype has been tested with a Directivity of more than 30 dB. The new directional coupler can also hold higher power compared to the old type, which is more useful for the future accelerator applications. Four power dividers using different structures are studied and the best one is chosen for fabrication. The prototype with matching rod in the middle has got qualified microwave cold test results and has been used during the whole microwave commissioning of an accelerating structure, the performance is quite stable.

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WEPMF033

RF Study And Cold Test of an S-band Spherical Cavity Pulse Compressor

cavity, simulation, vacuum, klystron

2429

J. Lei, X. He, M. Hou, X.P. Li, G. Pei, H. Wang, J.B. Zhao
IHEP, Beijing, People's Republic of China
S. Shu
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China

An S-band (2856 MHz) spherical cavity pulse compressor has been designed, fabricated and tested in the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS). The pulse compressor consists of a special 3 dB coupler and only one spherical energy storage cavity, two TE114 modes are chosen to oscillate in which for fairly high unload Q factor. The prototype was made of aluminum for studying the performance of the pulse compressor and checking the validity of the simulations. The cold test results of the aluminum cavity are also presented. The copper coating on the whole internal surface of the aluminum spherical cavity is in progress and the test results will also be presented in the future.

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WEPMF034

Development of Superconducting RF Double Spoke Cavity at IHEP

cavity, target, electron, proton

2432

Z.Q. Zhou, H.F.S. Feisi, W.M. Pan
IHEP, Beijing, People's Republic of China

Funding: State Key Development Program for Basic Research of China (Grant No.2014CB845500)
The China Initiative Accelerator Driven System (CiADS) has been approved to transmute long-lived radi-oisotopes in used nuclear fuel into shorter-lived fission products. IHEP is developing a 325MHz double spoke cavity at β0 of 0.5 for the CiADS linac. The cavity shape was optimized to minimize Ep/Ea while keeping Bp/Ep reasonably low, while the multipacting was analyzed. Meanwhile, mechanical design was applied to check stress, Lorentz force detuning and microphonic effects, and to minimize pressure sensitivity. A new RF coupling scheme was proposed to avoid electrons hitting directly on ceramic window. The detailed design for the cavity is addressed in this paper.

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WEPMF062

Simulation of Cavity Conditioning for the Diamond SCRF Cavity

cavity, GUI, simulation, operation

2509

S.A. Pande, C. Christou, P. Gu
DLS, Oxfordshire, United Kingdom

Diamond SCRF cavities are pulse conditioned every week in order to keep them operating reliably. During conditioning, the cavities are detuned in order to sweep the standing wave through the waveguide. To match these cavities at lower voltage (typically < 1.4 MV) and at higher power, 3 stub tuners are used in the waveguide feed. Simulations with CST studio show that a strong SW field exists between the RF window and the matching posts. As the cavity is detuned the electric field maximum passes through the window causing heating of the ceramic. Temperature measurements with thermal camera reveal that the temperature of the window increases to maximum when the cavity is detuned towards higher frequency. Based on the simulation results and the measurements, it was decided to reduce the conditioning voltage. These results are summarised.

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WEPMF065

High Efficiency, High Power, Resonant Cavity Amplifier For PIP-II

cavity, impedance, network, operation

2518

M.P.J. Gaudreau, N. Butler, D.B. Cope, P. H. Gordon, E.G. Johnson, M.K. Kempkes, R.E. Simpson
Diversified Technologies, Inc., Bedford, Massachusetts, USA

Funding: Funded under US DOE grant no. DE-SC0015780
Diversified Technologies, Inc. (DTI) is developing an integrated resonant-cavity combined solid-state amplifier for the Proton Improvement Plan-II (PIP-II) at Fermilab. The prototype has demonstrated multiple-transistor combining at 71% efficiency, at 675 watts per transistor at 650 MHz. The design simplifies solid-state transmitters to create straightforward scaling to high power levels. A crucial innovation is the reliable "soft-failure" mode of operation; a failure in one or more of these myriad combined transistors has negligible performance impact. The design couples the transistor drains directly to the cavity without first transforming to 50 Ohms, avoiding the otherwise-necessary multitude of circulators, cables, and connectors. DTI's design increases the power level at which it is cost-effective to employ a solid-state transmitter. DTI is upgrading the system to accommodate more transistors in each cavity module, and then will design and build a complete 100 kW-class transmitter which will consist of four such cavity modules and a combiner.

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WEPMF066

Fabrication of Split-Section X-band Structure Using Elastic Averaging

vacuum, alignment, electron, gun

2521

P. Borchard, S.A. Appert, J.S. Hoh
Dymenso LLC, San Francisco, USA

Conventional accelerator structures are manufactured using axial stacks of cylindrical components which, when brazed together, form the accelerator cell structure. Splitting the accelerator structure into two sections along the beam axis allows for a significant reduction in part count and vacuum joint length. The resultant single and coplanar vacuum joint between the two split sections allows for joining techniques such as electron beam welding or brazing of the parts to form the accelerator vacuum envelope. High precision alignment of the two sections is achieved through an elastic averaging interface coupling where improved accuracy is derived from the averaging of errors over a large number of relatively compliant contacting members. The monoblock split sections allow for highly optimized cooling configurations with enhanced heat removal in high heat flux regions, reducing vacuum wall thermal stresses and enabling higher power operation. This paper describes the engineering and manufacturing of four generations of brazed and electron beam welded X-band accelerator structures at both 9.3 GHz and 11.4 GHz frequencies.

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WEPMF069

High Shunt Impedance Accelerating Structure with Distributed Microwave Coupling

cavity, GUI, distributed, impedance

2531

S.P. Antipov, R.A. Kostin, S.V. Kuzikov
Euclid TechLabs, LLC, Solon, Ohio, USA
V.A. Dolgashev
SLAC, Menlo Park, California, USA

Funding: DOE SBIR
Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. In this paper we present results from an accelerating structure prototype with distributed microwave coupling, an approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. Thus there is no microwave power flow through the accelerating cavity, making this geometry favorable for high gradient operation and maximizing the shunt impedance.

