Keyword: HOM
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MOPRO112 Energy Recovering for Linac RF Injectors cavity, gun, SRF, linac 356
 
  • V. Volkov, Ya.V. Getmanov, O.A. Shevchenko, N. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  • A.N. Matveenko
    HZB, Berlin, Germany
  
  The article presents a new design of a CW RF high average current superconducting injector cavity. This design allows recovering energy in the injector, improving beam parameters and energy efficiency, reducing injector size, cost, and avoiding high average power coupler problem.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRO112  
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MOPRO113 Beam-based HOM Measurements in Cornell's ERL Main Linac Cavity cavity, dipole, quadrupole, linac 359
 
  • D.L. Hall, A.C. Bartnik, M.G. Billing, D. Gonnella, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  A search for HOMs in Cornell’s ERL main linac cavity installed in a Horizontal Test Cryomodule (HTC) has been carried out using a bunch charge modulation method, as part of the effort towards building an Energy Recovery Linac (ERL). The beam-based HOM measurements offer the significant advantage of being able to detect trapped modes invisible to both the RF pickup probes and HOM damping loads, and allow for measuring the R/Q of the modes. For each HOM detected during the search, measurements were taken to determine its nature (monopole, dipole, etc.), frequency, loaded quality factor and shunt impedance. A selection of the most notable modes found is presented, compared to 3D HOM simulations, and their potential impact on the BBU current of the future Cornell ERL is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRO113  
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MOPME009 Numerical Calculation of Electromagnetic Fields in Acceleration Cavities under Precise Consideration of Coupler Structures cavity, dipole, electromagnetic-fields, impedance 394
 
  • C. Liu, W.A. Ackermann2, W.F.O. Müller, T. Weiland
    TEMF, TU Darmstadt, Darmstadt, Germany
  
  Funding: Work supported by BMBF under contract 05H12RD5
During the design phase of superconducting radio frequency (RF) accelerating cavities a challenging and difficult task is to determine the electromagnetic field distribution inside the structure with the help of proper computer simulations. Although dissipation due to lossy materials is neglected in the current work, in reality, because energy transfer appears due to the design of the superconducting cavities, the numerical eigenmode analysis based on real-valued variables is no longer suitable to describe the dissipative acceleration structure. Dissipation can appear with the help of dedicated higher order mode (HOM) couplers, the power coupler as well as the beam tube once the resonance frequency is above the cutoff frequency of the corresponding waveguide. At the Computational Electromagnetics Laboratory (TEMF) a robust parallel eigenmode solver based on complex-valued finite element analysis is available. The eigenmode solver has been applied to the TESLA 1.3 GHz and the third harmonic 3.9 GHz nine-cell cavities to determine the resonance frequency, the quality factor and the corresponding field distribution of eigenmodes. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPME009  
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MOPME017 Study of Higher Order Modes in Multi-Cell Cavities for BESSY-VSR Upgrade cavity, SRF, dipole, linac 412
 
  • T. Galek, K. Brackebusch, Sh. Gorgi Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Funding: Work supported by Federal Ministry for Research and Education BMBF under contract 05K13HR1.
BESSY-VSR is a planned scheme to upgrade the existing BESSY II storage ring to support variable electron pulse lengths. In addition to the present 0.5 GHz energy replenishment cavity, two additional SRF bunch compressing cavities operating at 1.5 GHz (3rd harmonic) and 1.75 GHz (sub-harmonic), will be installed. These cavities are essential to produce short 1.5 ps bunches with current of up to 0.8 mA per bunch. In order to achieve such high beam currents, higher order modes must be damped in the superconducting cavities. In this work we present analysis of higher order modes in cavities with different mid-cell shapes. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPME017  
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MOPME018 Quantification of Geometric Uncertainties in Single Cell Cavities for BESSY VSR using Polynomial Chaos cavity, simulation, linac, SRF 415
 
  • J. Heller, T. Flisgen, C. Schmidt, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Funding: Federal Ministry for Research and Education Germany under contract 05K13HR1
The electromagnetic properties of SRF cavities are mostly determined by their shape. Due to fabrication tolerances, tuning and limited resolution of measurement systems, the exact shape remains uncertain. In order to make assessments for the real life behaviour it is important to quantify how these geometrical uncertainties propagate through the mathematical system and influence certain electromagnetic properties, like the resonant frequencies of the structure's eigenmodes. This can be done by using non-intrusive straightforward methods like Monte-Carlo (MC) simulations. However, such simulations require a large number of deterministic problem solutions to obtain a sufficient accuracy. In order to avoid this scaling behaviour, the so-called polynomial chaos (PC) expansion is used. This technique allows for the relatively fast computation of uncertainty propagation for few uncertain parameters in the case of computationally expensive deterministic models. In this paper we use the PC expansion to quantify the propagation of uncertain geometry on the example of single cell cavities used for BESSY VSR as well as to compare the obtained results with the MC simulation. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPME018  
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TUOAB01 Computation of Eigenmodes in Long and Complex Accelerating Structures by Means of Concatenation Strategies cavity, factory, coupling, FEL 947
 
