q-slope at high gradients ( niobium cavities ) review about experiments and explanations
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Q-Slope at High GradientsQ-Slope at High Gradients ( Niobium Cavities ) ( Niobium Cavities )
Review about ExperimentsReview about Experimentsand Explanationsand Explanations
Bernard VISENTIN CEA - SaclayBernard VISENTIN CEA - Saclay
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
2
IntroductionIntroduction
Q degradation at high accelerating fieldsQ degradation at high accelerating fields
Empirical Cure with cavity bakingEmpirical Cure with cavity baking
Problem only push away fartherProblem only push away farther
Understand Q-slope origin Understand Q-slope origin
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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OutlineOutline
Q-Q-Slope : Definition and FeaturesSlope : Definition and Features
Baking EffectBaking EffectExperimental Observations ( Q slope - RBCS - Rres ) Standard Chemistry ( BCP ) and Electropolishing ( EP )Consequences on Nb Surface ( diffusion process – oxides – BC )
Theoretical ModelsTheoretical ModelsDifferences between BCP & EPInterface OxideSuperconducting Parameters Change
Experiments Experiments Models Models
ConclusionConclusion
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Q-Slope : Definition and FeaturesQ-Slope : Definition and Features
quality factor quality factor strong degradation strong degradation
EEaccacc > 20 MV/m> 20 MV/m TTF cavities ( B TTF cavities ( Bpp > 85 mT ) > 85 mT ) field emission not involved ( field emission not involved ( no e no e --, no X rays, no X rays ) ) T map : T map : global heatingglobal heating ( B ( Bpp max ) max ) limitation by RF power supply or quenchlimitation by RF power supply or quench seemingly a typical feature of seemingly a typical feature of BCPBCP cavities cavities
““European Headache”European Headache”
superiority of superiority of EPEP
without Q-slopewithout Q-slope
( E. Kako et al. - SRF ’99 - Santa Fe )
( L. Lilje et al. - SRF ’99 - Santa Fe )
K. Saïto et al.
SRF ’97
( Abano Terme )
( Nb 1-cell cavity )
C1-03 / S-3 ( EP cavity )KEK 3
1E+9
1E+10
1E+11
0 10 20 30Eacc ( MV/m )
Q0
quench
1E+09
1E+10
1E+11
0 10 20 30Eacc (MV/m)
Q0
C1-16 ( 1.3 GHz )
no electronsno X-rays
RFpower
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking Effect on BCP Cavities Baking Effect on BCP Cavities ( Q ( Q slopeslope – R – RBCSBCS – R – Rresres ) )
““in-situ” baking discovered on in-situ” baking discovered on BCPBCP cavity cavity
slope improvement ( 90 < T < 120°C ) - degradation ( T > slope improvement ( 90 < T < 120°C ) - degradation ( T > 150°C ) 150°C )
C1-05 ( BCP cavity )
1E+08
1E+09
1E+10
1E+11
0 10 20 30Eacc ( MV/m )
Q0
no baking90°C - 48h110°C - 48h4.2 K (no baking)4.2 k ( 90°C )4.2 K ( 110°C )
quench
( B. Visentin et al. – EPAC ’1998 - Stockholm )
C1-05 ( BCP cavity )
1
10
100
1000
0,2 0,3 0,4 0,5 0,6 0,7
1/T ( K -1 )
RS
(nW)
no baking
90°C - 48h
110°C - 48h
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking Effect on EP CavitiesBaking Effect on EP Cavities
Same phenomenon on Same phenomenon on E.P.E.P. cavities cavities
before baking: Q-slope identical to BCP
after baking : Q-slope improvement
C1-03 / S-3 ( EP cavity )KEK 9 & 10
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
no baking
110°C / 30h
quenchRF powerlimitationapparent superiority of EP reported before ?
cleaning procedure at KEK
wet cavities ( High Power Rinsing )
directly pumped out and baked at 85°C/20h
to accelerate pumping speed ( Saclay cavity – EP & tested @ KEK )
1E+09
1E+10
1E+11
1E+12
0 10 20 30 40Eacc (MV/m)
Q0
C1-03 / S-3 ( EP - KEK 9 )D1-22 ( EP - Saclay A1 )C1-15 ( BCP - Saclay I1 )C1-16 ( BCP - Saclay P1 )C1-10 ( BCP - Saclay N1 )
Q-slopes before baking ( BCP and EP cavities )
RF PowerLimit
P. Kneisel. – TUP 044
K. Saïto. – TUP 031
L. Lilje et al. – TUA 001
B. Visentin et al. – TUP 015
SRF ’ 99
Santa Fe
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Surface Re-Oxidation after Baking ?Surface Re-Oxidation after Baking ?
