SRF2011 - List of Authors (Wu, G.)

Paper

Title

Page

Guided Cavity Repair with Laser, E‐Beam and Grinding

597

G. Wu
ANL, Argonne, USA

Funding: Work supported by U.S. Department of Energy under contract # DEAC02-07CH11359
Recent cavity processing statistics indicate that the development of RF superconductivity has reached a stage where more and more cavities were limited by quench and not by field emissions. The combination of high resolution optical inspection, cavity quench detection and surface replica revealed more than half of the cavity quenches were limited by identifiable surface features, namely pits or bumps. The quench field ranged from 12.7 MV/m up to 42 MV/m. Several methods have been explored in various laboratories to remove the surface features. Those included the laser re-melting, Electron beam re-melting and local mechanical grinding. This paper reports the latest development of those guided repair technologies and their benefits to improve cavity performances.

Slides WEIOB01 [2.818 MB]

THPO015

Repair SRFCavity by Re-Melting Surface Defects via High Power Laser Technique

740

G.M. Ge
CLASSE, Ithaca, New York, USA
E. Borissov, L.D. Cooley, D.T. Hicks, T.H. Nicol, J.P. Ozelis, J. Ruan, D.A. Sergatskov
Fermilab, Batavia, USA
G. Wu
ANL, Argonne, USA

As the field emission is gradually under control in recent SRF activities, cavity performance is limited by hard quench in the most case. Surface defect has been identified as one of main reasons caused cavity quench scattering cavity accelerating gradient from 12 MV/m to 40 MV/m. Laser processing is able to re-shape the steep flaws to be flat and smooth surface. In Fermilab, a sophisticated laser repair system has been built for 1.3GHz low performance SRF cavity which is limited by surface defect. The pit in a 1.3GHz single-cell cavity was re-melted by high power laser pulse, cavity took 30 μm light Electropolishing after that. The gradient achieved 39MV/m in initial run; after another 30 μm Electropolishing, it achieved 40 MV/m. The improved laser repair system is able to re-melt the surface defect in one meter long 9-cell SRF cavity. It successfully re-melted a pit in 9-cell SRF cavity TB9ACC017.

THPO051

Laser Re-Melting Influence on Nb Properties: Geometrical and Chemical Aspects

846

A.V. Dzyuba, L.D. Cooley, E. Toropov
Fermilab, Batavia, USA
A.V. Dzyuba
NSU, Novosibirsk, Russia
G.M. Ge
CLASSE, Ithaca, New York, USA
G. Wu
ANL, Argonne, USA

We present recent results on Laser re-melting system used to smoothen niobium surfaces of superconducting RF cavities in order to overcome quench. In the work we studied both chemical and geometrical aspects of the melting by means of electron backscattered diffraction microscopy and laser confocal microscopy. BCP, EP and HF impacts have been investigated on both single and large grain niobium samples. Appropriate post processing has been suggested.

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]

THPO008

Post-Baking Losses in Niobium Cavities Studied by Dissection

710

A. Romanenko, L.D. Cooley, G. Wu
Fermilab, Batavia, USA
G. Ciovati
JLAB, Newport News, Virginia, USA

Thermometry investigations on electropolished cavities, which underwent mild baking, and are limited by a localized quench at 150-200 mT, show that in the absence of the high field Q-slope there are still a few localized sources of dissipation. Identification of these areas along with the high field quench location followed by dissection and surface analysis of the resulting coupons allowed to gain insight into possible mechanisms of these effects, and will be reported in this contribution.

Paper	Title	Page
WEIOB01	Guided Cavity Repair with Laser, E‐Beam and Grinding	597
	G. Wu ANL, Argonne, USA
	Funding: Work supported by U.S. Department of Energy under contract # DEAC02-07CH11359 Recent cavity processing statistics indicate that the development of RF superconductivity has reached a stage where more and more cavities were limited by quench and not by field emissions. The combination of high resolution optical inspection, cavity quench detection and surface replica revealed more than half of the cavity quenches were limited by identifiable surface features, namely pits or bumps. The quench field ranged from 12.7 MV/m up to 42 MV/m. Several methods have been explored in various laboratories to remove the surface features. Those included the laser re-melting, Electron beam re-melting and local mechanical grinding. This paper reports the latest development of those guided repair technologies and their benefits to improve cavity performances.
	Slides WEIOB01 [2.818 MB]

THPO015	Repair SRFCavity by Re-Melting Surface Defects via High Power Laser Technique	740
	G.M. Ge CLASSE, Ithaca, New York, USA E. Borissov, L.D. Cooley, D.T. Hicks, T.H. Nicol, J.P. Ozelis, J. Ruan, D.A. Sergatskov Fermilab, Batavia, USA G. Wu ANL, Argonne, USA
	As the field emission is gradually under control in recent SRF activities, cavity performance is limited by hard quench in the most case. Surface defect has been identified as one of main reasons caused cavity quench scattering cavity accelerating gradient from 12 MV/m to 40 MV/m. Laser processing is able to re-shape the steep flaws to be flat and smooth surface. In Fermilab, a sophisticated laser repair system has been built for 1.3GHz low performance SRF cavity which is limited by surface defect. The pit in a 1.3GHz single-cell cavity was re-melted by high power laser pulse, cavity took 30 μm light Electropolishing after that. The gradient achieved 39MV/m in initial run; after another 30 μm Electropolishing, it achieved 40 MV/m. The improved laser repair system is able to re-melt the surface defect in one meter long 9-cell SRF cavity. It successfully re-melted a pit in 9-cell SRF cavity TB9ACC017.

THPO051	Laser Re-Melting Influence on Nb Properties: Geometrical and Chemical Aspects	846
	A.V. Dzyuba, L.D. Cooley, E. Toropov Fermilab, Batavia, USA A.V. Dzyuba NSU, Novosibirsk, Russia G.M. Ge CLASSE, Ithaca, New York, USA G. Wu ANL, Argonne, USA
	We present recent results on Laser re-melting system used to smoothen niobium surfaces of superconducting RF cavities in order to overcome quench. In the work we studied both chemical and geometrical aspects of the melting by means of electron backscattered diffraction microscopy and laser confocal microscopy. BCP, EP and HF impacts have been investigated on both single and large grain niobium samples. Appropriate post processing has been suggested.

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]

THPO008	Post-Baking Losses in Niobium Cavities Studied by Dissection	710
	A. Romanenko, L.D. Cooley, G. Wu Fermilab, Batavia, USA G. Ciovati JLAB, Newport News, Virginia, USA
	Thermometry investigations on electropolished cavities, which underwent mild baking, and are limited by a localized quench at 150-200 mT, show that in the absence of the high field Q-slope there are still a few localized sources of dissipation. Identification of these areas along with the high field quench location followed by dissection and surface analysis of the resulting coupons allowed to gain insight into possible mechanisms of these effects, and will be reported in this contribution.