RUI: Collaborative Research: Collisionless Heating During Strong Field Irradiation of Wavelength-scale Particles

RUI：合作研究：波长尺度粒子强场照射过程中的无碰撞加热

• 批准号: 0757989
• 负责人: Thomas Donnelly
• 金额: $ 16.6万
• 依托单位: Harvey Mudd College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0757989&HistoricalAwards=false
• 关键词: RUI; Collaborative; Research; Collisionless; Heating

The physics of the interaction of intense laser light with plasma when wavelength-scale particles are irradiated is investigated. While the nature of strong field interactions with atoms, molecules, small clusters and planar solids has been studied extensively for many years, how intense laser pulses interact with objects that are of a spatial scale comparable to the light?s wavelength is largely unexplored. These interactions are likely to exhibit properties which are quite distinct from the interactions of intense pulses with single atoms and molecules on one hand and large planar solid plasmas on the other. This work fills this gap in strong field physics with careful, well-designed experiments that isolate the effects which are peculiar to wavelength-scale targets. Previously, our investigations showed that strong field interactions could be enhanced by an appropriate choice of target particle size. Boundary conditions imposed by the particles create Mie enhancements in the local laser field and thereby increase the nonlinear response of the interaction. The specific focus of the current work is motivated by an important question that arose from our previous experimental and computation studies: is the nature of collisionless absorption by hot electrons around wavelength-scale plasmas different from collisionless absorption from a simple planar solid? A number of theories have recently surmised that such absorption is different at these scales, dominated by what has been termed multi-pass stochastic heating, in which hot electrons can absorb energy from the laser field by passing back and forth multiple times through the micron-scale plasma. This novel heating mechanism has been suggested as being important in a number of experiments and particle-in-cell simulations but there has as yet been no systematic experimental investigation. The current studies are designed to address this shortcoming. The experiments are designed to directly measure the electron and ion distributions generated in the collisionless heating process, and, by studying specific scalings in particles of well defined size, ascertain the importance or existence of this stochastic heating mechanism. The studies utilize a 20 TW, high temporal contrast laser at UT, electron and ion energy diagnostics, and a novel electrostatic particle injector as a target. These experiments are complemented by simulations using codes available at UT. The work is done through a unique collaboration between an academic research lab at the University of Texas and at Harvey Mudd College (HMC), an undergraduate institution. Application of these kinds of studies may aid in the development of novel bright, laser-driven x-ray sources for radiography and time resolved diffraction, or compact neutron sources for imaging of other scientific applications. In addition to these scientific impacts, this collaborative work promises to make a significant and somewhat novel impactin graduate and undergraduate education. In addition to its scientific merit, and support of graduate student research at UT, this research significantly adds to the scope and number of research opportunities available to physics undergraduate students at HMC. This work represents a unique situation in which an undergraduate group is involved directly and in a critical way in larger scale strong field optics research, a field which is otherwise prohibitively resource intensive for undergraduate-level research alone. The PIs have an excellent record of working together and meaningfully involving undergraduates in their collaborations. Undergraduates have the opportunity to do research at HMC, travel to UT in the summers to participate in research using equipment they have developed, and travel to conferences to present their work to the scientific community. This collaboration will continue to be an effective way to motivate undergraduates to seeking advanced degrees in science. Furthermore the PIs will continue to disseminate their work through publication in appropriate peer-reviewed journals and international conference as they have done actively during the past funding period.Funds for this award are provided by the Physics Division within the NSF's Mathematics and Physical Sciences Directorate and the Office of Fusion Energy Sciences of the DoE within the context of the NSF/DOE Partnership in Basic Plasma Science and Engineering.

研究了照射波长级粒子时强激光与等离子体相互作用的物理现象。虽然多年来人们已经广泛研究了与原子、分子、小团簇和平面固体之间的强场相互作用的性质，但强烈的激光脉冲如何与空间尺度与光波长相当的物体相互作用却很大程度上尚未被探索。这些相互作用可能表现出与强脉冲与单个原子和分子以及另一方面与大平面固体等离子体的相互作用截然不同的特性。这项工作通过仔细、精心设计的实验来隔离波长尺度目标特有的影响，从而填补了强场物理领域的这一空白。此前，我们的研究表明，通过适当选择目标颗粒尺寸可以增强强场相互作用。粒子施加的边界条件在局部激光场中产生米氏增强，从而增加相互作用的非线性响应。当前工作的具体重点是由我们之前的实验和计算研究中提出的一个重要问题所激发的：波长级等离子体周围热电子的无碰撞吸收的性质是否不同于简单平面固体的无碰撞吸收？许多理论最近推测，这种吸收在这些尺度上是不同的，主要是所谓的多程随机加热，其中热电子可以通过多次来回穿过微米来吸收来自激光场的能量。规模等离子体。这种新颖的加热机制在许多实验和细胞内粒子模拟中被认为很重要，但迄今为止还没有系统的实验研究。当前的研究旨在解决这一缺点。这些实验旨在直接测量无碰撞加热过程中产生的电子和离子分布，并通过研究明确尺寸的颗粒的特定比例，确定这种随机加热机制的重要性或存在。这些研究利用 UT 中的 20 TW、高时间对比度激光、电子和离子能量诊断以及新型静电粒子注入器作为目标。使用 UT 提供的代码进行模拟对这些实验进行了补充。这项工作是通过德克萨斯大学学术研究实验室和本科院校哈维穆德学院 (HMC) 之间的独特合作完成的。此类研究的应用可能有助于开发用于射线照相和时间分辨衍射的新型明亮激光驱动 X 射线源，或用于其他科学应用成像的紧凑中子源。除了这些科学影响之外，这项合作工作有望对研究生和本科生教育产生重大且有些新颖的影响。除了其科学价值和对 UT 研究生研究的支持之外，这项研究还显着增加了 HMC 物理本科生的研究机会的范围和数量。这项工作代表了一种独特的情况，其中本科生群体直接并以关键方式参与更大规模的强场光学研究，否则该领域仅对本科水平的研究而言就需要大量资源。 PI 有着良好的合作记录，并且让本科生有意义地参与他们的合作。本科生有机会在 HMC 进行研究，在夏季前往 UT 使用他们开发的设备参与研究，并参加会议向科学界展示他们的工作。这种合作将继续成为激励本科生寻求科学高级学位的有效方式。此外，PI 将继续通过在适当的同行评审期刊和国际会议上发表文章来传播他们的工作，就像他们在过去的资助期间积极所做的那样。该奖项的资金由 NSF 数学和物理科学理事会的物理部门提供，美国能源部聚变能源科学办公室在 NSF/DOE 基础等离子体科学与工程伙伴关系的背景下。