Precision Charge Control for Isolated Free-Falling Test Masses: LISA Pathfinder Results

TL;DR

This paper evaluates the performance of a contactless UV-based charge management system for free-falling test masses in the LISA Pathfinder mission, combining ground and in-flight measurements with detailed simulations to inform future gravitational wave detectors.

Contribution

It introduces a comprehensive simulation framework and experimental validation for UV charge control in space-based test masses, advancing the design of future gravitational wave observatories.

Findings

The UV discharge system effectively neutralized accumulated charge.

Simulations closely matched in-flight observations, validating the models.

Insights gained will guide future charge management systems for space missions.

Abstract

The LISA Pathfinder charge management device was responsible for neutralising the cosmic ray induced electric charge that inevitably accumulated on the free-falling test masses at the heart of the experiment. We present measurements made on ground and in-flight that quantify the performance of this contactless discharge system which was based on photo-emission under UV illumination. In addition, a two-part simulation is described that was developed alongside the hardware. Modelling of the absorbed UV light within the Pathfinder sensor was carried out with the GEANT4 software toolkit and a separate MATLAB charge transfer model calculated the net photocurrent between the test masses and surrounding housing in the presence of AC and DC electric fields. We confront the results of these models with observations and draw conclusions for the design of discharge systems for future experiments like LISA that will also employ free-falling test masses.