IPAC2012 - List of Authors (Hoffstaetter, G.H.)

Paper

Title

Page

Performance of the Cornell High-Brightness, High-Power Electron Injector

20

B.M. Dunham, A.C. Bartnik, I.V. Bazarov, L. Cultrera, J. Dobbins, C.M. Gulliford, G.H. Hoffstaetter, R.P.K. Kaplan, V.O. Kostroun, Y. Li, M. Liepe, X. Liu, F. Löhl, P. Quigley, D.H. Rice, E.N. Smith, K.W. Smolenski, M. Tigner, V. Veshcherevich, Z. Zhao
CLASSE, Ithaca, New York, USA
S.S. Karkare, H. Li, J.M. Maxson
Cornell University, Ithaca, New York, USA

Funding: NSF DMR-0807731
The last year has seen significant progress in demonstrating the feasibility of a high current, high brightness photoinjector as required for the Energy Recovery Linac driven X-ray source at Cornell University. Both low emittances (0.4 mm-mrad rms normalized for 100% of the beam at 20 pC per bunch and 0.15 mm-mrad rms core emittance with 70% of the beam, and twice these values at 80 pC per bunch) and high average currents with a good lifetime well in excess of 1000 Coulombs at 5 MeV, 20 mA have been demonstrated. If these beams can be accelerated to 5 GeV without diluting the phase space, it would already provide a beam brightness higher than any existing storage ring. Operational experience, results, and the outlook for the future will be presented.

Slides MOOAA01 [1.424 MB]

MOPPP026

Cryogenic Distribution System for the Proposed Cornell ERL Main Linac

619

E.N. Smith
Cornell University, Ithaca, New York, USA
Y. He, G.H. Hoffstaetter, M. Liepe, M. Tigner
CLASSE, Ithaca, New York, USA

Funding: This material is based upon work supported by the National Science Foundation under Grant No. DMR-0807731.
The proposed Cornell ERL main linac requires a total cooling power of nearly 8kW at 1.8K, 5kW at 5K and over 100kW at 80K. This is distributed over approximately 65 cryomodules, each containing 6 rf cavities and associated input couplers and higher order mode absorbers. situated in two underground tunnels. While the total heat load is comparable to that for each of the 8 individual LHC cryoplants, the very high ratio of dynamic heat load to static heat load, combined with the high power density at various sites produces interesting challenges for the cryogenic distribution system. A schematic view of the design choices selected, some of which are different from existing large cryogenic systems, and the basis for these decisions, is presented in this paper.

TUPPR045

Multi-cell VEP Results: High Voltage, High Q, and Localized Temperature Analysis

1918

F. Furuta, B. Elmore
Cornell University, Ithaca, New York, USA
A.C. Crawford
Fermilab, Batavia, USA
G.M. Ge, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA

We are developing Vertical Electro Polishing (VEP) system for niobium superconducting RF cavity at Cornell University. VEP has been successfully applied on different cell shapes (TESLA and Re-entrant), and single and multi-cell cavities. VEP achieved high gradient of 39MV/m with TESLA shape single cell and of 36MV/m with TESLA shape 9-cell, respectively. Preliminary results of R&D on VEPed cavities show removal dependence on cavity performance. Temperature oscillation asymmetry was also found during the VEP process. We will report these recent results and further R&D plan of Cornell VEP.

WEIC06

Accelerator R&D: Research for Science - Science for Society

2161

N.R. Holtkamp
SLAC, Menlo Park, California, USA
S. Biedron, S.V. Milton
CSU, Fort Collins, Colorado, USA
L. Boeh, J.E. Clayton, G. Zdasiuk
VMS GTC, Palo Alto, California, USA
S.A. Gourlay, M.S. Zisman
LBNL, Berkeley, California, USA
R.W. Hamm
R&M Technical Enterprises, Pleasanton, California, USA
S. Henderson
Fermilab, Batavia, USA
G.H. Hoffstaetter
CLASSE, Ithaca, New York, USA
L. Merminga
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
S. Ozaki
BNL, Upton, Long Island, New York, USA
F.C. Pilat
JLAB, Newport News, Virginia, USA
M. White
ANL, Argonne, USA

