SRF2015 - List of Keywords (dipole)

Paper	Title	Other Keywords	Page
MOPB078	Mode Sensitivity Analysis of 704.4 MHz Superconducting RF Cavities	HOM, cavity, operation, linac	311
	K. Papke, F. Gerigk, S. Horvath-Mikulas, S. Papadopoulos, E. Pilicer, F. Pillon CERN, Geneva, Switzerland U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Due to the large variety of beam patterns considered for the superconducting proton linac (SPL) at CERN it is likely that the frequencies of some HOMs are close to machine lines during operation. Hence, in the interest of developing a method to shift HOM frequencies away from machine lines, we study the influence of cavity detuning and re-tuning (e.g. by Lorentz forces, field flatness tuning, frequency tuning during operation) on HOMs. The sensitivity of HOMs with respect to the fundamental mode was studied for a mono-cell and for 5-cell high-beta SPL cavities operating at 704.4 MHz. First, the variation of the HOMs during the flat-field tuning was measured. In this process, several detuning and re-tuning cycles were made to estimate the range of possible HOM frequency shifts. Secondly the effect of the frequency tuner on the HOMs is presented and finally the frequency shifts of all modes due to the cool down.
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TUPB052	HTS Coatings for Impedance Reduction of Beam-Induced RF Image Currents in the FCC	impedance, radiation, collider, injection	695
	S. Calatroni CERN, Geneva, Switzerland
	The FCC-hh presently under study at CERN will make use of 16 T superconducting dipoles for achieving 100 TeV p-p center-of-mass collision energy in a 100 km ring collider. A copper coated beam screen, like in the LHC, is envisaged to shield the 1.9 K dipole cold bores from the 28 W/m/beam of synchrotron radiation. Operating temperature should be in the 50 K range, as best compromise temperature in order to minimize the wall-plug power consumption of the cryogenic system. However, preliminary studies indicate that copper at 50 K might not provide low enough beam coupling impedance in the FCC-hh. It has then been proposed to reduce the beam impedance by a thin layer of a High-Temperature Superconductor (HTS), which will thus effectively shield the beam-induced RF image currents. Purpose of this paper is to define the basic requirements for an HTS film in the RF field induced by beam image currents and exposed to a high magnetic field, and to identify the best candidate materials and coating processes.
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WEA2A02	High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell	cavity, niobium, HOM, factory	948
	S. Arsenyev MIT/PSFC, Cambridge, Massachusetts, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA
	Funding: DOE Office of Science/Office of High Energy Physics Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.
	Slides WEA2A02 [7.023 MB]
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THAA01	Recent Developments in Superconducting Deflecting-Mode Cavities	cavity, HOM, simulation, luminosity	987
	J.R. Delayen ODU, Norfolk, Virginia, USA
	In the last few years there has been a growing interest in compact superconducting cavities operating in a deflecting mode to be used either in rf separators or crabbing systems. This talk will give an overview of recent progress in global activities towards SRF deflecting mode cavities.
	Slides THAA01 [4.729 MB]
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THPB003	Calculations for RF Cavities with Dissipative Material	HOM, cavity, SRF, damping	1056
	F. Marhauser JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 3D simulations have been performed for a variety of SRF cavities which incorporate Higher Order Mode dampers, either in form of coaxial couplers or waveguide dampers. Instead of utilizing the rather standard approach of matching the output port of the dampers with a broadband coaxial or waveguide port, dissipative materials are modelled for RF field absorption. This for instance not only avoids the otherwise required definition of the number of modes considered for damping, which has an impact on the computational time, but also allows tailoring the load material to conform with experimental data of e.g. non-perfect absorbers. The new calculation scheme is presented. Findings are partially compared with those achieved with the standard waveguide port approach by means of external quality factors. CPU speeds are briefly discussed for both approaches.