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WEPMF089

Measurements of Electromagnetic Properties of Ferrites as a Function of Frequency and Temperature

kicker, impedance, injection, simulation

2592

A. Chmielinska, M.J. Barnes, F. Caspers, B.K. Popovic, C. Vollinger
CERN, Geneva, Switzerland

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

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WEPMK005

Preliminary Results from Validation Measurements of the Longitudinal Power Deposition Model for the LHC Injection Kicker Magnet

impedance, kicker, injection, operation

2636

V. Vlachodimitropoulos, M.J. Barnes, A. Chmielinska
CERN, Geneva, Switzerland
A. Chmielinska
EPFL, Lausanne, Switzerland

During Run 1 of the LHC, one of the injection kicker magnets (MKIs) exhibited an excessively high ferrite temperature, caused by coupling of the high intensity beam to the real impedance of the magnet. Beam-screen upgrades, implemented during Long Shutdown 1 (LS1), have been very effective in reducing beam coupling impedance and since then the MKIs have not limited LHC's availability. However, temperature measurements during operation have shown that one end of the MKI's ferrite yoke is consistently hotter than the other. Detailed simulation models and data post-processing algorithms have been developed to understand and mitigate the observed behaviour. In the present paper, the model used to obtain the power loss distribution along the magnet is presented. The model is subsequently applied to two MKI design configurations under study: (i) the one currently in operation and (ii) an upgraded magnet that was installed in the LHC tunnel during the Year End Technical Stop (YETS) 2017/18. In order to validate the expected behaviour a novel measurement technique was developed, applied in both configurations and compared to predictions. The results obtained are reported and conclusions regarding the effectiveness of the design are drawn.

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WEPMK007

INFN-LASA Design and Prototyping Activity for PIP-II

cavity, HOM, operation, linac

2640

A. Bignami, M. Bertucci, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
S. Pirani
ESS, Lund, Sweden

The design of the PIP-II medium-β, 5-cell, 650 MHz SRF elliptical cavity and the first steps of its prototyping activity are here presented. A design based on a three dies fabrication model has been chosen and fully characterized in terms of electromagnetic and mechanical parameters. Goal of the optimization has been to realize a highly performant cavity for CW operation with reasonably good performances when pulsed. A prototyping phase started with the production of three single-cell cavities used to validate the LASA model and to develop an optimal recipe for RF surface treatment according to the state-of-the-art of the high-Q frontier.

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WEPML003

Precision Q0 Measurement of an SRF Cavity with a Digital RF Techniques

cavity, SRF, impedance, GUI

2674

J.P. Holzbauer, B.M. Hanna, Y.M. Pischalnikov, W. Schappert, D.A. Sergatskov, A.I. Sukhanov
Fermilab, Batavia, Illinois, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Direct measurement of the quality factor of SRF cavity using traditional RF techniques is essential for cavity production and development. Systematic effects of the measurement can contribute significant amounts of error to these measurements if not accounted for. This paper will present measurements taken at Fermilab using a digital RF system to characterize and correct for these systematic effects and directly measure the quality factor versus gradient curve for a single spoke resonator in the Spoke Test Cryostat at Fermilab. These measurements will be compared to traditional calorimetric measurements, and a discussion of improving/extending these techniques to other testing situations will be included.

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WEPML032

The FAIR-SIS100 Bunch Compressor RF Station

cavity, power-supply, controls, electronics

2759

H.G. König, R. Balß, P. Hülsmann, H. Klingbeil, P.J. Spiller
GSI, Darmstadt, Germany
R. Gesche, J.H. Scherer
Aurion Anlagentechnik GmbH, Seligenstadt, Germany
A. Morato, C. Morri, G.T. Taddia
OCEM, Valsamoggia, Italy

In the frame of the Facility for Antiproton and Ion Research (FAIR) 9 bunch compressor RF stations were ordered for the first stage of realization of the SIS100 synchrotron. For RF gymnastics referred to as bunch rotation, one RF station has to provide a sudden rise in gap voltage of up to 40 kVp within less than 30 μs. The system is designed for a maximum RF burst of 3 ms per second. The RF frequency will be pre-selectable between 310 kHz and 560 kHz at a harmonic number of h=2 with respect to the beam. Compressed bunches with a peak current > 150 A and a width < 50 ns are the goal. For this purpose, a 1.218 m long cavity was designed using iron-based magnetic alloy cores. Variable vacuum capacitors are attached for tuning. The cavity is driven by a cross-coupled push-pull tetrode amplifier. This scheme minimizes the influence of the tetrode's DC current at the working point to the cores. The energy for the pulsed system is stored in a relatively small capacitor bank which will be charged semi-continuously and a voltage-stabilizing device is added. Cavity and power amplifier were realized by AURION Anlagentechnik GmbH ' the power supply unit is designed and built by OCEM Power Electronics.

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WEPML055

Simulation Study of Parasitic-Mode Damping Methods for a 1.5-GHz TM020-Mode Harmonic Cavity

cavity, impedance, damping, radiation

2822

N. Yamamoto, S. Sakanaka, T. Takahashi
KEK, Ibaraki, Japan

Design study of parasitic-mode (PM) damped structures has been conducted for the purpose to realize a normal conducting 1.5 GHz harmonic cavity which is based on the TM020 resonant mode*. We have investigated the performances of two PM-damping mechanisms, that are, rod-type antennas** and annular slots. The rod-type antennas locate at the node of electric field of the TM020 mode while the annular slots locate at the node of magnetic field. As a result of 3D electromagnetic simulations, suitable performances of PMs were confirmed by employing either of the PM-damping mechanisms. It was also shown that the slot-type structure is superior in PM-damping performance and in the unloaded Q of the TM020 mode.
* N. Yamamoto et al., IPAC'17, paper THOPIK037; N. Yamamoto Phys. Rev. Accel. Beams, 21, 1, 012001.
** T. Takahashi et al., IPAC'17, paper THPIK036.

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WEPML075

Test of Magnet Girder Prototypes for HEPS-TF

alignment, HOM, photon, site

2863

H. Wang, C. H. Li, S.J. Li, J. Liu, H. Qu, Z. Wang, L. Wu
IHEP, Beijing, People's Republic of China
H.Y. Zhu
Institute of High Energy Physics (IHEP), People's Republic of China

Auto-tuning magnet girder is one of the key technolo-gies to be solved for HEPS-TF (Test Facility of High Ener-gy Photon Source). The girder should have high adjusting accuracy, high stability and can be beam-based aligned, to obtain the stability requirements of beam orbit. There are two girders developed, and the tests have been done. The accuracy of girder motion is within 10 microns while the adjusting range is 1 mm and the resolution is better than 1 microns, the natural frequency is higher than 24 Hz.