In September 2011 the US Senate Appropriations Committee requested a ten-year strategic plan from the Department of Energy (DOE) that would describe how accelerator R&D today could advance applications directly relevant to society. Based on the 2009 workshop "Accelerators for America’s Future" an assessment was made on how accelerator technology developed by the nation’s laboratories and universities could directly translate into a competitive strength for industrial partners and a variety of government agencies in the research, defense and national security sectors. The Office of High Energy Physics, traditionally the steward for advanced accelerator R&D within DOE, commissioned a task force under its auspices to generate and compile ideas on how best to implement strategies that would help fulfill the needs of industry and other agencies, while maintaining focus on its core mission of fundamental science investigation.

Slides WEIC06 [3.678 MB]

WEPPC069

Construction, Evaluation, and Application of a Temperature Map for Multi-cell SRF Cavities

2369

G.M. Ge, F. Furuta, D.L. Hartill, K.M.V. Ho, G.H. Hoffstaetter, E.N. Smith
CLASSE, Ithaca, New York, USA

Temperature mapping (T-mapping) system is able to locate hot-spot of SRF cavity, thus it is a very powerful tool for cavity’s Q-value research. Recently Cornell University is developing a T-mapping system for multi-cell SRF cavities. The system includes more than two thousands Allen-Bradley resistors. Electronic of the system uses multiplexing of sensors which is able to dramatically reduce wire numbers, and allow the whole system is feasible for multi-cell cavity application. A new cavity testing insert which is for T-mapping system has been constructed.

WEPPC072

High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule

2378

M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
CLASSE, Ithaca, New York, USA

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 superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.

WEPPC073

Progress on Superconducting RF Work for the Cornell ERL

2381

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

Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.

WEPPC074

HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule

2384

N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
CLASSE, Ithaca, New York, USA

The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.

WEPPC075

Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL

2387

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

Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·10¹⁰ at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.

WEPPC078

Recent Developments in the Cornell Nb3Sn Initiative

2390

S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie
CLASSE, Ithaca, New York, USA

Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079

Residual Resistance Studies at Cornell

2393

S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe
CLASSE, Ithaca, New York, USA
J. Oh
Cornell University, Ithaca, New York, USA

The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPR037

First-Principle Approach for Optimization of Cavity Shape for High Gradient and Low Loss

3015

V.D. Shemelin, G.H. Hoffstaetter
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731.
Minimization of surface fields for a given accelerating rate is the subject of cavity optimization because high electric and magnetic fields lead to field emission or thermal breakdown, respectively. The ratio between peak electric and magnetic fields is a function of geometry and the desired ratio depends on application. For each application the optimal geometry may be different. The elliptic shape of the cavity have been found evolutionarily: starting from a pill-box with beam-pipes having rounded corners. No attempts up to now are known for a search of non-elliptical optimal shapes. Here we describe the search for a cavity shape that has the lowest surface fields, not restricting to the conventional elliptical cavity shapes.

WEPPC031

Completed Assembly of the Daresbury International ERL Cryomodule and its Implementation on ALICE

2272

P.A. McIntosh, M.A. Cordwell, P.A. Corlett, P. Davies, E. Frangleton, P. Goudket, K.J. Middleman, S.M. Pattalwar, 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
J.N. Corlett, D. Li, S.M. Lidia
LBNL, Berkeley, California, USA
G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich
CLASSE, Ithaca, New York, USA
T.J. Jones, J. Strachan
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
R.E. Laxdal
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
D. Proch, J.K. Sekutowicz
DESY, Hamburg, Germany
T.I. Smith
Stanford University, Stanford, California, USA

