Experimental Investigation of Spontaneous Double Layers in Expanding Plasmas

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Over the last decade, plasma researchers have observed the surprising result that when a plasma expands along a weakening magnetic field, beams of high speed ions shooting out along the magnetic field spontaneously appear. Expanding plasmas are common in nature, such as the atmosphere of the Sun, and in 21st century technology, such as in some rocket engines and industrial systems. This project explores the stability and the detailed structure of the ion acceleration process in hopes of developing a better understanding of the most important processes responsible for the ion acceleration.The group will measure the stability thresholds for spontaneously forming double layers (sheaths) in expanding single and multiple ion species plasmas; the effects of neutral density in the double layer region on double layer structure and stability; and the spatial structure and plasma parameter dependence of the electric fields in the expansion region that result in the formation of multiple ion beams. Integrated with these investigations is the application of new diagnostic tools for the measurement of densities and flows of ions and neutrals in low temperature plasmas. The formation and stability of double layers in single-ion and multi-ion plasmas is a fundamental plasma physics question with important ramifications for systems ranging from space plasmas to plasma thrusters. Beyond the scientific contributions that this research will make to our understanding of double layer formation and stability, the broader impact of the work involves the training of graduate students in a research environment that emphasizes the synergy between basic and applied plasma physics; improvement of the percentage of women and minorities obtaining advanced degrees in physics; attracting high quality undergraduates into physics through involvement in cutting-edge research activities; and support of a STEM education initiative that extends to over half the counties in West Virginia and that is continuing to expand.