LINAC2016 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
MOPLR006	Monopole HOMs Dumping in the LCLS-II 1.3 GHz Structure	cavity, linac, coupling, damping	142
	A. Lunin, T.N. Khabiboulline, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE Developing an upgrade of Linac Coherent Light Source (LCLS-II) is currently underway. The central part of LCLS-II is a continuous wave superconducting RF (CW SRF) electron linac. High order modes (HOMs) excited in SRF structures by passing beam may deteriorate beam quality and affect beam stability. In this paper we report the simulation results of monopole High Order Modes (HOM) spectrum in the 1.3 GHz accelerating structure. Optimum parameters of the HOM feedthrough are suggested for minimizing RF losses on the HOM antenna tip and for preserving an efficiency of monopole HOMs damping simultaneously.
	Poster MOPLR006 [0.647 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR006
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MOPLR007	Redesign of the End Group in the 3.9 GHz LCLS-II Cavity	cavity, dipole, linac, operation	145
	A. Lunin, I.V. Gonin, T.N. Khabiboulline, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE Development and production of Linac Coherent Light Source II (LCLS-II) is underway. The central part of LCLS-II is a continuous wave superconducting RF (CW SCRF) electron linac. The 3.9 GHz third harmonic cavity similar to the XFEL design will be used in LCLS-II for linearizing the longitudinal beam profile. The initial design of the 3.9 GHz cavity developed for XFEL project has a large, 40 mm, beam pipe aperture for better higher-order mode (HOM) damping. It is resulted in dipole HOMs with frequencies nearby the operating mode, which causes difficulties with HOM coupler notch filter tuning. The CW linac operation requires an extra caution in the design of the HOM coupler in order to prevent its possible overheating. In this paper we present the modified 3.9 GHz cavity End Group for meeting the LCLS-II requirements LCLS-II 3.9 GHz Cryomodules, Physics Requirements Document, LCLSII-4.1-PR-0097-R1, SLAC, USA, 2015
	Poster MOPLR007 [1.590 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR007
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MOPLR030	Electromagnetic Design of a Superconducting Twin Axis Cavity	cavity, coupling, linac, dipole	203
	S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA A. Hutton, F. Marhauser, H. Park JLab, Newport News, Virginia, USA
	The twin-axis cavity is a new kind of rf superconducting cavity that consists of two parallel beam pipes, which can accelerate or decelerate two spatially separated beams in the same cavity. This configuration is particularly effective for high-current beams with low-energy electrons that will be used for bunched beam cooling of high-energy protons or ions. The new cavity geometry was designed to create a uniform accelerating or decelerating fields for both beams by utilizing a TM110 dipole mode. This paper presents the design rf optimization of a 1497 MHz twin-axis single-cell cavity, which is currently under fabrication.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR030
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MOPLR031	Wakefield Analysis of Superconducting RF-Dipole Cavities	wakefield, cavity, impedance, dipole	206
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA
	RF-dipole crabbing cavities are being considered for a variety of crabbing applications. Some of the applications are the crabbing cavity systems for LHC High Luminosity Upgrade and the proposed Electron-Ion Collider for Jefferson Lab. The design requirements in the current applications require the cavities to incorporate complex damping schemes to suppress the higher order modes that may be excited by the high intensity proton or electron beams traversing through the cavities. The number of cavities required to achieve the desired high transverse voltage, and the complexity in the cavity geometries also contributes to the wakefields generated by beams. This paper characterizes the wakefield analysis for single cell and multi-cell rf-dipole cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR031
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MOP106002	X-Band Photonic Band Gap Accelerating Structures with Improved Wakefield Suppression	wakefield, dipole, acceleration, electron	307
	E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: This work is supported by U.S. Department of Energy (DOE) Office of High Energy Physics. We present the design of a novel photonic band gap (PBG) accelerating structure with elliptical rods and improved wakefields suppression. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. The experimental characterization of the wakefield spectrum in a beam test was performed at Argonne Wakefield Accelerator facility in 2015, and the superior wakefield suppression properties of the PBG structure were demonstrated. In 2013 the team from MIT and SLAC demonstrated that the X-band PBG structures with elliptical rods have reduced breakdown rate compared to PBG structures with round rods, presumably due to the reduced surface magnetic fields. However, the structure with elliptical rods designed by MIT confined the dipole higher order mode in addition to the accelerating mode and thus did not have superior wakefield suppression properties. We demonstrate that PBG resonators can be designed with 40% smaller peak surface magnetic fields while preserving and even improving their wakefield suppression properties as compared to the structure with round rods. The design of the new structure is presented. The structure will be fabricated, tuned, and tested for high gradients and for wakefield suppression.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106002
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MOP106018	Measurement of the Transverse Beam Dynamics in a TESLA-type Superconducting Cavity	cavity, simulation, experiment, alignment	323
