LINAC2014 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
MOPP013	Vertical Test Results of 704 MHz BNL3 SRF Cavities	cavity, SRF, electron, damping	73
	W. Xu, S.A. Belomestnykh, I. Ben-Zvi, H. Hahn, R. Porgueddu, R. Than, D. Weiss BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA M.D. Cole, D. Holmes, T. Schultheiss AES, Medford, New York, USA
	Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE, and Award No. DE-SC0002496 to Stony Brook University with the U.S. DOE. An electron-ion collider (eRHIC) proposed at BNL requires superconducting RF cavities able to support high average beam current. A 5-cell niobium SRF cavity, called BNL3, was designed for a conventional lattice eRHIC design. To avoid inducing emittance degradation and beam-break-up (BBU), the BNL3 cavity was optimized to damp all dangerous higher-order-modes (HOMs) by employing a large beam pipes and coaxial antenna-type couplers. Additionally, the cavity was designed for an acceptable cryogenic load and peak surface RF fields. Two BNL3 cavities have been fabricated and tested at a vertical test facility at BNL. This paper addresses development of the SRF cavities for eRHIC, including SRF cavity design, fabrication and test results.

MOPP046	On the Design of Higher Order Mode Antenna for LCLS II	cavity, coupling, higher-order-mode, simulation	161
	M.H. Awida, I.V. Gonin, T.N. Khabiboulline, K.S. Premo, O.V. Pronitchev, N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE The upgrade of the Linac Coherent Light Source (LCLS-II) necessitates a major modification to the higher order mode (HOM) antenna of the conventional ILC elliptical 9-cell cavity. Due to the continuous wave nature of the proposed LCLS II Linac, the HOM antenna is required to bare higher RF losses. A modified design of the HOM antenna is presented in this paper ahead with a thorough thermal quench study in comparison with the conventional ILC design.

MOPP052	Development of 5-Cell β=0.9 650 MHz Elliptical Cavities for Project X	cavity, linac, coupling, accelerating-gradient	171
	I.V. Gonin, M.H. Awida, M.H. Foley, A. Grassellino, C.J. Grimm, T.N. Khabiboulline, A. Lunin, A.M. Rowe, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Several 5-cell 650 MHz elliptical cavities have been fabricated for the PIP-II Project. Two versions of the cavities have been designed to accelerate protons of relative group velocity of β=0.9 and β=0.92 in the high energy region of the linac. In this paper, we report the development status of these cavities, summarize the results of the quality control measurements performed on five initial prototypes, and outline the VTS test results.

MOPP054	Continuous-Wave Horizontal Tests of Dressed 1.3 GHz SRF Cavities for LCLS-II	cavity, controls, SRF, linac	177
	A. Hocker, A.C. Crawford, M. Geynisman, J.P. Holzbauer, A. Lunin, D.A. Sergatskov, N. Solyak, A.I. Sukhanov Fermilab, Batavia, Illinois, USA
	Funding: United States Department of Energy, Contract No. DE-AC02-07CH11359 Fermilab’s Horizontal Test Stand has recently been upgraded to provide CW RF testing capabilities in support of the LCLS-II project at SLAC. Several cavities have been tested in this new configuration in order to validate component designs and processes for meeting the requirements of LCLS-II. Areas of study included gradient and Q0 performance and their dependence on extrinsic factors, thermal performance of the input coupler and HOM feedthroughs, and microphonics and RF control. A description of the testing and the results obtained are presented.
	Poster MOPP054 [0.276 MB]

MOPP070	Final Design for the BERLinPro Main Linac Cavity	cavity, linac, emittance, dipole	217
	A. Neumann, J. Knobloch HZB, Berlin, Germany K. Brackebusch, T. Flisgen, T. Galek, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany B. Riemann, T. Weis DELTA, Dortmund, Germany
	Funding: This work is partly funded by BMBF contract no. 05K10PEA and 05K10HRC The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW LINAC technology for 100-mA-class ERLs. High-current operation requires an effective damping of higher-order modes (HOMs) of the 1.3 GHz main-linac cavities. We have studied elliptical 7-cell cavities based on a modified Cornell ERL design combined with JLab's waveguide HOM damping approach. This paper will summarize the final optimization of the end-cell tuning for minimum external Q of the HOMs, coupler kick calculations of the single TTF fundamental power coupler as well as multipole expansion analysis of the given modes and a discussion on operational aspects.
	Poster MOPP070 [1.561 MB]

