1. Quench Studies in Single and Multicell N-Doped Cavities
Daniel Bafia
TTC at TRIUMF
6 February 2019

2. Effects of High Temperature N-Doping on Cavity Performance
Gives very high Q – 3 times higher than 120C bake
Anti Q-slope phenomenon & very low BCS
N2 doped
120C Bake
T=2K
f=1.3GHz
A. Grassellino et al, Superconductor Science and Technology, Volume 26, Number 10
7/24/2019
Daniel Bafia | TTC at TRIUMF

3. Effects of High Temperature N-Doping on Cavity Performance
Gives very high Q – 3 times higher than 120C bake
Anti Q-slope phenomenon & very low BCS
N2 doped
120C Bake
How do we optimize nitrogen doping to achieve higher gradients while still maintaining high Q0 and low BCS?
T=2K
f=1.3GHz
A. Grassellino et al, Superconductor Science and Technology, Volume 26, Number 10
7/24/2019
Daniel Bafia | TTC at TRIUMF

4. Exploring New Doping Recipes
Using Nb 3 cavities, we test sequential treatments with a 40µm EP surface reset in between
Working in the context of Fermilab R&D and LCLS-II HE, we studied the following recipes:
2/0 Doping - Fermilab
3/60 Doping - JLab
Pressure (torr)
Pressure (torr)
Temperature (K)
Temperature (K)
7/24/2019
Daniel Bafia | TTC at TRIUMF

5. 1.3GHz Single Cell Investigation
7/24/2019
Daniel Bafia | TTC at TRIUMF

6. Sequential Study of AES025: 1/4
2/6 + 5um EP (LCLS-II, baseline):
f=1.3GHz
T=2K
7/24/2019
Daniel Bafia | TTC at TRIUMF

7. Sequential Study of AES025: 2/4
2/6 + 5um EP (LCLS-II, baseline):
+40um EP reset
2/0 + 5um EP:
Higher Q and quench increases by +6MV/m
f=1.3GHz
T=2K
7/24/2019
Daniel Bafia | TTC at TRIUMF

8. Sequential Study of AES025: 3/4
2/6 + 5um EP (LCLS-II, baseline):
+40um EP reset
2/0 + 5um EP:
Higher Q and quench increases by +6MV/m
3/60 + 5um EP:
Quench improves by additional +2MV/m, 20MV/m!
f=1.3GHz
T=2K
7/24/2019
Daniel Bafia | TTC at TRIUMF

9. Sequential Study of AES025: 4/4
2/6 + 5um EP (LCLS-II, baseline):
+40um EP reset
2/0 + 5um EP:
Higher Q and quench increases by +6MV/m
3/60 + 5um EP:
Quench improves by additional +2MV/m, 20MV/m!
+5um EP
3/ um EP:
Quench decreases by -3MV/m
High Q and G
f=1.3GHz
T=2K
7/24/2019
Daniel Bafia | TTC at TRIUMF

10. Decomposition of Sequential Study on AES025: 1/4
7/24/2019
Daniel Bafia | TTC at TRIUMF

11. Decomposition of Sequential Study on AES025: 2/4
7/24/2019
Daniel Bafia | TTC at TRIUMF

12. Decomposition of Sequential Study on AES025: 3/4
3/60+5um EP recipe gives very low BCS
3/60+5um EP slightly increases residual resistance
7/24/2019
Daniel Bafia | TTC at TRIUMF

13. Decomposition of Sequential Study on AES025: 4/4
3/60+5um EP recipe gives very low BCS
3/60+10um EP recipe is closer to 2/0 and 2/6 doping
3/60+5um EP slightly increases residual resistance
7/24/2019
Daniel Bafia | TTC at TRIUMF

14. Thermometry Mapping of AES025 Post 3/60+10um EP
Equator
Top Iris
TMAP shows local heating in region above cavity equator
Small amount of x-rays present
Possibly due to multipacting
Beginning new studies to see how profile at quench evolves with sequential treatments
Bottom Iris
7/24/2019
Daniel Bafia | TTC at TRIUMF

15. Q0 vs Eacc Summary of Sequential Cavity Study
f=1.3GHz
T=2K
Overall increase in Q0 and quench fields over baseline
7/24/2019
Daniel Bafia | TTC at TRIUMF

16. BCS and Residual Resistance Summary of Sequential Cavity Study
3/60+5um EP recipe consistently gives lowest BCS for all tested cavities
Residual resistance stays low
7/24/2019
Daniel Bafia | TTC at TRIUMF

17. Average Quench and Q0 for Cavities Post Sequential Treatments
Average Quench Field
24MV/m
27MV/m
32MV/m
30MV/m
NEED TO INCLUDE AVERAGE BCS AT 20MV/m
update to include RI006 – maybe include 3/ /60+10 histos separately – don’t include +15
7/24/2019
Daniel Bafia | TTC at TRIUMF

18. Average Quench and Q0 for Cavities Post Sequential Treatments
Average Quench Field
Average Quality Factor
24MV/m
3.61E10
4.17E10
27MV/m
32MV/m
4.67E10
30MV/m
4.5E10
New recipes yield high quench fields while maintaining high Q0!
NEED TO INCLUDE AVERAGE BCS AT 20MV/m
update to include RI006 – maybe include 3/ /60+10 histos separately – don’t include +15
7/24/2019
Daniel Bafia | TTC at TRIUMF

19. Sensitivity vs Accelerating Field
f=1.3GHz
2/0 + 5um EP and 3/ um EP recipes give results similar to that of 2/6 doped cavities
3/60 + 5um EP yields sensitivity closer to that of more heavily doped cavities
3/ um EP sensitivity sits on lower branch of 2/6 doped cavities
7/24/2019
Daniel Bafia | TTC at TRIUMF

