TTC 2019 – WG1 summary 05-08 Feb. 2019 TRIUMF, Vancouver Julien Branlard, Rongli Geng

WG1 Performance limitation in operational facilities WG mission: Performance limitation in operational facilities including both elliptical and non-elliptical variants longer term operation of test facilities cavity performance experience Safe limits Multipacting limitations and mitigations Field emission Voltage and phase stability microphonics, Lorentz force detuning Vector sum (pulsed and cw) 4K vs 2K operation, trapped flux (local magnetic sources) cooldown dynamics 08.02.2019 TTC 2019 - WG1 summary

WG1.1 Cavity performance experience-safe limit Title Speaker Affiliation Long Term Operation of a Large Ensemble of SRF Cavities in CEBAF Arne Freyberger JLAB Long term experience with SRF cavities at ELBE  Peter Michel ELBE Summary of the maximum SCRF voltage in XFEL  Nick Walker DESY Operation and performance limits of the LHC cryomodule Katarzyna Turaj CERN Long term experience at INFN Legnaro  Giovanni Bisoffi INFN Overview of 12-year operation of the SCL at SNS  Sang-Ho Kim / John Mammosser ORNL 08.02.2019 TTC 2019 - WG1 summary

WG1.1 Cavity performance experience-safe limit Long term experience with SRF CEBAF running with original cryomodules (1990’s) and added new cryomodules since 2014 ELBE, LHC 17 years of operation ALPI running since 25 years and needs to go for another 20 years Eacc: general trend is down when you’re operating at the top, the only way is down Across the labs, mostly due to field emission 08.02.2019 TTC 2019 - WG1 summary

CEBAF 08.02.2019 TTC 2019 - WG1 summary

ELBE 08.02.2019 TTC 2019 - WG1 summary

WG1.1 Cavity performance experience-safe limit BUT SRF is a “survivor” (A. Freyberger) Mitigation approaches LHC: building spares CEBAF: refurbishment, maintenance, helium proc., avoid field emission by lowering gradient SNS: in situ plasma processing, spare cryomodules ELBE: partial gradient recovery through HPP ALPI : generation transition 08.02.2019 TTC 2019 - WG1 summary

CEBAF 08.02.2019 TTC 2019 - WG1 summary

SNS 08.02.2019 TTC 2019 - WG1 summary

WG1.1 Cavity performance experience-safe limit XFEL new but high statistics Particular case of VS (one cavity limiting 31) No degradation from HTS to tunnel (within error bars) On-going effort to assess and maintain max gradients 08.02.2019 TTC 2019 - WG1 summary

XFEL 08.02.2019 TTC 2019 - WG1 summary

WG1.2 Field emission and multipacting: experience and mitigation Title Speaker Affiliation Field Emission and Mitigation in the CEBAF Linacs  Bob Legg / Rongli Geng JLAB Exceptional events during operation of the European XFEL Mathieu Omet DESY Operational Experience of Cavity/CMs in ISAC-II QWR linac Zhongyuan Yao TRIUMF 08.02.2019 TTC 2019 - WG1 summary

Field emission and multipacting CEBAF Increased field emission over time He processing successful but not always Current approach is mitigation via cryomodule re-work and particulate control Plasma processing being considered EuXFEL Couple of examples of successful processing of field emitters Some cavities routinely operated in quench regime (cryo acceptable “soft” quench) Observed plasma discharges (e- quench) ISAC-II Maintenance and refurbishment program essential to increase available gradient Common issues: Q disease, magnetic pollution from solenoids, multipacting happens < 100 kV for QWR, field emission (residual gas after thermal cycle), Yearly warm up cool down (cost saving reasons but increase nb of issues) Multipacting processing in SEL  speed up process 08.02.2019 TTC 2019 - WG1 summary