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THPB004	HOM Calculations for Different Cavities and Beam Induced HOM Power Analysis of ESS	HOM, cavity, sextupole, quadrupole	1061
	H.J. Zheng, J. Gao IHEP, Beijing, People's Republic of China J.F. Chen INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	For different design of ESS superconducting cavities, the higher order modes (HOM's) of monopoles, dipoles, quadrupoles and sextupoles are found. Their R/Q values are also calculated. Main HOM related issues are the beam instabilities and the HOM induced power especially from TM monopoles. The analysis for the beam induced HOM voltage and power in this paper showed that, if the HOM frequency is a few kHz away from the beam spectrum, it is not a problem. In order to understand the effects of the beam structure, analytic expressions are developed. With these expressions, the induced HOM voltage and power were calculated by assuming external Q for each HOM. Our analysis confirm that, with thebeam structure of ESS and a good cavity design, no special tight tolerances are required for cavity fabrication and no HOM couplers in the cavity beam pipes are planned.
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THPB008	RF Simulations for an LCLS-II 3rd Harmonic Cavity Cyromodule	cavity, HOM, damping, cryomodule	1078
	L. Xiao, C. Adolphsen, Z. Li, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	The FNAL designed 3.9 GHz third harmonic cavity for XFEL will be used in LCLS-II for linearizing the longitudinal beam profile. The 3.9 GHz SRF cavity is scaled down from the 1.3 GHz TESLA cavity shape, but has a disproportionately large beampipe radius for better higher-order mode (HOM) damping. The HOM and fundamental power (FPC) couplers will generate asymmetric field in the beam region, and thereby dilute the beam emittance. Meanwhile, due to the large beampipe, all but a few of the HOMs are above the beampipe cutoff. Thus the HOM damping analyses need to be performed in a full cryomodule, rather than in an individual cavity. The HOM damping in a 4-cavity cryomodule was investigated to determine possible trapped modes using the parallel electromagnetic code suite ACE3P developed at SLAC. The coupler RF kicks induced by the HOM and FPC couplers in the 3.9 GHz cavity were evaluated. A possible cavity-to-cavity arrangement is proposed which could provide effective cancellation of these RF kicks. In this paper we present and discuss the RF simulation results in the 3.9 GHz third harmonic cavity cryomodule. Work supported by Department of Energy under contract Number DE-AC02-76SF00515.
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THPB047	Analysis of a 750 MHz SRF Dipole Cavity	cavity, simulation, cryogenics, cathode	1200
	A. Castilla, J.R. Delayen ODU, Norfolk, Virginia, USA A. Castilla, J.R. Delayen JLab, Newport News, Virginia, USA A. Castilla DCI-UG, León, Mexico
	Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177. There is a growing interest in using rf transverse deflecting structures for a plethora of applications in the current and future high performance colliders. In this paper, we present the results of a proof of principle superconducting rf dipole, designed as a prototype for a 750 MHz crabbing corrector for the Medium Energy Electron-Ion Collider (MEIC), which has been successfully tested at 4.2 K and 2 K at the Jefferson Lab’s Vertical Testing Area (VTA). The analysis of its rf performance during cryogenic testing, along with Helium pressure sensitivity, Lorentz detuning, surface resistance, and multipacting processing analysis are presented in this work. Detailed calculations of losses at the port flanges are included for completeness of the cavity’s cryogenic performance studies.
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THPB053	Electromagnetic Design of 400 MHz RF-Dipole Crabbing Cavity for LHC High Luminosity Upgrade	cavity, HOM, luminosity, impedance	1222
	S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA
	The beam crabbing proposed for the LHC High Luminosity Upgrade requires two crabbing systems operating in both horizontal and vertical planes. In addition, the crabbing cavity design needs to meet strict dimensional constraints and functional specifications of the cavities. This paper presents the detailed electromagnetic design including em properties, multipole analysis, multipacting levels of the 400 MHz rf-dipole crabbing cavity.
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THPB068	Practical Aspects of HOM Suppression Improvement for TM011	HOM, damping, cavity, simulation	1277
