SRF2013 - List of Authors (Hoffstaetter, G.H.)

Paper

Title

Page

75 mA Operation of the Cornell ERL Superconducting RF Injector Cryomodule

259

M. Liepe, B.M. Dunham, R.G. Eichhorn, G.H. Hoffstaetter, R.P.K. Kaplan, P. Quigley, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work is supported by the National Science Foundation (Grant No. DMR-0807731).
Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on 1.3 GHz superconducting RF technology, and has been tested extensively in the Cornell ERL injector prototype with world record CW beam currents exceeding 70 mA. High CW RF power input couplers and strong Higher-Order-Mode damping in the cavities are essential for high beam current operation. This paper summarizes the performance of the cryomodule during the high beam current operation.

MOP071

Record Quality Factor Performance of the Prototype Cornell ERL Main Linac Cavity in the Horizontal Test Cryomodule

300

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'Connel, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Supported by NSF grant DMR-0807731
Future SRF linac driven accelerators operated in CW mode will require very efficient SRF cavities with high intrinsic quality factors Q at medium accelerating fields. Cornell has recently ﬁnished testing the fully equipped 1.3 GHz, 7-cell main linac cavity for the Cornell Energy Recovery Linac in a horizontal test cryomodule (HTC). Measurements characterizing the fundamental mode’s quality factor have been completed, showing record Q performance. In this paper, we present detailed quality factor vs gradient results for three HTC assembly stages. We show that the performance of an SRF cavity can be maintained when installed into a cryomodule, and that thermal cycling reduces residual surface resistance. We present world record results for a fully equipped multicell cavity in a cryomodule, reaching intrinsic quality factors at operating accelerating field of Q(E =16.2 MV/m, 1.8K) > 6·10¹⁰ and Q(E =16.2 MV/m, 1.6K) > 1.0·10¹¹, corresponding to a very low residual surface resistance of 1.1 nOhm.

MOP086

Integration, Commissioning and Cryogenics Performance of the ERL Cryomodule Installed on ALICE-ERL Facility at STFC Daresbury Laboratory, UK

349

S.M. Pattalwar, R.K. Buckley, P.A. Corlett, P. Goudket, A.R. Goulden, A.J. May, P.A. McIntosh, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S.A. Belomestnykh
BNL, Upton, Long Island, New York, USA
A. Büchner, F.G. Gabriel, P. Michel
HZDR, Dresden, Germany
E.P. Chojnacki, J.V. Conway, R.G. Eichhorn, G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M.A. Cordwell, T.J. Jones, L. Ma, A.J. Moss, J. Strachan
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
J.N. Corlett, D. Li, S.M. Lidia
LBNL, Berkeley, California, USA
T. Kimura
Stanford University, Stanford, California, USA
R.E. Laxdal
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
J.K. Sekutowicz
DESY, Hamburg, Germany
T.J. Smith
SLAC, Menlo Park, California, USA

On successful assembly and preliminary testing of an optimised SRF cryomodule for application on ERL accelerators, which is being developed through an international collaboration the cryomodule has been installed on the 35 MeV ALICE (Accelerators and Lasers in Combined Experiments) Energy Recovery Linac (ERL) facility at STFC Daresbury Laboratory. Existing cryogenic infrastructure has a capacity to deliver approximately 120 W cooling power at 2 K, but the HOM (Higher Order Mode) absorbers, the thermal intercepts for the high power RF couplers and the radiation shield in the cryomodule are designed to be cooled (to 5 K and 80 K) with gaseous helium instead of liquid nitrogen. As a result the cryogenic infrastructure for ALICE had to be modified to meet these additional requirements. In this paper we describe our experience with the process of integration and the cryogenic commissioning, and present some initial results.

TUIOC01

Review on EP Advances Worldwide

F. Furuta, B. Elmore, G.H. Hoffstaetter, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Electro-Polishing is now applying on SRF Nb cavity world widely as baseline surface treatment technique in many projects, such as ILC, XFEL, JlabUpgrade, and so on. I will give some review on EP as titled, report the achievements and the newest R&D topics of EP.

