MDI Vacuum Status

Ray VENESSCERN TE-VSC

Introduction

o Pressure requirements for QD0 and the experimental sector

o Pressure profile for QD0o Vacuum layout in the MDIo Post-collision lineo Conclusions and open questions

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Pressure Requirements for QD0 and Experiment

o Requirements from beam dynamicso 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 105 nTorr (~1.3x10-4 mbar)

o He notes however that incoherent effects and emittance growth should be studied

o Requirements from the experimentso ILC simulations [2] suggest that beam-gas background is not an

issue at 103 nTorr (~1.3x10-6 mbar)o This needs to be confirmed for the CLIC experiments

o These pressure requirements suggest that a non-baked solution could be adopted for the QD0, and possibly also the experimental sector

CLIC-MDIWG 6 XI 09 MDI beam vacuum - R.Veness[1] G.Rumolo, CLIC-MDI meeting March 2010[2] T.Maruyama, LCWA 2009 Albuquerque

Unbaked QD0 Vacuum

o Geometryo Inner diameter of 7.6 mmo Separation between pumps ~4

m

o Assumptionso The system can be pumped for

100h before beamo … or it is not exposed to air during

the push-pull operation

o Unbaked, but UHV clean system, dominated by outgassing of H20

o Outgassing rates for unbaked systems are variable – uncertainty on result

o Assume 1x10-10 mbar.l.s.cm-2

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Outgassing rates of water on stainless steel [F.Dylla CAS 2006]

Unbaked Pressure Profile in QD0

o Static pressureso Average 4.8x10-7 mbar [~3.6x102

nTorr]o Peak 8.1x10-7 mbar [~6x102

nTorr]o Achievable pressure is dominated

by the small conductance of the tube and the outgassing rate

o Dynamic pressure componentso Additional gas load due to surface

bombardment by ions, electrons and photons will increase these static pressures

o Some data starting to arrive from A.Sailer, but calculations are time-consuming

o Beryllium in the experimental chamber has a high secondary electron yield and may need special coating

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Static partial pressure of H20 [mbar] along the QD0 beam tube [m]

QD0

Baseline Sectorisation Scheme

o Sectorso Separate machine, QD0, Detector and post-collision for independence and safety

during shutdownso Add additional sector valve to maintain cleanliness in both QD0 and detector

o Keep QD0 and experiment either under vacuum or dry gas during push-pullo Essential to reduce pump-down time after detector push-pull in a non-baked system

o Possibly add fast shutter to protect detectors from incidents in post-collision

CLIC-MDIWG 6 XI 09 MDI beam vacuum - R.Veness

Detector

QD0

Post-Collision Vacuum line

Machine Vacuum line

Post-Collision Vacuum line

Machine Vacuum line

= Sector valve= Fast shutter valve

QD0-Experiment Layout

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H.Gerwig, 8th MDI meeting

We are missing a pump here

..and a pumping port here

Is this transition acceptable?

Post Collision Line

o Absorberso Latest information from Edda

is that the baseline design is for absorber blocks outside the vacuum system

o This will mean a ‘reasonable’ gas load on the pumping system, but will require several vacuum windows

o Important to maintain contact between post-collision and vacuum system designers

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Conclusions and Open Issues

o Unbaked QD0 design presentedo Average static pressure 4.8x10-7 mbar [~3.6x102 nTorr]o This will need 2 sector valves between QD0 and experiment for rapid

recovery after push-pull and pumps on both ends of QD0o Pumping on both ends of QD0 is essential, as well as a port for pumping the

space between the 2 valves

o Open issues for pressure profileso Ion, electron and photon induced desorption rates need to be calculated

o Other beam dynamics requirements?o Incoherent effects and emittance growtho Wall impedance requirement for vacuum chambers

o low resistivity coatings?

o Beampipe geometry transitions?o Trapped RF modes giving coherent/incoherent losses and heating effects

o Next stepso Confirm the acceptability of unbaked design in QD0o Calculate static pressure profile in an unbaked experimental sector

FP420 13 X 08 Warm beampipe - R.Veness