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THPAF036

Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions

impedance, vacuum, factory, electromagnetic-fields

3040

M. Migliorati, L. Palumbo
Sapienza University of Rome, Rome, Italy
N. Biancacci
CERN, Geneva, Switzerland
M. Migliorati, L. Palumbo
INFN-Roma1, Rome, Italy
V.G. Vaccaro
Naples University Federico II and INFN, Napoli, Italy

Funding: Work supported by the CERN PS-LIU project
The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultra-relativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultra-relativistic particles. Even if some of the results, in particular in the ultra-relativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multi-layer vacuum chamber with different conductivities and of elliptic cross section.

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THPAF048

Destabilising Effect of the LHC Transverse Damper

damping, impedance, feedback, synchrotron

3076

E. Métral, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, K.S.B. Li
CERN, Geneva, Switzerland

Three questions motivated this study for the CERN Large Hadron Collider in terms of beam stability: (i) why a chromaticity close to zero seemed more critical than predicted during Run 1 (in 2011 and 2012) and during Run 2 (in 2015)?; (ii) why some past simulations with a chromaticity close to zero revealed a more critical situation with the transverse damper than without?; (iii) what should be the minimum operational chromaticity in the future in the LHC and High-Luminosity LHC? A new Vlasov solver (called GALACTIC) was developed to shed light on the destabilising mechanism of the transverse damper, which is a potential contributor to explain the LHC observation. Due to the features, which are discussed in this paper, the name 'ISR (for Imaginary tune Split and Repulsion) instability' is suggested for this new kind of single-bunch instability with zero chromaticity.

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THPAF051

Beam Impedance Evaluation for CERN PS Gate Valves by Simulation and Benchmark Measurement

impedance, simulation, wakefield, resonance

3080

B.K. Popovic, C. Vollinger
CERN, Geneva, Switzerland

The CERN High Luminosity LHC project calls for a doubling of beam intensity which requires a clear identification of possible longitudinal instability sources in the injector chain. This requirement yields the need to further improve the longitudinal impedance model for the Proton Synchrotron (PS). In this impedance model it is necessary to include not only obvious impedance sources, such as RF cavities and kickers but also seemingly innocuous elements like certain vacuum components. Individually these vacuum elements would give only a small impedance contribution, however, due to the large number of these elements in the machine, their resultant combined impedances impact the overall impedance budget. This paper presents the electromagnetic simulation analysis of the PS sector gate valves along with EM measurements confirming the simulation model. These measurements are especially crucial in this case since no complete mechanical model or drawings are available and assumptions had to be made regarding its interior mechanical structure.

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THPAF052

Impedance Analysis of New PS Internal Dump Design

impedance, HOM, resonance, vacuum

3083

B.K. Popovic, L. Teofili, C. Vollinger
CERN, Geneva, Switzerland

The High Luminosity Large Hadron Collider (HL-LHC) project at CERN calls for increasing beam intensity in the injector chain. In the Proton Synchrotron (PS), a pre-injector of the LHC, these intensities can result in beam instabilities and potential RF heating of machine components, such that impedance mitigation measures are required. To study these intensity effects, the PS impedance model has been developed and is continuously updated. Each new machine element that is to be added into the accelerator requires an impedance study to minimize its contribution with respect to the machine's overall impedance budget. In such a context, this paper presents the impedance analysis of the new design of the internal beam dump for the PS, showing the design process required to reduce the impedance contribution of this element. Furthermore, the impedance analysis of the currently installed beam dump is analysed in order to compare the impedance contributions of the two designs.

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THPAF057

Instability Observations in the Large Hadron Collider During Run 2

operation, simulation, electron, hadron

3099

L.R. Carver, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, G. Iadarola, K.S.B. Li, E.H. Maclean, L. Mether, E. Métral, B. Salvant, M. Schenk
CERN, Geneva, Switzerland
L. Mether, M. Schenk
EPFL, Lausanne, Switzerland

Instabilities of many different types and characteristics have been observed in the LHC during Run 2. The origin of these instabilities come from a variety of stabilising and destabilising mechanisms. Efforts to understand these instabilities and prevent their occurrence has improved the performance of the LHC in all stages of the machine cycle. This paper aims to give an overview into some of the instability observations and details the operational steps to prevent them.

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THPAF063

Identification of Imperfections in Impedance Shields on the SPS-QF Flanges via Non-Intrusive Measurements

resonance, impedance, shielding, cavity

3119

A. Farricker, P. Kramer, B.K. Popovic, E. Sunar, C. Vollinger, M. Wendt
CERN, Geneva, Switzerland

In order to achieve the highest beam intensities possible in the LHC the highest quality beam possible has to be supplied by the injector chain. The Super Proton Synchrotron (SPS) at CERN is the last accelerator in the injector chain of the LHC. One factor that is currently known to limit the intensity of the beam for injection to the LHC, is the longitudinal beam-coupling impedance in the SPS. One known source of multi-bunch instability is the vacuum flanges and campaigns to mechanically shield this source were completed in the year 2000. However, today it cannot be excluded that some of these shields may have partial or indeed full failures. Since these flanges are next to a QF magnet and are in most cases connected to a BPH (Beam Position Monitor Horizontal), it is possible to carry out via the BPH an in-situ measurement of the effectiveness of the shields. In this paper we present a methodology as well as measurement results taken with this non-intrusive in-situ method. From measurements, it is possible to identify if the flanges are without any impedance shield, equipped with either a fully functioning shield or a shield exhibiting non-ideal properties.

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THPAF067

Effects of Synchrotron Motion on Nonlinear Integrable Optics

synchrotron, optics, betatron, lattice

3131

S.D. Webb, N.M. Cook
RadiaSoft LLC, Boulder, Colorado, USA
J.S. Eldred
Fermilab, Batavia, Illinois, USA

Funding: This work was supported in part by the Department of Energy, Office of Science, Office of High Energy Physics under contract number DE-SC0011340.
An integrable Rapid-Cycling Synchrotron (iRCS) has been proposed as a replacement for the Fermilab Booster to achieve multi-MW beam power for the Fermilab high-energy neutrino program.* The successful application of nonlinear integrable optics to proton synchrotrons requires careful examination of single-particle longitudinal effects, especially synchrotron motion. For example, synchrobetatron coupling may excite transverse resonances in the ring. We will use the Synergia code to simulate the effects of this synchrobetatron coupling on the iRCS design with nonlinear inserts. Our goal will be to identify new invariants in the presence of this coupling. Assuming the synchrotron tune is sufficiently small, we have identified one or more adiabatic invariants of the motion. These invariants suggest that integrable optics with synchrobetatron coupling retains integrability when averaged over a synchrotron period.
* J. Eldred and A. Valishev, "Design Considerations for Proposed Fermilab Integrable RCS," arXiv 1703.00952 (2017).