Unaltered Q-slopeUnaltered Q-slope
after after Air Air exposure ( 3 hours to 2 months ) followed by exposure ( 3 hours to 2 months ) followed by :
High PressureHigh Pressure Water Water Rinse + Drying ( laminar flow – 3 h ) Rinse + Drying ( laminar flow – 3 h )
- standard conditioning for RF tests -- standard conditioning for RF tests -
3 hours ( cavity closed )
8 hours ( cavity closed )
RF test bench
1 day ( cavity closed )
9 days ( cavity open )
( under laminar-flow : class 10 )
in clean-room
2 months ( cavity open )
left on the shelf
D1-22 ( EP cavity )
1E+08
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
A1 - no bakingA2 - baking in situ 100°C /48hA7 - air exposure 1day + HPRA10 - air exposure 2month + HPR
quench
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking at the Atmospheric Pressure ?Baking at the Atmospheric Pressure ?
BCP + High Pressure RinseBCP + High Pressure Rinse
WetWet Cavity inside Drying Oven ( 110°C / 60 h ) Cavity inside Drying Oven ( 110°C / 60 h )
@ Atm. Pressure - no pumping @ Atm. Pressure - no pumping
new H.P.R. for RF testnew H.P.R. for RF test
BCP Cavity ( C1-10 )
Q-slope improvement
similar to “in-situ baking”
( B. Visentin et al. – this workshop )
1E+09
1E+10
1E+11
0 10 20 30Eacc (MV/m)
Q0
C1-10 O1 ( BCP )
C1-10 S1 ( BCP + baking @ Atm. Press. )
Quenchnon "in-situ" baking
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Differences between BCP and EPDifferences between BCP and EP higher efficiency of baking on EP cavities ( from 85°C )higher efficiency of baking on EP cavities ( from 85°C ) residual slope on BCP cavities even with baking ( 120°C )residual slope on BCP cavities even with baking ( 120°C )
higher quench field for EP cavities ( 40 MV/m )higher quench field for EP cavities ( 40 MV/m )
surface roughnesssurface roughness
( R.L. Geng et al. - SRF ’99 – Santa Fe )
BCP ( 117 m ) EP ( 90 m )
5-9 m ( statistic on step height) 2-5 m
100 100 mm100 100 mm
C1-10 ( BCP cavity )N 1 & 2
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
no baking
120°C / 60h
quench
RF powerlimitation
C1-03 / S-3 ( EP cavity )KEK 9 & 10
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
no baking
110°C / 30h
quenchRF powerlimitation
BCP
EP
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Some Exceptions ( ? )Some Exceptions ( ? )
TotalTotal removal of Q-slope after baking ( removal of Q-slope after baking ( BCPBCP cavities ) cavities )( with or without quench fields at 40 MV/m )
1E+09
1E+10
1E+11
1E+12
0 10 20 30 40Eacc (MV/m)
Q0
C1-03 / S-3 ( EP - KEK 10 )
C1-15 ( BCP - Saclay I2 )
C1-16 ( BCP - Saclay P2 ) Quench
( B. Visentin et al. – EPAC’2002 – Paris & this workshop )
Two Nb cavities : C1-15 & C1-16 ( BCP + 120°C/60h )
C1-15 ( inner surface )
not very smooth
large grains : 2-3 mm2
high steps : 4 to 8 m
( W. Singer et al. – SRF ’2001 - Tsukuba )
One NbCu clad cavity : 1NC2 ( BCP + 140°C/30h )
1 cm1 cm( P. Kneisel et al. – SRF ’1995 – Gif/Yvette )
Nb cavity “defect free” : ( BCP but no baking specified )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking Consequences on Nb Surface (1)Baking Consequences on Nb Surface (1)
RRBCSBCS ( T ( Tbakebake ) : ) : R RBCSBCS ( baking time ) ( baking time ) saturation
diffusion process
( 300 nm )
( P. Kneisel - SRF ’99 - Santa Fe )
kTFLBCS e
TAR
2
,,
L = 31 nm
F = 62 nm
= 1.46 meV
T = 4.2 K
RBCS @ T = 4.2 K
Tbake = 145°C
400
500
600
700
800
900
1000
1 10 100 1000 10000
( nm )
RBCS
( nW )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking Consequences on Nb Surface (2)Baking Consequences on Nb Surface (2)
Influence of oxide layers on Nb surface resistanceInfluence of oxide layers on Nb surface resistance
( Nb( Nb22OO55 and NbO ) and NbO )
Oxygen can diffuse at low temperature Oxygen can diffuse at low temperature
Change Change
of the structure oxide of the structure oxide
after baking after baking
( Nb( Nb22OO55 and NbO - NbO and NbO - NbO0.20.2 ) )
