Experimental Investigation of Spontaneous Double Layers in Expanding Plasmas

在过去的十年里，等离子体研究人员观察到一个令人惊讶的结果：当等离子体沿着一个减弱的磁场膨胀时，高速离子束沿着磁场自发地射出。膨胀的等离子体在自然界很常见，比如太阳的大气层，在21世纪的技术中也很常见，比如在一些火箭发动机和工业系统中。该项目探索了离子加速过程的稳定性和详细结构，希望能更好地理解导致离子加速的最重要过程。该小组将测量在膨胀的单离子和多离子等离子体中自发形成双层（鞘层）的稳定性阈值；双层区中性密度对双层结构及稳定性的影响；以及导致多离子束形成的膨胀区电场的空间结构和等离子体参数的依赖关系。与这些研究相结合的是应用新的诊断工具来测量低温等离子体中离子和中性物质的密度和流动。单离子和多离子等离子体中双层的形成和稳定性是一个基本的等离子体物理学问题，对从空间等离子体到等离子体推进器等系统具有重要的影响。除了这项研究将对我们对双层形成和稳定性的理解做出科学贡献之外，这项工作的更广泛影响还包括在一个强调基础和应用等离子体物理学之间协同作用的研究环境中培养研究生；提高妇女和少数民族获得物理学高级学位的比例；通过参与前沿研究活动，吸引高素质的本科生进入物理学领域；并支持一项STEM教育计划，该计划已扩展到西弗吉尼亚州一半以上的县，而且还在继续扩大。

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.