Retarding Potential Analyzer (RPA) Modeling and Design Optimization Using Ion-Optical Simulation for 3DVI/M-MATISSE Mission

Sammanfattning

This thesis presents the modeling, simulation, and design optimization of a Retarding PotentialAnalyzer (RPA) developed for the 3D Velocity of Ions (3DVI) instrument of the M-MATISSE mission. The primary objective of this thesis is to evaluate RPA performance under plasma conditionsrelevant to the Martian ionosphere and to optimize the instrument geometry to accurately retrieveplasma physical parameters, such as mean ion velocity, ion temperature, and ion density. Thestudy begins with a review of the analytical RPA measurement principle, describing the relationship between accumulated ion current and retarding potential. This analytical framework providesinsight into the effects of plasma parameters and ion incidence angle on the RPA response, but itrelies on ideal assumptions and does not account for geometric and electrostatic effects present inrealistic sensor designs. To address these limitations, an ion-optical simulation framework is developed using SIMION.An idealized RPA model is generated to validate the simulation methodology, ion phase-space definitions, and post-processing algorithms. A systematic strategy for quantization of ion phase spaceis introduced to ensure accurate numerical integration while maintaining computational efficiency.The simulated RPA responses are post-processed to retrieve physical parameters of the simulatedplasma condition with good accuracy. The simulation framework is then extended to investigatenon-ideal geometric effects, with particular emphasis on ion losses caused by the RPA enclosurewalls. Parametric studies are conducted by varying the physical dimensions of RPA, aperture radius, grid spacing, grid sequence, and grid dimensions. Based on these studies, an optimized RPAconfiguration is identified that reduces wall-induced ion losses while maintaining sufficient angularacceptance and measurement sensitivity. The optimized design demonstrates stable, reliable estimation of the physical parameters of simulated plasma conditions representative of the Martianionosphere. Overall, this thesis demonstrates that SIMION ion-optical simulations are an effective andessential tool for evaluating RPA performance and guiding instrument design and optimization.The results provide a practical, validated basis for implementing the RPA sensor for the 3DVIinstrument on the M-MATISSE mission.