Next generation laser-driven neutron sources for ultrafast studies

中子是原子的基本粒子之一，不带电荷。由于它们独特的到达原子核的能力，中子为物质物理学的许多方面提供了独特而有价值的见解，超出了任何带电粒子或电离辐射探测器的能力。我们现在看到的世界是在我们现有的中子探测器的极限上--关键的限制是时间分辨率。使用中子作为泵或探针进行超快（比百万分之一秒快得多）研究的可能性尚未被考虑，因为不存在如此短的中子脉冲的高通量源。由于激光技术和相关领域的持续发展，获得超强激光脉冲（远高于10^15瓦的脉冲功率，聚焦到人类头发直径的一小部分）已经开辟了等离子体物理学研究的几条新途径。其中之一是由强激光压力（也称为辐射压力（RP））驱动的离子加速的新兴场。取决于激光和目标参数，相互作用产生中等动能（对应于1000 Km/sec的速度）和高马赫数的近固体密度射流，或者超高能量的单能和准直离子脉冲（比射流离子高几个数量级）。该方案旨在开发、测试和应用一种新型的基于激光的中子源，利用RP驱动离子束前沿的独特参数组合，由于该源是由高效的激光驱动离子加速机构加速的离子驱动的，因此它为激光技术的快速发展奠定了下一代中子装置的基础。具有增强特性的源将使我们能够在从物理学到生物学的广泛学科中扩展对超快分子动力学的理解。激光驱动源可以在降低成本和紧凑性、减少放射性污染以及通过闭合耦合辐照实验进行辐射约束的能力方面带来进一步的优势，这将使该源对于工业、技术和医学应用（例如基于采用中子的新颖的、非常有前途的技术的癌症治疗中心）更具吸引力。

Neutrons are one of the fundamental particles of an atom with no charge. Because of their unique ability to reach nuclei, neutrons provide unique and valuable insights to many aspects of the physics of matter beyond the capability of any charged particle or ionizing radiation probes. We are now seeing the world at the very limits of our existing neutron probes - the key limitation being the temporal resolution. The possibility of ultrafast (significantly faster than a millionth of a second) studies using neutrons, either as a pump or a probe, has not yet been considered because no high flux sources of such short neutron pulses exist. Thanks to the continuing developments in laser technology and related areas, access to ultra-intense laser pulses (well above 10^15 watts of pulsed power focussed down to a spot of a fraction of the diameter of human hair) has opened several new avenues of research in plasma physics. One of them is the bourgeoning field of ion acceleration driven by the intense laser light pressure (also called radiation pressure (RP)). Depending on laser and target parameters, the interaction produces either moderate kinetic energy (corresponding to a speed of 1000 Km/sec) and near solid density jets of high Mach numbers, or mono-energetic and collimated ion pulses of ultra-high energy (orders of magnitude higher than the jet ions). The proposal is aimed to develop, test and apply a novel laser based neutron source, exploiting the unique combination of parameters at the frontier of RP driven ion bunches, Since the source is driven by the ions accelerated by a highly efficient laser driven ion acceleration mechanism, it lays a foundation towards next generation neutron facility in light of the rapid development in laser technology. The source with enhanced characteristics will enable expansion of our understanding of ultrafast molecular dynamics in a wide range of discipline, from physics to biology. A laser driven source may bring further advantages in terms of cost reduction and compactness, reduction of radioactive pollution and ability of radiation confinement by closed-coupled irradiation experiments, which will make the source more appealing for industrial, technological and medical applications, such as cancer therapy centre based on a novel, highly promising technique employing neutrons.