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THPAF069

Particle Tracking Simulation of Collective Modes - Parametric Landau Damping Off Coupling Resonance

damping, simulation, resonance, synchrotron

3137

A. Macridin, J.F. Amundson, A.V. Burov, P. Spentzouris, E.G. Stern
Fermilab, Batavia, Illinois, USA

Employing Synergia simulations with the DMD method we investigate the Landau damping of space charge modes in bunched beams. The simulations reveal two instances of the parametric damping mechanism in bunched beams. The first example occurs in the proximity of coupling resonance and is due to the oscillation of particles' amplitudes in the transverse plane. This oscillation modulates the mode-particle coupling with particle dependent trapping frequency. The second example is due to the modulation of the mode-particle coupling in one transverse plane by the oscillatory motion in the other plane.

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THPAF070

Design of a One-Dimensional Sextupole Using Semi-Analytic Methods

sextupole, lattice, quadrupole, focusing

3140

L. Gupta
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
S. Baturin
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
Y.K. Kim
University of Chicago, Chicago, Illinois, USA
S. Nagaitsev
Fermilab, Batavia, Illinois, USA

Funding: Work supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams
Sextupole magnets provide position-dependent momentum kicks and are tuned to provide the correct kicks to particles within a small acceptance region in phase space. Sextupoles are useful and even necessary in circular accelerators for chromaticity corrections. They are routinely used in most rings, i.e. CESR. Although sextupole magnets are necessary for particle energy corrections, they also have undesirable effects on dynamic aperture, especially because of their non-linear coupling term in the momentum kick. Studies of integrable systems suggest that there is an analytic way to create transport lattices with specific transfer matrices that limit the momentum kick to one dimension. A one-dimension sextupole is needed for chromaticity corrections: a horizontal sextupole for horizontal bending magnets. We know how to make a "composite" horizontal sextupole using regular 2D sextupoles and linear transfer matrices in an ideal thin-lens approximation. Thus, one could create an accelerator lattice using linear elements, in series with sextupole magnets to create a '1d sextupole'. This paper describes progress towards realizing a realistic focusing lattice resulting in a 1d sextupole.*
*S.A. Antipov, et. al., Single-particle dynamics in a nonlinear accelerator lattice: attaining a large tune spread with octupoles in IOTA, Journal of Instrumentation, Volume 12, April 2017.

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THPAF073

Beam Phase Space Tomography at Fast Electron Linac at Fermilab

experiment, lattice, MMI, linac

3146

A.L. Romanov
Fermilab, Batavia, Illinois, USA

FAST linear accelerator has been commissioned in 2017. Experimental program of the facility requires high quality beams with well-defined properties. Solenoidal fields at photoinjector, laser spot shape, space charge forces and other effects can distort beam distribution and introduce coupling. This work presents results of a beam phase space tomography for a coupled 4D case. Beam was rotated in two planes with seven quads by 180 degrees and images from YaG screen were used to perform SVD based reconstruction of the beam distribution.

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THPAF089

Mode Coupling Theory in Collisions With a Large Crossing Angle

dipole, synchrotron, collider, positron

3197

N. Kuroo
UTTAC, Tsukuba, Ibaraki, Japan
K. Hirosawa, K. Ohmi, D. Zhou
KEK, Ibaraki, Japan
K. Oide, F. Zimmermann
CERN, Geneva, Switzerland

We discuss a novel coherent beam-beam instability in collisions with a large crossing angle. The instability appears in the correlated head-tail motion of the two colliding beams. Cross wake force is introduced to represent the head-tail correlation between colliding beams. The cross wake force is localized at the collision point. Mode coupling theory based on the cross wake force is developed. Collision scheme with a large crossing angle is being very popular in design of electron positron collider. In SuperKEKB project, a collision with a large crossing angle is performed to boost the luminosity ~ 10³⁶ cm^-2s⁻¹. Future circular collider, FCC is also designed with a large crossing angle. Strong-strong simulations have shown a strong coherent head-tail instability, which can limit the performance of proposed future colliders. The mode coupling theory using the cross wake force explains the instability. The instability may affect all colliders designs based on the crab waist scheme.

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THPAK005

Measuring the Coupling Impedance of Vacuum Components for the Advanced Photon Source Upgrade Using a Goubau Line

impedance, cavity, simulation, vacuum

3211

M.P. Sangroula
IIT, Chicago, Illinois, USA
R.M. Lill, R.R. Lindberg, R.B. Zabel
ANL, Argonne, Illinois, USA

The Planned upgrade of the Advanced Photon Source to a multi-bend achromat (MBA) will increase the x-ray brightness by two to three orders of magnitude. Storing such an intense beam stably inside the narrow gap vacuum chambers requires sophisticated and appropriately designed rf-components that helps to minimize rf heating and collective instabilities associated with the impedance of these small-aperture vacuum components. As part of this effort, my research focuses on impedance measurement and simulation of various MBA vacuum components. In this paper, we briefly introduce the novel Goubau line (G-line) test fixture for the impedance measurement, at first, and then present our measurements data along with simulations with simulations for various vacuum components designed for the APS Upgrade.

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THPAK010

Optimization on the Optical Resonator of CTFEL

FEL, GUI, radiation, electron

3228

X.J. Shu, Y.H. Dou
Institute of Applied Physics and Computational Mathematics, People's Republic of China
M. Li, Z. Xu, Y. Xu, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

Funding: Program for the National Science Foundation of China (Grant No. 11105019) and the National Science Device Exploitation Foundation of China (Grant No. 2011YQ130018).
A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CTFEL) since October, 2011. The radiation frequency of the FEL facility will be tuned in range of 1~3 THz and the average output power is about 10 W. The system mainly consists of a GaAs photoemission DC gun, superconductor accelerator, the hybrid wiggler, optical cavity. The first lasing is obtained on Aug. 29, 2017. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and round-trip loss. The optical resonator consists of metal-coated reflect mirror, the center-hole output mirror, waveguide. The influence of waveguide and Rayleigh length on the quality of optical cavity is evaluated by the 3D-OSIFEL code. The waveguide size, mirror curvature radius, output hole radius is optimized to different frequencies between 1 THz to 3 THz.