	A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA N. Eddy, D.R. Edstrom, A. Lunin, P. Piot, J. Ruan, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: US Department of Energy (DOE) under contract DE-SC0011831 with Northern Illinois University. Fermilab is operated by the Fermi Research Alliance LLC under US DOE contract DE-AC02-07CH11359. Superconducting linacs are capable of producing intense, ultra-stable, high-quality electron beams that have widespread applications in Science and Industry. Many project are based on the 1.3-GHz TESLA-type superconducting cavity. In this paper we provide an update on a recent experiment aimed at measuring the transfer matrix of a TESLA cavity at the Fermilab Accelerator Science and Technology (FAST) facility. The results are discussed and compared with analytical and numerical simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106018
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MOP106023	Intra Bunch Train Transverse Dynamics in the Superconducting Accelerators FLASH and European XFEL	cavity, beam-transport, transverse-dynamics, operation	333
	T. Hellert, W. Decking, M. Dohlus DESY, Hamburg, Germany
	At FLASH and the European XFEL accelerator superconducting 9-cell TESLA cavities accelerate long bunch trains at high gradients in pulsed operation. Several RF cavities with individual operating limits are supplied by one RF power source. Within the bunch train, the low-level-RF system is able to restrict the variation of the vector sum voltage and phase of one control line below 3·10^-4 and 0.06 degree, respectively. However, individual cavities may have a significant spread of amplitudes and phases. Misaligned cavities in combination with variable RF parameters will cause significant intra-pulse orbit distortions, leading to an increase of the multi-bunch emittance. An efficient model including coupler kicks was developed to describe the effect at low beam energies. Comparison with start-to-end tracking and experimental data will be shown.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106023
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TUPLR011	Performance of the Novel Cornell ERL Main Linac Prototype Cryomodule	cavity, linac, cryomodule, SRF	492
	F. Furuta, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based X-ray light source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Cavities have achieved the specification values of 16.2MV/m with high-Q of 2.0·10¹⁰ in 1.8K in continuous wave (CW) mode. During initial MLC cavity testing, we encountered some field emission, reducing Q and lowering quench field. To overcome field emission and find optimal cool-down parameters, RF processing and thermal cycles with different cool-down conditions has been done. Here we report on these studies and present final results from the MLC cavity performance.
	Poster TUPLR011 [2.389 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR011
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TUPLR012	HOM Measurements for Cornell's ERL Main Linac Cryomodule	cavity, linac, cryomodule, simulation	496
	F. Furuta, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The main linac cryomodule (MLC) for a future energy-recovery linac (ERL) based X-ray source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. All HOMs in MLC have been scanned in 1.8K. The results show effective damping of HOMs, and also agree well with simulation results and the previous HOM scan results on one 7-cell cavity prototype test cryomodule. Here we present detailed results from these HOM studies.
	Poster TUPLR012 [2.773 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR012
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TUPLR040	The RF System of Thomx	cavity, controls, feedback, storage-ring	551
	M. El Khaldi, R. Marie, H. Monard, F. Wicek LAL, Orsay, France M. Diop, L.R. Lopes, A. Loulergue, M. Louvet, P. Marchand, F. Ribeiro, R. Sreedharan SOLEIL, Gif-sur-Yvette, France
	The RF system of the ThomX electron storage ring consists in a 500 MHz single cell copper cavity of the ELETTRA type, powered with a 50 kW CW solid state power amplifier (SSPA), and the associated Low Level RF feedback and control loops. The low operating energy of 50/70 MeV makes the impedances of the cavity higher order modes (HOMs) particularly critical for the beam stability. Their parasitic effects on the beam can be cured by HOM frequency shifting techniques, based on a fine temperature tuning and a dedicated plunger. A typical cavity temperature stability of ± 0.05°C within a range from 30 up to 70 °C can be achieved by a precise control of its water cooling temperature. On the other hand, the tuning of the cavity fundamental mode is achieved by changing its axial length by means of a motor-driven mechanism. A general description of the system and the state of its progress are reported together with some considerations of the effects of beam cavity interactions.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR040
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WE1A02	Assembly of XFEL Cryomodules: Lessons and Results	cavity, cryomodule, vacuum, controls	646
	S. Berry, O. Napoly CEA/DSM/IRFU, France
	The industrialized string and module assembly of 10³ European XFEL cryomodules has been performed at CEA-Saclay between September 2012 and the spring of 2016. The general features and achievements of this construction project will be reviewed, including lessons learned regarding organization, industrial transfer, quality control and assembly procedures. An overview of the cryomodule performance and RF test results will be presented.
	Slides WE1A02 [7.300 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-WE1A02
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THOP03	Cold Bead-Pull Test Stand for SRF Cavities	cavity, niobium, SRF, simulation	748
	A.V. Vélez, A. Frahm, J. Knobloch, A. Neumann HZB, Berlin, Germany
