Benchmarking collisional rates and hot electron transport in high-intensity laser-matter interaction

“高强度激光与物质的相互作用已被证明是一种多功能的高能质子源，具有理想的特性（例如超短持续时间），这是传统源无法实现的。这些特点可以促进诸如高剂量率放射生物学等具有社会影响的应用。在质子加速过程中，激光能量通过一个多步骤的过程转移到质子束，在这个过程中，目标材料被迅速电离，并产生一群高能量电子。正是这些“热”电子控制着目标材料的演变，以及由此产生的质子束的性质，决定了其应用的适用性，这些应用还包括医学同位素生成、材料测试和辐射损伤测试，以及与天体物理学和聚变能相关的基本高能密度（HED）物理学的探索。用飞秒时间分辨率测量“热”电子居群和致密等离子体目标的演化对于精确模拟从激光到质子束的能量转移以及优化这些辐射源以发挥其潜力至关重要。最近证明了一种新的诊断技术，该技术允许飞秒分辨率测量材料的超快速激发和弛豫。这依赖于共振激发的x射线线发射，它是由来自XFEL的高亮度、窄带宽x射线脉冲驱动的。通过利用结合了XFEL和高强度激光器的设备，这种诊断技术将允许前所未有的深入了解激光能量转移到质子束的超快速过程。此外，通过利用现代高强度激光器的新高重复率能力，可以利用诊断和实验控制之间的在线反馈来有效地绘制激光驱动质子加速的多维参数空间，并最佳地利用世界一流的设施。通过这种方法可以获得的高价值数据的大量增加也使跨学科工作能够利用新颖的机器学习工具来增强对基础HED物理学关键过程的理解，并加深对激光等离子体加速器的理解，从而促进其作为应用工具的发展。”

"The interaction of high-intensity lasers with matter has been demonstrated as a versatile source of energetic protons with desirable characteristics (e.g. ultra-short durations) that cannot be achieved with conventional sources. These characteristics could facilitate societally-impactful applications such a high-dose rate radiobiology. During the acceleration of the protons, the laser energy is transferred to the proton beam via a multi-step processes in which the target material is rapidly ionised and a population of highly energetic electrons are produced. It is these 'hot' electrons that govern the evolution of the target material and the properties of the resultant proton beam determining its suitability for applications which also include medical isotope generation, materials testing and radiation damage testing, and exploration of fundamental high-energy density (HED) physics of relevance to astrophysics and fusion energy. Measurement of the evolution of the 'hot' electron population and the dense plasma target with femtosecond temporal resolution is crucial to accurately model the transfer of energy from the laser to the proton beam and to optimise these radiation sources to fulfil their potential. A novel diagnostic technique which allows femtosecond resolution measurements of the ultra-fast excitation and relaxation of a material has recently been demonstrated. This relies upon resonantly stimulated x-ray line emission, which is driven using high-brightness, narrow bandwidth x-ray pulses from an XFEL. By utilising facilities which combine an XFEL and a high-intensity laser, this diagnostic technique will allow unprecedented insight into the ultra-fast process of laser energy transfer to proton beams. In addition, by exploiting the new high-repetition rate capability of modern high-intensity lasers, it is possible utilise online feedback between the diagnostics and experimental controls to efficiently map the multi-dimensional parameter space of laser-driven proton acceleration and optimally exploit access to world-class facilities. The huge increase in high-value data that can be obtained via this methodology also enables inter-disciplinary work employing novel machine learning tools to enhance understanding of processes key to fundamental HED physics as well as deepening understanding of laser plasma accelerators thereby facilitating their development as tools for applications. "