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THPAK015

Impedance and Heat Load Analysis of the Stripline Kicker in HEPS

kicker, impedance, simulation, injection

3234

N. Wang, J. Chen, Z. Duan, H. Shi, S.K. Tian, L. Wang, H.S. Xu
IHEP, Beijing, People's Republic of China

In the High Energy Photon Source (HEPS), strip-line kickers are adopted for beam injection and extraction. Beam coupling impedance contribution from the strip-line kicker is calculated. Detailed studies on the heat load dissipation have been performed. The peak electric field on the blade and the induced voltage on the feedthroughs due to the beam passage are also calculated.

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THPAK054

Optics Calibration and Measurement for Low Alpha Lattices in TPS Storage Ring

lattice, emittance, optics, operation

3343

F.H. Tseng, C.H. Chen, J.Y. Chen, P.C. Chiu, C.H. Huang, C.-C. Kuo, C.C. Liang, C.Y. Liao, Y.-C. Liu, H.-J. Tsai
NSRRC, Hsinchu, Taiwan

In order to provide short-pulse radiation for pump-probe experiments and coherent radiation for THz/IR measurements, we develop low alpha lattices to reduce the momentum compaction factor from nominal operation values 2.4*10^-4 to 2.6*10-5 or lower. The corresponding bunch length at 2.8 MV RF voltage and zero current are from 10.78 ps to 3.55 ps or less. In the low alpha operations, the bunch lengthening as a function of bunch current, the orbit drift and noise enhancements as well as rf stability effect are observed. In this report we will present our studies on the lattice design, optics correction, beam parameters measurements and alpha measurements.

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THPAK099

The Influence of Higher Order Multipoles of IR Magnets on Luminosity for SuperKEKB

sextupole, luminosity, multipole, octupole

3463

K. Hirosawa, T. Okada
Sokendai, Ibaraki, Japan
N. Kuroo
UTTAC, Tsukuba, Ibaraki, Japan
K. Ohmi, N. Ohuchi, D. Zhou
KEK, Ibaraki, Japan

SuperKEKB is an electron-positron circular collider upgraded from KEKB. To reach higher luminosity, values of beta are extremely small at Interaction Point. Although magnets in interaction region have a very strong focusing effect, they make a large disturbance to beams. Higher order multipoles and their skew components of magnetic fields of IR magnets are located at a very high beta section with pi/2 phase difference from IP. These multipoles can give critical effect to beam dynamics at interaction point and reduce luminosity on SuperKEKB design. In this study, we calculated beam dynamics for effect of skew components for multipole magnet, and estimated the influence on luminosity by them.

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THPAK110

Correction of ν_r-ν_z=1 Resonance in TRIUMF Cyclotron

resonance, cyclotron, TRIUMF, simulation

3492

Y.-N. Rao, R.A. Baartman, T. Planche
TRIUMF, Vancouver, Canada

Funding: TRIUMF receives federal funding via a contribution agreement through the National Research Council of Canada
The second order linear coupling resonance nu_r-nu_z=1 is driven by an asymmetry in the median plane of the cyclotron due to presence of the first harmonic in B_r component. In TRIUMF cyclotron, this resonance is encountered at about 166 MeV and 291 MeV, where nu_r=1.2 and nu_z=0.2. When the beam is off-centered radially to pass through this resonance, the radial oscillation gets converted into vertical oscillation, which can cause beam loss to occur, though these loss modes do not reduce the machine transmission under normal operation. In this paper, we present the results of simulations and measurements that we have performed to correct this resonance by using the existing harmonic coils.

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THPAK113

Cavity Characterization Studies With the Latest Revision of YACS

cavity, storage-ring, superconducting-cavity, higher-order-mode

3503

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

Funding: Work supported by the BMBF under contract no. 05K13PEB.
YACS is a 2.5D finite element method solver capable of solving for the full 3D eigenfrequency spectra of resonant axisymmetric structures while reducing the computational problem to a 2D rotation plane. The most recent revision of YACS now supports arbitrary order basis functions for the geometry and field discretization. In earlier revisions of YACS spurious modes were introduced by increasing the order of either the geometry or field basis functions. To prevent the emergence of spurious modes, YACS now matches the function spaces of the in-plane and out-plane function basis, and thus yields spurious free solutions. To demonstrate the capabilities of YACS, extensive cavity characterization studies on curved multicell microwave cavities are presented. Due to the combined utilization of the rotation symmetry, higher order basis functions and curved elements, eigenfrequency spectra above 10 GHz for L-band multicell structures can be easily obtained.

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THPAL002

RF System Operation of High Current RFQ in ADS Project

rfq, cavity, operation, LLRF

3613

L.P. Sun, R. Huang, C.X. Li, L. Lu, A. Shi, L.B. Shi, W.B. Wang, X.B. Xu, H.W. Zhao
IMP/CAS, Lanzhou, People's Republic of China
Y. Hu
TUB, Beijing, People's Republic of China

Funding: Work supported by Natural Science Foundation of China， No.11505253
New RF system has been upgraded several times for high-current operation, especially for extra beam power and detuning angle. The current was increased gradually resulting in more and more frequency detuning, and an effective method is to tune the temperature of cavity to compromise detuning. Of course, the power dissipated in cavity and high intensity beam are approximately 120kW resulting in too many power modules operated in the high risk of failure. The specific analysis and simulation were introduced in detail.

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THPAL037

Nano-engineering of Nb3Sn Thin Films to Improve Wire Performance and Reduce Cost

collider, lattice, electron, dipole

3720

S.A. Kahn, M.A. Cummings
Muons, Inc, Illinois, USA
E.Z. Barzi
Fermilab, Batavia, Illinois, USA

State-of-the-art Nb3Sn wires have plateaued in the performance of the critical current density Jc. Chemical and geometrical optimization of the wire layout have produced Nb3Sn wires with average Jc(4.2K, 16T) ~ 1,300 A/mm2. A future high energy hadron collider that is being considered to follow the LHC would need larger Jc and be cost effective. The approach to improving the performance of Nb3Sn conductor would be to introduce enhanced flux pinning mechanisms with nano-engineering techniques.

