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ESS-Bilbao Initiative Workshop. Overview of cryo-modules for proton accelerators

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Information about ESS-Bilbao Initiative Workshop. Overview of cryo-modules for proton...
Technology

Published on May 8, 2009

Author: ESS_BILBAO

Source: slideshare.net

Description

Overview of cryo-modules for proton accelerators
Paolo Pierini (INFN Milano)
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overview of cryomodules for proton accelerators Paolo Pierini INFN Sezione di Milano Laboratorio Acceleratori e Superconduttività Applicata Paolo.Pierini@mi.infn.it 19 March 2009 Bilbao

outline • discuss cryogenics & cryomodules design rationales • intent limited to modules for elliptical cavities and few considerations for spoke cavities – not covering other structures, especially QWR case • often not completely relevant (common vacuum, 4 K operation, small scale, ...) • trying not to concentrate on design details, rather explore interplay with the design choices/requirements of the machine / supporting systems March 19 2009 essbilbao initiative workshop - Paolo Pierini 2

SRF cavities and ancillaries - 1 cavities and ancillaries design are chosen on the basis of a complex optimization that depends on: • accelerated particles – velocity profile • beam energy – variety of resonator shapes • beam current – high current asks for consistent HOM damping – low current CW implies high external Q and tight resonance • beam quality requirements – alignment tolerances – High Order Mode damping requirements –… March 19 2009 essbilbao initiative workshop - Paolo Pierini 3

SRF cavities and ancillaries - 2 • pulsed operation – high field is dominant with respect to minimum losses – Lorentz Force Detuning impact the cavity/tuner design – active fast tuner required for high field – high peak power coupler for high current • CW operation – high Q, low losses, dominant with respect to maximum field – microphonics can be crucial – active fast tuner considered for low current – high average power coupler for high current • other machine dependent features – high filling factor: interconnections, tuner, magnets, etc – minimization of static losses : long cryo-strings March 19 2009 essbilbao initiative workshop - Paolo Pierini 4

general considerations • cryomodules are now more and more integrated in the concept/optimization of the accelerator – no longer viewed as the combination of a cavity system and an independently designed cryostat to contain it with minimum losses – modules are especially one (important) part of the overall cryogenic system • the cryostat is one of the cryomodule components and its optimization can affect the cavity package design – in a large size SRF machine the overall cryomodule cost and performances dominate that of individual components • components and systems reliability, and the accelerator availability, are concepts that are now included in the large accelerator design from the beginning – redundancy or MTTR (mean time to repair)? – improve QC for MTBF March 19 2009 essbilbao initiative workshop - Paolo Pierini 5

cryogenic plant: duties • primary – maintain cavities at normal operation temperature • below 2K for elliptical • below 4.5 K for spokes – provide fluid flow for thermal intercepts and shields at multiple temperature levels – supply liquefaction flow for power leads – cool-down and fill (and empty and warm-up) the accelerator – efficiently supports transient operating modes and off-nominal operation • including RF on/RF off and beam commissioning • secondary – allow cool-down and warm-up of limited-length strings for repair or exchange of superconducting accelerating components • to which extent is an important design choice (unit module, strings...) March 19 2009 essbilbao initiative workshop - Paolo Pierini 6

cryogenic distribution system functions • supports operation of the linac – within cooldown and warm-up rate limits and other constraints imposed by accelerating SRF components • time duration of cooldowns, transient thermal gradients, ... • guarantees safety – All cryo component and circuits should be guaranteed not to ever exceed their MAWP (Maximum Allowable Working Pressure) during fault conditions • guarantees machine protection – RF cavities from over pressurization under faulty conditions that can hinder performance • substantial difference with respect to SC magnets! March 19 2009 essbilbao initiative workshop - Paolo Pierini 7

cryogenic distribution system design • design should be independent of cooldown rates, cooldown sequences, or pressurization rates • includes many components to be designed/engineered – feed boxes – cryogenic transfer lines – bayonet cans – string/modules feed and end caps – string connecting and segmentation boxes – gas headers – ... • cryogenic distribution system and cryomodules are not engineered independently March 19 2009 essbilbao initiative workshop - Paolo Pierini 8

the cryomodule environment: a“cartoon” view to He production 2K supports and distribution 5-8 K system 40-80 K RF all “spurious” sources of heat RF penetrations cavities losses to the 2 K circuits need to be properly managed and intercepted at higher temperatures (e.g. conduction from penetration and supports, thermal radiation) these are the accelerator active devices with tight alignment constraints for beam “quality” March 19 2009 essbilbao initiative workshop - Paolo Pierini 9

