Development of Rotational Inertial Sensors for Gravitational Wave Detectors

Details

Supervisors

Bruno, Giacomo ; Van Ruymbeke, Michel

Faculty

Faculté des sciences

Degree label

Master [120] en sciences physiques, à finalité approfondie

Abstract

enThis project was motivated by the need to precisely measure rotational seismic motion for the improvement of seismic and Newtonian noise monitoring for the upcoming Einstein Telescope project. A symmetric vertical pendulum originally developed for the precise measurement of Newton’s gravitational constant G was reinstalled in an underground laboratory in the SC17 building in Louvain-la-Neuve, where it was modified to attempt to reach astatization and a working, linear electrostatic feedback system. The astatization (configuration where the gravitational restoring force is zero) of this symmetric vertical pendulum would allow for it to only respond inertially to rotational ground motion. This process was carried out by manually adjusting its center of mass closer to its axis of rotation and measuring the pendulum’s response to an external torque. A linear electrostatic feedback system would allow for this pendulum to operate at its astatization point while its inertial response is measured in the electrostatic feedback output. This electrostatic feedback system was developed using a PID controller that controlled the pulse width modulation of a fixed voltage into capacitor plates located on the sides of the pendulum, which is necessary due to the quadratic dependence of electrostatic force on voltage. Evidence for the mechanical astatization of the pendulum was achieved, as well as a working electrostatic feedback system that kept the pendulum stable long-term and whose signal reflected the external torque produced on the pendulum. The next step in the development of this instrument is to improve its testing conditions, to test its detection of seismic motion, and to characterize its sensitivity to compare it with state-of-the-art rotational seismometers.