The completion of an optimised SRF cryomodule for application on ERL accelerators has now culminated with the successful assembly of an integrated cryomodule, following an intensive 5 years of development evolution. The cryomodule, which incorporates 2 x 7-cell 1.3 GHz accelerating structures, 3 separate layers of magnetic shielding, fully adjustable & high power input couplers and fast piezo tuners, has been installed on the ALICE ERL facility at Daresbury Laboratory. It is intended that this will permit operational optimisation for maximised efficiency demonstration, through increased Qext adjustment whilst retaining both effective energy recovery and IR-FEL lasing. The collaborative design processes employed in completing this new cryomodule development are explained, along with the assembly and implementation procedures used to facilitate its successful installation on the ALICE ERL facility.

WEPPR086

Computed Wake Field Effects from Measured Surface Roughness in the Walls of the Cornell ERL

3132

M.G. Billing, G.H. Hoffstaetter, C.E. Mayes, K.W. Smolenski, H.A. Williams
CLASSE, Ithaca, New York, USA

Funding: Work supported by the NSF ERL Phase 1B Cooperative Agreement (DMR-0807731)
Wake fields arise from the discontinuities in a smooth vacuum chamber and will cause energy spread in the passing bunch. In an energy recovery linac (ERL), the spent bunches are decelerated before they are dumped to reuse the beam’s energy for the acceleration of new bunches. While the energy spread accumulated from wakes before deceleration is small compared to the beam’s energy after full acceleration, it becomes more important relatively as the beam’s energy decreases.* Thus, in an ERL wake fields can produce very significant energy spread in the beam as it is decelerated to the energy of the beam dump. We report on calculations of wake fields due to the roughness of the surface of the vacuum chamber walls as it affects the Cornell ERL design. These calculations include the effects from the measured roughness for real vacuum chamber wall surfaces.
* M. Billing, “Effect of Wake Fields in an Energy Recovery Linac”, PAC’09, Vancouver, BC, Canada, 4-8 May 2009.

Paper	Title	Page
MOOAA01	Performance of the Cornell High-Brightness, High-Power Electron Injector	20
	B.M. Dunham, A.C. Bartnik, I.V. Bazarov, L. Cultrera, J. Dobbins, C.M. Gulliford, G.H. Hoffstaetter, R.P.K. Kaplan, V.O. Kostroun, Y. Li, M. Liepe, X. Liu, F. Löhl, P. Quigley, D.H. Rice, E.N. Smith, K.W. Smolenski, M. Tigner, V. Veshcherevich, Z. Zhao CLASSE, Ithaca, New York, USA S.S. Karkare, H. Li, J.M. Maxson Cornell University, Ithaca, New York, USA
	Funding: NSF DMR-0807731 The last year has seen significant progress in demonstrating the feasibility of a high current, high brightness photoinjector as required for the Energy Recovery Linac driven X-ray source at Cornell University. Both low emittances (0.4 mm-mrad rms normalized for 100% of the beam at 20 pC per bunch and 0.15 mm-mrad rms core emittance with 70% of the beam, and twice these values at 80 pC per bunch) and high average currents with a good lifetime well in excess of 1000 Coulombs at 5 MeV, 20 mA have been demonstrated. If these beams can be accelerated to 5 GeV without diluting the phase space, it would already provide a beam brightness higher than any existing storage ring. Operational experience, results, and the outlook for the future will be presented.
	Slides MOOAA01 [1.424 MB]

MOPPP026	Cryogenic Distribution System for the Proposed Cornell ERL Main Linac	619
	E.N. Smith Cornell University, Ithaca, New York, USA Y. He, G.H. Hoffstaetter, M. Liepe, M. Tigner CLASSE, Ithaca, New York, USA
	Funding: This material is based upon work supported by the National Science Foundation under Grant No. DMR-0807731. The proposed Cornell ERL main linac requires a total cooling power of nearly 8kW at 1.8K, 5kW at 5K and over 100kW at 80K. This is distributed over approximately 65 cryomodules, each containing 6 rf cavities and associated input couplers and higher order mode absorbers. situated in two underground tunnels. While the total heat load is comparable to that for each of the 8 individual LHC cryoplants, the very high ratio of dynamic heat load to static heat load, combined with the high power density at various sites produces interesting challenges for the cryogenic distribution system. A schematic view of the design choices selected, some of which are different from existing large cryogenic systems, and the basis for these decisions, is presented in this paper.

