Design of an antenna for the detection of kHz electromagnetic disturbances on-board LISA

Abstract

The Laser Interferometer Space Antenna (LISA) is a mission led by the European Space Agency that seeks to be the first space-based observatory capable to detect and measure gravitational waves. Since it is a pioneer investigation, some of the required technologies have been never proved before in a space environment, but just on-ground, arising then the need of launching a technology demonstrator for the mission, the LISA Pathfinder (LPF). The scope was to prove that the technology was able to detect differential acceleration noises between two test masses in nominal free-fall up to 30 fm·s-2/√Hz. After two years of testing, the spacecraft provided the data of the performances of each of the units contributing to the payload, the so-called LISA Technology Package (LTP). The results confirmed that the experiment was successful – even better than expected – because LPF detected differential acceleration noises below the requirements. Nonetheless, several glitches of unknown sources were found throughout the overall noise spectrum and had to be removed from the data in order to provide the results. Otherwise, the peaks add an excess noise in the low frequencies. Since this effect is not negligible, many hypotheses have been proposed and discarded until the present day to try to explain the physical phenomena. One of them is related to the magnetic contribution, and asserts that the origin is given by the down-conversion of a high frequency (kHz) amplitude modulating magnetic field into the LISA measureable bandwidth, located in the low frequency region (mHz). These time varying signals will be detected with audio-range sensors. Hence, the objective of this work is to design the most feasible sensor capable to detect the offending signals, considering the LISA requirements, the distribution of the units onboard the spacecraft, the modulation of the respective magnetic fields, or the sensor design specifications. The results prove that a simple air-cored search coil can be used as the demanded sensor, achieving sensitivities below the required and, therefore, capable to detect amplitude modulating magnetic fields of different intensities and distances from the test masses.