CAREER: Bright Femtosecond x- and Gamma-Ray Pulse Production Using Ultra-Intense Lasers

该项目的研究目标是测量和模拟高强度激光-等离子体相互作用中产生的电子束的电磁相互作用所产生的辐射特性和复杂的电子动力学。传统的加速器设备必须很大，因为当电势差达到某个阈值时，加速场受到材料电击穿的限制。能量增益是力乘以距离，所以如果场强(也就是力)是有限的，那么必须增加距离以获得越来越高的粒子能量。这导致了许多英里规模的设施正在建设中。然而，如果我们使用完全电离的气体--等离子体--事实证明，可以产生一个加速结构，它不受场强的限制。换句话说，加速器可以微型化。基于等离子体的加速器中惊人的场强通常相当于一个2英里的传统加速器被缩减到半米长。等离子体加速器可以使用高强度激光来制造，这种激光会产生一个真空的离子腔，或者说是具有强大加速电场的“气泡”。事实证明，这种等离子体“气泡”也具有理想的特性，可以提供一种微型摇摆器结构；它是产生辐射的外部磁性结构(如1英里长的SLAC的LCLS延伸件)的替代方案。因此，等离子体既可以是加速器，也可以是摇摆器。或者，也可以使用第二束激光来摆动电子。在这两种情况下，类多普勒效应意味着相对论电子束发出的辐射被上移到比振荡结构的频率高得多的频率。因此，激光和等离子体的结合可以提供非常强烈、能量很高的x射线和伽马射线源。从帮助开发抗流感药物瑞乐沙或口蹄疫疫苗，到成像飞机机翼上的残余应力，或者通过分析贝多芬的头发样本来确定贝多芬是否中毒，人们对辐射源的研究受到了众多应用的推动。这推动了世界各地大型X射线光源的发展。这里提出的研究具有基础性，但也具有令人兴奋的适用性和潜在的技术影响。关于激光传播、等离子体行为和辐射产生，还有大量悬而未决的问题有待探索。然而，与这项研究相关的最令人兴奋的事情之一是微型和廉价的同步辐射光源的潜力，这种光源可以更广泛地获得；大学、小型研究机构或医院都可以使用。这可能会给一大批科学和工程学科带来革命性的变化，因为从生物技术到机械工程的研究人员目前正在等待现有的同步辐射光源。因此，更多地获得明亮的X射线光源可以促进许多领域的技术发展进步。

The research objective of this project is to measure and model the properties of radiation, and the complex electron dynamics, resulting from the electromagnetic interaction of electron beams generated in high-intensity laser-plasma interactions. Conventional accelerator facilities must be large because the accelerating fields are limited by electrical breakdown of the material when the potential difference reaches some threshold. Energy gain is force times distance, so if the field strength (and therefore force) is limited then the distance must be increased to achieve higher and higher particle energies. This has lead to many mile scale facilities being constructed. However, if we use completely ionized gas -- plasma -- it turns out that an accelerating structure can be generated that is not limited in field strength. In other words; an accelerator can be miniaturized. The astonishing field strength in a plasma based accelerator can typically be equivalent to a 2 mile conventional accelerator being reduced to half a meter in length. Plasma accelerators can be created using high intensity lasers, which generate an evacuated ionic cavity, or 'bubble' with strong accelerating electric fields. It turns out that this plasma 'bubble' also has ideal characteristics for providing a miniature wiggler structure; an alternative to an external magnetic structure (such as the 1 mile length LCLS extension to SLAC) for generating radiation. The plasma can therefore be both an accelerator and wiggler combined. Alternatively, a second laser beam can also be used to wiggle the electrons. In both caes, a Doppler-like effect means that the radiation emitted by the relativistic electron beam is upshifted to much higher frequencies than those of the oscillating structure. The combination of lasers and plasmas can therefore provide very intense, energetic sources of x and gamma rays.The drive for radiation sources is prompted by the numerous applications, from aiding the development of the anti-flu drug Relenza or a vaccine for foot and mouth disease to imaging residual stresses in aircraft wings or determining whether Beethoven was poisoned by analysis of a sample of his hair. This has motivated the development of large x-ray light sources around the world. The research proposed here is of a fundamental nature but also with an exciting applicability and potential technological impact. There are a vast number of unanswered questions on the laser propagation, plasma behavior, and radiation generation to be explored. However, one of the most exciting things associated with the research is the potential for miniature and inexpensive synchrotron light sources that could be available more widely; accessible to universities, small research facilities or hospitals. This could revolutionize a vast swath of scientific and engineering disciplines, as researchers from biotechnology to mechanical engineering are currently waiting for time on existing synchrotron light sources. Increased access to brilliant x-ray light sources could therefore increase the progress of technologic development in many fields.