  • T. Flisgen, J. Heller, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Funding: This research was partially funded by the EuCARD project which is co-funded by European Commission 7th in Framework Programme (FP7).
The computation of eigenmodes for complex accelerating structures is a challenging and important task for the design and operation of particle accelerators. Discretizing long and complex structures to determine its eigenmodes leads to demanding computations typically performed on super computers. This contribution presents an application example of a method to compute eigenmodes and other parameters derived from these eigenmodes for long and complex structures using standard workstation computers. This is accomplished by the decomposition of the complex structure into several single segments. In a next step, the electromagnetic properties of the segments are described in terms of a compact state space model. Subsequently, the state space models of the single structures are concatenated to the full structure. The results of direct calculations are compared with results obtained by the concatenation scheme in terms of computational time and accuracy. 		 
slides icon Slides TUOAB01 [1.781 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUOAB01  
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TUPME084 On the Frequency Choice for the eRHIC SRF Linac linac, SRF, cavity, electron 1547
 
  • S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, V. Ptitsyn, W. Xu
    BNL, Upton, Long Island, New York, USA
  • S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, V. Ptitsyn
    Stony Brook University, Stony Brook, USA
  
  Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
eRHIC is a future electron-hadron collider proposed at BNL. It will collide high-intensity hadron beams from one of the existing rings of RHIC with a 50-mA electron beam from a multi-pass 10-GeV superconducting RF (SRF) Energy Recovery Linac (ERL). A novel approach to the multi-pass ERL utilizing a non-scaling FFAG was recently proposed. It has many advantages over the previous designs including significant cost savings. The current design has 11 passes in two FFAG rings. To mitigate various beam dynamics effects, it was proposed to lower RF frequency of the SRF linac from 704 MHz used in the previous design. In this paper we consider different effects driving the frequency choice of the SRF ERL and present our arguments for choosing lower RF frequency. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME084  
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TUPRI043 Analysis of Coupled Bunch Instabilities in BESSY-VSR cavity, feedback, damping, impedance 1659
 
  • M. Ruprecht, P. Goslawski, A. Jankowiak, M. Ries, A. Schälicke, G. Wüstefeld
    HZB, Berlin, Germany
  • T. Weis
    DELTA, Dortmund, Germany
  
  BESSY-VSR, a scheme where 1.5 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring has recently been proposed*. The strong longitudinal bunch focusing is achieved by superconducting high gradient RF cavities. This paper presents investigations of coupled bunch instabilities driven by HOMs of superconducting multi cell cavities in BESSY-VSR. Analytical calculations and tracking simulations in time domain are performed in the longitudinal and the transverse planes and factors that influence the threshold currents are being discussed. Suitable candidates of cavities which are presently available or in the phase of design are compared with respect to their instability thresholds.
* G. Wüstefeld, A. Jankowiak, J. Knobloch, M. Ries, Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proceedings of IPAC2011, San Sebastián, Spain 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI043  
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TUPRI049 Geometric Beam Coupling Impedance of LHC Secondary Collimators impedance, factory, simulation, wakefield 1677
 
  • O. Frasciello, S. Tomassini, M. Zobov
    INFN/LNF, Frascati (Roma), Italy
  • A. Grudiev, N. Mounet, B. Salvant
    CERN, Geneva, Switzerland
  
  Funding: Work supported by European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404
The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep under control beam instabilities and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are the main impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were by about a factor of 2 higher with respect to the theoretical predictions based on the current model. Up to now the resistive wall impedance has been considered as the major impedance contribution for collimators. By carefully simulating their geometric impedance we show that for the graphite collimators with half-gaps higher than 10 mm the geometric impedance exceeds the resistive wall one. In turn, for the tungsten collimators the geometric impedance dominates for all used gap values. Hence, including the geometric collimator impedance into the LHC impedance model enabled us to reach a better agreement between the measured and simulated collimator tune shifts. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI049  
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TUPRI070 Analysis of Coupled-bunch Instabilities in the NSLS-II Storage Ring cavity, impedance, storage-ring, damping 1727
 
  • G. Bassi, A. Blednykh, F. Gao, J. Rose
    BNL, Upton, Long Island, New York, USA
  
  We discuss coupled-bunch instabilities thresholds for the NSLS-II Storage Ring. In particular, we analyze thresholds from the High Order Modes (HOMs) of the PETRA-III 7-cell cavity. Beam dynamics simulations with the code OASIS, using the measured HOMs, will be compared with machine studies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI070  
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WEOCA02 Recent Results from CTF3 Two Beam Test Stand wakefield, experiment, accelerating-gradient, diagnostics 1880
 
  • W. Farabolini, F. Peauger
    CEA/DSM/IRFU, France
  • Ch. Borgmann, J. Ögren, R.J.M.Y. Ruber
    Uppsala University, Uppsala, Sweden
  • R. Corsini, D. Gamba, A. Grudiev, M.A. Khan, S. Mazzoni, J.L. Navarro Quirante, R. Pan, J.R. Towler, N. Vitoratou, K. Yaqub
    CERN, Geneva, Switzerland
  
