Mechanical Design
of Main Linac Cryomodule (MLC)
Yun He, Dan Sabol, Joe Conway
On behalf of
Matthias Liepe, Eric Smith, James Sears,
Tim O’Connell, Ralf Eichhorn
Outline
 Design criteria
 Beamline and its support
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Beamline components
Helium gas return pipe
Support posts and alignment components
Vacuum vessel
 Thermal and magnetic design
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Post
40K thermal shield
Magnetic shields
Multi-layer insulation
 Cryogenic environment
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Layout of cooling pipes
2K cooling loop
 Materials, sizes and weights of sub-assemblies
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Design criteria
Cryomodule provides support, alignment, cryogenic environment, thermal
shielding and magnetic shielding for the cavities
Requirements
Design
Support
Beamline is supported by HGRP onto three posts mounted on vacuum vessel
Weights: Beamline ~1 Ton, Coldmass ~3 Ton, Module ~7 Ton
Alignment
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Allowable transverse offset (x,y): 2mm for cavities, 1.6 mm for quads
Allowable pitch: 1.5 mrad (1.2 mm over the length of cavity)
Precision machined support interfaces with alignment pins/keys provides
precision alignment at room temperature and allows for differential thermal
contractions at cold
Thermal shielding
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Minimize heat leak at 2 K, 5 K, and 40-80 K
Insulation vacuum to eliminate convective heat transfer by gases
40K thermal shield with multi-layer insulation to reduce radiation heat inleak
Support system with low thermal conductivity material G10
Magnetic shielding
Magnetic field at cavity location should be <3 mG
Two layers of magnetic shields, one wraps cavity and the other on 40K shield
Cryogenic environment
Cavities are immersed in 2 K liquid helium bath
Cryogenic piping is inside module, providing 2K, 5K and 40-80 K cooling
Vibration
Push resonant frequency higher with proper support/stiffness to cooling pipes
to minimize vibration effect on cavity tuning and RF power requirements
Cost
Minimize linac length and transverse diameter
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Cross-sectional view of module
HGRP support
post + alignment
Rails
40K shield
+ Mu-metal shield
Cryogenic valves
HGRP
4”
2K-2 Phase
9.5”
Input coupler
Vacuum vessel
38” dia. OD
Cavity in 2K Helium bath
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1. Beamline and its support
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Beamline string components
Helium gas return pipe
Support posts and alignment components
Vacuum vessel
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Beamline sub-assembly
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9.8 m long
six packages of 7-cell cavity/Coupler/tuner
a SC magnets/BPMs package downstream
five regular HOM absorbers/two taper HOM absorbers
A gate valve at each end to keep beamline a UHV unit
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One manual, to be opened once two modules are connected
One pneumatic
Cavity package with coupler,
tuner and HOM absorber
Beam
9.8 m
Beamline
interconnection
SC magnets/BPMs
Taper HOM load
Manual gate valve
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Taper HOM load
Pneumatic gate valve
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Supports for cavity
Material: Ti Grade 2
• LHe vessel
• supports
Alignment pins provides
horizontal alignment
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Flexible support allows 1mm differential thermal
displacement of helium vessel relative to HGRP during
cool-down/warm-up
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Supports for other beamline
components
Alignment keys allow for differential thermal displacement of
beamline components relative to HGRP
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SC magnets/BPMs package
High temperature
superconducting current leads
Port to 2K/2 phase line
Port for pre-cool
BPMs
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Dipole
Quads
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Beamline strongback - Helium gas
return pipe
 Beamline (~ 1 Ton) is suspended under HGRP via three support posts
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Center post fixed, side posts allow differential contractions during cool-down
 Material : Grade 2 Ti, ID Φ280mm, wall thickness 9.5mm
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Similar thermal expansion rate with niobium
Does not need transition for being welded to Nb
Fixed Point
Sliding post
Sliding post
High precision machined mounting surfaces with central pin holes
Provide precision alignments of beamline components
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Helium gas return pipe -- production
steps
 Final precision machining of top and bottom surfaces and pin holes with one set-up
 Heat treatment to relieve internal stress?
