SRF2011 - List of Authors (Palczewski, A.D.)

Paper

Title

Page

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.

THPO017

Probing the Fundamental Limit of Niobium in High Radiofrequency Fields by Dual Mode Excitation in Superconducting Radiofrequency Cavities

746

G.V. Eremeev, R.L. Geng, A.D. Palczewski
JLAB, Newport News, Virginia, USA

Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We have studied thermal breakdown in several multicell superconducting radiofrequency cavity by simultaneous excitation of two TM010 passband modes. Unlike measurements done in the past, which indicated a clear thermal nature of the breakdown, our measurements present a more complex picture with interplay of both thermal and magnetic effects. JLab LG-1 that we studied was limited at 40.5 MV/m, corresponding to Bpeak = 173 mT, in 8pi9 mode. Dual mode measurements on this quench indicate that this quench is not purely magnetic, and so we conclude that this field is not the fundamental limit in SRF cavities.

Poster THPO017 [1.110 MB]

THPO018

Quench Studies of ILC Cavities

750

G.V. Eremeev, R.L. Geng, A.D. Palczewski
JLAB, Newport News, Virginia, USA
J. Dai
PKU/IHIP, Beijing, People's Republic of China

Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Quench limits accelerating gradient in SRF cavities to a gradient lower than theoretically expected for superconducting niobium. Identification of the quenching site with thermometry and OST, optical inspection, and replica of the culprit is an ongoing effort at Jefferson Lab aimed at better understanding of this limiting phenomenon. In this contribution we present our finding with several SRF cavities that were limited by quench.

Poster THPO018 [1.064 MB]

THPO019

Design, Construction, and Initial Test of High Spatial Resolution Thermometry Arrays for Detection of Surface Temperature Profiles on SRF Cavities in Super Fluid Helium

755

A.D. Palczewski, G.V. Eremeev, R.L. Geng
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We designed and built two high resolution (0.6-0.55mm special resolution [1.1-1.2mm separation]) thermometry arrays prototypes out of the Allen Bradley 90-120 Ω 1/8 watt resistor to measure surface temperature profiles on SRF cavities. One array was designed to be physically flexible and conform to any location on a SRF cavity; the other was modeled after the common G-10/stycast 2850 thermometer and designed to fit on the equator of an ILC (Tesla 1.3GHz) SRF cavity. We will discuss the advantages and disadvantages of each array and their construction. In addition we will present a case study of the arrays performance on a real SRF cavity TB9NR001. TB9NR001 presented a unique opportunity to test the performance of each array as it contained a dual (4mm separation) cat eye defect which conventional methods such as OST (Oscillating Superleak second-sound Transducers) and full coverage thermometry mapping were unable to distinguish between. We will discuss the new arrays ability to distinguish between the two defects and their preheating performance.

THPO020

Exploration of Quench Initiation Due to Intentional Geometrical Defects in a High Magnetic Field Region of an SRF Cavity

759

J. Dai, K. Zhao
PKU/IHIP, Beijing, People's Republic of China
G.V. Eremeev, R.L. Geng, A.D. Palczewski
JLAB, Newport News, Virginia, USA

Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
A computer program which was used to simulate and analyze the thermal behaviors of SRF cavities has been developed at Jefferson Lab using C++ code. This code was also used to verify the quench initiation due to geometrical defects in high magnetic field region of SRF cavities. We built a CEBAF single cell cavity with 4 artificial defects near equator, and this cavity has been tested with T-mapping. The preheating behavior and quench initiation analysis of this cavity will be presented here using the computer program.
daijin@pku.edu.cn

THPO071

Detailed Surface Analysis of Incremental Centrifugal Barrel Polishing (CBP) of Single-Crystal Niobium Samples

908

A.D. Palczewski, C.E. Reece, H. Tian, O. Trofimova
JLAB, Newport News, Virginia, USA

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We performed Centrifugal Barrel Polishing (CBP) on single crystal niobium samples housed in a stainless steel sample holder following a polishing recipe recently developed at FNAL [*]. We were able to obtain a mirror-like finish after the final stage of tumbling, although some defects and imbedded particles remain. Our presentation will discuss the initial results from the coupon study, including qualitative and quantitative analysis of the surface characteristics from each step in the CBP process, followed by HPR and well controlled incremental EP. These will include surface roughness, size and character of contaminants, surface crystal structure, and overall finish. We will discuss how the surface characteristics should guide the SRF community in exploiting or adapting the Fermi recipe; including why minimal subsequent EP is needed, and possible places for modification of the recipe to reduce polishing time.
* CA Cooper, LD Cooley , “Mirror Smooth Superconducting RF Cavities by MechanicalPolishing with Minimal Acid Use,” http://lss.fnal.gov/archive/2011/pub/fermilab-pub-11-032-td.pdf, (May 31, 2011)

Paper	Title	Page
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.

