Particle simulations of ion generation and transport in microelectromechanical systems and microthrusters
Abstract
Field emission and evaporation are processes of electron and ion generation due to intense electric fields. This work presents a particle-based computational approach using the particle-in-cell/Monte Carlo collisions (PIC/MCC) and the direct simulation Monte Carlo (DSMC) method to study ion generation and transport in microelectromechanical systems (MEMS) and field emission electric propulsion (FEEP) microthrusters. Electrostatically actuated MEMS operate in intense electric fields > 107 V/m thereby resulting in electron emission from the cathode that has important implications on reliability and performance of these devices. The PIC/MCC method is used to develop compact models to provide closure to a mathematical model for the modified Paschen law which bridges breakdown in macroscale gaps with field emission driven breakdown at nano/microscales. The models have the capability to account for the influence of operating parameters including pressure, composition and cathode properties making it suitable for the analysis and design of electrostatic MEMS. This work also deals with the modeling of field emission ion thrusters used for in-space propulsion. Particle simulations are used to study performance parameters such as thrust and plume characteristics by comparison with experiments. While PIC simulations predict thrust values in excellent agreement with measurements, comparisons with measurements of current distribution in the plume indicate that ion-neutral collisions become increasingly important as the current increases. Good agreement for current distribution is obtained if the elastic scattering of ions by background neutrals in the vacuum chamber is included thereby providing a numerical framework for the design and optimization of these thrusters.
Degree
Ph.D.
Advisors
Alexeenko, Purdue University.
Subject Area
Aerospace engineering|Nanotechnology
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