ECE PhD Thesis Defense: Catriana Paw U

ECE PhD Thesis Defense: Catriana Paw U

Title: Magnetic Diverters for Space-borne X-ray Imaging Instruments

Presenter: Catriana Paw U

Advisor: Professor Brian Walsh, Professor Joshua Semeter

Chair: Professor Robert Kotiuga

Committee: Professor Brian Walsh, Professor Joshua Semeter, Professor Toshi Nishimura, Research Scientist Kip Kuntz

Google Scholar Link: https://scholar.google.com/citations?user=qjpqOXMAAAAJ&hl

Abstract: Near-Earth space hosts complex plasma environments that pose significant risks to space-based technology and crewed spacecraft operations. For space-borne X-ray instruments, such as the Lunar Environment heliospheric X-ray Imager (LEXI), mitigating charged particle contamination is essential for preserving signal integrity and achieving science objectives. LEXI, active on the lunar surface at Mare Crisium in March 2025, operated largely outside of Earth's magnetosphere, directly in the solar wind. To suppress charged particle flux from the solar wind, LEXI incorporated multiple particle suppression measures, including a 48-element neodymium magnet array. Starting with the LEXI magnet array diverter, this thesis investigates the efficacy of magnet-based shielding for instruments exposed to space plasma environments. The design of the magnet array for LEXI's unique environment and spacecraft requirements is described. Charged particle trajectories, under the influence of the Lorentz force, are modeled with a Runge-Kutta of order 5(4) to determine magnetic deflection. Further LEXI-specific factors, such as physical structures, filters, and optics, are included in determining particle suppression effectiveness. By considering the LEXI-specific suppression measures as well as the simulated magnetic diverter effectiveness, this thesis finds that LEXI should have had adequate charged particle suppression with an expected charged particle detector hit rate of less than 0.2-0.4 counts per second for a signal of 200 counts per second. The diverter analysis is then extended to a generalized LEXI-like, tiled-optics-based instrument to determine the influence of magnet strength and plasma environment on shielding performance. Three plasma environments and relativistic particle tracings are used to determine efficacy of the magnet arrays of various strengths. This analysis shows that protons and electrons, for different magnet strengths, had similar but offset curves of hit rate as a function of energy. It was found that there is a limit to the particle-deflection benefits of increasing the strength of magnets in a diverter. By characterizing trends across particle species and magnet strengths, this thesis seeks a generalizable framework for reducing the resources required for passive shielding modeling. The thesis finds that the curves of detector hit rate compared to energy for simulated electrons and protons collapse to a single curve when hit rate is plotted against a form of the gyroradius. It is also shown that non-relativistic particles that have the same value of this gyroradius form have identical trajectories. This collapsed curve and trajectory matching can be used to approximate hit rate beyond what is simulated, reducing the amount of particle species and energies required for modeling the effectiveness of a diverter.