Uploaded July 2022 | Updated September 2026, 2 hours ago
Observation of Test Mass charge fluctuations in continuous discharge mode: ground testing with torsion pendulum
The LISA spacecrafts will be constantly exposed to cosmic rays, which charge the Test Masses (TM). A UV photoelectric discharge system will be used to keep the TM potential within a threshold of roughly ±70 mV to limit electrostatic force noise.
In LISA Pathfinder the TM was rapidly discharged every few weeks, using UV light for short periods of time; other strategies allow to keep the TM close to neutrality by continuous illumination, without interrupting science acquisition. This however introduces additional noise in the TM charge, due to the Poissonian nature of electrons extraction process and possibly other photoelectric current fluctuations.
Here we present the results of a test campaign on this source of noise, performed with a prototype of LISA Pathfinder TM/electrode housing and a prototype pulsed UV LED light source, operating with μs light pulses synchronized to the GRS 100 kHz sensing field. The TM is suspended through a fiber in a torsion pendulum configuration, whose torque readout is used to measure its charge.
For discharge times of order 1 day, we detect the increase of charge noise for frequencies below 1 mHz, but at a level corresponding to an effective Poissonian shot noise below λeff less than 5000 /s, which is thus low enough to be compatible with LISA's acceleration noise requirements. We will also present an ongoing study of possible drifts of test mass equilibrium voltage during UV illumination.
Authors: Vittorio Chiavegato, William Joseph Weber, Rita Dolesi, Davide Dal Bosco, Antonella Cavalleri, Massimo Bassan, Fulvio De Persio, Giuseppe Masciantonio
Presenter: Vittorio Chiavegato
Observation of Test Mass charge fluctuations in continuous discharge mode: ground testing with torsion pendulum
The LISA spacecrafts will be constantly exposed to cosmic rays, which charge the Test Masses (TM). A UV photoelectric discharge system will be used to keep the TM potential within a threshold of roughly ±70 mV to limit electrostatic force noise.
In LISA Pathfinder the TM was rapidly discharged every few weeks, using UV light for short periods of time; other strategies allow to keep the TM close to neutrality by continuous illumination, without interrupting science acquisition. This however introduces additional noise in the TM charge, due to the Poissonian nature of electrons extraction process and possibly other photoelectric current fluctuations.
Here we present the results of a test campaign on this source of noise, performed with a prototype of LISA Pathfinder TM/electrode housing and a prototype pulsed UV LED light source, operating with μs light pulses synchronized to the GRS 100 kHz sensing field. The TM is suspended through a fiber in a torsion pendulum configuration, whose torque readout is used to measure its charge.
For discharge times of order 1 day, we detect the increase of charge noise for frequencies below 1 mHz, but at a level corresponding to an effective Poissonian shot noise below λeff less than 5000 /s, which is thus low enough to be compatible with LISA's acceleration noise requirements. We will also present an ongoing study of possible drifts of test mass equilibrium voltage during UV illumination.
Authors: Vittorio Chiavegato, William Joseph Weber, Rita Dolesi, Davide Dal Bosco, Antonella Cavalleri, Massimo Bassan, Fulvio De Persio, Giuseppe Masciantonio
Presenter: Vittorio Chiavegato
