[P-CG20] Future missions and instrumentation for space and planetary science

[PCG20-P07] Ion optics of the ±45° angular scanning deflectors for space plasma instruments

Yuuki Kitamura¹, *Shoichiro Yokota¹, Satoshi Kasahara², Kentaro Terada¹ (1.Graduate School of Science, Osaka University, 2.Graduate School of Science, The University of Tokyo)

Keywords:Space plasma measurements, Electrostatic analyzer, Field-of-view scanning

For three-dimensional energy analysis of low-energy ions and electrons in space, the top-hat electrostatic method has usually been applied because of its large geometric factor and uniform angular response while requiring relatively few resources. Typical top-hat spectrometers provide a wide field of view (FOV) (360° x ~5°), appropriate energy resolution (~10%), and an energy range from a few electronvolts to a few ten kilo-electronvolts, a reasonable geometric factor (~10^-4 cm² sr eV/eV), and good sunlight rejection by means of small weight, size and power. Complete spherical FOV (4pi steradian) is enabled by the spin motion of the spacecraft. In almost all optical experiments, however, three-axis stabilized satellites are preferred because most experiments require observation in the direction of the planetary atmosphere or surface. Three-axis stabilized satellites intrinsically restrict the FOV of top-hat analyzers to a plane. Electrostatic angular scanning derived from the differential ion flux probe is an effective way to extend the FOV while placing only small demands on resources. Furthermore, angular scanning deflectors and top-hat electrostatic analyzers form an excellent combination to provide hemispherical coverage of the FOV even on three-axis stabilized planetary explorers such as KAGUYA and Martian Moons eXploration (MMX). Therefore, we studied ion optics of the angular scanning deflectors of spaceborne low-energy particle experiments. Numerical models were used to comprehensively examine various geometries of the deflectors and evaluate the performance of each one in terms of deflection characteristics (±45°), energy-angle response, and sensitivity. An analytical model was developed to evaluate the performance of the deflector with respect to the geometry in all parameters. We confirmed that the outputs of the analytical model agree with that of the numerical model with an accuracy of approximately 10%. Here, we present the details of the ion optics for the deflector of the low-energy particle instruments, the analytical model we developed, and its evaluation.