Review of the Cryogenic Bypass Design for LHC DS Collimators Vacuum System (2011)

1. Review of the cryogenic by-pass for the LHC DS Collimators Vacuum Design May 26, 2011 presented by Paul Cruikshank with input and contributions from: V. Baglin, N. Provot, W. Maan TE/VSC, and the team working on the DS collimator project

2. Recall: Rules of the game... • No halogenated fluxes to be used anywhere • Vacuum brazing only • No ‘helium-to-beam vacuum’ welds (or brazes) • Partial penetration welds only • No demountable vacuum tight joints in cryogenic system • No ‘metal/ceramic’ vacuum tight joints in cryogenic system • Vessel walls with material lamination (inclusions) parallel to wall surface, otherwise forged material. • Minimise the number of thin-wall components • Favour flexible pipe loops to braided hoses • All components and subassemblies to be leak tested before installation • Combined pressure & leak test of finished assemblies  tooling • Thermal cycle of cryo assembles is strongly recommended

3. Design Principles • General • To minimise the work and reduce risks use validated designs – beam screens, PIMs, cold-to-warm transitions, cryostat construction, vacuum instrumentation. • Beam vacuum • Separation of cold and warm sectors with sector valves • Room temperature system is bakeable and equipped with permanent bakeout heaters (integration & radiation issue). • Removal of collimator without warm-up of arc • RF ball interface to validate PIM status in arcs 2-3 and 3-4 • Each cold volume has adequate pressure relief • Insulation vacuum • Integrate the collimator cryostat into the existing vacuum subsector • Each subsector has adequate pressure relief

4. Beam vacuum sectorisationeg IR3L RT vacuum sector Cold vacuum sector Q7L to Q7R • New beam vacuum sectors are created – cold & room temp • 16 additional sector valves in IR3L & R Before After

5. Beam vacuum sectors • New RT vacuum sectors are instrumented as LSS zones • New cold vacuum sectors will have at least one rupture disc as part of the arc beam vacuum consolidation in LS1

6. Beam vacuum – sector valve constraint • Actuator of the sector valve must be removed to fully open W sleeve on the right • Sector valve remains locked closed by design • The arc is always at RT for the intervention • The leak tightness can be monitored • In case of problem, the collimator could be re-baked in the shadow of the arc cool down • Actuator demounting has been validated

7. RF Ball implementation • RF ball test in LHC baseline to verify PIM integrity after warm-up • Existing interfaces at arc extremities • Ball cannot travel thro’ DS collimators (too large cross-section, vacuum integrity, sector valves closed) • New interface at QTC – DN35 flange on ‘cold side’ – also used for vacuum gauges. • PIMs will all be consolidated in Q11 to Q7 zone - only need to perform RF ball on arc side

8. Vacuum system assembly • Vacuum component preparation • Shopping list is complete • Validation of detail drgs by end June – then manufacturing of first beam screens in main workshop - to be delivered 31st October 2011. • QTC and Connection Cryostat preparation • Beam screen, cold-to-warm transition and PIM integration very similar to arc SSS and diploes • Beam screen integration work will be combined with other SSS and dipole preparation at a single site – SMI2? • fragile components, single team ,single assembly zone, centralisation of tooling • Collimator & other RT components • ‘Lego’ components will be prepared as for LHC in building 113 and 252 • Some pre-mounting of RT components on the QTC (eg sector valves) is under discussion

9. Insulation vacuum issues • Adequate cross-section for pumping through by-pass cryostat 0.18 m2 ~ C 3000 l/s • MCI pressure relief configuration to confirm for subsector • Existing equi-spaced pumping ports for additional mobile pumps if required at Q11, Q9 and Q7 • Radiation exposure of fixed pumping group at Q8 • exposure of equipment during operation & personnel during routine maintenance • move to Q9 - to discuss • Standard in-tunnel leak testing works • Machine interconnects • Jumper inetrconnects • New cryo-extension (Q9, Q7 and DFBA)

10. Operational considerations • Risks for operation start-up • Significant modification to LHC vacuum systems at IR3 • A lot of new vacuum hardware to be installed and tested • New cabling and revised controls software  Time must be reserved for system tests • Risks for operation • More hardware in the tunnel – reliability & maintenance • Collimators are very near to cold arcs - particle showers from the collimators may produce vacuum instabilities (eg heat loads to beam screens) resulting in sector valve closures • The beam vacuum design been made to mitigate against instabilities • Similar configurations already exist eg near Q4 • Clone of the existing LHC vacuum design • Conditioning of the collimators prior to installation & in-situ bakeout • Adequate pumping speed from ion pumps & NEG • Beam screens in QTC to provide vacuum stability and adequate pumping  No major operation concerns

11. Thank you for your attention!