Handling of large HOM powers Recovery of degraded cavities 20120221 MAC2012 Yoshiyuki MORITA Machine parameters and HOM power Machine parameter of SuperKEKB HER Beam Current 26A2500 bunches ID: 1042103
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1. Improvement of superconducting cavitiesHandling of large HOM powersRecovery of degraded cavities20120221 MAC2012Yoshiyuki MORITA
2. Machine parameters and HOM powerMachine parameter of SuperKEKB/HERBeam Current ：2.6A/2500 bunchesBunch length：5mmHOM powerCavity loss factor：1.2V/pC @σ=5mmExpected HOM power：31kWLBP damper load：26kWDamper loss=0.26 V/pCSBP damper load: 20kWDamper loss=0.30 V/pCTotal heat load per cavity：46kWLoss factor1.2V/pCParameters of HERMaximum current: 2.6A ←1.35ABunch length: 5 mm ←6-7mm# of bunches: 2500 ←1600Beam pipe: 150ΦCavity loss factorLBPSBP
3. Issues related to present ferrite HOM damper systemFerrite material is sintered on a copper base pipe by hot isostatic press (HIP) method. FerriteThickness: 4 mmFerrite surface temperature ：190℃ @2.6 AGas release from ferrite triggers high voltage breakdownCooling waterWater temperature＜60℃To prevent air bubblesDeaeration system >60℃Chiller unitTotal heat load：46 kW per cavityCooling capacity （with a safety margin）：60kWCooling capacity of present chiller: 27 kWHIPped ferrite （Thickness：4mm）Cupper pipe (3/8”) for cooling channelFlange: Stainless steel Beam currentSBP loadLBP load(A)(kW)(kW)212152.62026
4. Development of new HOM dampers for SuperKEKBTo suppress gas release from ferrite materialSuppress temperature rise of ferriteUse 3 mm thick ferrite (KEKB damper: 4 mm)For better thermal conductionDamper loss factor is expected to be reduced1/3 of the total load is damper self lossTo suppress temperature rise of cooling waterIntroduce double cooling structureFerrite thickness: 3 mmTwo cooling channelsPrototype damper with 3 mm thick ferriteA-type coolingB-type coolingDouble cooling structureSingle cooling structureThickness :4→3 mmTaper sectionHIPped ferrite
5. High power test results 3mm thick dampers with double cooling structurecc1cc3cc5cc2cc4cc6RF power flowSBP damperLBP damperAbsorbed powerExpected heat loads were absorbed in dampers but surface temperatures decreased only 20℃Cracks after HPTCracks were found after HPT3mm thick ferrite might not have enough strengthThermo-couple numberSCSDCSDouble cooling structure suppressed temperature rise of the copper baseTemperature distribution at 14 kW
6. Other methods to handle large HOM powerEnlarge beam pipe diameter150φ→200φDecrease loss factor Decrease HOM powerAdditional dampersAdd SiC dampers on the beam pipeTo reduce ferrite damper loadStudies for SiC damperBeam pipe structureLoss factor＠σ＝5mm（V/pC）Modifications to be madePresent BP (150φ)1.2200φ BP0.8GV dia.Bore dia. (Q-mag.)200φ BPTaper (200φ→150φ)0.95GV dia.200φ LBP onlyTaper (200φ→150φ)1.05LBP-GV dia.SiCSiCPresent beam pipe: 150Φ
7. Recovery of degraded cavitiesVacuum leakageVacuum leakage happened at cooldown in May 2010Indium sealed flange was suspected as a causeThe cavity was removed from KEKB ringThe cryomodule opened Bolts tightening flanges were loose (60kgｆcm)Thermal cycles might loosen those voltsThose bolts were retorqued (150kgｆcm)Cooled and high power testedNo vacuum leakageLoose bolts were cause of the leakageDegraded with strong field emissionsVoltage reached 1.3 MVLimited by the radiation safety ruleCavity surface was probably contaminated with dust particles Q factors of other cavitiesD10A, D10C, and D11C degraded with field emissions at high fieldsStill acceptable for SuperKEKB operationRecovery of degraded cavity is desirable for long time operationCold cathode gauge at BPMetal vacuum gauge at HPCLiquid level was kept at 10 %Pirani gauge at vacuum insulation ProcessedQo measured from cryogenic heat loads10%
8. Horizontal high pressure rinsingHigh pressure water rinsing (HPR) is effective to recover degraded cavities contaminated by dust particlesIf we can apply HPR to cavities in cryomodule, Saves a lot of time and costsR&D is ongoingUltrapure water jet (8MPa) from a stainless steel nozzleWasted water was collected by an aspirator at the equator areaEvacuated with residual waterHHPR in our clean roomStainless steel nozzle
9. RF performance after HHPR2009.3.30 EPII (10μm)2009.4.16 Baked at 120 ℃2009.5.21 Cold test after EPII2009.6.17 HHPR(1st trial) Evacuated in vertical positionResidual water dropped on BPF2009.6.25 Cold test after 1st HHPRWithout bake2010.2.8 HHPR(2nd trial)Evacuated in horizontal positionResidual water stayed in EQ2010.2.25 Cold test after 2nd HHPRWithout bakeProcessed once but no degradationApplicable for cavity rinsing in a cryomoduleAfter EPIIAfter 1st HHPRAfter 2nd HHPR
10. Plan of the next three yearsHOM power handlingStop development of 3 mm thick ferrite dampersDevelop 4 mm thick ferrite dampers with a double cooling structureAssemble 200ΦBP and install to the recovered cavityStudy SiC dampers to lower ferrite damper loadsRecovery of degraded cavitiesTry HHPR in a cryomodule for performance recoveryExchange the recovered cavity with one of degraded cavitiesFY2012FY2013FY2014HOM damper developmentHigh power test for 4mm thick dampers with double cooling structureStudy for SiC dampersRecovery of degraded cavity (CA-B03)and 200Φ beam pipeHHPR in cryomoduleHigh power testAssembly of 200Φ BP modulesIf not recover HHPR in clean room Cold test EPII (if necessary) Cold testAttach 200Φ BP for low LF High power testInstall in SuperKEKBCool-down test
11. backup
12. Damper loss factor Damper loss factors Use CST-PSCalculate 1 to 4 mm thick ferrite dampersNot reduced as expected (8%)σ=5 mm
13. Summary of leaked cavities and Q0 degradationsDateOperation phaseInstalled placeCavity IDLeaked at1998/10/23Cool-downD11BCA-B03He vessel, no influence on cavity vacuum pressureRepaired in April, 19991999/05/20Cool-downD11ACA-B02He vessel, no influence on cavity vacuum pressureJan. 2001Warm-upD10ACA-B06Indium seal of LBP, resealed in clean roomSep. 2001Cool-downD11CCA-B04Indium seal of LBP, resealed in clean room2004/01/09Cool-downD10CCA-B08Indium seal of LBP, resealed in clean room2004/12/25In beam operationD11ACA-B02HOM damper flange, HOM damper exchangedExchanged with CA-B01 in June 20062005/07/02Warm-upD10ACA-B06Indium seal of SBP or LBP, retorqued2008/07/07Summer shutdownD11ACA-B01Ion pump connector, retorqued2010/05/01Cool-downD11BCA-B03Indium seal of SBP or LBP, retorquedExchanged with CA-B02 in Nov. 2010High power input couplers exchangedduring summer shutdown in 2005Q0 degradation at Vc=2 MVCA-B02Resealed with 0.5 mm thick indium in Oct. 2006Metal gaskets exchanged in Dec. 2006Installed in KEKB in Nov. 2010HPC exchangedLeakLeak