VIRGO commissioning progress report

1. VIRGO commissioning progress report

2. Status in C4 • Recombined locked (full Virgo with PR misaligned) • Arms automatic alignment • Top stage tidal hierarchical control • Second stage of frequency stabilization (laser frequency controlled with the ITF common mode)

3. C4 sensitivity

4. After C4: hardware operation • Installation of new terminal benches support: terminal photodiode movements solved, possibility to perform DC drifts control • Rearrange optics on terminal benches: spherical aberrations solved, Gouy phase and telescope tuning for AA possible • MC mirror cleaning & check: attempt to reduce the scattering inside the Mode Cleaner, with no result (scattering still there) • ….

5. After C4: action performed • IB drift from the NE quadrants DC: not finished • BS drift control from the WE quadrants DC: complete • BS automatic alignment (as on the WI mirror): not yet finished • Low noise coil drivers (switch from high power for lock acquisition to low noise for lock keeping): complete • Compact DSP cards to overcome DSP memory limits: complete • IB local control acting from the marionette: complete • ‘New’ cavities automatic alignment: complete • Cavity full hierarchical control via marionette: not yet finished • M6 replacement (beam attenuation to 10%) to reduce the feedback from the PR in the IMC: complete

6. After C4: main control upgrades summary • NE filter 7 control: chain resonance (16 mHz) and filter 7 movement damping • IB control from the marionette: reduction of resonances in the IB control (introduced through the bench coils) • New coil drivers: reduction of DAC noise on the RM coils • Beam splitter automatic alignment: BS drift control and AC AA on the BS as on the WI mirror • Marionette control started (demonstrated successfully on a single arm) but need AA and SSFS to go on • Recycling locking started (stable lock of state 3) but need AA and new M6 to go on (PR feedback inside the IMC makes the system unstable)

7. Filter 7 control • LVDT used as sensor and actuator (in different frequency ranges) to damp the Filter 7 motion; • Damp the 16 mHz motion (chain mode), active up to 100 mHz; • Used only for damping

8. Chain resonance damping from Filter 7 16 mHz 32 mHz 32 mHz ON OFF OFF

9. IB marionette control • In C4 the Injection Bench was controlled locally through the IB bench coils; • Many resonances (bench, wires, Reference Cavity, …) where detected in the ITF signal; • A new control of the IB through the marionette has reduced or made disappear many of these peaks.

10. IB marionette control IB coils control Marionette control

11. New low noise coil drivers • DAC noise: 300 nV/sqrt(Hz) (17.5 effective bits) • Coil Driver noise: 80 nV/sqrt(Hz)

12. New low noise coil drivers • The required additional force for lock acquisition is provided by a transconductive amplifier. • During lock acquisition phase only DAC 1 is used. • During linear phase DAC 1 output set to zero and DAC 2 is used to keep the lock.

13. BS control • AC control of the AA added to the BS: local controls switched off; • DC BS drift using the West End quadrants on; • Never tested AC and drift correction together;

14. Cavity marionette control • Full hierarchical control of a cavity closed: RM+Marionette+IP tidal control • Yet without AA and Second Stage of Frequency Stabilization • Tested soon the full hierarchical control with AA and SSFS

15. North cavity full hierarchical control No change in the cavity power when control starts

16. North cavity full hierarchical control RMS reduction by a factor 3 at low frequency

17. Recycling locking: state 3 • Lock of the central cavity (CITF) on the sidebands + lock of the north arm (on the carrier) achieved

18. Virgo in state 3: effect of the PR alignment in the IMC When the PR is aligned fringes in the power inside the IMC appears: frequency noise, prenvents locking

19. Beam attenuation: M6 replacement • The light reflected in the IMC is partially scattered by the MC in the Virgo beam direction, creating spurious fringes; • The fringes in the IMC make frequency noise,which prevents the PR locking; • To temporary solve the problem of the PR feedback in the IMC it has been decided to attenuate the beam entering in the ITF by a factor 10 (factor 100 attenuation of fringes in the IMC; • To do this the last mirror injecting the beam in the ITF has been replaced with a 10% reflective mirror.

20. M6 replaced with a 10% reflecting IMC M6 From the laser To the interferometer Reference Cavity

21. After M6 replacement • Virgo is now working with 10% of the C4 power (about 0.7 W on the PR instead of the former 7 W); • Electronics and controls scaled to 10% power; • Recombined realigned and locked; • Arms automatic alignment restarted; • Fringes in the IMC when the ITF and the PR are aligned are strongly reduced; • Tests for full Virgo locking have started.

22. Future upgrade: new Injection Bench? • The PR reflection inside the IMC are a problem: the MC scattering in the IMC axis direction creates instabilities; • An isolation is necessary: on the present Injection Bench there is no space for a Faraday Isolator; • A new Injection Bench will be probably made: its main difference will be the presence of a Faraday Isolator; • The expected installation should take place in the begin of next year. In the meanwhile Virgo will work with 10% of its power.

23. New Injection Bench Faraday Isolator 900 mm

24. Progress in sensitivity

25. Changes with respect to C4 • Sensitivity measured before replacing M6 with the 10 % reflecting mirror (7 September 2004): • Low noise RM coils drivers; • No BS control at the level of the RM (no drift; correction, no marionetta notches compensation); • BS drift control (WE quadrants DC through BS marionette); • IB marionette control; • Input mirrors coils disconnected

26. 7 September data taking BS control upgrade Frequency stab.problems (?)

27. Next steps • In the next month the activity will be directed to the locking of the full Virgo; • The PR locking test have already started; • In the 10-100 Hz the noise is dominated by frequency or angular jitter noise coming from the Injection system: coupling with acoustic noise? IB internal resonances? This problem is being investigated.

28. Next run planned conditions • PR locking • Arms marionette control • Better BS control • New coils drivers • Full Automatic Alignment • … • When? (in one month from now?)