IntroductionIntroduction ToTo CryostatCryostat DesignDesign J. G. Weisend II National Science Foundation SLAC National Accelerator Laboratory CourseCourse GoalsGoals ProvideProvide anan introductionintroduction toto cryostatcryostat designdesign ExamineExamine cryostatscryostats asas integratedintegrated systemssystems ratherrather thenthen aa groupgroup ofof subsystemssubsystems ProvideProvide backgroundbackground informationinformation andand usefuluseful datadata ProvideProvide pointerspointers toto resourcesresources forfor moremore detaildetail ShowShow examplesexamples Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 2 SyllabusSyllabus IntroductionIntroduction CryostatCryostat RequirementsRequirements MaterialsMaterials SelectionSelection ThermalThermal IsolationIsolation andand HeatHeat LeakLeak StructuresStructures SafetySafety InstrumentationInstrumentation Seals,Seals, FeedFeed throughsthroughs andand BayonetsBayonets TransferTransfer LinesLines ExamplesExamples ReferencesReferences andand ResourcesResources Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 3 IntroductionIntroduction WhatWhat isis aa cryostat?cryostat? AA devicedevice oror systemsystem forfor maintainingmaintaining objectsobjects atat cryogeniccryogenic temperatures.temperatures. CryostatsCryostats whosewhose principalprincipal functionfunction isis toto storestore cryogeniccryogenic fluidsfluids areare frequentlyfrequently calledcalled DewarsDewars.. NamedNamed afterafter thethe inventorinventor ofof thethe vacuumvacuum flaskflask andand thethe firstfirst personperson toto liquefyliquefy hydrogenhydrogen Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 4 WhichWhich BringsBrings UsUs toto aa LimerickLimerick ““SirSir JamesJames DewarDewar isis aa betterbetter manman thanthan youyou areare NoneNone ofof youyou assesasses cancan liquefyliquefy gassesgasses”” Anon.Anon. Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 5 IntroductionIntroduction CryostatsCryostats areare oneone ofof thethe technicaltechnical buildingbuilding blocksblocks ofof cryogenicscryogenics ThereThere areare manymany differentdifferent typestypes ofof cryostatscryostats withwith differingdiffering requirementsrequirements TheThe basicbasic principlesprinciples ofof cryostatcryostat designdesign remainremain thethe samesame BeforeBefore wewe cancan dodo anythinganything elseelse wewe havehave toto definedefine ourour requirementsrequirements Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 6 E158E158 LHLH2 2 TargetTarget CryostatCryostat Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 7 CryostatCryostat RequirementsRequirements MaximumMaximum allowableallowable heatheat leakleak atat variousvarious temperaturetemperature levelslevels This may be driven by the number of cryostats to be built as well as by the impact of large dynamic heat loads (SCRF or target cryostats) AlignmentAlignment andand vibrationvibration requirementsrequirements Impact of thermal cycles Need to adjust alignment when cold or under vacuum? Alignment tolerances can be quite tight (TESLA : +/- 0.5 mm for cavities and +/- 0.3 mm for SC magnets) Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 8 CryostatCryostat RequirementsRequirements NumberNumber ofof feedfeed throughsthroughs forfor power,power, instrumentation,instrumentation, cryogeniccryogenic fluidfluid flows,flows, externalexternal manipulatorsmanipulators SafetySafety requirementsrequirements (relief(relief valves/burstvalves/burst discs)discs) Design safety in from the start. Not as an add on SizeSize andand weightweight Particularly important in space systems InstrumentationInstrumentation requiredrequired Difference between prototype and mass production Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 9 CryostatCryostat RequirementsRequirements EaseEase ofof accessaccess toto cryostatcryostat componentscomponents ExistingExisting codecode requirementsrequirements (e.g.(e.g. TUVTUV oror ASME)ASME) Need,Need, ifif any,any, forfor opticaloptical windowswindows PresencePresence ofof ionizingionizing radiationradiation ExpectedExpected cryostatcryostat lifelife timetime WillWill thisthis bebe aa oneone ofof aa kindkind devicedevice oror somethingsomething toto bebe massmass produced?produced? Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 10 CryostatCryostat RequirementsRequirements ScheduleSchedule andand CostCost ThisThis shouldshould bebe consideredconsidered fromfrom thethe beginningbeginning AllAll DesignDesign isis CompromiseCompromise Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 11 MaterialMaterial SelectionSelection MaterialMaterial propertiesproperties changechange significantlysignificantly withwith temperature.temperature. TheseThese changeschanges mustmust bebe allowedallowed forfor inin thethe design.design. ManyMany materialsmaterials areare unsuitableunsuitable forfor cryogeniccryogenic use.use. MaterialMaterial selectionselection mustmust alwaysalways bebe donedone carefully.carefully. TestingTesting maymay bebe required.required. Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 12 MaterialMaterial SelectionSelection Some suitable materials for cryogenic use include: Austenitic stainless steels e.g. 304, 304L, 316, 321 Aluminum alloys e.g. 6061, 6063, 1100 Copper e.g. OFHC, ETP and phosphorous deoxidized Brass Fiber reinforced plastics such as G –10 and G –11 Niobium & Titanium (frequently used in superconducting RF systems) Invar (Ni /Fe alloy) useful in making washers due to its lower coefficient of expansion Indium (used as an O ring material) Kapton and Mylar (used in Multilayer Insulation and as electrical insulation Quartz (used in windows) Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 13 MaterialMaterial SelectionSelection UnsuitableUnsuitable materialsmaterials include:include: Martensitic stainless steels Undergoes ductile to brittle transition when cooled down. Cast Iron – also becomes brittle Carbon steels – also becomes brittle. Sometimes used in 300 K vacuum vessels but care must be taken that breaks in cryogenic lines do not cause the vacuum vessels to cool down and fail. Rubber, Teflon and most plastics although plastic insulated wires are frequently OK as long as the wire is not repeatedly flexed which could lead to cracking of the insulation. Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 14 ThermalThermal ExpansivityExpansivity LargeLarge amountsamounts ofof contractioncontraction cancan occuroccur whenwhen materialsmaterials areare cooledcooled toto cryogeniccryogenic temperatures.temperatures. PointsPoints toto consider:consider: ImpactImpact onon alignmentalignment DevelopmentDevelopment ofof interferencesinterferences oror gapsgaps duedue toto dissimilardissimilar materialsmaterials IncreasedIncreased strainstrain andand possiblepossible failurefailure ImpactImpact onon wiringwiring MostMost contractioncontraction occursoccurs aboveabove 7777 KK Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 15 ThermalThermal ExpansivityExpansivity αα=1/L=1/L ((δδL/L/δδTT)) ResultsResults fromfrom anharmonicanharmonic componentcomponent inin thethe potentialpotential ofof thethe latticelattice vibrationvibration Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 16 ThermalThermal ExpansivityExpansivity α goes to 0 at 0 slope as T approaches 0 K α is T independent at higher temperatures For practical work the integral thermal contraction is more useful Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 17 IntegralIntegral ThermalThermal ContractionContraction Material ΔL / L ( 300 – 100 ) ΔL / L ( 100 – 4 ) Stainless Steel 296 x 10 -5 35 x 10 –5 Copper 326 x 10 -5 44 x 10 -5 Aluminum 415 x 10 -5 47 x 10 -5 Iron 198 x 10 -5 18 x 10 -5 Invar 40 x 10 -5 - Brass 340 x 10 –5 57 x 10 -5 Epoxy/ Fiberglass 279 x 10 –5 47 x 10 -5 Titanium 134 x 10 -5 17 x 10 -5 Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 18 IntegralIntegral ThermalThermal ContractionContraction RoughlyRoughly speakingspeaking MetalsMetals –– 0.5%0.5% oror lessless PolymersPolymers –– 1.51.5 –– 3%3% SomeSome amorphousamorphous materialsmaterials havehave 00 oror eveneven negativenegative thermalthermal contractioncontraction Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 19 HeatHeat CapacityCapacity oror SpecificSpecific HeatHeat ofof SolidsSolids CC == dU/dTdU/dT oror Q/Q/mmΔΔTT InIn general,general, atat cryogeniccryogenic temperatures,temperatures, CC decreasesdecreases rapidlyrapidly withwith decreasingdecreasing temperature.temperature. ThisThis hashas 22 importantimportant effects:effects: SystemsSystems coolcool downdown fasterfaster asas theythey getget coldercolder AtAt cryogeniccryogenic temperatures,temperatures, smallsmall heatheat leaksleaks maymay causecause largelarge temperaturetemperature risesrises Introduction to Cryostat Design J. G. Weisend II 11/10/2008 ICEC 2008 20 SpecificSpecific HeatHeat ofof SolidsSolids WhereWhere isis thethe heatheat storedstored ?? LatticeLattice vibrationsvibrations ElectronsElectrons (metals)(metals) TheThe explanationexplanation ofof thethe temperaturetemperature dependencedependence ofof thethe specificspecific heatheat ofof solidssolids waswas anan