Superconducting Cavity Cryomodule Designs for the Next Generation of CW Linacs: Challenges and Options

Superconducting Cavity Cryomodule Designs for the Next Generation of CW Linacs: Challenges and OptionsT. H. Nicol, Y. M. Orlov, T. J. Peterson, V. P. YakovlevFermilabJune 19, 2014tnicol@fnal.gov

Many thanks to our co-workers, colleagues, and collaborators at laboratories around the world and to the cooperative spirit we all share.FermilabFermilabOutlineCryomodule design overviewOverall configurationsSupport systemsThermal shields and insulationMagnetic shieldingCryogenic pipingTunersCouplersSummaryJune 19, 2014IPAC 2014 - Dresden2FermilabCryomodule Design OverviewThere are lots of cavity types being used in various superconducting RF linac designs around the worldSingle and multiple spokeHalf and quarter-waveElliptical resonatorsOperating in pulsed or CW modeSpanning frequencies from a few hundred megahertz to several gigahertzOperating nominally at 4.5 K or 2 KJune 19, 2014IPAC 2014 - Dresden3FermilabCryomodule Design Overview (contd)In spite of this variety, cryomodules for those cavities contain many common design features. They all haveOuter vacuum shellCold mass support systemOne or more layers of magnetic shieldingOne or more intermediate thermal shieldsMulti-layer insulationCryogenic pipingCavity tuning systemsInput and HOM couplersBeam vacuum gate valvesInstrumentationJune 19, 2014IPAC 2014 - Dresden4FermilabCryomodule Design Overview (contd)There are also features that might be unique to each designActive alignment systemsCavity position monitoring systemsInternal heat exchangersCold-to-warm-transitionsActive magnetic elementsCurrent leadsSegmentationAnd many othersJune 19, 2014IPAC 2014 - Dresden5FermilabCryomodule Design Overview (contd)The goal here is to describe some of the options available to designers of both pulsed and CW mode cryomodules.Focus will be on things that guide the design process and ultimately lead to a design choice.Most of the time there is no right or wrong choice.More often than not, final design features are a compromise between many factors.June 19, 2014IPAC 2014 - Dresden6FermilabOverall ConfigurationsJune 19, 2014IPAC 2014 - Dresden7

1.3 GHz elliptical cavity XFEL cryomodule at DESY(example of course segmentation)Technology demonstrator cryomodule for FRIBRound vessels tend to house elliptical cavities and spoke resonatorsRectangular vessels tend to house quarter and half-wave cavitiesFermilabOverall Configurations (contd)June 19, 2014IPAC 2014 - Dresden8

Quarter-wave cryomodule for the Atlas upgrade at ArgonneARIEL cryomodule at TriumfFermilabOverall Configurations (contd)

June 19, 2014IPAC 2014 - Dresden9Jefferson Lab cryomodule (example of fine segmentation)

FermilabStructural SupportsChallenges and OptionsStructural loads due to shipping and handling, cooldown, fluid flow, and ground motionLow heat load requirement to cavities, magnets, and thermal shieldsMaterial choices are generally composites, high strength stainless steel, and titaniumConfigurations include posts, tension members, space frames, and many othersJune 19, 2014IPAC 2014 - Dresden10FermilabStructural Supports (contd)

June 19, 2014IPAC 2014 - Dresden11FermilabStructural Supports (contd)

June 19, 2014IPAC 2014 - Dresden12FermilabSupport Systems (contd)June 19, 2014IPAC 2014 - Dresden13SSC magnet support

XFEL and ILC cryomodule support

FermilabSupport Systems (contd)

June 19, 2014IPAC 2014 - Dresden14FRIB cryomoduleFermilab

Support Systems (contd)June 19, 2014IPAC 2014 - Dresden15ESS magnet support and space frame

ESS cavity supported from the input couplerJefferson Lab upgrade cryomoduleFermilabThermal Shields and InsulationChallenges and OptionsProvide effective heat transfer of thermal radiation and provide a source for discreet interceptsShields can be single or multiple annular shellsUsually segmented or include features to minimize thermal bowing during cooldown and warm-upMaterials are most often aluminum (lighter, less expensive, difficult to connect to other piping) or copper (heavier, more expensive, easily soldered or brazed)MLI is usually double aluminized mylar with fabric or nylon spacers or aluminum foilTypical heat transfer rates are ~1 W/m2 for 30 layers from 300 K to 70 K and 50 to 100 mW/m2 for 10 layers below 80 KJune 19, 2014IPAC 2014 - Dresden16FermilabThermal Shields and Insulation (contd)

June 19, 2014IPAC 2014 - Dresden17XFEL cryomodule shields and MLIFermilabThermal Shields and Insulation (contd)June 19, 2014IPAC 2014 - Dresden18

