Torsion pendulum facility for direct force measurements of LISA GRS related disturbances

TL;DR

This paper describes a torsion pendulum setup designed to measure surface force disturbances relevant to the LISA gravitational reference sensor, achieving high sensitivity and analyzing environmental noise factors.

Contribution

The paper introduces a novel torsion pendulum facility with large-gap sensors for direct force disturbance measurements related to LISA GRS, including prototype results and noise analysis.

Findings

Achieved a torque noise near the thermal noise limit

Sensitivity of 300 fN/Hz^(1/2) at 1mHz, close to LISA goals

Identified gravity gradient noise as a potential limiting factor

Abstract

A four mass torsion pendulum facility for testing of the LISA GRS is under development in Trento. With a LISA-like test mass suspended off-axis with respect to the pendulum fiber, the facility allows for a direct measurement of surface force disturbances arising in the GRS. We present here results with a prototype pendulum integrated with very large-gap sensors, which allows an estimate of the intrinsic pendulum noise floor in the absence of sensor related force noise. The apparatus has shown a torque noise near to its mechanical thermal noise limit, and would allow to place upper limits on GRS related disturbances with a best sensitivity of 300 fN/Hz^(1/2) at 1mHz, a factor 50 from the LISA goal. Also, we discuss the characterization of the gravity gradient noise, one environmental noise source that could limit the apparatus performances, and report on the status of development of the facility.