Development of Laser Induced Fluorescence as a Diagnostic for Measuring Neutral, Ion, and Molecule Particle Fluxes in the PK-4 Experiment

这个项目将开发一种方法来测量尘埃等离子体中电离和中性原子的流动，尘埃等离子体是恒星和行星开始形成的物质。所谓的尘埃或复杂等离子体不仅由离子、电子和中性原子组成，而且还有大量直径只有千分之几毫米的微小尘埃颗粒。虽然以人类的标准来看，这些颗粒很小，但它们比离子重数十亿倍。颗粒不断受到离子和中性离子的撞击，这些碰撞会导致颗粒以有趣的方式移动。由于颗粒的大小，它们受到重力的影响，在地球上的实验中往往会掉下来。国际空间站上的等离子体晶体-4 （PK-4）实验的目标是研究复杂等离子体在零重力下受到离子和中性流碰撞力的行为。理论模型预测了离子和中性的流动模式，但从未实际测量过。加州理工学院的这个研究项目将开发一种诊断方法来测量这些流量。新的诊断将被开发用于德国PK-4实验的地面复制品，由此产生的测量结果将用于预测空间实验中的离子和中性流。这项工作是符合国家利益的基础科学，因为它揭示了占据可见宇宙大部分的物质状态的重要行为，但目前对其知之甚少。将利用加州理工学院现有的复杂等离子体实验开发用于流量测量的激光诱导荧光（LIF）诊断。诊断将通过调谐激光来补偿多普勒频移来确定离子和中性的速度，并将使用它来测量先前未确定的离子和中性的流动模式。加州理工学院的实验与PK-4实验的不同之处在于，尘埃颗粒由自发形成的水冰粒组成，而不是机械引入的固定大小的等离子体球体，但这种差异对于LIF开发的目的没有意义。LIF诊断将利用加州理工学院现有的大量硬件、以前LIF研究的专业知识，以及新的超窄带可调谐二极管激光器，这些激光器将提供出色的速度分辨率。还将对未来可能在国际空间站进行的微重力实验进行调查。通过提供一种更好地理解控制PK-4实验的潜在动力学的方法，提出的研究可能会揭示新的PK-4操作模式，其中有更好地控制中性，离子或分子流动或新的和有趣的制度。在加州理工学院开发的过程中，LIF诊断将解决加州理工学院实验中冰粒如何生长以及为什么这种生长饱和的关键问题；回答这个问题将对原行星吸积盘的天体物理模型产生重大影响。该奖项是在“NASA/NSF关于尘埃等离子体科学的合作伙伴关系：利用国际空间站上的PK-4设施”下颁发的；在联合项目下，NASA还将设立一个补充奖，以支持一名本科生。

This project will develop a way to measure the flows of ionized and neutral atoms in a dusty plasma, the material from which stars and planets begin to form. The so-called dusty, or complex, plasma consists of not only ions, electrons, and neutral atoms, but also has large numbers of tiny dust grains that are a few thousandths of a millimeter in diameter. Although small by human standards, these grains are many billions of times heavier than ions. The grains are continuously hit by ions and neutrals and these collisions can cause the grains to move in interesting ways. Because of the grains' size, they are affected by gravity and tend to fall in Earth-based experiments. The Plasma Krystal-4 (PK-4) experiment on board the International Space Station has the goal of studying the behavior of complex plasmas in zero gravity while subject to the forces from collisions from the ion and neutral flows. The ion and neutral flow patterns have been predicted by theoretical models but have never been actually measured. This Caltech research program will develop a diagnostic to measure these flows. The new diagnostic will be developed for use on a terrestrial replica of the PK-4 experiment located in Germany, and the resulting measurements will be used to predict the ion and neutral flows in the space-borne experiment. This work is fundamental science in the national interest because it reveals important behavior of the state of matter that occupies much of the visible Universe, but for which very little is now known.The laser induced fluorescence (LIF) diagnostic for the flow measurements will be developed using an existing complex plasma experiment at Caltech. The diagnostic will determine the ion and neutral velocities by detuning the laser to compensate for Doppler shifts and will use this to measure previously undetermined ion and neutral flow patterns. The Caltech experiment differs from the PK-4 experiment by having the dust grains consist of spontaneously-formed water ice grains rather than mechanically-introduced fixed-size plasma spheres, but this difference is of no significance for the purpose of LIF development. The LIF diagnostic will take advantage of substantial existing hardware at Caltech, expertise from previous LIF research, and new ultra-narrow-band tunable diode lasers that will provide excellent velocity resolution. Investigation of future microgravity experiments that could be carried out on the International Space Station will also be done. By providing a means for better understanding the underlying dynamics governing the PK-4 experiment, the proposed research is likely to reveal new PK-4 operational modes where there is better control of neutral, ion, or molecular flows or new and interesting regimes. In the course of being developed at Caltech, the LIF diagnostic will address the critical question of how ice grains grow in the Caltech experiment and why this growth saturates; answering this question will have substantial impact on astrophysical models of protoplanetary accretion disks. This award is made under a "NASA/NSF Partnership on Science of Dusty Plasmas: Utilizing the PK-4 Facility on board the International Space Station"; a complementary NASA award to support an undergraduate student is being made under the joint program.