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

The Laser Interferometer Space Antenna (LISA) is a space-based gravitational-wave observatory that uses free-falling test masses as inertial references to detect milliHertz frequency signals. Interactions between test masses and galactic or solar energetic particles cause charge buildup and Coulomb forces, source of acceleration noise that must be accurately modeled. LISA Pathfinder measurements showed that the Poissonian test mass charging noise was considerably larger than that in pre launch simulations, indicating missing physical processes in early models. Emission of low energy secondary electrons (LEE) from test mass and housing surfaces has been proposed as a key mechanism affecting charging and the sensor 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.