Physics of Nanosecond-Pulsed Non-Thermal Plasma Generation in Liquid Nitrogen

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This project will develop new understanding and models of plasmas in liquids. Plasmas are best known as ionized gases, but recently it was demonstrated that plasma phenomena can also occur in a liquid phase. In other words, liquids can also be ionized, just like gases, to create a plasma. Unique non-equilibrium properties of plasma in liquid medium, such as high densities of electrons, high energy light emission, and high electron energies within a low temperature liquid are associated with new opportunities that may have great impact in the fields of microelectronics, energy systems and novel materials. The focus of this study will be exploring the fundamental mechanisms of direct ionization of a dense liquid. This research will be among the first that develops a clear understanding and a physical model of liquid plasmas using a combination of targeted experiments and modeling. The project addresses a unique plasma regime in high (liquid) densities and non-equilibrium conditions provided by fast rising high voltage nanosecond pulses. Streamer discharges generated directly inside of the liquid phase, specifically in water, have been investigated by several research groups in the past few years. However, due to principal difficulties associated with spectroscopic characterization of these plasmas, no clear explanation of this phenomenon has been formulated to date. Cryogenic liquids to be used in this study will allow direct optical and spectroscopic measurements of local electric fields, densities, and temperatures during electrical breakdown of liquids. These measurements are expected to lead to developing a physical model of the process. Using experimental tools, two major hypotheses of fast breakdown in cryogenic liquids will be tested. These can be broadly described as direct ionization of a liquid and propagation of a cold “leader” (electrostriction-driven streamers) in a liquid. The combination of the obtained experimental data with analytical models and numerical simulations will make it possible to distinguish between the two hypotheses and improve our understanding of the non-thermal breakdown in liquids.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.