IPAC2013 - List of Keywords (higher-order-mode)

Paper	Title	Other Keywords	Page
MOPWO008	Eigenmode Computation for Elliptical Cavities Subject to Geometric Variation using Perturbative Methods	cavity, simulation, factory, SRF	900
	K. Brackebusch, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10H. Parametric studies of geometric variations are an essential part of the performance optimization and error estimation in the design of accelerator cavities. Using common eigenmode solvers the analysis of intentional and undesired geometric perturbations tend to be very extensive since any geometric variation involves an entire eigenmode recomputation. Perturbative methods constitute an efficient alternative for the computation of a multitude of moderately varying geometries. They require a common eigenmode computation of solely one (so called unperturbed) geometry and allow for deriving the eigenmodes of similar but modified (so called perturbed) geometries from these unperturbed eigenmodes. In [],[] the practicability of perturbative methods was already proven by means of simple cavity geometries. In this paper we investigate the applicability and efficiency for practically relevant cavities. For this, basic geometric parameters of elliptical cavities are varied and the respective eigenmodes are computed by using perturbative as well as common methods. The accuracy of the results and the computational effort of the different methods are compared. K. Brackebusch, H.-W. Glock, U. van Rienen, WEPPC096, IPAC 2011 **K. Brackebusch, U. van Rienen, MOPPC062, IPAC 2012

WEPWO047	A Double Quarter-Wave Deflecting Cavity for the LHC	cavity, HOM, multipole, simulation	2408
	R. Calaga CERN, Geneva, Switzerland S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: The HiLumi LHC Design Study (a sub-system of HL-LHC) is cofunded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404 An asymmetric quarter wave deflecting cavity at 400 MHz for crab crossing in the LHC was already proposed in 2011. Due to improved cancellation of on-axis longitudinal field and the higher order components of the deflecting field, a symmetric version is now considered as the baseline for the quarter wave geometry. Relevant RF properties of the symmetric cavity are compared to the original asymmetric cavity. Some aspects of input coupler design, higher order modes, multipacting and frequency tuning are also addressed.

WEPWO068	Cornell ERL Main Linac 7-cell Cavity Performance in Horizontal Test Cryomodule Qualifications	cavity, linac, cryomodule, HOM	2459
	N.R.A. Valles, R. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Funding: NSF DMR-0807731 Cornell has recently ﬁnished producing and testing the ﬁrst prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac, and completed the prototype cavity qualification program. This paper presents quality factor results from the horizontal test cryomodule (HTC) measurements, from the HTC-1 through HTC-3 experiments, reaching Q's up to 6 x 10¹⁰ at 1.6 K. We investigate the effect of thermal cycling on cavity quality factor and show that high quality factors can be preserved from initial mounting to fully outfitting the cavity with side-mounted input coupler and beam line absorbers. We also discuss the production of six additional main-linac cavities as we progress toward constructing a full 6-cavity cryomodule.

WEPWO069	HOM Studies of the Cornell ERL Main Linac Cavity: HTC-1 Through HTC-3	HOM, cavity, cryomodule, linac	2462
	N.R.A. Valles, R. Eichhorn, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF grant DMR-0807731 The Cornell energy recovery linac is designed to run a high energy (5 GeV), high current (100 mA), very low emittance beam (30 pm at 77 pC bunch charge). A major challenge to running such a large current continuously through the machine is the effect of strong higher-order modes(HOMs) that can lead to beam breakup. This paper presents the results of HOM studies for the prototype 7-cell cavity installed in a horizontal test cryomodule (HTC) from initial RF test, to being fully outfitted with side-mounted input coupler and beam line absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments.

WEPWO079	Superconducting Single-spoke Cavities for High-velocity Applications	cavity, multipole, electron, linac	2480
	C.S. Hopper, J.R. Delayen, R.G. Olave ODU, Norfolk, Virginia, USA
	Spoke cavities have been investigated for particle acceleration in the high-velocity regime. As part of these efforts, single-spoke cavities for particles traveling at the speed of light are being designed and built for proof-of-principle demonstration. We report here on the results of electromagnetic properties, design optimization, multipacting analysis, field non-linearities and higher order mode spectrum for a single-spoke cavity operating at 325 MHz.

