Numerical Modeling and Experimental Demonstration of Pulsed Charge Control for the Space Inertial Sensor used in LISA

Abstract

Electrostatic charge control of isolated free-falling test masses is a key enabling technology for space-based gravitational missions. Contact-free electrostatic charge control can be achieved using photoelectron emission from metal surfaces under illumination with deep UV light. A contact-free method minimizes force disturbances that can perturb measurements or interrupt science operations. In this paper we present charge control experiments using a gravitational reference sensor geometry relevant to the Laser Interferometer Space Antenna (LISA) gravitational wave observatory in a torsion pendulum apparatus. We use a UV LED light source to control the test mass potential, taking advantage of their high bandwidth to phase-lock the light output to 100 kHz electric fields used for capacitive position sensing of the test mass. We demonstrate charge-rate and test mass potential control by adjustment of the phase of the light with respect to the electric field. We present a simple physics-based model of the discharging process which explains our experimental results in terms of the UV light distribution in the sensor, surface work functions and quantum yields. A robust fitting method is used to determine the best-fit physical parameters of the model that describe the system.

Estimation of the electrostatic effects in the LISA-Pathfinder critical test mass dynamics via the method of moments

“…Such a system is however not active during the release and capture phases and would be too slow [6]. Even in LISA, where an UV-LED system is foreseen in place of the Hg lamps, the time constant is well above 1 s [23].…”