Utilizing an ExB probe for obtaining ion velocity distribution function for an electric propulsion system

Electric propulsion (EP) has been a key technology for contemporary and future space missions owing to its superior specific impulse and propellant efficiency relative to chemical propulsion. As EP applications expand from commercial constellations to deep-space exploration, the transition toward molecular and alternative propellants has introduced complex plasma environments that challenge conventional diagnostic methodologies. In such multispecies plasmas, multiple ion charge states and mass-to-charge ratios coexist, necessitating advanced diagnostics capable of resolving ion-specific velocity distributions with high fidelity. This dissertation presents a comprehensive theoretical and experimental investigation of the ExB probe as a quantitative diagnostic for obtaining ion velocity distribution functions (IVDFs) in EP systems. Building upon the fundamental operating principles of the ExB probe, a generalized analytical framework is developed to describe its transmission characteristics and to establish the convolution relationship between a measured current-voltage (IV) spectrum and the underlying IVDF. The concept of a transmittancy matrix is formulated to model the probe’s intrinsic blurring behavior, enabling the reconstruction of IVDFs through a newly developed regression approach that eliminates the need for conventional regularization techniques. A rigorous uncertainty propagation methodology is derived to quantify how measurement errors influence the reconstructed IVDF, thereby enabling statistically robust interpretation of experimental data. The proposed framework is validated experimentally using a dual-collector ExB probe developed at the University of Illinois Urbana-Champaign (UIUC), demonstrating reduced uncertainty when multiple spectra are analyzed concurrently. A novel negatively biased operation mode is subsequently introduced and verified through experiments employing a miniature ExB probe at the Naval Research Laboratory (NRL), effectively extending the probe’s measurement capability to low-energy ion populations. Among the tested configurations, the enclosed-body geometry exhibited near-complete conversion of applied potential into ion kinetic energy while preserving relative species fractions. The limitation of the analytical approach for obtaining the transmittancy matrix, and the analysis on two approaches for numerically obtaining transmittancy matrix are provided in this thesis. The influence of the charge-exchange and momentum exchange, particularly in the nitrogen plasma, and the space-charge effect on the ExB probe measurement are discussed, and correction formulas have been proposed. The integrated modeling, uncertainty analysis, and experimental validation presented herein collectively advance the diagnostic capability of the ExB probe from a qualitative mass spectrometer to a quantitative, ion-resolved kinetic diagnostic. The outcomes of this research furnish a robust foundation for characterizing multispecies plasma plumes in emerging molecular-propellant EP systems, thereby contributing to the next generation of efficient and sustainable space propulsion technologies.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Yamauchi, Toyofumi

Contributors dc:contributor

• Rovey, Joshua L
• Levin, Deborah A
• Ruzic, David N
• McDonald, Michael M

• ExB probe
• Electric Propulsion
• Plasma Diagnostics

Statement dc:rights

• Copyright 2025 Toyofumi Yamauchi

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132536

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132536