Physics of Ignition: Collaboration with the National Ignition Facility: Diagnosing Hot-Spot Mix via X-Ray Spectroscopy

点火物理学：与国家点火装置合作：通过 X 射线光谱诊断热点混合物

• 批准号: EP/L000849/1
• 负责人: Justin Wark
• 金额: $ 59.76万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FL000849%2F1
• 关键词: Physics; Ignition; Collaboration; National; Facility

The fusion of light nuclei is the energy source that powers the sun. If harnessed on earth, it could provide limitless low-carbon energy. The basic fuel - the Deuterium and Tritium (D&T) forms of heavy hydrogen, are either readily available in sea-water, or can be 'bred' from the abundant element Lithium (the element in a mobile phone battery). The primary nuclear waste products are harmless - the main being helium (an alpha particle), an inert gas found in party balloons. This all sounds too good to be true - and in a sense it is - because getting the reaction to occur is incredibly difficult - because pushing the D and T close together such that the strong force causes them to bind takes a lot of energy (they repel as they are positively charged nuclei). Getting them to move fast enough so that when by chance they have a head-on collision and get close enough to fuse corresponds to heating them to 100 million K. Confining such a hot plasma for long enough for the collisions to occur is no mean feat. There are two approaches: the first uses a magnetic bottle to keep a low density gas away from the walls of a container. As the density is low, collisions take several seconds - this is the magnetic fusion approach. The second idea uses lasers irradiating a small spherical balloon containing the heavy hydrogen. The laser heats the outside of the balloon from different directions, creating a hot plasma that expands into the vacuum, and then, like a spherical rocket, the shell moves towards the centre, compressing the heavy hydrogen to high temperatures and densities 100s of times denser than ordinary liquid. No magnetic fields are needed, because owing to the high density, the collisions are very rapid, and although the compressed miniature sun will expand again (and blow up more quickly if fusion takes place), the reaction occurs faster than the explosion itself - the material is confined by its own inertia. This is called inertial confinement fusion. In current studies at the National Ignition Facility in California, this goal is close to being realised. However, at present there are still problems to be overcome. One of the major ones is that the shell does not compress uniformly, and it is known that if the implosion is not close to being perfectly spherical, then any ripples will grow, breaking up the wall of the shell before the peak of the implosion. The shell of the balloon then mixes into the fuel, and starts to 'glow' due to the high temperatures, and cools the system, preventing fusion. Therefore, two interlinked problems need to be tackled - firstly, we need to find out how much of the shell is mixing into the heavy hydrogen core - and secondly we need to work out how to prevent this happening (either by making better targets, or illuminating the sphere more uniformly). This research grant addresses the first measurement problem. For various physics reasons the shell of the balloon contains some heavy elements (particularly Germanium) which, if they mix into the hot core, 'light-up' and emit characteristic X-ray lines. From a study of the absolute and relative brightness of these lines, it is possible to gain information on the temperature of the material, and of the density, and also, of the amount of the shell that has mixed into the core. Some of this work has already been performed by our US colleagues. However, at present the technique is not quite accurate enough to say if the amount that has mixed in is really enough to extinguish the reaction. The Oxford and York groups in the UK here put forward several new ideas to improve the theory and experimental technique to a point where we believe we will be able to say if the mix level is acceptable. These ideas are based on a new high resolution x-ray instrument, novel spectroscopic theory looking at the brightness of X-rays from different elements, and by performing sophisticated full 3 dimensional simulations of the emission process.

