• digital controller
• electromagnetic levitation
• eLISA
• FPGA
• inertial sensor
• LabVIEW
• laser intensity stabilization

Field Programmable Gate Arrays (FPGAs) are powerful and flexible instruments, particularly suited for the implementation of servo loops for experimental setups since they allow to frequently change the system without hardware modifications, thus resulting in a time and cost effective solution. Two FPGA-based controllers are presented in this thesis, developed in the frame of the construction of a laboratory model to investigate a novel inertial sensor concept for laser ranging space missions.

The specific context of this work is the study of an alternative opto-mechanical architecture for the eLISA mission payload, for which an inertial reference sensor with a spherical test mass and optical readout has been proposed. Thanks to the possibility to operate the system in a full drag-free mode offered by the geometry of the test mass and to the high accuracy of the interferometric measurement of its center of mass, an advantage in terms of noise sensitivity of the sensor should be achieved with respect to the current baseline design. To validate this concept, a proof of its feasibility and an assessment of its performance need to be obtained with an earthbound laboratory model, whose success also relies, among other things, on the possibility to have stable laser signals for interferometric detection and a free-flying test mass kept in a steady position by a levitation system.

Both these targets can be achieved through the implementation of an active control system stabilizing laser intensity via acousto-optic modulation in one case, and test mass height by means of a current modulated magnetic field in the other. The used servo loops, based on PID control scheme and implemented on a National Instruments FPGA board, are here described, focusing on the experimental characterization of the sensing and actuation hardware and on the controllers’ design through LabVIEW programming. Finally, the experimental trials carried out are illustrated, presenting the achieved results in terms of laser RIN reduction, the issues encountered for the test mass levitation and possible strategies for overcoming them in the continuation of the project.