CEBAF 08.02.2019 TTC 2019 - WG1 summary

XFEL 08.02.2019 TTC 2019 - WG1 summary

ISAC-II 08.02.2019 TTC 2019 - WG1 summary

WG1.3 Voltage and phase stability Title Speaker Affiliation LLRF system performance limiting factors during CW operation of high Ql cavities cryomodule Wojciech Cichalewski TUL LLRF compensation and mitigation of two cavity instability Ramona Leewe TRIUMF CEBAF C100 Fault Classification Based on Time Domain RF Signals Tom Powers JLAB Experience with LCLS-II cavity and cryomodule tests at Fermilab Elvin Harms FNAL 08.02.2019 TTC 2019 - WG1 summary

Field stability LCSL-II CMTB TRIUMF Cryomodule tests at FNAL (14/20), procedure Microphonics issues now under control Mass flow as preferred technique for Q0 measurement Coupler heating not an issue CMTB R&D program towards a CW EuXFEL Main challenge is CW in VS Static drops (manageable in SEL, but can be a real challenge in VS) Coupler heating leads to QL drop  more power for same gradient Cross coupling between neighboring cavities IOT as power source: non linear behavior TRIUMF E- linac (2 cavities operated in VS) Ponderomotive oscillations Analytical derivation to identify conditions leading to unstable behavior Unclear if piezo can offer a possible mitigation : to be tested 08.02.2019 TTC 2019 - WG1 summary

CW in VS 08.02.2019 TTC 2019 - WG1 summary

CW tests at CMTB 08.02.2019 TTC 2019 - WG1 summary

Field stability CEBAF Fault analysis using fault logger Time consuming task to identify and categorize faults Use data to perform machine learning and help identify common fault signatures Help operators take the right action ( smaller impact on gradient) Fault classification 08.02.2019 TTC 2019 - WG1 summary

WG1.4 2K versus 4K operations, He induced microphonics Title Speaker Affiliation The 8T solenoid and the local magnetic shielding in the FRIB cryomodules Kenji Saito MSU Comparision of 4K/2K operation performance CEBAF injector cryomodules Grigory Eremeev JLAB Experience with the CeC PoP 4K 1/4 Wave Photocathode Gun and 2K 5-Cell Cavity at RHIC Kevin Smith BNL Experience with cryogenics-induced microphonics on LCLS-II cryomodules Tom Peterson SLAC Commissioning of 704 MHz SRF Booster Cavity for LEReC Wencan Xu 08.02.2019 TTC 2019 - WG1 summary

WG1.4 – Microphonics, 2K versus 4K FRIB Local magnetic shielding developed and applied Demonstrated comparable Q0 with mu-metal for magnetic shield JLAB 4K vs 2K comparative test of two cryomodule designs Original cryomodule design permits large gradients at 4K close to 2K 4K test with beam : not significant difference in terms of beam quality BNL Multipacting issues  hard to condition away Developed a procedure for overcoming multipacting FNAL Valve leak at the origin of He gas bubbles Once problem understood, detuning +/- 40 Hz  +/- 20 Hz BNL (LEReC) Conversion of SRF gun cryomodule to and SRF booster cryomodule Issue with microphonics Conditioning of field emitter during operation 08.02.2019 TTC 2019 - WG1 summary

From TTC chairman’s report 08.02.2019 TTC 2019 - WG1 summary

Foster synergies and collaborations Microphonics oscillations mitigation in vector sum control TRIUMF DESY Efforts on-going for root cause studies – more needed Instrumentation needed for FE studies and perhaps operation control. More effective techniques for rapid performance recovery from FE needed. JLAB SLAC … 08.02.2019 TTC 2019 - WG1 summary

Lessons learnt Fortunate to have speakers who are “not conventional TTC participants”, valuable point of view for TTC Not enough time for discussion during session Schedule less talks More time for discussion We proposed a structure for WG1 talks: Problem statement, known solutions, future tests, proposed collaboration Several talks followed More needed - Focus on issues, (not a PR talk) 08.02.2019 TTC 2019 - WG1 summary

Thank you to all WG1 speakers and thank you for your attention! 08.02.2019 TTC 2019 - WG1 summary