Breaking the seismic wall: How to improve gravitational waves at low frequency
Lead Research Organisation:
University of Birmingham
Department Name: School of Physics and Astronomy
Abstract
With the first direct detection of gravitational waves and the first detection of merging neutron stars, a new era of multi-messenger astronomy has begun. While the overall sensitivity of the LIGO detectors has led to incredible advances, current detectors are plagued by technical noises at frequencies lower than 30Hz. These are caused in part by the limitations of current control loops and sensors in the detector, these must be eliminated to detect gravitational waves below 30Hz. These are caused in part by the residual motion of the isolation platforms (ISIs) and suspensions. This is a fundamentally difficult problem to overcome; seismic motion is around 9 orders of magnitude larger than a typical gravitational wave signal.
I have designed and built compact interferometers that can be used either as standalone displacement sensors or integrated with commercial seismometers to increase their resolution. On the simulation side, I have developed computer models to investigate the current limitations of the isolation platforms and how to improve the performance of them, as well as test the linearity of future sensors and their expected impact on the isolation systems currently in use.
I have designed and built compact interferometers that can be used either as standalone displacement sensors or integrated with commercial seismometers to increase their resolution. On the simulation side, I have developed computer models to investigate the current limitations of the isolation platforms and how to improve the performance of them, as well as test the linearity of future sensors and their expected impact on the isolation systems currently in use.
Organisations
People |
ORCID iD |
| Conor Mow-Lowry (Primary Supervisor) | |
| Samuel Cooper (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| ST/N503939/1 | 01/10/2015 | 30/03/2021 | |||
| 2142081 | Studentship | ST/N503939/1 | 01/10/2015 | 31/03/2019 | Samuel Cooper |
| Title | Gravitational waves at the Birmingham Thinktank Museum |
| Description | The project mentioned above is a long-standing exhibit (3.5 years currently), describing the process of detecting gravitational waves. At its heart is a 'Mini-LIGO' Michelson interferometer that shows the process of how gravitational waves are detected here on earth. The exhibit features a series of videos explaining topics from what causes gravitational waves out in space to how we detect them on the earth. These videos are no longer than 90 seconds in length and are accompanied by a slides of text and images for further explanation of this topic. Custom 'gravitational wave' signals can be sent into piezo-electric-transducers mounted on the back of one of the two mirrors of the interferometer allowing for the audience to see how the detector would react to a passing gravitational wave. |
| Type Of Art | Artistic/Creative Exhibition |
| Year Produced | 2016 |
| Impact | The exhibit was part of the Royal Society Summer Science Exhibition in 2017 where over 10,000 people attended the science festival. It has also been demonstrated at the Cheltenham science festival, Malvern Science Festival, Gravity fields, as well as numerous school visits. The exhibit is based in the Thinktank Science Museum which has 250,000 visitors a year. The exhibit has allowed countless people to understand what a gravitational wave is and how we detect them. |
| Description | IoP Branch award: Gravitational Waves and Virtual Reality |
| Amount | £700 (GBP) |
| Organisation | Institute of Physics (IOP) |
| Sector | Learned Society |
| Country | United Kingdom |
| Start | |
| Title | Development of a research tool allowing the design of digital control filters via particle swarm optimisation for use in Gravitational Wave Detectors |
| Description | Control fitlers are multi-dimensional problems (in the case of a 'simple' filter, this turned out to be 15), because of the high order dimensionality problem these become hard for people to design optimal filters for control of seismic isolation platforms. The new technique (paper in preparation) allows the work to be transferred from designing a highly complex digital filter to designing a single cost function that can be based on physical requirements. The particle swarm optimization process then optimizes the control filter to produce the lowest possible cost, and therefore the best performing filter. This is advantageous, as the seismic and local environmental noise (such as wind and earthquakes) is non-stationary and is time-varying (e.g. gusts of wind). Before this technique, new filters that are more suited to different ground and wind conditions would have had to be created by hand, a process that takes between 10-100 hours to do, with the new optimization method, new data can be obtained and a new filter designed within minutes. With this new method, not only do the filters perform better, resulting in, at worst, a 10% reduction in the ground injection to the platforms (more reduction is better), but in some cases this results in a factor 2-3 less motion being injected into the platform. Since low-frequency motion due to the wind has been recently linked to a decrease in the observatories binary neutron star range, this means that by better optimising the platforms, of which the detector is based, then some of this lost range could be recovered, by using the technique to design a new filter, which takes approximately 5 minutes to run on a workstation. These filters have been tried out at the detector sites to some success and should be run in the future. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| Impact | The notable impact of this tool is that new control filters that have been designed using this tool are being trialed at gravitational wave detector sites improving the isolation performance. Now that this technique has been tested and verified, the complexity of the optimization process can be increased, suspension filters or isolation filters can be tweaked using this technique. Something that would have been increasingly hard due to the cross-coupling and highly multi-dimensionality of the optimization problem. |