WEPWO080	Compact Superconducting RF-dipole Cavity Designs for Deflecting and Crabbing Applications	dipole, cavity, multipole, HOM	2483
	S.U. De Silva, A. Castilla, J.R. Delayen ODU, Norfolk, Virginia, USA A. Castilla DCI-UG, León, Mexico
	Over the years the superconducting parallel-bar design has evolved into an rf-dipole cavity with improved properties. The new rf-dipole design is considered for number of deflecting and crabbing applications. Some of those applications are the 499 MHz rf separator system for the Jefferson Lab 12 GeV upgrade, 400 MHz crabbing cavity system for the proposed LHC high luminosity upgrade, and 750 MHz crabbing cavity for the medium energy electron-ion collider in Jefferson Lab. In this paper we present the optimized rf design in terms of rf performance including rf properties, higher order mode properties, multipacting, multipole expansion for the above mentioned applications.

WEPWO086	Split Higher Order Modes in Superconducting Cavities	resonance, cavity, dipole, HOM	2495
	H. Hahn, S.A. Belomestnykh, W. Xu BNL, Upton, Long Island, New York, USA
	Funding: This work was 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 US DOE. Split resonances are a common appearance in superconducting cavities and were studied here on the specific example of the TE11 dipole resonance in five-cell copper models of the ERL and BNL3. The BNL3 cavity was designed to be suitable for the envisioned electron-hadron collider eRHIC. Achieving the required high-current performance depends on avoiding beam break-up instabilities by minimizing the Higher Order Modes (HOM) Q-values. This was attempted in the design phase and will be done with appropriate mode dampers in operation. The availability of a copper model provided a convenient opportunity to confirm the design and to study potentially nefarious high-Q resonances. The appearance of split resonances impeded the HOM identification and the theoretical interpretation as elipticity deformation is presented in this report.

THPFI090	Accuracy of Measurements of ε and μ of Lossy Materials	HOM, simulation, insertion, damping	3499
	V.D. Shemelin, J.J. Kaufman CLASSE, Ithaca, New York, USA
	Funding: NSF award DMR-0807731 Measurements of samples of lossy ceramic and ferrites for Higher Order Mode Loads are performed routinely in our Lab. Some difference of results for different batches of materials can be explained not only by technological deviations in the material production but also by errors in the dimensions of the measured samples. Simulations with MicroWave Studio for samples in the form of coaxial washers in the frequency range from 1 to 12.4 GHz helped to define the main sources of errors and to improve accuracy of measurements.

Paper

Title

Other Keywords

Page

MOPWO008

Eigenmode Computation for Elliptical Cavities Subject to Geometric Variation using Perturbative Methods

cavity, simulation, factory, SRF

900

K. Brackebusch, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10H.
Parametric studies of geometric variations are an essential part of the performance optimization and error estimation in the design of accelerator cavities. Using common eigenmode solvers the analysis of intentional and undesired geometric perturbations tend to be very extensive since any geometric variation involves an entire eigenmode recomputation. Perturbative methods constitute an efficient alternative for the computation of a multitude of moderately varying geometries. They require a common eigenmode computation of solely one (so called unperturbed) geometry and allow for deriving the eigenmodes of similar but modified (so called perturbed) geometries from these unperturbed eigenmodes. In [*],[**] the practicability of perturbative methods was already proven by means of simple cavity geometries. In this paper we investigate the applicability and efficiency for practically relevant cavities. For this, basic geometric parameters of elliptical cavities are varied and the respective eigenmodes are computed by using perturbative as well as common methods. The accuracy of the results and the computational effort of the different methods are compared.
*K. Brackebusch, H.-W. Glock, U. van Rienen, WEPPC096, IPAC 2011
**K. Brackebusch, U. van Rienen, MOPPC062, IPAC 2012

WEPWO047

A Double Quarter-Wave Deflecting Cavity for the LHC

cavity, HOM, multipole, simulation

2408

R. Calaga
CERN, Geneva, Switzerland
S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: The HiLumi LHC Design Study (a sub-system of HL-LHC) is cofunded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404
An asymmetric quarter wave deflecting cavity at 400 MHz for crab crossing in the LHC was already proposed in 2011. Due to improved cancellation of on-axis longitudinal field and the higher order components of the deflecting field, a symmetric version is now considered as the baseline for the quarter wave geometry. Relevant RF properties of the symmetric cavity are compared to the original asymmetric cavity. Some aspects of input coupler design, higher order modes, multipacting and frequency tuning are also addressed.

