Outgassing, Temperature Gradients and the Radiometer Effect in LISA: A Torsion Pendulum Investigation

TL;DR

This study uses a torsion pendulum to experimentally investigate outgassing, temperature gradients, and the radiometer effect in LISA's gravitational reference sensor, providing data to validate thermal models and assess noise contributions.

Contribution

The paper presents a novel torsion balance setup to measure thermal effects like outgassing and radiometer forces under conditions similar to LISA, aiding in model validation.

Findings

Current GRS models are mostly consistent with measurements.

Thermal effects are not a major noise source for LISA.

Discrepancies exist in temperature dependence predictions.

Abstract

Thermal modeling of the LISA gravitational reference sensor (GRS) includes such effects as outgassing from the proof mass and its housing and the radiometer effect. Experimental data in conditions emulating the LISA GRS are required to confidently predict the GRS performance. Outgassing and the radiometer effect are similar in characteristics and are difficult to decouple experimentally. The design of our torsion balance allows us to investigate differential radiation pressure, the radiometer effect, and outgassing on closely separated conducting surfaces with high sensitivity. A thermally controlled split copper plate is brought near a freely hanging plate-torsion pendulum.We have varied the temperature on each half of the copper plate and have measured the resulting forces on the pendulum. We have determined that to first order the current GRS model for the radiometer effect, outgassing, and radiation pressure are mostly consistent with our torsion balance measurements and therefore these thermal effects do not appear to be a large hindrance to the LISA noise budget. However, there remain discrepancies between the predicted dependence of these effects on the temperature of our apparatus.