  From mid-2012, the Two Beam Test Stand (TBTS) in the CTF3 Experimental Facility is hosting 2 high gradient accelerating structures powered by a single power extraction and transfer structure in a scheme very close to the CLIC basic cell. We report here about the results obtained with this configuration as: energy gain and energy spread in relation with RF phases and power, octupolar transverse beam effects compared with modeling predictions, breakdown rate and breakdown locations within the structures. These structures are the first to be fitted with Wake Field Monitors (WFM) that have been extensively tested and used to further improve the structures alignment on the beam line. These results show the unique capabilities of this test stand to conduct experiments with real beams.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEOCA02  
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WEPRO005 Development of Superconducting Spoke Cavity for Laser Compton Scattered Photon Sources cavity, linac, brightness, photon 1946
 
  • M. Sawamura, R. Hajima, R. Nagai
    JAEA, Ibaraki-ken, Japan
  • H. Fujisawa, Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • T. Kubo
    KEK, Ibaraki, Japan
  
  Funding: This work is supported by Photon and Quantum Basic Research Coordinated Development Program.
We have launched a 5-year research program to develop superconducting spoke cavity for laser Compton scattered (LCS) photon sources. For realizing a wide use of LCS X-ray and gamma-ray sources in academic and industrial applications, we adopt 325-MHz superconducting spoke cavity to electron beam drivers for the LCS sources. The spoke cavity, originally invented for ion and proton acceleration, can be used for electron accelerators, in which we can make best use of features of spoke cavity: relative compactness in comparison with a TM cavity of the same frequency, robustness with respect to manufacturing inaccuracy due to its strong cell-to-cell coupling, couplers on outer conductor for the better packing in a linac, and so on. In this paper, we present our research plan and results of cavity shape optimization. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRO005  
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WEPME054 Design and Fabrication of the Novel-type Ceramic Chamber vacuum, site, detector, electron 2393
 
  • L.H. Wu, C.K. Chan, J.-R. Chen, G.-Y. Hsiung, S-N. Hsu, T.Y. Lee
    NSRRC, Hsinchu, Taiwan
  • J.-R. Chen
    National Tsing Hua University, Hsinchu, Taiwan
  
  A ceramic chamber of novel type has been designed and fabricated. The uniformity of its inner thin film of deposited metal is improved to have a thickness error about 1 %. The average straightness error of the chamber (length 550 mm) is developed to be less than 55 μm. To fabricate the ceramic chamber of novel type, we first cleaned and joined the two halves; the metal films were deposited by sputtering. These two halves were next sealed with a glass powder colloid to become a ceramic tube. The rate of outgassing of this colloid is 3.57×10-12 Torr L s−1 cm-2 after baking. The ceramic tube was connected to a stainless-steel flange with the aid of a glass powder colloid and TIG welding. This ceramic test chamber will be installed in the experimental system to analyze the residual gas.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME054  
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WEPRI008 First Cavity Design Studies for the BESSY-VSR Upgrade Proposal cavity, damping, coupling, impedance 2493
 
  • A. Neumann, A. Burrill, P. Goslawski, A. Jankowiak, J. Knobloch, M. Ries, M. Ruprecht, A.V. Vélez, G. Wüstefeld
    HZB, Berlin, Germany
  
  Funding: Work supported by German Bundesministerium für Bildung und Forschung and Land Berlin
Recently HZB proposed an upgrade of the 3rd generation synchrotron light source BESSY II allowing simultanous long and short pulse operation*. For this scheme to work superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. Given an appropiate choice of the higher harmonics the resulting gradient leads to a beating effect of the effective longitudinal focussing voltage at the stable fix points resulting in different bunch lengths in subsequent buckets. This project places stringent requirements on the cavity performance, as high accelerating fields, excellent HOM damping capabilities and high reliability as they will operate in a 300 mA 24/7 user facility. In this paper we describe the requirements for the cavity design and first designs steps.
* G. Wüstefeldt et al., Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proc. of IPAC'11, San Sebástian, Spain 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI008  
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WEPRI009 Parameter Studies and Geometry Optimization on Superconducting Multicell RF Cavity Resonators factory, cavity, coupling, RF-structure 2496
 
  • B.D. Isbarn, B. Riemann, M. Sommer, T. Weis
    DELTA, Dortmund, Germany
  
  Funding: Work partly supported by the BMBF under contract No. 05K13PEB
Modern accelerator concepts for high intensity electron beams often require superconducting multicell RF-cavity-resonators in circular accelerators (e.g. storage rings). Caused by strong beam-cavity interaction and due to high quality factors of superconducting RF-structures special care of lower order (LOM) and higher order (HOM) modes must be taken. Various numerical studies were performed to numerically calculate the dependence of different figures of merit (e.g. external quality factors Qext) with respect to the geometry parameters and cell number of the RF-structure, focused on the propagation and damping of low and higher order modes. To ease the numerical effort an optimization routine has been developed which automatically optimizes the geometry based on goal functions. In this context it turned out that cell geometries defined by spline functions have advantages compared to the standard elliptical parametrization regularly used. The number of free parameters is substantially reduced which facilitates the search for optimum solutions. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI009  
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WEPRI013 Investigation of Cryomodules for the Mainz Energy-recovering Superconducting Accelerator MESA cryomodule, linac, operation, higher-order-mode 2505
 
