* Environmental Noise Studies (May-July09)

I.Fiori, Virgo Week, Commissioning Meeting, 20 July 2009byThe VIRGO Commissioning TeamandEGO Vacuum, Electronics, Infrastructure Teams

TopicsDiffused light from End benchesExternal Injection BenchTurbo pumpsCryo-trap Coil Drivers cratesU-pure-water sys (investigation) HVAC

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Diffused light from WEB,mitigation of bench motion Diffused light from WEB was limiting sensitivity before May 2009 (purple) WEB motion at legs resonance (20Hz) has been reduced by: Slow down HVAC fan (-10%) New cover box (more rigid and compact) Resonant damper on bench

MicroseismVSR2 inauguration, with exceptional microseism (

Noise in 40-50HzContributions not yet fully understood, but progressing:TCS noise seems to contribute (see G.Vajente).Some cooling fans (turbo pumps, CD crates) found to contribute and are being mitigated (see later in this talk).External Injection Bench is suspected to couple seismic noise in this region because of its large motion at 41-47 Hz (bench vertical modes).

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EIB noise?Coherence changes , and now it is much lower than in May.Coupling path is being investigated (indications that it might depend on IMC transmitted power).Understand coupling and study possible reduction of EIB motion is also important for V+MS.

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EIB vertical resonances: investigationSimulation: 40 Hz resonance is a mechanical mode of the top plate of bench legs.

*F.Richard and T.ZelenovaRuggi, Paoletti, Fiori Measurement with mini-accelerometersconfirmed prediction.

EIB: mitigations?Stiffening actual legs: attemps made but not successfulSorbothane: pads between bench and legs, can move vertical mode down to 15 Hz, and well dampedBUT, Test in Optics Laboratory: >> measured large drifts (100m) which cannot be tollerated by BMS.

OTHER SOLUTIONS:Resonant damper (both V and H modes): under study (thanks F.Frasconi). Tests off-line, if good results, installation easy.Conical legs: (have some on site) solid material, tests in Optics-Lab.>>> Role of EIB noise in V+MS to be addressed.

*E.Genin

Turbo pumps, related Excess noise at InjectionBrewsterNI tower motionPeaks from Turbo cooling fans

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Excess noise at INJ Brewster*eLogs 23216, 23261, 23267, 23307, 23419Evidence: 100-200Hz noise coherent with seismic noise at INJ Brewster, but also EIB and BMS.Noise decrease when IB pump off.Residual coherence from PR turbo pump.IB and PR pumps ONIB turbo OFFPR pump OFFEffect of switching off IB pump:

Excess noise at INJ BrewsterACTIONS: (Pasqualetti and Vacuum Team)1) IB pump now kept off, and replaced by MC pump (MC pump looks safer, i.e. no coherence with dark fringe).

2) Bellow installed on PR pump: cut all pump noise at Brewster below 100Hz

* Switching on PR pump after bellow installation: NO EFFECT! Only noise from PR reaching INJBrewis that of cooling fans. >>> Role of INJ Brewster to be better studied for V+MS.

Bellow at PRlpaoli, vacuum team - 14:44, Tuesday 30 June 2009 (23412) *

NI motionRuggi (eLogs 23408, 23436, 23452, 23457)

ITF was disturbed by repetitive events of NI motion, which caused unlocks or holes in the horizon.Tracked to Saturation of one accelerometer on NI top stage.The NI top stage seems more coupled to environment than other towers (reasons to be investigated).*Meanwhile, ACTIONS:

Temporary cure: tower vibration reduced by switching off NI turbo pump and use Auxiliary NI pump.

Installation of bellow on NI turbo (soon, during Tuesday maintenances).

Turbo cooling fanseLogs 23353, 23757, Vacuum teamPeaks at 45Hz from WI turbo, coherent with TCS bench seism.

Mitigation attempt: fans detached from turbo and attached to platform. seismic excitation reduced (tower, TCS bench) by 5-10. First action, to test the damping principle. The method of damping shall be better defined, if needed implemented on all disturbing fans, in the forthcoming maintenance breaks.*

Fans of Coil Drivers crates: BS and NE eLogs: 23471, 23714; 23684, 23536, 23483, 23477, 23410: Marque, Vajente, Huet, NoceraPeaks in dark fringe at (44Hz, 88Hz) and (28Hz, 56Hz, 84Hz) present in NE/BS coil current monitoring even with ITF unlocked (if coil driver in low noise)Disappear when coil driver fans are switched off.

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CD crates, mitigations:FACTS:Culprit seems magnetic noise emission from crates fans. Magnetic noise seems local to crate, not present few meters away( coupling: likely not Env. to mirrors magnets, but via the current sent to the coils).2) Noisy crates (NE and BS) are of one type. No noise detected from the CD crate of WE, which is of different type.

ACTIONS:Noise path inside crate to be better investigated (mechanical, ground loops, electromagnetic...) to plan proper actions.Simple check: if problem related just to fans type (if so, change just fans could be sufficient).Ultimatey, evaluate if necessary to purchase crates of the good type.*

Cryo-trap noise eLogs: 23722, 23637, 23636, 23634, 23794, Swinkels, Ruggi, Vajente. Noise increase in 60-120Hz after routine Cryo-trap refillsCorresponds to increased vibration of LN tank and pipe.*

Cryo-trap noiseNoise (dark fringe and seismometers) decreases with time constant of 1.5day, which is correlated to the average temperature of the tank.When listening to sismometer on Cryo-trap, it sounds like bubbles.Vacuum group interested to understand this mechanisms for future installations. Tests to be planned during next maintenances.

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Cryo-trap noise: mitigation?Hypothesis: since the removal of the suspended baffles (May 15), the wall of the Cryo-trap can now be seen from the detection bench. Any light scattering e.g. from L1 could thus hit the wall of the tank.

Possible ACTIONS:Install a new baffle, to cover the naked Cryotrap (careful design to avoid upconversion noise effects, very rigid one)Reduce back-reflected light from L1, replace with better lens superpolished (J.Marque).*

Infrastructures related noisesWater pump #1: Noisy during VSR1. Replaced. New pump produces no detectable environmenatal noise in CB hall. However, pump is off, apparently not needed.

U-pure-water production sys: needs to run in stand-by mode during VSR2. Noise investigated (eLog 23519, Ciardelli, Fiori). One pump that starts periodically produces some seismic noise on EIB. No detectable effect in dark fringe. Mitigation tests to do during maintenances.*

Infrastructure related noisesLines in dark fringe (23, 37, 48Hz) associated to DAQ room HVAC (eLog 23736). Some mitigation possible, to be defined.*

Thanks also toJ.Ramsay, R.M.Goetz: summer students from IREU program.Joseph initiated a study of effects of vehicles crossing EGO roads, bridges (shall be ready for following meetings).*

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