权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Experimental characterisation of shock waves launched by high intensity laser interaction with over-dense media

高强度激光与过密介质相互作用发射的冲击波的实验表征

基本信息

批准号：
EP/I030018/1
负责人：
John Pasley
金额：
$ 12.53万
依托单位：
University of York
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI030018%2F1
关键词：
Experimental characterisation shock waves launched

项目摘要

I propose a programme of experiments to develop and then utilise a novel diagnostic technique to better understand the formation of shock waves in the immediate vicinity of a high intensity laser interaction with over-dense plasma*. Ultra-high intensity lasers offer the ability to generate some of the most extreme conditions available to scientists here on earth. However it can be challenging to experimentally diagnose the behaviour where it is at its most extreme: within a few picoseconds and a few microns of the interaction. This is particularly true of the hydrodynamic behaviour that results from such interactions, since such observations typically rely upon detection of macroscopic motion of fluid which may take many tens of picoseconds to become apparent. Here we propose to use the Doppler shift of a short wavelength probe laser to interrogate the expanding shock wave as it forms near the laser focus. This diagnostic relies upon the high velocity of the shocked fluid Doppler-shifting the reflected laser light, rather than upon it examining how far perturbations in the fluid have travelled. Therefore it is capable of resolving shock waves when they are forming, and well before the motion of the fluid would be detectable by more conventional x-ray diagnostic techniques, which typically have resolutions on the order of 15-20 microns. A preliminary experiment has been performed, and the results published in Physical Review Letters in September 2010. This experiment used a solid density target, however, greatly limiting the possibilities for extracting information on shock wave behaviour, since most of the target was opaque to the probe laser. Here we plan to employ low density foam targets which are over-dense to the pump pulse, but only become over-dense to the probe when strongly shocked. The use of such targets allows for the shock wave evolution to be observed from all angles, and also for the possibility of determining if there are multiple regions of shock formation, since it is likely that, in some cases, shock waves will be launched both by the direct action of the laser and indirectly by laser generated energetic electrons that deposit their energy deep within the target. The data obtained is of interest for understanding the behaviour of extremely strong shock waves such as occur in extreme astrophysical scenarios like supernovae; it is also of tremendous relevance to the fast ignition approach to inertial fusion energy, where similarly intense laser pulses are used to heat fusion fuel. The physics responsible for launching shock waves in this scenario is not well understood. Gaining a clearer insight into the relative importance of the various mechanisms responsible is critical to progress in this field, since the behaviour of the shock waves in a fast ignition target directly affects the ignition process and plays a role in determining the required laser specifications for ignition. These experiments will provide critical data that will enable the benchmarking of sophisticated computer simulation codes that can then be applied to the design of fast ignition fusion targets.* Over-dense plasma is that in which a laser beam of a given frequency can no longer propagate due to the density of the electron gas being sufficiently high that oscillatory electron motion is readily established at the frequency of the laser; specifically it refers to plasma in which the electron plasma frequency exceeds the frequency of the laser radiation. At very high laser intensities the density at which the plasma meets this criterion increases due to the effective mass of the electrons increasing, as they are accelerated to relativistic velocities in the field of the laser.

我提出了一个实验计划，以开发并利用一种新的诊断技术，以更好地了解高强度激光与过高密度等离子体相互作用附近冲击波的形成*。超高强度激光提供了产生地球上科学家所能获得的一些最极端条件的能力。然而，在行为最极端的地方，在几皮秒和几微米的相互作用范围内，对行为进行实验诊断可能是具有挑战性的。这种相互作用导致的流体动力学行为尤其如此，因为这种观测通常依赖于对流体宏观运动的检测，而宏观运动可能需要数十皮秒才能变得明显。在这里，我们建议使用短波长探测激光的多普勒频移来询问在激光焦点附近形成的膨胀冲击波。这种诊断依赖于受冲击的流体的高速多普勒移动反射的激光，而不是依靠它来检查流体中的扰动已经传播了多远。因此，它能够在冲击波形成时和流体运动被更传统的X射线诊断技术检测到之前分解冲击波，传统的X射线诊断技术通常具有15-20微米的分辨率。已经进行了初步实验，结果发表在2010年9月的《物理评论快报》上。然而，这个实验使用的是固体密度靶，极大地限制了提取冲击波行为信息的可能性，因为大多数靶对探测激光是不透明的。在这里，我们计划使用低密度泡沫靶，这些靶对泵浦脉冲来说密度过高，但只有在强烈冲击时才会变得对探测器来说过密。使用这种靶可以从所有角度观察冲击波的演变，还可以确定是否存在多个激波形成区域，因为在某些情况下，激波很可能既由激光的直接作用发射，又由激光产生的高能电子间接发射，激光产生的高能电子将其能量储存在目标的深处。获得的数据对于理解极强冲击波的行为很有意义，例如在超新星等极端天体物理场景中发生的冲击波；它也与惯性聚变能量的快速点火方法密切相关，在这种方法中，类似强度的激光脉冲被用于加热聚变燃料。在这种情况下发射冲击波的物理机制还没有得到很好的理解。更清楚地了解各种机制的相对重要性对这一领域的进展至关重要，因为激波在快速点火目标中的行为直接影响点火过程，并在确定点火所需的激光规格方面发挥作用。这些实验将提供关键数据，以便能够对复杂的计算机模拟代码进行基准测试，然后将这些代码应用于快速点火聚变目标的设计。*过密集等离子体是指由于电子气的密度足够高而使给定频率的激光束不能再传播，从而很容易在激光的频率上建立电子振荡运动；具体地说，它指的是电子等离子体频率超过激光辐射频率的等离子体。在很高的激光强度下，由于电子的有效质量增加，当电子在激光场中加速到相对论速度时，满足这个标准的等离子体密度会增加。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Ultrafast dynamics of a near-solid-density layer in an intense femtosecond laser-excited plasma

DOI：
10.1063/1.4882675
发表时间：
2014-06
期刊：
Physics of Plasmas
影响因子：
2.2
作者：
A. Adak;D. Blackman;G. Chatterjee;P. Singh;A. D. Lad;P. Brijesh;A. Robinson;J. Pasley;G. Kumar
通讯作者：
A. Adak;D. Blackman;G. Chatterjee;P. Singh;A. D. Lad;P. Brijesh;A. Robinson;J. Pasley;G. Kumar

Probing ultrafast dynamics of solid-density plasma generated by high-contrast intense laser pulses

DOI：
10.1063/1.5005176
发表时间：
2018
期刊：
Physics of Plasmas
影响因子：
2.2
作者：
K. Jana;D. Blackman;M. Shaikh;A. D. Lad;D. Sarkar;I. Dey;A. Robinson;J. Pasley;G. Kumar
通讯作者：
K. Jana;D. Blackman;M. Shaikh;A. D. Lad;D. Sarkar;I. Dey;A. Robinson;J. Pasley;G. Kumar

Role of low temperature resistivity on fast electron transport in disordered aluminium and copper