LCLS-II Cavity Production and Vertical Testing Fermilab and JLab: 3 cavities/cool-down (IB-1 VT2 and VT3, Test-lab D5) Compare with DESY/XFEL AMTF 4 cavities/cool-down LCLS-II/Cryo systems Weekly meeting

Cryogenic Systems Scope: Component Count Parameters Linac Cryomodules 1.3GHz - 35 ea 3.9 GHz - 2 ea Linac – 4 cold sections 8 cavities per cryomodule (1.3 & 3.9 GHz) 1.3 GHz Cryomodule (CM) 8 cavities/CM 13 m long. Cavities + SC Magnet package + BPM 3.9 GHz Cryomodule 6.2 m long. Cavities + BPM Additional Cryomodules 1.3 GHz: 4 production + 1 spare 3.9 GHz: 1 spare 1.3 GHz 9-cell cavity 320 each 16 MV/m; Q0 ~ 2.7e10 (avg); 2.0 K; gradient reach to 19 MV/m (No Q-spec); bulk niobium sheet - metal 3.9 GHz 9-cell cavity 24 each 13.4 MV/m; Q0~2.0e9 Cryoplant (CP1/CP2) 2 each 4.5 K / 2.0 K cold boxes; 4 kW @ 2.0 K; 18 kW @ 4.5 K; 3.7 kW nom. tot. load Spare compressors 2 Warm He Comp. 1 spare Cold Comp. Cryogenic Distribution System (CDS) 210 m vacuum-jacketed line, 2 each distribution boxes, 6 each feedcap / 2 each endcap No use of “spares” LCLS-II DOE Status Review, Jun 13-15, 2017

Background - SRF Cavities LCLS-II Specification: Q0≥ 2.7x1010 @ Eacc = 16 MV/m in 5 mG remnant field Additionally the cavities must reach 19 MV/m in VT – accounts for errors in gradient measurement Specification designed to reduce 2K cryogenic load, and thus operating cost of machine. Made possible by Nitrogen doping of SRF cavities. Comes with 2 trade-offs. Losses from trapped flux in doped cavities can be up to 3.6 times higher than un-doped cavities Reduction in maximum achievable gradient of cavity – not an issue for LCLS-II Remedied by: Improved magnetic hygiene and shielding Optimized design and cooldown procedures Gonnella – March 17, 2017 - LCLS-II Collaboration Meeting

Performance Summary for the first 11 cryomodules Data Source Average Q Avg Gradient [MV/m] F1.3-1 (pCM) CM Test 3.0x1010 18.2 J1.3-1 (pCM) 3.3x1010 * 132.8 F1.3-2 2.1x1010 20.0 J1.3-2 Vertical Test 2.1x1010 ** 21.5 F1.3-3 3.31x1010 23.2 J1.3-3 3.61x1010 22.2 F1.3-4 3.33x1010 23.0 J1.3-4 3.62x1010 23.9 F1.3-5 3.01x1010 21.6 J1.3-5 2.69x1010 22.7 F1.3-6 2.82x1010 Totals 2.86x1010 21.9 pCMs Retesting after shipping test now in-progress 800 C bake 900 C bake * Q measured on 2 of 8 cavities (JLab pCM Jan 2017) ** VT Q scaled based upon measured field in the first 2 CMs. Q0 Spec = 2.7 x 1010 (ensemble average) LCLS-II DOE Status Review, Jun 13-15, 2017

Yield of Production Cavities Received 129 42% of total 304 Tested 107 Total qualified 81 76% yield Qualified as received 46 Qualified after re-HPR 35 43% (2 re-HPR 2x) LCLS-II DOE Status Review, 12-15 June 2017

Field Emission Uncontrolled processes at both vendors lead to high rates of field emission JLab, SLAC, and FNAL personnel worked with personnel at both vendors to develop and implement clean manufacturing procedures. Both vendors were required to revise procedures and submit to JLab for approval Improvements were made to procedures at cavities 17, 53, and 73. Cavities 1-17: 75% FE Cavities 17-53: 47% FE Cavities 53-73: 23% FE Cavities 73+: 9% FE (below 19 MV/m) Rerinsing is effective for cavities with FE. Out of over 30 cavities with FE, only two had to be rerinsed twice.

Significant capabilities beyond our initial consideration. Cavity Q0 Performance in VT Cavity Gradient Reach in VT 19 MV/m LCLS-II Spec 16 MV/m 800/140 in Low Bamb 900/200 in 5-10 mG Sheet type Sheet type

Q = G/ Rs where RS = RBCS + R0 + RTF Background - Obtaining and preserving Q ≥ 2.7e10 at 16 MV/m, 2K Q = G/ Rs where RS = RBCS + R0 + RTF RTF= s * η* Bamb Trapped magnetic flux residual Doping Intrinsic residual Sensitivity to mag field Flux trapping percentage Total Rs budget for Q~ 2.7e10 = 10 nanoOhms pCM material: RBCS ~ 4.5 nΩ + R0 ~ 1-2 nΩ + RTF ~ 1.4*(<0.2)*B = if B ~5 mG = 7.5 nΩ => Q ~3.5e10 if B ~1 mG = 6.5 nΩ => Q ~4e10 Gonnella – March 17, 2017 - LCLS-II Collaboration Meeting

