20180313 saravan - 650 mhz q studies & material...
TRANSCRIPT
Saravan K. Chandrasekaran, Martina Martinello, Anna GrassellinoPIP-II meeting13 March 2018
Update on Q0 studies & Nb for PIP-II 650 MHz cavities
• Primarily focused on TESLA type 1.3 GHz cavities, with sufficient statistics to industrialize and implement in LCLS-II– N-doping– Surface resistance contributions– Sensitivity to magnetic flux trapping with & without N-doping
• Cool down rates & their influence on flux trapping
• Preliminary studies on 650 MHz 1-cell & 5-cell cavities – N-doping (1.3 GHz optimized recipe)– Sensitivity to magnetic flux trapping with & without N-doping
Studies so far…
3/13/2018 S.K. Chandrasekaran | Update on Q & Nb studies for PIP-II 650 MHz cavities2
The discovery of N-doping
S.K. Chandrasekaran & A. Grassellino
0 5 10 15 20 25 30 35 40109
1010
1011
Q0
Eacc (MV/m)
T= 2K
Q‐factor improvement after N‐doping – up to 4 times higher Q than standard Nb cavities
Typical Q vs Eacc curve obtained with 120C bake (standard ILC treatment)
Average Q at 16MV/m:
• Standard ILC treatment:
~1.7 · 10
• N‐doping:
~3.5 · 10
Anti‐Q‐slope
A. Grassellino et al., Supercond. Sci. Technol. 26, 102001 (2013) – Rapid Communications
Slide courtesy M. Martinello 3 9/20/17
N-doping process
• 800 C standard degas• Inject N2 at 25 mTorr
– 99.9999% purity• Pump to high vacuum &
short soak• Or cooldown
S.K. Chandrasekaran & A. Grassellino
M. Merio, MOPB111 SRF ‘15
4 9/20/17
N-Doping: small variation from standard protocol, large difference in performance
9/20/17 S.K. Chandrasekaran & A. Grassellino
Example from a doping process developedfor LCLS-2:
• Bulk EP• 800 C anneal for 3 hours in vacuum• 2 minutes @ 800C nitrogen diffusion• 800 C for 6 minutes in vacuum• Vacuum cooling• 5 microns EP
Cavity after Equator Welding
EP 140 um
Ethanol Rinse
External 20 um BCP
Short HPR
800C HT Bake
RF Tuning
EP 40 um
Ethanol Rinse
Long HPR
Final Assembly
Long HPR
Helium Tank Welding
Procedure
VT Assembly
HPR
HOM Tuning
Ship to DESY
Leak Check
120C bake
XFE
L
X
5
9/20/17 S.K. Chandrasekaran & A. Grassellino
N2
Nb
Slides adapted from M. Martinello
First breakthrough for Q: N doping of Nb cavities800C UHV, 3
hours800C UHV, 6 minutes
800C UHV, 6 minutes UHV coolingUHV cooling 5 um EP5 um EP
N
Final RF Surface
800C UHV, 6 minutes UHV cooling 5 um EP
800C N2p = 25 mTorr 2
minutes
800C N2p = 25 mTorr 2
minutes
800C N2p = 25 mTorr 2
minutes
N Interstitial
Nbx N
y
Y. Trenikhina et al, Proc. of SRF 2015
Y. Trenikhina et al, Proc. of SRF 2015
6
9/20/17S.K. Chandrasekaran & A. Grassellino7
HB650 RF Test Results: N-doping vs 120C baking
Martina Martinello | P2MAC - Apr 2017
PIP‐II specs
HB650 RF Test Results: N-doping vs 120C baking
Martina Martinello | P2MAC - Apr 2017
PIP‐II specs
ANTI‐Q SLOPE NOT PRESENT, YET.DOPING PARAMETERS NEED TO BE OPTIMIZED
HB650 5-cells Test Result
Martina Martinello | P2MAC - Apr 2017
PIP‐II specs
First Results of Rs(Eacc) at 650 MHz
Martina Martinello | P2MAC - Apr 2017
·
• 2/6 N‐doped gives very low R0 but higher sensitivity
• RBCS seems to be very similar for the 2/6 N‐doped and the 120C baked (not optimal doping recipe!), but still lower at high fields
Trapped flux surface resistance
Martina Martinello | P2MAC - Apr 2017
These losses can be reduced by minimizing these contributions:
• Magnetic shielding/hygiene improvement
• Fast Cooling• Material Optimization
S• Optimizing mean free path
Trapped flux surface resistance
Martina Martinello | P2MAC - Apr 2017
These losses can be reduced by minimizing these contributions:
• Magnetic shielding/hygiene improvement
• Fast Cooling• Material Optimization
S• Optimizing mean free path
External magnetic field
Minimization of remnant field in the cryomodule
Martina Martinello | P2MAC - Apr 2017
Demagnetization
Empty vacuum vessel Assembled Cryomodule
Coils for magnetic field demagnetization
Demagnetization
Minimization of remnant field in the cryomodule
Martina Martinello | P2MAC - Apr 2017
Demagnetization
Empty vacuum vessel Assembled Cryomodule
Coils for magnetic field demagnetization
Demagnetization
SIMILAR TECHNIQUES CAN BE OPTIMEZED FOR 650 MHz CMs
Trapped flux surface resistance
Martina Martinello | P2MAC - Apr 2017
These losses can be reduced by minimizing these contributions:
• Magnetic shielding/hygiene improvement
• Fast Cooling• Material Optimization
S• Optimizing mean free path
Flux Expulsion Efficiency
Fast cooldown helps flux expulsion
• Fast cool‐down lead to large thermal gradients→ efficient flux expulsion• Slow cool‐down lead to small thermal gradients→ poor flux expulsion
A. Romanenko et al., Appl. Phys. Lett. 105, 234103 (2014)A. Romanenko et al., J. Appl. Phys. 115, 184903 (2014)D. Gonnella et al, J. Appl. Phys. 117, 023908 (2015)M. Martinello et al., J. Appl. Phys. 118, 044505 (2015)S. Posen et al., J. Appl. Phys. 119, 213903 (2016)S. Huang, Phys. Rev. Accel. Beams 19, 082001 (2016)