TUPPR045	Multi-cell VEP Results: High Voltage, High Q, and Localized Temperature Analysis	1918
	F. Furuta, B. Elmore Cornell University, Ithaca, New York, USA A.C. Crawford Fermilab, Batavia, USA G.M. Ge, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA
	We are developing Vertical Electro Polishing (VEP) system for niobium superconducting RF cavity at Cornell University. VEP has been successfully applied on different cell shapes (TESLA and Re-entrant), and single and multi-cell cavities. VEP achieved high gradient of 39MV/m with TESLA shape single cell and of 36MV/m with TESLA shape 9-cell, respectively. Preliminary results of R&D on VEPed cavities show removal dependence on cavity performance. Temperature oscillation asymmetry was also found during the VEP process. We will report these recent results and further R&D plan of Cornell VEP.

WEIC06	Accelerator R&D: Research for Science - Science for Society	2161
	N.R. Holtkamp SLAC, Menlo Park, California, USA S. Biedron, S.V. Milton CSU, Fort Collins, Colorado, USA L. Boeh, J.E. Clayton, G. Zdasiuk VMS GTC, Palo Alto, California, USA S.A. Gourlay, M.S. Zisman LBNL, Berkeley, California, USA R.W. Hamm R&M Technical Enterprises, Pleasanton, California, USA S. Henderson Fermilab, Batavia, USA G.H. Hoffstaetter CLASSE, Ithaca, New York, USA L. Merminga TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada S. Ozaki BNL, Upton, Long Island, New York, USA F.C. Pilat JLAB, Newport News, Virginia, USA M. White ANL, Argonne, USA
	In September 2011 the US Senate Appropriations Committee requested a ten-year strategic plan from the Department of Energy (DOE) that would describe how accelerator R&D today could advance applications directly relevant to society. Based on the 2009 workshop "Accelerators for America’s Future" an assessment was made on how accelerator technology developed by the nation’s laboratories and universities could directly translate into a competitive strength for industrial partners and a variety of government agencies in the research, defense and national security sectors. The Office of High Energy Physics, traditionally the steward for advanced accelerator R&D within DOE, commissioned a task force under its auspices to generate and compile ideas on how best to implement strategies that would help fulfill the needs of industry and other agencies, while maintaining focus on its core mission of fundamental science investigation.
	Slides WEIC06 [3.678 MB]

WEPPC069	Construction, Evaluation, and Application of a Temperature Map for Multi-cell SRF Cavities	2369
	G.M. Ge, F. Furuta, D.L. Hartill, K.M.V. Ho, G.H. Hoffstaetter, E.N. Smith CLASSE, Ithaca, New York, USA
	Temperature mapping (T-mapping) system is able to locate hot-spot of SRF cavity, thus it is a very powerful tool for cavity’s Q-value research. Recently Cornell University is developing a T-mapping system for multi-cell SRF cavities. The system includes more than two thousands Allen-Bradley resistors. Electronic of the system uses multiplexing of sensors which is able to dramatically reduce wire numbers, and allow the whole system is feasible for multi-cell cavity application. A new cavity testing insert which is for T-mapping system has been constructed.

WEPPC072	High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule	2378
	M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich CLASSE, Ithaca, New York, USA
	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 superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.

WEPPC073	Progress on Superconducting RF Work for the Cornell ERL	2381
	M. Liepe, F. Furuta, G.M. Ge, Y. He, G.H. Hoffstaetter, T.I. O'Connell, S. Posen, J. Sears, M. Tigner, N.R.A. Valles, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.