MOPP071	BESSY VSR 1.5 GHz Cavity Design and Considerations on Waveguide Damping	damping, cavity, SRF, operation	221
	A.V. Velez, J. Knobloch, A. Neumann HZB, Berlin, Germany
	The BESSY VSR upgrade of the BESSY II light source represents a novel approach to simultaneously store long (ca. 15ps) and short (ca. 1.5ps) bunches in the storage ring with the present user optics. To this end, new high-voltage L-Band superconducting multi-cell cavities must be installed in one of the straights of the ring. These 1.5 GHz and 1.75 GHz cavities are based on 1.3 GHz systems being developed for the BERLinPro energy-recovery linac. This paper describes the baseline electromagnetic design of the first 5-cell cavity operating at 1.5 GHz.
	Poster MOPP071 [1.088 MB]

MOPP126	Untrapped HOM Radiation Absorption in the LCLS-II Cryomodules	cryomodule, cavity, impedance, linac	351
	K.L.F. Bane, C. Adolphsen, C.D. Nantista, T.O. Raubenheimer SLAC, Menlo Park, California, USA A. Saini, N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: Work supported by Department of Energy contract DE–AC02–76SF00515. The superconducting cavities in the continuous wave (CW) linacs of LCLS-II are designed to operate at 2 K, where cooling costs are very expensive. One source of heat is presented by the higher order mode (HOM) power deposited by the beam. Due to the very short bunch length-especially in L3 the final linac-the LCLS-II beam spectrum extends into the terahertz range. Ceramic absorbers, at 70 K and located between cryomodules, are meant to absorb much of this power. In this report we perform two kinds of calculations to estimate the effectiveness of the absorbers and the amount of beam power that needs to be removed at 2 K.

MOPP133	Measurements of Cavity Misalignment by Beam Induced HOM Excited in 9-cell Superconducting Cavities	cavity, simulation, dipole, experiment	370
	A. Kuramoto Sokendai, Ibaraki, Japan N. Baboi DESY, Hamburg, Germany H. Hayano KEK, Ibaraki, Japan
	Detection of cavity misalignment in the ILC superconducting cavities inside of the cryomodules can be done by using beam induced Higher Order Modes (HOM). It is beneficial to identify possible source of emittance growth by cavity misalignment. Beam pipe modes which are localized in both ends of the cavity and TE111 1/9 pi mode which is localized in the center of the cavity are focused in this research. Deviations of these electrical centers from beam trajectory reference indicate cavity misalignment and bending. We measured beam-induced HOM in STF cavities of the STF accelerator at KEK in 2012 – 2013 and TESLA cavities of FLASH at DESY in 2013. We could identify beam pipe modes and TE111 1/9 pi mode in STF cavities and TESLA cavities at around 2.1 GHz and 1.6 GHz, both of which were very small signals. The electrical center of these beam pipe mode are studied by stretched wire method, beads perturbation method and simulations by CST MICROWAVE STUDIO 2012 and HFSS 12. In this paper, the results of these measurements and simulations are summarized.

TUPP108	HOM and Impedance Study of RF Separators for LCLS II	cavity, dipole, superconducting-RF, impedance	674
	S.U. De Silva, J.R. Delayen, B.R.P. Gamage, G.A. Krafft, T. Satogata ODU, Norfolk, Virginia, USA R.G. Olave Old Dominion University, Norfolk, Virginia, USA
	The LCLS-II upgrade requires an rf spreader system to guide bunches into a switchyard delivering beam to two undulators and the primary beam dump. The beam pattern therefore needs a 3-way beam spreader. An rf deflecting cavity concept was proposed that includes both superconducting and normal conducting options. We characterize the higher order modes (HOM) of these rf separator cavities and evaluate beam dynamics effects due to potential HOM excitation. This study includes both short term wake and multi-bunch effects.
	Poster TUPP108 [1.032 MB]