Slides TUIOC01 [20.715 MB]

TUP048

Preparations and VT Results of ERL7-cell at Cornell

521

F. Furuta, B. Bullock, R.G. Eichhorn, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

We have fabricated 7 ERL 7-cell cavities for Cornell ERL project. 4 nu-stiffened and 3-stiffened cavities have been fabricated in house so far. Specification values of our 7-cell is 16.2MV/m with Qo of 2.0·10¹⁰ at 1.8K. In this report, we will describe our surface treatments recipe which is based on BCP and the results of vertical tests of these 7-cell cavities.

TUP049

Cornell VEP Update, VT Results and R&D on Nb Coupon

524

F. Furuta, B. Elmore, G.H. Hoffstaetter, D.K. Krebs, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell's SRF group have been led development of Vertical Electro-Polishing(VEP) on SRF Nb Cavity. We have done many VEP on singel-/multi-cell cavities. We also have started VEP'ed Nb coupon surface analysis based on surface roughness measurement. In this report, we will describe our status of VEP R&D, the results of VEP'ed cavity vertical testing, and fundamental study on VEP using Nb coupons.

TUP059

TM-Furnace Qualification at Cornell

561

F. Furuta, B. Bullock, R.G. Eichhorn, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell's SRF group had new vacuum furnace for hydrogen degassing of SRF Nb cavity. Systematic study and testing have been done to qualify this new furnace. We will report the results of those qualification tests include cavity bake and vertical testing.

TUP097

Study of the Temperature Interface Between Niobium and Superfluid Helium. Temperature Waves Measurements from Heat Sources

700

A. Ganshin, F. Furuta, D.L. Hartill, G.H. Hoffstaetter, K.M. Price, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431.
One of the most important properties of Superconducting Radio Frequency (SRF) cavities is their ability to disperse generated heat from the internal cavity wall to the external super fluid helium bath. When the generated heat is not removed fast enough, an effect known as thermal feedback dominates, resulting in medium field Q-slope. This medium field Q-slope has the ability to reduce the Q factor should it become strong enough. To determine what physical factors affect the creation of the medium field Q-slope we will be computationally modeling the medium field Q-slope with varying parameters, such as Kapitza conductivity, wall thickness, RF frequency, bath temperature, residual resistivity ratio, residual resistance, and phonon mean path. Our results show that the medium-field Q slope is highly dependent on the Kapitza conductivity and that by doubling the Kapitza conductivity the medium field Q-slope reduces significantly. Understanding and controlling the medium ﬁeld Q-slope will benefit future continuous wave (CW) applications such as the Energy Recovery Linacs (ERL) where cryogenics costs dominate due to CW operation at medium ﬁelds (< 20 MV/m).

TUP104

Temperature Waves in SRF Research

719

A. Ganshin, R.G. Eichhorn, D.L. Hartill, G.H. Hoffstaetter, E.N. Smith, N.R.A. Valles
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
X. Mi
Cornell University, Ithaca, New York, USA

Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431
Previously Cornell University developed Oscillating Superleak Transducers (OST) to locate quench spots on superconducting cavities in superfluid helium. This work builds upon this research and presents a technique to automatically visualize quench locations from OST data (1). This system is now fully automated. The current system consists of between 8 and 16 OSTs, a high gain low noise preamplifier, and a data acquisition card that can log up to 16 simultaneously recorded inputs. The developed software allows computing quench locations on various cavity geometries, adjustment of the location of each OST and a choice between several quench finding algorithms. Observed results are in excellent agreement with optical inspection and temperature map data.
1. http://newsline.linearcollider.org/2011/04/21/the-sound-of-accelerator-cavitie

TUP105

Investigation of the Surface Resistivity of SRF Cavities via the Heat and Srimp Program as Well as the Multi-Cell T-Map System

724

G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, H. Padamsee
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
F. Furuta
Cornell University, Ithaca, New York, USA

