SRF2011 - List of Authors (Cooper, C.A.)

Paper

Title

Page

Development and Scale-Up of an HF Free Electropolishing Process in Single-Cell Niobium SRF Cavities

397

M.E. Inman, H.M. Garich, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, USA
L.D. Cooley, C.A. Cooper, A.M. Rowe
Fermilab, Batavia, USA

The performance of niobium SRF cavities is strongly dependent on a microscopically smooth and clean surface, achieved using buffered chemical polishing or electropolishing, which require a viscous electrolyte containing hydrofluoric acid to achieve niobium oxide breakdown and current distribution control. An ideal polishing process would include: electrolyte free of hydrofluoric acid; control of surface roughness to less than 0.1 micron; surface free from contamination; current distribution control enabling uniform polishing; removal of at least 100 microns. Faraday is working with Fermilab to develop and scale-up the FARADAYIC Electropolishing process to achieve these conditions. FARADAYIC Electropolishing combines pulse reverse electric fields and low viscosity aqueous electrolytes to control current distribution and oxide formation during metal removal. Recent results on coupon polishing will be presented including polishing rates up to 1 micron/min, control of electrolyte temperature to below 20 C, and surface finishes less than 0.2 microns over 4 mm length scales. Construction of a single-cell cavity electropolishing apparatus at Faraday are discussed.

Poster TUPO017 [1.931 MB]

TUPO025

Integrated Cavity Processing Apparatus at Fermilab: SRF Cavity Processing R&D

424

C.A. Cooper, M.S. Champion, L.D. Cooley, V. Poloubotko, O. Pronitchev, A.M. Rowe, M. Wong
Fermilab, Batavia, USA

A center for cavity processing R&D at Fermilab, called the Integrated Cavity Processing Apparatus, is currently in the final stages of installation and commissioning. This facility contains centrifugal barrel polishing, a horizontal electropolishing tool, a 1000°C vacuum furnace, a high pressure rinse tool utilizing ultrapure water, ISO class 4, 5 and 6 clean rooms for cavity assembly work and various other associated pieces of support equipment. All the operations are designed for single cell and nine cell 1.3 GHz Tesla type cavities except for the electropolishing tool which will initially be only for single cell use. Upgrades are currently being examined for single and five cell 650 MHz cavities. The current status of the facility and plans for future work are discussed.

TUPO029

Gradient Improvement by Removal of Identified Local Defects

436

R.L. Geng, W.A. Clemens
JLAB, Newport News, Virginia, USA
C.A. Cooper
Fermilab, Batavia, USA
H. Hayano, K. Watanabe
KEK, Ibaraki, Japan

Funding: This work was authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Recent experience of ILC cavity processing and testing at Jefferson Lab has shown that some 9-cell cavities are quench limited at a gradient in the range of 15-25 MV/m. Further studies reveal that these quench limits are often correlated with sub-mm sized and highly localized geometrical defects at or near the equator weld. There are increasing evidence to show that these genetic defects have their origin in the material or in the electron beam welding process (for example due to weld irregularities or splatters on the RF surface and welding porosity underneath the surface). A local defect removal method has been proposed at Jefferson Lab by locally re-melting the niobium material. Several 1-cell cavities with known local defects have been treated by using the JLab local e-beam re-melting method, resulting in gradient and Q0 improvement. We also sent 9-cell cavities with known gradient limiting local defects to KEK for local grinding and to FNAL for global mechanical polishing. We report on the results of gradient improvements by removal of local defects in these cavities.

WEIOA02

Centrifugal Barrel Polishing (CBP) of SRF Cavities Worldwide

571

C.A. Cooper
Fermilab, Batavia, USA
B. Bullock
CLASSE, Ithaca, New York, USA
S.C. Joshi
RRCAT, Indore (M.P.), India
A.D. Palczewski
JLAB, Newport News, Virginia, USA
K. Saito
KEK, Ibaraki, Japan

Much interest was generated in the mid to late 1990s in an alternative cavity surface processing technique called CBP, that mechanically polishes the inside of SRF cavities by rotating them at high speeds while filled with abrasive media. This work, which was originally done at KEK by Kenji Saito & Tamawo Higuchi, has received renewed interest recently because of work done at Fermilab which has produced mirror like finishes on the 1.3 GHz Tesla-type cavity SRF surface. In addition to Fermilab & KEK, Cornell, Jefferson Lab and RRCAT are all exploring CBP as a cavity processing technique. CBP is interesting as a cavity processing technique because it removes defects associated with the manufacturing process, it can yield surface finishes (Ra) on the order of 10s of nanometers, it is a simple technology that could transfer easily to industry, it could help increase cavity yields and it requires less acid than other techniques. Recent progress and the current status of CBP as a baseline and repair technique will be discussed.

