Overview of the L HC RF Operation in 2017

1. Overview of theLHC RF Operation in 2017 H. Timko, CERN, BE-RF Acknowledgements: P. Baudrenghien, P. Martinez Yanez, M. Therasse, K. Turaj

2. LHC RF Installations (P4) Klystron gallery, Faraday cages, HV bunkers SRF workshop 31/05/2018

3. LHC RF Installations (P4) 8 RF cavities/beam SRF workshop 31/05/2018

4. Typical RF Start-up YEARLY RECOMMISSIONING

5. Recommissioning Timeline Typicaltimeline after an (E)YETS First beam SRF workshop 31/05/2018

6. HV and Klystron Tests • Annual teststobeperformed (~3 weeks in total) • Placingshortcircuits • Verificationof HV bunkers • Services, crowbars, modulators • Verificationof HV interlocks • Verificationofklystrons • Klystrons, circulators, focus power supplies, power meters • Services: waterflow, vacuum • Klystron power calibration • Calibrationofklystron DC power againstcollector thermal power (derivedfromwaterflow) • Circulator, interlock level, andmanyotheradjustments SRF workshop 31/05/2018

7. CavityConditioning • Increasing pulse length from200 µs to CW • Conditionthe operational workingpoints • QL = 20,000 • Flat bottomsettings: QL = 20,000 with 0.75 MV/cavity • QL = 60,000, upto 2 MV/cavity • Flat top settings: QL = 60,000 with1.5 MV/cavity • In dedicatedmeasurements, upto 2 MV/cavitymaybeused • QL = 40,000 (intermediate position) • Criterion for a ‘conditioned’ cavity: no activity for 12 hours SRF workshop 31/05/2018

8. Cavity Controller Setting-up • Adjustment of cavity feedback loop • Calibration of offsets, delays, phases, and gains in the LLRF modules • Step-by-step procedure, closing different parts of the overall loop one after the other • To make sure the loops are stable and have enough stability margin • In operation, this is done during the switching ON sequence • Automatized using python scripts SRF workshop 31/05/2018

9. Commissioning Experience • All setting up from high power to LLRF has to be done for 16 lines • Many things can be automatized, but still human intervention is necessary: a few lines will always show unexpected behaviour at some stage of the commissioning  experts needed • Work parallelisation is best done with several trained persons • Everything changes at the same time • Technical stops are shortened to a minimum and often commissioning has to be performed with modified hardware & software, or one has to cope with last-minute modifications during the commissioning • Sometimes difficult to debug faults • Several teams work in parallel; good coordination & communication needed SRF workshop 31/05/2018

10. Operational Aspectsofthe LHC RF • Reliable system with relatively high availability • Yet, hardware faults occur and are expected to be more frequent with ageing equipment • Software constantly evolves, or is migrated, leading to some faults • LHC requests evolve with time as well, requiring new solutions • For all these, a fast response time from experts/piquet is expected • Deployment of modifications often limited to technical stops • Modifications need to consider machine protection, interlocks… • Extensive remote control & diagnostics • Most faults can be diagnosed and fixed remotely, actual accesses only needed for hardware faults • Maintaining a high availability through preparing solutions in advance and mitigating problems before they occur SRF workshop 31/05/2018

11. Longitudinal Beam Dynamics • Beam dynamics studies are an integral part of the RF operation • Measurements, theory, simulations • Diagnostics and tools for operation and experts • Keep on developing new tools Simulatedandmeasuredbeam instabilities on flat bottom SRF workshop 31/05/2018

12. Maintenance of Operational Spare • Module exchangeduring LS1. Toensure a smooth operation: • Spare cavityprogramme • Maintenance of operational spare • E.g. newpumpingcrossestoavoidleaks SRF workshop 31/05/2018

13. Summary ofFaultsandIssues Interventions 2017

14. Availabilty in 2017 • The peakoffaultsistypicallyoccuringduringtheintensityramp-up; onedifficultinterventionof 14 h 31 faults 47.3 h downtime From28th April till 10th November SRF workshop 31/05/2018

15. Faults Hardware Faults Controls Faults FESA process missing or needs restarting (3) FEC needs reboot (1) Crates down (2) Communication issuesbetween different FESA classes(3) • Klystron (4) • Cooling, vacuum level, thyratron oil level, high cathode current • Power supplies (3) • Spurious trips or arcs (6) • Spurious interlocks (2) • Vacuum level, main coupler temperature • LLRF module replacement (1) Other Faults • Loose connection on interlock crate (3 interventions, 14.0 h) • Loose cable on C4B2 main coupler bias (3 events, 4.8 h) SRF workshop 31/05/2018

16. Antenna Problems • Duringtheconditioning in March 2017, thefieldlevelreading in C1B1 was roughly 10 dB lessthanexpected • Wrong tune andcouplerpositionwereruled out • Traced back to a problemwiththeantenna • Measuringthetransmissionbetween operational and spare antennashowedindeed 10 dB lesssignal on C1B1 than on othercavities • Presentlyoperating on the spare antenna, investigationsongoing SRF workshop 31/05/2018

17. New since 2017: FullDetuning • Withthefull-detuning beam-loadingcompensationscheme, theflat top power consumptionwas reducedfrom 190 kW to 100 kW • Power required is independent on beam current; smooth operation 03/11/2017 Full detuning Expect 104 kW at 1.5 MV, QL=60k Estimated accuracy on power measurement ±20 % SRF workshop 31/05/2018

18. Summary • The LHC RF system is working reliably throughout the years • Operation includes • Yearly recommissioning, from klystrons to LLRF • Fast follow-up of issues and problems • Continuous changes, improvements • Studies for the future • Huge amount of work performed also in 2017 to • Maintain the hardware • Commission new tools • Develop software for diagnostics and expert tools Thank you for your attention! SRF workshop 31/05/2018