ngVLAThe Next Generation Very Large Array
NATIONAL RADIO ASTRONOMY OBSERVATORY
AdvancedCryocoolersForngVLALarryD’Addario,Caltech
ngVLA Workshop,Socorro,2017June26
The Next Generation Very Large Array
Outline
•Howcolddoweneedtoget?•Tutorialoncryocoolers(justafewslides)•Cyrocooler industry:suppliersandcustomers•Existingradiotelescopecryocoolers•Surveyofavailablecryocoolers•RecommendationsforngVLA
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The Next Generation Very Large Array
HowColdisColdEnough?I will show some plots based on the following model, covering physical temperatures of 0-80K and frequencies 1-50 GHz• LNA based on InP HEMT transistors from “cryo3” wafer (well
modeled)• Input transistor operated at optimum input impedance (for each
temperature and frequency)• Transistors subject to self-heating of up to 18K [1].• Feed is cooled to the same temperature as LNA and has 1% loss• Dewar window is at 300K and has 1% loss• Antenna is pointed at 45º elevation• Spillover noise is 3K, independent of frequency• Sky noise from the Bryan Butler model for VLA site with 6 mm PWV
[1] J. Schleeh et al., “Phonon black-body radiation limit for heat dissipation in electronics.” Nature Materials, 10 Nov 2014 (on line).
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Tsys vs.FrequencyandTphys
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The Next Generation Very Large Array
DiminishingReturns
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The Next Generation Very Large Array
CostofGettingColder
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SunPower MT SHIRDK101D/CNA11C SHIRDK408D2/CSA71A
The Next Generation Very Large Array
CryocoolerThermodynamics– Ideal
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Efficiency = QL/W = COP
(ideally) = TL/(TH - TL) [Carnot]
300K to 20K: ηc = 20/280 = 7.1%
Carnotcycle
TH
TL
The Next Generation Very Large Array
CryocoolerThermodynamics– Practical
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Sterling (reverse)
Gifford-McMahon
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PulseTubeRefrigerators
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Sterling Type GM Type
• Nomovingpartsinthecoldregion->lowmaintenance,lowvibration• Generallylessefficientthanparenttype
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Multi-StageCryocoolers
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• Fortemperatures<30K,itisoftenadvantageoustoachievethelowesttemperatureintwostages.
• Typically60-80K atstage1.• Simplestversionshavecommoncompressorandcommondrivetodisplacer.
• Simplifiessecondstagedesignbynotrequiringsealsandmaterialstoworkoverwiderange300to~10K.
• Providesauxiliarycoolingatstage1temperature,often veryuseful
• Coolingofradiationshieldsandotherintermediatestructures.• Reducedloadatlowesttemperature.• Higheroverallefficiencythanhavingallloadsatlowtemp.
• Normalizedefficiency(C.S.Kirkconnel andK.D.Price,Cryocoolers11,2001)• 𝐶𝑂𝑃$%&'(),'(&+ =
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Two-stageGMcryocooler(SHI)
Stage1coldstation
Stage2coldstation
The Next Generation Very Large Array
CryocoolerIndustry• Magneticresonanceimaging:superconductingmagnets
• 1W coolingat4K• >40,0004K GMcryocoolerssoldsince1995.
• Infraredsensors• Primarilymilitaryapplications(nightvision,weaponguidance)• 0.3to1.75W coolingat65to120K• ~180,000coolerssince1970s
• Highvacuum:cyropumping,primarilyforsemiconductorprocessing• afewwattsat15K• ~20,000peryearatpeakofsemiconductorbusiness
• Space:IRandX-raydetectors,otherspecializedapplications• mission-specific• lowpower,lowmass• smallquantities,veryexpensive
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The Next Generation Very Large Array
CryocoolerManufacturers• Commercial
• CTI->HelixTechnologies->BrooksAutomation(one- andtwo-stageGM)• SHICryogenics[Sumitomo](one- andtwo-stageGMandGM-typePT)• Cryomech (single-stageGM)• OxfordCryosystems (one- andtwo-stageGM)• Qdrive (largesingle-stageSterling)• Sunpower (smallsingle-stageSterling)
• Aerospace/Military• BallAerospace• Raytheon• NorthropGrumman• HoneywellAerospace
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The Next Generation Very Large Array
SpecialConsiderationsforRadioAstronomy• Variableorientationwithrespecttogravity• Needtocoolsubstantialmass(feed,waveguides,mechanicalstructures)
• Cooldowntimecanbeverylong• Cu,300K to77K:73kJ/kg->20.3h/kg/W.• Wouldlikehighcapacityduringcooldown,butlessinequilibrium.• Cryocoolerisoftenoversizedtoachievecooldown.
• Withgooddesign,coolingloadisdominatedbyconnectionstotheoutsideratherthandissipationinside
• Radiationthroughinputwindow:20cmdiameteradmits14.4W of300K radiation.• Conductionthroughwaveguides,coaxcablesandwires.
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The Next Generation Very Large Array
CryocoolersinExistingRadioTelescopes• Almostallaretwo-stageGMtypes,reaching15-25K dependingonheatload.• Manytelescopesusecryocoolerdesignsthatare30-40yearsold.• GMcryocoolerinventedin1960
• Two-stageversionscommercialized~1970withCTImodel1020(stillinproduction!).