TUPP119	Design Studies for Medium and High beta SCRF Cavities for Indian Spallation Neutron Source	cavity, linac, lattice, quadrupole	699
	A.R. Jana, V. Kumar RRCAT, Indore, India
	There is a plan to build a 1 GeV H⁻ linac for the proposed Indian Spallation Neutron Source (ISNS) at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. The medium and high energy section of the ISNS linac will consist of beta_g=0.61, as well as beta_g = 0.9, 650 MHz, 5-cell superconducting radiofrequency (SCRF) cavities, for which detailed electromagnetic design studies have been performed. During our design study, we have evolved a generalized procedure for the optimization of geometrical parameters of multi-cell SCRF cavities. Studies on higher order modes supported by the cavity and its effect on beam dynamics, as well as on heat load to the cavity have been performed, which constitute an important aspect of the design study. Finally, detailed studies on Lorentz Force Detuning (LFD) have been performed, and design of the cavity has been optimized to minimize the effect due to the LFD. The paper discussed the details of the calculations and the studies that have been performed during the design study.

THPP017	Beam-Based HOM Studies of the Cornell Energy Recovery Linac 7-Cell SRF Cavity	cavity, linac, cryomodule, experiment	869
	D.L. Hall, A.C. Bartnik, M.G. Billing, R.G. Eichhorn, G.H. Hoffstaetter, M. Liepe, C.E. Mayes, P. Quigley, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Grant DMR-0807731 The 1.3 GHz 7-cell SRF cavity for the Cornell ERL main linac is optimized for high beam current ERL operation with injected CW beam currents of 100 mA. Beam stability at 100 mA requires very strong damping of the Higher-Order-Modes (HOM) in the cavity by HOM beamline absorbers at the ends of the cavity. To verify the optimized design of the cavity and the HOM damping scheme, a prototype 7-cell main linac cavity was installed into the Cornell Horizontal Test Cryomodule (HTC), and inserted into the beamline of the Cornell ERL high current photo-injector. A beam-based method was then used to search for the presence of dangerous HOMs. Individual HOMs were excited using a charge-modulated beam, after which their effect upon an unmodulated beam was observed using a BPM. Data collected was used to calculate loaded Q of observed HOMs. Results show that it is very unlikely that HOMs will cause BBU in the Cornell ERL. In addition, measurements of the temperature rise of the HOM absorber rings during high current CW beam tests were consistent with simulations, indicating that the optimized main linac cavity is capable of operating at the specified current of 100mA in an ERL configuration.

THPP022	Efficiency of High Order Modes Extraction in the European XFEL Linac	cavity, damping, dipole, linac	883
	A.A. Sulimov, J. Iversen, D. Kostin, W.-D. Möller, D. Reschke, J.K. Sekutowicz, J.H. Thie DESY, Hamburg, Germany D. Karolczyk, K. Kasprzak, S. Myalski, M. Wiencek, A. Zwozniak IFJ-PAN, Kraków, Poland
	The serial production of components for the European XFEL linac was started in 2011 and reached the planned level of 8 cavities (1 module) per week in 2013. The measurements of High Order Modes (HOM) characteristics under cryogenic conditions (2K) are being done at the Accelerating Module Test Facility (AMTF) by the IFJ-PAN Team in collaboration with DESY groups. More than 50 % of the cavities have been already produced and 30 % of the whole amount were measured during either cavity vertical tests or module tests. We present first statistics of these measurements and analyze the efficiency of HOM extraction.
	Poster THPP022 [0.801 MB]

THPP051	Design of a Quasi-Waveguide Multicell Deflecting Cavity for the Advanced Photon Source	cavity, dipole, impedance, damping	966
	A. Lunin, I.V. Gonin, T.N. Khabiboulline, V.P. Yakovlev Fermilab, Batavia, Illinois, USA A. Zholents ANL, Argonne, Ilinois, USA
	This paper reports the electromagnetic design of a 2815 MHz Quasi-waveguide Multicell Resonator (called QMiR) being considered as a transverse RF deflecting cavity for the Advanced Photon Source’s (APS) Short Pulse X-ray project. QMiR forms a trapped dipole mode inside a beam vacuum chamber while High Order Modes (HOM) are heavily loaded. It results a sparse HOM spectrum, makes HOM couplers unnecessary and allows to simplify the cavity mechanical design. The form of electrodes is optimized for producing 2 MV of deflecting voltage and keeping low peak surface electric and magnetic fields of 54 MV/m and 75 mT respectively. Results of detailed EM analysis, including HOM damping at the actual geometry of beam vacuum chamber, will be presented.
	Poster THPP051 [1.250 MB]

