ESS-Bilbao Initiative Workshop. Overview of cryo-modules for proton accelerators
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Transcript of ESS-Bilbao Initiative Workshop. Overview of cryo-modules for proton accelerators
19 March 2009 Bilbao
overview of cryomodules
for proton accelerators
Paolo PieriniINFN Sezione di Milano
Laboratorio Acceleratori e Superconduttività [email protected]
March 19 2009 essbilbao initiative workshop - Paolo Pierini 2
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
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SRF cavities and ancillaries - 1
• 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– …
cavities and ancillaries design are chosen on the basis of a complex optimization that depends on:
March 19 2009 essbilbao initiative workshop - Paolo Pierini 4
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
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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
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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...)
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• 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!
cryogenic distribution system functions
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• 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
cryogenic distribution system design
March 19 2009 essbilbao initiative workshop - Paolo Pierini 9
supports
the cryomodule environment: a“cartoon” view
all “spurious” sources of heat 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)
RFcavities RF penetrations
to He production and distribution
system
2 K
5-8 K
40-80 K
these are the accelerator active devices with tight alignment
constraints for beam “quality”
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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
– 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
thc
ch
TTT
QW η⋅−⋅=
March 19 2009 essbilbao initiative workshop - Paolo Pierini 11
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, …
40 K to 80 K 5 K to 8 K 2 KTemperature level Temperature level Temperature level(module) (module) (module)
Temp in (K) 40,00 5,0 2,4Press in (bar) 16,0 5,0 1,2Enthalpy in (J/g) 223,8 14,7 4,383Entropy in (J/gK) 15,3 3,9 1,862Temp out (K) 80,00 8,0 2,0Press out (bar) 14,0 4,0 saturated vaporEnthalpy out (J/g) 432,5 46,7 25,04Entropy out (J/gK) 19,2 9,1 12,58
]J/g[]g/s[]W[ hmP flowremoved ∆=@2 K 20 J/g latent heat
March 19 2009 essbilbao initiative workshop - Paolo Pierini 12
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)
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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 14
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
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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
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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
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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
• structural support of the cold mass– different thermal contractions of
materials– precise alignment capabilities and
reproducibility with thermal cycling
12 m, 38” diameter, string of 8 cavities and magnet
cavity size
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TESLA/ILC/(XFEL) modular cryogenic concept
• each module contains all cryo piping– each cavity tank in module
connected to two phase line– vapor is collected from 2 phase
line once per module in the GRP
• several modules are connected in strings– single two phase line along the
string– a JT valve once per string fills
two phase line via subcooled 2.2 K line
• strings are connected into units– each unit is fed by a single
cryogenic plant
modules without with withoutquad quad quad
RF unit (lengths in meters) 12.652 12.652 12.652three modules
RF unit RF unit RF unit RF unit end boxstring (vacuum length) 37.956 37.956 37.956 37.956 2.500
twelve modules plus string end box
string string string stringpossible segmentation unit 154.324 154.324 154.324 154.324
48 modules (segmentation box is the same as string end box (2.5 m) and all contain vacuum breaks)
service service box end segment segment segment segment box end
Cryogenic Unit 2.500 617.296 617.296 617.296 614.796 2.500
(16 strings) (1 cryogenic unit = 192 modules = 4 segments*48 CM with string end boxes plus service boxes.)
2471.7 meters
ILC scheme for segmentation and distribution
unit length limited by size of cryo plantneeded (25 kW equivalent at 4.5 K seems
max reasonable extrapolation of 18 kW LHC)
Cryo-string Cryo-string Cryo-string Cryo-string
Pumping return
Sub-cooled LHe supply
5 K supply
8 K return
50 K supply
75 K return
Cryogenic distribution box
Cryo-unit
Line D
Line E
Line F
Line C
Line A
Line B
March 19 2009 essbilbao initiative workshop - Paolo Pierini 19
schematicallyA
ll lin
es in
mod
ule
inner shield
outer shield
GRP
subcooled forward line
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cryostrings in TTF&FLASH
March 19 2009 essbilbao initiative workshop - Paolo Pierini 21
The cross section
Shield gas feeding
Heliumtank
Couplerport
Thermalshields
