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

Abstract

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.

The effect of oxygen concentration on the speciation of laser ablated uranium

“…Although, to our knowledge, no spectra of am-UO x have been reported below 600 cm −1 , many uranium-containing molecules produce U–O stretching modes near 500 cm −1 giving additional support for this assignment 46 , 49 . Furthermore, plume dynamic modeling of laser ablated uranium suggests higher oxides (e.g., UO 3 ) will form at the outer edge of the plume-atmosphere interface 50 , in agreement with the observed major products here. As previously mentioned, Koroglu et al 23 conclude α-UO 3 is produced when uranium nitrate and O 2 are passed through an ICP and allowed to cool.…”

Remote Detection of Uranium Using Self-Focusing Intense Femtosecond Laser Pulses

“…In the past, those features were interpreted as arising mostly from a complex, unresolved atomic emission spectrum [41]. Recently, it has been shown that the unresolved features of uranium oxides contribute to a notable background in the emission spectrum of uranium-containing plasmas formed in the presence of oxygen [41,42]. These emission features from certain gas-phase uranium oxides heavier than uranium monoxide (U x O y , such that x ≥ 1 and y > 1, e.g., UO 2 , UO 3 , U 3 O 8 ) are still largely unidentified [43] and remain the subject of current studies.…”

Laser-produced uranium plasma characterization and Stark broadening measurements

“…[18][19][20] Moreover, LA of U in reactive environments and the formation of molecules add a large number of additional spectral lines, which often overlap to result in an unresolved broad spectrum. 21,22 The high density of states in high-Z molecules produces fine features which interfere with the measurement of the atomic and ionic emission spectra. In such a dense and complex system, the choice of emission lines plays an important role in quantitative analysis.…”