THPP054	Study of Coupler's Effect in Third Harmonic Section of LCLS-II SC Linac	cavity, cryomodule, linac, emittance	969
	A. Saini, A. Lunin, N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA T.O. Raubenheimer SLAC, Menlo Park, California, 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 4 GeV superconducting (SC) linac which will use two stage bunch compression scheme in order to achieve short bunches with high peak current. In order to reduce non-linear effects in first bunch compressor, third harmonic section is utilized to linearize longitudinal phase space of the beam. However, transverse phase space of beam may get distorted due to coupler RF kicks and coupler wake kicks resulting from the asymmetry of input and HOM couplers in 3.9 GHz cavity. In this paper, we discuss coupler's effects and estimate resulting emittance dilution in third harmonic section. Local compensation of coupler kicks using different orientation of cavities are also addressed.

THPP060	Effect of Cavity Couplers Field on the Beam Dynamics of the LCLS-II Injector	simulation, cavity, emittance, cryomodule	989
	A. Vivoli, A. Lunin, A. Saini, N. Solyak Fermilab, Batavia, Illinois, USA A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA D. Dowell, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou SLAC, Menlo Park, California, USA D. Filippetto, R. Huang, C. F. Papadopoulos, H.J. Qian, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA
	LCLS-II is a new light source based on a continuous wave (cw) superconducting linac to be built at SLAC. The Injector section of the linac creates the elecron beam and accelerates it up to about 100 MeV. The couplers of the accelerating cavities produce an asymmetric field resulting in a beam offset and, most importantly, in a significant transverse emittance dilution, if not compensated. In this paper we describe the simulations of the LCLS-II injector taking into account the cavity couplers effect and some mitigation techniques to reduce its impact on the beam quality.

THPP069	Status and Outlook of the 325 MHz 4-Rod RFQ	rfq, dipole, simulation, impedance	1010
	B. Koubek, H. Podlech, A. Schempp, J.S. Schmidt IAP, Frankfurt am Main, Germany
	In order to built a Radio Frequency Quadrupole (RFQ) at 325 MHz for the FAIR proton linac, a 4-rod structure has been investigated. The RF design, especially the dipole and fringe fields and higher order modes, has been studied with simulations. A prototype has been built and power tested to verify the simulation results and investigate the high power performance. This paper summarizes the results of the research concerning the 325 MHz 4-rod RFQ and gives an overview about the next steps in this project.

THPP109	History of Cryomodule Repairs at SNS	cryomodule, cavity, operation, linac	1108
	M.P. Howell, M. Doleans, D.L. Douglas, S.-H. Kim ORNL, Oak Ridge, Tennessee, USA R. Afanador, B. DeGraff, B.S. Hannah, C.J. McMahan, T.S. Neustadt, S.W. Ottaway, J. Saunders, P.V. Tyagi, D.M. Vandygriff ORNL RAD, Oak Ridge, Tennessee, USA
	The operation of the Superconducting linear accelerator (SCL) has matured and now averages less than one trip per day. The availability of the SCL including radiofrequency systems, high voltage converter modulators, controls, vacuum and other support systems over the last three years is approximately 98%. The SNS has been in operation for ten years including the commissioning period. In support of achieving the stability of operation, multiple cryomodule repairs have been performed. Repairs to cryomodules have included instruments, helium leaks, valve actuators, cavity tuners, insulating vacuum repairs and upgrades, power supplies, higher order mode (HOM) feedthroughs, coupler windows, and coupler cooling components. Performance degradation has been experienced in multiple cavities. This has been corrected by thermal cycling the cryomodules with the affected cavities. Only two cavities have displayed slight permanent degradation that could not be corrected by thermal cycling. Repairs made to the SNS cryomodule will be detailed in this paper.