Slidingsupport
HeliumGRP
Cryogenicsupport
Two phaseflow
Pressurizedhelium feeding
Shield gas feeding
Heliumtank
Couplerport
Thermalshields
Slidingsupport
HeliumGRP
Cryogenicsupport
Two phaseflow
Pressurizedhelium feeding
Heliumtank
Couplerport
Thermalshields
Slidingsupport
HeliumGRP
Cryogenicsupport
Two phaseflow
Pressurizedhelium feeding
Low thermal conduction composite supports
cavity
RF Penetration
(large because of pressure drop, usedas structural backbone)
March 19 2009 essbilbao initiative workshop - Paolo Pierini 22
three generations of cryomodules in TTF
�������� �������� �� �������� ��� ��
1�2 Simplification of fabrication (tolerances), assembling & alignment strategy2�3 Longitudinal references, redistribution of cross section (42”�38”)
March 19 2009 essbilbao initiative workshop - Paolo Pierini 23
from prototype to Cry 3
Extensive FEA modeling (ANSYS™) of the cryomodule
– Transient thermal analysis during 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
Braid-cooled Cry 1 - 1997
March 19 2009 essbilbao initiative workshop - Paolo Pierini 24
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 25
cooldown behavior
• Fairly sophisticated non linear transient FEM models – reproduce with good accuracy
the cooldown behavior– assess max thermal gradients
and stresses during transients– allow to identify suitable
cooldown rates to keep thermal stresses below safe limits 0
30
60
90
120
150
180
210
240
270
300
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (h)
Tem
pera
ture
(K
)
T out (CMTB)T in (CMTB)Delta T (CMTB)T in (ANSYS)T out (ANSYS)Delta T (ANSYS)
0
30
60
90
120
150
180
210
240
270
300
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (h)
Tem
pera
ture
(K
)
T in (CMTB)T out (CMTB)Delta T (CMTB)DeltaT (ANSYS)T in (ANSYS)T out (ANSYS)
5 K shield
70 K shield
comparison FEM with CMTB cooldown
March 19 2009 essbilbao initiative workshop - Paolo Pierini 26
linac performances, low static load budget
~ 70 W ~ 13 W < 3.5 W
March 19 2009 essbilbao initiative workshop - Paolo Pierini 27
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 28
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 29
different design: SNS cryomodule
cryo distribution feed/end boxes
March 19 2009 essbilbao initiative workshop - Paolo Pierini 30
SNS He flowHe Supply 5 K, 3 bar
He Return
2 K
50 K Shield/thermalization
Coupler and flange thermalization with 4.5 K flow
Counterflow HEX
Cry
o lin
es
outs
ide
mod
ule
March 19 2009 essbilbao initiative workshop - Paolo Pierini 31
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 32
design for shipment (TJNAF to ORNL)
g/2
5 g
4 g
spaceframe concept
March 19 2009 essbilbao initiative workshop - Paolo Pierini 33
Around the cold mass
Tank
50 K thermal shield
Magnetic shields
Vacuum chamberEnd Plate
• 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
March 19 2009 essbilbao initiative workshop - Paolo Pierini 34
Alignment strategy
• 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.
• 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.
March 19 2009 essbilbao initiative workshop - Paolo Pierini 35
Project-X baseline cryogenics
• 2-phase He at 4.5 K• Strings are fed in parallel
– first string SC solenoids, warm RF– second string SSR/TSR modules
• Cryomodules are fed in series
• Revised TESLA cryo string concept
• 2 phase He line at 2 K
– concurrent liquid supply and vapor return flow in the string
• Double thermal shielding in strings to limit radiation flow at 2 K
March 19 2009 essbilbao initiative workshop - Paolo Pierini 36
Item Static Dynamic Static Dynamic Static Dynamic Static DynamicWRF Solenoid 19 - - 42 99 - - 536 -SSR1 2 - - 42 1 - - 1003 2SSR2 3 - - 62 10 - - 1279 8TSR 7 - - 93 50 - - 1965 40S-ILC 7 27 17 - - 69 18 517 477ILC-1 9 35 43 - - 105 47 727 1,226ILC-2 28 110 133 - - 328 146 2,260 3,813SCB, End Boxes, etc 1 50 - 100 - - - 500 -
Auxiliary Load 1 - - - - - - 1000 -
222 193 338 160 502 211 9787 5566
4.5K 5K 40K or 80K
Project X ICD
25 MV/m, 1.5 msec, 5Hz, 20 mA, 1.25 FT Qty
[# ]
Heat Load2K
29.9 Design Capacity, [kW] 0.8 1.0 1.4 Estimated, [W]
Plug Power, [MW] 2.38.24.5K Eqv [kW]
Project-X head load table
March 19 2009 essbilbao initiative workshop - Paolo Pierini 37
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 38
HINS - SSR1 conceptual cryomodule layoutstring on strongback, dressed, aligned, shielded
vessel replicates assembly table supports
March 19 2009 essbilbao initiative workshop - Paolo Pierini 39
strongback concept
Support lugs
Support post pockets
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spoke/solenoid mounting scheme
Analysis of the strongbackdeflections unders dead loadswith support optimization
March 19 2009 essbilbao initiative workshop - Paolo Pierini 41
Vacuum vessel with internal strongback supports
March 19 2009 essbilbao initiative workshop - Paolo Pierini 42
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 independentlyfed 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 43
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 44
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 45
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 46
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