Charge-Induced Force Noise on Free-Falling Test Masses: Results from LISA Pathfinder

Abstract

We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on freefalling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0 fm s −2 Hz −1=2 across the 0.1-100 mHz frequency band that is crucial to an observatory such as the Laser Interferometer Space Antenna (LISA). Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray PRL 118, 171101 (2017) P H Y S I C A L R E V I E W L E T T E R S week ending 28 APRIL 20170031-9007=17=118(17)=171101 (7) 171101-1 © 2017 American Physical Society electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

Electric-field noise from thermally activated fluctuators in a surface ion trap

“…Progress in this field has wide-ranging applications for precision measurements close to surfaces. For instance, patch potentials affect Casimir force measurements [3,4] and limit the sensitivity of gravitational experiments that use test masses [5,6]. Electric-field noise from surfaces is also detrimental to the performance of solid-state quantum bits in diamond [7,8].…”

Charge induced acceleration noise in the LISA gravitational reference sensor

“…This has been studied in detail for LISA Pathfinder [26] and we use results from that study to provide representative performance data. Figure 2 in [26] shows an amplitude spectral density between 0.05mHz and 30mHz which we approximate to The charge noise, S 1/2 Q to be used in equations 12, 14, 19 and 24 was first derived using Monte-Carlo simulations [19] but has since been modified by in-orbit measurements made by LISA Pathfinder [14]. The charging process is due to the interaction of cosmic-rays within the proof-mass and surrounding structures.…”

“…In principle terms driven by the same noisy parameter should be added linearly but in practice they also contain factors whose absolute sign is uncertain. The values of all the parameters have been set a Assuming dc compensation following [22] as demonstrated on LISA Pathfinder [14] b Expressed as an effective single-sided gradient from the two sensing electrodes as assumed for LISA Pathfinder [14] c (∂C i /∂k) /d d Taking the very conservative early estimate [17] reduced by a further factor of 3 for the newer more closed designs e See [27] f Estimated from S 1/2 y,z . Note f in Hz g See [30] to those appropriate for continuous discharge during science mode operations, as shown in table 1, with a charge level, Q, set to 5 × 10 6 elementary charges.…”

The LISA–Taiji network

“…It is expected to launch in 2030-2035, with a mission lifetime of 4 years extendable to 10 years. Recently, some technologies have been successfully tested in the LISA pathfinder mission [2]. Taiji is a gravitational-wave space facility proposed by the Chinese Academy of Sciences [3].…”