| Title | A frequency domain model for an Advanced Laser Interferometer Gravitational Wave Observatory Horizontal Access Module Seismic Isolation Platform |
| Description | The model is a frequency domain noise budget and performance analysis model for the seismic (ground) isolation platforms currently in use at the LIGO observatories in the United States of America. The model allows the prediction of the on-table isolation performance to be estimated using out of loop sensors. This is important as it allows for each of the noise coupling paths to be investigated individually, this allows for the dominant cause of the motion experienced by the chamber to be found and reduced, improving the performance of the seismic isolation table and the detectors as a whole. Due to the model's modular nature, it can also be used to estimate the improvement that new sensors, such as the ones that I'm currently developing would have on the isolation platforms. Moreover, control filters can be changed allowing for new configurations to be tested for future detectors. |
| Type Of Material | Computer model/algorithm |
| Year Produced | 2018 |
| Provided To Others? | No |
| Impact | The model is available on request and is used within the (LIGO) gravitational wave community to test new sensors and control schemes for isolation platforms in use at the observatories. This has resulted in some key developments in the area, 1) An understanding of what the limiting noise terms are in terms of seismic isolation in different degrees of freedom. 2) Methods of reduction of the source of one of the contributors to technical noise in the gravitational wave detector. 3) Evaluation of new sensors and control strategies of improving seismic isolation at current observatories. 4) Allows the testing of new control filters before applying them to the detector site, allowing their performance and limitations to be analyzed in more depth before deploying them to an active observatory. 5) Allows for the work on improving the seismic isolation platforms to be focussed down to the critical parts directing future research to where it is most needed. |
| Title | Chirp Gravitational Wave Alerts |
| Description | Chirp is a web-app that listens to the GCN system and displays the information in a friendly format, with links to LIGO-Virgo Gravitational Wave Candidate Event Database (GraceDB) pages for more detailed information.The mobile apps, available for Android and iOS allow people to be notified in near-real time of new gravitational wave alerts as the detectors see them. |
| Type Of Technology | Webtool/Application |
| Year Produced | 2019 |
| Impact | Chirp has between 800-1400 daily users and approximately 3000 monthly users, the websites and apps receive between 4000-13000 page views per day. This has changed how people in the collaboration share information about the latest gravitational wave alerts. |
| URL | http://chirp.sr.bham.ac.uk/ |
| Description | Chirp Gravitational Wave Alerts |
| Form Of Engagement Activity | Engagement focused website, blog or social media channel |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Public/other audiences |
| Results and Impact | Chirp is a web, iOS and Android app that allows users to ger near-real-time alerts of Gravitational Wave candidates to their phones or computers. Information such as the area in the sky, distances, most likely causes is explained in a clear and understanding way. Chirp offers near-real-time access to alerts for gravitational wave detection candidates. The app is aimed at members of the public, hence we collate the data that is distributed to the astronomical community and present it in a public-friendly way. The most likely origins of the signals, usually, but not limited to, black holes and/or neutron stars, are clearly and concisely displayed together with other important event information: its distance from the earth and position in the sky (as a probability map), the probability of being a false alarm and the list of triggered observatories. This app is heavily promoted by the LIGO Scientific Community. The result of this development is an app that has approximately 800-1300 unique active users, and between 4000-12000 page views per day. This includes members of the public, as well as other scientists. At the time of writing the app has been downloaded 8800 times since its launch in November 2019. |
| Year(s) Of Engagement Activity | 2019,2020 |
| URL | http://chirp.sr.bham.ac.uk/ |
| Description | Gravitational Waves at the Thinktank Science Museum |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Public/other audiences |
