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VAC – Vacuum system modifications

Cascina, 03Nov08A.Pasqualetti for the VAC contributors

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Summary of the presentation

• Tasks list

• Requirements, solutions and present status for each task:Vacuum upgradeLarger links and towers displacementUHV air flux improvementSR tower upgradeControl System

• Manpower

Summary

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VAC Subsystem Breakdown: deliverables

1. Vacuum upgrade: upgrade the present system to bring residual pressure compatible with AdV sensitivity

2. Larger links: larger links between towers, including larger valves

3. Towers displacement: displacement of some towers of the central area to allow changes in the interferometer configuration

4. UHV clean air: Improvement of the clean air flow in the mirror compartments

5. SR tower: Upgrade the SR tower to a full size UHV mirror tower

6. Vacuum Control System upgrade

VAC Tasks list

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Vacuum system layout

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Vacuum system upgrade: present vacuum level

Pressure around 2.10-7mbar, system unbaked.

Towers are frequently vented and connected to the tubes after a few days of pumping. Pressure can reach

temporarily 10-6 mbar

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Vacuum system upgrade: phase noise by residual gas fluctuation

10-23

10-22

10-24

Water vapor 1.5E-7 mbar

Total noise with excess gas

Noise level to be reduced by one order of magnitude

AdV reference

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Vacuum system proposed upgrade

Including all gases the noise would be about 1x10-23 1/Hz0.5

It is needed to reduce the noise by one order of magnitude, hence to improve the vacuum by two orders of magnitude.

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Baking only tubes plus ‘cryotraps’Cryotraps are needed to avoid spoiling the vacuum when connecting baked

tubes to unbaked towers. Successfully in use by LIGO .Cryotraps are recommended also to lower the contaminants pressure in mirror

chambers, possibly risky for AdV mirrors

Full bake at 150°C, beam tubes + towers, already tested:

Towers can’t be baked because time consuming + risky

Increasing pumping speed: it was already discarded in the original design, not feasible to get a factor 100

Vacuum system upgrade: proposed solution

Species Pressure, mbar Noise, 1/Hz

H2 1E-9 2.1E-25

H2O 5E-11 1.5E-25

Air+others 5E-11 1.9E-25

HC 1E-13 3.5E-25

total 1.1E-9 4.7E-25

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Cryotrap layout

”large option” Small option

An additional simplified valveis necessary

Principle is already present in Virgo (towers conductance, DT cryotrap) Different positions can be studied, looking into effectiveness, operative procedures, thermal disturbances

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Cryotrap about 4m long, 1m diameter, can be a LN2 reservoir made out of aluminum and put inside the first portion of tube (Ligo courtesy)

4 m

1.4

m

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Bake of tubes could be postponed when convenient for sensitivity or commissioning reasons. During the initial phase, the pressure in tubes will improve in the10-8 mbar range

ITF duty cycle: faster recovery of tower service after venting

provide pumping for water and contaminants coming from bench towers

pumping system environmental noise reduction

The need of prototypes and long design phase is reduced thanks to Ligo experience

Advantages of having cryotraps

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Vacuum system upgrade: next actions

Installation of cryotraps is the reference proposal The design is in progress Under development: traps geometry, traps operation, thermal effect on optics, gas load from bench towers, LN2 supply equipment (relevant for running costs and duty cycle)

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Tube baking scheme

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Larger links and towers displacement

Links diameter from 250/400mm to 600mm or 1m

Towers displaced up to nearly 1m

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Larger links

Present link diameter (400mm with 250mm valves) is not fitting with the increased beam radius and with secondary beams transmitted between towers.

Possible scenarios are being analyzed:

•The basic option is to enlarge links diameter up to 600mm links + valves 500mm: A first study has been done, with a first cost estimate. The work is considered straightforward.•The extreme option is to enlarge links diameter up to 1000mm without valves. Feasible, but with drawbacks limiting the present accessibility to towers (becoming a unique vacuum chambers) and increasing risks of mirror pollution

Intermediate solutions are possible, considering also different diameters for the different links: The best tradeoff among optical and vacuum constraints is under study

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In the different hypothesis the concerned towers are:

1_Due to concrete constraints, the 2m diameter flange will be no more accessible

2_Long time duration and conflicts with other activities need accurate planning (4 months is the preliminary figure, from a previous displacement of MC tower)

3_It is advantaging if NI and WI are moved toward BS, because the existing tube design

Towers displacement

• Beam Splitter could move by a few cm in X and Y• North Input ~ < 0.8m to reduce the ‘Schnupp

asymmetry’• West Input could move up to ~ 0.4m opposite to BS

• Signal Recycling could move by ~ 0.7m

• Power Recycling could move by ~ 0.3m

NI

BSWI

PR

SR

640

600

560 600

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Larger links and towers displacement: next actions

VAC shall interact with interfaces (ISC, OSD) to define requirements, looking for a tradeoff especially about the option of having links with diameter of 1m without valves

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Improvement of the UHV clean air flux Basic requirements are defined

Present ‘side’ flow changed in descending ‘laminar’ flow

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Clean air inlets

Metallic duct and feeders

Air feeder to be designed, interfacing with PAY ( Marionette design )

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‘ready’ to start the call for tender for the SR upgrade

N.3 viroles + separating roof

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It comprehends 22 control stations and relevant SW servers + several others equipments

Known issues on HW obsolete componentsand SW upgrades i.e. OS9 operating system

Evolutions for AdV are needed also to deal with new required functionalities and equipment.Different possibilities : integration with present control system orcomplete renewal

Evaluations for the choice is starting together with advancing in the vacuum equipment design (i.e. cryotraps presence ...)

Considered criteria: manpower, cost, evolutivity, gui integration, validation effort

Control System Upgrade

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manpower

Share of charges is partially achieved: contributions from the traditionally responsible laboratories and new competences of laboratories joining recently the collaboration.

Presently involved teams:

•Ego•InfnGE•Infn PI•LAL•Lapp•LMA•Nikhef•Roma2

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next milestone is the next spring review

meetings (working discussions) every 2 weeks to define requirements and to advance in the design

main dates Design: 2009-2010Call for tender and main expenditure: starts in 2010Fabrication times for main HW items: 6-12 months Installation: mid 2011 – end 2012

Plans toward completion