Paper

Title

Other Keywords

Page

MOPP013

Vertical Test Results of 704 MHz BNL3 SRF Cavities

cavity, SRF, electron, damping

73

W. Xu, S.A. Belomestnykh, I. Ben-Zvi, H. Hahn, R. Porgueddu, R. Than, D. Weiss
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
M.D. Cole, D. Holmes, T. Schultheiss
AES, Medford, New York, USA

Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE, and Award No. DE-SC0002496 to Stony Brook University with the U.S. DOE.
An electron-ion collider (eRHIC) proposed at BNL requires superconducting RF cavities able to support high average beam current. A 5-cell niobium SRF cavity, called BNL3, was designed for a conventional lattice eRHIC design. To avoid inducing emittance degradation and beam-break-up (BBU), the BNL3 cavity was optimized to damp all dangerous higher-order-modes (HOMs) by employing a large beam pipes and coaxial antenna-type couplers. Additionally, the cavity was designed for an acceptable cryogenic load and peak surface RF fields. Two BNL3 cavities have been fabricated and tested at a vertical test facility at BNL. This paper addresses development of the SRF cavities for eRHIC, including SRF cavity design, fabrication and test results.

MOPP046

On the Design of Higher Order Mode Antenna for LCLS II

cavity, coupling, higher-order-mode, simulation

161

M.H. Awida, I.V. Gonin, T.N. Khabiboulline, K.S. Premo, O.V. Pronitchev, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE
The upgrade of the Linac Coherent Light Source (LCLS-II) necessitates a major modification to the higher order mode (HOM) antenna of the conventional ILC elliptical 9-cell cavity. Due to the continuous wave nature of the proposed LCLS II Linac, the HOM antenna is required to bare higher RF losses. A modified design of the HOM antenna is presented in this paper ahead with a thorough thermal quench study in comparison with the conventional ILC design.

MOPP052

Development of 5-Cell β=0.9 650 MHz Elliptical Cavities for Project X

cavity, linac, coupling, accelerating-gradient

171

I.V. Gonin, M.H. Awida, M.H. Foley, A. Grassellino, C.J. Grimm, T.N. Khabiboulline, A. Lunin, A.M. Rowe, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Several 5-cell 650 MHz elliptical cavities have been fabricated for the PIP-II Project. Two versions of the cavities have been designed to accelerate protons of relative group velocity of β=0.9 and β=0.92 in the high energy region of the linac. In this paper, we report the development status of these cavities, summarize the results of the quality control measurements performed on five initial prototypes, and outline the VTS test results.

MOPP054

Continuous-Wave Horizontal Tests of Dressed 1.3 GHz SRF Cavities for LCLS-II

cavity, controls, SRF, linac

177

A. Hocker, A.C. Crawford, M. Geynisman, J.P. Holzbauer, A. Lunin, D.A. Sergatskov, N. Solyak, A.I. Sukhanov
Fermilab, Batavia, Illinois, USA

Funding: United States Department of Energy, Contract No. DE-AC02-07CH11359
Fermilab’s Horizontal Test Stand has recently been upgraded to provide CW RF testing capabilities in support of the LCLS-II project at SLAC. Several cavities have been tested in this new configuration in order to validate component designs and processes for meeting the requirements of LCLS-II. Areas of study included gradient and Q0 performance and their dependence on extrinsic factors, thermal performance of the input coupler and HOM feedthroughs, and microphonics and RF control. A description of the testing and the results obtained are presented.

Poster MOPP054 [0.276 MB]

MOPP070

Final Design for the BERLinPro Main Linac Cavity

cavity, linac, emittance, dipole

217

A. Neumann, J. Knobloch
HZB, Berlin, Germany
K. Brackebusch, T. Flisgen, T. Galek, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
B. Riemann, T. Weis
DELTA, Dortmund, Germany

Funding: This work is partly funded by BMBF contract no. 05K10PEA and 05K10HRC
The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW LINAC technology for 100-mA-class ERLs. High-current operation requires an effective damping of higher-order modes (HOMs) of the 1.3 GHz main-linac cavities. We have studied elliptical 7-cell cavities based on a modified Cornell ERL design combined with JLab's waveguide HOM damping approach. This paper will summarize the final optimization of the end-cell tuning for minimum external Q of the HOMs, coupler kick calculations of the single TTF fundamental power coupler as well as multipole expansion analysis of the given modes and a discussion on operational aspects.

