high efficiency klystron development for particle accelerators · high efficiency klystron...
TRANSCRIPT
HighEfficiencyKlystronDevelopmentforParticleAccelerators
D.A.ConstableOnbehalfofHEIKA (HighEfficiencyInternationalKlystronActivity)
C.Lingwood,G.Burt,V.Hill- LancasterUniversity&CockcroftInstituteI.Syratchev - CERNA.Yu.Baikov -MoscowUniversityofFinance&LawI.Guzilov - VDBTR.Marchesin - ThalesGroupR.Kowalcyzk - L-3CommunicationsElectronDevicesA.Jensen- SLACC.Marrelli - ESS
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
Whyinvestigatehighefficiencyklystrons?• RFdemandsofproposedlargescaleparticleaccelerators:
– ~100MWlevelpoweroutput.– Highefficiencydesirable.– Reliable,robustvacuumtubes.– Operation~1-12GHz.– Candidatetubes:klystrons&IOTs.
• Stateoftheartklystrons:– Fewdevicesdeliverefficienciesover65%.– LHCemploys300kW,400MHz,65%efficiencyklystrons.
• Newresearch:– Focusonhighefficiency,ratherthanhighpower.– Utilise moderncomputationalmethods.– Strongunderstandingofunderlyingphysics.– Newideasandthinking.– HEIKA collaborationseekstoaddressthis.
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
linear
ILCe+e-:Pulsed,1.3GHz,PRF total=88MW0.5TeV
3.0TeV
CLICe+e-:Pulsed,1.0GHz,PRF total=180MW
FutureParticleAccelerators&RFRequirements
FCC
FCCee:CW,0.8GHz,PRF total=100MW
circular
Forcomparison:LHC:CW,0.4GHz,PRF total=5MW
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
CandidateTubes:MBKs
• MultipleBeamKlystrons:– Highefficiency.– Reductioninbeamvoltage.– Splitcurrentacrossseveral
cathodes.
• TypicalMBKdevices,L-band:– Maximumcurrentefficiency,~70%.– Theoreticalefficiencies,~80%.– Maxsaturatedoutputpower,~10
MW.
• Challenges:– Increasedcomplexity.– Tubeperformancelimitedby
slowestelectron(avoidreflectedparticles).
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
ExampleTarget:ProposedFCC-ee HEKCWTube
HEIKA workingteam:I. I.Syratchev(CERN)II. G.Burt(Lancaster)III. C.Lingwood(Lancaster)IV. D.Constable(Lancaster)V. V.Hill(Lancaster)VI. R.Marchesin (Thales)VII. Q.Vuillemin (Thales/CERN)VIII. A.Baikov(MUFA)IX. I.Guzilov(VDBT)X. C.Marrelli(ESS)XI. R.Kowalczyk (L-3com)XII. T.Habermann (CPI)XIII. A.Jensen(SLAC)
16beamsMBKcavityR/Q=22Ohm/beam
Tubeparameters:• 1.5MW• Voltage:40kV• Totalcurrent:42A• Targetefficiency:90%• Nbeams:16• µK/beamx106 :0.23• Ncavities:8• Frequency:800MHz
HEKCW
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
“Traditional”ElectronBunching
• Forhighefficiency,traditionallywechaselowperveance:– Perveance isameasureofthespacechargeofelectronbeam.– Lowperveance achievedthrougheither:
• Highvoltages• Lowcurrents(manybeamsinanMBK)
• Forhighpowerbothbecome“unpleasant”.
• Performancelimitedbytheslowestelectronsafteroutputcavity(must avoidtrappingorreflectingelectrons).
• Traditionaltheoreticalefficiencylimitedto80%.
• Toimprovetubeefficiencies,non-traditionalbunchingmechanismsarerequired:– CoreOscillationMethod(COM).
• COM2.– Bunching-Alignment-Collection(BAC)method.– Useofhigherharmoniccavities.
𝑃𝑒𝑟𝑣𝑒𝑎𝑛𝑐𝑒 = 𝐼𝑉,..
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
CoreOscillationMethod(COM)
• Coreoscillationmethod:– Centreofbunchallowedtobunchandde-bunch
betweencavities.– Coreexperienceslargerspacechargeforce.– Outsidersbroughtmonotonicallytobunch.– Outsidersexperiencelargerphaseshiftduetosmaller
spacechargeforces.• Tubesusingcoreoscillations:
– Longerinlength.– Suitableforhighfrequency(X-band).– Moreelectronscontainedwithinbunchatoutputgap.– Therefore,highermaximumefficiency.
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
HEKCW08-SeriesCoreOscillation– 800MHz
• 8cavity,singlebeamtube:– ProofofprincipleofCOM.– 1-D&2-Dmodelling:KlypWin,AJDISK,TESLA,MAGIC.– Numberoftubeiterations,frequencies,driftlengths.– Beamparameters,133.85kV,12.551A.– ConsistentefficienciesacrossHEIKAcodes.– Tubelength,~6m;impracticalat800MHz.
• BestCOMresult(08-04-08):– MAGIC2-D,84.62%.– Stableacrosstransfercurve.
• RadialstratificationofelectronbunchinPIC:– Bunchvelocityvarieswithradialposition.– Notobservedin1-D/2-Dcodes.– ElectronsclosetoaxisnotaffectedbyRF.