the efficiency of the thermal cycle • thermal cycle efficiency – efficiency of the thermal cycle, to extract heat Q deposited at Tc we need a work W at temperature Th always greater than the Carnot cycle Th − Tc ⋅ηth W = Q⋅ Tc – including the efficiency of the thermal machine (20% for Tc = 2 K) we need 750 W at room temperature for 1 W at 2 K – all sources of parasitical heat loads need to be carefully avoided if we do not want to pay such a high price! – accurate thermal design in order to minimize the heat losses • Static: Always present, needed to keep the module cold. • Dynamic: Only when RF is on. Due to power deposition by RF fields. • N.B. at different intercept temperatures • when Tc = 4.2 K we have ~ 250 W/W • when Tc = 50-80 K we have ~ 20-10 W/W March 19 2009 essbilbao initiative workshop - Paolo Pierini 10

heat removal by He • heat is removed by increasing the energy content of the cooling fluid (liquid or vapor) – heating the vapor – spending the energy into the phase transition from liquid to vapor • cooling capacity is then related to the enthalpy difference between the input and output helium (∝ to mass flow) • the rest is “piping” design to ensure the proper mass flow, convective thermal exchange coefficient, pressure drop, … @2 K 20 J/g latent heat Premoved [ W] = m flow[g/s] ∆h[J/g ] 40 K to 80 K 5 K to 8 K 2K Temperature level Temperature level Temperature level (module) (module) (module) Temp in (K) 40,00 5,0 2,4 Press in (bar) 16,0 5,0 1,2 Enthalpy in (J/g) 223,8 14,7 4,383 Entropy in (J/gK) 15,3 3,9 1,862 Temp out (K) 80,00 8,0 2,0 Press out (bar) 14,0 4,0 saturated vapor Enthalpy out (J/g) 432,5 46,7 25,04 Entropy out (J/gK) 19,2 9,1 12,58 March 19 2009 essbilbao initiative workshop - Paolo Pierini 11

isothermal saturated bath • to operate the cavities the heat load is ultimately carried away by evaporation in an isothermal bath – either saturated bath of LHe at ambient pressure (4.2 K) – or saturated bath of subatmospheric superfluid LHe (< 2.1 K) March 19 2009 essbilbao initiative workshop - Paolo Pierini 12

state of the art • two main different solutions • the TESLA cryostring concept developed for a superconducting linear collider – tested in the TTF (now FLASH) – used for the European XFEL linac construction (1.7 km) – assumed for the ILC design (~30 km) – concept studied also for proton machines • SPL at CERN, Project X at FNAL • the SNS linac – short & independent units – fast replacement of a single faulty unit – concept used for ADS linac March 19 2009 essbilbao initiative workshop - Paolo Pierini 13

TESLA cryomodule design rationales • high filling factor – maximize ratio between real estate gradient and cavity gradient – long cryomodules/cryo-units and short interconnections • moderate cost per unit length – simple functional design based on reliable technologies – use the cheapest allowable material that respect requirements – minimum machining steps per component – minimum number of different components – low static heat losses in operation • effective cold mass alignment strategy – room temperature alignment preserved at cold • effective and reproducible assembling procedure – class 100/10 clean room assembly just for the cavity string – minimize time consuming operations for cost and reliability March 19 2009 essbilbao initiative workshop - Paolo Pierini 14

consequences/I • The combined request for a high filling factor [machine size] and the necessity to minimize static heat losses [operation cost] leads to integrate the cryomodule concept into the design of the whole cryogenic infrastructure – Each cold-warm transition or cryogenic feed require space and introduces additional static losses • Thus, long cryomodules, containing many cavities (and the necessary beam focusing elements) are preferred, and they should be cryogenically connected, to form cryo- strings, in order to minimize the number of cryogenic feeds – Limit to each cryomodule unit is set by fabrication (and cost) issues, module handling, and capabilities to provide and guarantee alignment March 19 2009 essbilbao initiative workshop - Paolo Pierini 15

consequences/II • The cryogenic distribution for the cryo-string is integrated into the cryomodule, again to minimize static losses – several cryogenic circuits running along the cold mass to provide the coolant for the cavities and for the heat interception at several temperatures • To take out the RF power dissipated along the long cryo- string formed by many cryomodules connected together a large mass flow of 2 K He gas is needed, leading to a large diameter He Gas Return Pipe (HeGRP) to reduce the pressure drop – This pipe was made large and stiff enough so that it can act as the main structural backbone for the module cold mass • cavities (and magnet package) can be supported by the HeGRP • The HeGRP (and the whole cold mass) hangs from the vacuum vessel by means of low thermal conduction composite suspension posts March 19 2009 essbilbao initiative workshop - Paolo Pierini 16

the TESLA module provides • cryogenic environment for the cold mass operation – cavities/magnets in their vessels filled with sub atmospheric He at 2 K – contains He coolant distribution lines at required temperatures – collect large flow of return gas from the module string without pressure increase – Low losses penetrations for RF, cryogenics and instrumentation • shield “parasitical” heat transfer – double thermal shield cavity • structural support of the cold mass size – different thermal contractions of materials 12 m, 38” diameter, string of 8 cavities and magnet – precise alignment capabilities and reproducibility with thermal cycling March 19 2009 essbilbao initiative workshop - Paolo Pierini 17