  • F. Schlander, K. Aulenbacher, R.G. Heine, D. Simon
    IKP, Mainz, Germany
  • A. Arnold
    HZDR, Dresden, Germany
  
  Funding: Work supported by the German Federal Ministery of Education and Research (BMBF) and German Research Foundation (DFG) under the Cluster of Excellence "PRISMA"
For the multiturn accelerator MESA it is planned to employ superconducting technology for the main linac, which is supposed to provide an energy gain of 50 MeV per turn. As continuous wave operation is mandatory for the experiments, it is important to minimise the cryogenic losses, hence to find cavities and the corresponding cryomodule meeting the framework conditions for the accelerator. The findings and the current statuts will be reported. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI013  
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WEPRI016 Status of the Vertical Testing of the XFEL Third Harmonic Cavity Series cavity, coupling, linac, operation 2508
 
  • J.F. Chen, M. Bertucci, A. Bosotti, M. Fusetti, C. Maiano, P. Michelato, L. Monaco, M. Moretti, C. Pagani, R. Paparella, P. Pierini, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  
  The prototype cavities of the XFEL 3rd harmonic system at the XFEL injector have been tested vertically before their final integration into the He tank. The Vertical Test facility has been upgraded in preparation of the series and the results so far obtained are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI016  
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WEPRI025 Studies of Fabrication Procedure of 9-cell SRF Cavity for ILC Mass-production at KEK. cavity, electron, gun, linear-collider 2528
 
  • T. Saeki, Y. Ajima, K. Enami, H. Hayano, H. Inoue, E. Kako, S. Kato, S. Koike, T. Kubo, S. Noguchi, M. Satoh, M. Sawabe, T. Shishido, A. Terashima, N. Toge, K. Ueno, K. Umemori, K. Watanabe, Y. Watanabe, S. Yamaguchi, A. Yamamoto, Y. Yamamoto, M. Yamanaka, K. Yokoya
    KEK, Ibaraki, Japan
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto, Japan
  • N. Kawabata, H. Nakamura, K. Nohara, M. Shinohara
    SPS, Funabashi-shi, Japan
  • F. Yasuda
    The University of Tokyo, Institute of Physics, Tokyo, Japan
  
  We had been constructing a new facility for the fabrication of superconducting RF cavity at KEK from 2009 to 2011. In the facility, we have installed a deep-drawing machine, a half-cup trimming machine, an electron-beam welding machine, and a chemical etching room in one place. We started the studies on the fabrication of 9-cell cavity for International Linear Collier (ILC) using this facility. The studies are focusing on the cost reduction with keeping high performance of cavity, and the goal is the establishment of mass-production procedure for ILC. We already finished the fabrication of two 9-cell cavities in this facility. This article reports the current status of the studies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI025  
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WEPRI029 Simulations and Measurements of Beam Pipe Modes excited in 9-cell Superconducting Cavities cavity, dipole, simulation, experiment 2540
 
  • A. Kuramoto
    Sokendai, Ibaraki, Japan
  • N. Baboi
    DESY, Hamburg, Germany
  • H. Hayano
    KEK, Ibaraki, Japan
  
  Higher order modes (HOM) excited in 9-cell superconducting cavities have been studied to detect cavity alignment. Dipole modes have been monitored, since their magnitude is proportional to beam offsets from their electrical centers. Detection of cavity alignment is important for the ILC to confirm alignment accuracy and furthermore possible source of emittance growth. We are particularly interested in beam pipe modes because they are localized in both ends of the cavity. We measured beam-induced HOM in the STF accelerator at KEK in 2012 – 2013. From the results of the measurement, we found some modes whose behaviors are like dipole mode at around 2.1 GHz instead of 2.28 GHz as calculated by R. Wanzenberg for an ideal cavity [TESLA 2001-33, September 2001]. We also measured beam induced HOM in the TESLA superconducting cavities in FLASH at DESY. In order to identify beam pipe modes and to compare the measurement with the calculation, we calculate beam pipe modes of 9-cell superconducting cavity by CST MICROWAVE STUDIO 2012 and HFSS 12. We will discuss about these calculations and the measurement.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI029  
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WEPRI037 Comparison of High Order Modes Damping Techniques for 800 MHz Single Cell Superconducting Cavities cavity, damping, luminosity, dipole 2558
 
  • Ya.V. Shashkov, N.P. Sobenin
    MEPhI, Moscow, Russia
  • M. Zobov
    INFN/LNF, Frascati (Roma), Italy
  
  Currently, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOM) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOM damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOM damping is analyzed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI037  
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WEPRI041 Progress of HOM Couplers for CERN SPL Cavities simulation, cavity, niobium, factory 2568
 
  • K. Papke, F. Gerigk
    CERN, Geneva, Switzerland
  • U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
In this paper we present the progress of the Higher-Order-Mode (HOM) coupler design for the high beta CERN SPL (Superconducting Proton Linac) cavities. This includes the RF transmission behavior as well as mechanical and thermal requirements and their optimizations. Warm RF measurements are presented for the first four high beta SPL Cavities made of bulk niobium. Moreover the first prototype of a HOMcoupler will be introduced and we discuss its characteristics and its tuning possibilities. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI041  
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WEPRI045 Key Design Features of Crab-Cavity Cryomodule for HiLumi LHC cavity, cryomodule, cryogenics, radiation 2580
 
