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

The Next Generation Very Large Array

PulseTubeRefrigerators

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Sterling Type GM Type

• Nomovingpartsinthecoldregion->lowmaintenance,lowvibration• Generallylessefficientthanparenttype

The Next Generation Very Large Array

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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The Next Generation Very Large Array

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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