T1
T2
All flux trapped
Efficient flux expulsion
Bsc/Bnc=1.74 after complete Meissner effect
Bsc/Bnc=1 after full flux trapping
B sc/B n
c
Q0
Martina Martinello | P2MAC - Apr 2017
Current understanding of flux expulsion issue
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II18
• Problem: Substantial magnetic flux may get trapped in cavities’ bulk Nb decreasing Q0– Observed in LCLS-II, despite cavities being manufactured from
Nb of XFEL/007 (or LCLS-II) spec. & fast cool down
Figures courtesy: S. Posen
Current understanding of flux expulsion issue
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II19
• Problem: Substantial magnetic flux may get trapped in cavities’ bulk Nb decreasing Q0– Observed in LCLS-II, despite cavities being manufactured from
Nb of XFEL/007 (or LCLS-II) spec. & fast cool down
Figures courtesy: S. Posen
LCLS‐II 1.3 GHz
Current understanding of flux expulsion issue
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II20
• Solution: Heat treat cavity at T>900 C, some even 950 C– Grain growth & lowering of tensile properties seem to correlate
to better flux expulsion in these problematic Nb
Figures courtesy: S. Posen
Current understanding of flux expulsion issue
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II21
• Solution: Heat treat cavity at T>900 C, some even 950 C– Grain growth & lowering of tensile properties seem to correlate
to better flux expulsion in these problematic Nb
Figures courtesy: S. Posen
LCLS‐II 1.3 GHz
• Dislocations and unrecovered/unrecrystallized regions may be the key…
• Role of purity (RRR) unclear at this time
Current understanding of flux expulsion issue
3/13/2018 S.K. Chandrasekaran | Update on Q & Nb studies for PIP-II 650 MHz cavities22
Large grain cavities – lower grain boundary contribution
Sliced & formed
Sliced, rolled, & formed
Figures courtesy: S. Posen
Available:• Fermilab ED0371037 Rev C
– Aimed at high gradient cavities• DESY 2009
– Aimed at high gradient 1.3 GHz cavities for XFEL• XFEL/007, 2010 (also LCLS-II)
– Aimed at high gradient 1.3 GHz cavities– Must have license with DESY to view/use
What is needed for PIP-II• Above + high Q (i.e. good flux expulsion)
– Fermilab version may already address this…
Nb specifications
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II23
• ASTM B393 Type 5 RRR Nb
Fermilab ED0371037 Rev C
3/13/2018 S.K. Chandrasekaran | Nb Specification update for PIP-II24
Trapped flux surface resistance
Martina Martinello | P2MAC - Apr 2017
These losses can be reduced by minimizing these contributions:
• Magnetic shielding/hygiene improvement
• Fast Cooling• Material Optimization
S• Optimizing mean free pathTrapped
Flux Sensitivity
10 100 10000.0
0.5
1.0
1.5
2.0
(nm)
Doped
EP/BCP
Sensitivity data @ 5 MV/m Sensitivity data @ 16 MV/m
S (n
/m
G)
120 Cbaked
Light doping to minimize trapped flux sensitivity
Martina Martinello | P2MAC - Apr 2017
Trapped flux sensitivity:
• Bell‐shaped trend of asa function of mean freepath
• N‐doping cavities presenthigher sensitivity thanstandard treated cavities
• Light doping is neededto minimize trapped fluxsensitivityM. Martinello et al., App. Phys. Lett. 109, 062601 (2016)
Minimizing at 16 MV/m
Martina Martinello | P2MAC - Apr 2017
• Very low values of RBCS
• Acceptable values of sensitivity
• Low residual resistance
The best surface treatmentminimizes both andcontributions:
For LCLS‐II was chosen lightdoping:
Minimizing at 16 MV/m
Martina Martinello | P2MAC - Apr 2017
• Very low values of RBCS
• Acceptable values of sensitivity
• Low residual resistance
The best surface treatmentminimizes both andcontributions:
For LCLS‐II was chosen lightdoping:
SIMILAR STUDIES TO BE DONE FOR 650 MHz
9/20/17S.K. Chandrasekaran & A. Grassellino
The advantage of N-doping in condition of full flux-trapping
12
15
N-doping wins over standardtreatments as long as the fieldtrapped is <10 mG
M. Martinello et al., App. Phys. Lett. 109, 062601 (2016)
Martina Martinello | APT Seminar29
9/20/17S.K. Chandrasekaran & A. Grassellino
The advantage of N-doping in condition of full flux-trapping
12
15
N-doping wins over standardtreatments as long as the fieldtrapped is <10 mG
M. Martinello et al., App. Phys. Lett. 109, 062601 (2016)
Martina Martinello | APT Seminar30
SIMILAR ANALYSIS REMAINS TO BE PERFORMED FOR 650 MHz CAVITIES WITH
SIGNIFICANT STATISTICS
• Extensive studies performed for 1.3 GHz cavities– Same level of statistics may not be obtained for 650 MHz
• Several studies remain for 650 MHz cavities– Studies structure determined from 1.3 GHz experience– Optimized N-doping for 16—18 MV/m
• Lower RBCS & obtain anti-Q slope– Flux trapping sensitivity of N-doped vs 120 C
• More statistics needed
Summary
3/13/2018 S.K. Chandrasekaran | Update on Q & Nb studies for PIP-II 650 MHz cavities31