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

该项目将发展对液体等离子体的新认识和新模型。等离子体是最著名的电离气体，但最近证明等离子体现象也可以发生在液相中。换句话说，液体也可以像气体一样被电离，从而产生等离子体。等离子体在液体介质中的独特非平衡特性，如高密度电子、高能量发光、低温液体中的高电子能量等，在微电子、能源系统和新型材料等领域具有重要的应用前景。本研究的重点是探讨致密液体直接电离的基本机制。这项研究将是第一个利用有针对性的实验和建模相结合，对液体等离子体有一个清晰的认识和物理模型的研究。该项目解决了在高（液体）密度和非平衡条件下由快速上升的高压纳秒脉冲提供的独特等离子体状态。在过去的几年里，几个研究小组已经对直接在液相内部，特别是在水中产生的拖缆排放进行了研究。然而，由于与这些等离子体的光谱表征相关的主要困难，迄今为止还没有对这一现象作出明确的解释。在本研究中使用的低温液体将允许在液体电击穿过程中对局部电场、密度和温度进行直接的光学和光谱测量。这些测量预计将导致开发过程的物理模型。使用实验工具，将测试低温液体中快速击穿的两个主要假设。这些可以被广泛地描述为液体的直接电离和液体中冷“先导”（电伸缩驱动的拖缆）的传播。将得到的实验数据与分析模型和数值模拟相结合，将有可能区分这两种假设，并提高我们对液体非热击穿的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.