\chapter{Reducing differential motion of aLIGO seismic platforms}
\chapter{Reducing differential motion of aLIGO seismic platforms}
\label{CPSdiff}
During 2019, I spent some months working on LIGO Hanford site (Washington, USA). This experience allowed me to be critically involved in the complicated life of a gravitational-wave interferometer. In particular, I was given the opportunity to study how to improve LIGO performances at low-frequency, focussing on the reduction of seismic motion of the platforms where the optics live.\\
During 2019, I spent some months working on LIGO Hanford site (Washington, USA). This experience allowed me to be critically involved in the complicated life of a gravitational-wave interferometer. In particular, I was given the opportunity to study how to improve LIGO performances at low-frequency, focussing on the reduction of seismic motion of the platforms where the optics live.\\
In this chapter and I am going to demonstrate in detail how we can modify the software set up of LIGO in order to obtain a different and possibly better performance. This work has been developed in collaboration with LIGO Hanford and LIGO Livingston laboratories, Stanford University, MIT and UoB.\\
In this chapter I will demonstrate how we can modify the software set up of LIGO in order to obtain different and possibly better performances for seismic motion stabilization, faster and longer locking mode and, ultimately, gravitational waves detections. The detailed computations included in this chapter are original and partially presented to the LIGO community and stored in LIGO DCC.\\
This work has been developed in collaboration with LIGO Hanford and LIGO Livingston laboratories, Stanford University, MIT and UoB and completed at UoB during 2020.\\
This chapter is partially including some technical notes I shared with LIGO collaboration and the contents of this study have been presented at conferences and workshops.\\
This chapter is partially including some technical notes I shared with LIGO collaboration and the contents of this study have been presented at conferences and workshops.\\
Essential information about the sections of LIGO involved in this study has been exposed in detail in Chapter \ref{LIGO}.
Essential information about the sections of LIGO involved in this study has been exposed in detail in Chapter \ref{LIGO}.
...
@@ -68,7 +70,7 @@ The idea which should stabilize ISIs to follow the ground motion is to lock the
...
@@ -68,7 +70,7 @@ The idea which should stabilize ISIs to follow the ground motion is to lock the
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.\\
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!]
\begin{figure}[h!]
\centering
\centering
\includegraphics[scale=1]{images/IMC.png}
\includegraphics[scale=0.8]{images/IMC.png}
\caption[Optical layout of the HAM2 and HAM3 chambers]{Optical layout of the HAM2 and HAM3 chambers.}
\caption[Optical layout of the HAM2 and HAM3 chambers]{Optical layout of the HAM2 and HAM3 chambers.}
\label{imc}
\label{imc}
\end{figure}\\
\end{figure}\\
...
@@ -78,7 +80,6 @@ In the next section we will demonstrate that CPS are good witnesses to sense dif
...
@@ -78,7 +80,6 @@ In the next section we will demonstrate that CPS are good witnesses to sense dif
\section{Sensing differential motion via CPS}
\section{Sensing differential motion via CPS}
Capacitive Position Sensors (CPS) measure the relative motion between two stages of the isolation system. On HAM chambers, they are are set between HEPI and ground, and between Stage 1 and HEPI. On BSC chambers, they also measure the relative motion between Stage 1 and Stage 2. Plots is Fig. \ref{diff} show the differential motion seen by the CPS between BSC and HAM chambers: the sensors are reliable for this measurement, and they put in evidence that the HAM chambers have a more synchronized motion with respect to the motion between HAM and BSC and BSCs only. This means that the block of HAM chambers on x arm is more relatively stable and can be used as driver for the other chambers, with the mode cleaner acting as witness.\\
Capacitive Position Sensors (CPS) measure the relative motion between two stages of the isolation system. On HAM chambers, they are are set between HEPI and ground, and between Stage 1 and HEPI. On BSC chambers, they also measure the relative motion between Stage 1 and Stage 2. Plots is Fig. \ref{diff} show the differential motion seen by the CPS between BSC and HAM chambers: the sensors are reliable for this measurement, and they put in evidence that the HAM chambers have a more synchronized motion with respect to the motion between HAM and BSC and BSCs only. This means that the block of HAM chambers on x arm is more relatively stable and can be used as driver for the other chambers, with the mode cleaner acting as witness.\\
Typically, the amplitude of a gravitational wave is of the order of $h \sim10^{-21}$$1/\sqrt{Hz}$, very small: masses able to deform the fabric of the spacetime and generate gravitational waves are of the order of more than the solar mass $M_{\odot}$, so they need to be looked for in the Universe.