	A.A. Sulimov, A. Ermakov, J.H. Thie DESY, Hamburg, Germany A. Gresele Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
	Some Higher Order Modes (HOM) pass bands were controlled during cryo-tests at DESY for the European XFEL cavities. The second monopole mode (TM011) showed most instabilities and suppression degradation. The authors will explain this phenomenon on the example of cavity CAV00553 and present the practical method of TM011 damping improvement.
	Poster THPB068 [0.182 MB]
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THPB072	Higher Order Mode Damping in a Higher Harmonic Cavity for the Advanced Photon Source Upgrade	HOM, cavity, impedance, simulation	1293
	S.H. Kim, J. Carwardine, Z.A. Conway, G. Decker, M.P. Kelly, B. Mustapha, P.N. Ostroumov, G.J. Waldschmidt ANL, Argonne, Illinois, USA
	Funding: Results in this report are derived from work performed at Argonne National Laboratory. Argonne is operated by UChicago Argonne, LLC, for the U.S. Department of Energy under contract DE-AC02-06CH11357. A superconducting higher-harmonic cavity (HHC) is under development for the Advanced Photon Source Upgrade based on a Multi-Bend Achromat lattice. This cavity will be used to improve the Touschek lifetime and the single bunch current limit by lengthening the beam. A single-cell 1.4 GHz (the 4th harmonic of the main RF) cavity is designed based on the TESLA shape. Two adjustable fundamental mode power couplers are included. The harmonic cavity voltage of 0.84 MV will be driven by the 200 mA beam with a bunch length of >50 ps RMS. Higher-order modes (HOM) must be extracted and damped. This will be done with two silicon carbide beamline HOM absorbers to minimize heating of RF structures such as the superconducting cavity and/or couplers and suppress possible beam instabilities. The HHC system is designed such that 1) most monopole and dipole HOMs are extracted along the beam pipes and damped in the ‘beamline’ silicon carbide absorbers and 2) a few HOMs, resulting from introduction of the couplers, are extracted through the coupler and dissipated in a room temperature water-cooled load. We will present time and frequency domain simulation results and discuss damping of HOMs.
	Poster THPB072 [2.187 MB]
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THPB081	FPC and HOM Coupler Test Boxes for HL-LHC Crab Cavities	HOM, cavity, coupling, operation	1321
	A.R.J. Tutte, G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, A. Macpherson, E. Montesinos CERN, Geneva, Switzerland S.U. De Silva ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	The LHC luminosity upgrade will involve the installation of thirty-two 400 MHz SRF crab cavities. The cavities have two variants known as the RF dipole and double quarter-wave crab cavities. Each cavity has a fundamental power coupler (FPC) at 400 MHz and two or three HOM couplers. Before integration onto the cavities it is necessary to condition the FPC, and to measure the transmission on the HOM couplers at low power to ensure the operate as designed, each requiring a special test box. The FPC test box should provide a high transmission between two couplers without creating high surface fields. The low power HOM test boxes should be terminated to a load such that the natural stop and pass-bands of the couplers are preserved allowing the reflection to me measured and compared to simulations. In addition, due to the possibility of high HOM power in the LHC crab cavities, the concept of creating a broadband high power HOM coupler test box in order to condition and test the couplers at high power has been investigated. The Rf design of all test boxes is presented and discussed.
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THPB093	A 1.3 GHz Waveguide to Coax Coupler for Superconducting Cavities With a Minimum Kick	cavity, emittance, niobium, electron	1360
	J.A. Robbins, C. Egerer, R.G. Eichhorn, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Transversal forces as a result of asymmetric field generated by the fundamental power couplers have become a concern for low emittance beam in future accelerators. In pushing for smallest emittances, Cornell has finished a physics design for a symmetric coupler for superconducting accelerating cavities. This coupler consists of a rectangular waveguide that transforms into a coaxial line inside the beam pipe, eventually feeding the cavity. We will report on the RF design yielding to the extremely low transversal kick. In addition, heating, heat transfer and thermal stability of this coupler has been evaluated.
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Paper