THPO017	Probing the Fundamental Limit of Niobium in High Radiofrequency Fields by Dual Mode Excitation in Superconducting Radiofrequency Cavities	746
	G.V. Eremeev, R.L. Geng, A.D. Palczewski JLAB, Newport News, Virginia, USA
	Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We have studied thermal breakdown in several multicell superconducting radiofrequency cavity by simultaneous excitation of two TM010 passband modes. Unlike measurements done in the past, which indicated a clear thermal nature of the breakdown, our measurements present a more complex picture with interplay of both thermal and magnetic effects. JLab LG-1 that we studied was limited at 40.5 MV/m, corresponding to Bpeak = 173 mT, in 8pi9 mode. Dual mode measurements on this quench indicate that this quench is not purely magnetic, and so we conclude that this field is not the fundamental limit in SRF cavities.
	Poster THPO017 [1.110 MB]

THPO018	Quench Studies of ILC Cavities	750
	G.V. Eremeev, R.L. Geng, A.D. Palczewski JLAB, Newport News, Virginia, USA J. Dai PKU/IHIP, Beijing, People's Republic of China
	Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Quench limits accelerating gradient in SRF cavities to a gradient lower than theoretically expected for superconducting niobium. Identification of the quenching site with thermometry and OST, optical inspection, and replica of the culprit is an ongoing effort at Jefferson Lab aimed at better understanding of this limiting phenomenon. In this contribution we present our finding with several SRF cavities that were limited by quench.
	Poster THPO018 [1.064 MB]

THPO019	Design, Construction, and Initial Test of High Spatial Resolution Thermometry Arrays for Detection of Surface Temperature Profiles on SRF Cavities in Super Fluid Helium	755
	A.D. Palczewski, G.V. Eremeev, R.L. Geng JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We designed and built two high resolution (0.6-0.55mm special resolution [1.1-1.2mm separation]) thermometry arrays prototypes out of the Allen Bradley 90-120 Ω 1/8 watt resistor to measure surface temperature profiles on SRF cavities. One array was designed to be physically flexible and conform to any location on a SRF cavity; the other was modeled after the common G-10/stycast 2850 thermometer and designed to fit on the equator of an ILC (Tesla 1.3GHz) SRF cavity. We will discuss the advantages and disadvantages of each array and their construction. In addition we will present a case study of the arrays performance on a real SRF cavity TB9NR001. TB9NR001 presented a unique opportunity to test the performance of each array as it contained a dual (4mm separation) cat eye defect which conventional methods such as OST (Oscillating Superleak second-sound Transducers) and full coverage thermometry mapping were unable to distinguish between. We will discuss the new arrays ability to distinguish between the two defects and their preheating performance.

THPO020	Exploration of Quench Initiation Due to Intentional Geometrical Defects in a High Magnetic Field Region of an SRF Cavity	759
	J. Dai, K. Zhao PKU/IHIP, Beijing, People's Republic of China G.V. Eremeev, R.L. Geng, A.D. Palczewski JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 A computer program which was used to simulate and analyze the thermal behaviors of SRF cavities has been developed at Jefferson Lab using C++ code. This code was also used to verify the quench initiation due to geometrical defects in high magnetic field region of SRF cavities. We built a CEBAF single cell cavity with 4 artificial defects near equator, and this cavity has been tested with T-mapping. The preheating behavior and quench initiation analysis of this cavity will be presented here using the computer program. daijin@pku.edu.cn*

THPO071	Detailed Surface Analysis of Incremental Centrifugal Barrel Polishing (CBP) of Single-Crystal Niobium Samples	908
	A.D. Palczewski, C.E. Reece, H. Tian, O. Trofimova JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We performed Centrifugal Barrel Polishing (CBP) on single crystal niobium samples housed in a stainless steel sample holder following a polishing recipe recently developed at FNAL []. We were able to obtain a mirror-like finish after the final stage of tumbling, although some defects and imbedded particles remain. Our presentation will discuss the initial results from the coupon study, including qualitative and quantitative analysis of the surface characteristics from each step in the CBP process, followed by HPR and well controlled incremental EP. These will include surface roughness, size and character of contaminants, surface crystal structure, and overall finish. We will discuss how the surface characteristics should guide the SRF community in exploiting or adapting the Fermi recipe; including why minimal subsequent EP is needed, and possible places for modification of the recipe to reduce polishing time. CA Cooper, LD Cooley , “Mirror Smooth Superconducting RF Cavities by MechanicalPolishing with Minimal Acid Use,” http://lss.fnal.gov/archive/2011/pub/fermilab-pub-11-032-td.pdf, (May 31, 2011)