( F. Palmer – IEEE Trans. Mag. - 1987 )
C. Antoine et al. - SRF ’99 - Santa Fe
A. Dacca et al. - Applied Surf. Science - 1998
Q. Ma et al. - SRF ’01 - Tsukuba ( A. Daccà - sample 4 - T=150°C )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Baking Consequences on Nb Surface (3)Baking Consequences on Nb Surface (3)
Surface Magnetic Field : Surface Magnetic Field : ( B. Steffen - TTF Meeting - 2003 )
Susceptibility measurements ( on sample )
Surface field : BC3surf = 1.7 BC2
bulk
larger field for EP compare to BCP
All values are increased by baking
( interpreted by enhancement of impurities : O ? )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Experiments ModelsExperiments Models
Difference ( EP/BCP )Difference ( EP/BCP )
Surface RoughnessSurface Roughness
( grain boundaries )( grain boundaries )
Modification ofModification of
Interface Oxide / MetalInterface Oxide / Metal
( Oxygen Diffusion )( Oxygen Diffusion )
Change of Change of
Superconducting ParametersSuperconducting Parameters
( R( RBCSBCS , B , BCC … ) … )
Magnetic Field Enhancement Magnetic Field Enhancement
Interface Tunnel ExchangeInterface Tunnel Exchange
Thermal FeedbackThermal Feedback
Magnetic Field Dependence of Magnetic Field Dependence of
Granular Superconductivity Granular Superconductivity
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Theoretical Models Theoretical Models Experiments Experiments
1E+09
1E+10
1E+11
1E+12
0 10 20 30 40Eacc (MV/m)
Q0
C1-03 / S-3 ( EP - KEK 10 )
C1-15 ( BCP - Saclay I2 )
C1-16 ( BCP - Saclay P2 ) Quench
1E+09
1E+10
1E+11
1E+12
0 10 20 30 40Eacc (MV/m)
Q0
C1-03 / S-3 ( EP - KEK 9 )D1-22 ( EP - Saclay A1 )C1-15 ( BCP - Saclay I1 )C1-16 ( BCP - Saclay P1 )C1-10 ( BCP - Saclay N1 )
Q-slopes before baking ( BCP and EP cavities )
RF PowerLimit
Q-Slope
Fit
Slope before baking ( EP BCP )
Slope Improvement after baking
No change after 2 m.
air exposure
Slope after baking ( EP < BCP )
Exceptional Results ( BCP )
Quench ( EP > BCP )
BCP Quench unchanged
after baking
D1-22 ( EP cavity )
1E+08
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
A1 - no bakingA2 - baking in situ 100°C /48hA7 - air exposure 1day + HPRA10 - air exposure 2month + HPR
quench
C1-03 / S-3 ( EP cavity )KEK 9 & 10
1E+09
1E+10
1E+11
0 10 20 30 40Eacc ( MV/m )
Q0
no baking
110°C / 30h
quenchRF power
limitation
C1-05 ( BCP cavity )
1E+08
1E+09
1E+10
1E+11
0 10 20 30Eacc ( MV/m )
Q0
no baking
90°C - 48h
110°C - 48h quench
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Magnetic Field Enhancement at G.B.Magnetic Field Enhancement at G.B.( J. Knobloch - SRF ’99 - Santa Fe ) microstructure on RF surface
( surface roughness - step height 10 m )
magnetic field enhancement
normal conducting region if
factor ( BCP )
Hm
Cm HH
5.26.1 m
( K. Saïto - PAC ’2003 - Portland )
EP : ( HC/m= 223 mT ) m=1
BCP : ( HC/m = 95 mT ) m=2.34electromagnetic code + thermal simulation Q0(Eacc)
Q-slope origin
the most dissipative G.B. quench (equator)
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Comments ( H - enhancement )Comments ( H - enhancement )
Explanations :Explanations :
Q-slope for BCP before baking ( good simulation )
Q-slope improvement after baking ( HC )
better slope for EP after baking ( m lower ~ 1 )
Not consistent with :Not consistent with :
slope before baking for EP cavities
( same slope with m lower and HC higher than BCP )
flat slope ( and 40 MV/m ) on BCP cavities C1-15 & C1-16
( roughness : 4 to 8 m > 2 m high m )
quench value unchanged for BCP after baking ( in spite of HC )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Interface Tunnel ExchangeInterface Tunnel Exchange
( J. Halbritter - SRF ’01 – Tsukuba )
( IEEE Trans. on Appl. Supercond. 11, 2001 )
RF field on
metallic surface
metalcleanfornegligibleZemissionelectroncausesE
seriesTaylorHHRRZHE
CHH ...1 22*0
Dielectric oxide layer on metal enhancement of ZE by I.T.E.
