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The Virgo noise budget

The Virgo noise budget. Romain Gouaty For the Virgo collaboration. GWADW 2006, Isola d’Elba. Summary. Introduction : the sensitivity curves of Virgo Commissioning Analysis of the technical noises : - Length control noise - Angular control noise - Mirror actuator noise

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The Virgo noise budget

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  1. The Virgo noise budget Romain Gouaty For the Virgo collaboration GWADW 2006, Isola d’Elba

  2. Summary • Introduction : the sensitivity curves of Virgo Commissioning • Analysis of the technical noises : - Length control noise - Angular control noise - Mirror actuator noise - Oscillator phase noise - Laser frequency noise • Noise budget of the C7 run (September 2005) • Conclusion

  3. The sensitivity curves of Virgo Commissioning Single Fabry-Perot cavity Recombined (7 W) Recycled (0.7 W) 10 W (10 W) Nominal sensitivity To reach the Virgo nominal sensitivity :  Technical noises have to be identified in order to be cured

  4. 6.25 MHz Dark fringe signal The recycled interferometer : locking scheme ACp = demodulated signal at 0° ACq = demodulated signal at 90° + Recycling mirror Modulation Beam Splitter Laser - 0 B5 B2_3f_ACp B1_ACp Differential Mode control loop B5_ACq Laser frequency stabilisation B5_ACp

  5. Sensitivity during the C5 run West Input mirror angular control noise Beam Splitter angular control noise Beam Splitter longitudinal control noise Mirror actuator noise Oscillator phase noise Control noise Oscillator phase noise C7 sensitivity Noise budget of the C5 run (december 2004) Nominal sensitivity How these noises have been identified ? Which technical upgrades between C5 and C7 runs ?

  6. Beam Splitter longitudinal control noise • Noise analysis in 3 steps : • Identification of the noise source • Analysis of the propagation mechanism • Noise projection on the sensitivity curve + Recycling mirror Beam Splitter Laser - 0 B5 B2_3f_ACp B1_ACp Differential Mode control loop B5_ACq Laser frequency stabilisation B5_ACp

  7. 1 2 3 leq/2 Correction signal (Volts) Resonant Fabry-Perot  32 round-trips Filter Sensitivity during the C5 run (Dec 2004) Beam Splitter longitudinal control noise leq/2 TF(actuators) Volts meters B5_ACq Beam Splitter longitudinal control noise Coherence : Dark fringe signal vs Correction signal Looking for coherent channels to identify the source Analytical model leq = Correction signal x TF(actuators) x 2 x 1/32

  8. Technical upgrades :  Filter optimization Sensitivity during the C5 run (Dec 2004) Beam Splitter longitudinal control noise Sensitivity during the C5 run (Dec 2004) Beam Splitter longitudinal control noise during C5 Beam Splitter longitudinal control noise during C6 Sensitivity during the C6 run (Aug 2005) Sensitivity during the C5 run (Dec 2004) Beam splitter longitudinal control noise during C5 Beam splitter longitudinal control noise during C6 F B5 Improvements of the Beam Splitter angular control (coupling z  x) Better filtering of the Beam Splitter longitudinal control noise Nominal sensitivity Nominal sensitivity Nominal sensitivity Reduction of the Beam Splitter control noise : from C5 to C6

  9. Alpha technique +  Efficient substraction requires a fine tuning of the  coefficient  - Reduction of the Beam Splitter control noise : from C6 to C7 Technical upgrades : Substraction of the Beam Splitter control noise by sending appropriate corrections to the end arm mirrors (= Alpha technique) + Laser - Beam Splitter longitudinal control B5 B1 F

  10. Sensitivity during the C6 run (Aug 2005) Beam Splitter longitudinal control noise during C6 Beam Splitter longitudinal control noise during C7 Sensitivity during the C7 run (Sept 2005) Sensitivity during the C6 run (Aug 2005) Beam splitter longitudinal control noise during C6 Beam splitter longitudinal control noise during C7 Sensitivity during the C6 run (Aug 2005) Beam splitter longitudinal control noise during C6 Alpha technique   coefficient tuned with an accuracy of 7% Nominal sensitivity Nominal sensitivity Nominal sensitivity Reduction of the Beam Splitter control noise : from C6 to C7 Technical upgrades : Substraction of the Beam Splitter control noise by sending appropriate corrections to the end arm mirrors (= Alpha technique) • How to obtain further improvements ? • With a better tuning of  (1%) • By reducing angular control noise (coupling z  x) ?

