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

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

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

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

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

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

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

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, Q0=6E10 @ 20MV/m! f=1.3GHz T=2K 7/24/2019 Daniel Bafia | TTC at TRIUMF

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, Q0=6E10 @ 20MV/m! +5um EP 3/60 + 10um EP: Quench decreases by -3MV/m High Q and G f=1.3GHz T=2K 7/24/2019 Daniel Bafia | TTC at TRIUMF

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

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

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

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

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

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

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

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+5 + 3/60+10 histos separately – don’t include +15 7/24/2019 Daniel Bafia | TTC at TRIUMF

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+5 + 3/60+10 histos separately – don’t include +15 7/24/2019 Daniel Bafia | TTC at TRIUMF

Sensitivity vs Accelerating Field f=1.3GHz 2/0 + 5um EP and 3/60 + 10um 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 3/60 + 15um EP sensitivity sits on lower branch of 2/6 doped cavities 7/24/2019 Daniel Bafia | TTC at TRIUMF

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

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

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

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

9 Cell Performance Post 2/0 + 7um EP: TB9RI022 f=1.3GHz T=2K Quench @ 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

2/0 Doping of Two More 9 Cells f=1.3GHz T=2K CAV017 Quench @ 20MV/m Q0 @ 16MV/m: 3.63E10 CAV018 Quench @ 19.3MV/m Q0 @16MV/m: 3.09E10 Early quench - Investigate with second sound and mode measurements 7/24/2019 Daniel Bafia | TTC at TRIUMF

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

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

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

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

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

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

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