Title

Other Keywords

Page

MOPB078

Mode Sensitivity Analysis of 704.4 MHz Superconducting RF Cavities

HOM, cavity, operation, linac

311

K. Papke, F. Gerigk, S. Horvath-Mikulas, S. Papadopoulos, E. Pilicer, F. Pillon
CERN, Geneva, Switzerland
U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Due to the large variety of beam patterns considered for the superconducting proton linac (SPL) at CERN it is likely that the frequencies of some HOMs are close to machine lines during operation. Hence, in the interest of developing a method to shift HOM frequencies away from machine lines, we study the influence of cavity detuning and re-tuning (e.g. by Lorentz forces, field flatness tuning, frequency tuning during operation) on HOMs. The sensitivity of HOMs with respect to the fundamental mode was studied for a mono-cell and for 5-cell high-beta SPL cavities operating at 704.4 MHz. First, the variation of the HOMs during the flat-field tuning was measured. In this process, several detuning and re-tuning cycles were made to estimate the range of possible HOM frequency shifts. Secondly the effect of the frequency tuner on the HOMs is presented and finally the frequency shifts of all modes due to the cool down.

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TUPB052

HTS Coatings for Impedance Reduction of Beam-Induced RF Image Currents in the FCC

impedance, radiation, collider, injection

695

S. Calatroni
CERN, Geneva, Switzerland

The FCC-hh presently under study at CERN will make use of 16 T superconducting dipoles for achieving 100 TeV p-p center-of-mass collision energy in a 100 km ring collider. A copper coated beam screen, like in the LHC, is envisaged to shield the 1.9 K dipole cold bores from the 28 W/m/beam of synchrotron radiation. Operating temperature should be in the 50 K range, as best compromise temperature in order to minimize the wall-plug power consumption of the cryogenic system. However, preliminary studies indicate that copper at 50 K might not provide low enough beam coupling impedance in the FCC-hh. It has then been proposed to reduce the beam impedance by a thin layer of a High-Temperature Superconductor (HTS), which will thus effectively shield the beam-induced RF image currents. Purpose of this paper is to define the basic requirements for an HTS film in the RF field induced by beam image currents and exposed to a high magnetic field, and to identify the best candidate materials and coating processes.

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WEA2A02

High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell

cavity, niobium, HOM, factory

948

S. Arsenyev
MIT/PSFC, Cambridge, Massachusetts, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA
W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: DOE Office of Science/Office of High Energy Physics
Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.

Slides WEA2A02 [7.023 MB]

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THAA01

Recent Developments in Superconducting Deflecting-Mode Cavities

cavity, HOM, simulation, luminosity

987

J.R. Delayen
ODU, Norfolk, Virginia, USA

In the last few years there has been a growing interest in compact superconducting cavities operating in a deflecting mode to be used either in rf separators or crabbing systems. This talk will give an overview of recent progress in global activities towards SRF deflecting mode cavities.

Slides THAA01 [4.729 MB]

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THPB003

Calculations for RF Cavities with Dissipative Material

HOM, cavity, SRF, damping

1056

F. Marhauser
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
3D simulations have been performed for a variety of SRF cavities which incorporate Higher Order Mode dampers, either in form of coaxial couplers or waveguide dampers. Instead of utilizing the rather standard approach of matching the output port of the dampers with a broadband coaxial or waveguide port, dissipative materials are modelled for RF field absorption. This for instance not only avoids the otherwise required definition of the number of modes considered for damping, which has an impact on the computational time, but also allows tailoring the load material to conform with experimental data of e.g. non-perfect absorbers. The new calculation scheme is presented. Findings are partially compared with those achieved with the standard waveguide port approach by means of external quality factors. CPU speeds are briefly discussed for both approaches.

