1. Advanced Virgo ISC subsystem
Maddalena Mantovani
For the ISC group
VIR-0287A-19

2. Introduction
The Advanced Virgo detector show its best sensitivity only when the main mirrors (PR,BS,NI,NE,WI,WE) are in precise microscopic positions (so called working point)
Arm cavities on resonance
Central interferometer on destructive interference
Power recycling cavity on resonance
Mirrors aligned with respect the main beam
For this reason a very sofisticated control system has been developed and implemented
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

3. Longitudinal degrees of freedom
Dofs to be controlled
Longitudinal degrees of freedom
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

4. Angular degrees of freedom
Dofs to be controlled
Arm cavities modes:
Common(+) and Common(-)
Differential(+) and Differential(-) PR BS
The accuracy requirements are ~nrad for the cavity mirrors!!!
Angular degrees of freedom
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

5. Control principle
The mirrors are controlled by using the signals coming from the main beams, with a technique which is based on the modulation/demodulation technique (Pound-Drever-All technique).
Phase modulation: create sidebands around the carrier (ω0) at ± the modulation frequency, Ω.
Error signal → beat note between carrier and non-resonant sidebands
Similar technique for the angular control
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

6. Lock acquisition and steady state
The ISC subsystem take cares of bringing all the mirrors from un- controlled state to the final working point (which is called lock acquisition) and to maintain the final working with good performance, i.e. low noise and high duty cycle (steady state = science configuration).
The lock acquisition has been developed as the adiabatic transition from steady states going towards more and more complex configurations
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

7. Lock acquisition Variable-finesse technique Steady state
Lock aquisition
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

8. Steady state performance
The duty cycle ensured by the ISC subsystem is usally larger than 80%
Virgo Week - ISC - Jan 22th 2019
Maddalena Mantovani

9. the end …
Virgo Week - ISC - Jan 22th 2019