THIOA07

Single-cell SC Cavity Development in India

659

A. Puntambekar, J. Dwivedi, P.D. Gupta, S.C. Joshi, G. Mundra, P. Shrivastava
RRCAT, Indore (M.P.), India
C.A. Cooper, M.H. Foley, T.N. Khabiboulline, C.S. Mishra, J.P. Ozelis, A.M. Rowe
Fermilab, Batavia, USA
P.N. Potukuchi
IUAC, New Delhi, India
G. Wu
ANL, Argonne, USA

Under Indian Institutions and Fermilab Collaboration (IIFC), Raja Ramanna Centre for Advanced Technology (RRCAT) Indore, India has initiated the development of SCRF cavity technology in collaboration with Fermi National Accelerator Laboratory (FNAL) USA. The R & D efforts are focused on the proposed Project-X accelerator complex at FNAL and High Intensity Proton Accelerator activities in India. As an initial effort, two prototype 1.3 GHz single cell bulk niobium cavities have been developed in collaboration with the Inter University Accelerator Centre (IUAC), New Delhi. Learning from the experience gained and the initial results of these prototypes (achieving Eacc ~23 MV/m), two more improved 1.3 GHz single cell cavities are being developed. These two improved single cell cavities will also be processed and tested at FNAL. Development of a 1.3 GHz, 5-cell SCRF cavity with simple end groups, development of end group, and fabrication of a single -cell 650 MHz (β=0.9) prototype cavity are being undertaken as the next stage in these efforts. This paper will present the development and test results on the 1.3 GHz single cell cavities and status of the ongoing work.

Slides THIOA07 [2.937 MB]

Paper	Title	Page
TUPO017	Development and Scale-Up of an HF Free Electropolishing Process in Single-Cell Niobium SRF Cavities	397
	M.E. Inman, H.M. Garich, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, USA L.D. Cooley, C.A. Cooper, A.M. Rowe Fermilab, Batavia, USA
	The performance of niobium SRF cavities is strongly dependent on a microscopically smooth and clean surface, achieved using buffered chemical polishing or electropolishing, which require a viscous electrolyte containing hydrofluoric acid to achieve niobium oxide breakdown and current distribution control. An ideal polishing process would include: electrolyte free of hydrofluoric acid; control of surface roughness to less than 0.1 micron; surface free from contamination; current distribution control enabling uniform polishing; removal of at least 100 microns. Faraday is working with Fermilab to develop and scale-up the FARADAYIC Electropolishing process to achieve these conditions. FARADAYIC Electropolishing combines pulse reverse electric fields and low viscosity aqueous electrolytes to control current distribution and oxide formation during metal removal. Recent results on coupon polishing will be presented including polishing rates up to 1 micron/min, control of electrolyte temperature to below 20 C, and surface finishes less than 0.2 microns over 4 mm length scales. Construction of a single-cell cavity electropolishing apparatus at Faraday are discussed.
	Poster TUPO017 [1.931 MB]

TUPO025	Integrated Cavity Processing Apparatus at Fermilab: SRF Cavity Processing R&D	424
	C.A. Cooper, M.S. Champion, L.D. Cooley, V. Poloubotko, O. Pronitchev, A.M. Rowe, M. Wong Fermilab, Batavia, USA
	A center for cavity processing R&D at Fermilab, called the Integrated Cavity Processing Apparatus, is currently in the final stages of installation and commissioning. This facility contains centrifugal barrel polishing, a horizontal electropolishing tool, a 1000°C vacuum furnace, a high pressure rinse tool utilizing ultrapure water, ISO class 4, 5 and 6 clean rooms for cavity assembly work and various other associated pieces of support equipment. All the operations are designed for single cell and nine cell 1.3 GHz Tesla type cavities except for the electropolishing tool which will initially be only for single cell use. Upgrades are currently being examined for single and five cell 650 MHz cavities. The current status of the facility and plans for future work are discussed.

