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Vacuum in the MDI Region

Vacuum in the MDI Region. Ray VENESS CERN TE/VSC With thanks for useful discussions with: Konrad Elsener, Cedric Garion, Lau Gatignon, Alain Herve, Andre Sailer, Edda Gschwendtner. Introduction. CLIC MDI Vacuum Three separate systems: CLIC detector(s), QD0, post-collision line

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Vacuum in the MDI Region

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  1. Vacuum in the MDI Region Ray VENESS CERN TE/VSC With thanks for useful discussions with: Konrad Elsener, Cedric Garion, Lau Gatignon, Alain Herve, Andre Sailer, Edda Gschwendtner

  2. Introduction • CLIC MDI Vacuum • Three separate systems: CLIC detector(s), QD0, post-collision line • Significantly different geometry and functional requirements • Linked by the same CLIC vacuum system • Physically linked by vacuum chambers • Coupled by beam dynamics and pressure distributions • Status • CLIC MDI Vacuum is still at a conceptual level, but we are not starting from zero- We can learn from: • CLIC machine (module) vacuum design • ILC design - particularly for detectors • LHC vacuum – particularly for technology • Contents of the talk • For each of the 3 systems: Detectors, QD0, post-collision • Brief overview of what we know • Issues that need to be addressed for the CLIC CDR MDI beam vacuum - R.Veness

  3. MDI beam vacuum - R.Veness

  4. Detector Beampipes • Geometry • Cylindrical central section, diameter of ~60 mm • Conical forward sections, pointing at IP • Similar design concept to CMS, ALICE and (to some extent) LHCb experiments • Material • Baseline is beryllium • Best material in terms of transparency (radiation length, specific stiffness) • Many constraints in use (chemical safety, fragility, cost, availability), so only use where necessary • CERN (with industry) developed the technology for these chambers for the LHC • Alternatives • Carbon composite is not far behind beryllium for transparency, and should not be forgotten, particularly for non-baked designs Conical beryllium pipes for LHCb MDI beam vacuum - R.Veness

  5. Detector Beampipes • Pressure • Simulations made for ILC [1] show that “..beam-gas background is negligible compared with (nominal) luminosity background even at 1000 nT.” • Verification for CLIC beams • Beam-gas background could be more significant if CLIC operates at lower than nominal luminosity (Re: LHC) • Machine pressure requirement • Uncoated beryllium has high desorption yields which can give beam dynamics issues • Particle stimulated gas desorption will give a dynamic gas load and can lead to pressure instabilities • Other issues • Impedance and trapped RF modes • Conical transitions or RF shields • Vacuum pumps and gauges RF screen in the CMS end cap beampipe Vacuum instrumentation in ATLAS forward MDI beam vacuum - R.Veness [1] T.Maruyama,LCWA 2009 Albuquerque

  6. QD0 Vacuum • Geometry • QD0 magnet beampipe ~7.6mm inner diameter, magnetic length ~2.75m giving a vacuum chamber length of 3~3.5m • Post-collision beampipe with 10 mrad opening angle passes through magnet structure ‘Hybrid v2’ QD0 cross-section, showing incoming and post-collision beamlines M.Modena, CLIC 09 Workshop MDI beam vacuum - R.Veness

  7. QD0 Magnet Vacuum • Vacuum system • Requirements • ILC simulations suggest beam-gas is not an issue (see detector beamipes slides) • Beam dynamics requirement for CLIC is under investigation (G.Rumolo) • Design options • CLIC module concept • uses distributed pumping (NEG strips) to achieve 10-8 mbar (10 nT) dynamic pressure specification. • This solution will not fit inside the QD0 permanent magnet design • NEG-coated tube • Cylindrical chamber with ~1 µm of NEG alloy sputtered on inner wall. • Activated by heating the chamber under vacuum to 180+ºC • Activation compatible with Curie temperature of permanent magnets • Technology for sputtering inside small tubes and activation heating to be developed • Unbaked tube • Simple, unbaked cylindrical chamber, pumped from extremities of magnet • Pump-down time is conductance limited and may prove excessive, depending on pressure requirement • Preliminary calculation gives ~5 x 10 -7 mbar (~400 nT) after 100 hours pumping MDI beam vacuum - R.Veness

  8. MDI beam vacuum - R.Veness

  9. Post-Collision Line • Geometry • 150m+ length of large diameter (~1m) vacuum chambers • Absorbers • Several absorbers in the kW- 200 kW capacity range • Inside the vacuum chambers? • Water cooled? –Reliability? • Ensure that the vacuum chambers are protected by the absorbers • Beam dump entrance window • Large diameter (~1m) window • High continuous power (~10 MW) • ‘Transparent’ window • Cooling required? • Could 50 Hz beam repetition rate induce thermal fatigue? LHC beam dump window: 600mm aperture, made from carbon-carbon composite supporting a leak-tight foil MDI beam vacuum - R.Veness

  10. Post-Collision Line • Vacuum system issues • Large volumes at medium-high vacuum • Pressure requirement for CLIC operation? • Cf. LHC beam dump at 10-7 mbar (~100 nT) • High pumping speeds will be required • Outgassing of large surface areas • Local gas loads from absorbers • .. therefore large pumps • Radiation environment • Pumps need to be close to the chambers to maximise conductance • Need access to pumping systems for maintenance LHC beam dump line, showing ion pump MDI beam vacuum - R.Veness

  11. Sectorisation • Why sectorise (separate by valves)? • Independence of systems • Independent installation and testing of sub-systems (QD0, detector, post-collision..) • Bakeout / NEG activation of part of the system • Off-line push-pull detector preparation • Availability • Avoid venting the system to air • Gain in time to have the machine operational after an intervention or push-pull • Safety • Reduced the impact of an incident during a shut-down (sector valves) • Reduced the impact of a incident during operation (fast shutter valves) • Issues with sectorisation • A vacuum sector implies additional material and space • 63 mm aperture sector valve is 75 mm long from flange to flange • Each sector needs pumping and instrumentation to measure pressure and ‘interlock’ the valves • Valves can become highly activated, and require some maintenance • Fast shutter valves • The potential consequences of accidental closure must be weighed against the advantages MDI beam vacuum - R.Veness

  12. Possible Sectorisation Scheme • Sectors • Separate machine, QD0, Detector and post-collision for independence and safety during shutdowns • Add additional sector valve to maintain cleanliness in both QD0 and detector • Potential significant gain in recovery time after detector push-pull • Possibly add fast shutter to protect detectors from incidents in post-collision Detector Post-Collision Vacuum line Machine Vacuum line QD0 Machine Vacuum line QD0 Post-Collision Vacuum line = Sector valve = Fast shutter valve MDI beam vacuum - R.Veness

  13. Summary • Pressure requirements • Dynamic (ie, with beam) pressure requirements need to be specified • For QD0, detector and post-collision regions • Sum of requirements from both detectors and machine • Some information exists for ILC • This needs to be verified for CLIC • This is an urgent pre-requisite for the QD0 vacuum system design • Sectorisation • Complete design not essential now, but space in critical areas (eg, between detector and QD0?) should be reserved • Linked to questions of bakeout of components and re-start time after push-pull MDI beam vacuum - R.Veness

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