Poster MOPP070 [1.561 MB]

MOPP071

BESSY VSR 1.5 GHz Cavity Design and Considerations on Waveguide Damping

damping, cavity, SRF, operation

221

A.V. Velez, J. Knobloch, A. Neumann
HZB, Berlin, Germany

The BESSY VSR upgrade of the BESSY II light source represents a novel approach to simultaneously store long (ca. 15ps) and short (ca. 1.5ps) bunches in the storage ring with the present user optics. To this end, new high-voltage L-Band superconducting multi-cell cavities must be installed in one of the straights of the ring. These 1.5 GHz and 1.75 GHz cavities are based on 1.3 GHz systems being developed for the BERLinPro energy-recovery linac. This paper describes the baseline electromagnetic design of the first 5-cell cavity operating at 1.5 GHz.

Poster MOPP071 [1.088 MB]

MOPP126

Untrapped HOM Radiation Absorption in the LCLS-II Cryomodules

cryomodule, cavity, impedance, linac

351

K.L.F. Bane, C. Adolphsen, C.D. Nantista, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
A. Saini, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Work supported by Department of Energy contract DE–AC02–76SF00515.
The superconducting cavities in the continuous wave (CW) linacs of LCLS-II are designed to operate at 2 K, where cooling costs are very expensive. One source of heat is presented by the higher order mode (HOM) power deposited by the beam. Due to the very short bunch length-especially in L3 the final linac-the LCLS-II beam spectrum extends into the terahertz range. Ceramic absorbers, at 70 K and located between cryomodules, are meant to absorb much of this power. In this report we perform two kinds of calculations to estimate the effectiveness of the absorbers and the amount of beam power that needs to be removed at 2 K.

MOPP133

Measurements of Cavity Misalignment by Beam Induced HOM Excited in 9-cell Superconducting Cavities

cavity, simulation, dipole, experiment

370

A. Kuramoto
Sokendai, Ibaraki, Japan
N. Baboi
DESY, Hamburg, Germany
H. Hayano
KEK, Ibaraki, Japan

Detection of cavity misalignment in the ILC superconducting cavities inside of the cryomodules can be done by using beam induced Higher Order Modes (HOM). It is beneficial to identify possible source of emittance growth by cavity misalignment. Beam pipe modes which are localized in both ends of the cavity and TE111 1/9 pi mode which is localized in the center of the cavity are focused in this research. Deviations of these electrical centers from beam trajectory reference indicate cavity misalignment and bending. We measured beam-induced HOM in STF cavities of the STF accelerator at KEK in 2012 – 2013 and TESLA cavities of FLASH at DESY in 2013. We could identify beam pipe modes and TE111 1/9 pi mode in STF cavities and TESLA cavities at around 2.1 GHz and 1.6 GHz, both of which were very small signals. The electrical center of these beam pipe mode are studied by stretched wire method, beads perturbation method and simulations by CST MICROWAVE STUDIO 2012 and HFSS 12. In this paper, the results of these measurements and simulations are summarized.

TUPP108

HOM and Impedance Study of RF Separators for LCLS II

cavity, dipole, superconducting-RF, impedance

674

S.U. De Silva, J.R. Delayen, B.R.P. Gamage, G.A. Krafft, T. Satogata
ODU, Norfolk, Virginia, USA
R.G. Olave
Old Dominion University, Norfolk, Virginia, USA

The LCLS-II upgrade requires an rf spreader system to guide bunches into a switchyard delivering beam to two undulators and the primary beam dump. The beam pattern therefore needs a 3-way beam spreader. An rf deflecting cavity concept was proposed that includes both superconducting and normal conducting options. We characterize the higher order modes (HOM) of these rf separator cavities and evaluate beam dynamics effects due to potential HOM excitation. This study includes both short term wake and multi-bunch effects.

