environmental effects on the performance of high efficiency srf cavities ganapati myneni & jlab...
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Environmental effects on the performance of high efficiency SRF
cavities
Ganapati Myneni
& JLab
ALCW15-SRF-WGKEK, Tsukuba, Japan
April 24, 2015
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IntroductionContamination from environment surrounding the SRF cavities always limits the performance of the linacs at all stages
• Intrinsic and extrinsic contamination
• Flux trapping
• Potential remedies
• Conclusions
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Environmental contamination of Nb surfaces determines the performance of the cavities
• Surface contamination– Molecular and
particulate
• During cavity processes• Cryomodule assembly• Operations (field
emission enhancement)
• Magnetic flux trapping
• Niobium is a prolific hydrogen absorber in the absence of the natural surface oxide
– Hydride formation (Ti and N alloying help to prevent hydrides) – Dislocations (residual
stress)
Extrinsic Intrinsic
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Oil contamination and vacuum leaks
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Cavity surface contamination with pump oils
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Multipactoring problem
CEBAF Single cell cavity, large grain CBMM ingot "B"
1E+09
1E+10
1E+11
0 5 10 15 20 25 30Eacc [MV/m]
Q0
Problem with MultipactingLeaking valve on test-stand replaced
T=1.7K
14
710
1316
1922
2528
3134
S1S3
S5S7
S9 S11 S1
3 S15
0
0.04
0.08
0.12
0.16
0.2
0.24
T (K)
AzimuthBottom Iris
Top Iris
Equator
Q0 = 2.8 109
Eacc = 11 MV/m
T-map showing MP at equator
Gigi Ciovati
Re-contaminating vacuum systems drastically degrade the performance of the cavities
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Particulates collected from cavities
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Particulates in the Cavity Pair
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Evacuation is the Final Process step
Recontamination from vacuum systems is a major problem with SRF linacs
Ion-Turbo systemcross contamination,particulate & hydro carbon problems
Improved turbo pump system with minimumcontamination
Schematic of the cavitytest system
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Comparison of oil and oil free vacuum systems
Minimizing organic and particulate recontamination is crucial
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JLab’s FEL was the first SRF linac that implemented contamination control procedures
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Cavity ion pump particulates
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Ion Pump particulates
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High pressure water/steam wash of all components
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Contamination control workshopwas organized by Jlab - March 1997
JLab and DESY procedures werereviewed during the first decadeof 21st century
CEA Saclay’s 2014 workshopresurrected the contamination controlstrategies
ILC project needs to convene periodicreview of environmental effects as it requires very high gradientsustainability at high Q’s
Re-contamination prevention short courses were organized at JLab in 1997, 2000 and 2005
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Active NEG backed turbo pump
Low contamination pumping system with nano filter gas inlet and high sensitivity He leak detection <1e-12 atm ccs-1
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JLab-VCU magnetization studies
In press
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Low RRR uniform grain niobium ingot slice
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Conclusions• Contamination free vacuum systems &
particulate free components and processes are crucial for creating and sustaining high performance SRF linacs
• Magnetic shielding sub-systems must be annealed for minimizing the trapped flux
• Uniform grained ingot niobium technology can be expected to generate high performance, low cost and sustainable SRF accelerator systems
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International Symposium On Hydrogen In Matter (ISOHIM)
Publications Hydrogen in Materials and Vacuum Systems AIP CP 671
http://www.virtualjournals.org/dbt/dbt.jsp?KEY=APCPCS&Volume=671&Issue=1
Hydrogen in Matter AIP CP 837http://www.virtualjournals.org/dbt/dbt.jsp?KEY=APCPCS&Volume=837&Issue=1
Single Crystal Large Grain Niobium AIP CP 927http://www.virtualjournals.org/dbt/dbt.jsp?KEY=APCPCS&Volume=927&Issue=1
Superconducting Science and Technology of Ingot Niobium AIP CP 1352 http://scitation.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1352&Issue=1
Science and Technology of Ingot Niobium for Superconducting Radio Frequecy Applications to be released Dec 2015
Slide 21
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Worldwide network of collaborators
Tadeu Carneiro, Rogerio Ribas, Marcos Stuart – CBMM ingot niobium technologyF. Stevie, P. Maheswari (grad student), D. Griffis – NCSU niobium surface scienceR. Ricker – NIST
hydrogen-niobium systemJ. Wallace – Casting Analysis Corporation co-PI DOE ONP ARRA
Q0 improvement program
Björgvin Hjörvarsson – Uppsala University hydrogen-niobium system
B. Lanford – UNY, Albanynuclear reaction analysis
R. Pike and summer student interns – W&M XRD analysis of niobiumHani Elsayed-Ali, Ashraf Hassan Farha (grad student) – ODU niobium nitride Asavari Dhavale & J. Mondal (grad students) – BARC/HBNI ingot niobium propertiesSindhunil Roy – RRCAT
SC properties of niobiumSaravan Chandrasekaran – MSU ingot
niobium properties
International Symposium On Hydrogen In Matter (ISOHIM) non profit organization for
education/trainingAcknowledgements to all colleagues at JLab