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Measurement of Stray Electric Fields via Test Mass Charge Modulation

Presentation #436.06 in the session Space-Based Instruments.

Published onJun 29, 2022
Measurement of Stray Electric Fields via Test Mass Charge Modulation

This presentation describes a new method of measuring the stray electric field within gravitational reference sensors used for space-borne gravitational wave observation by modulating the charge of the sensor’s free-floating test mass and measuring the resulting coherent Coulomb force. Stray electric fields in an inertial sensor can couple with a charge on the sensor’s test mass to introduce additional noise into measurements. It is therefore necessary to effectively measure and compensate for the sensor’s stray electric field. This technique was demonstrated on the University of Florida torsion pendulum facility’s LISA-like inertial sensor using UV LEDs as a method of contactless test mass charge management via photoemission. The UV light was synchronized with an oscillating potential induced on the test mass through voltages applied to surrounding electrodes. The phase of UV light relative to this oscillating potential can be changed to control the direction of the photoelectron current, allowing for bidirectional charge management using one UV light source. In this new method of measuring the stray electric field, the test mass charge is modulated sinusoidally at an arbitrarily chosen frequency by varying the relative phase of UV light with respect to the oscillating test mass potential at an appropriate rate. Measurement of the equivalent stray potential of the sensor was demonstrated with millivolt precision in 104 s using the UF torsion pendulum. The applicability of this technique for use in the upcoming LISA space gravitational wave observatory mission will be discussed. It is predicted that this method could allow for the measurement of the stray potential in LISA’s inertial sensors with a precision of less than 0.1 mV in 200 s. This method could also allow for the simultaneous measurement of the stray potential on multiple LISA test masses by choosing different modulation frequencies, providing significant time savings compared to previous measurement techniques in which the stray electric field is determined from observing the DC force change resulting from a step change in the test mass charge.

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