轻核的聚变是为太阳提供动力的能源。如果在地球上得到利用，它可以提供无限的低碳能源。基本燃料——氘和氚 (D&T) 形式的重氢，要么很容易在海水中获得，要么可以从丰富的锂元素（手机电池中的元素）中“培育”出来。主要的核废料是无害的——主要是氦气（一种阿尔法粒子），一种在派对气球中发现的惰性气体。这一切听起来好得令人难以置信——从某种意义上来说确实如此——因为让反应发生是极其困难的——因为将 D 和 T 推近，使强力使它们结合需要大量能量（它们排斥，因为它们是带正电的原子核）。让它们移动得足够快，以便当它们偶然发生正面碰撞并足够接近以发生融合时，相当于将它们加热到 1 亿 K。将如此热的等离子体限制足够长的时间以使碰撞发生绝非易事。有两种方法：第一种方法使用磁性瓶来保持低密度气体远离容器壁。由于密度低，碰撞需要几秒钟——这就是磁聚变方法。第二个想法是使用激光照射含有重氢的小球形气球。激光从不同方向加热气球的外部，产生热等离子体，膨胀到真空中，然后，像球形火箭一样，气球壳向中心移动，将重氢压缩到高温和密度数十倍的密度比普通液体。不需要磁场，因为由于密度高，碰撞非常迅速，尽管压缩的微型太阳会再次膨胀（如果发生聚变，爆炸得更快），但反应发生的速度比爆炸本身更快 -物质受到自身惯性的限制。这称为惯性约束聚变。在加州国家点火装置目前的研究中，这一目标已接近实现。但目前仍存在一些问题有待克服。主要问题之一是壳压缩不均匀，众所周知，如果内爆不接近完美的球形，那么任何波纹都会增长，在内爆峰值之前破坏壳壁。然后，气球壳混合到燃料中，并由于高温而开始“发光”，并冷却系统，防止融合。因此，需要解决两个相互关联的问题 - 首先，我们需要找出有多少壳混合到重氢核中 - 其次，我们需要找出如何防止这种情况发生（通过制定更好的目标，或更均匀地照亮球体）。这项研究资助解决了第一个测量问题。由于各种物理原因，气球的外壳含有一些重元素（特别是锗），如果它们混合到热的核心中，就会“发光”并发射特征 X 射线。通过研究这些线条的绝对和相对亮度，可以获得有关材料温度、密度以及混合到核心中的壳量的信息。其中一些工作已经由我们的美国同事完成。然而，目前该技术还不够准确，无法确定混合的量是否真的足以消除反应。英国牛津和约克的研究小组提出了一些新的想法，以改进理论和实验技术，使我们相信我们能够判断混合水平是否可以接受。这些想法基于新型高分辨率 X 射线仪器、观察不同元素 X 射线亮度的新颖光谱理论，以及对发射过程进行复杂的全 3 维模拟。

项目成果

Detailed model for hot-dense aluminum plasmas generated by an x-ray free electron laser

X 射线自由电子激光器产生的热致密铝等离子体的详细模型

• DOI: http://dx.10.1063/1.4942540
• 发表时间: 2016
• 期刊: Physics of Plasmas
• 影响因子: 2.2
• 作者: Ciricosta O

Measurements of the K-Shell Opacity of a Solid-Density Magnesium Plasma Heated by an X-Ray Free-Electron Laser.

X 射线自由电子激光器加热的固体密度镁等离子体的 K 壳不透明度测量。

• DOI: http://dx.10.1103/physrevlett.119.085001
• 发表时间: 2017
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Preston TR

Observation of Reverse Saturable Absorption of an X-ray Laser.

X 射线激光反向饱和吸收的观察。

• DOI: http://dx.10.1103/physrevlett.119.075002
• 发表时间: 2017
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Cho BI

The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

在 ICF 相关点光谱实验中使用几何效应诊断离子密度

• DOI: http://dx.10.1016/j.hedp.2019.01.005
• 发表时间: 2019
• 期刊: High Energy Density Physics
• 影响因子: 1.6
• 作者: Pérez

Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy.

• DOI: 10.1103/physrevlett.120.055002
• 发表时间: 2018-02-01
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Q. Y. V. D. Berg;E. V. Fernández;T. Burian;J. Chalupský;H. Chung;O. Ciricosta;G. Dakovski
• 通讯作者: G. Dakovski