RUI: Using Atomic Physics to Achieve Strong Electron Coupling in Ultracold Plasmas

摘要：等离子体态在宇宙中无处不在——据估计，宇宙中99%的原子物质都处于等离子体态。超冷中性等离子体（UNPs）是一种等离子体，其初始电子和离子温度明显低于任何其他已知系统，但其密度足够高，使其静电相互作用能与其动能（所谓的“强耦合”状态）相当。在这种状态下，可能会出现类似结晶的具有长程结构的物质状态。UNPs也与强激光聚焦成固体时形成的等离子体有许多相似之处，例如在激光诱导聚变中。PI将在他在Colby学院的实验室里，在本科生的帮助下，对UNPs进行实验，同时进行数值模拟。在实验中，激光冷却的铷原子将在磁光阱（MOT）中使用脉冲激光进行光电离，并通过使用飞行时间技术检测电子和离子来观察等离子体的演变。除了从实验中获得的新知识外，这个项目还有一个重要的本科生研究训练组成部分。此外，PI在将他的研究项目中的仪器纳入物理教学课程方面有着良好的记录。该项目由原子、分子和光学实验物理项目、刺激竞争性研究的既定项目（EPSCoR）和等离子体物理项目共同资助。摘要：近年来，在使用冷碱土原子制成的超冷中性等离子体（UNPs）中，利用光学探针揭示了离子温度和耦合强度的演变，这些实验取得了重大成功。此外，激光被用来冷却等离子体中的离子，极大地增加了离子耦合参数。相反，电子对离子有几种额外的加热机制，主要是由于电子与离子复合时的加热，这限制了可以达到的最低温度（和最大耦合强度）。PI和他的本科生将使用嵌入式里德伯原子，看看他实验室中已经确定的冷却机制是否可以定制，以克服这些加热机制，并将电子耦合参数提高到0.5。该研究的第二个目标将是探索测量UNPs中电子温度的可靠方法。具体来说，将使用嵌入式里德伯原子传感器的毫米波光谱进行等离子体电场的时空映射，并将这种方法与通过快速电场脉冲淬灭UNP并观察产生的离子飞行时间光谱的等离子体膨胀的直接空间测量进行比较。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。

General audience abstract:The plasma state is ubiquitous in the universe - it is estimated that 99% of the atomic matter in the universe is in the plasma state. Ultracold neutral plasmas (UNPs) are plasmas in which the initial electron and ion temperatures are significantly lower than any other known systems yet have densities high enough for their electrostatic interaction energies to be comparable with their kinetic energies (the so-called “strongly coupled” regime). In this regime, states of matter with long range structure, similar to crystallization, may occur. UNPs also have many similarities with plasmas formed when intense lasers are focused into solids, for instance in laser-induced fusion. The PI will carry out experiments on UNPs in his lab at Colby College with the assistance of undergraduate students, and simultaneously pursue numerical simulations. In the experiments, laser-cooled rubidium atoms in a magneto-optical trap (MOT) will be photoionized using pulsed lasers, and the plasma evolution will be observed by detecting the electrons and ions using time-of-flight techniques. In addition to new knowledge gained from the experiments, there is a significant undergraduate research training component to this project. Furthermore, the PI has a strong record of incorporating instrumentation from his research program in the physics teaching curriculum. This project is jointly funded by the Atomic, Molecular, and Optical Experimental Physics program, the Established Program to Stimulate Competitive Research (EPSCoR), and the Plasma Physics program.Technical audience abstract:There has been significant recent success in experiments that have revealed the evolution of ion temperature and coupling strength using optical probes in ultracold neutral plasmas (UNPs) made using cold alkaline earth atoms. Additionally, lasers have been used to cool the ions in such plasmas, dramatically increasing the ionic coupling parameter. In contrast, electrons have several additional heating mechanisms to ions, primarily due to heating when electrons recombine with ions, that limit the minimum temperature (and maximum coupling strength) that can be achieved. The PI and his undergraduate students will use embedded Rydberg atoms to see if cooling mechanisms already identified in his lab can be tailored to overcome these heating mechanisms, and push the electron coupling parameter as high as 0.5. A second goal of the research will be to explore robust methods for measuring electron temperatures in UNPs. Specifically, spatial and temporal mapping of plasma electric fields will be carried out using mm-wave spectroscopy of embedded Rydberg atom sensors, and this method will be compared with direct spatial measurements of the plasma expansion by quenching the UNP with a fast electric field pulse and observing the resulting ion time-of-flight spectra.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.