Typically, the amplitude of a gravitational wave is of the order of $h \sim10^{-21}$$1/\sqrt{Hz}$, very small: masses able to deform the fabric of the spacetime and generate gravitational waves are of the order of more than the solar mass $M_{\odot}$, so they need to be looked for in the Universe.
%servono masse molto grandi, quindi vanno cercate nell'Universo: possibili candidati
%servono masse molto grandi, quindi vanno cercate nell'Universo: possibili candidati
\subsection{Sources of gravitational waves}
Fig. \ref{spec} summarizes the possible objects that can be gravitational waves sources, their frequency emission and what kind of instrument can detect them. The terrestrial interferometric detectors are the most involved at present times, but the efforts of the scientific community are going towards the development of new detectors both ground- and space-based in order to widen the frequency window of observation.
\begin{figure}[h!]
\centering
\includegraphics[scale=1.6]{images/spectrum}
\caption[Sources of gravitational waves]{Spectrum of emission of sources of gravitational waves (adapted from https://lisa.nasa.gov).}
\label{spec}
\end{figure}
\noindent
The best modelled sources are binary systems, typically Neutron Stars (NS), White Dwarfs and Black Holes (BH), orbiting each other. Fig. \ref{binary} shows the main phases of the evolution of the systems, emitting gravitational waves at different frequencies, depending on the phase.
\begin{figure}[h!]
\centering
\includegraphics[scale=1]{images/bin.png}
\caption[Phases of gravitational waves emission by a binary system]{The three phases of a BH-BH binary system emitting gravitational waves (amplitude vs time) \cite{first}. \textbf{Inspiral phase}: the orbits shrink, velocity increases and frequency of the waves emitted increases as $f_{gw}=2f_{orbital}$. \textbf{Merging phase}: the objects merge and the signal is maximum. \textbf{Ring-down phase}: a new BH is formed and the signal emitted decreases in frequency as a damped sinusoid.}
\label{binary}
\end{figure}
\noindent
Gravitational waves from binary systems can provide several information about the equation of state of Neutron stars, masses and spin of Black holes, test of General Relativity theory.\\
Currently, the ground-based observatories are tuned to detect binary systems sources: interferometers are the instruments that have been able to detect gravitational waves from binary systems.\\
\noindent
The first detection of gravitational waves happened on the 14th September 2015 and confirmed the Theory General Relativity, opening a new window on the Universe: the signal from a merger of two black holes have been observed thanks to the emission of gravitational waves, confirming the existence of these objects, still mostly unknown \cite{first}. The detector responsible of the new discovery is based in the USA and it is one of the terrestrial interferometers currently in use for gravitational waves detection.
The scientific research exposed in this thesis focusses on the improvement of ground-based gravitational-wave detectors at low frequency. This chapter intends to frame the work done in this context and highlight why the lower frequency window is so important. The discussion around this topic is relatively recent and it has been widely discussed during dedicated workshops which the author of this thesis attended since 2018.
\subsection{Sources of gravitational waves}
Fig. \ref{spec} summarizes the possible objects that can be gravitational waves sources, their frequency emission and what kind of instrument can detect them. The terrestrial interferometric detectors are the most involved at present times, but the efforts of the scientific community are going towards the development of new detectors both ground- and space-based in order to widen the frequency window of observation.
\begin{figure}[h!]