Q = G/ Rs where RS = RBCS + R0 + RTF How to obtain and preserve Q > 2.7e10 at 16 MV/m, 2K? Q = G/ Rs where RS = RBCS + R0 + RTF Trapped magnetic flux residual Doping Intrinsic residual Total Rs budget for Q~ 2.7e10 = 10 nanoOhms pCM material: RBCS ~ 4.5 nΩ + R0 ~ 1-2 nΩ + RTF ~ 1.4*(<0.2)*B = production material: RBCS ~ 4.5 nΩ + R0 ~ 4-5 nΩ + RTF ~ 1.4*(>0.7)*B = if B ~5 mG = 7.5 nΩ => Q ~3.5e10 if B ~1 mG = 6.5 nΩ => Q ~4e10 if B ~5 mG = 14 nΩ => Q ~ 1.9e10 if B ~1 mG = 10 nΩ => Q ~ 2.7e10 Two issues to be fixed: 1) higher intrinsic R0; 2) Flux expulsion Grassellino | Director's review

2014, Q degradation risk: discovery of slow cooldown trapping all flux, fast helping expulsion Slow and homogeneous cooldown through Tc does not provide enough force to expel magnetic flux from the material Fast cooldown with larger thermogradients helps expelling magnetic flux Dressed N doped nine cell cavity vertical test at T=2K A. Romanenko, A. Grassellino, O. Melnychuk, D. A. Sergatskov, J. Appl. Phys. 115, 184903 (2014) A. Romanenko, A. Grassellino, A.Crawford, D. A. Sergatskov, Appl. Phys. Lett. 105, 234103 (2014) D. Gonnella et al, J. Appl. Phys. 117, 023908 (2015) M. Martinello, M. Checchin, A. Grassellino, A. Romanenko, A. Crawford, D. A. Sergatskov, O. Melnychuk, J. Appl. Phys. 118, 044505 (2015) Grassellino | Director's review

2014: Q degradation risk – Flux expulsion via fast cooling needed to maintain low residual resistance Full expulsion 100 - 0% flux trapping Full trapping Bottom-top cell Low thermogradient detrapping threshold seen in early cavities (Wah Chang) A. Romanenko, A. Grassellino, O. Melnychuk, D. A. Sergatskov, J. Appl. Phys. 115, 184903 (2014) A. Romanenko, A. Grassellino, A.Crawford, D. A. Sergatskov, Appl. Phys. Lett. 105, 234103 (2014) D. Gonnella et al, J. Appl. Phys. 117, 023908 (2015) M. Martinello, M. Checchin, A. Grassellino, A. Romanenko, A. Crawford, D. A. Sergatskov, O. Melnychuk, J. Appl. Phys. 118, 044505 (2015) Grassellino | Director's review

2015: Later Studies: Worrisome Expulsion Trend Found With Batches of AES Cavities Findings triggered production material assessment S.Posen et al, J. Appl. Phys. 119, 213903 (2016) Wah Chang Tokyo Denkai 7:30 AES Single Cells Batch 1 AES Single Cells Batch 2 10 K thermogradient: 30% vs 100% flux expulsion Grassellino | Director's review

900 C (versus 800C) improves expulsion 2015: Bulk heat treatment has effect: can convert from poor to strong expulsion via 900C treatment Complete Expulsion S.Posen et al, J. Appl. Phys. 119, 213903 (2016) 900 C (versus 800C) improves expulsion Based on available cooldown flow rates > 30 g/sec per CM [1] , DT achievable in tunnel > 5K, from horizontal test studies [2, 3] Complete Trapping [1] T.Peterson et al, LCLSII-4.5-EN-0479-R0 [2] D. Gonnella et al , J. Appl. Phys. 117, 023908 (2015) [3] A. Grassellino et al, Proceedings of SRF15, MOPB028 Grassellino | Director's review

Flux expulsion statistics.

pCM Measurement of Temperature and Magnetic Field 45-deg tilted fluxgate sensor Transverse fluxgate sensor measuring transverse field Cernox sensor Helium Inlet Helium Return Four Cavities Fully Instrumented G. Wu et al. | 2017 TESLA Technology Collaboration at MSU

Q0 under Different Cooldown Mass Flow LCLS-II/Cryo systems Weekly meeting

Q0 under Different Cool Down Mass Flow Temperature difference from top of the cavities and bottom of cavities  Mass Flow 80 g/s 47 g/s 25 g/s Slow Cool Down Cavity  T(K) CAV1 4.1 3.3 2.6 ≤0.08 CAV4 4.9 4.7 4.4 CAV5 7.0 7.1 7 CAV8 5.6 2.89 Average Q0  2.99e10  ~2.46e10  ~2.26e10 2.06e10  Flow injected at each cavity bottom, return to GHRP between CAV4 and CAV5. Linac cryogenic capacity 120 g/s Sensors are at limited locations. Fast cool down with sufficient mass flow can achieve effective flux expulsion G. Wu et al. | 2017 TESLA Technology Collaboration at MSU

Cryomodule cooldown (1)

Cryomodule cooldown (2)