20. Relationship of BCS and Sensitivity with Mean Free Path
BCS Resistance vs MFP
In line with previous findings – advantage of doping comes at higher fields but CANNOT be explained by MFP alone
7/24/2019
Daniel Bafia | TTC at TRIUMF

21. Relationship of BCS and Sensitivity with Mean Free Path
BCS Resistance vs MFP
Sensitivity vs MFP
In line with previous findings – advantage of doping comes at higher fields but CANNOT be explained by MFP alone
Sensitivity continues to follow non-monotonic dependence on the mean free path
7/24/2019
Daniel Bafia | TTC at TRIUMF

22. Realizing 2/0 Doped 1.3GHz 9 Cells
CAV0017 – 3/60 and 2/0
CAV0018 – 2/0 only
7/24/2019
Daniel Bafia | TTC at TRIUMF

23. 9 Cell Performance Post 2/0 + 7um EP: TB9RI022
f=1.3GHz
T=2K
32.3MV/m!
7/24/2019
Daniel Bafia | TTC at TRIUMF

24. 9 Cell Performance Post 2/0 + 7um EP: TB9RI022
f=1.3GHz
T=2K
32.3MV/m!
Lower Q0 comes from high residual resistance – old material – poor flux expulsion
Possible to obtain high quench fields while maintaining low BCS
7/24/2019
Daniel Bafia | TTC at TRIUMF

25. 2/0 Doping of Two More 9 Cells
f=1.3GHz
T=2K
CAV017
20MV/m
16MV/m: 3.63E10
CAV018
19.3MV/m
3.09E10
Early quench - Investigate with second sound and mode measurements
7/24/2019
Daniel Bafia | TTC at TRIUMF

26. Second Sound + Mode Measurements
Second sound - used to locate origin of quench
Cavity instrumented with eight 2nd sound sensors
Quench spot serves as a heat source - heat wave
Sensors measure the time for the heat wave to arrive – work backwards to get quenching cell
2nd sound sensor #7
2nd sound sensor #8
2nd sound sensor #5 (behind)
2nd sound sensor #6
2nd sound sensor #4
2nd sound sensor #3
2nd sound sensor #1 (behind)
2nd sound sensor #2
Cell # 1
FPC
7/24/2019
Daniel Bafia | TTC at TRIUMF

27. Second Sound + Mode Measurements
Second sound - used to locate origin of quench
Cavity instrumented with eight 2nd sound sensors
Quench spot serves as a heat source - heat wave
Sensors measure the time for the heat wave to arrive – work backwards to get quenching cell
2nd sound sensor #7
2nd sound sensor #8
2nd sound sensor #5 (behind)
2nd sound sensor #6
Mode measurements allow for estimates of quench fields in each cell
2nd sound sensor #4
2nd sound sensor #3
2nd sound sensor #1 (behind)
2nd sound sensor #2
Cell # 1
FPC
7/24/2019
Daniel Bafia | TTC at TRIUMF

28. Hints of Non-Uniformity in Nitrogen Concentration in 9 Cells
FPC
Cell #
CAV018 Quench Field (MV/m)
CAV017 Quench Field (MV/m) 1
19.2 20 2
>22
26.4 3
>25
>30 4
>24.88
>27 5
>34.2
32.8 6 7 8
>26.4 9
>19.2
>20
Cell #1 (closest to FPC) quenches early
Quench field increases toward cell #5
Could this be due to a change in nitrogen concentration between cells?
7/24/2019
Daniel Bafia | TTC at TRIUMF

29. Hints of Non-Uniformity in Nitrogen Concentration in 9 Cells
FPC
Cell #
CAV018 Quench Field (MV/m)
CAV017 Quench Field (MV/m) 1
19.2 20 2
>22
26.4 3
>25
>30 4
>24.88
>27 5
>34.2
32.8 6 7 8
>26.4 9
>19.2
>20
Cell #1 (closest to FPC) quenches early
Quench field increases toward cell #5
Could this be due to a change in nitrogen concentration between cells?
Nitrogen Inlet
7/24/2019
Daniel Bafia | TTC at TRIUMF

30. Hints of Non-Uniformity in Nitrogen Concentration in 9 Cells
FPC
Cell #
CAV018 Quench Field (MV/m)
CAV017 Quench Field (MV/m) 1
19.2 20 2
>22
26.4 3
>25
>30 4
>24.88
>27 5
>34.2
32.8 6 7 8
>26.4 9
>19.2
>20
Cell #1 (closest to FPC) quenches early
Quench field increases toward cell #5
Could this be due to a change in nitrogen concentration between cells?
Nitrogen Inlet
Cell#1
Cell#1
CAV018
CAV017
7/24/2019
Daniel Bafia | TTC at TRIUMF

31. Conclusions + Future Work
Single cells subject to new doping recipes show that very high gradients are achievable while maintaining high Q0; 3E10 at 35MV/m for 3/60+5um EP!
BCS resistance is kept to exceptionally low values
Sensitivity to trapped magnetic flux is comparable to or better than LCLS-II 2/6 doping recipe and follows expected trends with the mean free path
2/0 doping is capable of giving high gradient, high Q0 9 cells with very low BCS
Require further investigation of the possibility of non-uniform 9-cell doping
SIMS analysis on cavity cutouts
“Flipping” orientation of 9 cell in the furnace
7/24/2019
Daniel Bafia | TTC at TRIUMF

32. Acknowledgments LCLS-II HE Collaborators My advisors: Anna Grassellino
Alexander Romanenko
John Zasadzinski
7/24/2019
Daniel Bafia | TTC at TRIUMF