\centering
\includegraphics[scale=1.6]{images/spectrum}
\caption[Sources of gravitational waves]{Spectrum of emission of sources of gravitational waves (adapted from https://lisa.nasa.gov).}
\label{spec}
\end{figure}
\noindent
The best modelled sources are binary systems, typically Neutron Stars (NS), White Dwarfs and Black Holes (BH), orbiting each other. Fig. \ref{binary} shows the main phases of the evolution of the systems, emitting gravitational waves at different frequencies, depending on the phase.
\begin{figure}[h!]
\centering
\includegraphics[scale=1]{images/bin.png}
\caption[Phases of gravitational waves emission by a binary system]{The three phases of a BH-BH binary system emitting gravitational waves (amplitude vs time) \cite{first}. \textbf{Inspiral phase}: the orbits shrink, velocity increases and frequency of the waves emitted increases as $f_{gw}=2f_{orbital}$. \textbf{Merging phase}: the objects merge and the signal is maximum. \textbf{Ring-down phase}: a new BH is formed and the signal emitted decreases in frequency as a damped sinusoid.}
\label{binary}
\end{figure}
\noindent
Gravitational waves from binary systems can provide several information about the equation of state of Neutron stars, masses and spin of Black holes, test of General Relativity theory.\\
Currently, the ground-based observatories are tuned to detect binary systems sources: interferometers are the instruments that have been able to detect gravitational waves from binary systems.\\
\noindent
The first detection of gravitational waves happened on the 14th September 2015 and confirmed the Theory General Relativity, opening a new window on the Universe: the signal from a merger of two black holes have been observed thanks to the emission of gravitational waves, confirming the existence of these objects, still mostly unknown \cite{first}. The detector responsible of the new discovery is based in the USA and it is one of the terrestrial interferometers currently in use for gravitational waves detection.
Most of the work exposed in this thesis has been physically done in laboratories and on LIGO sites. In this chapter I will briefly introduce interferometers and LIGO, and I will explain in details only the structures of LIGO that have been subject of study: this is essential to fully embrace the work exposed in Chapter \ref{CPSdiff} in particular, and in general for the devices described in the whole thesis, and I will often refer to the information contained in this chapter throughout the thesis.
\section{Interferometric detectors}
\section{Interferometric detectors}
%COSA SONO GLI INTERFEROMETRI\\
%INTERAZIONE COL DETECTOR E LAVORO A POTENZA ZERO (DARK FRINGE)\\
The interaction of gravitation waves with two objects moving along the x axis produces effects on their distance $d = x_2- x_1$:
The interaction of gravitation waves with two objects moving along the x axis produces effects on their distance $d = x_2- x_1$:
Here I will certify that the work done is original from myself.
\chapter{Abstract}
\chapter{Abstract}
...
@@ -36,7 +37,7 @@ A brief summary of the project goes here, with main results.
...
@@ -36,7 +37,7 @@ A brief summary of the project goes here, with main results.
\chapter{Acknowledgements}
\chapter{Acknowledgements}
Here I need to acknowledge for any funding (UoB, RAS, Caltech).
Here I need to acknowledge for any funding (UoB, RAS, IOP, Caltech).
\tableofcontents
\tableofcontents
...
@@ -72,6 +73,7 @@ CPS = Capacitive Position Sensors\\
...
@@ -72,6 +73,7 @@ CPS = Capacitive Position Sensors\\
CS = Corner Station\\
CS = Corner Station\\
DAC = Digital-to-Analogue Converter\\
DAC = Digital-to-Analogue Converter\\
DARM = Differential Arm Length\\
DARM = Differential Arm Length\\
DCC = Document Control Center\\
DIFF2SE = Differential to Single-Ended\\
DIFF2SE = Differential to Single-Ended\\
ETM = End Test Mass\\
ETM = End Test Mass\\
ET = Einstein Telescope\\
ET = Einstein Telescope\\
...
@@ -146,7 +148,6 @@ Appendix C: first GW detection
...
