Inertial Confinement Fusion - exploring the options for ignition.

太阳发出的大量能量是由热核融合产生的。在地球上利用核聚变发电一直是科学家的目标，因为它将提供几乎无限的安全、清洁的电力供应。在实验室里，研究核聚变的实验包括将氢的同位素加热到非常高的温度，从而形成等离子体。如果等离子体足够热，那么带正电的离子的快速运动可以克服静电斥力，从而产生核聚变反应。产生这些条件的主要方法之一是惯性约束聚变（ICF）。热核燃料最初被装入一个半径为1毫米的球形胶囊中。这个胶囊是用高功率激光压缩的，这样在几十亿分之一秒内，它的密度就会比水大1000倍，温度也会比太阳核心高1000倍。ICF的关键过程是点火，核反应释放的高能α粒子使燃料进一步加热。这导致了一个自我维持的燃烧波的反应，释放大量的能量。对于核聚变研究来说，这是一个非常激动人心的时刻，因为劳伦斯利弗莫尔国家实验室（LLNL）的国家点火装置（NIF）目前正在运行，在实验室从未观察到的温度和密度下产生热核等离子体。美国国家点火装置最近的研究结果表明，在聚变反应中产生的能量释放比聚变燃料的热能更大，这是一项具有里程碑意义的成就。然而，聚变反应的数量仍然太少，不足以启动点火过程，因此，释放的能量仍然远远低于每次实验使用的总能量。pi先前的工作首先强调了三维不对称对融合性能的不利影响。这种不对称现在被广泛认为是实现更高能源产量的主要障碍。在过去的三年中，pi和PDRAs与LLNL的科学家进行了广泛的合作，以了解工作中的关键物理过程，并确定可用于分离产量降低主要原因的诊断方法。对于这个提议，我们希望利用我们从研究NIF实验中获得的经验，探索在惯性约束聚变中推进点火的一系列未来选择。我们的工作将结合密集等离子体的先进理论模型，使用我们的多维辐射流体动力学代码进行大规模并行计算，以及对实验数据的详细分析。我们将扩展我们的计算机模型，以计算目前在NIF上引入的广泛的新诊断的预期反应。这将有助于我们优化诊断设计和方法，用于隔离性能降低的主要原因。我们将利用这些数据来确定描述聚变等离子体如何被限制的理论模型需要如何修改以考虑不对称性，以及如何学习与不对称性共存导致不同的方法来优化产量。我们将使用这些方法来评估对NIF当前实验设计的一些拟议变更可能产生的影响。我们还提出了一种不同的实验设计方法，它避免了与追求高能量产量相关的一些风险，其目标是提供一种可靠的方法来研究点火过程本身的物理特性。最后，通过利用控制所有惯性聚变实验最后阶段的共同物理过程，我们将利用从NIF实验中获得的见解来评估实现点火和高能量产量的替代方法的长期可行性。

The vast quantity of energy emitted by the Sun is produced by thermonuclear fusion. Harnessing fusion power on earth has long been a goal for scientists as it would provide an almost limitless supply of safe, clean electrical power. In the laboratory, experiments to study fusion involve heating isotopes of hydrogen to very high temperatures such that a plasma is formed. If the plasma is sufficiently hot then the rapid motion of the positively charged ions can overcome the electrostatic repulsive force resulting in a nuclear fusion reaction. One of the main approaches to producing these conditions is Inertial Confinement Fusion (ICF). The thermonuclear fuel is initially contained in a spherical capsule with a 1 mm radius. This capsule is compressed using high-power lasers such that within a few billionths of a second it becomes more than 1000 times denser than water and hotter than the core of the Sun. The key process in ICF is ignition in which the energetic alpha particles emitted by nuclear reactions cause further heating of the fuel. This results in a self-sustaining burn wave of reactions which releases copious amounts of energy. This is a very exciting time for fusion research because the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) is currently operational, producing thermonuclear plasmas at temperatures and densities never before observed in the laboratory.Recent results from the National Ignition Facility have demonstrated a landmark achievement in generating an energy release from fusion reactions that is greater than thermal energy of the fusion fuel. Nevertheless, the number of fusion reactions remains too low to initiate the ignition process and as a consequence, the energy released is still far lower than the total energy used by each experiment. Previous work by the PIs was amongst the first to highlight the detrimental effects that three-dimensional asymmetries can have on the fusion performance. Such asymmetries are now widely believed to be the principal obstacle to achieving higher energy yields. Over the last three years, the PIs and PDRAs have worked extensively with scientists at LLNL to understand the key physical processes at work and to identify diagnostic methods which can be employed to isolate the principal causes of reduced yields.For this proposal we wish to capitalise upon the experience we have gained from studying experiments on the NIF to explore a range of future options for progressing towards ignition in Inertial Confinement Fusion. Our work will make use of a combination of advanced theoretical models of dense plasmas, large scale parallel computing using our multi-dimensional radiation hydrodynamics codes and detailed analyses of experimental data. We will extend our computer models to calculate the anticipated response from a broad range of new diagnostics currently being introduced on NIF. This will help us contribute to the optimisation of diagnostic design and the methods used to isolate the principal causes of reduced performance. We will use this data to establish how theoretical models describing how the fusion plasma is confined need to be modified to take into account asymmetry and how learning to live with asymmetry leads to different approaches to the optimisation of yield. We will use these approaches to assess the likely impact of a number of proposed changes to the design of current experiments on NIF. We also propose a different approach to the design of experiments, which avoids some of risks associated with the pursuit of high energy yields, where the objective is instead to provide a reliable means of studying the physics of the ignition process itself. Finally, by exploiting the common physical processes which govern the final stages all inertial fusion experiments, we will use insights gained from experiments on NIF to evaluate the longer term viability of alternative approaches to achieving ignition and high energy yields.