Identifying the Key Factors Currently Preventing Ignition in Inertial Confinement Fusion Experiments.

热核聚变是太阳产生能量的机制。几十年来，科学家们一直试图利用聚变发电，因为它作为一种安全，清洁和几乎取之不尽的能源供应提供了巨大的优势。在实验室实验中，通常通过将氢的重同位素加热到非常高的温度来研究聚变，形成等离子体，其中带正电的离子的快速运动足以克服它们的静电排斥并允许它们进行核反应。从这些反应中提取能量的主要方法之一是惯性约束聚变。这涉及到通过高功率激光驱动的球形内爆将热核燃料组装到毫米级胶囊内的超高密度（超过水密度的1000倍）。这种方法的核心是点火过程，在这个过程中，从反应中产生的高能α粒子本身被用来进一步加热燃料，从而产生一个自我维持的燃烧波，释放出大量的能量。这对聚变研究来说是一个非常激动人心的时刻，因为随着劳伦斯利弗莫尔国家实验室（LLNL）的国家点火装置（NIF）的建成，第一个有能力演示点火的实验室设施现在已经投入使用。然而，NIF的早期结果突出了计算机模型的预测与观察到的行为之间的差异。最重要的是，核反应的数量仍然太低，无法引发点火。PI和Co-我在这个基金上与LLNL的科学家们进行了广泛的合作，以了解这些差异的根源，并参加了点火科学研讨会，该研讨会确定了解决这些问题的优先研究方向。对于这个提案，我们希望利用我们在极高密度和温度的等离子体方面的经验，解决惯性约束聚变实验设计和物理过程中的关键不确定性。的点火和工作提供了一个解释，为什么目前的设计没有实现点火和燃烧。研究的关键领域将包括了解用于驱动内爆的辐射在胶囊表面被吸收的方式，内爆胶囊对流体动力学不稳定性的敏感性，这种不稳定性导致燃料在完全压缩之前解体，以及燃料的高温和低温区域搅拌和混合在一起的趋势，从而熄灭燃烧。我们还将研究点火过程本身的物理学，评估高能α粒子是否能够在沉积能量之前逃离燃料，以及自发产生的磁场的作用，这些磁场提供了一种热绝缘形式并用于保持燃料内的热量。部分工作将涉及开发一些先进的计算机建模能力。除了用于聚变研究外，这些能力还可用于利用大型激光设施进行等离子体物理学、核物理学和实验室天体物理学的基础研究。使用这些计算机模型来模拟我们故意引入缺陷的聚变舱，我们可以计算出这种缺陷的特征签名嵌入在反应燃料发出的高能中子和X射线的通量中。将合成诊断数据与实验中获得的数据进行比较，然后使我们能够分离出哪些物理过程是限制聚变性能的原因。然后，相同的计算机模型可以用于设计减轻这些影响的改进，并使我们能够朝着实现点火的方向取得进展。因此，本提案中描述的工作为英国科学界提供了一个机会，使其能够为重大科学成就做出重大贡献。

Thermonuclear fusion is the mechanism by which energy is generated in the Sun. For decades scientists have been attempting to harness fusion for electrical power production because of the huge advantages it offers as a safe, clean and almost inexhaustible supply of energy. In laboratory experiments, fusion is normally studied by heating the heavy isotopes of hydrogen to very high temperatures forming a plasma, in which the rapid motion of the positively charged ions is sufficient to overcome their electrostatic repulsion and allow them to undergo nuclear reactions. One of the main approaches to extracting energy from these reactions is Inertial Confinement Fusion. This involves assembly of the thermonuclear fuel to ultra-high density (over 1000 times the density of water) inside a mm-scale capsule through a spherical implosion driven by high-power lasers. Central to this method is the process of ignition in which the energetic alpha particles emerging from the reactions are themselves used to further heat the fuel, resulting in a self-sustaining burn wave which releases copious amounts of energy. This is a very exciting time for fusion research because with the completion of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), the first laboratory facility with the capacity to demonstrate ignition is now operational.Early results from the NIF however have highlighted differences between the predictions of computer models and the behaviour observed. Most importantly the number of nuclear reactions has remained too low to initiate ignition. The PI and Co-I on this grant have worked extensively with scientists at LLNL to understand the origins of these discrepancies and participated in the Science of Ignition workshop which identified priority research directions to address these issues.For this proposal we wish to capitalise upon our experience with plasmas of extremely high density and temperature to address key uncertainties in the design of inertial confinement fusion experiments and the physics of ignition and work to provide an explanation of why the current design does not achieve ignition and burn. Key areas of research will include understanding the way in which the radiation used to drive the implosion is absorbed in the surface of the capsule, the susceptibility of the imploding capsule to hydrodynamic instabilities which cause the fuel to disintegrate before it is fully compressed and the tendency of the high temperature and low temperature regions of the fuel to stir and mix together which quenches the burn. We will also investigate the physics of the ignition process itself, evaluating whether the energetic alpha particles are able to escape the fuel before depositing their energy and the role of spontaneously generated magnetic fields which provide a form of thermal insulation and serve to keep the heat within the fuel. Part of the work will involve developing a number of advanced computer modelling capabilities. In addition to their use in fusion research, these capabilities can also be used to exploit large scale laser facilities for fundamental research in plasma physics, nuclear physics and laboratory astrophysics. Using these computer models to simulate a fusion capsule in which we deliberately introduce an imperfection, we can calculate what characteristic signatures of this defect are embedded within the flux of energetic neutrons and X-rays emanating from the reacting fuel. Comparing synthetic diagnostic data with that obtained in experiment then allows us to isolate which physical processes are responsible for limiting fusion performance. The same computer models can then be used to design improvements which mitigate these effects and allow us to make progress towards achieving ignition. The work described in this proposal therefore represents an opportunity for UK science to make a significant contribution to what would be a major scientific achievement.