High Efficiency Klystron Development for Particle Accelerators · High Efficiency Klystron Development for Particle Accelerators ... R. Marchesin-Thales Group ... KlypWin, AJDISK,

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.


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


CandidateTubes:MBKs

• MultipleBeamKlystrons:– Highefficiency.– Reductioninbeamvoltage.– Splitcurrentacrossseveral

cathodes.

• TypicalMBKdevices,L-band:– Maximumcurrentefficiency,~70%.– Theoreticalefficiencies,~80%.– Maxsaturatedoutputpower,~10

MW.

• Challenges:– Increasedcomplexity.– Tubeperformancelimitedby

slowestelectron(avoidreflectedparticles).


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


“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,..


CoreOscillationMethod(COM)

• Coreoscillationmethod:– Centreofbunchallowedtobunchandde-bunch

betweencavities.– Coreexperienceslargerspacechargeforce.– Outsidersbroughtmonotonicallytobunch.– Outsidersexperiencelargerphaseshiftduetosmaller

spacechargeforces.• Tubesusingcoreoscillations:

– Longerinlength.– Suitableforhighfrequency(X-band).– Moreelectronscontainedwithinbunchatoutputgap.– Therefore,highermaximumefficiency.


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%


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


XL-5Klystron(A.Jensen)


XL-5KlystronwithCOM(A.Jensen)


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


BunchingAlignmentCollectionMethod(BAC)• Alsobasedoncoreoscillations.• Interactionspaceiswasted“waiting”forspacechargeforcestodebunch.• SeriesofthreecavitiescanachievethesameeffectasCOMacrossashorterdistance:

– Aligningelectronvelocities.– 2nd harmoniccavitiesallowforfurtherreductioninlength.– BringoutsiderelectronsintobunchoverlessspacethaninCOM.

• StructurehalfthelengthofCOMwhilemaintainingefficiency.• MorecavitiesrequiredcomparedwithCOM:

– Difficultathighfrequencywithharmonics.– SignificantnumberofcavitiesifmultipleBACsectionsareused.

• ImplementedsofarinS-bandtubes.


SLAC5045S-BandBACRetrofit(A.Jensen)

• S-bandSLACklystron5045upgradedwithaBACbunchingsector.• Thisisthemostmass-produced(>800)highpeakRFpower(65MW)tube.• Firsttestsarescheduledtobedoneinspring2016.


VDBTS-BandBACKlystron(I.Guzilov)


VDBTS-BandBACKlystronNumericalResults(I.Guzilov)


VDBTS-BandBACKlystronExperimentalResults


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%


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


ComparisonofBunchingMethodsAJDISK- 800MHz


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.


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High Efficiency Klystron Development for Particle Accelerators · High Efficiency Klystron Development for Particle Accelerators ... R. Marchesin-Thales Group ... KlypWin, AJDISK,