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THPAL041

Power Coupler Design for the LUCRECE Project

cavity, simulation, SRF, linac

3732

H. Guler, D. Auguste, J. Bonis, O. Bouras, M. El Khaldi, W. Kaabi, P. Lepercq
LAL, Orsay, France

The LUCRECE project aims at developing an elementary RF system (cavity, power source, LLRF and controls) suitable for continuous (CW) operation at 1.3 GHz. This effort is made in the framework of the advanced and compact FEL project LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation), using superconducting linac technology for high repetition rate and multi-user operation (www.lunex5.com). In this context, based on its large experience on coupler design and RF conditioning, LAL Laboratory is in charge of the design and the fabrication of RF couplers that could operate at up to 15-20 kW in CW mode. For this purpose, geometry based on CORNELL 65kW CW couplers will me modified to fulfil the LCLS2 type cavity with the high necessary coupling level. Electromagnetic simulations and optimisation and associated thermal heating will be discussed. Methods to decrease the thermal impact, and strategy for RF conditioning will be considered.

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THPAL049

Power Supply Decoupling Design

controls, power-supply, simulation, electron

3751

Y.T. Li, F.Y. Chang
NSRRC, Hsinchu, Taiwan

After an actual operation of the phase-shifted magnet's power supply was conducted, it was found that the currents in the two modules of magnets would be coupled each other. In order to solve this mutual coupling current, a decoupling controller is designed. From the experiment results indicate that it does not only solve the issue of coupling current but also shorten the rising time of the power supply current. This helps to increase the power supply bandwidth.

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THPAL061

Simulation of Pulsed Temperature Rise in Cryogenic Copper RF Cavity Achieving a Very High Accelerating Field

cavity, simulation, accelerating-gradient, cryogenics

3788

T. Tanaka, K. Hayakawa, Y. Hayakawa, K. Nogami, T. Sakai, Y. Sumitomo
LEBRA, Funabashi, Japan

A cryogenic C-band photocathode RF electron gun cavity has been studied at Nihon University LEBRA in cooperation with KEK. The RF properties of a cold model measured at 20 K have shown good agreement with those expected from computer simulations using the cavity surface resistance predicted by the theory of the anomalous skin effect. Recent studies on the vacuum RF breakdown at high electric fields suggest that the temperature in the cavity surface during the high power RF pulse has a significant effect on the behavior of the breakdown rate. In order to investigate the breakdown property of the cryogenic cavity aiming at a very high accelerating field with as low breakdown rate as possible, one-dimensional simulations of the temperature rise in the cavity surface have been done for various combinations of the RF pulse width and the peak input RF power. The evaluation will be taken into consideration in the design of a new high power cryogenic cavity that has basically the same configuration with the cold model.

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THPAL080

Parallel-Feed SRF Accelerator Structures

cavity, SRF, simulation, impedance

3835

P.B. Welander, Z. Li, M.H. Nasr, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This work is supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Development of SRF accelerator technology that enables both higher gradient and higher efficiency is crucial for future machines. While much of the recent R&D focus has been on materials and surface science, our aim is to optimize the cavity geometry to maximize performance with current materials. The recent demonstration of a highly efficient parallel-feed NCRF structure at SLAC has served as a proof-of-concept. Applied to SRF, such a structure could dramatically reduce power consumption while boosting the achievable gradient. Instead of coupled elliptical cells, our structure employs isolated reentrant cells. To feed RF power to the cavities, each cell is directly coupled to an integrated manifold. The structure is made in two parts, split along the beam axis, which are then joined. Such a structure has been fabricated from bulk Cu and tested at SLAC - designed for X-band, it operates at a record gradient of 150 MV/m. Adapting to SRF at 1.3 GHz and fabricating from Nb, such a cavity could achieve more than 50% lower RF loss and 40% higher gradient compared to the TESLA cavity. We will describe our simulations and propose an experimental roadmap for demonstrating this technology.

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THPAL109

The New 118 MHz Cavity for RF Development Activities of the RF for Accelerator Laboratory at SLRI

cavity, simulation, HOM, impedance

3895

N. Juntong, K. Kittimanapun, P. Sunwong
SLRI, Nakhon Ratchasima, Thailand
A. Sutchada
Walailak University, Nakhon Si Thammarat, Thailand

The RF for accelerator laboratory is established at SLRI to perform RF related development activities of the current light source and the future synchrotron light facility in Thailand. One of activities is to build an in-house RF cavity. It will be used for testing of RF amplifier unit and the developed LLRF system. The cavity is a nose-cone pill-box cavity operating at 118 MHz and aiming at 100 kV gap voltage. Details of designing in particular the inner surface profile, the RF properties, the higher order modes properties, the RF power coupler, and the tuning mechanism will be presented with the manufacturing timeline.

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THPAL110

High-Power RF Test of Coaxial Couplers for the Injection Linac of XiPAF

cavity, vacuum, multipactoring, linac

3899

Y. Lei, X. Guan, R. Tang, X.W. Wang, Q.Z. Xing, H.Y. Zhang, S.X. Zheng
TUB, Beijing, People's Republic of China
J. Jiang, H. Li, C. Yu
Beijing Aerospace Guagntong Technology Co., Beijing, People's Republic of China

For the high-power RF test of the coaxial couplers which will be employed on the linac injector of the XiPAF (Xi'an Proton Application Facility) project, a high-power conditioning cavity was designed and manufactured [1]. There are some optimized aspects on the cavity and couplers to obtain better RF performance during the high-power testing process. The traveling-wave test and full-power-reflection test were executed to check whether the coupler can afford the enough power level for the linac operation, and whether only one coupler can afford the total power for the RFQ. The construction of the testing stand, optimization of RF parameters and results of high-power RF test are presented in this paper.

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THPAL152

Study of X-Band Phase Shifter Using Ferrite Material

cavity, GUI, simulation, insertion

4005

Y.L. Jiang, D.Z. Cao, H.B. Chen, J. Shi, P. Wang, H. Zha
TUB, Beijing, People's Republic of China

Ferrite has the feature of the permeability depended on the external static magnetic field, thus could be used to shift the phase of the propagating radio frequency (RF) signal. In this paper, we introduce a novel design of ferrite-based RF phase shifter. The design changes the resonant frequency of a ferrite-filled pill-box cavity to implement the phase changing. This design has a lower local RF field and a higher sensitivity on the phase changing than those of waveguide phase shifter, which may bring advantages such as higher power capacity, fast changing speed and lower insertion loss. Theory and simulation results are also presented in this paper.

