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Observations of low-energy-electron production and experimental characterization of the test-mass charging process in the LISA gravitational reference sensor with the BART experiment

Francesco Dimiccoli1,2,*, Francesco Venturelli1,†, Valerio Ferroni1,2,‡, Antonella Cavalleri1,§, Teodoro Klaser1,∥, Matteo Tomasi1,3,¶, Davide Dal Bosco1,2,**, Enrico Verroi2,††, Rita Dolesi1,2,‡‡ et al.

William J. Weber1,2,§§

  • *Contact author: francesco.dimiccoli@unitn.it
  • †Contact author: francesco.venturelli@unitn.it
  • ‡Contact author: valerio.ferroni@unitn.it
  • §Contact author: antonella.cavalleri@unitn.it
  • ∥Contact author: teo.klaser@outlook.it
  • Contact author: matteo.tomasi-1@unitn.it
  • **Contact author: davide.dalbosco-1@unitn.it
  • ††Contact author: enrico.verroi@tifpa.infn.it
  • ‡‡Contact author: rita.dolesi@unitn.it
  • §§Contact author: williamjoseph.weber@unitn.it
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Phys. Rev. D 114, 043010 – Published 4 August, 2026

DOI: https://doi.org/10.1103/kgw1-wm9j

Abstract

The Laser Interferometer Space Antenna (LISA) is a space-based gravitational-wave observatory that uses free-falling test masses as inertial references to detect mHz-frequency signals. Interactions between these test masses and galactic or solar energetic particles cause charge buildup and Coulomb forces, a major source of acceleration noise that must be accurately modeled. LISA Pathfinder measurements showed that the Poissonian test-mass charging noise, an important entry in the noise budget, was considerably larger than that in prelaunch simulations, indicating missing physical processes in early models. Emission of low-energy secondary electrons (LEEs) from test-mass and housing surfaces has been proposed as a key mechanism affecting charging and the sensor’s electrostatic response. We report a particle accelerator-based experiment that directly tests the LEE hypothesis by measuring proton-induced test-mass charging in a LISA-like Gravitational Reference Sensor geometry as a function of the test-mass electrostatic potential. A flight-representative test mass and the capacitive sensor electrode housing surrounding it are exposed in vacuum to monoenergetic 70–230 MeV proton beams, while test-mass charging currents are measured with femtoampere sensitivity. By varying the test-mass potential by volts during irradiation, we gain sensitivity to eV-scale charge carriers whose transport and collection depend on these fields. The measurements yield stable, reproducible picoampere-level charging currents and a clear dependence of the net charging rate on test-mass potential. This behavior directly supports the role of low-energy secondary electrons in test-mass charging and is consistent with the LEE-based interpretation of LISA Pathfinder data. These are the first controlled laboratory measurements of low-energy electron effects in test-mass charging for a LISA-like sensor and provide a benchmark for validating charging models and charge-management strategies for LISA and future space-based precision interferometry missions.

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Outline

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Phys. Rev. D 114, 043010– Published 4 August, 2026
  • Received 25 May 2026
  • Accepted 14 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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