SRF2013 - List of Keywords (dipole)

Paper	Title	Other Keywords	Page
THP020	Measuring the Higher Order Mode Spectrum of the TRIUMF 9-cell Cavity	cavity, HOM, TRIUMF, simulation	936
	P. Kolb, B. Amini, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	The ARIEL eLINAC consists of five nine cell cavities, produced by PAVAC, and will accelerate 10 mA electrons to 50 MeV. This 500 kW beam will be used for rare isotope production. Future upgrade plans include a recirculating beam line. Recirculating the beam, for either energy doubling or energy recovery to drive a FEL, brings the risk of multi-pass beam break up (BBU). Therefore it is necessary to avoid higher order modes (HOMs) with high shunt impedance. The goal of the cavity design is to reduce the highest shunt impedance of any dipole HOM to 1 *10⁶Ω or less. Measurements on the nine cell cavity with bead pulling have been done to identify dipole modes and their geometric shunt impedance R/Q as well as measurements at 2 K to estimate the quality factor of those HOMs. Results of these measurements will be shown and compared to computer simulations done with ACE3P.

THP048	The Influence of Tuners and Temperature on the Higher Order Mode Spectrum for 1.3 GHz SCRF Cavities	cavity, HOM, quadrupole, higher-order-mode	1016
	R. Ainsworth Royal Holloway, University of London, Surrey, United Kingdom N. Baboi, M.K. Grecki, T. Wamsat DESY, Hamburg, Germany N. Eddy Fermilab, Batavia, USA S. Molloy ESS, Lund, Sweden P. Zhang CERN, Geneva, Switzerland
	Higher Order Modes are of concern for superconducting cavities as they can drive instabilities and so are usually damped and monitored. With special dedicated electronics, HOMs can provide information on the position on the beam. It has been proposed that piezo tuners used to keep the cavities operating at 1.3 GHz could alter the HOM spectrum altering the calibration constants used to read out the beam position affecting long term stability of the system. Also, of interest is how the cavity reacts to the slow tuner. Detuning and the retuning the cavity may alter the HOM spectrum. This is of particular interest for future machines not planning to use dedicated HOM damping as the tuning procedure may shift the frequency of HOMs onto dangerous resonances. The effect of temperature on the HOM spectrum is also investigated. An investigation of these effects has been performed at FLASH and the results are presented including numerical simulations used to predict the resulting cavity distortion.

THP059	HOM Coupler Design Adjustment for CW operation of the 1.3 GHz 9-cell TESLA Type SRF Cavity	HOM, cavity, operation, simulation	1051
	D. Kostin, W.-D. Möller, J.K. Sekutowicz DESY, Hamburg, Germany
	One of the key features of a modern research facility is its versatility, ability to adjust for a multitude of the applications and user needs. A challenge for the coming European XFEL is to become a multipurpose laboratory with a broad applications spectrum. Primarily, the XFEL is a pulsed machine. Encompassing the CW mode would be a worthy addition. CW operation of the 1.3GHz 9-cell TESLA Type SRF Cavity was performed several times at DESY and other Labs successfully. One of the difficulties was a heat load of the High Order Mode (HOM) couplers. To amend this HOM coupler design adjustement is proposed, simulated and modelled. Results are presented and discussed.

THP064	HOM Couplers for CERN SPL Cavities	HOM, coupling, cavity, linac	1066
	K. Papke, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Gerigk CERN, Geneva, Switzerland
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.

THP070	Analysis of High Order Modes in 1.3 GHz CW SRF Electron Linac for a Light Source	HOM, cavity, linac, emittance	1085
	A.I. Sukhanov, A. Vostrikov, V.P. Yakovlev Fermilab, Batavia, USA
	Design of a Light Source (LS) based on the continuous wave superconducting RF (CW SRF) electron linac is currently underway. This facility will provide soft coherent X-ray radiation for a broad spectrum of basic research applications. Quality of the X-ray laser radiation is affected by the electron beam parameters such as the stability of the transverse beam position and longitudinal and transverse beam emittances. High order modes (HOMs) excited in the SRF structures by a passing beam may deteriorate the beam quality and affect the beam stability. Deposition of HOM energy in the walls of SRF cavities adds to the heat load of the cryogenic system and leads to the increased cost of building and operation of the linac. In this paper we evaluate effects of HOMs in an LS CW SRF linac based on Tesla-type 9-cell 1.3 GHz cavities. We analyze non-coherent losses and resonance excitation of HOMs. We estimate heat load due to the very high frequency HOMs. We study influence of the HOMs on the transverse beam dynamics.

