Chris Christou on behalf of the RF group Contents of presentation Statistics and reliability Cavity failure and repair Cavity reliability IOT update Plans for hybrid operation RF group responsibilities ID: 1042098
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1. Status of RF at Diamond Light Source and overview of upgrade plans Chris Christouon behalf of the RF group
2. Contents of presentationStatistics and reliabilityCavity failure and repairCavity reliabilityIOT updatePlans for hybrid operation
3. RF group responsibilitiesLinac: 3GHz2 x 5.2m Cu DESY structures2 x 35MW klystronsbunchersBooster: 500MHz1 x 5 cell Cu PETRA cavity1 x 60kW IOTStorage ring: 500MHz2 x 1 cell Nb Cornell cavities installed3 x 300kW IOT combined amplifier
4. SR RF SystemsLLRF , DAs and Aux SuppliesHV PSUIOTs and combinerCirculator and loadCryogenic plantRF test facilitySuperconducting cavities
5. Machine reliability2016 to date:Global MTBF is 94 hoursSR RF MTBF is 202 hoursStorage ring RF has contributed 20 of 43 beam trips this year9 vacuum faults, 6 controls faults, 8 othersVirtually all RF beam trips have been amplifier faultsNo more spontaneous “fast vacuum trips” in normal operation
6. Cavity changes since 2007DLS owns 4 CESR-B cavities, all from Accel/RI:Cavities installed in 2 of 3 spaces in RF straightCavity failure can have a lasting effect on machine performanceRepair of cavities can be painfully slow
7. Cavity failure September 2014Helium leak into UHVFailed during cool-down from room temperatureNo more warm-ups unless absolutely necessaryIndium seal at waveguide flangeReturned to RI in December 2014Cavity returned to DLS in 2016Failed acceptance test with leak at indium seal on FBTFault is still not resolved
8. Cavity failure July 2015Failure of ceramic-metal braze at window10 months after abbreviated acceptance testDuring normal operation after standard conditioningRepaired on-site at RAL in February 2016Installed spare window assemblyUsed RAL Space satellite assembly cleanroomISO class 5 cleanroom with 5 tonne craneTested to 2.1MV operation in RF test facility
9. Fast vacuum tripsTrips have been eliminated by operating cavities below threshold voltagesReliable operating voltagesCavity 11.1 MVCavity 21.2 MVCavity 31.4 MVCavity 40.8 MVEach cavity has a different “safe” operating voltageCavity 4 has the lowest thresholdOperation suffered in 2014 before safe voltage was establishedCavity fast vacuum trips are no longer a problem in normal operation
10. Fast vacuum tripsLow alpha operation requires high cavity voltage: generally 1.7MV per cavityUsually one or two weeks low alpha operation per yearNo low alpha operation in 2016SRLEm3psStable short bunch low α1.7MV, 3.5psSRLETHzBursting short bunch low α1.7MV, 3.5psSR21Normal operation at high V1.7MV, 16psCompare two low alpha modes with normal optics operating at the same voltageBunch structure strongly influences trip rate
11. IOT performanceFilament hours of IOTs in operatione2v IOTD2130Two 4-IOT amplifiers driving cavities for normal operationOne 4-IOT amplifier for test/conditioning/standbySingle IOT booster amplifierOne IOT >57,600 hours operationSeveral >20,000 hours
12. IOT switchingOne high voltage power supply is used for all four IOTs in an amplifierVoltage is removed from all four IOTs when a fault is detected on any IOT in order to protect the tubeAmplifier turns off and beam is lost for every IOT faultCan we isolate an IOT by another mechanism?Investigating high voltage MOSFET switchSwitch has been installed on test amplifierTests are ongoing
13. Booster amplifier upgradeBooster IOT failed during January 2016 start-upStill using Thales TH793 tubeExcessive ion pump current on operating tubeSpare IOTs failed, some catastrophicallyDCX Millennium amplifier modifiedChanged to e2v IOTD2130New trolley conflicted with amplifier firmwareAmplifier expected two cavity broadcast configurationSame as storage ring tubesReady supply of spares
14. Linac maintenanceLinac operates with two Thales TH2100 klystronsRated at 37MW, operating at 18MWBoth klystrons were last changed in 2009Filament hours: 47,000 and 45,000Eimac YU171 cathode in gunFirst cathode changed after 45,000 hoursObserved degradation of gun emissionSecond cathode changed this shutdown after 20,000 hoursBunch charge has been doubledHivolt capacitors in modulator PFNSome oil leakage at sealTo be replaced by spares
15. Helium plant performanceSystem has been very reliable to dateNo significant downtime from any fault in cryogenic plantOnly warmed up for periodic maintenance by Air LiquideOnly time when cavities are taken up to room temperatureContamination introduced during cavity test in RFTF in January 2015Degradation of performance noticed immediatelyContaminants trapped on top heat exchangerPerformance closely monitored and interlock overriddenContaminants cleared during maintenance warm-up in June 2016
