Electron Energy Distribution and Transfer Phenomena in Non-Equilibrium Gases

Abstract : During this 3-year in-house experimental research task, researchers in the Electrical Systems Branch of the Air Force Research Laboratory (AFRL/RQQE) applied advanced spectroscopic and laser techniques to measure, monitor and ultimately control the distribution of electronic and kinetic energies within low temperature plasmas and enhance the understanding of phenomena associated with non-equilibrium energy distributions. The experimental results from this task provided insight into the potential for further technological advancements, including plasma switching, ignition enhancement, laser medium excitation, and plasma surface treatments. Advances in kinetic modeling have also generated accurate computations that represent the energy-dependent behavior of charged species in the non-equilibrium environment and have allowed the simulation of breakdown phenomena in potential Air Force applications. Specifically, measurement techniques of temperatures and energy distributions within micro-discharges were developed and optimized, advanced multi-photon absorption and ionization techniques for both diagnostics and pre-ionization seeding for gas breakdown were analyzed, and ion chemistry leading to ignition of advanced fuel molecules was investigated. The experimental approaches applied include advanced ultraviolet spectroscopic techniques with methods in subtractive triple-grating spectroscopy, laser scattering techniques, optical emission spectroscopy, multi-photon laser techniques to both detect and stimulate laboratory gas systems, and finally Fourier transform mass spectroscopy for ion analysis. The experimental results focus on laser scatter diagnostics of air microdischarge kinetics, resonant laser induced breakdown of air for fuel-air ignition, and ion chemistry analysis of fuel molecules.