Poster TUPP108 [1.032 MB]

TUPP119

Design Studies for Medium and High beta SCRF Cavities for Indian Spallation Neutron Source

cavity, linac, lattice, quadrupole

699

A.R. Jana, V. Kumar
RRCAT, Indore, India

There is a plan to build a 1 GeV H⁻ linac for the proposed Indian Spallation Neutron Source (ISNS) at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. The medium and high energy section of the ISNS linac will consist of beta_g=0.61, as well as beta_g = 0.9, 650 MHz, 5-cell superconducting radiofrequency (SCRF) cavities, for which detailed electromagnetic design studies have been performed. During our design study, we have evolved a generalized procedure for the optimization of geometrical parameters of multi-cell SCRF cavities. Studies on higher order modes supported by the cavity and its effect on beam dynamics, as well as on heat load to the cavity have been performed, which constitute an important aspect of the design study. Finally, detailed studies on Lorentz Force Detuning (LFD) have been performed, and design of the cavity has been optimized to minimize the effect due to the LFD. The paper discussed the details of the calculations and the studies that have been performed during the design study.

THPP017

Beam-Based HOM Studies of the Cornell Energy Recovery Linac 7-Cell SRF Cavity

cavity, linac, cryomodule, experiment

869

D.L. Hall, A.C. Bartnik, M.G. Billing, R.G. Eichhorn, G.H. Hoffstaetter, M. Liepe, C.E. Mayes, P. Quigley, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF Grant DMR-0807731
The 1.3 GHz 7-cell SRF cavity for the Cornell ERL main linac is optimized for high beam current ERL operation with injected CW beam currents of 100 mA. Beam stability at 100 mA requires very strong damping of the Higher-Order-Modes (HOM) in the cavity by HOM beamline absorbers at the ends of the cavity. To verify the optimized design of the cavity and the HOM damping scheme, a prototype 7-cell main linac cavity was installed into the Cornell Horizontal Test Cryomodule (HTC), and inserted into the beamline of the Cornell ERL high current photo-injector. A beam-based method was then used to search for the presence of dangerous HOMs. Individual HOMs were excited using a charge-modulated beam, after which their effect upon an unmodulated beam was observed using a BPM. Data collected was used to calculate loaded Q of observed HOMs. Results show that it is very unlikely that HOMs will cause BBU in the Cornell ERL. In addition, measurements of the temperature rise of the HOM absorber rings during high current CW beam tests were consistent with simulations, indicating that the optimized main linac cavity is capable of operating at the specified current of 100mA in an ERL configuration.

THPP022

Efficiency of High Order Modes Extraction in the European XFEL Linac

cavity, damping, dipole, linac

883

A.A. Sulimov, J. Iversen, D. Kostin, W.-D. Möller, D. Reschke, J.K. Sekutowicz, J.H. Thie
DESY, Hamburg, Germany
D. Karolczyk, K. Kasprzak, S. Myalski, M. Wiencek, A. Zwozniak
IFJ-PAN, Kraków, Poland

The serial production of components for the European XFEL linac was started in 2011 and reached the planned level of 8 cavities (1 module) per week in 2013. The measurements of High Order Modes (HOM) characteristics under cryogenic conditions (2K) are being done at the Accelerating Module Test Facility (AMTF) by the IFJ-PAN Team in collaboration with DESY groups. More than 50 % of the cavities have been already produced and 30 % of the whole amount were measured during either cavity vertical tests or module tests. We present first statistics of these measurements and analyze the efficiency of HOM extraction.

Poster THPP022 [0.801 MB]

THPP051

Design of a Quasi-Waveguide Multicell Deflecting Cavity for the Advanced Photon Source

cavity, dipole, impedance, damping

966

A. Lunin, I.V. Gonin, T.N. Khabiboulline, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
A. Zholents
ANL, Argonne, Ilinois, USA

This paper reports the electromagnetic design of a 2815 MHz Quasi-waveguide Multicell Resonator (called QMiR) being considered as a transverse RF deflecting cavity for the Advanced Photon Source’s (APS) Short Pulse X-ray project. QMiR forms a trapped dipole mode inside a beam vacuum chamber while High Order Modes (HOM) are heavily loaded. It results a sparse HOM spectrum, makes HOM couplers unnecessary and allows to simplify the cavity mechanical design. The form of electrodes is optimized for producing 2 MV of deflecting voltage and keeping low peak surface electric and magnetic fields of 54 MV/m and 75 mT respectively. Results of detailed EM analysis, including HOM damping at the actual geometry of beam vacuum chamber, will be presented.