JLab upgrade thermal shieldFermilabThermal Shields and Insulation (contd)June 19, 2014IPAC 2014 - Dresden19

ILC cryomodule shields and MLIThermal shield bowingFermilabThermal Shields and Insulation (contd)June 19, 2014IPAC 2014 - Dresden20

MLI blanketsFermilabMagnetic ShieldingChallenges and OptionsShield the superconducting cavities from the Earths magnetic field and stray fields internal to the cryomodule from magnets and magnetized componentsPlays a role in maintaining cavity Q, especially in high-Q designs like LCLS-IIDifficult to minimize penetrations and material degradation due to handling and joiningCan be single or multiple shells, warm, cold or both, materials can be conventional mu-metal or materials optimized for low temperatureJune 19, 2014IPAC 2014 - Dresden21FermilabMagnetic Shielding (contd)June 19, 2014IPAC 2014 - Dresden22

Cold internal magnetic shieldRoom temperature magnetic shieldFermilabMagnetic Shielding (contd)June 19, 2014IPAC 2014 - Dresden23

1st Pair Attached3rd Pair Attached Over 1st and 2nd Pair and AroundChimney23All Shield Parts 1mm ThickFermilabMagnetic Shielding (contd)June 19, 2014IPAC 2014 - Dresden24

Interconnect Shield Fixed End2nd Layer Interconnect ShieldInterconnect ShieldSliding Joint24FermilabCryogenic PipingChallenges and OptionsProvides supply and return for cavities, magnets, thermal shields, and interceptsSizing must accommodate 2 K speed limit and meet the requirements of maximum heat loadSizing, wall thickness, and materials must meet applicable pressure vessel code requirementsOptions depend on segmentation, the need for internal valves, whether an internal heat exchanger is required, etc.Materials can include stainless steel, aluminum, copper, and titaniumJune 19, 2014IPAC 2014 - Dresden25FermilabCryogenic Piping (contd)June 19, 2014IPAC 2014 - Dresden26

Cryomodule piping connections for course segmentationMay also serve as the pressure relief lineFermilabCryogenic Piping (contd)

June 19, 2014IPAC 2014 - Dresden27Cryomodule piping connections for fine segmentationFermilabCryogenic Piping (contd)June 19, 2014IPAC 2014 - Dresden28

Connection diameter vs. heat flux5 meter/sec speed limit for vapor over liquid sets 2-phase pipe sizePIP-II Total CM Heat Loads [W]70 K5 K2 KPulsed2,860895256CW2,8608951819FermilabCryogenic Piping (contd)

June 19, 2014IPAC 2014 - Dresden29

1.3 GHz elliptical cavity XFEL cryomodule at DESY12 GeV upgrade cryomodule at JLabFermilabTunersChallenges and OptionsFrequency change adjustment due to manufacturing errors, cooldown, Lorentz forces, fluid flow, external displacements, ground motion, and rotating machineryTuning range from a few Hz to several kilohertzTuner types include lever, blade, and diaphragm or local deformationActuators can include motors or pressurized actuators and can be internal or external to the cryomoduleFine and fast tuning may require piezo-electric cartridgesJune 19, 2014IPAC 2014 - Dresden30FermilabTuners (contd)

June 19, 2014IPAC 2014 - Dresden31

Lever tunerBlade tunerFermilabTuners (contd)

June 19, 2014IPAC 2014 - Dresden32Scissors jack tuner at JLabFermilabTuners (contd)June 19, 2014IPAC 2014 - Dresden33

Lever style tuner on a single spoke resonatorFermilabCouplersChallenges and OptionsProvide multi-megawatt power for pulsed or CW operationMultipacting, breakdown, and heating are common issuesDesigned for clean assemblyCopper coated bellows have proven challengingCouplers can be coaxial, waveguide or a combination of bothOne or more vacuum windows are usually requiredExternal cooling may be required, especially for high power CW systemsJune 19, 2014IPAC 2014 - Dresden34FermilabCouplers (contd)June 19, 2014IPAC 2014 - Dresden35

1.3 GHz cavity coaxial input couplerFermilabCouplers (contd)June 19, 2014IPAC 2014 - Dresden36

Waveguide sections in JLab upgrade cryomoduleFermilabCouplers (contd)June 19, 2014IPAC 2014 - Dresden37

Single window coaxial coupler for SSR1 cavities at FermilabFermilabSummarySuperconducting RF linac projects are being built in laboratories around the world.In spite of their differences all share many common features.They remain challenging due to cleanliness requirements, high RF power, high-Q cavities, low thermal losses, multipacting, mode extraction, tuning, alignment, and cost.For now at least, they seem to be the dominant direction being taken in accelerator research, taking full advantage of all our cooperative spirit.June 19, 2014IPAC 2014 - Dresden38FermilabThanks very much

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