TESLA/ILC/(XFEL) modular cryogenic concept ILC scheme for segmentation and distribution • each module contains all cryo modules without with without quad quad quad piping RF unit (lengths in meters) 12.652 12.652 12.652 three modules – each cavity tank in module connected to two phase line RF unit RF unit RF unit RF unit end box 37.956 37.956 37.956 37.956 2.500 string (vacuum length) twelve modules plus string end box – vapor is collected from 2 phase line once per module in the string string string string 154.324 154.324 154.324 154.324 possible segmentation unit GRP 48 modules (segmentation box is the same as string end • several modules are connected box (2.5 m) and all contain vacuum breaks) in strings service service box end segment segment segment segment box end Cryogenic Unit – single two phase line along the 2.500 617.296 617.296 617.296 614.796 2.500 (16 strings) (1 cryogenic unit = 192 modules = 4 segments*48 CM string with string end boxes plus service boxes.) 2471.7 meters – a JT valve once per string fills unit length limited by size of cryo plant needed (25 kW equivalent at 4.5 K seems two phase line via subcooled Cryogenic max reasonable extrapolation of 18 kW LHC) distribution box 2.2 K line Line F 75 K return • strings are connected into units Line E 50 K supply Line D 8 K return Line C 5 K supply – each unit is fed by a single Line A Sub-cooled LHe supply cryogenic plant Line B Pumping return Cryo-string Cryo-string Cryo-string Cryo-string Cryo-unit March 19 2009 essbilbao initiative workshop - Paolo Pierini 18

schematically outer shield All lines in module inner shield subcooled forward line GRP March 19 2009 essbilbao initiative workshop - Paolo Pierini 19

cryostrings in TTF&FLASH March 19 2009 essbilbao initiative workshop - Paolo Pierini 20

The cross section Low thermal conduction composite supports Cryogenic Pressurized support helium feeding Helium GRP Shield gas (large because of feeding pressure drop, used as structural backbone) Thermal shields cavity Two phase RF Penetration flow Sliding Coupler support Helium port tank March 19 2009 essbilbao initiative workshop - Paolo Pierini 21

three generations of cryomodules in TTF 1 2 Simplification of fabrication (tolerances), assembling & alignment strategy 2 3 Longitudinal references, redistribution of cross section (42” 38”) March 19 2009 essbilbao initiative workshop - Paolo Pierini 22

from prototype to Cry 3 Extensive FEA modeling (ANSYS™) of the cryomodule – Transient thermal analysis during Braid-cooled Cry 1 - 1997 cooldown/warmup cycles, – Coupled structural/thermal simulations – Full nonlinear material properties Detailed sub-modeling and testing of new components – Finger-welding for stress-relief – Cryogenic tests of the sliding supports March 19 2009 essbilbao initiative workshop - Paolo Pierini 23

Cold mass alignment strategy • The Helium Gas Return Pipe (HeGRP) is the system backbone – 3 Taylor-Hobson spheres are aligned wrt the HeGRP axis, as defined by the machined interconnecting edge flanges • Cavities are aligned and transferred to the T-H spheres • Cavity (and Quad) sliding planes are parallel to the HeGRP axis by machining (milling machine) – Longitudinal cavity movement is not affecting alignment – Sliding supports and invar rod preserve the alignment while disconnecting the cavities from the huge SS HeGRP contraction • 36 mm over the 12 m module length cooling from 300 K to 2 K • Variation of axis distances by differential contraction are fully predictable and taken into account March 19 2009 essbilbao initiative workshop - Paolo Pierini 24

