1. Virgo commissioning update - VSR1 first month summary E. Tournefier WG1 meeting, Cascina June 20 th,2007

2. Activities since last WG1 meeting (March 28 th ) Virgo complete electrical shutdown (April 6 th -> 18 th ) Infrastructure works: –Electrical works: UPS replacement, reorganisation,… –Computing: civil work, re-organisation, new file server,… Detector improvements -Acoustic enclosure around external detection bench -Replacement of Brewster window with a larger one Restart went ok: ITF relocked within ~2days 1 month of commissioning before the run –Acoustic enclosures at end benches –Diffused light investigations + some noise reduction –Improvements of controls (longitudinal, angular, suspensions) –Change of naming convention (V1:channel_name)for easier data exchange with LSC VSR1 started on May 18 th as planned –Short commissioning breaks for improvements / problem fixing

3. Acoustic enclosures External detection bench: –Displace bench from the tower (~50cm) –Install acoustic panels (a room into the room) End benches: –Simpler: build a room around the benches Detection End buildings

4. Acoustic noise reduction: end benches Tentative acoustic noise projection before Tentative acoustic noise projection with acoustic enclosure Seismic noise on the optical bench - No acoustic enclosure - With acoustic enclosure - Previous actions: Improvement of the optical setup But: projection of acoustic noise of end benches was still close to the measured sensitivity  Acoustic enclosure needed Result: impact reduced above 100 Hz

5. New Brewster window Why change the detection Brewster window: - Brewster-detection tower was shown to be an area very sensitive to acoustic noise - tentative noise projections: Brewster could be a limiting factor - old Brewster didn’t respect the rule: diameter > 5 x beam waist Brewster link Detection tower Tentative projection of ‘Brewster noise’  Replace Brewster with a larger one (April shutdown) Followed by diffused light investigations No obvious improvement in sensitivity See Raffaele’s talk

6. Other actions for noise reductions Replaced pump of SR tower with a smaller one (noise reduced but path is unclear) BS actuator noise reduced (last WG1 meeting)

7. Mirror actuator noise reduction Electronic noise of the coil drivers + DAC  Shaping filters, more gain to reduce its impact zCorr I (A) to mirror coil  BS actuator noise reduced in May  The arm mirrors actuators need to be improved can be done during VSR1

8. Actuators calibration Actuation TFsSimple pendulum Simple cavity filtering (500 Hz pole) More precise measurement of the actuators response  frequency dependence could be due to Eddy current effects  Change of 20% at high frequencies 10%

9. Longitudinal controls  PRCL  MICH B2_ACpmix Usual noise subtraction (online): -MICH and PRCL corrections sent to the end mirrors to subtract the noise reintroduced by these loops into the dark fringe -  coefficient is frequency dependent MICH noise reduction ~ 50 - with  =0 - with measured  (f) See Bastian’s talk

10. Longitudinal controls: noise budget BS control noise limits the sensitivity below 40 Hz => What is the origin of this noise? - B1_ACp - BS control noise - PR control noise

11. Origin of BS control noise ? Related with acoustic noise inside the laser lab  Beam jitter seen by B2 photodiode (used for PR & BS)? Sometimes disappears … but acoustic noise does not change Input beam jitter Acoustic noise in laser lab Beam jitter vs acoustic noise Beam jitter vs dark fringe dark fringe

12. Angular controls Second modulation frequency (8MHz) now used for Q22 => Get rid of DC signal Control loops improvements Mirror centering ~ 1mm Angular noise budget -Angular controls do not limit the sensitivity - Reduction of electronic/shot noise in error signal still possible

13. Suspension control: z ->  couplings Compensation of non-linear coupling: Large seismic activity  large correction sent to marionetta (zM)  y motion of F7 and payload  Side effects on alignment Solution: compensate for z ->  y coupling Need a quadratic compensation: Dark fringe -No quadratic compensation -With quadratic compensation  y=c*zM +d*zM 2

