Overview
A new gravitational calibrator design for gravitational wave observatories has been proposed, featuring a novel geometry of four quadrupole rotors. This configuration aims to generate a pseudo plane-wave sinusoidal gravitational acceleration, addressing limitations in existing calibrators related to their dependence on the relative position between the calibrators and the observatory's test masses.
Research Context
Existing gravitational calibrators in gravitational wave observatories exhibit precision limitations due to their sensitivity to the relative positional arrangement of the calibrators and the test masses. Variations in this relative position can introduce uncertainties in the calibration signal, affecting the accuracy of measurements. The research sought to develop a calibrator that mitigates this positional dependence, thereby improving the reliability of gravitational acceleration measurements.
Approach
The proposed calibrator design utilizes a geometric arrangement of four quadrupole rotors. These rotors are positioned at the vertices of a rectangle, with the center of this rectangle aligned with the test mass. The phases and rotation directions of these rotors are specifically selected to achieve the desired gravitational acceleration profile. This configuration is intended to produce a pseudo plane-wave sinusoidal gravitational acceleration. The performance of this geometry was analyzed concerning its sensitivity to test mass positioning and the resulting uncertainty in acceleration amplitude.
Findings
The novel geometry of four quadrupole rotors, arranged at the vertices of a rectangle centered on the test mass, was found to produce a pseudo plane-wave sinusoidal gravitational acceleration. The amplitude of this acceleration is approximately $100 \text{ fm/s}^2$. A key finding is that this acceleration exhibits minimal dependence on the position of the test mass relative to the rotor array. The design is capable of yielding a 0.15% acceleration amplitude uncertainty, even when tolerating a 1-cm uncertainty in the test mass's position. Furthermore, the acceleration generated by this system can be directed precisely along the optical axis of the interferometer arm. The design also ensures that no torque is applied to the test mass. The small size of the rotors is noted to offer engineering and safety benefits.