Ultrafast laser-driven ion interactions in matter: Evolving dose distribution at the nanoscale and nonlinear response

在物理学中，标度定律提供了一个双重功能。首先，它们可以通过建立系统如何响应变化或扰动来揭示控制系统的潜在物理机制。这是特别真实的非线性标度律，在输入扰动的微小变化可能导致系统的响应的巨大变化。其次，标度律为研究人员提供了一种工具，他们可以用它来预测一个系统在给定的输入参数下将如何演化。这是朝着提供高度针对性的尖端应用迈出的关键一步。正是在这个框架内，我们建议研究的超快动力学，从物质中的离子相互作用，以确定如何与入射离子通量的介质尺度的特征响应。 为了直接研究任何超快过程，使系统发生变化的扰动明显短于系统的自然恢复时间是至关重要的。如果扰动比这个恢复时间长得多，那么在一次相互作用中就会有重复的激发和弛豫循环。这抑制了在没有复杂的近似和假设的情况下提取关于系统的基本信息的能力。不幸的是，到目前为止，这一直是研究物质中离子相互作用的首要问题。已经从大型加速器设施获得的离子脉冲的持续时间为100皮秒，其显著长于物质响应于照射的飞秒和几皮秒特征恢复时间。因此，与离子物质相互作用的最早可达阶段有关的现有实验结果具有过大的相关不确定性。我们的方法通过使用激光驱动离子加速器产生超快离子脉冲来克服这个问题。这种性能将允许在飞秒和皮秒时间尺度上研究物质中高能离子（> 1 MeV/核子）的停止。我们将利用这种能力来了解如何通过改变离子的入射通量来控制由此产生的平衡途径，并研究这为辐射化学和强子疗法的高级应用提供的新的可能性。贝尔法斯特女王大学等离子体物理中心目前正在建造世界上能量最高的少光周期激光系统TARANIS-X，预计将于2016年底上线。这种独特的环境将使我们能够产生迄今为止在实验室中产生的最短的离子脉冲。有了这种最先进的设备，就有可能在真实的时间内测试物质中离子相互作用的基本极限。了解这种行为是这项研究的一个关键目标。特别是将这些实验扩展到水中的离子相互作用，将使我们能够研究强子（或离子束）治疗期间剂量输送的新模式的潜力。这是因为水占人体细胞的70%以上，因此它是研究电离辐射对人体影响的理想系统。最后，这一建议的关键动机之一是在低时间分辨率的实验，以支持这项工作的科学情况下，离子通量的非线性响应的指示。与我们在德国（慕尼黑）和美国（得克萨斯州）的国际合作伙伴一起，我们将研究多种不同的相互作用机制，以确定这种非线性响应的缩放，并与GEANT 4 DNA合作，我们将开发数值方法，以形成对其管理的缩放定律（或定律）的清晰理解。

In physics, scaling laws provide a dual function. First, they can reveal the underlying physical mechanisms that govern a system by establishing how the system responds to changes or perturbations. This is particularly true of nonlinear scaling laws where small changes in an input perturbation can lead to dramatic changes in the response of the system. Secondly scaling laws provide researchers with a tool that they can use to predict how a system will evolve for a given set of input parameters. This is a crucial step towards providing highly-targeted, cutting-edge applications. It is within this framework that we propose to study the ultrafast dynamics that result from ion interactions in matter to determine how the characteristic response of the medium scales with the incident ion flux. To study any ultrafast process directly it is critical that the perturbation causing the system to change is significantly shorter than the natural recovery time of the system. If the perturbation is significantly longer that this recovery there will be repeated cycles of excitation and relaxation within a single interaction. This inhibits the ability to extract fundamental information about the system without complicated approximations and assumptions. Unfortunately, to date, this has been the overriding problem for the study of ion interactions in matter. The ion pulses that have been available from large accelerator facilities have been 100's of picoseconds in duration which is significantly longer than the femtosecond and few picosecond characteristic recovery times of matter in response to irradiation. Accordingly, existing experimental results relating to the earliest accessible stages of ion matter interactions have prohibitively large associated uncertainties. Our approach overcomes this issue by generating ultrafast pulses of ions using laser driven ion accelerators. This performance will allow the stopping of energetic ions (> 1 MeV/nucleon) in matter to be studied on femtosecond and picosecond timescales. We will use this capability to understand how the resulting pathways to equilibrium can be controlled by varying the incident flux of ions and investigate the new possibilities this offers for advanced applications in both radiation chemistry and hadrontherapy. The Centre for Plasma Physics in Queen's University Belfast is currently constructing the world's highest energy few-optical-cycle laser system, TARANIS-X, due to come online in late 2016. This unique environment will allow us to generate the shortest pulses of ions produced in the laboratory to date. With this state of the art facility it will be possible to test, in real time, the fundamental limits of ion interactions in matter. Understanding this behaviour is a key goal of this research. In particular extending these experiments to ion interactions in water will allow us to investigate the potential for new modalities of dose delivery during hadron (or ion beam) therapy. This is because water makes up over >70% of human cells and so it makes for an ideal system in which to study the effects of ionising radiation in the human body. Finally, one of the key motivators for this proposal is the indication of nonlinear response with respect to ion flux in low temporal resolution experiments performed to support the scientific case for this work. Together with our international partners in Germany (Munich) and the U.S. (Texas) we will investigate multiple different interaction regimes to determine the scaling of this nonlinear response and, in partnership with the GEANT4 DNA collaboration, we will develop numerical approaches to form a clear understanding of the scaling law (or laws) that governs it.