SRF2013 - List of Keywords (impedance)

Paper	Title	Other Keywords	Page
MOIOC02	A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor	cavity, electron, niobium, superconductivity	63
	B. P. Xiao, C.E. Reece JLab, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: This manuscript has been authored in part by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. There is a need to understand the intrinsic limit of RF surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors, based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and Fermi Lab with carefully prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.
	Slides MOIOC02 [3.122 MB]

MOP022	Preliminary Design of CEPC RF Superconducting System	cavity, HOM, cryogenics, storage-ring	140
	H.J. Zheng, J. Gao, S. Jin, Y. Liu, Z.C. Liu, J.Y. Zhai, T.X. Zhao IHEP, Beijing, People's Republic of China
	In order to study Higgs Boson, scientists proposed to construct a Higgs factory. Chinese scientists are also actively involved in research of the construction of Higgs factory. Construction of a circular collider and several construction solutions were proposed. Electron and positron are eventually accelerated to the center of mass energy 240GeV. RF superconducting acceleration system is indispensable to ensure the normal operation of machine. This article mainly introduces the RF parameters in the design of 700MHz China Higgs Factory (CHF) system. It mainly includes choose of cavity type, couplers and relevant parameters of cryogenic system.

MOP092	Computation of Wakefields and HOM Port Signals by Means of Reduced Order Models	wakefield, cavity, HOM, operation	364
	J. Heller, T. Flisgen, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	The investigation of wakefields is an important task in the design and operation of particle accelerators. Computer simulations are a reliable tool to extend the understanding of these effects. This contribution presents an application example of a new method to compute wakefields as well as parameters derived from those fields, such as higher order mode (HOM) port signals. The method is based on a reduced order model of the structure created by as set of 3D eigenmodes, a set of 2D waveguide port modes and the current density of the beam. In contrast to other wakefield computations, the proposed method operates directly on the reduced order model. Therefore, once having established this model, the beam-excited fields can be determined quickly for different beam parameters. As a matter of fact, only a small part of the reduced system has to be recomputed for every sweep point. From these advantages it is obvious, that the method is highly compatible for beam parameter studies. In a proof of principal the effectiveness of the method compared to established methods of wakefield computations in terms of computational time and accuracy is shown.

TUP011	A Parametric Study of BCS RF Surface Impedance with Magnetic Field Using Xiao Code	niobium, SRF, superconductivity, survey	444
	C.E. Reece JLab, Newport News, Virginia, USA B. P. Xiao JLAB, Newport News, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A recent new analysis of field-dependent BCS RF surface impedance based on moving Cooper pairs has been presented.* Using this analysis coded in Mathematica™, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the “best theoretical” performance available to potential applications with corresponding materials. * Xiao B. P. et al, Physica C: Superconductivity, 490, 2013, pp. 26–31

TUP071	Development of Nb3Sn Cavity Vapor Diffusion Deposition System	niobium, cavity, vacuum, controls	603
	G.V. Eremeev, W.A. Clemens, K. Macha, H. Park, R.S. Williams JLAB, Newport News, Virginia, USA H. Park ODU, Norfolk, Virginia, USA
	Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Alternative BCS superconductors with the superconducting critical temperature higher than that of niobium theoretically surpass the limitations of niobium. The feasibility of technology has been demonstrated at 1.5 GHz with Nb3Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb3Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb3Sn vapor diffusion deposition system within an R&D development program towards compact light sources. Here we present the current progress of the system development.

WEIOB02	Proof of Concept Thin Films and Multilayers Toward Enhanced Field Gradients in SRF Cavities	SRF, shielding, cavity, radio-frequency	782
	R.A. Lukaszew, D. Beringer, W.M. Roach The College of William and Mary, Williamsburg, USA G.V. Eremeev, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA C.E. Reece JLab, Newport News, Virginia, USA X. Xi TU, Philadelphia, USA
	Funding: Defense Threat Reduction Agency (DTRA) Due to the very shallow penetration depth of the RF fields, SRF properties are inherently a surface phenomenon involving a material thickness of less than 1 micron thus opening up the possibility of using thin film coatings to achieve a desired performance. The challenge has been to understand the dependence of the SRF properties on the detailed characteristics of real surfaces and then to employ appropriate techniques to tailor these surface properties for greatest benefit. Our aim is to achieve gradients >100 MV/m and no simple material is known to be capable of sustaining this performance. A theoretical framework has been proposed which could yield such behavior [1] and it requires creation of thin film layered structures. I will present our systematic studies on such proof-of-principle samples. Our overarching goal has been to build a basic understanding of key nano-scale film growth parameters for materials that show promise for SRF cavity multilayer coatings and to demonstrate the ability to elevate the barrier for vortex entry in such layered structures above the bulk value of Hc1 for type-II superconductors and thus to sustain higher accelerating fields. [1]. A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006).
	Slides WEIOB02 [15.612 MB]

