Collaborative Research: Plasma Physics At Small Coulomb Logarithms

合作研究：小库仑对数下的等离子体物理

• 批准号: 1714144
• 负责人: Michael Murillo
• 金额: $ 1.5万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-07 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1714144&HistoricalAwards=false
• 关键词: Collaborative; Research; Plasma; Physics; Small

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.

这个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。人们可以通过比较高速离子碰撞的能量和它们之间的电磁力来测量碰撞的剧烈程度。最剧烈的离子碰撞，对于扩展我们的科学知识和发展技术应用都是最重要的，是非常难以测量或计算的。它们发生在极热、密度极高的带电粒子气体中，这种气体被称为等离子体。在这个项目中，新的想法将被用来测量和理解这些碰撞。激光将用于减慢原子的速度，从每秒近1000米的速度降至每秒约一英寸的爬行速度；然后把这些慢速原子变成离子。然后将使用额外的激光来测量这些离子如何相互碰撞。这些慢动作碰撞中的离子与离子-离子电作用力相比具有相同的碰撞能量，这意味着碰撞结果可以直接与任何能量的类似碰撞进行比较。该项目将使用最先进的大型计算机模拟来制作离子-离子碰撞的电影，并将其与实验测量结果进行比较。当计算被证明是足够精确时，将逐渐引入近似并进行测试，以加快计算速度。这些结果将为等离子体中离子碰撞的精确和快速计算设定标准。几名学生将参与这个项目：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较小的系统中的能量松弛。这是高能量密度系统的典型现象，剧烈的小碰撞参数碰撞会导致大的粒子偏转。了解这些碰撞是推进基础等离子体物理学和准确模拟高能量密度等离子体中的小冲击参数碰撞的优先事项。拟议的工作将在传统诊断受到限制的血浆状态中产生高质量的数据。提出的工作将结合新的双种超冷中性等离子体实验数据和最先进的模拟来研究中等耦合等离子体的温度平衡，其中经典等离子体假设无效。双种等离子体将在相同的磁光阱中通过共振光电离激光冷却的Yb和Ca原子产生。激光诱导荧光测量将用于同时测量每种离子的随时间变化的离子速度分布。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、化学计量和几何形状。计算将通过直接积分多体轨迹提供碰撞过程的第一性原理描述。用动态多体筛分法计算任意复杂的轨道将自一致。多体相动力学将被反转以产生高精度的有效库仑对数，为高能量密度社区提供重要的信息。该项目每年资助杨百翰大学一名研究生，为期三年，杨百翰大学两名本科生，武汉大学两名本科生，南京医学中心两名博士后。