THP094	Beam Induced HOM Analysis in STF	HOM, cavity, alignment, cryomodule	1144
	A. Kuramoto Sokendai, Ibaraki, Japan H. Hayano KEK, Ibaraki, Japan
	Requirements of superconducting cavity (SC) alignment for ILC are less than 300 μm offset and 300 μrad tilt with respect to cryomodule. It is necessary to measure their offset and tilt inside of cryomodule. Cavity offset has been already measured by using beam induced HOM at FLASH in DESY. Cavity deformation during assembly and by cooling contraction has not been examined yet. To detect their tilt and bending, we measured HOM signals with beam trajectory sweep. Our interesting modes are pi over nine mode in the first dipole passband (TE111-1) which is trapped mode has maximum radial electric field in the middle cell and beam pipe modes localized in the both end-group of the SC. These modes tell us electrical center of middle cell and electrical centers at both beam pipe. We can know cavity tilt and bending from combinations of them. The experiment to find these HOM was performed at STF accelerator. Electron beam extracted from the RF Gun was accelerated to 40 MeV by the SC cavities. We could find TE111-1 and beam pipe modes. These HOM signals were correlated with beam orbit, accelerating field gradient. The detailed data analysis is introduced in this paper.

THP097	Use of Waveguide Probes as Beam position and Tilt Monitoring Diagnostics with Baseline and Alternative Superconducting Deflecting Cavities for the APS Upgrade	cavity, monitoring, diagnostics, HOM	1155
	X. Sun, G. Decker, G. Wu ANL, Argonne, USA
	Funding: *Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC-02-06CH11357. A set of superconducting deflecting cavities were studied for the APS Upgrade. A TM-mode baseline deflecting cavity design has been developed and prototyped, while an alternative design based on a TE-like mode is being studied. Waveguide field probes associated with the baseline and alternative superconducting deflecting cavities are explored as beam position and tilt monitoring diagnostics. Microwave Studio was used to simulate the technique of detecting the fields excited by a Gaussian bunch passing through the cavities to determine beam position relative to the electrical center. Probes installed on the horizontal midplane in the beam pipe are promising diagnostics for monitoring beam position and tilt in both designs. The probes in the power coupler also work as beam position monitors for the alternative deflecting cavities.

FRIOA01	LHC Crab Cavity .Progress and Outlook	cavity, luminosity, cryomodule, operation	1161
	R. Calaga, E. Jensen CERN, Geneva, Switzerland
	Three novel superconducting RF crab cavity designs proposed for the LHC luminosity upgrade have rapidly progressed. First Niobium prototypes are reaching close to the design performance and beyond. The highlights of the RF test results from the prototypes along with design modifications for initial beam tests in the SPS are presented. The status of the cryomodule development, integration into the SPS and the beam tests in view of validating the crab cavity system for LHC upgrade are addressed.
	Slides FRIOA01 [12.063 MB]

FRIOA04	Superconducting RF-Dipole Deflecting and Crabbing Cavities	cavity, HOM, impedance, luminosity	1176
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA
	Recent interests in designing compact deflecting and crabbing structures for future accelerators and colliders have initiated the development of novel rf structures. The superconducting rf-dipole cavity is one of the first compact designs with attractive properties such as higher gradients, higher shunt impedance, the absence of lower order modes and widely separated higher order modes. Two rf-dipole designs of 400 MHz and 499 MHz have been designed, fabricated and tested as proof-of-principle designs of compact deflecting and crabbing cavities for the LHC high luminosity upgrade and Jefferson Lab 12 GeV upgrade. The first rf tests have been performed on the rf-dipole geometries at 4.2 K and 2.0 K in a vertical test assembly with excellent results. The cavities have achieved high gradients with high intrinsic quality factors, and multipacting levels were easily processed.
	Slides FRIOA04 [6.218 MB]

