Studying High Pressure Matter with X-Ray Lasers

恒星的环境又热又密，导致物质在高温下电离，并且原子间的间距足够接近，以至于特定离子的束缚态受到其邻居的强烈影响，从而减少了原子电离所需的能量（这种现象称为电离势压低）。类似的情况也出现在惯性约束聚变舱的中心。我们小组内部的研究最近表明，我们可以使用世界上最强大的X射线激光器，位于加州的SLAC，在200万度的温度下制造固体密度物质，然后探测它以准确地找出电离势的值。令人惊讶的是，我们发现这些值与被广泛使用了半个世纪的标准理论完全不一致。借助从头算量子计算，我们开始理解为什么会出现这种情况，但还需要做更多的工作。在这个项目中，学生将参与进一步的实验，在实验室中制造“微型恒星”，并在类似于太阳中心一半的条件下对原子性质进行基本量子计算。这些结果也可能对通过惯性聚变技术产生几乎无限能量的探索产生直接影响，该小组与美国国家点火设施有着密切的正式联系。

Stellar environments are hot and dense, leading to ionized matter at high temperatures, and with interatomic spacings sufficiently close that the bound states of a particular ion are strongly influenced by their neighbours, reducing the energy needed to ionize the atom (a phenomenon known as ionization potential depression. Similar circumstances arise in the centre of inertial confinement fusion capsules. Research within our group has recently shown that we can use the world's most powerful x-ray laser, based at SLAC California, to make solid density matter at 2 million degrees, and then probe it to find out exactly the value of the ionization potentials. Surprisingly we found that the values were completely at odds with the standard theory that has been in wide use for over half a century. With the aid of ab initio quantum calculations we are starting to understand why this is the case, but much more work needs to be done. In this project the student will be engaged in further experiments to make 'miniature stars' in the laboratory, as well as embark on fundamental quantum calculations of the properties of atoms under similar conditions to those that exist half way to the centre of the sun. The results could also have a direct impact on the quest to produce virtually limitless energy via inertial fusion techniques, and the group has strong formal links with the US National Ignition Facility.