cooldown behavior 300 T in (CMTB) 270 T out (CMTB) Delta T (CMTB) 240 DeltaT (ANSYS) T in (ANSYS) 210 T out (ANSYS) Temperature (K) 180 150 120 70 K shield 90 60 30 0 0 5 10 15 20 25 30 35 40 45 50 55 60 Time (h) comparison FEM with CMTB cooldown • Fairly sophisticated non linear 300 T out (CMTB) transient FEM models 270 T in (CMTB) Delta T (CMTB) 240 T in (ANSYS) – reproduce with good accuracy T out (ANSYS) 210 Delta T (ANSYS) the cooldown behavior Temperature (K) 180 – assess max thermal gradients 150 and stresses during transients 120 5 K shield 90 – allow to identify suitable 60 cooldown rates to keep thermal 30 stresses below safe limits 0 0 5 10 15 20 25 30 35 40 45 50 55 60 Time (h) March 19 2009 essbilbao initiative workshop - Paolo Pierini 25

linac performances, low static load budget ~ 70 W ~ 13 W < 3.5 W March 19 2009 essbilbao initiative workshop - Paolo Pierini 26

proven design, still few details to clean up • XFEL introduced small enhancements – quad sliding fixture (as for cavities) – better heat sinking (all coupler sinking style) – cables, cabling, connectors and feed-through – module interconnection: vacuum vessel sealing, pipe welds, etc. – coupler provisional fixtures and assembly – preparing large production at qualified industries • important actions for ILC – move quadrupole to center (vibrations) – short cavity design (decrease cutoff tube) – cavity interconnections: flanges and bellows (Reliability) – fast tuner (need coaxial so that filling factor can be further increased!) March 19 2009 essbilbao initiative workshop - Paolo Pierini 27

TESLA cryomodule concept summary positive • very low static losses • very good filling factor: best real estate gradient • low cost per meter in term both of fabrication and assembly project dependent • long cavity strings, few warm to cold transitions • large gas return pipe inside the cryomodule cavities and quads position controlled at ± 300 µm (rms) • • reliability and redundancy for longer MTTR (mean time to repair) • lateral access and cold window natural for the coupler negative • Long MTTR in case of non scheduled repair • Moderate (± 1 mm) coupler flexibility required March 19 2009 essbilbao initiative workshop - Paolo Pierini 28

different design: SNS cryomodule cryo distribution feed/end boxes March 19 2009 essbilbao initiative workshop - Paolo Pierini 29

SNS He flow He Supply 5 K, 3 bar outside module He Return Cryo lines Coupler and flange thermalization with 4.5 K flow 2K Counterflow HEX 50 K Shield/thermalization March 19 2009 essbilbao initiative workshop - Paolo Pierini 30

design rationales • Fast module exchange and independent cryogenics (bayonet connections) 1 day exchange 2K production in CM • Warm quad doublet Moderate filling factor • Designed for shipment 800 km from TJNAF to ORNL • No need to achieve small static losses single thermal shield March 19 2009 essbilbao initiative workshop - Paolo Pierini 31

design for shipment (TJNAF to ORNL) 4g 5g g/2 spaceframe concept March 19 2009 essbilbao initiative workshop - Paolo Pierini 32

Around the cold mass • Helium to cool the SRF linac is provided by the central helium liquefier • He from (8 kW) 4.5K cold box sent through cryogenic transfer lines to the cryomodules • Joule Thomson valves on the cryomodules produce 2.1 K (0.041 bar) LHe for cavity cooling, and 4.5 K He for fundamental power coupler cooling • boil-off goes to four cold-compressors recompressing the stream to 1.05 bar and 30 K for counter-flow cooling in the 4.5K cold box Magnetic shields 50 K thermal shield Vacuum chamber Tank End Plate March 19 2009 essbilbao initiative workshop - Paolo Pierini 33

Alignment strategy • indexing off of the beamline flanges at either end of each cavity • Nitronic support rods used to move the cavity into alignment • targets on rods on two sides of each flange. • cavity string is supported by the spaceframe • each target sighted along a line between set monuments (2 ends and sides) • the nitronic rods are adjusted until all the targets are within 0.5 mm of the line set by the monuments • cavity string in the vacuum vessel: the alignment is verified and transferred (fiducialized) to the shell of the vacuum vessel. March 19 2009 essbilbao initiative workshop - Paolo Pierini 34

Project-X baseline cryogenics • 2-phase He at 4.5 K • Revised TESLA cryo string concept • Strings are fed in parallel • 2 phase He line at 2 K – first string SC solenoids, warm RF – concurrent liquid supply and vapor – second string SSR/TSR modules return flow in the string • Cryomodules are fed in series • Double thermal shielding in strings to limit radiation flow at 2 K March 19 2009 essbilbao initiative workshop - Paolo Pierini 35