THP013	A New Cavity Design for Medium Beta Acceleration	cavity, linac, cryomodule, target	920
	F.S. He, R.A. Rimmer, H. Wang JLAB, Newport News, Virginia, USA
	Funding: Work supported by DOE Heavy duty or CW, superconducting proton and heavy ion accelerators are being proposed and constructed worldwide. The total length of the machine is one of the main drivers in terms of cost. Thus HWR and spoke cavities at medium beta are usually optimized to achieve low surface field and high gradient. A novel accelerating structure at β=0.5 evolved from spoke cavity is proposed, with lower surface fields but slightly higher heat load. It would be an interesting option for pulsed and CW accelerators with beam energy of more than 200MeV/u.

THP036	Design of a 4 Rod Crab Cavity Cryomodule System for HL-LHC	cavity, cryomodule, HOM, luminosity	982
	G. Burt, B.D.S. Hall Cockcroft Institute, Lancaster University, Lancaster, United Kingdom T.J. Jones, N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom P.A. McIntosh, S.M. Pattalwar, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom T.J. Peterson Fermilab, Batavia, USA L.A. Wright CERN, Geneva, Switzerland
	The LHC requires compact SRF crab cavities for the HL-LHC and 3 potential solutions are under consideration. One option is to develop a 4 rod cavity utilising for quarter wave rods to maintain a dipole field. The cavity design has been developed including power and LOM/HOM couplers have been developed, as well as a conceptual design of a complete cryomodule system including ancillaries and this is presented. The cryomodule is designed to allow easy access during testing and uses a novel support system and contains the opposing beamline section to fit inside the LHC envelope.

FRIOA04	Superconducting RF-Dipole Deflecting and Crabbing Cavities	cavity, dipole, HOM, 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

MOIOC02

A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor

cavity, electron, niobium, superconductivity

63

B. P. Xiao, C.E. Reece
JLab, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: This manuscript has been authored in part by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
There is a need to understand the intrinsic limit of RF surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors, based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and Fermi Lab with carefully prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.

Slides MOIOC02 [3.122 MB]

MOP022

Preliminary Design of CEPC RF Superconducting System

cavity, HOM, cryogenics, storage-ring

140

H.J. Zheng, J. Gao, S. Jin, Y. Liu, Z.C. Liu, J.Y. Zhai, T.X. Zhao
IHEP, Beijing, People's Republic of China

In order to study Higgs Boson, scientists proposed to construct a Higgs factory. Chinese scientists are also actively involved in research of the construction of Higgs factory. Construction of a circular collider and several construction solutions were proposed. Electron and positron are eventually accelerated to the center of mass energy 240GeV. RF superconducting acceleration system is indispensable to ensure the normal operation of machine. This article mainly introduces the RF parameters in the design of 700MHz China Higgs Factory (CHF) system. It mainly includes choose of cavity type, couplers and relevant parameters of cryogenic system.

MOP092

Computation of Wakefields and HOM Port Signals by Means of Reduced Order Models

wakefield, cavity, HOM, operation

364

J. Heller, T. Flisgen, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

The investigation of wakefields is an important task in the design and operation of particle accelerators. Computer simulations are a reliable tool to extend the understanding of these effects. This contribution presents an application example of a new method to compute wakefields as well as parameters derived from those fields, such as higher order mode (HOM) port signals. The method is based on a reduced order model of the structure created by as set of 3D eigenmodes, a set of 2D waveguide port modes and the current density of the beam. In contrast to other wakefield computations, the proposed method operates directly on the reduced order model. Therefore, once having established this model, the beam-excited fields can be determined quickly for different beam parameters. As a matter of fact, only a small part of the reduced system has to be recomputed for every sweep point. From these advantages it is obvious, that the method is highly compatible for beam parameter studies. In a proof of principal the effectiveness of the method compared to established methods of wakefield computations in terms of computational time and accuracy is shown.

