Shocks and Oscillations in the Dynamics of Expanding Coulomb Clouds

这个项目将探索更好地控制电子束的可能性。电子束在科学、技术和医学中的应用非常广泛，包括半导体器件制造和接近皮肤表面的癌症的放射治疗。这项研究特别关注用于在很短的时间和长度尺度上对最基本的原子水平过程进行成像的电子束，这项技术被称为“制作分子电影”。这些电影为复杂分子和材料中发生的原子过程提供了独特的见解，有可能为量子计算等下一代颠覆性技术设计新的设备。高强度电子束中的电子处于空间电荷主导区域，在这种区域中，强大的库仑斥力会导致发射度增加等有害效应。这个项目的一个关键方面是利用分析流体模型和大规模计算研究的组合，发展了扩展库仑云和光束中的动力激波的概念。一个令人惊讶的预测是，动态激波的形成可能提供了一种通过明智地使用束流孔径来减少发射度的途径。我们称这种效应为库仑冷却，因为它与囚禁原子实验中所用的蒸发冷却有一些相似之处。还将探索将这些模型和方法应用于其他背景下产生的等离子体，如天体物理和星系团物理。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will explore possibilities for better control of electron beams. Electron beams are used in an enormous variety of applications in science, technology and medicine, including semiconductor device fabrication and in radiation treatment of cancers which are close to the skin surface. This study is particularly focused on electron beams utilized for imaging the most fundamental atomic level processes at very short time and length scales, a technology that has been called "making the molecular movie". These movies provide unique insights into atomic processes occurring in complex molecules and materials, potentially enabling design of new devices for next generation disruptive technologies such as quantum computing.The electrons in high intensity electron beams are in the space charge dominated regime where strong Coulomb repulsion leads to deleterious effects such as emittance growth. A key aspect of this project develops the concept of dynamical shocks in expanding Coulomb clouds and beams, using a combination of analytic fluid models and large scale computational studies. A surprising prediction is that dynamical shock formation may provide an avenue for reducing emittance by judicious use of beam apertures. We call this effect Coulomb cooling as it has some similarities with evaporative cooling utilized in trapped atom experiments. Applications of the models and methods to plasmas arising in other contexts, such as astrophysics and cluster physics, will also be explored.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.