  • S.M. Pattalwar, A.J. May, P.A. McIntosh, A.E. Wheelhouse
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • G. Burt, B.D.S. Hall
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • O. Capatina
    CERN, Geneva, Switzerland
  • T.J. Jones, N. Templeton
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • T.H. Nicol
    Fermilab, Batavia, Illinois, USA
  
  A prototype Superconducting RF (SRF) cryomodule, comprising multiple compact crab cavities is foreseen to realise a local crab crossing scheme for the “Hi-Lumi LHC”, a project launched by CERN to increase the luminosity performance of LHC. A cryomodule with two cavities will be initially installed and tested on the SPS drive accelerator at CERN to evaluate performance with high-intensity proton beams. STFC in collaboration with, University of Lancaster, CERN and FNAL has developed a concept cryomodule that has overcome most of the critical challenges imposed by a series of boundary conditions arising from; the complexity of the cavity design, the requirement for multiple RF couplers, the close proximity to the second LHC beam pipe and the tight space constraints in the SPS tunnel. This paper highlights some of the key design features of the cryomodule with the results of the associated mechanical and thermal analysis.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI045  
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WEPRI048 Testing and Dressed Cavity Design for the HL-LHC 4R Crab Cavity cavity, luminosity, cryomodule, dipole 2589
 
  • B.D.S. Hall, G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • R. Calaga, S. Calatroni, E. Jensen, A. Macpherson, M. Navarro-Tapia
    CERN, Geneva, Switzerland
  • T.J. Jones, N. Templeton
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • A.J. May, P.A. McIntosh, S.M. Pattalwar, A.E. Wheelhouse
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  The High luminosity upgrade to the LHC (HL-LHC) calls for crab cavities to reduce the luminosity loss due to the crossing angle and help provide luminosity levelling. The 4 Rod Crab Cavity (4RCC) is one of three proposed options under consideration. A bare cavity has been prototyped and has undergone recent vertical tests and the results are presented. The dressed cavity includes a power coupler, a lower order mode coupler and two HOM couplers will be presented and discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI048  
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WEPRI050 Development and Test Results of a Quasi-waveguide Multi-cell Resonator cavity, niobium, cathode, impedance 2595
 
  • Z.A. Conway, A. Barcikowski, S.M. Gerbick, M. Kedzie, M.P. Kelly, J.S. Kerby, S.H. Kim, S.V. Kutsaev, R.C. Murphy, A. Nassiri, P.N. Ostroumov, T. Reid, T.L. Smith, A. Zholents
    ANL, Argonne, Illinois, USA
  
  Funding: Work supported by the U.S. Department of Energy, Offices of Nuclear Physics and Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
This paper reports the successful fabrication and test results of a novel 2815 MHz superconducting deflecting cavity operating in a TE-mode trapped in a quasi-waveguide structure with extremely high shunt impedance. The waveguide structure of this cavity allows for the free propagation of all higher order modes (HOMs) out of the cavity via the beam ports, eliminating the need for HOM dampers inside the cavity when operated with high beam current. The absence of HOM dampers greatly simplifies the cavity fabrication and operation at cryogenic temperatures. This cavity with its high shunt impedance is ideal for the spatial rotation of short bunches in a small physical space, a requirement for the generation of sub-picosecond short pulse x-rays in electron storage rings or luminosity upgrades of colliders. Results characterizing the fabrication accuracy and precision, the RF performance at 2 K, and frequency tuning considerations will be discussed here. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI050  
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WEPRI073 High Order Modes Survey and Mitigation of the CEBAF C100 Cryomodules cavity, impedance, cryomodule, survey 2660
 
  • J. Guo, M. Stirbet, H. Wang, S. Wang
    JLab, Newport News, Virginia, USA
  
  Funding: Funding Agency: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Ten new C100 cryomodules have been installed for the CEBAF 12GeV upgrade in the last few years. The high order modes (HOM) of these cryomodules need to be controlled to avoid beam breakup (BBU) instability. We surveyed the HOM for all the 80 cavities of the C100 modules in both the JLab cryomodule test facility (CMTF) and the CEBAF tunnel. Additional measures such as waveguide filters were applied to bring down out of spec modes. In this paper, we will present the HOM survey setup and results. The mitigation measures and their effects will also be discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI073  
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WEPRI075 A Compact Beam Spreader using RF Deflecting Cavities for the LCLS-II cavity, dipole, septum, electron 2666
 
  • S.U. De Silva, J.R. Delayen, R.G. Olave
    ODU, Norfolk, Virginia, USA
  • L.R. Doolittle, M. Placidi, A. Ratti
    LBNL, Berkeley, California, USA
  • P. Emma
    SLAC, Menlo Park, California, USA
  
