Mechanical Design of Main Linac Cryomodule (MLC)
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Transcript of Mechanical Design of Main Linac Cryomodule (MLC)
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
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Outline
Design criteria
Beamline and its support• Beamline components• Helium gas return pipe• Support posts and alignment components• Vacuum vessel
Thermal and magnetic design• Post• 40K thermal shield• Magnetic shields• Multi-layer insulation
Cryogenic environment• 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 cavitiesRequirements Design
Support Beamline is supported by HGRP onto three posts mounted on vacuum vesselWeights: Beamline ~1 Ton, Coldmass ~3 Ton, Module ~7 Ton
Alignment • 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 • 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 mGTwo layers of magnetic shields, one wraps cavity and the other on 40K shield
Cryogenic environment Cavities are immersed in 2 K liquid helium bathCryogenic 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 diameterYun HE, MLC External Review10/3/2012
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Cross-sectional view of module
HGRP
Vacuum vessel38” dia. OD
Input coupler
HGRP support post + alignment
40K shield + Mu-metal shield
Rails
2K-2 Phase
Cryogenic valves
4”
9.5”
Cavity in 2K Helium bath
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1. Beamline and its support
• Beamline string components• Helium gas return pipe• Support posts and alignment components• Vacuum vessel
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Beamline sub-assembly
Taper HOM load Taper HOM loadSC magnets/BPMs
Manual gate valve
Beamline interconnection
Pneumatic gate valve
9.8 m
Beam
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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
• One manual, to be opened once two modules are connected• One pneumatic
Cavity package with coupler, tuner and HOM absorber
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Alignment pins provides horizontal alignment
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Supports for cavity
Flexible support allows 1mm differential thermal displacement of helium vessel relative to HGRP during cool-down/warm-up
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Material: Ti Grade 2 •LHe vessel •supports
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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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QuadsDipoleBPMs
Port for pre-cool
SC magnets/BPMs package
Port to 2K/2 phase lineHigh temperature superconducting current leads
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Beamline (~ 1 Ton) is suspended under HGRP via three support posts• Center post fixed, side posts allow differential contractions during cool-down Material : Grade 2 Ti, ID Φ280mm, wall thickness 9.5mm• Similar thermal expansion rate with niobium• Does not need transition for being welded to Nb
Sliding postFixed Point
Sliding post
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Beamline strongback - Helium gas return pipe
High precision machined mounting surfaces with central pin holesProvide 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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Adjust post position Bellows
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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
Post
Suspension bracket
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Vacuum vessel top flange
HGRP
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Port for coupler Port for instrumentation and access to tuner
Hanger for lifting & transportation
Ports for GV& SC magnets
Port for postPorts for cryogenic valves
Rails for cold mass insertion
ɸ37-1/4” ID, 3/8 Thickness
Material: 38” OD x 3/8” wall carbon steel cylinderSS 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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Vacuum vessel
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Port for pressure relief
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Vacuum vessel – reinforcements and references
Stiffening rings to top port
Reference arm for survey target
Cross-section of top port
Reinforcement around the opening
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SS flange with O-ring seal
Brackets for waveguide supports
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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
• 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. Thermal design
• Support post• 40K thermal shield• Magnetic shields• Multi-layer insulation
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2nd stage -- 5K intercept (Al)
5K braids clamped to 5K manifold
3rd stage -- 40K intercept (Al)
2K HGRP
300K
G-10 tube
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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
Conduction
4th stage -- 300K (SS 316L)
1st stage -- 2K (SS 316L)
40K shield
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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
Support post – production steps
G10 tube Al disk Tooling
• Cool down Al disk along with tooling to LN2
• Put on G10 tube• Press top plate• Let assembly #1 warm up to room temperature
Al ring
• Warm up Al ring along with tooling to 200 oC• Put on assembly #1• Let assembly #2 cool down to room temperature
Step #1 Step #2 Step #3 Step #4
Step #5 Step #6 Step #7 Step #8
Step #1 Step #2
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Then repeat Step #2 & #3
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
Top sheets (1/4” thick) support 40-80 K manifolds and lower portion of the shield
Intermediate cover connects two adjacent sections
Lower sheet , 1/8” thick
Extruded pipe to supply 40K helium gas cooling
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40K thermal shield – general information
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Fixed Point Sliding postSliding post
A cone shaped shield will be attached to the coupler penetration opening
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welded
Array of 1”x2” fingers with 0.08” gap
bolted
welded
Fingers increase the elasticity , reduce thermal stress due to temperature gradient during cool-down
40K thermal shield – finger welding
40-80 K cooling pipes
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40K thermal shield – materials
Al 1100-H14 for shield• 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
Temperature Tensile strength Yield strength
Al 1100-H14 77 K 205 MPa 140 MPa
300 K 125 MPa 115 MPa
Al 6063-T52 4 K 385 MPa 250 MPa
300 K 220 MPa 195 MPa
Data from AMS handbook
Data from Cryogenic materials data handbook
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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• 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 • 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
HGRP1.8K gas
6K returnGas @3 bar
80K returnGas @18 bar
2K-2 Phase1/3 full level
4.5K supplyFluid @3 bar
40K deliveryGas @20 bar
40K supply•Gas @20 bar
2K supplysubcooled liquid @1.2 bar
2K
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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
Material of 2K-2 phase, HGRP pipes and LHe vessel•Grade 2 Ti
• Similar thermal expansion rate with niobium• Does not need transition for being welded to Nb
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2K cooling loop
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2K-2 phase•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
HGRPΦ280mm
9.5mm wall
Cavity immersed in 2K helium bath
Large diameter provides low impedance for large mass flow
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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
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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
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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/tuner1 set of magnets/BPMs
9.8 m
Vacuum vessel Carbon steel 9.15 m x Ф 0.96 m
Helium gas return pipe2K-2phase pipe
Ti, grade 2 9.65 m x Ф 0.28 m9.65 m x Ф 0.10 m
Support post G10 (FRP)w/ Al & SS rings/disks
40 K thermal radiation shield Al 1100-H14Al 6063-T52
9.65 m Upper: 6.35 mm thickLower: 3.175 mm thick
Cryogenic piping SS 316L Five Φ50mm pipes + local distribution pipes
Interconnection module Carbon steel
Cryo-feed entry module Carbon steel 2.2 mYun HE, MLC External Review10/3/2012