1 Virgo commissioning since the end of VSR1 E. Tournefier for the commissioning team ILIAS WG1, Cascina March 5 th,2008

2 The end of VSR1: mystery death Noise structures ( Hz Hz) highly non-stationary: depend on the quality of the ITF alignment realignments

3 Mystery noise investigations Noise also seen in the suspended injection bench error signals  investigations in laser lab, around injection tower (electronics, seismic noise, laser chiller, tapping tests,…)  investigations on the injection suspended bench Guilty = piezo-actuators on the suspended bench Mechanism: Piezo driver noise => actuator motion => IB shaken => IMC length noise + jitter noise External injection bench Laser bench Suspended bench Tower window

4 Dihedron resonance Mystery noise = beam jitter Solution: low pass filter the signal of the piezo drivers  impressive decrease of frequency noise and beam jitter noise  (no more) mystery structures disappear from DF Dark fringe Frequency noise

5 Noise budget at the end of VSR1 Control noises Shot noise Environmental noise Actuacor noise Eddy currents

6 Noise budget now Control noises Shot noise Environmental noise Actuator noise Eddy currents

7 Summary Control noise reduction: –Longitudinal controls: use a second modulation frequency, noise subtraction,… –Angular controls: more efficient filters, mirrors centering,… Actuator noise: –DAC noise filtering –Magnetic noise: replaced magnets on input mirrors (strength/5.5 + good polarity) Environmental noise investigations –Noise sources: air conditioning (<150 Hz), electronic racks –Path to dark fringe: injection beam jitter, diffused light on benches, detection/Brewster Environmental noise reduction: –Beam jitter reduced –Diffused light mitigation on end benches, improved telescopes –Air conditioning improvement started –Brewster => cryotrap to be installed soon

8 Alignment noise reduction Post VSR1 alignment noise reductions: –More efficient filters –Mirror centering improved –NI+WI local control noise reduced  The alignment noise is below V+ design above 20 Hz Ongoing improvements: –Find cleaner signals for BS and input mirrors (under drift control)  New end benches and new quadrant on B1p have been installed 8MHz -> Drift control (10mHz) -> Drift control see Maddalena’s talk

9 Upgrade of the end benches New end benches telescopes + rearrangement –Hoping for better quality alignment signals –Galvos installed at that occasion (centring during science operation) –Better telescope helps to reduce diffused light Remaining problem: quadrant signals polluted by air flux and bench motion Telescope Quadrant setting Now Virgo+ Galvos

10 Longitudinal noise reduction Post VSR1 activities: 1/ Characterization of the ITF response (2 weeks immediately after the run): - response of actuators (mechanics + electronics) / also a cross check for calibration - optical gains (W/m) : mirror displacement  photodiode signals 2/ Improvement of the controls for noise reduction: - adapt filters and driving matrix to the actuator response - adapt the sensing matrix to the optical response - use cleaner signal from the second modulation frequency (8MHz) for MICH control - new filters for marionetta to avoid exciting 16/46 Hz resonances - and: better noise subtraction, more flexible Gc algorithm,… 8MHz B2_8MHz

11 Longitudinal control noise reduction Longitudinal control noises are not anymore limiting the sensitivity ! Longitudinal control noises are now limited by environmental noises –Beam jitter subtraction imlemented for B2_8MHz –Long term solution: reduction of environmental noises Sensing for central cavity: New B2 signal (8MHz) + new sensing matrix -VSR1 - now Environmental noise error signals control signals see Gabriele’s talk

12 Environmental noises Test: switch OFF the air conditioning in ALL buildings (NE,WE, CE, MC)  Identifed sources and path to dark fringe - diffused light from end benches (now almost completely cured) - beam jitter induced by AC in laser lab - diffused light from Brewster/detection induced by Central hall + DAQ room AC AC ON AC OFF Central hall AC Water pump of CE CleanRooms AC  Laser lab DAQ room (+CE hall) North End AC Other identified sources: electronic racks (peaks above 200 Hz)