| Results and Impact | I was part of a team of people that developed a long-standing museum exhibit teaching members of the general public about everything from sources of gravitational waves to how we detect them on earth. This exhibit has been running in the Birmingham Thinktank Science Museum for almost 4 years, which receives around 250,000 people a year. The core of the exhibit, the main Michelson 'mini-LIGO' interferometer was replicated and taken to many science festivals, such as the Royal Society Summer Science exhibition, which had an audience in excess of 10,000 people over a week. The exhibit was taken to other science festivals, such as the Cheltenham science festival, Gravity fields amongst others, in which 3000+ people attended. In all of these, demonstrators, including myself, were present to answer any questions participants had about the exhibit, in the majority of cases people reported a substantial increase in interest both in Physics and gravitational waves. A paper is in preparation describing the exhibit and the impact it had on people surveyed. |
| Year(s) Of Engagement Activity | 2016,2017,2018,2019,2020 |
| URL | https://www.birmingham.ac.uk/news/latest/2016/07/Birmingham's-role-in-gravitational-wave-detection-c... |
| Description | Improving HAM ISI performance with Interferometric sensors |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Talk was given at a conference describing how interferometric inertial sensors can improve the seismic isolation performance of isolation tables used in current gravitational wave observatories. This potentially allows for some of the low-frequency noise to be reduced expanding the capabilities of current generation detectors. 30 people were present in the session, this prompted questions about how these sensors could be used in current and future detectors and sparked further discussion and plans for the future. |
| Year(s) Of Engagement Activity | 2018 |
| Description | Interferometric sensors for low frequency isolation and control |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The talk was given at the Gravitational wave advanced detector workshop in 2019 where I talked about future displacement and inertial sensing that can be used in future gravitational wave detectors. The talk was attended by approximately 100 people from around the world, who are actively researching or maintaining the gravitational wave detector network. The key outcome of this talk was that my work was selected as a key outcome of the workshop and something that was a promising candidate for use in future detectors. |
| Year(s) Of Engagement Activity | 2019 |
| Description | LHO Fellows Talk: Update on Ham Modelling and Particle Swarming |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The talk was given at the LIGO Hanford observatory in which 20 people attended. The talk focused on the Modelling of Seismic isolation systems and the improvements to isolation control filters using particle swarm optimisation as well as an early study on how earthquakes impacted the observatories functions during 2016-2017. This resulted in many discussions and future areas of work that are on-going to this day. The technique is now used to design some control filters that are used at the LIGO Hanford Gravitational Wave Observatory. |
| Year(s) Of Engagement Activity | 2017 |
| Description | Low Frequency Compact Interferometers |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The talk was given at a conference, at which 30 people attended on the benefits of using compact interferometers for low-frequency control of suspensions in gravitational wave detectors. This resulted in further discussion and collaboration of projects. |
| Year(s) Of Engagement Activity | 2017 |
| Description | Optical Sensors (Low Frequency Workshop) |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | This was a talk that I gave at a workshop for the design and improvement of the low-frequency sensitivity of future gravitational wave detectors on different optical sensors that could be used for low-frequency control. There was approximately 25 people in the audience for this talk which sparked part of a weeks-long discussion on the future of the field. |
| Year(s) Of Engagement Activity | 2018 |
| Description | Talk given at Harrogate Ladies College titled Listening to Einsteins Universe. |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Schools |
| Results and Impact | Talk aimed at 9-11-year-olds on Space, astronomy and gravitational waves. This was attended by approximately 40 students who were actively engaged through the 40-minute talk and resulted in an hour question and answer session afterward. The major outcome of this was students who were previously not interested in doing astrophysics as a career are now interested in a career in science and astrophysics. |
| Year(s) Of Engagement Activity | 2018 |
| Description | Talk given at School Visit: Catching a gravitational wave |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Schools |
| Results and Impact | A talk given at multiple schools, notably at the William Brooks School in Much Wenlock on gravitational waves and how to detect them. The talk was aimed at students and parents who attend the school, the talk and following interaction were attended by approximately 50 people. This sparked hours of discussions about students who were interested in researching more in the field as future careers. |
| Year(s) Of Engagement Activity | 2016,2017 |
| Description | Talk given at the West Yorkshire Astronomical Society titled "Catching a Gravitational Wave" |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Public/other audiences |
| Results and Impact | The talk was given at the West Yorkshire astronomical society titled "How to catch a gravitational wave" to members of the public and amateur astronomers. The talk detailed links between electromagnetic astronomy and gravitational wave astronomy and was aimed at educating other educators present in the society about gravitational wave astronomy. This sparked hours of discussions afterwards on this and related subjects. |
| Year(s) Of Engagement Activity | 2016 |