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Support post -- alignment
components
 Three posts connected to HGRP to support cold mass ( ~3 Ton)
 Posts are fastened to suspension brackets
 Adjustable brackets allow alignment of cold mass position to vacuum vessel references
Adjust post position
Suspension bracket
Bellows
Vacuum vessel
top flange
Post
HGRP
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Vacuum vessel
Ports for cryogenic valves
Ports for GV
& SC magnets
Port for pressure relief
Port for coupler
Port for post
Port for instrumentation
and access to tuner
 Material:
38” OD x 3/8” wall carbon steel cylinder
SS 316L for all flanges
 Lining with Co-Netric mu-metal shielding
Or a mu-metal shield on 40K shield? To be decided
 Painted:
interior with polyurethane and exterior with marine paints
 A top port for spring-loaded gas relief disk (ID 4”)
to prevent insulation vacuum from over pressurization in
case of accidental spills of LHe
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Hanger for lifting & transportation
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Rails for cold mass insertion
ɸ37-1/4” ID, 3/8 Thickness
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Vacuum vessel – reinforcements and
references
Cross-section of top port
Reinforcement around the opening
Reference arm for
survey target
Stiffening rings to top port
Brackets for
waveguide supports
SS flange with O-ring seal
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Vacuum vessel – production steps
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Weld supports/end flanges
Align end flanges holes within 0.1°
0.002” flatness/coplanar/parallelism for
bottom plates to vessel cylinder reference
and each other
Drill the holes
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Weld side flanges and brackets for
waveguide supports
Weld top flanges and survey arms
Weld rail supports and align them within
0.02”
• Final machining on all flanges’ sealing surfaces, holes on bottom supports and
waveguide brackets
• Precision machining of survey arms
• Install rails
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2.
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Thermal design
Support post
40K thermal shield
Magnetic shields
Multi-layer insulation
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Support post – thermal design
 A major source of heat leak via conduction
 Same design/size as those in TTF, supports up to 5 Ton weight Material: Fiber
reinforced plastic (FRP) G10, low thermal conductivity, from ACPT
 Four stages of shrink-fit metal discs/rings, with MLI on intercept discs
300K
4th stage -- 300K (SS 316L)
Conduction
3rd stage -- 40K intercept (Al)
40K shield
G-10 tube
2nd stage -- 5K intercept (Al)
2K HGRP
1st stage -- 2K (SS 316L)
5K braids clamped to
5K manifold
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Support post – production steps
 Plan to use the same company who built the posts for ILC cryomodule
 Four stages of shrink-fit metal discs/rings, w/ interferences of 0.15-0.3 mm
Step #1
G10 tube
Step #2
Al disk
Tooling
Step #2
Cool down Al disk along with tooling to LN2
Put on G10 tube
Press top plate
Let assembly #1 warm up to room temperature
Step #5
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Step #4
Al ring
Step #1
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Step #3
Step #6
• Warm up Al ring along with tooling to 200 oC
• Put on assembly #1
• Let assembly #2 cool down to room temperature
Then repeat Step #2 & #3
Step #7
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Step #8
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40K thermal shield – general
information
 Three sections, each mounted on a post, fixed joint on middle post and flexible joints on side posts
 Three sections are rigidly connected by intermediate covers as a whole
 Material: Al 1100-H14, high thermal conductivity and light weight
+ Mu-metal (?, to be decided) + MLI (30 layers)
 40-80 K helium gas cooling in extruded pipe which is welded to upper sheet
 Shield sheets are connected by fasteners
 Venting holes to prevent excessive pressure build-up in case of accidental spills of LHe
Fixed Point
Sliding post
Sliding post
Top sheets (1/4” thick) support 40-80 K manifolds and lower portion of the shield
Lower sheet , 1/8” thick