@@ -146,7 +148,6 @@ Appendix C: first GW detection
\include{A}
\include{A}
\include{B}
\include{B}
\include{C}
\include{C}
%\appendix C on my work in LIGO labs
\backmatter
\backmatter
...
@@ -160,9 +161,11 @@ Appendix C: first GW detection
...
@@ -160,9 +161,11 @@ Appendix C: first GW detection
\bibitem{mag} M. Maggiore \textit{Gravitational waves - Vol. 1: Theory and Experiments}, Oxford University Press, 2013
\bibitem{mag} M. Maggiore \textit{Gravitational waves - Vol. 1: Theory and Experiments}, Oxford University Press, 2013
%chapt 2
\bibitem{first} B. P. Abbott, \textit{Observation of Gravitational Waves from a Binary Black Hole Merger}, Phys. Rev. Lett. 116, 061102, 2016
\bibitem{first} B. P. Abbott, \textit{Observation of Gravitational Waves from a Binary Black Hole Merger}, Phys. Rev. Lett. 116, 061102, 2016
%chapt3
%chapt3
\bibitem{ligo} Advanced LIGO Systems Group, \textit{Advanced LIGO Systems Design}, DCC document T010075-v3, 2017
\bibitem{ligo} Advanced LIGO Systems Group, \textit{Advanced LIGO Systems Design}, DCC document T010075-v3, 2017
...
@@ -177,33 +180,33 @@ Beginning of Gravitational Wave Astronomy}
...
@@ -177,33 +180,33 @@ Beginning of Gravitational Wave Astronomy}
%oplev
%oplev
\bibitem{phd} D. Tuyenbayev, \textit{Extending the scientific reach of Advanced LIGO by compensating for temporal variations in the calibration of the detector.}, PhD thesis, University of Texas, 2017
\bibitem{mca} C. Di Fronzo \textit{Optical sensors for improving low-frequency performance in GW detectors}, Mid-Course Assessment, University of Birmingham, 2018
\bibitem{intro} B. Lantz et al., \textit{Estimates of HAM-ISI motion for A+}, T1800066-v2, March 2018, https://dcc.ligo.org/LIGO-T1800066
\bibitem{poster2} C. Di Fronzo et al., \textit{Optical Lever for interferometric inertial isolation}, poster, LVC meeting, Maastricht 2018, https://dcc.ligo.org/LIGO-G1801693
\bibitem{intro2} S. Cooper et al., \textit{Ham ISI model}, Technical note, University of Birmingham, March 2018, https://dcc.ligo.org/LIGO-T1800092
\bibitem{lantz} B. Lantz et al., \textit{Estimates of HAM-ISI motion for A+}, T1800066-v2, March 2018, https://dcc.ligo.org/LIGO-T1800066
\bibitem{ven} Venkateswara et al., \textit{Subtracting tilt from a horizontal-seismometer using a ground-rotation-sensor}, Bulletin of the Seismological Society of America (2017) 107 (2): 709-717
\bibitem{cooper} S. Cooper et al., \textit{Ham ISI model}, Technical note, University of Birmingham, March 2018, https://dcc.ligo.org/LIGO-T1800092
\bibitem{mca} C. Di Fronzo \textit{Optical sensors for improving low-frequency performance in GW detectors}, Mid-Course Assessment, University of Birmingham, 2018
\bibitem{sina} S. M. Köhlenbeck, \textit{Towards the SQL Interferometer Length Stabilization at the AEI 10 m-Prototype}, PhD thesis, Gottfried Wilhelm Leibniz Universität Hannover, 2018
