1. VIRGO Superattenuator performance and its evolution in the SAFE Project F. Frasconi – INFN Pisa (ET-WP2 Workshop – Roma – February 27, 2009)

2. February 27, 2009F. Frasconi - INFN Pisa2 The VIRGO Suspension System The Superattenuator (SA) is the mechanical system adopted to isolate the optical components from seismic activities (local disturbances). It is based on the working principle of a multistage pendulum.The Superattenuator (SA) is the mechanical system adopted to isolate the optical components from seismic activities (local disturbances). It is based on the working principle of a multistage pendulum. Hybrid system: active control below 4 Hz and passive attenuation starting from 4 Hz.Hybrid system: active control below 4 Hz and passive attenuation starting from 4 Hz.

3. February 27, 2009F. Frasconi - INFN Pisa3 Main features of SA Thermal Noise During the SA development the seismic attenuation performance have been evaluated. The indirect system response was obtained combining the measured “stage by stage” TFs (red curve) of each mechanical filter along the chain.During the SA development the seismic attenuation performance have been evaluated. The indirect system response was obtained combining the measured “stage by stage” TFs (red curve) of each mechanical filter along the chain. Attenuation factor @ 10 Hz is about 10 15.Attenuation factor @ 10 Hz is about 10 15.

4. February 27, 2009F. Frasconi - INFN Pisa4 Passive attenuation measurements/CITF Hor. Vert. Thermal Noise Measured Upper Limit

5. February 27, 2009F. Frasconi - INFN Pisa5 Passive attenuation measurements/CITF Horizontal Vertical Upper Limits of the residual seismic vibrations along the beam are below (but close) to the VIRGO Thermal Noise

6. February 27, 2009F. Frasconi - INFN Pisa6 New Measurements A measurement campaign has been recently done: the suspension point has been excited at known frequencies and ITF has been used to measure the motion transmitted to the mirror.A measurement campaign has been recently done: the suspension point has been excited at known frequencies and ITF has been used to measure the motion transmitted to the mirror. Noise lines at 4, 6, 10 and 18 Hz have been injected on NI and WI suspensions. Noise lines at 4, 6, 10 and 18 Hz have been injected on NI and WI suspensions.

7. February 27, 2009F. Frasconi - INFN Pisa7 New Measurements/ITF frequency ( Hz ) Displacement ( m. Hz -1/2 ) Top Mirror Attenuation factor > 10 10

8. February 27, 2009F. Frasconi - INFN Pisa8 Upper Limit for AdV h (f) frequency (Hz) AdV Sensitivity

9. February 27, 2009F. Frasconi - INFN Pisa9 ID and Payload Swing ID effectiveness: residual swing induced by the mechanical resonances < 0.1 µm rms BUT at low frequency (below 200 mHz) when the seism is dominated by the ground tilt, the control uses the wrong strategy. For principle reasons the horizontal accelerometer misinterprets the ground tilt affecting ID.

10. February 27, 2009F. Frasconi - INFN Pisa10 Spoiled Performance WINDSEA Marionette Correction With standard weather conditions the payload swing is OK (see VSR1).With standard weather conditions the payload swing is OK (see VSR1). Problem arises with bad weather conditions Too large correction dynamic for AdV requirementToo large correction dynamic for AdV requirement

11. February 27, 2009F. Frasconi - INFN Pisa11 The Present Actuation Noise RM actuator noise is compliant with AdVRM actuator noise is compliant with AdV Marionette actuator noise has to be reduced for Adv by about a factor 10 in the 10-30 Hz regionMarionette actuator noise has to be reduced for Adv by about a factor 10 in the 10-30 Hz region AdV VIRGO

12. February 27, 2009F. Frasconi - INFN Pisa12 Marionette actuation range optimization Marionette actuation range (and thus noise) can be reduced by a factor 5, loosing only 1% of duty cycle, setting it at 2.2 VoltMarionette actuation range (and thus noise) can be reduced by a factor 5, loosing only 1% of duty cycle, setting it at 2.2 Volt Calm Any

13. February 27, 2009F. Frasconi - INFN Pisa13 Marionette DAC noise reduction Adv sensitivity with a factor 5 DAC noise reductionAdv sensitivity with a factor 5 DAC noise reduction

14. February 27, 2009F. Frasconi - INFN Pisa14 Present limitations on Suspension control Sensitivity to ground tiltSensitivity to ground tilt - feedback gain at the top stage can not be extended at very low frequency [ see VIR-NOT-FIR-1390-318.pdf ] - ground tilt gives horizontal acceleration signal, generating noise - more problematic with bad weather conditions IP mechanical structureIP mechanical structure - leg flexural resonance around 10 Hz limiting the control band - improving the rigidity acting on the present leg structure and F0 crossbar - installation of tilt control actuators Reduce actuation noiseReduce actuation noise

15. February 27, 2009F. Frasconi - INFN Pisa15 The SAFE Project SupeAttenuator Facility at EGO site Duplicate a long suspension chain with minor differences, is a fundamental step forward for future VIRGO upgrades: - to implement and test new technical solutions; - to test the tilt control using tilt sensors and PZTs; - to implement and test new control strategies; - to be used as a test bench for new control electronics; - to test the control of SA with new last stage; - to be used as a playground for young physicists; - to reduce the commissioning period.

16. February 27, 2009F. Frasconi - INFN Pisa16 The Base Line

17. February 27, 2009F. Frasconi - INFN Pisa17 The VIRGO IP Features: - Aluminum non monolithic legs (heavy metallic interconnection joint); - low stiffness legs ( Al pipe with 130 mm of outer diameter and 125 mm inner diameter); - room available within the feet for PIEZO accommodation.