WEPPC074	HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule	2384
	N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes CLASSE, Ithaca, New York, USA
	The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.

WEPPC075	Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL	2387
	N.R.A. Valles, F. Furuta, G.M. Ge, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, M. Tigner, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·10¹⁰ at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.

WEPPC078	Recent Developments in the Cornell Nb3Sn Initiative	2390
	S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie CLASSE, Ithaca, New York, USA
	Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC079	Residual Resistance Studies at Cornell	2393
	S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe CLASSE, Ithaca, New York, USA J. Oh Cornell University, Ithaca, New York, USA
	The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.

WEPPR037	First-Principle Approach for Optimization of Cavity Shape for High Gradient and Low Loss	3015
	V.D. Shemelin, G.H. Hoffstaetter CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731. Minimization of surface fields for a given accelerating rate is the subject of cavity optimization because high electric and magnetic fields lead to field emission or thermal breakdown, respectively. The ratio between peak electric and magnetic fields is a function of geometry and the desired ratio depends on application. For each application the optimal geometry may be different. The elliptic shape of the cavity have been found evolutionarily: starting from a pill-box with beam-pipes having rounded corners. No attempts up to now are known for a search of non-elliptical optimal shapes. Here we describe the search for a cavity shape that has the lowest surface fields, not restricting to the conventional elliptical cavity shapes.

WEPPC031	Completed Assembly of the Daresbury International ERL Cryomodule and its Implementation on ALICE	2272
	P.A. McIntosh, M.A. Cordwell, P.A. Corlett, P. Davies, E. Frangleton, P. Goudket, K.J. Middleman, S.M. Pattalwar, 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 J.N. Corlett, D. Li, S.M. Lidia LBNL, Berkeley, California, USA G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich CLASSE, Ithaca, New York, USA T.J. Jones, J. Strachan STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom R.E. Laxdal TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada D. Proch, J.K. Sekutowicz DESY, Hamburg, Germany T.I. Smith Stanford University, Stanford, California, USA
	The completion of an optimised SRF cryomodule for application on ERL accelerators has now culminated with the successful assembly of an integrated cryomodule, following an intensive 5 years of development evolution. The cryomodule, which incorporates 2 x 7-cell 1.3 GHz accelerating structures, 3 separate layers of magnetic shielding, fully adjustable & high power input couplers and fast piezo tuners, has been installed on the ALICE ERL facility at Daresbury Laboratory. It is intended that this will permit operational optimisation for maximised efficiency demonstration, through increased Qext adjustment whilst retaining both effective energy recovery and IR-FEL lasing. The collaborative design processes employed in completing this new cryomodule development are explained, along with the assembly and implementation procedures used to facilitate its successful installation on the ALICE ERL facility.

WEPPR086	Computed Wake Field Effects from Measured Surface Roughness in the Walls of the Cornell ERL	3132
	M.G. Billing, G.H. Hoffstaetter, C.E. Mayes, K.W. Smolenski, H.A. Williams CLASSE, Ithaca, New York, USA
	Funding: Work supported by the NSF ERL Phase 1B Cooperative Agreement (DMR-0807731) Wake fields arise from the discontinuities in a smooth vacuum chamber and will cause energy spread in the passing bunch. In an energy recovery linac (ERL), the spent bunches are decelerated before they are dumped to reuse the beam’s energy for the acceleration of new bunches. While the energy spread accumulated from wakes before deceleration is small compared to the beam’s energy after full acceleration, it becomes more important relatively as the beam’s energy decreases.* Thus, in an ERL wake fields can produce very significant energy spread in the beam as it is decelerated to the energy of the beam dump. We report on calculations of wake fields due to the roughness of the surface of the vacuum chamber walls as it affects the Cornell ERL design. These calculations include the effects from the measured roughness for real vacuum chamber wall surfaces. * M. Billing, “Effect of Wake Fields in an Energy Recovery Linac”, PAC’09, Vancouver, BC, Canada, 4-8 May 2009.