	Bead-pull measurements represent a final step in the fabrication process of an SRF cavity. These tests allow to characterize the flatness of the field profile in order to perform mechanical tuning if needed. These test has been always performed at room temperature, where material properties differ from the superconducting state properties. Still questions like mechanical deformation due to assymetrical thermal shrincage have not yet been answered experimentaly. In this paper, an upgrade of the former Cold-Bead pull system developed by HZB [1] is presented. This test stand is capable of holding a 9-cell Tesla cavity at LHe temperature providing a realistic insight to cavity parameters under realistic conditions. A copper test pill-box is placed in series with the multi-cell cavity in order to perform 1.8K calibration of the bead. Results will be presented on this paper and compared to electromagnetic simulations.
	Slides THOP03 [2.731 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP03
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THOP04	Measurements of the Beam Break-Up Threshold Current at the Recirculating Electron Accelerator S-DALINAC	linac, electron, recirculation, optics	751
	T. Kürzeder, M. Arnold, L.E. Jürgensen, J. Pforr, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany
	Funding: *Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05K13RDA. Linear accelerators, in particular those with a recirculating design and superconducting cavities, have to deal with the problem of Beam Break-Up (BBU). This instability can limit the maximum beam current in such accelerators. Knowing the effectiveness of prevention strategies is of great interest especially for future accelerators like energy recovery linacs (ERL) which aim for high beam currents. One option is to optimize the cavities and higher order mode couplers of those machines. In addition one may adapt the beam line lattice for further suppressing BBU. The superconducting recirculating accelerator S-DALINAC at the Technische Universität Darmstadt provides electron beams in c.w. for nuclear physics experiments since 1991. As the SRF components were never optimized for higher order mode suppression the S-DALINAC suffers from BBU at relatively low beam currents of a few μA. While those currents are sufficient for most nuclear physics experiments we can investigate BBU with respect to the beam optics. We will report on first measurements of threshold currents at different beam energies of the S-DALINAC. The results of a first test to increase the BBU limit by using skew quadrupoles will be presented.
	Slides THOP04 [1.473 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP04
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THPRC014	RF Losses in 1.3 GHz Cryomodule of The LCLS-II Superconducting CW Linac	cryomodule, linac, cavity, cryogenics	798
	A. Saini, A. Lunin, N. Solyak, A.I. Sukhanov, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	The Linac Coherent Light Source (LCLS) is an x-ray free electron laser facility. The proposed upgrade of the LCLS facility is based on construction of a new 4 GeV superconducting (SC) linac that will operate in continuous wave (CW) mode. The major infrastructure investments and the operating cost of a SC CW linac are outlined by its cryogenic requirements. Thus, a detail understanding of RF losses in the cryogenic environment is critical for the entire project. In this paper we review RF losses in a 1.3 GHz accelerating cryomodule of the LCLS-II linac. RF losses due to various sources such untrapped higher order modes (HOMs), resonant losses etc. are addressed and presented here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPRC014
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THPLR018	HOM Suppression Improvement for Mass Production of EXFEL Cavities at RI	cavity, damping, linac, coupling	879
	A.A. Sulimov, J.H. Thie DESY, Hamburg, Germany M. Pekeler, D. Trompetter RI Research Instruments GmbH, Bergisch Gladbach, Germany
	During cold RF tests of the European XFEL (EXFEL) cavities at DESY it was observed that the damping of the second monopole mode (TM011) showed the largest variation, which was sometimes up to 2-3 times lower than the originally allowed limit. It was concluded that this TM011-damping degradation was caused by cavity geometry deviation within the specified mechanical tolerances. The particular influence of different mechanical parameters was analyzed and additional RF measurements were carried out to find the most critical geometry parameters. Stability of the equator welding and regularity of chemical treatment were investigated for different cavity cells. In spite of the high fabrication rate during EXFEL cavity mass production the TM011 suppression was improved to an acceptable level.
	Poster THPLR018 [0.378 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR018
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THPLR037	Development of a Superconducting Twin Axis Cavity	cavity, niobium, linac, SRF	932
	H. Park, A. Hutton, F. Marhauser JLab, Newport News, Virginia, USA S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA
	Superconducting cavities with two separate accelerating axes have been proposed in the past for energy recovery linac applications. While the study showed the advantages of such cavity, the designs present serious fabrication challenges. Hence the proposed cavities have never been built. The new design, elliptical twin cavity, proposed by Jefferson Lab and optimized by Center for Accelerator Science at Old Dominion University, allows similar level of engineering and fabrication techniques of a typical elliptical cavity. This paper describes preliminary LOM and HOM spectrum, engineering and fabrication processes of the twin axis cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR037
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Paper