A high-sensitive temperature mapping system for multi-cell SRF cavities has been constructed at Cornell University. The resolution of the system is 1mK. Hence it’s able to detect small temperature increases when cavities reach at low accelerating gradients e.g. 3MV/m. The surface resistivity of superconductor under radio-frequency electromagnetic field can be calculated from the temperature increases. In this contribution, the surface resistance map of multi-cell SRF cavities is shown. The temperature mapping result is possible to establish a relationship between the surface resistivity and the magnetic field as well. Unlike the RF method which is average value of the surface resistance, the T-map results give local surface resistivity versus magnetic field. BCS theory assumes the surface resistivity is independent to the magnetic field. The T-map results, however, suggest that the surface resistance at high-loss region is field dependent and caused Q-slope.

THIOB02

High Q Cavities for the Cornell ERL Main Linac

844

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

While SRF research for linear colliders was focused on achieving high gradients, Cornell’s proposal for an energy recovery linac (ERL) demanded for low cw losses. Starting several years ago, a high-Q R&D phase was launched that led to remarkable results recently: A fully dressed cavity (7 cells, 1.3 GHz) with side-mounted input coupler and beamline HOM absorbers achieved a Q of 3.5·10¹⁰ ((16 MV/m, 1.8 K). This talk will review the staged approach we have chosen in testing a single cavity in a horizontal short cryomodule (HTC), report results on each step and conclude on our findings about preserving high Q from vertical testing. We also discuss the production of six additional cavities as we progress toward constructing a full 6-cavity cryomodule as a prototype for Cornell’s main linac module

Slides THIOB02 [8.378 MB]

THP007

Cornell's ERL Cavity Production

909

R.G. Eichhorn, B. Bullock, B. Clasby, B. Elmore, F. Furuta, G.H. Hoffstaetter, J.J. Kaufman, B.M. Kilpatrick, J. Sears, V.D. Shemelin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Kürzeder
TU Darmstadt, Darmstadt, Germany

The phase 1 R&D program launched in preparation to building a 5 GeV Energy Recovery Linac (ERL) at Cornell, a full main linac cryomodule is currently built, housing six 7-cell cavities. In order to control the beam break-up limit, the shape of the cavity was highly optimized and stringent tolerances on the cavity production were targeted. We will report on the details of the cavity production, the accuracy of the cups forming the individual cells, the trimming procedure for the dumbbells, the cavity tuning and final accuracy of the cavity concerning field flatness, resonant frequency and overall length within this small series production.

THP008

High Voltage Cavity R&D at Cornell, RE and ICHIRO

F. Furuta, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

We have been investigated 1.3GHz high gradient SRF Nb cavity with shape of low Hpk/Eacc, such as re-entrant(RE) and KEK low-loss (ICHIRO) shapes. We have single-/multi-cell RE cavities and ICHIRO single-cell cavities at Cornell. We have processed those cavities based on buffered chemical-polishing(BCP), vertical electro-polishing(VEP), and centrifugal barrel-polsihing(CBP). In this paper, we will report the details of processes and the results of vertical tests of these cavities.

THP071

HOM Studies of the Cornell ERL Main Linac Cavity in the Horizontal Test Cryomodule

1090

N.R.A. Valles, R.G. Eichhorn, D.A. Goldman, G.H. Hoffstaetter, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Supported by NSF grant DMR-0807731
The Cornell energy recovery linac will accelerate a 100 mA beam to 5 GeV, while maintaining very low emittance (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) in the SRF cavities 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). HOM measurements were done for three HTC assembly stages, from initial measurements on the bare cavity to being fully outﬁtted with side-mounted RF input coupler and beam line HOM absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments, demonstrating excellent damping of all dipole higher order modes.