Outputpower
Cavity8Cavity7
Klystronlengthefficiency
8_04_XXseriessummary
KlypWin:88.6%Klys2D:81.6%
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
HEKCW08H-SeriesHollowBeam,withCoreOscillation– 800MHz
• Removestratificationeffectsbyusingahollowbeam:– Sameoperationalparametersas08-Series.– Onaxisparticlesremovedfromsituation.– Beamdensitykeptconstantwith08-series.– Consistentefficiencypredictionsacross2-Dcodes,
>85%.– Stableacrossallinputpowers.– Wellbunchedelectronbeam.– Veryfewparticlesoutsideofbunch.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70
Efficiency(%)
InputPower(W)
Magic
TESLA
AJDISK
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
XL-5Klystron(A.Jensen)
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
XL-5KlystronwithCOM(A.Jensen)
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
COM2(A.Baikov,O.Baikova)
• ExtensionofCOM,introductionof2ndharmoniccavities:– PrinciplesofCOM,withreducedlength.– Outsiderelectronsexperiencelarger
phaseshiftdueto2nd harmoniccomparedtofundamentalharmonic.
– Thus,outsidersbroughtintobunchinshorterdistancethanCOM.
– Advantageousatlowerfrequency(lesscomplicatedcavities).
• Twopossibleschemes:– Pairsof1st and2nd harmoniccavities:
• Doublingofthenumberofcavities.• Spacingbetweencavitiescould
becomesmall.– 1st &2nd harmonicsinthesamecavity:
• Increasedcavitycomplexity.• Drivingsignalattwofrequencies.
– 1-Dsimspredictefficiencies>90%.
...2f
f 2f f 2f f f
RF Output
fbeam
2f f
f+2f
f+2f
...
f+2f
f+2f
f+2f
f RF Output2f
beamf
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
BunchingAlignmentCollectionMethod(BAC)• Alsobasedoncoreoscillations.• Interactionspaceiswasted“waiting”forspacechargeforcestodebunch.• SeriesofthreecavitiescanachievethesameeffectasCOMacrossashorterdistance:
– Aligningelectronvelocities.– 2nd harmoniccavitiesallowforfurtherreductioninlength.– BringoutsiderelectronsintobunchoverlessspacethaninCOM.
• StructurehalfthelengthofCOMwhilemaintainingefficiency.• MorecavitiesrequiredcomparedwithCOM:
– Difficultathighfrequencywithharmonics.– SignificantnumberofcavitiesifmultipleBACsectionsareused.
• ImplementedsofarinS-bandtubes.
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
SLAC5045S-BandBACRetrofit(A.Jensen)
• S-bandSLACklystron5045upgradedwithaBACbunchingsector.• Thisisthemostmass-produced(>800)highpeakRFpower(65MW)tube.• Firsttestsarescheduledtobedoneinspring2016.
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
VDBTS-BandBACKlystron(I.Guzilov)
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
VDBTS-BandBACKlystronNumericalResults(I.Guzilov)
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
VDBTS-BandBACKlystronExperimentalResults
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
F-Tube/FG-Tube(C.Marrelli,V.Hill)
• ExtensionofBACmethod:– Uses1st,2nd and3rd harmonic
cavities.– 2nd and3rd harmonicsallow
collectionofoutsidersinreduceddistance.
– KlystronshalfthelengthofCOMtubes(~2metres).
– ForFCC(800MHz),3rd harmoniccavitiesnotdifficulttoconstruct.
– Outputpower<2MW.– Designedtominimise electron
phasecrossover.– Presents”ideal”bunchatoutput.
• F-Tube:– Frequency,800MHz.– Numberofcavities,6.– FG-Tubeuses2additional1st
harmoniccavities.• Allowsmoregradual/gentler
collectionofparticles.– Efficiencies>80%predictedin
AJDISK.
FG-Tube
80.87%
F-Tube
80.25%
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
F-Tube/FG-Tube(C.Marrelli,V.Hill)
• EarlyPICresults:– F-Tubeefficiency,80%.– FG-Tubeefficiency,73%.
• Phasespace comparison:– Additional1st harmonic
cavitiesinFG-Tuberesultsinmoreslablikeprofileatoutputcavity.
– F-Tubebunchisunder-rotatedincomparison:• Spreadofelectron
velocitiesacrossbunchlength.
– Slightincreaseintubelengthof~cm.
FG-Tube,Efficiency:73%
FG-Tube
F-Tube
F-Tube
FG-Tube
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
ComparisonofBunchingMethodsAJDISK- 800MHz
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016
Summary&FutureResearch
• Employingnewbunchingmechanisms,efficiencies>80%attainableforFCC/CLIC/ESS/ILC:– Nonewmaterialsormanufacturingtechniques.– Noadditionalcomplexity.
• CoreOscillationMethod:– 84.6%efficiencyachievedinPIC,butverylongtubes.– Hollowelectronbeamallowsmitigationofradialstratificationinbunch– efficiency>86%.– IdealcandidateforX-band – modifiedXL-5tubepredictsbetterthan70%efficiency.– COM2predictsfurtherincreasesinefficiency,suitableatlowerfrequencies.
• Bunching-Alignment-CollectionMethod:– ReducedtubelengthincomparisontoCOM.– Retrofittingandtestingoftubesdemonstratesincreaseinefficiency.– 60%efficiencyshownexperimentally(increaseof18%)atSband.
• F-Tube/FG-Tube:– ~80%efficiencypredictedinPIC.– IdealcandidateforFCC– highefficiency,~2mlong,3rd harmonicnotcomplexat800MHz.
• Future:– Extendmodellingto3-D.– Designrefinement,construction,testingoftubes.
eeFACT16,CockcroftInstitute,Daresbury,24-27October2016