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THPB004

HOM Calculations for Different Cavities and Beam Induced HOM Power Analysis of ESS

HOM, cavity, sextupole, quadrupole

1061

H.J. Zheng, J. Gao
IHEP, Beijing, People's Republic of China
J.F. Chen
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

For different design of ESS superconducting cavities, the higher order modes (HOM's) of monopoles, dipoles, quadrupoles and sextupoles are found. Their R/Q values are also calculated. Main HOM related issues are the beam instabilities and the HOM induced power especially from TM monopoles. The analysis for the beam induced HOM voltage and power in this paper showed that, if the HOM frequency is a few kHz away from the beam spectrum, it is not a problem. In order to understand the effects of the beam structure, analytic expressions are developed. With these expressions, the induced HOM voltage and power were calculated by assuming external Q for each HOM. Our analysis confirm that, with thebeam structure of ESS and a good cavity design, no special tight tolerances are required for cavity fabrication and no HOM couplers in the cavity beam pipes are planned.

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THPB008

RF Simulations for an LCLS-II 3rd Harmonic Cavity Cyromodule

cavity, HOM, damping, cryomodule

1078

L. Xiao, C. Adolphsen, Z. Li, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The FNAL designed 3.9 GHz third harmonic cavity for XFEL will be used in LCLS-II for linearizing the longitudinal beam profile. The 3.9 GHz SRF cavity is scaled down from the 1.3 GHz TESLA cavity shape, but has a disproportionately large beampipe radius for better higher-order mode (HOM) damping. The HOM and fundamental power (FPC) couplers will generate asymmetric field in the beam region, and thereby dilute the beam emittance. Meanwhile, due to the large beampipe, all but a few of the HOMs are above the beampipe cutoff. Thus the HOM damping analyses need to be performed in a full cryomodule, rather than in an individual cavity. The HOM damping in a 4-cavity cryomodule was investigated to determine possible trapped modes using the parallel electromagnetic code suite ACE3P developed at SLAC. The coupler RF kicks induced by the HOM and FPC couplers in the 3.9 GHz cavity were evaluated. A possible cavity-to-cavity arrangement is proposed which could provide effective cancellation of these RF kicks. In this paper we present and discuss the RF simulation results in the 3.9 GHz third harmonic cavity cryomodule.
Work supported by Department of Energy under contract Number DE-AC02-76SF00515.

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THPB047

Analysis of a 750 MHz SRF Dipole Cavity

cavity, simulation, cryogenics, cathode

1200

A. Castilla, J.R. Delayen
ODU, Norfolk, Virginia, USA
A. Castilla, J.R. Delayen
JLab, Newport News, Virginia, USA
A. Castilla
DCI-UG, León, Mexico

Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.
There is a growing interest in using rf transverse deflecting structures for a plethora of applications in the current and future high performance colliders. In this paper, we present the results of a proof of principle superconducting rf dipole, designed as a prototype for a 750 MHz crabbing corrector for the Medium Energy Electron-Ion Collider (MEIC), which has been successfully tested at 4.2 K and 2 K at the Jefferson Lab’s Vertical Testing Area (VTA). The analysis of its rf performance during cryogenic testing, along with Helium pressure sensitivity, Lorentz detuning, surface resistance, and multipacting processing analysis are presented in this work. Detailed calculations of losses at the port flanges are included for completeness of the cavity’s cryogenic performance studies.

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THPB053

Electromagnetic Design of 400 MHz RF-Dipole Crabbing Cavity for LHC High Luminosity Upgrade

cavity, HOM, luminosity, impedance

1222

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

The beam crabbing proposed for the LHC High Luminosity Upgrade requires two crabbing systems operating in both horizontal and vertical planes. In addition, the crabbing cavity design needs to meet strict dimensional constraints and functional specifications of the cavities. This paper presents the detailed electromagnetic design including em properties, multipole analysis, multipacting levels of the 400 MHz rf-dipole crabbing cavity.