\bibitem{poster2} C. Di Fronzo et al., \textit{Optical Lever for interferometric inertial isolation}, poster, LVC meeting, Maastricht 2018, https://dcc.ligo.org/LIGO-G1801693
\bibitem{tuyen} D. Tuyenbayev, \textit{Extending the scientific reach of Advanced LIGO by compensating for temporal variations in the calibration of the detector.}, PhD thesis, University of Texas, 2017
\bibitem{sina} S. M. Köhlenbeck, \textit{Towards the SQL Interferometer Length Stabilization at the AEI 10 m-Prototype}, PhD thesis, Gottfried Wilhelm Leibniz Universität Hannover, 2018
\bibitem{venka} Venkateswara et al., \textit{Subtracting tilt from a horizontal-seismometer using a ground-rotation-sensor}, Bulletin of the Seismological Society of America (2017) 107 (2): 709-717
\bibitem{J} R.V. Jones et al., \textit{Some developments and applications of optical levers}, 1961 J. Sci. Instrum. 38 37
\bibitem{jones} R.V. Jones et al., \textit{Some developments and applications of optical levers}, 1961 J. Sci. Instrum. 38 37
\bibitem{kaz} K. Agatsuma, \textit{Optical lever for KAGRA}, GW monthly seminar at Tokyo, 2014
\bibitem{agatzuma} K. Agatsuma, \textit{Optical lever for KAGRA}, GW monthly seminar at Tokyo, 2014
\bibitem{lan} B. Lantz et al. \textit{Review: Requirements for a Ground Rotation Sensor to Improve Advanced LIGO}, Bulletin of the Seismological Society of America, Vol. 99, No. 2B, 2009
\bibitem{lantz2} B. Lantz et al. \textit{Review: Requirements for a Ground Rotation Sensor to Improve Advanced LIGO}, Bulletin of the Seismological Society of America, Vol. 99, No. 2B, 2009
\bibitem{coll} C. Collette et al. \textit{Review: Inertial Sensors for Low-Frequency Seismic Vibration Measurement}, Bulletin of the Seismological Society of America, Vol. 102, No. 4, 2012
\bibitem{collette} C. Collette et al. \textit{Review: Inertial Sensors for Low-Frequency Seismic Vibration Measurement}, Bulletin of the Seismological Society of America, Vol. 102, No. 4, 2012
\bibitem{dan} D. E. Clark, \textit{Control of Differential Motion Between Adjacent Avanced LIGO Seismic Isolation Platforms}, PhD thesis, Stanford University, 2013
\bibitem{clark} D. E. Clark, \textit{Control of Differential Motion Between Adjacent Avanced LIGO Seismic Isolation Platforms}, PhD thesis, Stanford University, 2013
\bibitem{ast} S. M. Aston at al., \textit{Update on quadruple suspension design for Advanced LIGO}, Class. Quantum Grav., 29 (2012) 235004 (25pp)
\bibitem{aston} S. M. Aston at al., \textit{Update on quadruple suspension design for Advanced LIGO}, Class. Quantum Grav., 29 (2012) 235004 (25pp)
\bibitem{image} B. Shapiro, \textit{Brief Introduction to Advanced LIGO Suspensions}, LAAC Talk, August 2014, https://dcc.ligo.org/LIGO-G1400964
\bibitem{shapiro} B. Shapiro, \textit{Brief Introduction to Advanced LIGO Suspensions}, LAAC Talk, August 2014, https://dcc.ligo.org/LIGO-G1400964
%cpsdiff
%cpsdiff
...
@@ -225,10 +228,8 @@ Beginning of Gravitational Wave Astronomy}
...