Paper

Title

Other Keywords

Page

THP020

Measuring the Higher Order Mode Spectrum of the TRIUMF 9-cell Cavity

cavity, HOM, TRIUMF, simulation

936

P. Kolb, B. Amini, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

The ARIEL eLINAC consists of five nine cell cavities, produced by PAVAC, and will accelerate 10 mA electrons to 50 MeV. This 500 kW beam will be used for rare isotope production. Future upgrade plans include a recirculating beam line. Recirculating the beam, for either energy doubling or energy recovery to drive a FEL, brings the risk of multi-pass beam break up (BBU). Therefore it is necessary to avoid higher order modes (HOMs) with high shunt impedance. The goal of the cavity design is to reduce the highest shunt impedance of any dipole HOM to 1 *10⁶Ω or less. Measurements on the nine cell cavity with bead pulling have been done to identify dipole modes and their geometric shunt impedance R/Q as well as measurements at 2 K to estimate the quality factor of those HOMs. Results of these measurements will be shown and compared to computer simulations done with ACE3P.

THP048

The Influence of Tuners and Temperature on the Higher Order Mode Spectrum for 1.3 GHz SCRF Cavities

cavity, HOM, quadrupole, higher-order-mode

1016

R. Ainsworth
Royal Holloway, University of London, Surrey, United Kingdom
N. Baboi, M.K. Grecki, T. Wamsat
DESY, Hamburg, Germany
N. Eddy
Fermilab, Batavia, USA
S. Molloy
ESS, Lund, Sweden
P. Zhang
CERN, Geneva, Switzerland

Higher Order Modes are of concern for superconducting cavities as they can drive instabilities and so are usually damped and monitored. With special dedicated electronics, HOMs can provide information on the position on the beam. It has been proposed that piezo tuners used to keep the cavities operating at 1.3 GHz could alter the HOM spectrum altering the calibration constants used to read out the beam position affecting long term stability of the system. Also, of interest is how the cavity reacts to the slow tuner. Detuning and the retuning the cavity may alter the HOM spectrum. This is of particular interest for future machines not planning to use dedicated HOM damping as the tuning procedure may shift the frequency of HOMs onto dangerous resonances. The effect of temperature on the HOM spectrum is also investigated. An investigation of these effects has been performed at FLASH and the results are presented including numerical simulations used to predict the resulting cavity distortion.

THP059

HOM Coupler Design Adjustment for CW operation of the 1.3 GHz 9-cell TESLA Type SRF Cavity

HOM, cavity, operation, simulation

1051

D. Kostin, W.-D. Möller, J.K. Sekutowicz
DESY, Hamburg, Germany

One of the key features of a modern research facility is its versatility, ability to adjust for a multitude of the applications and user needs. A challenge for the coming European XFEL is to become a multipurpose laboratory with a broad applications spectrum. Primarily, the XFEL is a pulsed machine. Encompassing the CW mode would be a worthy addition. CW operation of the 1.3GHz 9-cell TESLA Type SRF Cavity was performed several times at DESY and other Labs successfully. One of the difficulties was a heat load of the High Order Mode (HOM) couplers. To amend this HOM coupler design adjustement is proposed, simulated and modelled. Results are presented and discussed.

THP064

HOM Couplers for CERN SPL Cavities

HOM, coupling, cavity, linac

1066

K. Papke, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
F. Gerigk
CERN, Geneva, Switzerland

Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.

THP070

Analysis of High Order Modes in 1.3 GHz CW SRF Electron Linac for a Light Source

HOM, cavity, linac, emittance

1085

A.I. Sukhanov, A. Vostrikov, V.P. Yakovlev
Fermilab, Batavia, USA

Design of a Light Source (LS) based on the continuous wave superconducting RF (CW SRF) electron linac is currently underway. This facility will provide soft coherent X-ray radiation for a broad spectrum of basic research applications. Quality of the X-ray laser radiation is affected by the electron beam parameters such as the stability of the transverse beam position and longitudinal and transverse beam emittances. High order modes (HOMs) excited in the SRF structures by a passing beam may deteriorate the beam quality and affect the beam stability. Deposition of HOM energy in the walls of SRF cavities adds to the heat load of the cryogenic system and leads to the increased cost of building and operation of the linac. In this paper we evaluate effects of HOMs in an LS CW SRF linac based on Tesla-type 9-cell 1.3 GHz cavities. We analyze non-coherent losses and resonance excitation of HOMs. We estimate heat load due to the very high frequency HOMs. We study influence of the HOMs on the transverse beam dynamics.