Paper	Title	Page
MOP061	75 mA Operation of the Cornell ERL Superconducting RF Injector Cryomodule	259
	M. Liepe, B.M. Dunham, R.G. Eichhorn, G.H. Hoffstaetter, R.P.K. Kaplan, P. Quigley, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work is supported by the National Science Foundation (Grant No. DMR-0807731). Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on 1.3 GHz superconducting RF technology, and has been tested extensively in the Cornell ERL injector prototype with world record CW beam currents exceeding 70 mA. High CW RF power input couplers and strong Higher-Order-Mode damping in the cavities are essential for high beam current operation. This paper summarizes the performance of the cryomodule during the high beam current operation.

MOP071	Record Quality Factor Performance of the Prototype Cornell ERL Main Linac Cavity in the Horizontal Test Cryomodule	300
	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'Connel, S. Posen, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Supported by NSF grant DMR-0807731 Future SRF linac driven accelerators operated in CW mode will require very efficient SRF cavities with high intrinsic quality factors Q at medium accelerating fields. Cornell has recently ﬁnished testing the fully equipped 1.3 GHz, 7-cell main linac cavity for the Cornell Energy Recovery Linac in a horizontal test cryomodule (HTC). Measurements characterizing the fundamental mode’s quality factor have been completed, showing record Q performance. In this paper, we present detailed quality factor vs gradient results for three HTC assembly stages. We show that the performance of an SRF cavity can be maintained when installed into a cryomodule, and that thermal cycling reduces residual surface resistance. We present world record results for a fully equipped multicell cavity in a cryomodule, reaching intrinsic quality factors at operating accelerating field of Q(E =16.2 MV/m, 1.8K) > 6·10¹⁰ and Q(E =16.2 MV/m, 1.6K) > 1.0·10¹¹, corresponding to a very low residual surface resistance of 1.1 nOhm.

MOP086	Integration, Commissioning and Cryogenics Performance of the ERL Cryomodule Installed on ALICE-ERL Facility at STFC Daresbury Laboratory, UK	349
	S.M. Pattalwar, R.K. Buckley, P.A. Corlett, P. Goudket, A.R. Goulden, A.J. May, P.A. McIntosh, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S.A. Belomestnykh BNL, Upton, Long Island, New York, USA A. Büchner, F.G. Gabriel, P. Michel HZDR, Dresden, Germany E.P. Chojnacki, J.V. Conway, R.G. Eichhorn, G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M.A. Cordwell, T.J. Jones, L. Ma, A.J. Moss, J. Strachan STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom J.N. Corlett, D. Li, S.M. Lidia LBNL, Berkeley, California, USA T. Kimura Stanford University, Stanford, California, USA R.E. Laxdal TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada J.K. Sekutowicz DESY, Hamburg, Germany T.J. Smith SLAC, Menlo Park, California, USA
	On successful assembly and preliminary testing of an optimised SRF cryomodule for application on ERL accelerators, which is being developed through an international collaboration the cryomodule has been installed on the 35 MeV ALICE (Accelerators and Lasers in Combined Experiments) Energy Recovery Linac (ERL) facility at STFC Daresbury Laboratory. Existing cryogenic infrastructure has a capacity to deliver approximately 120 W cooling power at 2 K, but the HOM (Higher Order Mode) absorbers, the thermal intercepts for the high power RF couplers and the radiation shield in the cryomodule are designed to be cooled (to 5 K and 80 K) with gaseous helium instead of liquid nitrogen. As a result the cryogenic infrastructure for ALICE had to be modified to meet these additional requirements. In this paper we describe our experience with the process of integration and the cryogenic commissioning, and present some initial results.

TUIOC01	Review on EP Advances Worldwide
	F. Furuta, B. Elmore, G.H. Hoffstaetter, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Electro-Polishing is now applying on SRF Nb cavity world widely as baseline surface treatment technique in many projects, such as ILC, XFEL, JlabUpgrade, and so on. I will give some review on EP as titled, report the achievements and the newest R&D topics of EP.
	Slides TUIOC01 [20.715 MB]

TUP048	Preparations and VT Results of ERL7-cell at Cornell	521
	F. Furuta, B. Bullock, R.G. Eichhorn, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We have fabricated 7 ERL 7-cell cavities for Cornell ERL project. 4 nu-stiffened and 3-stiffened cavities have been fabricated in house so far. Specification values of our 7-cell is 16.2MV/m with Qo of 2.0·10¹⁰ at 1.8K. In this report, we will describe our surface treatments recipe which is based on BCP and the results of vertical tests of these 7-cell cavities.