( localized states of Nb2O5-y and density of state of Nb )
with electron diffusion at NbOx - Nb2O5-y interface
I.T.E. quantitative description of Q-slope
E
C
E eR*
80:
:* ERRbyfittednallyconvention
factortenhancemenfieldelectricE
ITE reduction by :
•smoothening surface ( EP )
( * and E° )
•baking : Nb2O5-y vanished - better interface
( reduction of localised states )
valueonsetEatstarting
1E+09
1E+10
1E+11
0 10 20 30Eacc (MV/m)
Q0
C1-16 ( 1.3 GHz )
no electronsno X-rays
RFpower
RH
RE
E°
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Comments ( I.T.E. )Comments ( I.T.E. )
Explanations :Explanations :
Q-slope improvement after baking ( Nb2O5 )
better slope for EP after baking ( smooth surface - lower * )
Not consistent with :Not consistent with :
similar slopes ( before baking ) for EP and BCP cavities
( surface roughness and * are different )
unaltered slope after a surface re-oxidation ( Nb2O5 - 2 months later )
exceptional flat slopes on BCP cavities C1-15 & C1-16 ( in spite of roughness : 4 to 8 m - higher * )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Thermal FeedbackThermal Feedback
Temperature Dependence of Surface ResistanceTemperature Dependence of Surface Resistance
TT
RTRTRHRPRTH S
SSSSdissthermS
)()(2/ 02
( V. Kurakin - EPAC’94 - London )
( E. Haebel - TTF Meeting - 1998 )
).1( 2
0
acc
SS EC
TRTR
2
0 . accS EbaRGQ
T
RC
mVC
S8
215
10.2
/10.1fit parameter :
( B.V. et al. SRF’99 - Santa Fe )
T
R
h
eC S
KNb
Nb
9
2
0
9
10.2
110.4
2
1
baking effect :
kTFLBCS e
TAR
2
,,
AT
RS
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Energy Gap DependenceEnergy Gap Dependence
Exponential variation Exponential variation
kTeT
ARQGR FLresS
2
0 ),,(
magnetic field dependence of
2210 CHHH
( A. Didenko - EPAC ’ 96 - Sitges )
( V. Mathur et al. - Phys. Rev. Let. 9, 374 - 1962 )
only rigorous and experimentally proved
for thin films
( normal state transition 2nd order if d/ < 51/2 )
for T/TC < 0.36
for bulk material ( d >> )
(H) : few % variation
BC = 180 mT BC = 195 mT
BC “fit factor”
Rres, A, (0) from RS(1/T) at low field
( B.V. et al. - EPAC ’ 98 - Stockholm )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Granular SuperconductivityGranular Superconductivity
( H. Safa et al. – SRF ’99 – Santa Fe )
Grain Boundaries contribution to surface resistance ?Grain Boundaries contribution to surface resistance ?
( polycrystalline nature of Nb ) - Grain Boundary weak link ( Josephson junction )
( B. Bonin and H. Safa - Superc. Sci. Tech. 4, 1991 )
Theory valid for sputtered thin films
effect negligible for bulk niobium ( grains ~ 10m ) :
exception :
segregation of impurities located at grain boundaries
Difficulties to apprehend the baking as a way to clean G.B.Difficulties to apprehend the baking as a way to clean G.B.