TUP011

A Parametric Study of BCS RF Surface Impedance with Magnetic Field Using Xiao Code

niobium, SRF, superconductivity, survey

444

C.E. Reece
JLab, Newport News, Virginia, USA
B. P. Xiao
JLAB, Newport News, Virginia, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A recent new analysis of field-dependent BCS RF surface impedance based on moving Cooper pairs has been presented.* Using this analysis coded in Mathematica™, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the “best theoretical” performance available to potential applications with corresponding materials.
* Xiao B. P. et al, Physica C: Superconductivity, 490, 2013, pp. 26–31

TUP071

Development of Nb3Sn Cavity Vapor Diffusion Deposition System

niobium, cavity, vacuum, controls

603

G.V. Eremeev, W.A. Clemens, K. Macha, H. Park, R.S. Williams
JLAB, Newport News, Virginia, USA
H. Park
ODU, Norfolk, Virginia, USA

Funding: Work supported by DOE. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Alternative BCS superconductors with the superconducting critical temperature higher than that of niobium theoretically surpass the limitations of niobium. The feasibility of technology has been demonstrated at 1.5 GHz with Nb3Sn vapor deposition technique at Wuppertal University. The benefit at these frequencies is more pronounced at 4.2 K, where Nb3Sn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of Nb3Sn vapor diffusion deposition system within an R&D development program towards compact light sources. Here we present the current progress of the system development.

WEIOB02

Proof of Concept Thin Films and Multilayers Toward Enhanced Field Gradients in SRF Cavities

SRF, shielding, cavity, radio-frequency

782

R.A. Lukaszew, D. Beringer, W.M. Roach
The College of William and Mary, Williamsburg, USA
G.V. Eremeev, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA
C.E. Reece
JLab, Newport News, Virginia, USA
X. Xi
TU, Philadelphia, USA

Funding: Defense Threat Reduction Agency (DTRA)
Due to the very shallow penetration depth of the RF fields, SRF properties are inherently a surface phenomenon involving a material thickness of less than 1 micron thus opening up the possibility of using thin film coatings to achieve a desired performance. The challenge has been to understand the dependence of the SRF properties on the detailed characteristics of real surfaces and then to employ appropriate techniques to tailor these surface properties for greatest benefit. Our aim is to achieve gradients >100 MV/m and no simple material is known to be capable of sustaining this performance. A theoretical framework has been proposed which could yield such behavior [1] and it requires creation of thin film layered structures. I will present our systematic studies on such proof-of-principle samples. Our overarching goal has been to build a basic understanding of key nano-scale film growth parameters for materials that show promise for SRF cavity multilayer coatings and to demonstrate the ability to elevate the barrier for vortex entry in such layered structures above the bulk value of Hc1 for type-II superconductors and thus to sustain higher accelerating fields.
[1]. A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006).

Slides WEIOB02 [15.612 MB]

THP013

A New Cavity Design for Medium Beta Acceleration

cavity, linac, cryomodule, target

920

F.S. He, R.A. Rimmer, H. Wang
JLAB, Newport News, Virginia, USA

Funding: Work supported by DOE
Heavy duty or CW, superconducting proton and heavy ion accelerators are being proposed and constructed worldwide. The total length of the machine is one of the main drivers in terms of cost. Thus HWR and spoke cavities at medium beta are usually optimized to achieve low surface field and high gradient. A novel accelerating structure at β=0.5 evolved from spoke cavity is proposed, with lower surface fields but slightly higher heat load. It would be an interesting option for pulsed and CW accelerators with beam energy of more than 200MeV/u.

THP036

Design of a 4 Rod Crab Cavity Cryomodule System for HL-LHC

cavity, cryomodule, HOM, luminosity

982

G. Burt, B.D.S. Hall
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
T.J. Jones, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
P.A. McIntosh, S.M. Pattalwar, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T.J. Peterson
Fermilab, Batavia, USA
L.A. Wright
CERN, Geneva, Switzerland

The LHC requires compact SRF crab cavities for the HL-LHC and 3 potential solutions are under consideration. One option is to develop a 4 rod cavity utilising for quarter wave rods to maintain a dipole field. The cavity design has been developed including power and LOM/HOM couplers have been developed, as well as a conceptual design of a complete cryomodule system including ancillaries and this is presented. The cryomodule is designed to allow easy access during testing and uses a novel support system and contains the opposing beamline section to fit inside the LHC envelope.

FRIOA04

Superconducting RF-Dipole Deflecting and Crabbing Cavities

cavity, dipole, HOM, 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]