TUP049	Cornell VEP Update, VT Results and R&D on Nb Coupon	524
	F. Furuta, B. Elmore, G.H. Hoffstaetter, D.K. Krebs, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell's SRF group have been led development of Vertical Electro-Polishing(VEP) on SRF Nb Cavity. We have done many VEP on singel-/multi-cell cavities. We also have started VEP'ed Nb coupon surface analysis based on surface roughness measurement. In this report, we will describe our status of VEP R&D, the results of VEP'ed cavity vertical testing, and fundamental study on VEP using Nb coupons.

TUP059	TM-Furnace Qualification at Cornell	561
	F. Furuta, B. Bullock, R.G. Eichhorn, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell's SRF group had new vacuum furnace for hydrogen degassing of SRF Nb cavity. Systematic study and testing have been done to qualify this new furnace. We will report the results of those qualification tests include cavity bake and vertical testing.

TUP097	Study of the Temperature Interface Between Niobium and Superfluid Helium. Temperature Waves Measurements from Heat Sources	700
	A. Ganshin, F. Furuta, D.L. Hartill, G.H. Hoffstaetter, K.M. Price, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431. One of the most important properties of Superconducting Radio Frequency (SRF) cavities is their ability to disperse generated heat from the internal cavity wall to the external super fluid helium bath. When the generated heat is not removed fast enough, an effect known as thermal feedback dominates, resulting in medium field Q-slope. This medium field Q-slope has the ability to reduce the Q factor should it become strong enough. To determine what physical factors affect the creation of the medium field Q-slope we will be computationally modeling the medium field Q-slope with varying parameters, such as Kapitza conductivity, wall thickness, RF frequency, bath temperature, residual resistivity ratio, residual resistance, and phonon mean path. Our results show that the medium-field Q slope is highly dependent on the Kapitza conductivity and that by doubling the Kapitza conductivity the medium field Q-slope reduces significantly. Understanding and controlling the medium ﬁeld Q-slope will benefit future continuous wave (CW) applications such as the Energy Recovery Linacs (ERL) where cryogenics costs dominate due to CW operation at medium ﬁelds (< 20 MV/m).

TUP104	Temperature Waves in SRF Research	719
	A. Ganshin, R.G. Eichhorn, D.L. Hartill, G.H. Hoffstaetter, E.N. Smith, N.R.A. Valles Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA X. Mi Cornell University, Ithaca, New York, USA
	Funding: This work has been supported by NSF award PHY-0969959 and DOE award DOE/SC00008431 Previously Cornell University developed Oscillating Superleak Transducers (OST) to locate quench spots on superconducting cavities in superfluid helium. This work builds upon this research and presents a technique to automatically visualize quench locations from OST data (1). This system is now fully automated. The current system consists of between 8 and 16 OSTs, a high gain low noise preamplifier, and a data acquisition card that can log up to 16 simultaneously recorded inputs. The developed software allows computing quench locations on various cavity geometries, adjustment of the location of each OST and a choice between several quench finding algorithms. Observed results are in excellent agreement with optical inspection and temperature map data. 1. http://newsline.linearcollider.org/2011/04/21/the-sound-of-accelerator-cavitie

