Mechanical Design of Main Linac Cryomodule (MLC)

1. 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

2. 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 Yun HE, MLC External Review

3. Design criteria Cryomodule provides support, alignment, cryogenic environment, thermal shielding and magnetic shielding for the cavities Yun HE, MLC External Review

4. 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 Yun HE, MLC External Review

5. Beamline and its support • Beamline string components • Helium gas return pipe • Support posts and alignment components • Vacuum vessel Yun HE, MLC External Review

6. Beamline sub-assembly • 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 Beam 9.8 m Beamline interconnection SC magnets/BPMs Taper HOM load Taper HOM load Manual gate valve Pneumatic gate valve Yun HE, MLC External Review

7. Supports for cavity • Material: Ti Grade 2 • LHe vessel • supports Flexible support allows 1mm differential thermal displacement of helium vessel relative to HGRP during cool-down/warm-up Alignment pins provides horizontal alignment Yun HE, MLC External Review

8. Supports for other beamline components Alignment keys allow for differential thermal displacement of beamline components relative to HGRP Yun HE, MLC External Review

9. SC magnets/BPMs package High temperature superconducting current leads Port to 2K/2 phase line Port for pre-cool BPMs Dipole Quads Yun HE, MLC External Review

10. Beamline strongback - Helium gas return pipe • 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 Fixed Point Sliding post Sliding post High precision machined mounting surfaces with central pin holes Provide precision alignments of beamline components Yun HE, MLC External Review

11. 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? Yun HE, MLC External Review

12. 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 Bellows Suspension bracket Vacuum vessel top flange Post HGRP Yun HE, MLC External Review

13. Vacuum vessel Port for post Ports for cryogenic valves Port for pressure relief Hanger for lifting & transportation Port for coupler Ports for GV & SC magnets 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 Rails for cold mass insertion ɸ37-1/4” ID, 3/8 Thickness Yun HE, MLC External Review

14. 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 Yun HE, MLC External Review

15. Vacuum vessel – production steps • 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 Yun HE, MLC External Review

16. 2. Thermal design • Support post • 40K thermal shield • Magnetic shields • Multi-layer insulation Yun HE, MLC External Review

17. 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 4th stage -- 300K (SS 316L) 300K 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 Yun HE, MLC External Review

18. 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 Step #2 Step #3 Step #4 G10 tube Al disk Tooling Al ring Step #1 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 • 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 #5 Step #7 Step #6 Step #8 Yun HE, MLC External Review

19. 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 Intermediate cover connects two adjacent sections Extruded pipe to supply 40K helium gas cooling A cone shaped shield will be attached to the coupler penetration opening Yun HE, MLC External Review

20. 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 Yun HE, MLC External Review

21. 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 Data from Cryogenic materials data handbook Data from AMS handbook Yun HE, MLC External Review

22. 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 Yun HE, MLC External Review

23. Cryogenic environment • Layout of cooling pipes • 2K cooling loop Yun HE, MLC External Review

24. 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 subcooled liquid @1.2 bar 6K return Gas @3 bar • 40K supply • Gas @20 bar 80K return Gas @18 bar HGRP 1.8K gas 2K-2 Phase 1/3 full level 40K delivery Gas @20 bar 4.5K supply Fluid @3 bar 2K Yun HE, MLC External Review

25. 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 • 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 • Similar thermal expansion rate with niobium • Does not need transition for being welded to Nb Yun HE, MLC External Review

26. 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 Yun HE, MLC External Review

27. Material and size of sub-assemblies Yun HE, MLC External Review