1. 1 VAC – Vacuum system modifications Cascina, 03Nov08 A.Pasqualetti for the VAC contributors

2. 2 Summary of the presentation Tasks list Requirements, solutions and present status for each task: Vacuum upgrade Larger links and towers displacement UHV air flux improvement SR tower upgrade Control System Manpower Summary

3. 3 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

4. 4 Vacuum system layout

5. 5 Vacuum system upgrade: present vacuum level Pressure around 2.10 -7 mbar, system unbaked. Towers are frequently vented and connected to the tubes after a few days of pumping. Pressure can reach temporarily 10 -6 mbar

6. 6 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

7. 7 Vacuum system proposed upgrade Including all gases the noise would be about 1x10 -23 1/Hz 0.5 It is needed to reduce the noise by one order of magnitude, hence to improve the vacuum by two orders of magnitude.

8. 8  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 SpeciesPressure, mbar Noise, 1/  Hz H2H2 1E-92.1E-25 H2OH2O5E-111.5E-25 Air+others5E-111.9E-25 HC1E-133.5E-25 total1.1E-94.7E-25

9. 9 Cryotrap layout ”large option” Small option An additional simplified valve is necessary Principle is already present in Virgo (towers conductance, DT cryotrap) Different positions can be studied, looking into effectiveness, operative procedures, thermal disturbances

10. 10 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

11. 11  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

12. 12 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)

13. 13 Tube baking scheme

14. 14 Larger links and towers displacement Links diameter from 250/400mm to 600mm or 1m Towers displaced up to nearly 1m

15. 15 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

16. 16 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 BS WI PR SR 640 600 560600

17. 17 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

18. 18 Improvement of the UHV clean air flux Basic requirements are defined Present ‘side’ flow changed in descending ‘laminar’ flow

19. 19 Clean air inlets Metallic duct and feeders Air feeder to be designed, interfacing with PAY ( Marionette design )

20. 20 ‘ready’ to start the call for tender for the SR upgrade N.3 viroles + separating roof

21. 21 It comprehends 22 control stations and relevant SW servers + several others equipments Known issues on HW obsolete components and 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 or complete 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

22. 22 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

23. 23 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: 2009-2010 Call for tender and main expenditure: starts in 2010 Fabrication times for main HW items:6-12 months Installation:mid 2011 – end 2012 Plans toward completion