THP094

Beam Induced HOM Analysis in STF

HOM, cavity, alignment, cryomodule

1144

A. Kuramoto
Sokendai, Ibaraki, Japan
H. Hayano
KEK, Ibaraki, Japan

Requirements of superconducting cavity (SC) alignment for ILC are less than 300 μm offset and 300 μrad tilt with respect to cryomodule. It is necessary to measure their offset and tilt inside of cryomodule. Cavity offset has been already measured by using beam induced HOM at FLASH in DESY. Cavity deformation during assembly and by cooling contraction has not been examined yet. To detect their tilt and bending, we measured HOM signals with beam trajectory sweep. Our interesting modes are pi over nine mode in the first dipole passband (TE111-1) which is trapped mode has maximum radial electric field in the middle cell and beam pipe modes localized in the both end-group of the SC. These modes tell us electrical center of middle cell and electrical centers at both beam pipe. We can know cavity tilt and bending from combinations of them. The experiment to find these HOM was performed at STF accelerator. Electron beam extracted from the RF Gun was accelerated to 40 MeV by the SC cavities. We could find TE111-1 and beam pipe modes. These HOM signals were correlated with beam orbit, accelerating field gradient. The detailed data analysis is introduced in this paper.

THP097

Use of Waveguide Probes as Beam position and Tilt Monitoring Diagnostics with Baseline and Alternative Superconducting Deflecting Cavities for the APS Upgrade

cavity, monitoring, diagnostics, HOM

1155

X. Sun, G. Decker, G. Wu
ANL, Argonne, USA

Funding: *Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC-02-06CH11357.
A set of superconducting deflecting cavities were studied for the APS Upgrade. A TM-mode baseline deflecting cavity design has been developed and prototyped, while an alternative design based on a TE-like mode is being studied. Waveguide field probes associated with the baseline and alternative superconducting deflecting cavities are explored as beam position and tilt monitoring diagnostics. Microwave Studio was used to simulate the technique of detecting the fields excited by a Gaussian bunch passing through the cavities to determine beam position relative to the electrical center. Probes installed on the horizontal midplane in the beam pipe are promising diagnostics for monitoring beam position and tilt in both designs. The probes in the power coupler also work as beam position monitors for the alternative deflecting cavities.

FRIOA01

LHC Crab Cavity .Progress and Outlook

cavity, luminosity, cryomodule, operation

1161

R. Calaga, E. Jensen
CERN, Geneva, Switzerland

Three novel superconducting RF crab cavity designs proposed for the LHC luminosity upgrade have rapidly progressed. First Niobium prototypes are reaching close to the design performance and beyond. The highlights of the RF test results from the prototypes along with design modifications for initial beam tests in the SPS are presented. The status of the cryomodule development, integration into the SPS and the beam tests in view of validating the crab cavity system for LHC upgrade are addressed.

Slides FRIOA01 [12.063 MB]

FRIOA04

Superconducting RF-Dipole Deflecting and Crabbing Cavities

cavity, HOM, impedance, luminosity

1176

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

Recent interests in designing compact deflecting and crabbing structures for future accelerators and colliders have initiated the development of novel rf structures. The superconducting rf-dipole cavity is one of the first compact designs with attractive properties such as higher gradients, higher shunt impedance, the absence of lower order modes and widely separated higher order modes. Two rf-dipole designs of 400 MHz and 499 MHz have been designed, fabricated and tested as proof-of-principle designs of compact deflecting and crabbing cavities for the LHC high luminosity upgrade and Jefferson Lab 12 GeV upgrade. The first rf tests have been performed on the rf-dipole geometries at 4.2 K and 2.0 K in a vertical test assembly with excellent results. The cavities have achieved high gradients with high intrinsic quality factors, and multipacting levels were easily processed.

Slides FRIOA04 [6.218 MB]