@@ -225,10 +228,8 @@ Beginning of Gravitational Wave Astronomy}
\chapter{Optical Levers for tilt motion reduction}
\chapter{Optical Levers for tilt motion reduction}
\label{oplevs}
\label{oplevs}
In this chapter I will introduce the sensors dedicated to measure the seismic motion. They need to account for horizontal, vertical and tilt displacements in all degrees of freedom in order to be efficient and the technology for their improvement is currently pushing and competing on sensing as low as possible seismic motion. On an interferometric detector, seismic motion affects the stabilization of the supports where the optics lie. This produces unwanted noise at low frequencies (< 30 Hz), which reduces the sensitivity of the detector.\\
The sensors dedicated to measure the seismic motion need to account for horizontal, vertical and tilt displacements in all degrees of freedom in order to be efficient: the technology for their improvement is currently pushing and competing on sensing as low seismic motion as possible. On an interferometric detector, seismic motion affects the stabilization of the supports where the optics lie. This produces unwanted noise at low frequencies (< 30 Hz), which reduces the sensitivity of the detector.\\
During the first year of my PhD studies, I investigated the use of optical levers to reduce tilt motion: a device has been built at UoB, and tested at the Albert Einstein Institute (AEI) in Hannover in June 2019.\\
During the first year of my PhD studies, I investigated the use of optical levers to reduce tilt motion: a device has been built at UoB, and tested at the Albert Einstein Institute (AEI) in Hannover in June 2019.\\
The content of this chapter has been re-adapted from my MCA report \cite{mca}. A poster about this project has been presented at the LVK meeting in Maastricht (September 2018) \cite{poster}.
The content of this chapter has been re-adapted from my MCA report \cite{mca}. A poster about this project has been presented at the LVK meeting in Maastricht (September 2018) \cite{poster2}.
\section{Inertial sensors affected by tilt-coupling}
\section{Inertial sensors affected by tilt-coupling}
There are many contributions affecting aLIGO sensitivity at low frequency. One of the most investigated is the tilt of HAM vacuum chamber of ISI benches, which dominates above 1 Hz \cite{intro}.\\
There are many contributions affecting aLIGO sensitivity at low frequency. One of the most investigated is the tilt of HAM vacuum chamber of ISI benches, which dominates above 1 Hz \cite{lantz}.\\
For the rotational degrees of freedom, getting a good estimate of ground motion is not trivial because no rotational sensors capable of measuring the ground motion in rotation at low frequencies have been installed yet on aLIGO \cite{intro2}.\\
For the rotational degrees of freedom, getting a good estimate of ground motion is not trivial because no rotational sensors capable of measuring the ground motion in rotation at low frequencies have been installed yet on aLIGO \cite{cooper}.\\
However, there could be a possible way to measure angular displacements of the benches very precisely (10$^{-12}$ rad/$\sqrt{Hz}$) and to actively control them. This could be done by optical levers.
However, there could be a possible way to measure angular displacements of the benches very precisely (10$^{-12}$ rad/$\sqrt{Hz}$) and to actively control them. This could be done by optical levers.
\begin{figure}[h!]
\begin{figure}[h!]
\centering
\centering
\includegraphics[scale=0.8]{images/HAMoplev.PNG}
\includegraphics[scale=0.8]{images/HAMoplev.PNG}
\caption[Example of tilt-coupling contributions at LHO]{Plot of the contributions to the Suspension point L motion at LHO HAM5. The pitch (RX) contribution dominates above 1\,Hz (Figure taken from \cite{intro}).}
\caption[Example of tilt-coupling contributions at LHO]{Plot of the contributions to the Suspension point L motion at LHO HAM5. The pitch (RX) contribution dominates above 1\,Hz (Figure taken from \cite{lantz}).}
\end{figure}
\end{figure}
\newpage
\newpage
\paragraph*{Horizontal sensors}
\paragraph*{Horizontal sensors}
...
@@ -513,7 +513,7 @@ Also, the alignment of the optical fibre has been checked during the process.\\
...
@@ -513,7 +513,7 @@ Also, the alignment of the optical fibre has been checked during the process.\\
%\subsection{Temperature trend}
%\subsection{Temperature trend}
\subsection{30mbar test}
\subsection{30mbar test}
Fig. \ref{LVDT} shows the movement of South bench along z axis, that we use as a reference measurement for bench adjustments with temperature variations.
Fig. \ref{LVDT} shows the movement of South bench along z axis, that we use as a reference measurement for bench adjustments with temperature variations. The variable under examination is displacement tested by a Linear Variable Displacement Transformer (LVDT).
