Optimization of the Advanced LIGO gravitational-wave detectors duty cycle by reduction of parametric instabilities and environmental impacts

Abstract : The LIGO project is a large-scale physics experiment the goal of which is to detect and study gravitational waves of astrophysical origin. It is composed of two instruments identical in design, located in the United States. The two instruments are specialized versions of a Michelson interferometer with 4km-long arms. They observed a gravitational-wave signal for the first time in September 2015 from the merger of two stellar-mass black holes. This is the first direct detection of a gravitational wave and the first direct observation of a binary black hole merger. Five more detections from binary black hole mergers and neutron stars merger have been reported to date, marking the beginning of a new era in astrophysics. As a result of these detections, many activities are in progress to improve the duty cycle and sensitivity of the detectors. This thesis addresses two major issues limiting the duty cycle of the LIGO detectors: environmental impacts, especially earthquakes, and the issue of unstable opto-mechanical couplings in the cavities, referred to as parametric instabilities. The control strategies and tools developed to tackle these issues are presented. Early results have shown a downtime reduction during earthquakes of ~40% at one of the LIGO sites. Moreover, the electro-mechanical device called ‚Acoustic Mode Damper™ designed and tested during the thesis should completely solve the issue of parametric instabilities for LIGO. In conclusion, we will show that the problems tackled in this thesis improved the overall duty cycle of LIGO by 4.6%, which corresponds to an increase of the gravitational-wave detection rate by 14%.
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Sébastien Biscans. Optimization of the Advanced LIGO gravitational-wave detectors duty cycle by reduction of parametric instabilities and environmental impacts. Mechanics of materials [physics.class-ph]. Université du Maine, 2018. English. ⟨NNT : 2018LEMA1019⟩. ⟨tel-01893462⟩

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