Title

Other Keywords

Page

MOPLR006

Monopole HOMs Dumping in the LCLS-II 1.3 GHz Structure

cavity, linac, coupling, damping

142

A. Lunin, T.N. Khabiboulline, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE
Developing an upgrade of Linac Coherent Light Source (LCLS-II) is currently underway. The central part of LCLS-II is a continuous wave superconducting RF (CW SRF) electron linac. High order modes (HOMs) excited in SRF structures by passing beam may deteriorate beam quality and affect beam stability. In this paper we report the simulation results of monopole High Order Modes (HOM) spectrum in the 1.3 GHz accelerating structure. Optimum parameters of the HOM feedthrough are suggested for minimizing RF losses on the HOM antenna tip and for preserving an efficiency of monopole HOMs damping simultaneously.

Poster MOPLR006 [0.647 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR006

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MOPLR007

Redesign of the End Group in the 3.9 GHz LCLS-II Cavity

cavity, dipole, linac, operation

145

A. Lunin, I.V. Gonin, T.N. Khabiboulline, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE
Development and production of Linac Coherent Light Source II (LCLS-II) is underway. The central part of LCLS-II is a continuous wave superconducting RF (CW SCRF) electron linac. The 3.9 GHz third harmonic cavity similar to the XFEL design will be used in LCLS-II for linearizing the longitudinal beam profile*. The initial design of the 3.9 GHz cavity developed for XFEL project has a large, 40 mm, beam pipe aperture for better higher-order mode (HOM) damping. It is resulted in dipole HOMs with frequencies nearby the operating mode, which causes difficulties with HOM coupler notch filter tuning. The CW linac operation requires an extra caution in the design of the HOM coupler in order to prevent its possible overheating. In this paper we present the modified 3.9 GHz cavity End Group for meeting the LCLS-II requirements
* LCLS-II 3.9 GHz Cryomodules, Physics Requirements Document, LCLSII-4.1-PR-0097-R1, SLAC, USA, 2015

