Towards modeling of electron-impact ionization in warm dense matter

Abstract

The unique properties of x-ray free-electron lasers (XFELs), such as their immense brilliance, ultrashort pulse duration, and high photon energies, make XFELs an incredibly useful tool in a plethora of different scientific fields. Their applications include unique imaging techniques used in struc- tural biology and bio-engineering, the study of new effects in nanophysics, and the creation and probing of exotic states of matter used to investigate astrophysical objects and phenomena. Due to the development of XFELs over the last few decades, there has been an increasing need to theoretically describe the x-ray–matter interactions, and subsequent radiation-induced interactions, that are prevalent in various kinds of irradiated systems. This dissertation is dedicated to the theoretical modeling of electron-impact ion- ization in warm dense matter (WDM). Electron-impact ionization is a pre- dominant contributor to radiation damage induced by an XFEL pulse in dense materials. The first part considers the process of electron-impact ionization for an isolated atom. Specifically, I consider how the cross section for this process changes for different electronic configurations of the same ion. I find that this change may be quite substantial. It depends on the charge state of the ion, the energy of the ionizing electron, and on how much the two electronic configurations being compared differ from each other. The second part revolves around the theoretical description of warm dense matter states. I develop a novel toolkit called xcrystal, which cal- culates electronic states present in a transient state of nonisothermal WDM from first principles. With xcrystal, I calculate the electronic energies for these WDM states, which allows for predictions of the ionization potential depression caused by the presence of a dense and charged environment. In addition, I investigate the temperature dependence of the band structure of a WDM system and provide physical justifications for the observed trends. The third and final part uses the results of the previous two parts to model electron-impact ioinization in the warm dense matter states described by xcrystal. Here, I develop the theory to calculate the cross section in this system and provide an in-depth discussion on its practical implementation.