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THPB068

Practical Aspects of HOM Suppression Improvement for TM011

HOM, damping, cavity, simulation

1277

A.A. Sulimov, A. Ermakov, J.H. Thie
DESY, Hamburg, Germany
A. Gresele
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy

Some Higher Order Modes (HOM) pass bands were controlled during cryo-tests at DESY for the European XFEL cavities. The second monopole mode (TM011) showed most instabilities and suppression degradation. The authors will explain this phenomenon on the example of cavity CAV00553 and present the practical method of TM011 damping improvement.

Poster THPB068 [0.182 MB]

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THPB072

Higher Order Mode Damping in a Higher Harmonic Cavity for the Advanced Photon Source Upgrade

HOM, cavity, impedance, simulation

1293

S.H. Kim, J. Carwardine, Z.A. Conway, G. Decker, M.P. Kelly, B. Mustapha, P.N. Ostroumov, G.J. Waldschmidt
ANL, Argonne, Illinois, USA

Funding: Results in this report are derived from work performed at Argonne National Laboratory. Argonne is operated by UChicago Argonne, LLC, for the U.S. Department of Energy under contract DE-AC02-06CH11357.
A superconducting higher-harmonic cavity (HHC) is under development for the Advanced Photon Source Upgrade based on a Multi-Bend Achromat lattice. This cavity will be used to improve the Touschek lifetime and the single bunch current limit by lengthening the beam. A single-cell 1.4 GHz (the 4th harmonic of the main RF) cavity is designed based on the TESLA shape. Two adjustable fundamental mode power couplers are included. The harmonic cavity voltage of 0.84 MV will be driven by the 200 mA beam with a bunch length of >50 ps RMS. Higher-order modes (HOM) must be extracted and damped. This will be done with two silicon carbide beamline HOM absorbers to minimize heating of RF structures such as the superconducting cavity and/or couplers and suppress possible beam instabilities. The HHC system is designed such that 1) most monopole and dipole HOMs are extracted along the beam pipes and damped in the ‘beamline’ silicon carbide absorbers and 2) a few HOMs, resulting from introduction of the couplers, are extracted through the coupler and dissipated in a room temperature water-cooled load. We will present time and frequency domain simulation results and discuss damping of HOMs.

Poster THPB072 [2.187 MB]

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THPB081

FPC and HOM Coupler Test Boxes for HL-LHC Crab Cavities

HOM, cavity, coupling, operation

1321

A.R.J. Tutte, G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga, A. Macpherson, E. Montesinos
CERN, Geneva, Switzerland
S.U. De Silva
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

The LHC luminosity upgrade will involve the installation of thirty-two 400 MHz SRF crab cavities. The cavities have two variants known as the RF dipole and double quarter-wave crab cavities. Each cavity has a fundamental power coupler (FPC) at 400 MHz and two or three HOM couplers. Before integration onto the cavities it is necessary to condition the FPC, and to measure the transmission on the HOM couplers at low power to ensure the operate as designed, each requiring a special test box. The FPC test box should provide a high transmission between two couplers without creating high surface fields. The low power HOM test boxes should be terminated to a load such that the natural stop and pass-bands of the couplers are preserved allowing the reflection to me measured and compared to simulations. In addition, due to the possibility of high HOM power in the LHC crab cavities, the concept of creating a broadband high power HOM coupler test box in order to condition and test the couplers at high power has been investigated. The Rf design of all test boxes is presented and discussed.

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THPB093

A 1.3 GHz Waveguide to Coax Coupler for Superconducting Cavities With a Minimum Kick

cavity, emittance, niobium, electron

1360

J.A. Robbins, C. Egerer, R.G. Eichhorn, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Transversal forces as a result of asymmetric field generated by the fundamental power couplers have become a concern for low emittance beam in future accelerators. In pushing for smallest emittances, Cornell has finished a physics design for a symmetric coupler for superconducting accelerating cavities. This coupler consists of a rectangular waveguide that transforms into a coaxial line inside the beam pipe, eventually feeding the cavity. We will report on the RF design yielding to the extremely low transversal kick. In addition, heating, heat transfer and thermal stability of this coupler has been evaluated.

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