WEPWO068

Cornell ERL Main Linac 7-cell Cavity Performance in Horizontal Test Cryomodule Qualifications

cavity, linac, cryomodule, HOM

2459

N.R.A. Valles, R. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
CLASSE, Ithaca, New York, USA

Funding: NSF DMR-0807731
Cornell has recently ﬁnished producing and testing the ﬁrst prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac, and completed the prototype cavity qualification program. This paper presents quality factor results from the horizontal test cryomodule (HTC) measurements, from the HTC-1 through HTC-3 experiments, reaching Q's up to 6 x 10¹⁰ at 1.6 K. We investigate the effect of thermal cycling on cavity quality factor and show that high quality factors can be preserved from initial mounting to fully outfitting the cavity with side-mounted input coupler and beam line absorbers. We also discuss the production of six additional main-linac cavities as we progress toward constructing a full 6-cavity cryomodule.

WEPWO069

HOM Studies of the Cornell ERL Main Linac Cavity: HTC-1 Through HTC-3

HOM, cavity, cryomodule, linac

2462

N.R.A. Valles, R. Eichhorn, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF grant DMR-0807731
The Cornell energy recovery linac is designed to run a high energy (5 GeV), high current (100 mA), very low emittance beam (30 pm at 77 pC bunch charge). A major challenge to running such a large current continuously through the machine is the effect of strong higher-order modes(HOMs) that can lead to beam breakup. This paper presents the results of HOM studies for the prototype 7-cell cavity installed in a horizontal test cryomodule (HTC) from initial RF test, to being fully outfitted with side-mounted input coupler and beam line absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments.

WEPWO079

Superconducting Single-spoke Cavities for High-velocity Applications

cavity, multipole, electron, linac

2480

C.S. Hopper, J.R. Delayen, R.G. Olave
ODU, Norfolk, Virginia, USA

Spoke cavities have been investigated for particle acceleration in the high-velocity regime. As part of these efforts, single-spoke cavities for particles traveling at the speed of light are being designed and built for proof-of-principle demonstration. We report here on the results of electromagnetic properties, design optimization, multipacting analysis, field non-linearities and higher order mode spectrum for a single-spoke cavity operating at 325 MHz.

WEPWO080

Compact Superconducting RF-dipole Cavity Designs for Deflecting and Crabbing Applications

dipole, cavity, multipole, HOM

2483

S.U. De Silva, A. Castilla, J.R. Delayen
ODU, Norfolk, Virginia, USA
A. Castilla
DCI-UG, León, Mexico

Over the years the superconducting parallel-bar design has evolved into an rf-dipole cavity with improved properties. The new rf-dipole design is considered for number of deflecting and crabbing applications. Some of those applications are the 499 MHz rf separator system for the Jefferson Lab 12 GeV upgrade, 400 MHz crabbing cavity system for the proposed LHC high luminosity upgrade, and 750 MHz crabbing cavity for the medium energy electron-ion collider in Jefferson Lab. In this paper we present the optimized rf design in terms of rf performance including rf properties, higher order mode properties, multipacting, multipole expansion for the above mentioned applications.

WEPWO086

Split Higher Order Modes in Superconducting Cavities

resonance, cavity, dipole, HOM

2495

H. Hahn, S.A. Belomestnykh, W. Xu
BNL, Upton, Long Island, New York, USA

Funding: This work was 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 US DOE.
Split resonances are a common appearance in superconducting cavities and were studied here on the specific example of the TE11 dipole resonance in five-cell copper models of the ERL and BNL3. The BNL3 cavity was designed to be suitable for the envisioned electron-hadron collider eRHIC. Achieving the required high-current performance depends on avoiding beam break-up instabilities by minimizing the Higher Order Modes (HOM) Q-values. This was attempted in the design phase and will be done with appropriate mode dampers in operation. The availability of a copper model provided a convenient opportunity to confirm the design and to study potentially nefarious high-Q resonances. The appearance of split resonances impeded the HOM identification and the theoretical interpretation as elipticity deformation is presented in this report.

THPFI090

Accuracy of Measurements of ε and μ of Lossy Materials

HOM, simulation, insertion, damping

3499

V.D. Shemelin, J.J. Kaufman
CLASSE, Ithaca, New York, USA

Funding: NSF award DMR-0807731
Measurements of samples of lossy ceramic and ferrites for Higher Order Mode Loads are performed routinely in our Lab. Some difference of results for different batches of materials can be explained not only by technological deviations in the material production but also by errors in the dimensions of the measured samples. Simulations with MicroWave Studio for samples in the form of coaxial washers in the frequency range from 1 to 12.4 GHz helped to define the main sources of errors and to improve accuracy of measurements.