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THPAL153

High Power Test of the S-Band Spherical Pulse Compressor at Tsinghua University

cavity, FEL, polarization, klystron

4008

P. Wang, D.Z. Cao, H.B. Chen, C. Cheng, J. Shi, Z.H. Wang, H. Zha
TUB, Beijing, People's Republic of China

We designed, fabricated and high power tested an S-band spherical pulse compressor for the high-power test facility at Tsinghua University. The pulse compressor comprises a spherical resonant cavity with an unloaded quality factor of 100, 000 and an RF polarizer with two rectangular ports and a circular port. To achieve high efficiency and large power gain, the coupling coefficient was optimized to 8 with input pulse length of 3.6 us and compression ratio of 12. After conditioning the RF system, the pulse compressor generated RF pulses with peak power of more than 400MW. And during the operation, the pulse compressor has very low breakdown rate and was extremely stable.

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THPMF028

Coherent Stacking Scheme for Inverse-Compton Scattering at MHz Repetition Rates

laser, cavity, simulation, feedback

4103

P. Piot, D. Mihalcea
Northern Illinois University, DeKalb, Illinois, USA
T.J. Campese, A.Y. Murokh
RadiaBeam Systems, Santa Monica, California, USA
D. Mihalcea, P. Piot, J. Ruan
Fermilab, Batavia, Illinois, USA

Funding: Work sponsored by the DNDO award 2015-DN-077-ARI094 to Northern Illinois University and US DOE contract DE-AC02-07CH11359 to Fermilab.
An experiment to produce 1-MeV gamma rays via Compton back-scattering of infrared photons on 250-MeV electron bunches is currently in preparation at the Fermilab Accelerator Science & Technology (FAST) facility. To increase the gamma-ray flux the energy of the infrared laser pulses are planned to be amplified within the interaction region using a resonant cavity. This passive amplifier composed of a Fabry-Perot cavity will allow the laser pulse bunches to coherently and constructively stack. Our estimates, based on theoretical models, show that the laser pulse energy can be increased from approximately 1-2 mJ at the exit of the last active amplifier to 5 -10 mJ at the interaction point when the laser repetition rate is set at the nominal value of 3 MHz. This paper details the cavity design option(s) and associated wave-optic simulations.

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THPMF050

High-Efficient XFELO Based on Optical Resonator with Self-Modulated Q-Factor

undulator, FEL, laser, electron

4172

S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia
S.P. Antipov, S.V. Kuzikov
Euclid TechLabs, LLC, Solon, Ohio, USA

In this paper we describe an efficient XFELO having a new non-stationary out-coupling scheme. It consists of two undulator sections placed inside optical cavity. The first section is a conventional uniform undulator and the second one is a tapered undulator. At start time point X-ray radiation is mostly produced by the uniform section. Mirrors of XFELO's optical resonator are designed so that diffraction Q-factor reaches the highest value, i.e losses are near zero. As X-ray power increases the tapered undulator begins to contribute more to radiation power. However a portion of that power misses mirrors of the optical cavity, because those are tuned to confine radiation produced by the first undulator. This process establishes a steady state operation of the XFELO.

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THPMF060

Touschek Beam Loss Simulation for Light Source Storage Rings

electron, scattering, storage-ring, simulation

4206

M. Takao, K. Soutome
JASRI/SPring-8, Hyogo-ken, Japan
Y. Shimosaki
JASRI, Hyogo, Japan
K. Soutome, H. Tanaka
RIKEN SPring-8 Center, Hyogo, Japan

In light source storage rings, it is important to know the distribution of lost electrons due to the Touschek scattering for protecting insertion devices (IDs) from radiation damage. This will become crucial especially in future light sources where narrow gap in-vacuum IDs are normally used. While the Touschek scattered electron begins to oscillate in the horizontal direction with the amplitude proportional to the dispersion at the scattering point and to the momentum deviation after scattering, the motion is converted into the vertical direction due to the betatron coupling and some of the scattered electrons are lost at the narrow gaps of in-vacuum IDs. The momentum deviation by the Touschek scattering reaches 5% more, and according to which the vertical oscillation is more excited. Hence electrons even scattered at small horizontal dispersion are also lost at narrow gap IDs. We carried out computer simulations by taking the present SPring-8 storage ring and a planned 3GeV low-emittance ring as examples. The results and possible measures for ID protection will be presented.

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THPMK018

Design of a rotationally symmetric S-band photocathode RF gun

gun, cathode, impedance, emittance

4336

Zh. X. Tang
USTC, Hefei, Anhui, People's Republic of China
Z.G. He, W.W. Li, Y.J. Pei, L. Wang
USTC/NSRL, Hefei, Anhui, People's Republic of China

The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell with a symmetrical distribution of four grooves is concatenated to the first 0.6 cell at the photocathode end to form a new resonant cell (NRC) to mantain the symmetric multi-pole field in 1.6 cell. Our simulations indicate that 3D multi-pole fields of NRC are with the perfect symmetry. After that, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Our simulations demonstrate promising outlook of using coaxial cell for photocathode RF guns with various applications.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK018

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THPMK130

Study of Beam Instabilities with a Higher-Harmonic Cavity for the HALS

cavity, storage-ring, HOM, quadrupole

4623

Y.G. Tang, W. Li, Z.B. Sun, L. Wang, C.-F. Wu
USTC/NSRL, Hefei, Anhui, People's Republic of China

Hefei Advanced Light Source (HALS), a diffrac-tion-limited storage ring is on the design. In HALS project, a passive higher-harmonic cavity may be added in order to increase the beam lifetime of the storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the high-er-harmonic cavity. In this paper, we run an algorithm (analytic modeling) to consider the Robinson instabilities for normal and superconducting cavity respectively. The Robinson instabilities are predicted with and without mode coupling. Coupled-bunch instability induced by resonant interaction with parasitic longitudinal mode is also considered. The analytic modeling may be used to give rf-cavity parameters that are more conducive to stability. The results show that the storage ring can oper-ate at a higher beam current and the parasitic high-er-order mode of the fundamental cavity has less impact on the beam by using superconducting harmonic cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK130

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THPMK139

Design of 9/6 MeV S-band Electron Linac Structure with 1.5 Bunching Cells

linac, bunching, electron, simulation

4635

Y. Joo, P. Buaphad, H.R. Lee
University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
S.C. Cha, Y. Kim
KAERI, Daejon, Republic of Korea

