Fast Optical Emission Spectroscopy for Plasma Modeling and Hall Thruster Development

This proposal is focused on fast optical emission spectroscopy, which implements the concept of OES discussed above at high speeds, thus posing as a method capable of gaining insight into plasma turbulence. A challenge with fast optical emission spectroscopy is capturing enough light with an intensity above the noise threshold. Previous optical emission spectroscopy systems have implemented spectrometers as an instrument for capturing light and have been successful in detecting a signal far above the noise level. However, spectrometers integrate the signal over an exposure time rather than making high-speed, time-resolved measurements. With faster measurements with frequencies ranging from hundreds of kilohertz to hundreds of megahertz, the measured signal has a much lower intensity, making it difficult to distinguish the signal from noise, especially for operating conditions that produce dimmer discharge plumes. This research will contribute to improved modeling of plasma turbulence by characterizing the behavior of plasma parameters including electron temperature at high frequencies. This, in turn, will allow for further Hall Thruster development in terms of efficiency, power, and reliability. To characterize plasma turbulence, there is a need for a non-intrusive diagnostic to determine time-resolved plasma parameters. This research seeks to develop such a diagnostic, and experiments conducted using the proposed fast optical emission spectroscopy will expand the scientific understanding of fundamental physics governing Hall Thrusters. With further development, electric propulsion systems made up of Hall Thrusters have potential for longer and more complex space missions such as a possible manned mission to Mars, and this research will contribute to the necessary development. Furthermore, a non-invasive method such as the one described could be developed as an in-flight diagnostic for remotely determining time-resolved plasma parameters of Hall Thrusters on satellite propulsion systems. This would be valuable since Hall Thruster behavior in a testing facility vacuum chamber is not necessarily the same as behavior in space. With further development, such as finding a way to accomplish temperature stabilization of the avalanche photodiodes in space, the proposed method of fast optical emission spectroscopy is a conceivable diagnostic for characterization of any discrepancies.

With further development, electric propulsion systems made up of Hall Thrusters have potential for longer and more complex space missions such as a possible manned mission to Mars, and this research will contribute to the necessary development. Further, the proposed method of fast optical emission spectroscopy is a conceivable diagnostic for characterization of any discrepancies.

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