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MDI Vacuum Status

MDI Vacuum Status. Ray VENESS CERN TE-VSC. Introduction. Pressure requirements for QD0 and the experimental sector Pressure profile for QD0 Vacuum layout in the MDI Post-collision line Conclusions and open questions. Pressure Requirements for QD0 and Experiment.

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MDI Vacuum Status

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  1. MDI Vacuum Status Ray VENESS CERN TE-VSC

  2. Introduction • Pressure requirements for QD0 and the experimental sector • Pressure profile for QD0 • Vacuum layout in the MDI • Post-collision line • Conclusions and open questions Warm beampipe - R.Veness

  3. Pressure Requirements for QD0 and Experiment • Requirements from beam dynamics • Recent calculations from Rumolo[1] show that coherent instabilities are not an issue if pressures with pressures in the last 20m of the BDS upto 105nTorr (~1.3x10-4 mbar) • He notes however that incoherent effects and emittance growth should be studied • Requirements from the experiments • ILC simulations [2] suggest that beam-gas background is not an issue at 103nTorr (~1.3x10-6 mbar) • This needs to be confirmed for the CLIC experiments • These pressure requirements suggest that a non-baked solution could be adopted for the QD0, and possibly also the experimental sector [1] G.Rumolo, CLIC-MDI meeting March 2010 [2] T.Maruyama, LCWA 2009 Albuquerque MDI beam vacuum - R.Veness

  4. Unbaked QD0 Vacuum • Geometry • Inner diameter of 7.6 mm • Separation between pumps ~4 m • Assumptions • The system can be pumped for 100h before beam • … or it is not exposed to air during the push-pull operation • Unbaked, but UHV clean system, dominated by outgassing of H20 • Outgassing rates for unbaked systems are variable – uncertainty on result • Assume 1x10-10 mbar.l.s.cm-2 Outgassing rates of water on stainless steel [F.Dylla CAS 2006] Warm beampipe - R.Veness

  5. Unbaked Pressure Profile in QD0 • Static pressures • Average 4.8x10-7 mbar [~3.6x102nTorr] • Peak 8.1x10-7 mbar [~6x102nTorr] • Achievable pressure is dominated by the small conductance of the tube and the outgassing rate • Dynamic pressure components • Additional gas load due to surface bombardment by ions, electrons and photons will increase these static pressures • Some data starting to arrive from A.Sailer, but calculations are time-consuming • Beryllium in the experimental chamber has a high secondary electron yield and may need special coating Static partial pressure of H20 [mbar] along the QD0 beam tube [m] Warm beampipe - R.Veness

  6. Baseline SectorisationScheme • 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 • Keep QD0 and experiment either under vacuum or dry gas during push-pull • Essential to reduce pump-down time after detector push-pull in a non-baked system • 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

  7. QD0-Experiment Layout Is this transition acceptable? We are missing a pump here ..and a pumping port here H.Gerwig, 8th MDI meeting Warm beampipe - R.Veness

  8. Post Collision Line • Absorbers • Latest information from Edda is that the baseline design is for absorber blocks outside the vacuum system • This will mean a ‘reasonable’ gas load on the pumping system, but will require several vacuum windows • Important to maintain contact between post-collision and vacuum system designers Warm beampipe - R.Veness

  9. Conclusions and Open Issues • Unbaked QD0 design presented • Average static pressure 4.8x10-7 mbar [~3.6x102nTorr] • This will need 2 sector valves between QD0 and experiment for rapid recovery after push-pull and pumps on both ends of QD0 • Pumping on both ends of QD0 is essential, as well as a port for pumping the space between the 2 valves • Open issues for pressure profiles • Ion, electron and photon induced desorption rates need to be calculated • Other beam dynamics requirements? • Incoherent effects and emittance growth • Wall impedance requirement for vacuum chambers • low resistivity coatings? • Beampipe geometry transitions? • Trapped RF modes giving coherent/incoherent losses and heating effects • Next steps • Confirm the acceptability of unbaked design in QD0 • Calculate static pressure profile in an unbaked experimental sector Warm beampipe - R.Veness

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