Poster THPP051 [1.250 MB]

THPP054

Study of Coupler's Effect in Third Harmonic Section of LCLS-II SC Linac

cavity, cryomodule, linac, emittance

969

A. Saini, A. Lunin, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
T.O. Raubenheimer
SLAC, Menlo Park, California, 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 4 GeV superconducting (SC) linac which will use two stage bunch compression scheme in order to achieve short bunches with high peak current. In order to reduce non-linear effects in first bunch compressor, third harmonic section is utilized to linearize longitudinal phase space of the beam. However, transverse phase space of beam may get distorted due to coupler RF kicks and coupler wake kicks resulting from the asymmetry of input and HOM couplers in 3.9 GHz cavity. In this paper, we discuss coupler's effects and estimate resulting emittance dilution in third harmonic section. Local compensation of coupler kicks using different orientation of cavities are also addressed.

THPP060

Effect of Cavity Couplers Field on the Beam Dynamics of the LCLS-II Injector

simulation, cavity, emittance, cryomodule

989

A. Vivoli, A. Lunin, A. Saini, N. Solyak
Fermilab, Batavia, Illinois, USA
A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
D. Dowell, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou
SLAC, Menlo Park, California, USA
D. Filippetto, R. Huang, C. F. Papadopoulos, H.J. Qian, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA

LCLS-II is a new light source based on a continuous wave (cw) superconducting linac to be built at SLAC. The Injector section of the linac creates the elecron beam and accelerates it up to about 100 MeV. The couplers of the accelerating cavities produce an asymmetric field resulting in a beam offset and, most importantly, in a significant transverse emittance dilution, if not compensated. In this paper we describe the simulations of the LCLS-II injector taking into account the cavity couplers effect and some mitigation techniques to reduce its impact on the beam quality.

THPP069

Status and Outlook of the 325 MHz 4-Rod RFQ

rfq, dipole, simulation, impedance

1010

B. Koubek, H. Podlech, A. Schempp, J.S. Schmidt
IAP, Frankfurt am Main, Germany

In order to built a Radio Frequency Quadrupole (RFQ) at 325 MHz for the FAIR proton linac, a 4-rod structure has been investigated. The RF design, especially the dipole and fringe fields and higher order modes, has been studied with simulations. A prototype has been built and power tested to verify the simulation results and investigate the high power performance. This paper summarizes the results of the research concerning the 325 MHz 4-rod RFQ and gives an overview about the next steps in this project.

THPP109

History of Cryomodule Repairs at SNS

cryomodule, cavity, operation, linac

1108

M.P. Howell, M. Doleans, D.L. Douglas, S.-H. Kim
ORNL, Oak Ridge, Tennessee, USA
R. Afanador, B. DeGraff, B.S. Hannah, C.J. McMahan, T.S. Neustadt, S.W. Ottaway, J. Saunders, P.V. Tyagi, D.M. Vandygriff
ORNL RAD, Oak Ridge, Tennessee, USA

The operation of the Superconducting linear accelerator (SCL) has matured and now averages less than one trip per day. The availability of the SCL including radiofrequency systems, high voltage converter modulators, controls, vacuum and other support systems over the last three years is approximately 98%. The SNS has been in operation for ten years including the commissioning period. In support of achieving the stability of operation, multiple cryomodule repairs have been performed. Repairs to cryomodules have included instruments, helium leaks, valve actuators, cavity tuners, insulating vacuum repairs and upgrades, power supplies, higher order mode (HOM) feedthroughs, coupler windows, and coupler cooling components. Performance degradation has been experienced in multiple cavities. This has been corrected by thermal cycling the cryomodules with the affected cavities. Only two cavities have displayed slight permanent degradation that could not be corrected by thermal cycling. Repairs made to the SNS cryomodule will be detailed in this paper.