  The LCLS-II project currently under development is designed to accelerate electron bunches up to 4 GeV and transport them to one of two FEL undulators located more than 2 km downstream of the end of the LCLS-II linac. The upgrade requires a spreader system to separate the baseline electron bunches and transport them to two undulator lines or a local dump. Fast bipolar kickers (FK) or transverse electric rf deflectors (RFD) are considered as fast-switching devices (FSD). In the RFD approach described here three design options operating at 325 MHz are studied including a superconducting rf-dipole cavity, a normal conducting rf-dipole cavity, and a normal conducting 4-rod cavity. Optional compact splitting schemes involving a combination of vertical and horizontal initial deflections are addressed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI075  
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WEPRI076 Higher Order Mode Damping in Superconducting Spoke Cavities cavity, damping, higher-order-mode, superconductivity 2669
 
  • C.S. Hopper, J.R. Delayen
    ODU, Norfolk, Virginia, USA
  
  Parasitic higher order modes (HOMs) can be severely detrimental to the performance of superconducting cavities. For this reason, the mode spectrum and beam coupling strength must be examined in detail to determine which modes must be damped. One advantage of the spoke cavity geometry is that couplers can be placed on the outer body of the cavity rather than in the beam line space. We present an overview of the HOM properties of spoke cavities and methods for suppressing the most harmful ones.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI076  
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WEPRI078 Development of a Quarter-wave Coaxial Coupler for 1.3 GHz Superconducting Cavities cavity, coupling, niobium, SRF 2675
 
  • Y. Xie, A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • N. Solyak, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Superconducting ILC-type cavities have an rf coupler that is welded on. A detachable coupler will reduce conditioning time (can be conditioned separately), reduce cost and improve reliability. The problem with placing an extra flange in the superconducting cavity is creating a possible quench spot. Euclid Techlabs LLC designed a coupler and optimized its geometry that yielding an area on the surface with zero magnetic field (hence zero surface current). By placing a flange in that area we are able to avoid disturbing surface currents that typically lead to a quench. The coupler is optimized to preserve the axial symmetry of the cavity and rf field. The rf test results of this type coupler with a 1.3 GHz ILC-type single-cell cavity at Fermilab will be reported and discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI078  
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THPRO046 100 MHz RF System as an Alternative for the Iranian Light Source Facility cavity, storage-ring, operation, emittance 2968
 
  • S. Pirani, H. Ghasem, M. Moradi, Kh.S. Sarhadi
    ILSF, Tehran, Iran
  
  The Iranian Light Source Facility (ILSF) RF system was conceptually designed based on ILSF requirements for a 3GeV storage ring and 400 mA beam current at 500 MHz RF frequency. The development of HOM damped cavity with simpler structure at 100MHz and advantages of reducing frequency as investigated at MAX Lab, provided an alternative of 100MHz RF system to be explored for ILSF. RF frequency change and its effects on the beam and machine parameters as well as the availability and cost of RF system components have been studied for ILSF. The conceptual design of a 100MHz RF system and the comparison between 500 MHz and 100 MHz RF frequencies are presented in this report. This paper, furthermore, provides details about the 100MHz RF cavity designed by ILSF RF group based on MAX Lab cavity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO046  
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THPRO061 New and Unifying Formalism for Study of Particle-Spin Dynamics Using Tools Distilled From Theory of Bundles resonance, polarization, lepton, framework 3014
 
  • K.A. Heinemann, J.A. Ellison
    UNM, Albuquerque, New Mexico, USA
  • D.P. Barber
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • D.P. Barber, M. Vogt
    DESY, Hamburg, Germany
  
  Funding: The work of JAE and KH was supported by DOE under DE-FG-99ER41104 and the work of DPB and MV was supported by DESY.
We summarize our recent work on spin motion in storage rings *. In fact we return to our study ** of spin motion in storage rings. We again focus on spin tunes, polarization fields etc. but in contrast to ** we base the description on one turn maps and refine and expand our toolset from that in * by using a rather modern method from Dynamical-Systems theory, developed in the 1980's by R. Zimmer and others based on bundles **, ***. With this we obtain new insights into invariant spin fields, invariant frame fields, spin tunes and spin-orbit resonances. At the same time we get a unified way to treat spin-1/2 and spin-1 particles. The bundle aspect is pointed out and we briefly mention the relation to Yang-Mills Theory as well.
* K.Heinemann, D.P.Barber, J.A.Ellison, M.Vogt. To be submitted.
** D.P.B., J.A.E., K.H., PRSTAB 7 (2004) 124002.
*** K.Heinemann, PhD Thesis, University of New Mexico, 2010 (available on the web). 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO061  
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THPRO072 Field Parametrisation for the ESS Superconducting Cavities cavity, linac, simulation, space-charge 3044
 
  • T. Lindqvist
    Lund University, Lund, Sweden
  • E. Laface
    ESS, Lund, Sweden
  
  Here we present a method for constructing a parametrization of the electric field in the superconducting elliptic cavities of the ESS linac. The parametrization is done by replicating the electric field from measured data using trigonometric and exponential functions. The field generated by the parameters exhibits a mean error of 0.28% ( maximum error of 3.8% and s.t.d. error 1.1%), with the advantage of only taking up a fraction of the required data. The field in the entire cavity is extrapolated by combining the Maxwell equations with the parametrized form of the field. We also present particle simulations based on the parametrization model to showcase some typical accelerator behaviour. Additionally we present a small extension of the parametrization method to also model spoke cavities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO072  
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THPRO078 Time-dependent Behaviour of Gas Ejected from an Accelerating Structure after a Discharge vacuum, distributed, injection, damping 3062
 