Project-X head load table Project X ICD 25 MV/m, 1.5 msec, Heat Load Qty 5Hz, 20 mA, 1.25 FT 2K 4.5K 5K 40K or 80K [# ] Item Static Dynamic Static Dynamic Static Dynamic Static Dynamic WRF Solenoid 19 42 99 536 - - - - - SSR1 2 42 1 1003 2 - - - - SSR2 3 62 10 1279 8 - - - - TSR 7 93 50 1965 40 - - - - S-ILC 7 27 17 69 18 517 477 - - ILC-1 9 35 43 105 47 727 1,226 - - ILC-2 28 110 133 328 146 2,260 3,813 - - SCB, End Boxes, etc 1 50 100 500 - - - - - Auxiliary Load 1 - 1000 - - - - - - Estimated, [W] 222 193 338 160 502 211 9787 5566 Design Capacity, [kW] 0.8 1.0 1.4 29.9 4.5K Eqv [kW] 8.2 Plug Power, [MW] 2.3 March 19 2009 essbilbao initiative workshop - Paolo Pierini 36

Project-X cryo r&d plan • cryo distribution and segmentation – study existing cryomodules thermal cycling experience – stationary, transient, fault, maintenance and commissioning scenarios – component over pressure protection study – define cryogenic string size limits and segments – liquid helium level control strategy development – development of tunnel ODH mitigation strategy • capital and operational cost optimization – lifecycle cost optimization & Cryogenic Plant Cycle – heat shields operating parameter optimization • heat load analysis – static and dynamic loads analysis for components/sub systems – define overcapacity and uncertainty factors – fault scenarios heat flux study March 19 2009 essbilbao initiative workshop - Paolo Pierini 37

HINS - SSR1 conceptual cryomodule layout string on strongback, dressed, aligned, shielded vessel replicates assembly table supports March 19 2009 essbilbao initiative workshop - Paolo Pierini 38

Support post pockets strongback concept Support lugs March 19 2009 essbilbao initiative workshop - Paolo Pierini 39

spoke/solenoid mounting scheme Analysis of the strongback deflections unders dead loads with support optimization March 19 2009 essbilbao initiative workshop - Paolo Pierini 40

Vacuum vessel with internal strongback supports March 19 2009 essbilbao initiative workshop - Paolo Pierini 41

EUROTRANS prototype module • short, single cavity module under fabrication for the European program on ADS assisted nuclear waste transmutation EUROTRANS (CW) – based on the SNS concept of short independently fed and rapidly exchangeable units – will be used for long testing for the reliability characterization of components • reliability/beam availability is the key goal for ADS linacs, rather than performance INFN MI & IPN Orsay March 19 2009 essbilbao initiative workshop - Paolo Pierini 42

emerging issues • pressure vessel regulation (in a EU contest) – will big machines in the near future require formal certification of components as pressure vessels? • non standard materials, welds & T ranges, not in PV codes – XFEL effort in collaboration with German TÜV • “Crash tests” performed in Cryomodule Test Bench – slow and fast loss of all vacuum spaces (coupler, iso, beam) – very successful • hydraulic testing of HeTank space at 1.43 MAWP=6 bar, according to safety regulations – although ok for beta=1 cavities, treacherous issue for low beta structures • resolving issues of integrating different components contributed “in- kind” from several partner into a single object • worldwide approach from ILC GDE – how can a truly worldwide project deal with many different regulations across the three regions (Europe, Asia, America) – also linked to “plug-compatibility” approach on components March 19 2009 essbilbao initiative workshop - Paolo Pierini 43

XFEL crash tests • No major damage – cavities unchanged • pressure behavior in circuits confirmed – beam pipe venting shows that pressure drop needs 3.6 s to propagate to other side of module - Good March 19 2009 essbilbao initiative workshop - Paolo Pierini 44

trade offs & choices for cryomodule design • Main decision: Filling factor vs. fast module exchange – Linac length vs. availability/reliability concerns – Real estate gradient is more strongly influenced by module length constraints or cavity ancillaries than from intrinsic cavity accelerating gradient • Heat load balances and cryo system layout – need in iterations to estabilish layout • Can’t “buy” a single design, as it is – Can surely transfer design ideas and subcomponents • TESLA attractive for filling factor • SNS for module exchange capabilities • LEP has easy access to cold mass, but not compatible with 2 K March 19 2009 essbilbao initiative workshop - Paolo Pierini 45

Acknowlegments • I want to thank many colleagues, since I have been using their material from privately and publicly available presentations and tutorials, in particular (but not limited to...) • Tom Peterson, Arkadiy Klebaner, Tom Nicol, Don Mitchell, Vittorio Parma, Joe Preble, ... • Whole TTF/XFEL colleagues in DESY & INFN Milano March 19 2009 essbilbao initiative workshop - Paolo Pierini 46

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