16. Effect of lattice upgrade on RFDBA cell is being replaced this shutdown by double DBA achromat Effects on RF operation are limitedRF frequency is raised by 25kHzWell within bandwidth of IOTsCavity tuning range can accommodate this changeLinac must be tuned by change of water temperatureOperation at the new frequency has been demonstratedLinac and booster have run with beamCavities have been run and conditioned
17. RF resilience upgradeSuperconducting cavities are reliable in operation but can be very disruptive when they failFull warm-up lasting several days is necessary before work is done on any cold componentRepair can take years to completeMajor disassembly is required to access interior of cryostatBCP and HPR surface treatment is required following interventionCavity UHV leak seen in 2014 is still being repairedWe will support superconducting cavity operation with two normal conducting cavities of the EU HOM-damped designAdvice from Alba and BESSY has been invaluable
18. Location of NC cavitiesTwo cavities have been ordered from RI for delivery in early 201750cm flange-to-flange distance gives some freedom in locationPumped tapers on either side of the cavities increases length requiredWould prefer not to be close to the superconducting cavities because of risk of contamination of SC cavities by gas evolved from warm NC cavitiesWill locate upstream of IDs in straights immediately before and after RF straight
19. Interaction with BPM in RF straightIf interference from cavity disturbs the BPM reading then the beam will be shifted in the ID and the beamline will be misalignedCST simulations have been carried out to investigate interactionBPM is 734mm from cavity centreTM01 modes and TE11 modes are below cut-off and are strongly attenuatedModel indicates well over 200dB attenuation of all modes along beam pipe from cavity to BPMAt limits of simulation but no effects are foreseen
20. Amplifier modificationsCombiners, circulators and loads are too large and complex to removeMust accommodate any one of three cavities failing300kW amplifier comprises four nominal 80kW IOTsTwo amplifiers power our two SC cavities, one amplifier is in reserveNC cavities rated at 150kW maximumThird amplifier can be used to power both NC cavitiesNeed a new amplifier for RF test facility
21. Splitting the powerIgnore higher power combination and take line off first stage rejection loadCombine-dephase-split and take off second stage rejection loadCan use existing circulator and loadOnly one new penetration into tunnelFirst stage rejection load available if isolation is imperfect
22. Tests of power splittingComark testsDiamond testsWith two IOTs off (-60dB)-2.95dB (49.3%) transmission: 158kW-56.3dB (0.0%) pollution: 0.75WWhat are the effects of imperfect tuning, temperature fluctuations…
23. Power distributionCavity in straight 16 uses existing circulator, load and penetrationCavity in straight 18 needs new circulator: load and transmission line comes in through personnel labyrinthUse 9 inch coaxial line instead of 18 inch waveguide
24. Additional benefitsPower and voltage requirements on four cavities are modest1.0MV, 150kW on superconducting cavities0.3MV, 100kW on normal conducting cavitiesSuperconducting cavity trip rate increases rapidly with operating voltageReducing voltage reduces risk of cavity tripNeed to accommodate any combination of “safe” voltages of superconducting cavities1.1MV, 1.2MV, 1.4MV, 0.8MVNormal conducting cavity wall losses can be considerableLow voltage to minimise power demandReduced power gives sufficient overhead in amplifiers to allow live switching of individual IOTs
25. Digital low-level RFNew cavities will require new LLRFCollaboration with Angela Salom at Alba to adapt the Max IV DLLRF to DiamondEnormous “thank you” to Angela and all at Alba for providing the DLLRF design and codeTo be rolled out to all RF cavities at DiamondNormal conducting cavitiesSuperconducting cavitiesBooster cavityUse one DLLRF unit per cavity in the first instance
26. DLLRF tests on the Diamond boosterDiamond booster is in separate tunnel from storage ring, allowing beam tests to be carried out in a machine shutdownDLLRF operation has been demonstrated in the last monthCode has been modified and EPICS interface developedInterfaces allow rapid switch between analogue and digital systemsLoops have been closed and RF can be maintainedBeam has been accelerated from 100MeV to 3GeV using DLLRFFieldCurrent
27. SummaryStatistics and reliabilityYear-on-year improvement in machine reliabilityRF performance is improving but we still constitute almost half of all machine tripsCavity failure and repairTwo cavity failures in recent yearsOne repaired in on-site cleanroomOne cavity still to be repairedCavity reliabilityCavity fast vacuum trips are under controlIOT updateNow use exclusively e2v IOTsIOTs and klystrons have now accumulated many hours of operationPlans for hybrid operationTwo normal conducting cavities will be installed in 2017Preparations for installation are well developedNew DLLRF has been tested on the booster
28. The Diamond RF GroupChris ChristouPengda GuMatt Maddock Peter Marten Shivaji PandeAdam RankinDavid SpinkThank you for your attentionAny questions?