18. February 27, 2009F. Frasconi - INFN Pisa18 The monolithic IP leg The new IP design has been conceived with: - Aluminum monolithic legs; - increased sectional area (higher momentum of inertia - 160 mm outer diameter and 150 mm inner diameter); -using the same elastic element (Maraging flex joint) - with these improvements the leg flexural frequency will be around 20 Hz.

19. February 27, 2009F. Frasconi - INFN Pisa19 The PIEZO actuators Since the beginning the IP mechanical structure was conceived with the possibility to install three piezoelectric actuators within the feet structure; Since the beginning the IP mechanical structure was conceived with the possibility to install three piezoelectric actuators within the feet structure; The IP was designed to be controllable in all six degree of freedom (including the tilt control): the PIEZO actuator acts against the elastic element mounted on each IP foot. The IP was designed to be controllable in all six degree of freedom (including the tilt control): the PIEZO actuator acts against the elastic element mounted on each IP foot.

20. February 27, 2009F. Frasconi - INFN Pisa20 PIEZO accommodation Three PIEZO (PZT) actuators can be accommodated within the feet structure Room for PZT accommodation Bottom ring Tilt meter

21. February 27, 2009F. Frasconi - INFN Pisa21 PZT accommodation (cont.)

22. February 27, 2009F. Frasconi - INFN Pisa22 IP control for Vertical ID improvements The measurements set-up for the IP & PZTs characterization can be used for a study of new control strategy improving the ID vertical control The measurements set-up for the IP & PZTs characterization can be used for a study of new control strategy improving the ID vertical control LVDTLVDT Accelerometer Bottom Ring Room for PZT Accommodation

23. February 27, 2009F. Frasconi - INFN Pisa23 Tilt-meter Status (R&D activity in collaboration with INFN Roma Tor Vergata) A force balance sensor using a pivoting bar accommodated inside a rigid box has been conceived:A force balance sensor using a pivoting bar accommodated inside a rigid box has been conceived: - a ground tilt induces a tilt of the box but not of the balance that, above the angular resonance frequency, can be considered freely rotating around the pivot. The characterization measurements performed with the first prototype put in evidence the fragility of the commercial flex pivot used.The characterization measurements performed with the first prototype put in evidence the fragility of the commercial flex pivot used. The two sensors have been mounted again with more rigid pivots and a test bench of both sensors will be done soon.The two sensors have been mounted again with more rigid pivots and a test bench of both sensors will be done soon.

24. February 27, 2009F. Frasconi - INFN Pisa24 Tilt-meter

25. February 27, 2009F. Frasconi - INFN Pisa25 SAFE: the New IP Main features: Short Al monolithic legs (4277 mm instead of 5340 mm);Short Al monolithic legs (4277 mm instead of 5340 mm); Right sectional area (160 mm outer diameter);Right sectional area (160 mm outer diameter); Same elastic element (Maraging flex joint);Same elastic element (Maraging flex joint); Same tunable counterweight approach for a precise percussion point positioning;Same tunable counterweight approach for a precise percussion point positioning; Available room within feet for PZTs actuator accommodation.Available room within feet for PZTs actuator accommodation.

26. February 27, 2009F. Frasconi - INFN Pisa26 SAFE: pendulum length Even if the distance between two consecutive mechanical filters is shorter (900 mm instead of 1150) and one stage is missing, SAFE is not conceived as an experimental set-up for seismic isolation performance measurements.Even if the distance between two consecutive mechanical filters is shorter (900 mm instead of 1150) and one stage is missing, SAFE is not conceived as an experimental set-up for seismic isolation performance measurements. The distance between the last seismic filter and the payload is identical to the VIRGO oneThe distance between the last seismic filter and the payload is identical to the VIRGO one The SA prototype should be considered as a test bench to check the response of new mechanical, electronic and control solutions.The SA prototype should be considered as a test bench to check the response of new mechanical, electronic and control solutions.

27. February 27, 2009F. Frasconi - INFN Pisa27 Activities in progress The old SA prototype has been moved on site;The old SA prototype has been moved on site; The new IP prototype has been built. It is ready on site to be assembled and tested;The new IP prototype has been built. It is ready on site to be assembled and tested; The PIEZO actuators and their driver electronic boards are available;The PIEZO actuators and their driver electronic boards are available; The test set-up for PIEZO actuators characterization within the feet is in preparation;The test set-up for PIEZO actuators characterization within the feet is in preparation; The first ring of the vacuum tank has been modified and it is ready for a vacuum seal test;The first ring of the vacuum tank has been modified and it is ready for a vacuum seal test; The scaffolding installation has just started.The scaffolding installation has just started.

28. February 27, 2009F. Frasconi - INFN Pisa28 Final Considerations Passive attenuation performance of SA are compliant with AdV requirement Potential problems can arise with bad weather conditions (windy days): micro-seism is tilt dominated Potential problems can arise with bad weather conditions (windy days): micro-seism is tilt dominated The development of a very high sensitivity tilt-sensor (10 -8 rad/√Hz @ 30 mHz) is the direct solution of the tilt problem ( very difficult task ). Alternative solutions are available for AdV The development of a very high sensitivity tilt-sensor (10 -8 rad/√Hz @ 30 mHz) is the direct solution of the tilt problem ( very difficult task ). Alternative solutions are available for AdV The new IP mechanical structure and PIEZO actuators could be used to improve ID performance The new IP mechanical structure and PIEZO actuators could be used to improve ID performance The SAFE facility has a key role for future VIRGO upgrades. It could be used as a playground to install, test and control a new payload prototype. The SAFE facility has a key role for future VIRGO upgrades. It could be used as a playground to install, test and control a new payload prototype.