Interferometer Sensing and Control challenges for Advanced Virgo

Interferometer Sensing and Control challenges for Advanced Virgo

Interferometer Sensing and Control challenges for Advanced Virgo Maddalena Mantovani For the Virgo Collaboration VIR-0479A-19 Introduction ISC 1st generation of GW detectors have proven working principle of the GW detectors, but unfortunately the sensitivity was too low to be able to detect a GW signal. The target of the 2nd generation sensitivity by a factor 10! was to improve the Thermal noise (suspensions and coating)

Need of reducing the fundamental noises Quantum noise Best sensitivity of Virgo (2011) 22th of May 2019 GWADW19 Maddalena Mantovani 2 Introduction ISC Several changes have been performed, but most of them had a direct impact on the complexity of the ISC subsystem commissioning Reducing the Quantum noise: - increase the Arm finesse - Dynamical effects in the cavity locking signals - Radiation pressure effects - increase the input power - Larger thermal effects - Radiation pressure effects - inject squeezed light Reducing the Thermal noise: - Increase the mirror masses - Increase the beam size on the mirrors

This led to have a marginally stable recycling cavity (space constrain) - Monolithic suspensions 22th of May 2019 GWADW19 Maddalena Mantovani 3 Introduction ISC Several changes have been performed, but most of them had a direct impact on the complexity of the ISC subsystem commissioning Reducing the Quantum noise: - increase the Arm finesse - Dynamical effects in the cavity locking signals - Radiation pressure effects - increase the input power - Larger thermal effects - Radiation pressure effects - inject squeezed light Reducing the Thermal noise: - Increase the mirror masses - Increase the beam size on the mirrors

This led to have a marginally stable recycling cavity (space constrain) - Monolithic suspensions 22th of May 2019 GWADW19 Maddalena Mantovani 4 Guided lock improved algo ISC The standard Guided lock technique measure the cavity speed as: Corr. fact. Ringing Cal. fact. [*] K. Izumi et al Guided lock of a suspended optical cavity enhanced by a higherorder extrapolation, Appl. Opt. 56 (19) (2017) Thanks to this

technique, the cavity velocity is measured at one peak and it is slowed down at the following peak. An alternative and more efficient algorithm has been implemented for Advanced Virgo 22th of May 2019 GWADW19 Maddalena Mantovani 5 Guided lock improved algo ISC The idea is to measure the raising time between the 10% and the 40% of the maximum power which has a linear dependency with the cavity speed. The main advantages are: No need of calibration and correction factors The impulse can be sent while the cavity is passing trough the resonance 22th of May 2019 GWADW19

Maddalena Mantovani 6 Guided lock improved algo ISC The idea is to measure the raising time between the 10% and the 40% of the maximum power which has a linear dependency with the cavity speed. The main advantages are: No need of calibration and correction factors The impulse can be sent while the cavity is passing trough the resonance To be submitted to Astr. Phy. 22th of May 2019 GWADW19 Maddalena Mantovani 7 Introduction ISC

Several changes have been performed, but most of them had a direct impact on the complexity of the ISC subsystem commissioning Reducing the Quantum noise: - increase the Arm finesse - Dynamical effects in the cavity locking signals - Radiation pressure effects - increase the input power - Larger thermal effects - Radiation pressure effects - inject squeezed light Reducing the Thermal noise: - Increase the mirror masses - Increase the beam size on the mirrors This led to have a marginally stable recycling cavity (space constrain) - Monolithic suspensions 22th of May 2019 GWADW19 Maddalena Mantovani 8 Radiation pressure effects ISC During the trial of running the ITF @ 25W we

experience the radiation pressure effects on the angular direction. Input Power After this the OLTF of the opto-mechanical system (in presence of radiation pressure has been modeled with OCTOPUS [*]) [*] L. Trozzo Low Frequency Optimization and Performance of Advanced Virgo Seismic Isolation System Phd Thesis Dark Fringe Unstable pole Cavity Power P. Ruggi

22th of May 2019 GWADW19 Maddalena Mantovani 9 Introduction ISC Several changes have been performed, but most of them had a direct impact on the complexity of the ISC subsystem commissioning Reducing the Quantum noise: - increase the Arm finesse - Dynamical effects in the cavity locking signals - Radiation pressure effects - increase the input power - Larger thermal effects - Radiation pressure effects - inject squeezed light Reducing the Thermal noise: - Increase the mirror masses - Increase the beam size on the mirrors This led to have a marginally stable recycling cavity (space constrain) - Monolithic suspensions

22th of May 2019 GWADW19 Maddalena Mantovani 10 Marginally Stable cavity ISC The most challenging peculiarity of Advanced Virgo ITF is given by the stability of the recycling cavity. the low Intracavity power This choice is a consequence of the need of increasing the beam size on the input mirrors and space constrains The solution is to use high modulation frequency (lower finesse) to be more robust against aberration, but still a marginally stable cavity is strongly affected by

defects... 22th of May 2019 GWADW19 J. Casanueva 1-g1g2 ~1.9e-5 Maddalena Mantovani 11 Marginally stable cavity vs Thermal aberrations ISC CMRF Dark Fringe <0.12mW Sidebands ~0.008mW CMRF ~1-2-9 @ 1111Hz Good WP Not good CMRF (7e-6) B4 112MHz B1p DC Good CMRF (1e-6) Not stable locking position