14. Suspension control: top stage control Old problem: environmental noise (  seism) reintroduced by Lvdt used for top stage control => Use the ITF longitudinal error signal instead (Global Inverted Pendulum Control) => z correction to the mirror well reduced GC (reconstructed z) LVDT VSR1: enabled only for NE-WE No GIPC With GIPC

15. Sensitivity vs wind and sea activity Matteo’s empirical formula: Horizon = H 0 (1 - a x  seism – b x wind) WSR1 (Sept 2006) VSR1 (May 2007) a= 0.37, b= 0.37 a= 0.07, b= 0.04 => Sensitivity to bad weather conditions is well reduced

16. Lock acquisition: thermal transient troubles Variations in the thermal transient : seems related to activities in laser lab Sometimes need to wait few hours before being able to lock

17. Thermal effects: sidebands image Image of the sidebands (first step of phase camera): scanning system on B5 beam: - the beam is scanned on a pin-hole + photodiode - demodulated signal is used to reconstruct the sidebands shape Waiting for thermal compensation system + complete phase camera

18. VSR1 noise budget Still magnetic noise? Mystery noise

19. Some observations: –Coupling to DF increases with misalignments –Sudden decreases/increases (also seen in frequency noise) –Structures not excited with noise injections/tapping tests around benches/towers Keep searching…

20. VSR1: first month summary Thanks to Roberto for the material

21. Run organisation Goal: –Take science data for a minimum period of 4 months starting from the 18 th May 2007 at 23:00 (LT) Shifts have been planned until 20 th September 2007: 18 weeks, 378shifts. –Shift team and time schedule: Team: 1 operator + 1 physicist, Shift period: 8 hours Shift start times: 07:00 – 15:00 – 23:00 Permanent ON Call: –11 Virgo ITF Sub-systems: (Alignment, DAQ, Detection, Electronics, Locking, Global Control, Laser &Injection, MSC, On line Computing &Network, Software, Suspension Electronics & Software) –4 EGO Site Services: (Network & Global Security System, Site Infrastructure-Conditioning, Site Infrastructure-Electricity, Vacuum)

22. Duty cycle –Duty cycle in science mode ~ 85% –42 unlocks from “Science Mode” registered up to 17/06/07 –Longest Lock: about 58.5 hours, Longest Unlock: about 16.1 hours

23. Science mod recovery time –Longest unlock: 16 hours –Smallest ~ 30mn (time needed for lock acquisition)

24. Lock duration –Longest lock: 58 hours

25. Unlocks Analysis of unlocks ongoing (preliminary statistics) Main unlock reasons: -IMC fast unlocks Partially cured (loop gain reduced) -Global control crashes Pb = longer recovery (susp excited) -Earthquakes Manual unlocks for: -Weekly maintenance -Commissioning breaks Only 3 unlocks due to bad weather

26. Commissioning breaks Alignment drifts observed during long locks: related to Q81 quadrant mis-centering (used for BS control) => spoils error signal (AC)  Temporary solution: realign quadrant from time to time  Improvement: include Q81 asymmetry in the error signal for BS control Small drifts still there  Try to use another error signal (B1p?) or  Install galvanometer to keep centering in science mode realignment Dark fringe Q81 asymmetry IMC Fast unlocks - Reduction of IMC loop gain 1 unlock per couple of day => ~ 1 per week - more investigations ongoing (electronics) Suspension controls: some improvements /tests

27. Long term observations: Etalon effect! Etalon effect: small FP cavity inside input mirrors (due to AR face) => effective reflectivity modulated with mirror thickness (temperature) B7/B8 phd -FP transmitted power -Input mirror temperature Temperature variation FP Transmitted power

28. Some short term plans Continue noise investigations –‘Mystery noise’ (  200Hz) –Magnetic noise (50 - 100 Hz) –Low frequency noise in laser lab (=> BS error signal) –Reduce mirror actuator noise (cavity mirrors) Controls: –Alignment drifts: get rid of Q81 or use galvanometer –Suspension control improvements in preparation