@@ -66,14 +66,14 @@ Differential motion affects the ISI of the HAM and BSC chambers in the CS: these
In particular, CPS sensors are placed in every chambers at all stages: it is easy to compare motion between HAM and BSC chambers through the signal of a device sensing the same motion on every chamber.\\
The idea which should stabilize ISIs to follow the ground motion is to lock the chambers to each other, in order to make them move on a synchronized way, following a common motion given by a driver chamber (or block of chambers).
\subsection{Role of the mode cleaner}
\paragraph*{Role of the mode cleaner}
We started our design on chambers of x arm. Along this direction, the Input Mode Cleaner (IMC) lies totally on HAM2 and HAM3 platforms: it can be used as a reference, or witness, of the motion between chambers, once they are locked together.\\
\begin{figure}[h!]
\centering
\includegraphics[scale=0.8]{images/IMC.png}
\caption[Optical layout of the HAM2 and HAM3 chambers]{Optical layout of the HAM2 and HAM3 chambers.}
\label{imc}
\end{figure}\\
%\begin{figure}[h!]
%\centering
%\includegraphics[scale=0.8]{images/IMC.png}
%\caption[Optical layout of the HAM2 and HAM3 chambers]{Optical layout of the HAM2 and HAM3 chambers.}
%\label{imc}
%\end{figure}\\
\noindent
In the next section we will demonstrate that CPS are good witnesses to sense differential motion and they also can be used to lock the chambers with each other.
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@@ -391,7 +391,7 @@ Plot in Fig. \ref{diffham} shows the differential motion of HAM2 and HAM3 in iso
\begin{figure}[h!]
\centering
\includegraphics[scale=0.5]{images/cpsdiff.png}
\caption[HAM chambers in CPS locking condition]{HAM chambers in CPS locking condition: the plot shows the motion of each chamber, where HAM3 depends on HAM2, through CPS locking, and the differential motion between them. There is an improvement of the differential motion in the new configuration (purple trace) with respect to the situation in isolation (green dotted trace) below 0.1 Hz (highlighted by the grey area), but above this frequency it looks not convenient.}
\caption[HAM chambers in CPS locking condition]{HAM chambers in CPS locking condition: the plot shows the motion of each chamber, where HAM3 depends on HAM2, through CPS locking, and the differential motion between them. There is an improvement of the differential motion in the new configuration (purple trace) with respect to the situation in isolation (green dotted trace) by a factor of 3 in order of magnitude below 0.1 Hz.}
\label{cpsdiff}
\end{figure}
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@@ -525,6 +525,8 @@ After every simulation which could possibly work for the system, we locked the i
\end{figure}
\section*{Conclusions}
This study is promising to give an impactful contribution to the improvement of the LSC signals of LIGO and its stabilization when in observing mode. As we saw, the implications go straight to the basics of the instrument: a more stable detector produces a less noisy signal which can last longer into the cavities, assuring a longer observing time and giving the possibility to observe more gravitational waves, in lower ranges of frequency.\\
LIGO Livingston site has also actuated a similar process, following the progression at LHO during 2019 collaboration. Due to the stretched time, it was not possible to take further measurements of ISI motion and LSC signals, especially with an accurate study of the blending filters, but since the software skeleton of the new configuration has been built and installed on both LIGO CDSs, further studies and tests were due in 2020 to complete the last steps and test it fully on the interferometer. However the pandemic and the correlated travel restrictions have moved forward in the future the schedule for these tests.
This study is promising to provide a significant contribution to the improvement of LIGO LSC signals and the detector stability when it is running in observing mode. The tests at LHO demonstrated that the experiment succeeded in lowering the seismic motion of the platforms by a factor of 3 at low frequencies and that also the DARM signal benefited from it. The simulations have shown that it is possible to reduce the differential motion of the chambers by a factor of 3 in order of magnitude. The test on the Power Recycling Cavity Length highlighted that the signal can be controlled by the ISI according with the software simulations.\\
As we saw, the implications go straight to the basics of the instrument: a more stable detector produces a less noisy signal which can last longer into the cavities, assuring a longer observing time and giving the possibility to detect more gravitational waves and in lower ranges of frequency.
LIGO Livingston site has also actuated a similar process, following the progression at LHO during the work on site in 2019. Due to the limited time of the commissioning break, it was not possible to take further measurements of ISI motion and LSC signals, especially with an accurate study of the blending filters. However, since the software skeleton of the new configuration has been built and installed on both LIGO CDSs, further studies and tests were due in 2020 to complete the last steps and test it fully on the interferometer. The results make the experiment worthy of future developments and we are confident that these tests could be carried out in the coming months.
@@ -84,6 +84,7 @@ HAM = Horizontal Access Module\\
HEPI = Hydraulic External Pre-Isolator\\
HoQI = Homodyne Quadrature Interferometer\\
HP = High Pass filter\\
HSTS = \\
IMC = Input Mode Cleaner\\
IMCL = Input Mode Cleaner Length\\
ISI = Internal Seismic Isolation\\
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@@ -213,13 +214,31 @@ Beginning of Gravitational Wave Astronomy}
%cpsdiff
%SAM HAM MODEL TECHNOTE
%cita tutte le technote tue
%parte intro
%tesi kissel?
%tesi Jenne
%talk di Brian
%lavori di LLO
\bibitem{biscans} S. Biscans et al., \textit{Control strategy to limit duty cycle impact of earthquakes on the LIGO gravitational-wave detectors}, arXiv:1707.03466, 2017
\bibitem{lantztalk} B. Lantz, \textit{System-wide upgrades to improve the Seismic Isolation and control of detectors beyond A+}, talk, 2020
\bibitem{kisseltalk} J. Kissel, \textit{Advanced LIGO Active Seismic Isolation}, talk, 2011
\bibitem{lantztech} B. Lantz et al., \textit{Estimates of HAM-ISI motion for A+}, technical note, 2018, DCC T1800066-v2
\bibitem{hammodel} S. Cooper et al., \textit{Ham ISI Model}, technical note, 2018
\bibitem{kisselthesis} J. Kissel, \textit{Calibrating and improving the sensitivity of the LIGO detectors}, PhD thesis, 2010
\bibitem{proposal} C. Di Fronzo et al., \textit{Proposal for an experiment at LHO: Locking PRCL to IMCL}, proposal, 2019, DCC T1900656-v2
\bibitem{technote1} C. Di Fronzo et al., \textit{Reducing differential motion using CPS sensors}, technical note, 2019, DCC T1900777-v1
\bibitem{technote2} C. Di Fronzo et al., \textit{Reducing differential motion of Advanced LIGO seismic platforms to improve interferometer control signals: block diagrams and maths}, technical note, 2020, DCC T2000108-v1
\bibitem{technote3} C. Di Fronzo et al., \textit{Reducing differential motion of Advanced LIGO seismic platforms to improve interferometer control signals:analysis of feasibility}, technical note, 2020, DCC T2000365-v2
\bibitem{chiatalk} C. Di Fronzo, \textit{Reducing differential motion of Advanced LIGO seismic platforms to improve interferometer control signals}, talk, LVK September 2020
\bibitem{llo} A. Pele' et al., \textit{ECR: Differential CPS and cavity offload}, proposal, 2019, DCC E1900330-v1
\bibitem{jenne} J. Driggers, \textit{Noise Cancellation for Gravitational Wave Detectors}, PhD thesis, 2016
