Nanosecond Pulsed Discharge in Liquid Nitrogen
Authors:   , Song Zhiheng , Dobrynin Danil , Fridman Alexander A. 
Published: December 2024

Plasma is the fourth state of matter along with solids, liquids, and gases. Plasma is usually a gas phase phenomenon but during recent years there have been increasing attention on plasma in liquids due to its promising applications, such as water decontamination, nanomaterial synthesis, ocean exploration, and the modification of metallic and organic surfaces in contact with the treated liquid. Plasma in liquid is a complex phenomenon involving various physical and chemical reactions that generate active species, UV emission, and shockwaves. The generation of these products directly depends on plasma parameters, such as electron density and temperature, which are closely related to the discharge modes in water under various experimental conditions. Additionally, vaporization, charge distributions at the liquid/gas interface, and the development of ionization in different phases complicate the exploration of discharge mechanisms. Therefore, thorough investigations into the initiation, propagation, and breakdown of different streamer modes are essential for a better understanding of underwater discharges. Generating plasma in liquid is challenging due to the difficulty in overcoming the energy barrier of the liquid-gas phase transition. In general, electrical discharges propagating inside a liquid phase (e.g. water) can be initiated easily through the bubbles (gas breakdown) which existed in the liquid or formed due to the local heating of the liquid. The bubble breakdown in water typically occurs in slow-pulsed discharge systems driven by high voltage waveforms of microsecond duration. Recent work at the C. & J. Nyheim Plasma Institute illustrated the possibility that nanosecond-pulsed discharges could initiate plasma directly in the liquid phase without any gas phase involved, at an electric field strength lower than the theoretical direct-ionization thresholds. Very few studies have been conducted to understand the ignition mechanism, plasma characteristics, and potential applications. The nanosecond-pulsed discharge also showed potential for generating high-energy density polymeric nitrogen material. This material was synthesized by nanosecond-pulsed discharge in liquid nitrogen using different precursors and stabilized by various porous adsorbent materials. The main goal of this dissertation is to qualitatively and quantitatively understand the mechanism of nanosecond-pulsed discharge in liquids, characterize plasma properties, and explore potential applications across different fields. The analytical methods used in this dissertation to study the mechanism, plasma characteristics, and potential applications include time-resolved optical diagnostics such as direct imaging, transmission imaging (shadow), optical emission spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), and Raman spectroscopy. This dissertation investigates the ignition mechanism and plasma characteristics of nanosecond-pulsed discharge in liquid nitrogen and the generation of high-energy density polymeric nitrogen. Utilizing optical characterizations, the study provides a comprehensive analysis of plasma interactions in liquid nitrogen. The results indicate significant advancements in the synthesis and stabilization of polymeric nitrogen, offering potential applications in high-energy materials. These findings contribute to a broader understanding of plasma discharge in liquids and present new methodologies for the efficient generation of high-energy materials.