Temperature Relaxation in Dense, Reacting Plasmas

了解高能量密度物质的性质既是基本的物理问题，也是惯性约束聚变能够提供清洁且几乎无限的能源之前需要解决的核心问题之一。目前正朝着这一目标迈出重大步骤：位于美国利弗莫尔的国家点火设施已于去年完成，点火(定义为输出能量大于输入)预计将于今年秋季实现。NIF上的点火将对物理和社会产生类似的影响，就像在欧洲核子研究中心使用大型强子对撞机进行粒子物理实验一样。第一个实验结果支持全面聚变实验的积极预测：它们展示了192束光束进入毫米尺寸腔的大规模激光系统的良好能量耦合。现在，我们必须探索燃烧等离子体的物理学。这是通过实验和大规模模拟相结合的方式完成的。后者是该项目的关键要素，因为实验很少(一天最多两次)，而且非常昂贵。模拟需要包含许多物理过程；并不是所有的物理过程都被完全理解。因此，目前使用的近似模型对未来的发展提出了明确的警告。这个项目的目的是在一个重要的量：电子-离子耦合上实质性地改善这种情况。它将对燃料加热到1000万度的聚变温度期间发生的所有参数的能量转移率给出明确的答案。需要这些能量转移率来描述燃烧波在预压缩燃料中的传播，这是一个允许高增益目标的过程。有趣的是，当等离子体相对较冷时，第一阶段最难描述，因为在这里，电子的量子性质和离子之间的强大作用力起着主要作用。申请人开发的量子统计模型对这一应用将被证明是无价的。针对聚变计划中的特定问题(状态方程、熔化或输运性质)，在过去的几年里已经进行了一系列中等规模的实验。这里应用的快速能量沉积到样品中创建了具有不同电子和离子温度的系统。同样，温度平衡是设计和解释实验的主要问题。此外，复合和电离过程通常是由激光的能量沉积驱动的。该项目的主要部分旨在消除有关松弛过程描述中的理论不确定性。特别是，它将描述变化的物种温度、离子变化的电荷状态和依赖于时间的关联之间的全面相互作用。在所研究的致密物质中，所有这些能量贡献都是相同的数量级，都不能被忽视。非常有趣的是，注意到中等尺度的激光实验经常达到类似于天体物理对象的条件，如巨型行星(包括太阳系外迅速增加的数量)、老恒星和昏暗的中型天体。对这种状态的实验研究被称为实验室天体物理学，需要达到热力学平衡。因此，松弛时间在这里是特别重要的，因为它定义了系统创建和探测之间的最小时间延迟。这里发展的理论将提供这些时代。

Understanding the properties of high energy density matter is both fundamental physics and one of the central problems that needs to be resolved before inertial confinement fusion can provide a clean and almost infinite energy source. Major steps toward this goal are being made at the moment: the National Ignition Facility in Livermore, USA has been completed last year and ignition (defined as larger energy output than input) is expected to be achieved this autumn. Ignition at NIF will have a similar impact on physics and society as the particle physics experiments using the LHC at CERN.The first experimental results support the positive predictions for full scale fusion experiments: they have demonstrated excellent energy coupling from the large scale laser systems with 192 beams into the millimeter-size cavity. Now the physics of a burning plasma has to be explored. This is done by a combination of experiments and large scale simulations. The latter are a key element of the project as the experiments are infrequent (maximum two shots a day) and very expensive. The simulations need to incorporate many physical processes; not all of them are fully understood. As a result, approximate models are currently used with represents a clear caveat for future progress.This project is aimed to substantially improve this situation for one important quantity: the electron-ion coupling. It will give definitive answers for the energy transfer rates for the whole range of parameters that occur during the heating of the fuel to fusion temperature of 10 million degrees. These energy transfer rates are needed to describe the propagation of a burn wave in the pre-compressed fuel, a process that allows for high gain targets. Interestingly, the first phase when the plasma is relatively cold is most difficult to describe as here the quantum nature of the electrons and strong forces between the ions play a major role. The quantum statistical model developed by the applicant will prove invaluable for this application.Dedicated to a specific problem within the fusion program (equation of state, melting or transport properties), a series of intermediate scale experiments has been performed over the last years. The rapid energy deposition into samples applied here creates systems with different electron and ion temperatures. Again, temperature equilibration is a major issue for the design and interpretation of the experiments. Moreover, recombination and ionisation processes are often driven by the energy deposition of the laser. The main part of this project aims to remove the theoretical uncertainties in the description of the relaxation processes involved. In particular, it will give a description of the full interplay between the changing species temperatures, the changing charge state of the ions and time-dependent correlations. In the dense matter under investigation, all of these energy contributions are of the same order of magnitude and neither can be neglected.It is very interesting to notice that intermediate scale laser experiments often reach conditions similar to those in astrophysical objects such as giant planets (including a rapidly growing number outside of our solar system), old stars and dim, midsize objects. The experimental investigation of such states, called laboratory astrophysics, requires that thermodynamic equilibrium is reached. Thus, the relaxation time is here of particular interest as it defines the minimum time delay between creation of the system and the probing. The theory developed here will provide these times.