Poster MOPLR007 [1.590 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR007

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MOPLR030

Electromagnetic Design of a Superconducting Twin Axis Cavity

cavity, coupling, linac, dipole

203

S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
A. Hutton, F. Marhauser, H. Park
JLab, Newport News, Virginia, USA

The twin-axis cavity is a new kind of rf superconducting cavity that consists of two parallel beam pipes, which can accelerate or decelerate two spatially separated beams in the same cavity. This configuration is particularly effective for high-current beams with low-energy electrons that will be used for bunched beam cooling of high-energy protons or ions. The new cavity geometry was designed to create a uniform accelerating or decelerating fields for both beams by utilizing a TM110 dipole mode. This paper presents the design rf optimization of a 1497 MHz twin-axis single-cell cavity, which is currently under fabrication.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR030

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MOPLR031

Wakefield Analysis of Superconducting RF-Dipole Cavities

wakefield, cavity, impedance, dipole

206

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

RF-dipole crabbing cavities are being considered for a variety of crabbing applications. Some of the applications are the crabbing cavity systems for LHC High Luminosity Upgrade and the proposed Electron-Ion Collider for Jefferson Lab. The design requirements in the current applications require the cavities to incorporate complex damping schemes to suppress the higher order modes that may be excited by the high intensity proton or electron beams traversing through the cavities. The number of cavities required to achieve the desired high transverse voltage, and the complexity in the cavity geometries also contributes to the wakefields generated by beams. This paper characterizes the wakefield analysis for single cell and multi-cell rf-dipole cavities.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR031

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MOP106002

X-Band Photonic Band Gap Accelerating Structures with Improved Wakefield Suppression

wakefield, dipole, acceleration, electron

307

E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: This work is supported by U.S. Department of Energy (DOE) Office of High Energy Physics.
We present the design of a novel photonic band gap (PBG) accelerating structure with elliptical rods and improved wakefields suppression. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. The experimental characterization of the wakefield spectrum in a beam test was performed at Argonne Wakefield Accelerator facility in 2015, and the superior wakefield suppression properties of the PBG structure were demonstrated. In 2013 the team from MIT and SLAC demonstrated that the X-band PBG structures with elliptical rods have reduced breakdown rate compared to PBG structures with round rods, presumably due to the reduced surface magnetic fields. However, the structure with elliptical rods designed by MIT confined the dipole higher order mode in addition to the accelerating mode and thus did not have superior wakefield suppression properties. We demonstrate that PBG resonators can be designed with 40% smaller peak surface magnetic fields while preserving and even improving their wakefield suppression properties as compared to the structure with round rods. The design of the new structure is presented. The structure will be fabricated, tuned, and tested for high gradients and for wakefield suppression.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106002

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MOP106018

Measurement of the Transverse Beam Dynamics in a TESLA-type Superconducting Cavity

cavity, simulation, experiment, alignment

323

A. Halavanau, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
N. Eddy, D.R. Edstrom, A. Lunin, P. Piot, J. Ruan, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: US Department of Energy (DOE) under contract DE-SC0011831 with Northern Illinois University. Fermilab is operated by the Fermi Research Alliance LLC under US DOE contract DE-AC02-07CH11359.
Superconducting linacs are capable of producing intense, ultra-stable, high-quality electron beams that have widespread applications in Science and Industry. Many project are based on the 1.3-GHz TESLA-type superconducting cavity. In this paper we provide an update on a recent experiment aimed at measuring the transfer matrix of a TESLA cavity at the Fermilab Accelerator Science and Technology (FAST) facility. The results are discussed and compared with analytical and numerical simulations.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106018

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MOP106023

Intra Bunch Train Transverse Dynamics in the Superconducting Accelerators FLASH and European XFEL

cavity, beam-transport, transverse-dynamics, operation

333

T. Hellert, W. Decking, M. Dohlus
DESY, Hamburg, Germany

At FLASH and the European XFEL accelerator superconducting 9-cell TESLA cavities accelerate long bunch trains at high gradients in pulsed operation. Several RF cavities with individual operating limits are supplied by one RF power source. Within the bunch train, the low-level-RF system is able to restrict the variation of the vector sum voltage and phase of one control line below 3·10^-4 and 0.06 degree, respectively. However, individual cavities may have a significant spread of amplitudes and phases. Misaligned cavities in combination with variable RF parameters will cause significant intra-pulse orbit distortions, leading to an increase of the multi-bunch emittance. An efficient model including coupler kicks was developed to describe the effect at low beam energies. Comparison with start-to-end tracking and experimental data will be shown.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOP106023

