Collaborative Research: Plasma Physics At Small Coulomb Logarithms

这一合作研究项目将促进对高速离子群如何相互碰撞和相互作用的基本理解。人们可以通过比较碰撞中的高速离子的能量和它们之间的电动力来测量碰撞的剧烈程度。最猛烈的离子碰撞，对于扩展我们的科学知识和发展技术应用都是最重要的，非常难以测量或计算。它们出现在极热、密度极高的被称为等离子体的带电粒子气体中。在这个项目中，将使用新的想法来测量和理解这些碰撞。激光将被用来将原子的速度从每秒近1000米减慢到大约每秒一英寸的爬行速度；然后将这些缓慢的原子转化为离子。然后将使用额外的激光来测量这些离子是如何相互碰撞的。与离子-离子电动力相比，这些慢动作碰撞中的离子具有相同的碰撞能量，这意味着可以直接将碰撞结果与任何能量下的类似碰撞进行比较。这个项目将使用最先进的大规模计算机模拟来拍摄离子-离子碰撞的电影，并将这些电影与实验测量结果进行比较。当计算被证明足够准确时，将逐步引入和测试近似，以加快计算速度。这些结果将为准确和快速地计算等离子体中的离子碰撞设定标准。几个学生将在这个项目上工作：本科生、研究生和博士后科学家将与威拉米特大学(俄勒冈州)、杨百翰大学(犹他州)和新墨西哥州联盟(新墨西哥州)的专家科学家密切合作。拟议的合作研究项目将研究库仑对数值很小的系统中的能量松弛。这是典型的高能量密度系统，在这种系统中，剧烈的小参数碰撞会导致大的粒子偏转。理解这些碰撞是推进基础等离子体物理和精确模拟高能量密度等离子体中小碰撞参数碰撞的首要任务。拟议的工作将在传统诊断受到限制的等离子体系统中产生高质量的数据。这项拟议的工作将结合一个新的双物种超冷中性等离子体实验和最先进的模拟来研究中等耦合等离子体中的温度平衡，其中经典的等离子体假设是无效的。双组分等离子体将通过共振光致电离激光冷却Yb和Ca原子在同一磁光陷阱中产生。激光诱导荧光测量将被用来同时测量每个离子物种随时间演化的离子速度分布。通过延迟一种物质相对于另一种物质的电离，可以确定完全能量弛豫的时间尺度。将进行最先进的分子动力学模拟，以匹配实验的密度、化学计量比和几何形状。这些计算将通过直接积分多体轨迹来提供碰撞过程的第一性原理描述。通过动态多体筛选，可以自洽地计算任意复杂的轨道。多体相动力学将被反转，以产生高精度的有效库仑对数，向高能量密度社区提供重要信息。该项目将在三年内支持杨百翰大学每年一名研究生，在杨百翰大学每年两名本科生，在吴大学每年两名本科生，在NMC两年内每年支持一名博士后。

This collaborative research project will advance fundamental understanding of how groups of high speed ions crash into and interact with each other. One can measure just how violent a collision is by comparing the energy of the crashing high-speed ions with the electrical force between them. The most violent ion collisions, the ones that are most important both for extending our scientific knowledge and for developing technological applications, are very difficult to measure or calculate. They occur in extremely hot and very dense gases of charged particles called plasmas. In this project, new ideas will be used to measure and understand these collisions. Lasers will be used to slow atoms from speeds of nearly 1000 meters per second to a crawl of about an inch per second; and then to turn these slow atoms into ions. Additional lasers will then be used to measure how these ions crash into each other. The ions in these slow-motion collisions have the same amount of crash energy compared to the ion-ion electrical force, which means that the collision results can be directly compared to similar collisions at any energy. This project will use state-of-the-art large-scale computer simulations to make movies of the ion-ion collisions and compare these to the experimental measurements. When the computations are proven to be sufficiently accurate, approximations will be gradually introduced and tested in order to speed up the computations. These results will then set the standard for accurate and fast computations of ion collisions in plasmas. Several students will work on this project: Undergraduate and graduate students and post-doctoral scientists will work closely with expert scientists at Willamette University (Oregon), Brigham Young University (Utah), and the New Mexico Consortium (New Mexico).The proposed collaborative research project will investigate energy relaxation in a system in which the value of the Coulomb logarithm is small. This is typical of high-energy-density systems, where violent small-impact-parameter collisions result in large particle deflections. Understanding these collisions is a priority for advancing fundamental plasma physics and for accurately modeling small impact parameter collisions in high energy density plasmas. The proposed work will generate high quality data in plasma regimes where traditional diagnostics are limited. The proposed work will combine data from a new dual-species ultracold neutral plasma experiment and state-of-the-art simulations to study temperature equilibration in moderately coupled plasmas, in which classic plasma assumptions are invalid. The dual-species plasma will be generated by resonantly photo-ionizing laser-cooled Yb and Ca atoms in the same magneto-optical trap. Laser-induced fluorescence measurements will be used to measure the time-evolving ion velocity distribution for each ion species simultaneously. By delaying the ionization of one species relative to the other, the time scale for full energy relaxation can be determined. State-of-the-art molecular dynamics simulations will be performed that match the density, stoichiometry, and geometry of the experiments. The calculations will provide a first-principles description of collision processes by directly integrating many-body trajectories. Arbitrarily complicated orbits will be computed self-consistently with dynamical many-body screening. The many-body phase dynamics will be inverted to yield highly accurate effective Coulomb logarithms, providing important information back to the high energy density community. This project will support one graduate student per year for three years at BYU, two undergraduate students per year at BYU, two undergraduate students per year at WU, and one post-doc per year for two years at NMC.