Funding: University of Science and Technology of Korea
The Korea Atomic Energy Research Institute (KAERI) has been developing several 9/6 MeV dual energy S-band RF electron linear accelerators (linacs) for non-destructive testing such as container inspection system. Until now the bunching cell of the linac has a full-cell geometry. However, to maximize the acceleration of electrons after emission from the electron gun, the geometry of the first bunching cell is modified from a full-cell to a half-cell. The optimization of Q-factor and flatness of electric field along the linac structure can be obtained by adjusting diameters of bunching and power coupling cells. By adjusting gap of the first side-coupling cell, we can optimize the field ratio between the bunching cells and normal accelerating cells. In this paper, we describe design concepts of a 9/6 MeV linac with 1.5 bunching cells as well as optimization of RF parameters such as the quality factor, resonance frequency, and electric field distribution.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK139

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THPML047

Design and Measurement of the X-Band Pulse Compressor for TTX

cavity, GUI, vacuum, ISOL

4745

Y.L. Jiang, H.B. Chen, C. Cheng, W. Gai, J. Shi, P. Wang, Z.H. Wang, X.W. Wu, H. Zha
TUB, Beijing, People's Republic of China

A radio frequency (RF) pulse compressor had been designed for the X-band (11.424 GHz) high power test stands at the Accelerator Laboratory of Tsinghua University. It is the SLED-I type pulse compressor, which uses a high quality factor corrugated circular cavity to store the RF power. An RF polarizer couples two quadrature modes into the cavity so that the pulse compressor needs only one cavity. The cavity implements HE1-1-14 mode, with the Q0 of 115, 000 and the coupling factor (β) of 3.23. The design and the microwave measurement before brazing of this pulse compressor are presented in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML047

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THPML095

Improvement of Wire-Stretching Technique to the RF Measurements of E-Center and Multipole Field for the Dipole Cavities

cavity, kicker, simulation, electron

4885

G.-T. Park, J. Guo, H. Wang
JLab, Newport News, Virginia, USA
A. Overstreet
ODU, Norfolk, Virginia, USA
B. P. Xiao, T. Xin
BNL, Upton, Long Island, New York, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
After the first publication* of wire-stretching technique from its principle to measure the electrical center of a deflecting cavity, more refinements of this techniques including the review of its analytical and simulation results, RF circuit improvement to improve the signal to noise ratio and its application to other cavities have been developed. These applications include the electrical center measurements for the LHC RFD and DQW crabbing cavity prototypes, multi-frequency harmonic kicker cavity for JLEIC electron cooler**, TE011 cavity developed for the beam magnetization measurement***, and a separator cavity at BNL****. Further development of measurement calibration, error reduction, alignment of cavity installation to the machine beam line, and multipole field analysis for the beam dynamics will be presented.
*H. Wang, Proceedings of NAPAC2016, pp225-228
**S. A. Overstreet, BS Thesis 2017, Guilford College, Greensboro, NC
***J. Guo et al. these proceedings
****T. Xin et al, these proceedings

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML095

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THPML096

A Non-Invasive Magnetic Momentum Monitor Using a TE011 Cavity

cavity, impedance, electron, GUI

4889

J. Guo, J. Henry, M. Poelker, R.A. Rimmer, R. Suleiman, H. Wang
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC with Laboratory Directed Research and Development funding, under U.S. DOE Contract No. DE-AC05-06OR23177.
The Jefferson Lab Electron-Ion Collider (JLEIC) design relies on cooling of the ion beam with bunched electron beam. The bunched beam cooler complex consists of a high current magnetized electron source, an energy recovery linac, a circulating ring, and a pair of long solenoids where the cooling takes place. A non-invasive real time monitoring system is highly desired to quantify electron beam magnetization. The authors propose to use a passive copper RF cavity in TE011 mode as such a monitor. In this paper, we will show the mechanism and scaling law of this device, as well as the design and testing results of the prototype cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML096

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THPML113

Design and Simulation of the Waveguide Coupler for the Cavity Beam Monitor

GUI, cavity, simulation, electromagnetic-fields

4932

Q. Wang, Q. Luo, B.G. Sun, F.F. Wu, Y.L. Yang, Z.R. Zhou
USTC/NSRL, Hefei, Anhui, People's Republic of China
Y.W. Wu
USTC, Hefei, Anhui, People's Republic of China

Funding: Supported by The National Key Research and Development Program of China (2016YFA0401900), NSFC (11375178, 11575181) and the Fundamental Research Funds for the Central Universities (WK2310000046)
The waveguide coupling is an important way to extract the signals of the specific eigenmodes required. The design of the waveguide coupler, including the waveguide-to-coaxial adapter behind it for the cavity bunch length monitor is presented. The influence of the dimension parameters is analyzed, which offers the theoretical support for the design and application of cavity bunch length monitor or cavity beam position monitor (CBPM). A series simulation based on CST is performed to verify the feasibility, and the simulation results show good performance.

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THPML117

Study of the Impact of Linear Coupling on Off-Axis Injection

resonance, injection, dynamic-aperture, quadrupole

4943

X. Huang
SLAC, Menlo Park, California, USA
T. Zhang
USTC/NSRL, Hefei, Anhui, People's Republic of China

The next generation of storage ring light sources will likely operate with high linear coupling, which could potentially prevent the use of off-axis injection as large horizontal oscillation of the injected beam is coupled to the vertical plane. We did experiments on the SPEAR3 storage ring to study how linear coupling impact the dynamic aperture and the off-axis injection efficiency. The results show that the dynamic aperture is significantly reduced and injection efficiency can drop to zero when operated on the coupling resonance. However, with large nonlinear detuning, the dynamic aperture and high injection efficiency can survive with the stored beam at full coupling because the injected beam is shifted away from the coupling resonance.

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THPML125

Efficiency Analysis of High Average Power Linacs for Environmental and Industrial Applications

linac, impedance, beam-loading, higher-order-mode

4970

M. Shumail, V.A. Dolgashev
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy, HEP under Research Opportunities in Accelerator Stewardship: LAB 16-1438.
We present comprehensive efficiency equations and useful scaling laws to optimally determine design parameters for high efficiency rf linacs. For the first time we have incorporated the parasitic losses due to the higher order cavity modes into the efficiency analysis of the standing wave (SW) and travelling wave (TW) accelerators. We have also derived the efficiency equations for a new kind of attenuation-independent-impedance travelling wave (ATW) accelerators where the shunt impedance can be optimized independent of the group velocity. We have obtained scaling laws which relate the rf to beam efficiency to the linac length, beam aperture radius , phase advance per cell, and the type of accelerating structure: SW versus TW, disk-loaded (DL) versus nose-cone (NC). We give an example of using these scaling laws to determine a feasible set of parameters for a 10 MeV, 10 MW linac with 97.2% efficiency.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML125

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