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TUPLR011

Performance of the Novel Cornell ERL Main Linac Prototype Cryomodule

cavity, linac, cryomodule, SRF

492

F. Furuta, J. Dobbins, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based X-ray light source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Cavities have achieved the specification values of 16.2MV/m with high-Q of 2.0·10¹⁰ in 1.8K in continuous wave (CW) mode. During initial MLC cavity testing, we encountered some field emission, reducing Q and lowering quench field. To overcome field emission and find optimal cool-down parameters, RF processing and thermal cycles with different cool-down conditions has been done. Here we report on these studies and present final results from the MLC cavity performance.

Poster TUPLR011 [2.389 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR011

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TUPLR012

HOM Measurements for Cornell's ERL Main Linac Cryomodule

cavity, linac, cryomodule, simulation

496

F. Furuta, R.G. Eichhorn, M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The main linac cryomodule (MLC) for a future energy-recovery linac (ERL) based X-ray source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. All HOMs in MLC have been scanned in 1.8K. The results show effective damping of HOMs, and also agree well with simulation results and the previous HOM scan results on one 7-cell cavity prototype test cryomodule. Here we present detailed results from these HOM studies.

Poster TUPLR012 [2.773 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR012

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TUPLR040

The RF System of Thomx

cavity, controls, feedback, storage-ring

551

M. El Khaldi, R. Marie, H. Monard, F. Wicek
LAL, Orsay, France
M. Diop, L.R. Lopes, A. Loulergue, M. Louvet, P. Marchand, F. Ribeiro, R. Sreedharan
SOLEIL, Gif-sur-Yvette, France

The RF system of the ThomX electron storage ring consists in a 500 MHz single cell copper cavity of the ELETTRA type, powered with a 50 kW CW solid state power amplifier (SSPA), and the associated Low Level RF feedback and control loops. The low operating energy of 50/70 MeV makes the impedances of the cavity higher order modes (HOMs) particularly critical for the beam stability. Their parasitic effects on the beam can be cured by HOM frequency shifting techniques, based on a fine temperature tuning and a dedicated plunger. A typical cavity temperature stability of ± 0.05°C within a range from 30 up to 70 °C can be achieved by a precise control of its water cooling temperature. On the other hand, the tuning of the cavity fundamental mode is achieved by changing its axial length by means of a motor-driven mechanism. A general description of the system and the state of its progress are reported together with some considerations of the effects of beam cavity interactions.

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR040

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WE1A02

Assembly of XFEL Cryomodules: Lessons and Results

cavity, cryomodule, vacuum, controls

646

S. Berry, O. Napoly
CEA/DSM/IRFU, France

The industrialized string and module assembly of 10³ European XFEL cryomodules has been performed at CEA-Saclay between September 2012 and the spring of 2016. The general features and achievements of this construction project will be reviewed, including lessons learned regarding organization, industrial transfer, quality control and assembly procedures. An overview of the cryomodule performance and RF test results will be presented.

Slides WE1A02 [7.300 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-WE1A02

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THOP03

Cold Bead-Pull Test Stand for SRF Cavities

cavity, niobium, SRF, simulation

748

A.V. Vélez, A. Frahm, J. Knobloch, A. Neumann
HZB, Berlin, Germany

Bead-pull measurements represent a final step in the fabrication process of an SRF cavity. These tests allow to characterize the flatness of the field profile in order to perform mechanical tuning if needed. These test has been always performed at room temperature, where material properties differ from the superconducting state properties. Still questions like mechanical deformation due to assymetrical thermal shrincage have not yet been answered experimentaly. In this paper, an upgrade of the former Cold-Bead pull system developed by HZB [1] is presented. This test stand is capable of holding a 9-cell Tesla cavity at LHe temperature providing a realistic insight to cavity parameters under realistic conditions. A copper test pill-box is placed in series with the multi-cell cavity in order to perform 1.8K calibration of the bead. Results will be presented on this paper and compared to electromagnetic simulations.

