PAC2013 - List of Authors (Liepe, M.)

Paper

Title

Page

SRF Cavities Beyond Niobium: Challenges and Potential

754

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

After many years of development, current preparation methods for niobium SRF cavities regularly achieve performance levels very close to the fundamental limitations of the material. Continued progress requires looking to alternative superconductors, but fabricating a high quality RF surface from these materials has proven uniquely challenging. In this talk, I will discuss the worldwide progress towards fabricating SRF cavity surfaces with alternative materials such as Nb3Sn, NbN, and MgB2. I will also discuss thin films and multilayer films of alternative materials, proposed as an alternative to bulk superconductors. I will present an improved theoretical understanding of the potential of such films. I will discuss new results and make suggestions for future directions beyond niobium.

Slides WEZBA1 [4.418 MB]

WEPAC11

Cornell's Main Linac Cryo-module Prototype

811

R.G. Eichhorn, G.M. Ge, Y. He, G.H. Hoffstaetter, M. Liepe, T. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731
In preparation to built an energy-recovery linac (ERL) based synchrotron-light facility at Cornell University which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac, a phase 1 R&D program was launched, adressing critical challenges in the design. One of them being a full linac cryo-module, housing 6 superconducting cavities (operated at 1.8 K in cw mode), 7 HOM absorbers and 1 magnet/ BPM section. The final design will be presented and a report on the fabrication status that started in late 2012 will be given

WEPAC12

Theoretical Description of SIS Multilayer Films for SRF Cavities

814

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
G. Catelani
Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany
J.P. Sethna
Cornell University, Ithaca, New York, USA
M.K. Transtrum
M.D.A.C.C., Houston, Texas, USA

As surface magnetic fields in niobium superconducting RF (SRF) cavities prepared with modern techniques approach the fundamental limit of niobium’s superheating field, SRF researchers are looking to alternative superconductors to sustain even higher fields. However, the short coherence length of these superconductors may represent a critical vulnerability to vortex penetration at very small defects in the surface. A. Gurevich has proposed* a method of defeating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the accelerator community, to help researchers to optimize cavities made from alternative superconductors.
* A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)

THOBA2

First Cavity Results from the Cornell SRF Group's Nb3Sn Program

1091

S. Posen, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

As an alternative material for SRF accelerator cavities, Nb3Sn presents two important benefits. Its large Tc gives it a very small surface resistance, leading to a huge reduction in cooling costs; and its predicted Hsh of nearly 400 mT would allow for very high gradients and therefore fewer cavities in high energy linacs. Researchers in the Cornell SRF group have recently fabricated two 1.3 GHz cavities coated with Nb3Sn. Testing of these first cavities has produced encouraging results, including a very high Tc and some very high performing regions. These cavity results as well as new sample results under TEM will be presented.

Slides THOBA2 [4.880 MB]

THPMA07

Cryomodule Performance of the Main Linac Prototype Cavity for Cornell's Energy Recovery Linac

1367

N.R.A. Valles, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, D.L. Hall, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF Grants: NSF DMR-0807731 and NSF PHY-1002467
Energy Recovery Linacs (ERLs) require strong damping of higher-order modes in main linac cavities to avoid beam loss from beam break-up effects. In addition, the cavities need to have very high intrinsic quality factors to minimize the size of cryogenic plants in CW cavity operation. We present world record results for a fully equipped multicell cavity in a cryomodule, reaching intrinsic quality factors at operating accelerating field of Q₀(E =16.2 MV/m, 1.8~K) > 6.0\ee10 and Q₀(E =16.2 MV/m, 1.6~K) = 1.0\ee{11}, corresponding to a residual surface resistance of 1.1~nΩ.

Paper	Title	Page
WEZBA1	SRF Cavities Beyond Niobium: Challenges and Potential	754
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	After many years of development, current preparation methods for niobium SRF cavities regularly achieve performance levels very close to the fundamental limitations of the material. Continued progress requires looking to alternative superconductors, but fabricating a high quality RF surface from these materials has proven uniquely challenging. In this talk, I will discuss the worldwide progress towards fabricating SRF cavity surfaces with alternative materials such as Nb3Sn, NbN, and MgB2. I will also discuss thin films and multilayer films of alternative materials, proposed as an alternative to bulk superconductors. I will present an improved theoretical understanding of the potential of such films. I will discuss new results and make suggestions for future directions beyond niobium.
	Slides WEZBA1 [4.418 MB]

WEPAC11	Cornell's Main Linac Cryo-module Prototype	811
	R.G. Eichhorn, G.M. Ge, Y. He, G.H. Hoffstaetter, M. Liepe, T. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731 In preparation to built an energy-recovery linac (ERL) based synchrotron-light facility at Cornell University which can provide greatly improved X-ray beams due to the high electron-beam quality that is available from a linac, a phase 1 R&D program was launched, adressing critical challenges in the design. One of them being a full linac cryo-module, housing 6 superconducting cavities (operated at 1.8 K in cw mode), 7 HOM absorbers and 1 magnet/ BPM section. The final design will be presented and a report on the fabrication status that started in late 2012 will be given

WEPAC12	Theoretical Description of SIS Multilayer Films for SRF Cavities	814
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA G. Catelani Forschungszentrum Jülich, Peter Gruenberg Institut (PGI-2), Jülich, Germany J.P. Sethna Cornell University, Ithaca, New York, USA M.K. Transtrum M.D.A.C.C., Houston, Texas, USA
	As surface magnetic fields in niobium superconducting RF (SRF) cavities prepared with modern techniques approach the fundamental limit of niobium’s superheating field, SRF researchers are looking to alternative superconductors to sustain even higher fields. However, the short coherence length of these superconductors may represent a critical vulnerability to vortex penetration at very small defects in the surface. A. Gurevich has proposed* a method of defeating this vulnerability: coating a bulk superconducting cavity with a series of very thin insulating and superconducting films. In this work, we present a thorough mathematical description of the SIS thin films proposed by Gurevich in the language of the accelerator community, to help researchers to optimize cavities made from alternative superconductors. * A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)

THOBA2	First Cavity Results from the Cornell SRF Group's Nb3Sn Program	1091
	S. Posen, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As an alternative material for SRF accelerator cavities, Nb3Sn presents two important benefits. Its large Tc gives it a very small surface resistance, leading to a huge reduction in cooling costs; and its predicted Hsh of nearly 400 mT would allow for very high gradients and therefore fewer cavities in high energy linacs. Researchers in the Cornell SRF group have recently fabricated two 1.3 GHz cavities coated with Nb3Sn. Testing of these first cavities has produced encouraging results, including a very high Tc and some very high performing regions. These cavity results as well as new sample results under TEM will be presented.
	Slides THOBA2 [4.880 MB]

THPMA07	Cryomodule Performance of the Main Linac Prototype Cavity for Cornell's Energy Recovery Linac	1367
	N.R.A. Valles, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, D.L. Hall, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Grants: NSF DMR-0807731 and NSF PHY-1002467 Energy Recovery Linacs (ERLs) require strong damping of higher-order modes in main linac cavities to avoid beam loss from beam break-up effects. In addition, the cavities need to have very high intrinsic quality factors to minimize the size of cryogenic plants in CW cavity operation. We present world record results for a fully equipped multicell cavity in a cryomodule, reaching intrinsic quality factors at operating accelerating field of Q₀(E =16.2 MV/m, 1.8~K) > 6.0\ee10 and Q₀(E =16.2 MV/m, 1.6~K) = 1.0\ee{11}, corresponding to a residual surface resistance of 1.1~nΩ.