  • V.G. Ziemann
    Uppsala University, Uppsala, Sweden
  
  Funding: This work is supported by the 7th European Framework program EuCARD under grant number 227579.
A discharge or RF-breakdown event in a CLIC acceleration structure causes the localized release of gas molecules inside a thin conduction limited system with distributed pumping. We discuss the transient behavior of such a system in the molecular flow regime that allows an analytical solution with the help of Greens functions. They describe the temporal evolution of the gas density and the gas flow ejected from the ends of thin pipes of finite length. Distributed pumping, for example through the HOM damping slits is taken into account. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO078  
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THPME018 Global Search Methods for Electromagnetic Optimization of Compact Linac Tanks coupling, linac, proton, cavity 3253
 
  • O. Losito, V. Dimiccoli, G. Rutigliani
    ITEL, Ruvo di Puglia, Italy
  • L. De Palma, F. Prudenzano
    Politecnico di Bari (DEI), Bari, Italy
  
  We shows the optimization of a five cell tank to be included as first multi-cavity within a LINAC section accelerating a proton beam from 7 MeV to higher energies, useful for proton therapy. The tank performance depends on a set of physical (beam characteristics) and geometrical parameters (radius and lengths of accelerating and coupling cavities, radius and thickness of the coupling holes among accelerating cells, the radius and the thickness of the coupling holes between off-axis coupling cells and accelerating ones). PSO (Particle Swarm Optimization) and ACO (Ant Colony Optimization) have been used as approaches for the electromagnetic optimization. The model used for the fitness calculation takes into account all the most important effects occurring in the tank coupled cavities loaded by the proton beam. The codes based on PSO and ACO have enabled the global and stochastic identification of about ten optimized parameters. The design goodness has been tested via Particle and Microwave CST Studio © simulation. The optimized tank accelerates the proton beam input energy from Ein=7 MeV to about Eout= 8.2 MeV. These values, well agree with other designs reported in literature.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME018  
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THPRI022 The Accelerator Reliability Forum operation, controls, instrumentation, software 3813
 
  • A. Lüdeke
    PSI, Villigen PSI, Switzerland
  • R. Giachino
    CERN, Geneva, Switzerland
  • L. Hardy
    ESRF, Grenoble, France
  
  A high reliability is a very important goal for most particle accelerators. The biennial Accelerator Reliability Workshop covers topics related to the design and operation of particle accelerators with a high reliability. In order to optimize the over-all reliability of an accelerator one needs to gather information on the reliability of many different subsystems. While a biennial workshop can serve as a platform for the exchange of such information, the authors aimed to provide a further channel to allow for a more timely communication: the Particle Accelerator Reliability Forum (http://reliability.forumotion.com). This contribution will describe the forum and advertise it's usage in the community.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI022  
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THPRI042 Design and RF Test of Damped C-Band Accelerating Structures for the ELI-NP Linac damping, operation, linac, vacuum 3856
 
  • D. Alesini, S. Bini, R. D. Di Raddo, V.L. Lollo, L. Pellegrino
    INFN/LNF, Frascati (Roma), Italy
  • L. Ficcadenti, V. Pettinacci
    INFN-Roma, Roma, Italy
  • L. Palumbo
    URLS, Rome, Italy
  • L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  
  The linac energy booster of the European ELI-NP proposal foresees the use of 12 traveling wave C-Band structures, 1.8 m long with a field phase advance per cell of 2pi/3 and a repetition rate of 100 Hz. Because of the multi-bunch operation, the structures have been designed with a damping of the HOM dipoles modes in order to avoid beam break-up (BBU). They are quasi-constant gradient structures with symmetric inputs couplers and a strong damping of the HOM in each cell. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce their cost. In the paper we shortly review the whole design criteria and we illustrate the low and high power RF test results on prototypes that shown the feasibility of the structure realization and the effectiveness of the HOM damping.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI042  
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THPRI043 Thermal-mechanical Analysis of the RF Structures for the ELI-NP Proposal gun, RF-structure, linac, cathode 3860
 
  • V. Pettinacci
    INFN-Roma, Roma, Italy
  • D. Alesini, L. Pellegrino
    INFN/LNF, Frascati (Roma), Italy
  • L. Palumbo
    URLS, Rome, Italy
  
  The room temperature RF structures in the ELI-NP Linac will operate in multi-bunch with high repetition rate (100 Hz). For these reasons they are subject to some kW of power dissipated on the internal cavities surfaces. The resulting thermal deformation of the cavities shapes could imply variations in their electromagnetic fields. To limit these effects and optimize the cooling design, a fully coupled ElectroMagnetic- Thermal-Mechanical analysis has been performed on the S-Band Radiofrequency Gun and on the C-Band multi-cell structures. In the paper the study done in Ansys Workbench with HFSS and Ansys Mechanical is reviewed  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI043  
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THPRI054 Permittivity and Permeability Measurement Methods for Particle Accelerator Related Materials impedance, simulation, resonance, cavity 3893
 
