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The end of VSR1: mystery death

Virgo commissioning since the end of VSR1 E. Tournefier for the commissioning team ILIAS WG1, Cascina March 5 th ,2008. The end of VSR1: mystery death. Noise structures (200-300 Hz + 600-1000 Hz) highly non-stationary: depend on the quality of the ITF alignment. realignments.

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The end of VSR1: mystery death

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

  2. The end of VSR1: mystery death • Noise structures (200-300 Hz + 600-1000 Hz) highly non-stationary: depend on the quality of the ITF alignment realignments

  3. Mystery noise investigations Suspended bench • 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 Tower window External injection bench Laser bench

  4. Mystery noise = beam jitter Dihedron resonance • 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 Environmental noise Actuacor noise Shot noise Eddy currents

  6. Noise budget now Actuator noise Environmental noise Control noises Shot 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 -> Drift control (10mHz) 8MHz -> Drift control • 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 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 Galvos Telescope Virgo+ Now Quadrant setting 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 see Gabriele’s talk • 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 control signals error signals Environmental noise • VSR1 • now

  12. Environmental noises DAQ room (+CE hall) North End AC CleanRooms AC  Laser lab Central hall AC Water pump of CE • 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 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 • 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? Detection benches BS Dark fringe Coherence with Brewster Seismometer

  15. Diffused light at detection port • 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 Detection benches BS

  16. Diffused light reduction (?) at detection • Indication of light reflected/diffused by the detection bench: Dedicated experiment:rotate the suspended bench by 100 rad OB rotation 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 Air conditioning OFF DeEmphasis DeEmphasis Emphasis Emphasis CoilDriver • Reduction of the mirror actuator electronics noise during VSR1 (arm mirrors) DSP DAC G 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 21st 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 see Michele’s talk • 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

  25. Thermal effects • Before/ aftercleaning Locking step Dark fringe Sidebands power 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?

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