Extruded pipe to supply 40K
helium gas cooling
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Intermediate cover connects
two adjacent sections
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A cone shaped shield will be
attached to the coupler
penetration opening
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40K thermal shield – finger welding
40-80 K cooling pipes
Fingers increase the elasticity , reduce thermal stress due to temperature gradient during cool-down
welded
Array of 1”x2” fingers with 0.08” gap
welded
bolted
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40K thermal shield – materials
 Al 1100-H14 for shield
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high thermal conductivity and high strength
It is used on Injector cryomodule/HTC thermal shields – good workability
 Al 6063-T52 (or T6), for extruded pipe
Data from Cryogenic materials
data handbook
Data from AMS handbook
Al 1100-H14
Al 6063-T52
Temperature
Tensile strength
Yield strength
77 K
205 MPa
140 MPa
300 K
125 MPa
115 MPa
4K
385 MPa
250 MPa
300 K
220 MPa
195 MPa
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Magnetic shields and multi-layer
insulation
 Two layers of magnetic shielding
 A sheet of Mu-metal 4K (0.04” thick A4K) shield on the cavity LHe vessel
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Hydrogen annealed after welding for optimal performance at 2K
Mounted in half shells; Perm nuts for joining the overlap seams
 A sheet of Mu-metal (0.02” thick A4K) shield on 40K shield or lining on vacuum vessel?
 Multi-layer insulation (MLI) blankets
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30 layers on the 40K thermal shield
5 layers on He vessel, HGRP, all cryogen pipes
 Venting holes to prevent excessive pressure build-up in case of accidental spills of LHe
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3. Cryogenic environment
• Layout of cooling pipes
• 2K cooling loop
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Cryogenic manifolds
 Six lines of ɸ50 mm pipes @ 2K, 4.5-6K, 40-80K running half-linac length
 Each cryomodule has local manifolds with the flow adjusted by four valves
2K supply
6K return
subcooled liquid @1.2 bar
Gas @3 bar
40K supply
• Gas @20 bar
80K return
HGRP
1.8K gas
Gas @18 bar
2K-2 Phase
1/3 full level
40K delivery
Gas @20 bar
4.5K supply
Fluid @3 bar
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2K
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2K cooling loop
A JT valve controls liquid helium to 2K-2 phase line
2K-2 phase pipe feeds helium to helium vessels of cavities and SC magnets
Vapor returns back to cryogenic feed box via
HGRP through single connection in the middle
Large diameter provides low impedance for large mass flow
HGRP
Φ280mm
9.5mm wall
2K-2 phase
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1/3 full, monitored by a level sensor
ɸ87 mm, adequate area for superfluid counterflow
Chimney w/ large cross-section for gas flow to HGRP
Cavity immersed in 2K helium bath
Material of 2K-2 phase, HGRP pipes and LHe vessel
• Grade 2 Ti
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Similar thermal expansion rate with niobium
Does not need transition for being welded to Nb
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2K-2 phase pipe
 A bellows section in chimney allows differential thermal
contractions of beamline vs. HGRP during cool down
 A welding lip allows cut-off/re-weld a mal-functional cavity
A few supports attached to HGRP to increase pipe’s
natural frequency
Kapton thermofoil heater, to keep the refrigeration
load constant when RF power is off
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Material and size of sub-assemblies
Material
Size
Beamline
6 sets of
cavity/coupler/HOM/tuner
1 set of magnets/BPMs
9.8 m
Vacuum vessel
Carbon steel
9.15 m x Ф 0.96 m
Helium gas return pipe
2K-2phase pipe
Ti, grade 2
9.65 m x Ф 0.28 m
9.65 m x Ф 0.10 m
Support post
G10 (FRP)
w/ Al & SS rings/disks
40 K thermal radiation shield
Al 1100-H14
Al 6063-T52
9.65 m
Upper: 6.35 mm thick
Lower: 3.175 mm thick
Cryogenic piping
SS 316L
Five Φ50mm pipes + local
distribution pipes
Interconnection module
Carbon steel
Cryo-feed entry module
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Carbon steel
2.2 m
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