RUI: Rydberg Atoms and their Effect on Ultra-Cold Plasma Dynamics

科尔比学院PI实验室的研究方向是表征和控制超冷中性等离子体(UNPS)。特别是，我们正在研究UNPS中电子温度的非光学测量，以及提供在等离子体演化过程中控制电子温度的技术。我们的UNPS是由激光冷却、磁性囚禁的Rb原子的脉冲激光光致电离制成的。这样的等离子体最初是95%中性的，初始电子温度和离子密度是脉冲激光强度和频率的容易控制的函数。原子过程，主要涉及里德堡态，是等离子体演化过程的关键，通常在等离子体的初始阶段加热。然而，UNP的存在时间可能超过100微秒。当它膨胀时，电子温度降低，电子从等离子体中蒸发。在由碱土原子制成的UNPS中，光学可达的离子跃迁被用来从等离子体离子膨胀速度中提取电子温度的精确值。然而，这在像Rb这样的碱性原子中是不可行的。我们正在研究碱性等离子体中的几种电子温度测量技术，这些技术可能提供与碱土UNPS中的光学技术相同的精度。此外，在PI的实验室中，里德堡原子嵌入到UNP中的初步实验表明，有可能控制电子-原子碰撞，以抵消三体复合引起的UNP的加热，并将UNP推入强耦合方案。等离子体无处不在：它们以荧光灯的形式照亮我们的生活；物理学家的一个长期目标是使用等离子体进行受控的热核聚变；它们在宇宙和我们的日常生活中出现在许多其他现象中。UNPS具有根本的意义，因为它们可以在极低的电子(0-1000K)和离子(1K)温度下制成，而且它们接近强耦合区域，在该区域中，粒子之间的相互作用势能与它们的动能相当。因此，它们在原子系统和固态或液态之间的关联之间架起了桥梁。此外，UNPS是测试等离子体物理中使用的理论建模技术的一个特别有用的环境。实验可以以一种非常可重复性的方式进行，并且与其他类型的等离子体实验相比，具有以高精度设置初始条件的能力。在更实际的层面上，PI对UNPS的研究是在一个仅限本科生参加的机构进行的，本科生在从设备建设和数据采集编程到执行实验的各个层面都得到了关键的参与。

Research in the PI's laboratory at Colby College is directed towards characterizing and controlling ultra-cold neutral plasmas (UNPs). In particular, we are investigating non-optical measurements of the electron temperature in UNPs, and techniques that offer the ability to control the electron temperature during the plasma evolution process. Our UNPs are made by pulsed-laser photoionization of laser-cooled, magnetically trapped rubidium atoms. Such a plasma is initially 95% neutral, and the initial electron temperature and ion density are easily controllable functions of the pulsed laser intensity and frequency. Atomic processes, principally involving Rydberg states, are critical to the plasma evolution process, and generally heat the plasma in its initial stage. Nevertheless, the UNP may exist for longer than 100 microseconds. As it expands, the electron temperature decreases, and electrons evaporate from the plasma. In UNPs made from alkaline-earth atoms, optically accessible ionic transitions are used to extract precise values for the electron temperature from the plasma ion expansion velocity. However, this is not feasible in alkali atoms such as rubidium. We are pursuing several electron temperature measurement techniques in alkali plasmas that potentially offer precision equal to the optical technique in alkaline earth UNPs. In addition, preliminary experiments in the PI's lab, in which Rydberg atoms are embedded in a UNP, indicate that it may be possible to control electron-atom collisions to counteract heating of the UNP caused by three-body recombination, and push the UNP into the strongly-coupled regime.Plasmas are ubiquitous: they illuminate our lives in the form of fluorescent lights,; a long-existing goal of physicists is to use plasmas to perform controlled thermonuclear fusion; and they occur in many other manifestations in the Universe and our everyday lives. UNPs are of fundamental interest because they can be made with uniquely low electron (0-1000 K) and ion (1 K) temperatures, and because they approach the strongly-coupled regime in which the potential energy of interaction between particles becomes comparable to their kinetic energies. They therefore bridge the gap between atomic systems and the correlations found in the solid or liquid state. In addition, UNPs are an exceptionally useful environment for testing theoretical modeling techniques used in plasma physics. Experiments can be carried out in a very reproducible manner, and one has the ability to set the initial conditions with a high degree of precision compared with other kinds of plasma experiment. At a more practical level, the PI's research on UNPs is carried out at an undergraduate-only institution, and undergraduates have been critically involved at all levels of the research, from equipment construction and data-acquisition programming, through to performing the experiments.