( low temperature - diffusion O )
Experiment on Grain Boundaries Specific Resistance
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Similarities EP / Similarities EP / BCPBCP
Q-Slope
Fit
Slope before baking ( EP BCP )
Slope Improvement after baking
Slope after baking ( EP < BCP )
No change after 2 m.
air exposure
Exceptional Results ( BCP )
Quench ( EP > BCP )
BCP Quench unchanged
after baking Validity
Magnetic Field
Enhancement
YY
NN ( m et HC )
YY ( HC )
YY ( m < ; HC > )
-- NN ( high m )
YY ( m < ; HC > )
NN ( HC )
YY
Interface Tunnel
Exchange YY ( E8 )
NN ( )
YY ( Nb2O5-y )
YY ( low )
NN ( Nb2O5-y )
NN ( high )
-- --
YY
Thermal Feedback YY
( parab. )
YY
YY ( RBCS Rres )
NN
--
NN
-- -- NN ( coeff. C )
Magnetic Field
Dependence of
YY ( expon. )
NN ( HC )
YY ( HC )
YY ( HC > )
--
NN
-- -- NN ( thin film )
Segregation of Impurities -- NN
( segreg. )
NN ( only O )
-- -- YY ( cleaning )
-- --
YY
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Experimental Program at J.Lab.Experimental Program at J.Lab.
“ “ H enhancement at grain bound. ” H enhancement at grain bound. ” “ Interface Tunnel “ Interface Tunnel Exchange ”Exchange ”
• Single cell cavity ( BCP - EP - w/o Baking ) excited in modes TM010 or TM011 : HS
• Two cell cavity TM010 ( 0- mode ) : scan the surface ( E, H )
• Q0 ( Bpeak ) - ( BCP - EP - w/o Baking )
• Preliminary results :( G. Ciovati et al. - PAC ’ 2003 - Portland )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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ConclusionConclusion
Experiments and Models have to progress in the futureExperiments and Models have to progress in the futureto understand the phenomenon and to cure itto understand the phenomenon and to cure it
all the more so since Q-slope is not totally removed by baking Q-slope is not totally removed by baking ( even for EP cavities )( even for EP cavities )
if quench improvement possible ( > 40 MV/m ) Q-slope appearance
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
0 500 1000 1500 2000
E2acc
( MV/m )
R/R0
D1-22 ( EP - Saclay A2 )C1-03 ( EP - KEK 10 )C1-15 ( BCP - Saclay I2 )C1-16 ( BCP - Saclay P2 )C1-10 ( BCP - Saclay N2 )
High-Field Slopes after baking
( BCP and EP cavities )
0
1
2
3
4
5
6
7
8
9
0 500 1000 1500 2000
E2acc
( MV/m )2
R/R0
D1-22 ( EP - Saclay A1 )
C1-03 ( EP - KEK 9 )
C1-15 ( BCP - Saclay I1 )
C1-16 ( BCP - Saclay P1 )
C1-10 ( BCP - Saclay N1 )
High-Field Slopes before baking
( BCP and EP cavities )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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Papers at this WorkshopPapers at this Workshop Q-slope
A Review of High-Field Q-Slope Studies at Cornell - H. Padamsee et al. ( Mo-P14 )Why does the Q-slope of a Nb cavity change…? - I.V. Bazarov et al. ( Th-P02 )Q-slope analysis of niobium SC RF cavities - K Saito ( Th-P19 )Q-Slope : Comparison BCP and EP - Modification by Plasma… - B. Visentin et al. ( Mo-P19 )
Baking
A Pleasant Surprise: Mild Baking Gives Large Improvement… - G. Eremeev et al. ( Mo-P18 )Low temperature heat treatment effect on high-field EP cavities - J. Hao et al. ( Mo-P16 )Effect of low temperature baking on niobium cavities - G. Ciovati et al. ( We-O14 )
Surface Analysis
In situ XPS investigation of the baking effect … - K Kowalski et al. ( Th-P09 ) Near-Surface Composition of Electropolished Niobium … - A.M. Valente et al. ( Mo-P15 )Grain boundary specific resistance and RRR measurements… - S. Berry et al. ( Th-P03 )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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0