TUP105	Investigation of the Surface Resistivity of SRF Cavities via the Heat and Srimp Program as Well as the Multi-Cell T-Map System	724
	G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, H. Padamsee Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA F. Furuta Cornell University, Ithaca, New York, USA
	A high-sensitive temperature mapping system for multi-cell SRF cavities has been constructed at Cornell University. The resolution of the system is 1mK. Hence it’s able to detect small temperature increases when cavities reach at low accelerating gradients e.g. 3MV/m. The surface resistivity of superconductor under radio-frequency electromagnetic field can be calculated from the temperature increases. In this contribution, the surface resistance map of multi-cell SRF cavities is shown. The temperature mapping result is possible to establish a relationship between the surface resistivity and the magnetic field as well. Unlike the RF method which is average value of the surface resistance, the T-map results give local surface resistivity versus magnetic field. BCS theory assumes the surface resistivity is independent to the magnetic field. The T-map results, however, suggest that the surface resistance at high-loss region is field dependent and caused Q-slope.

THIOB02	High Q Cavities for the Cornell ERL Main Linac	844
	R.G. Eichhorn, B. Bullock, B. Clasby, B. Elmore, F. Furuta, A. Ganshin, G.M. Ge, D. Gonnella, D.L. Hall, Y. He, K.M.V. Ho, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connel, S. Posen, P. Quigley, J. Sears, V.D. Shemelin, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	While SRF research for linear colliders was focused on achieving high gradients, Cornell’s proposal for an energy recovery linac (ERL) demanded for low cw losses. Starting several years ago, a high-Q R&D phase was launched that led to remarkable results recently: A fully dressed cavity (7 cells, 1.3 GHz) with side-mounted input coupler and beamline HOM absorbers achieved a Q of 3.5·10¹⁰ ((16 MV/m, 1.8 K). This talk will review the staged approach we have chosen in testing a single cavity in a horizontal short cryomodule (HTC), report results on each step and conclude on our findings about preserving high Q from vertical testing. We also discuss the production of six additional cavities as we progress toward constructing a full 6-cavity cryomodule as a prototype for Cornell’s main linac module
	Slides THIOB02 [8.378 MB]

THP007	Cornell's ERL Cavity Production	909
	R.G. Eichhorn, B. Bullock, B. Clasby, B. Elmore, F. Furuta, G.H. Hoffstaetter, J.J. Kaufman, B.M. Kilpatrick, J. Sears, V.D. Shemelin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Kürzeder TU Darmstadt, Darmstadt, Germany
	The phase 1 R&D program launched in preparation to building a 5 GeV Energy Recovery Linac (ERL) at Cornell, a full main linac cryomodule is currently built, housing six 7-cell cavities. In order to control the beam break-up limit, the shape of the cavity was highly optimized and stringent tolerances on the cavity production were targeted. We will report on the details of the cavity production, the accuracy of the cups forming the individual cells, the trimming procedure for the dumbbells, the cavity tuning and final accuracy of the cavity concerning field flatness, resonant frequency and overall length within this small series production.

THP008	High Voltage Cavity R&D at Cornell, RE and ICHIRO
	F. Furuta, B. Elmore, A. Ganshin, G.M. Ge, G.H. Hoffstaetter, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We have been investigated 1.3GHz high gradient SRF Nb cavity with shape of low Hpk/Eacc, such as re-entrant(RE) and KEK low-loss (ICHIRO) shapes. We have single-/multi-cell RE cavities and ICHIRO single-cell cavities at Cornell. We have processed those cavities based on buffered chemical-polishing(BCP), vertical electro-polishing(VEP), and centrifugal barrel-polsihing(CBP). In this paper, we will report the details of processes and the results of vertical tests of these cavities.

THP071	HOM Studies of the Cornell ERL Main Linac Cavity in the Horizontal Test Cryomodule	1090
	N.R.A. Valles, R.G. Eichhorn, D.A. Goldman, G.H. Hoffstaetter, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Supported by NSF grant DMR-0807731 The Cornell energy recovery linac will accelerate a 100 mA beam to 5 GeV, while maintaining very low emittance (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) in the SRF cavities 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). HOM measurements were done for three HTC assembly stages, from initial measurements on the bare cavity to being fully outﬁtted with side-mounted RF input coupler and beam line HOM absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments, demonstrating excellent damping of all dipole higher order modes.