  • C. Vollinger, F. Caspers, E. Jensen
    CERN, Geneva, Switzerland
  
  For the special requirements related to particle accelerators, knowledge of the different material parameters of dielectrics and other materials are needed in order to carry out simulations during the design process of accelerator components. This includes also properties of magnetically biased ferrites of which usually little information is available about material characteristics, especially in magnetic bias fields. Several methods of measurement are discussed and compared of which some require delicate sample preparation whereas others can work with unmodified material shapes that makes those methods also suited for acceptance checks on incoming materials delivered by industry. Applications include characterization of different materials, as absorbers in which dielectric losses play an increasing role, as well as low frequency measurements on ferrites that are used for tunable cavities. We present results obtained from both broadband and resonant measurements on different materials determined in the same sample holder. Where possible, the results were confirmed with alternative methods.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI054  
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THPRI055 The New 118 MHz Normal Conducting RF Cavity for SIAM Photon Source at SLRI cavity, storage-ring, electron, impedance 3896
 
  • N. Juntong, S. Krainara
    SLRI, Nakhon Ratchasima, Thailand
  
  The Siam Photon Source (SPS) is the 1.2 GeV second generation light source in Thailand. It is managed by the Synchrotron Light Research Institute (SLRI). The institute is located inside the campus of Suranaree University of Technology (SUT), which is approximately 20 km from the city of Nakhon Ratchasima (or normally called Korat). Korat is 250 km north-east of Bangkok. Two insertion devices (IDs) have been installed in the SPS storage ring during June to August 2013. These IDs require additional electrical field energy from RF cavity to compensate electron energy loss in the storage ring. The existing RF cavity has been pushed to its maximum capability and the new RF cavity is in the procurement process. The design and study of the new RF cavity will be presented. Electromagnetic fields of the cavity are studied together with the effects to electron beam instabilities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI055  
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THPRI066 Design of a 1.3 GHz Two-cell Buncher for APEX cavity, impedance, dipole, vacuum 3924
 
  • H.J. Qian, K.M. Baptiste, J.A. Doyle, D. Filippetto, S. Kwiatkowski, C. F. Papadopoulos, D. Patino, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, California, USA
  
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The design of a 1.3 GHz buncher cavity for the APEX project, a MHz repetition rate high-brightness photoinjector, is presented. The buncher cavity operates at 240 kV in CW mode, and it compresses the 750 keV beam from APEX gun through ballistic compression. Compared with a single cell design, a two-cell cavity doubles the shunt impedance to 7.8 MΩ, which greatly relaxes the requirements for both RF amplifier and cavity cooling. Coupler design, multipacting analysis, HOM analysis and thermal analysis will be presented in this paper. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI066  
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THPRI076 Laser Triggered RF Breakdown Study Using an S-band Photocathode Gun laser, gun, experiment, cathode 3943
 
  • J.H. Shao, W. Gai
    ANL, Argonne, Illinois, USA
  • H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, C.-X. Tang, L.X. Yan
    TUB, Beijing, People's Republic of China
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • F.Y. Wang
    SLAC, Menlo Park, California, USA
  
  A laser triggered RF breakdown experiment was carried out with an S-band photocathode gun at Tsinghua University for attempting understanding of the RF breakdown processes. By systematic measurement of the time dependence of the breakdown current at the gun exit and the stored RF energy in the cavity, one might gain insight into the time evolution of RF breakdown physics. A correlation of the stored energy and field emission current has been analysed with an equivalent circuit model. Experimental details and analysis methods are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI076  
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THPRI111 Higher Order Mode Absorbers for High Current ERL Applications cavity, linac, cryomodule, damping 4037
 
  • R.G. Eichhorn, J.V. Conway, Y. He, Y. Li, T.I. O'Connel, P. Quigley, J. Sears, V.D. Shemelin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Efficient damping of the higher-order modes (HOMs) of the superconducting cavities is essential for any high current linac, especially for the proposed energy recovery linac at Cornell that aims for high beam currents and short bunches. This contribution will present the design and first result on the HOM absorbers built for the Main Linac Cryomodule (MLC).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI111  
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THPRI112 Basic Research on RF Absorbing Ceramics for Beam Line HOM Absorbers damping, vacuum, higher-order-mode, linac 4040
 
  • R.G. Eichhorn, P. Quigley, V.D. Shemelin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • M. Carty
    Alfred University, Alfred, New York, USA
  • J. Matteson, A. Rae
    NanoMaterials Innovation Center LLC, Painted Post, USA
  
  Higher Order Mode (HOM) absorbers for future high current machines have been a challenging component for many years. Even though many different materials are commercially, none of them seems to fully qualify for accelerator applications. Some of them are brittle or chippy, others porous, have small bandwidth of absorption, a high dc resistivity leading to charge-up or are unreliable in terms of batch to batch variations. Alfred University and Cornell University have recently partnered in developing a dedicated absorber ceramic material that tries to overcome these limitations. We will report on results from small samples of different compositions we produced based on SiC, graphene and graphite.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI112  
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