10
20
30
40
50
60
70
0 200 400 600 800 1000 1200 1400 1600 1800
E2acc ( MV/m )2
R/R0 D1-22 ( EP - Saclay A1 )
C1-03 ( EP - KEK 9 )
C1-15 ( BCP - Saclay I1 )
C1-16 ( BCP - Saclay P1 )
C1-10 ( BCP - Saclay N1 )
High-Field Slopes before baking
( BCP and EP cavities )
0
1
2
3
4
5
6
7
8
9
0 200 400 600 800 1000 1200 1400 1600 1800
E2acc ( MV/m )2
R/R0 D1-22 ( EP - Saclay A2 )C1-03 ( EP - KEK 10 )C1-15 ( BCP - Saclay I2 )C1-16 ( BCP - Saclay P2 )C1-10 ( BCP - Saclay N2 )Théorie
High-Field Slopesafter baking
( BCP and EP cavities )
0
1
2
3
4
5
6
7
8
9
0 200 400 600 800 1000 1200 1400 1600 1800
E2acc ( MV/m )2
R/R0 D1-22 ( EP - Saclay A1 )
C1-03 ( EP - KEK 9 )
C1-15 ( BCP - Saclay I1 )
C1-16 ( BCP - Saclay P1 )
C1-10 ( BCP - Saclay N1 )
High-Field Slopes before baking
( BCP and EP cavities )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
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HH22-slope ( Intermediate Fields )-slope ( Intermediate Fields )
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
0 200 400 600 800 1000 1200 1400 1600 1800
E2acc
( MV/m )2
R/R0
D1-22 ( EP - Saclay A2 )C1-03 ( EP - KEK 10 )C1-15 ( BCP - Saclay I2 )C1-16 ( BCP - Saclay P2 )C1-10 ( BCP - Saclay N2 )Théorie
High-Field Slopesafter baking
( BCP and EP cavities )
OeH
HHR
R
C
C
20003.3*
22*0
1E+09
1E+10
1E+11
1E+12
0 10 20 30 40Eacc (MV/m)
Q0
D1-22 ( EP - Saclay A2 )C1-03 / S-3 ( EP - KEK 10 )C1-15 ( BCP - Saclay I2 )C1-16 ( BCP - Saclay P2 )C1-10 ( BCP - Saclay N2 ) Quench
Q-slopes after baking ( BCP and EP cavities )
22*0 1 CH HHRR
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
29
Surface Treatment by PlasmaSurface Treatment by Plasma
Correlation between O and Q-slope Correlation between O and Q-slope
preliminary results of recent experiment
surface treatment of Nb cavity by oxygen plasma
( RCE discharge - E O+~50 eV - no sputtering )
ionic implantation & diffusion
XPS sample analysis show NB2O5
O2 : 5.10-3 mbar
f = 2.45 GHz
B = 875 G
PRF : 1500 W
time : 1/2 hour
Tsurface < 80°C
C1-17 O/P BCP Cavity
1,E+09
1,E+10
1,E+11
0 5 10 15 20 25 30
Eacc (MV/m )
Q0
Standard BCP
After O plasma
( B. Visentin et al. – this workshop )
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
30
Quench position on BCP cavitiesQuench position on BCP cavities
1
3
5
7
9
11
13
15
17
30
40
51
61
72
82
92
10
0
04008001200160020002400280032003600400044004800520056006000
T (mK)
Thermal SensorPosition
( degree )
C1-17 ( S1 )
181
199
215
231
1 2 3 4 5 6 7 8 91
01
11
21
31
41
51
61
7
0400800
12001600200024002800
3200
3600
4000
4400
4800
5200
5600
T (mK)
Position(degree )Thermal Sensor
C1-17 ( Q1 )
Quench Position
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0 90 180 270 360 Position ( degree )
Th
erm
al s
en
so
r (
1:1
cm
) C1-10
C1-15
C1-17
upper iris
lower iris
equator - EB weld ( 5 mm )
11
10
9
EB weld
SRF’2003 ( 11 SRF’2003 ( 11 thth Workshop ) Workshop ) Q-Slope at High GradientsQ-Slope at High Gradients Bernard VisentinBernard Visentin
31
Frequency Dependence of Q-slope Frequency Dependence of Q-slope
1E+09
1E+10
1E+11
0 10 20 30Eacc (MV/m)
Q0
A1-02 ( 700 MHz )
C1-16 ( 1300 MHz )
L1-05 ( 1500 MHz )
quench
no electronsno X-rays
RFpower
RFpower
1E+09
1E+10
1E+11
0 20 40 60 80 100 120 140
Bp (mT)
Q0
A1-02 ( 700 MHz )
C1-16 ( 1300 MHz )
no electronsno X-rays
RFpower
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