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

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

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

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

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

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

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

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

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