Slides THOP03 [2.731 MB]

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THOP04

Measurements of the Beam Break-Up Threshold Current at the Recirculating Electron Accelerator S-DALINAC

linac, electron, recirculation, optics

751

T. Kürzeder, M. Arnold, L.E. Jürgensen, J. Pforr, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany

Funding: *Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05K13RDA.
Linear accelerators, in particular those with a recirculating design and superconducting cavities, have to deal with the problem of Beam Break-Up (BBU). This instability can limit the maximum beam current in such accelerators. Knowing the effectiveness of prevention strategies is of great interest especially for future accelerators like energy recovery linacs (ERL) which aim for high beam currents. One option is to optimize the cavities and higher order mode couplers of those machines. In addition one may adapt the beam line lattice for further suppressing BBU. The superconducting recirculating accelerator S-DALINAC at the Technische Universität Darmstadt provides electron beams in c.w. for nuclear physics experiments since 1991. As the SRF components were never optimized for higher order mode suppression the S-DALINAC suffers from BBU at relatively low beam currents of a few μA. While those currents are sufficient for most nuclear physics experiments we can investigate BBU with respect to the beam optics. We will report on first measurements of threshold currents at different beam energies of the S-DALINAC. The results of a first test to increase the BBU limit by using skew quadrupoles will be presented.

Slides THOP04 [1.473 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP04

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THPRC014

RF Losses in 1.3 GHz Cryomodule of The LCLS-II Superconducting CW Linac

cryomodule, linac, cavity, cryogenics

798

A. Saini, A. Lunin, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

The Linac Coherent Light Source (LCLS) is an x-ray free electron laser facility. The proposed upgrade of the LCLS facility is based on construction of a new 4 GeV superconducting (SC) linac that will operate in continuous wave (CW) mode. The major infrastructure investments and the operating cost of a SC CW linac are outlined by its cryogenic requirements. Thus, a detail understanding of RF losses in the cryogenic environment is critical for the entire project. In this paper we review RF losses in a 1.3 GHz accelerating cryomodule of the LCLS-II linac. RF losses due to various sources such untrapped higher order modes (HOMs), resonant losses etc. are addressed and presented here.

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THPLR018

HOM Suppression Improvement for Mass Production of EXFEL Cavities at RI

cavity, damping, linac, coupling

879

A.A. Sulimov, J.H. Thie
DESY, Hamburg, Germany
M. Pekeler, D. Trompetter
RI Research Instruments GmbH, Bergisch Gladbach, Germany

During cold RF tests of the European XFEL (EXFEL) cavities at DESY it was observed that the damping of the second monopole mode (TM011) showed the largest variation, which was sometimes up to 2-3 times lower than the originally allowed limit. It was concluded that this TM011-damping degradation was caused by cavity geometry deviation within the specified mechanical tolerances. The particular influence of different mechanical parameters was analyzed and additional RF measurements were carried out to find the most critical geometry parameters. Stability of the equator welding and regularity of chemical treatment were investigated for different cavity cells. In spite of the high fabrication rate during EXFEL cavity mass production the TM011 suppression was improved to an acceptable level.

Poster THPLR018 [0.378 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR018

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THPLR037

Development of a Superconducting Twin Axis Cavity

cavity, niobium, linac, SRF

932

H. Park, A. Hutton, F. Marhauser
JLab, Newport News, Virginia, USA
S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA

Superconducting cavities with two separate accelerating axes have been proposed in the past for energy recovery linac applications. While the study showed the advantages of such cavity, the designs present serious fabrication challenges. Hence the proposed cavities have never been built. The new design, elliptical twin cavity, proposed by Jefferson Lab and optimized by Center for Accelerator Science at Old Dominion University, allows similar level of engineering and fabrication techniques of a typical elliptical cavity. This paper describes preliminary LOM and HOM spectrum, engineering and fabrication processes of the twin axis cavity.

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