Simulation of uranium plasma plume dynamics in atmospheric oxygen produced via femtosecond laser ablation

Laser ablation is an easily accessible method of producing metallic plasmas in reactive, atmospheric environments. The use of laser ablation for the study of uranium plasma chemistry in atmospheric ablation plumes is highly relevant for nuclear forensics and standoff detection, but the behavior of such systems is currently not well understood. One of the main difficulties in studying these systems is that the already considerable complexity of plume dynamics in vacuum conditions is further enhanced by shockwave formation and plasma-chemical behavior in reactive, atmospheric environments. Therefore, in order to understand the ablation dynamics of an atmospheric uranium ablation system, both the transport and kinetics of the reactive uranium plasma plume have to be accounted for. In this work, we present a two-dimensional compressible, reactive, multi-species fluid model of the early stages of femtosecond uranium plume expansion in atmospheric oxygen. This model utilizes a previously constructed uranium-oxygen plasma chemistry reaction mechanism consisting of 172 reaction channels and 30 species in order to treat the reaction kinetics of a uranium ablation plume. The model captures both the complex compressible dynamics of the ablation shockwave and the stratification of the ablation plume into regions of varying reactivities and molecular compositions due to the plasma-chemical interactions between the plume and the reactive atmosphere. The result is a detailed picture of the spatial and temporal evolution of both the fluid moments and the major plasma-chemical species concentrations of the ablation plume.