TUPO029	Gradient Improvement by Removal of Identified Local Defects	436
	R.L. Geng, W.A. Clemens JLAB, Newport News, Virginia, USA C.A. Cooper Fermilab, Batavia, USA H. Hayano, K. Watanabe KEK, Ibaraki, Japan
	Funding: This work was authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Recent experience of ILC cavity processing and testing at Jefferson Lab has shown that some 9-cell cavities are quench limited at a gradient in the range of 15-25 MV/m. Further studies reveal that these quench limits are often correlated with sub-mm sized and highly localized geometrical defects at or near the equator weld. There are increasing evidence to show that these genetic defects have their origin in the material or in the electron beam welding process (for example due to weld irregularities or splatters on the RF surface and welding porosity underneath the surface). A local defect removal method has been proposed at Jefferson Lab by locally re-melting the niobium material. Several 1-cell cavities with known local defects have been treated by using the JLab local e-beam re-melting method, resulting in gradient and Q0 improvement. We also sent 9-cell cavities with known gradient limiting local defects to KEK for local grinding and to FNAL for global mechanical polishing. We report on the results of gradient improvements by removal of local defects in these cavities.

WEIOA02	Centrifugal Barrel Polishing (CBP) of SRF Cavities Worldwide	571
	C.A. Cooper Fermilab, Batavia, USA B. Bullock CLASSE, Ithaca, New York, USA S.C. Joshi RRCAT, Indore (M.P.), India A.D. Palczewski JLAB, Newport News, Virginia, USA K. Saito KEK, Ibaraki, Japan
	Much interest was generated in the mid to late 1990s in an alternative cavity surface processing technique called CBP, that mechanically polishes the inside of SRF cavities by rotating them at high speeds while filled with abrasive media. This work, which was originally done at KEK by Kenji Saito & Tamawo Higuchi, has received renewed interest recently because of work done at Fermilab which has produced mirror like finishes on the 1.3 GHz Tesla-type cavity SRF surface. In addition to Fermilab & KEK, Cornell, Jefferson Lab and RRCAT are all exploring CBP as a cavity processing technique. CBP is interesting as a cavity processing technique because it removes defects associated with the manufacturing process, it can yield surface finishes (Ra) on the order of 10s of nanometers, it is a simple technology that could transfer easily to industry, it could help increase cavity yields and it requires less acid than other techniques. Recent progress and the current status of CBP as a baseline and repair technique will be discussed.

THIOA07	Single-cell SC Cavity Development in India	659
	A. Puntambekar, J. Dwivedi, P.D. Gupta, S.C. Joshi, G. Mundra, P. Shrivastava RRCAT, Indore (M.P.), India C.A. Cooper, M.H. Foley, T.N. Khabiboulline, C.S. Mishra, J.P. Ozelis, A.M. Rowe Fermilab, Batavia, USA P.N. Potukuchi IUAC, New Delhi, India G. Wu ANL, Argonne, USA
	Under Indian Institutions and Fermilab Collaboration (IIFC), Raja Ramanna Centre for Advanced Technology (RRCAT) Indore, India has initiated the development of SCRF cavity technology in collaboration with Fermi National Accelerator Laboratory (FNAL) USA. The R & D efforts are focused on the proposed Project-X accelerator complex at FNAL and High Intensity Proton Accelerator activities in India. As an initial effort, two prototype 1.3 GHz single cell bulk niobium cavities have been developed in collaboration with the Inter University Accelerator Centre (IUAC), New Delhi. Learning from the experience gained and the initial results of these prototypes (achieving Eacc ~23 MV/m), two more improved 1.3 GHz single cell cavities are being developed. These two improved single cell cavities will also be processed and tested at FNAL. Development of a 1.3 GHz, 5-cell SCRF cavity with simple end groups, development of end group, and fabrication of a single -cell 650 MHz (β=0.9) prototype cavity are being undertaken as the next stage in these efforts. This paper will present the development and test results on the 1.3 GHz single cell cavities and status of the ongoing work.
	Slides THIOA07 [2.937 MB]