(too misaligned) If the TCS (Thermal Compensation System) is not properly compensating the thermal aberrations, the ISC subsystem is strongly affected (especially alignment) having the ITF working point not reliable anymore (offsets on the error signals). Aligned position BS yaw I. Nardecchia d Ba RF M C The BS angular control can not be engaged anymore 22th of May 2019 GWADW19

Maddalena Mantovani 12 Marginally stable cavity vs Thermal aberrations ISC Dark Fringe <0.12mW Sidebands ~0.008mW CMRF ~1-2-9 @ 1111Hz Good WP Optimal CMRF (0.7e-6) B4 112MHz Still good CMRF (1.5e-6) I. Nardecchia d Ba RF M C

Aligned position CD B1p DC CMRF If the TCS (Thermal Compensation System) is not properly compensating the thermal aberration, the ISC subsystem is strongly affected (especially alignment) having the ITF working point not reliable anymore (offsets on the error signals). BS yaw A stable working point can be reached 22th of May 2019 GWADW19 Maddalena Mantovani 13 ISC More ISC features to improve the noise

22th of May 2019 GWADW19 Maddalena Mantovani 14 50Hz Feed-Forward optimized ISC Parameter loops convergence The 50Hz line reduction is done with an evolved technique: The 50Hz line is measured using and electrical probe and it is multiplied for a gain G and de-phased for a phase , and sent to the WI mirror actuators.

Step response Blue : fixed parameters for G and Red : optimal parameters for G and (obtained using a feed-back loop) The 50Hz line reduction can be optimally reduced if the parameters G and are obtained with a feed-back loop P. Ruggi 22th of May 2019 GWADW19 Maddalena Mantovani 15 50Hz Feed-Forward optimized ISC

The 50Hz line reduction is done with an evolved technique: Blue : fixed parameters for G and Red : optimal parameters for G and (obtained using a feed-back loop) The 50Hz line is measured using and electrical probe and it is multiplied for a gain G and de-phased for a phase , and sent to the WI mirror actuators. The 50Hz line reduction can

be optimally reduced if the parameters G and are obtained with a feed-back loop 22th of May 2019 GWADW19 Maddalena Mantovani 16 PRCL->SSFS subtraction ISC The PRCL loop is now subtracted to the SSFS instead of the DARM loop. The PRCL noise is affecting the SSFS signal and then pollutes DARM. The coupling of PRCL to DARM is then

indirect, depends on the CMRF of the ITF, and the coupling varies continuously. Removing PRCL from SSFS is more direct and removes the noise on the correct signal M. Was, M. Mantovani, J. Casanueva, D. Bersanetti, A. Masserot 22th of May 2019 GWADW19 Maddalena Mantovani 17 ISC reliability and sensitivity ISC Longitudinal noise budget Angular noise budget PRCL without substraction 22th of May 2019 GWADW19 Maddalena Mantovani

18 ISC reliability and sensitivity ISC I. Nardecchia 22th of May 2019 GWADW19 Maddalena Mantovani 19 Conclusion & next steps ISC The ISC subsystem is strongly affected by the ITF behavior, especially in case of Marginally Stable recycling cavity, thus strong efforts have been employed to ensure the ITF reliability. The tuning of the ITF working point has to be carried out together with the compensation of the thermal effects. The system turned out to be robust and well behaving 22th of May 2019 GWADW19 Maddalena Mantovani

20 ISC the end 22th of May 2019 GWADW19 21 Introduction ISC Several changes have been performed, but most of them had a direct impact on the complexity of the ISC subsystem commissioning Reducing the Quantum noise: - increase the Arm finesse - Dynamical effects in the cavity locking signals - Radiation pressure effects - increase the input power - Larger thermal effects - Radiation pressure effects - Larger scattered light - Inject squeezed light Reducing the Thermal noise: - Increase the mirror masses - Increase the beam size on the mirrors

This led to have a marginally stable recycling cavity (space constrain) - Monolithic suspensions 22th of May 2019 GWADW19 Maddalena Mantovani 22 ISC DIFF(+) yaw error signal vs Suspended detection bench alignment The DIFFp TY error signal was asymmetric and was not possible to run @ the correct working point (the minimum of B1p DC). The behavior pointed towards scattered light issues on the SDB1 bench. Optimal wp This mis-behavior could be cured by tuning the angular position of the SDB1 bench to minimize the scattering

on the dark fringe path (clipping, etc...) 22th of May 2019 GWADW19 Maddalena Mantovani 23 ISC DIFF(+) yaw error signal vs Suspended detection bench alignment Mantovani, Casanueva, Tacca, Gouaty, Bonnand BEFORE ratio = 0.11 The symmetry of the parabola has been evaluated as a function of the SDB1 alignment and the symmetry and

good behavior have been recovered. 22th of May 2019 GWADW19 AFTER ratio = 1.06 Maddalena Mantovani 24

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