13 Beam jitter at the injection Mechanical resonances of the Beam Monitoring System mount + PZT seen in dark fringe  Mount + PZT replaced with better one: Move resonances at higher frequencies + they are less easily excited Identified vertical/horizontal resonance (~45/18Hz) of the injection bench  beam jitter  Damping of these resonances under study

14 Diffused light at the detection Detection benches BS Many structures above ~100 Hz are coherent with the motion of the Brewster window Tapping tests  Brewster is the most sensitive of all vacuum pieces But difficult to make separate what comes from detection tower and from Brewster  Diffused light / modulation by Brewster?  Diffused light by detection bench on tower walls or Brewster link / back into the ITF? Dark fringe Coherence with Brewster Seismometer

15 Diffused light at detection port BS Detection benches Investigate the path for diffused light –Diffused light on the tower walls?  baffles installed – no visible effect –Diffused light inside the Brewster link?  better baffles have been installed (any effect?) –Light diffused by detection optics?  bench rotation experiment-some unclear effect –Coupling through the Brewster window?  replace it with cryotrap next week

16 Diffused light reduction (?) at detection OB rotation 100  rad Indication of light reflected/diffused by the detection bench: Dedicated experiment: rotate the suspended bench by 100  rad  30 Hz and 45 Hz bumps disappeared (related to air conditioning noise in central hall)  No clear effect at higher frequencies Other rotation experiments were not so clear (??) Which is the mechanism?

17 ‘Brewster noise’ variations with alignment Noise varies with the alignment/power on dark fringe True only above 100 Hz What about the low frequency which seemed to change with bench rotation?

18 Environmental noise reductions Diffused light at end benches well reduced (beam dump + new optics) Beam jitter reduced (new BMS) Air conditioning improved inside the DAQ room Some pumps used for AC are OFF (do not seem needed…) => Impact of AC well reduced

19 New DAQ room air conditioning machine

20 Actuator noise reduction Reduction of the mirror actuator electronics noise during VSR1 (arm mirrors) DAC DSP CoilDriver G EmphasisDeEmphasis Emphasis Air conditioning OFF Impact of DAC noise reduced: BS: –marionetta reallocation now working => CD gain decreased by 4 (DAC + CD noise reduction) Arms: gain decreased by factor 4 (reduced dynamic) => new coil driver with several (switchable) low noise sections next step: better emphasis filters + Improved measurement of low frequency DAC noise performed No clear improvement observed…

21 Actuator noise now Marionetta DAC noise below 20 Hz? We’ll add some filtering this week, let’s see… Eddy currents

22 Magnetic noise? Direct coupling of magnetic noise through the magnets attached to the mirror Magnetic lines injections, modelling => tentative projection (upper limit) see Bas’s talk

23 Magnetic noise? We replaced the magnets of the input towers with less strong ones (/5) + restored the good polarity No real improvement observed… Dec 21 st Mar 3rd AC OFF

24 Thermal effects Cleaning of the input mirrors was performed at the end of November –Some visual improvement was observed for both WI mirror :  Observation before cleaning : with an halogen lamp coupled to a fiber some large particules on the coatings center part : a little bit ‘opaque’ (~ Ø1 cm) a lot of condensation points but not on the coating  Observation after cleaning : no more large particles center part : clearer(# Ø1 cm) visual aspect better than before cleaning –But no clear improvement in the thermal effects: - thermal transient similar to before - increase of the sidebands power ~ 25% only see Michele’s talk

25 Thermal effects Before / after cleaning Sidebands power Dark fringe Locking step B5, carrier

26 Plans before Virgo+ shutdown Replace Brewster with cryotrap next week Thermal Compensation System installation this month –TCS commissioning Understand effect of the magnets replacement (magnetic noise, Eddy currents) –Also replace those of the end mirrors?