  11. x l = d.x l Miscentering : d Sensitivity during C5 (Dec 2004, recombined) Beam Splitter angular control noise Angular control noise  Impact of angular control noise proportional to the beam miscentering Hypothesis : d  1.5 cm From C5 to C7 : reduction of Beam Splitter angular control noise During C7 : sensitivity limited by Input Mirrors (NI, WI) angular control noise April-May 2006 : A vertical miscentering of about 1 cm has been corrected (see H. Heitmann’s talk)  sensitivity improvements are expected

  12. Serial resistor Coil driver coil (i) DAC l Mirror actuator noise Pendulum Origin : DAC and coil driver noise Measurement of the coil current  Actuator noise estimation Correction Sensitivity during the C6 run (Aug 2005) Mirror actuator noise Virgo nominal sensitivity  C6 sensitivity limited by actuator noise between 50 and 300 Hz

  13. Serial resistor Coil driver coil (i) DAC l Reduction of the actuator noise : from C6 to C7 Serial resistor increased from 250  to 6 k (arm mirrors) • Actuator noise reduced by a factor 23 Problem : the maximum strength applied to the mirror has to be reduced (because of the DAC saturation voltage)  Hierarchical control is needed (see G. Losurdo’s talk) Sensitivity during the C6 run (Aug 2005) Mirror actuator noise during C6 Sensitivity during the C7 run (Sep 2005) Mirror actuator noise during C7 Nominal sensitivity Marionette Mirror

  14. Serial resistor Coil driver coil (i) • Fine tuning of the DAC electronics DAC • Implementation of an analog “deemphasis” filter l Reduction of the actuator noise : towards the design Next upgrades: Sensitivity during the C7 run (Sep 2005) Mirror actuator noise during C7 Actuator noise with a perfect tuning of the electronics Actuator noise with deemphasis filter • Some additional improvements ? • Further increase the resistor : - already possible (correction at 20% of the DAC saturation level during C7) • - improve hierarchical control Nominal sensitivity

  15. démodulation Sensitivity during the C5 run Shot noise + electronic noise ? Sensitivity during the C5 run Shot noise + electronic noise Oscillator phase noise x 20  C5 sensitivity limited by oscillator phase noise Noise at high frequency during the C5 run @ high frequency : Noise higher than electronic noise and shot noise by a factor 20

  16. B1_ACp high frequency noise Vs Amplitude of B1_ACq ACp =.ACq   = 0.52 rad/Hz B1_ACp high frequency noise (V/Hz) C5 data Evidence of phase noise Demodulated at 0°  Noise in the ACp channel proportional to the amount of signal in the ACq channel Demodulated at 90° Photodiode • Origin of phase noise ? S LO board:distribution of the oscillator signal to the demodulation boards LO board DC LO ACp Measurement of the noise induced by LO boards:  = 0.47 rad/Hz (agrees with C5 estimation) ACq Demodulation board Oscillator phase noise • Coupling during the demodulation process: Photodiode signal : S = Sp + Sq = sp cos(t) + sq sin(t) Oscillator signal : LO = cos (t + ) Demodulation process S x LO Dark fringe signal : B1_ACp = S x LO = (sp+ sq)/2 Oscillator phase noise

  17. Sensitivity during the C5 run (Dec 2004) Oscillator phase noise during C5 Sensitivity during the C6 run (Aug 2005) Oscillator phase noise during C6 Reduction of the oscillator phase noise • Technical upgrades after C5 : • ACp =.ACq • Improvement of the LO boards  Reduction of  • Alignment conditions improvedwith the mirror automatic alignment  Reduction of the ACq signal  Phase noise reduced by  100 at 1 kHz Laser phase modulation Nominal sensitivity Interferometer RF To reach the Virgo nominal sensitivity : Reduction of the generator phase noise  Marconi 2040 replaced by LNFS-100 (less noisy) Generator (6.25 MHz) LO Demodulation board

  18. Sensitivity during the C6 run Frequency noise B1 shot noise B1 electronic noise Laser frequency noise Coherence between B1_ACp and B5_ACp  sensitivity limited by laser frequency noise B5_ACp : measures the laser frequency noise Laser  B5_ACp B1_ACp • Propagation of frequency noise compatible with a CMRF (arm asymmetry) of about 10-3 • Reduction of the CMRF by improving the arm symmetry • Main origin suspected : shot noise in the B5_ACp signal •  Reduction of the shot noise by increasing the power of the incoming beam Nominal sensitivity

  19. Control noises B1 and B5 shot noise Environmental noise (see F. Paoletti’s talk) Noise budget of the C7 run (Sep 2005)

  20. Conclusion • The sensitivity of the C7 run is well understood • The main sources of noise are : • - Control noises (above all angular) @ low frequency • - Environmental noise (sometimes correlated with diffused light) • - Shot noise @ high frequency • How the sensitivity will be improved ? • - Centering of the beam with respect to the mirrors (started) • - Implementation of the full automatic alignment system(started) • - Fine tuning of the alpha technique (planned) • - Reduction of actuator noise (started) • - Isolation of the optical benches (planned) • - Power increased x 10 (already performed)

  21.  Former generator Generator installed during fall 2005 Specifications for generator phase noise

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