• Superconductingreceivers(SISmixers,somebolometers)[notforngVLA]• Requirecoolingto~4K• Until~15yearsago,reliedonopen-cyclecoolingwithliquidHeoraddingaJoule-Thompson3rdstagetoa2-stageGM.
• Veryinefficient• Now2-stageGMcoolersreaching<4K areavailableduetoexoticregeneratormaterials(Er3Ni,HoCu).
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The Next Generation Very Large Array
VLAAntennaReceiverCabin
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8frontends(4shown),eachinaseparatevacuumchamberwithitsowncryocooler.
1 ea.CTI1050(L)6ea.CTI350(S,C,X,Ku,K,Ka)1ea.CTI22(Q)
3compressors,18kWtotal
The Next Generation Very Large Array
19-ElementPhasedArrayFeedReceiver(forGBT)
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CTI1050cryocooler(3W at15K,60W at70K;~5500W input)
G.Cortes-Medellinetal.,"AFullyCryogenicPhasedArrayCameraforRadioAstronomy," IEEETransonAP,63:2471-2481,June2015.
70cmdiameter
The Next Generation Very Large Array
Covers 30-950 GHz with 10 receivers in a single large cryostat.Cryocooler is shown in red
Uses a “special” three stage GM cryocooler ordered from Sumitomo1st stage 33W @ 68K2nd Stage 8W @ 13.7K3rd Stage 1W @ 4.2K
ALMA
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Surveyofavailabletwo-stagecryocoolers
Includes:• COTSmachines• Publishedlaboratorydemos• Spaceapplications(small
quantity)
COTS:SterlingCryogenics
Raytheon:RSP2 hybrid
The Next Generation Very Large Array
Sterlingvs.GM(includingPT)
Sterling(andSterling-type PT) Gifford-McMahon(and GM-typePT)
Carnot efficiency~10% Carnotefficiency ~3%
Compressoradjacenttocoldhead Compressorcanberemote
Little tonomaintenancefor>10years Replacementofsealsevery12-24 months
Varypowerinput/capacitybyamplitudeorfrequency Varypower input/capacitybyfrequency
Canshiftcapacitybetweenstagesbyphaseadjustment Capacityratioofstagesfixed
PTversionmayhaveslight orientationdependence
PTversionmayhavelargeorientationdependence
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The Next Generation Very Large Array
RaytheonRSP2:Sterling-PTHybrid• Sterling1st stageandpulsetube2nd stage.Nomovingpartsatlowtemp.• Designedforspaceapplications,evolvedover15yearsofdevelopment
• Prototypebuiltin2000 2.2W at80K 0.5W at35K• Publishedin2009 16.2W at80K 2.6W at35K 513W input 11.35%• Publishedin2014(LT-RSP2) 6W at55K 0.31W at10K 450W input 7.94%• AnalysisforngVLA (LT-RSP2) 6W at60K 2.1W at20K 450W input 11.87%
• Comparablecooling:SHISDK-101D withCNA-11C compressorat3x powerinput:
• 2.5W at20K,4.5W at60K,1400W input• NormalizedCarnotefficiency3.8%
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Sterlingcompressor
PTcompressor
Intertance tubeandreservoir Stage2
Stage1PhotocurtesyofTedConrad,RaytheonCompany
The Next Generation Very Large Array
RecommendationsforngVLA• Don’ttrytoachieveverylowtemperatures,especiallyat1.2-3GHz• Engagewiththeaerospaceindustry• AllocatefundsforNRE
• Develophardwarematchedtoourspecificneeds• Don’tcountonoff-the-shelfprocurement
• Hireanin-houseexpert• Couldsuperviseanin-housedevelopmentteam• Ifdevelopmentisdonebycontracting(morelikely),in-houseexpertisstillneededforproperoversight
• ConsiderspendingmoreonconstructionandNRE tosaveonoperations• Pay-backtimeforpowersavingsiseasytocalculate
• Saving20kWperantennafor200antennasisabout1M$/year->worthseveralM$investment.• Maintenancesavingislikelytobesignificanttoo
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The Next Generation Very Large Array
Backup
• Backupslidesfollow
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The Next Generation Very Large Array
ImportantParameters
• Netrefrigerationpower: dQ/dt• Powerinput,P: P=dW/dt• ActualCoefficientofPerformance,COP : COP=(dQ/dt) /P• Ideal(Carnot)COPCarnot : COPCarnot =Tc/(Th-Tc)• Efficiency,η: η =COP/COPCarnot• SpecificPower 1/COP
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The Next Generation Very Large Array
ComponentsofSystemNoiseat30GHz
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The Next Generation Very Large Array
SystemNoiseModelwithNoSelfHeating
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The Next Generation Very Large Array
RaytheonLT-RSP2
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Optimizationsfor20K operation:–InertanceTube Length–ReservoirVolume–FillPressure–OperatingFrequency
ImagesfromSchaefer2014,Cryocoolers18.
SimulationforngVLAbyTedConway,RaytheonCompany
