Recovering particle velocity and size distributions in ejecta with Photon Doppler Velocimetry

TL;DR

This paper introduces a method to extract particle size distributions from Photon Doppler Velocimetry data in ejecta experiments by modeling light scattering with the Radiative Transfer Equation and comparing simulations to experimental spectrograms.

Contribution

It presents a novel approach combining RTE modeling with hydrodynamic simulations to retrieve particle size distributions from PDV spectrograms in ejecta experiments.

Findings

Successfully simulated PDV spectrograms using RTE and hydrodynamic data.

Demonstrated the ability to constrain ejecta particle size distributions.

Enhanced understanding of ejecta transport and light scattering in gas environments.

Abstract

When a solid metal is struck, its free surface can eject fast and fine particles. Despite the many diagnostics that have been implemented to measure the mass, size, velocity or temperature of ejecta, these efforts provide only a partial picture of this phenomenon. Ejecta characterization, especially in constrained geometries, is an inherently ill-posed problem. In this context, Photon Doppler Velocimetry (PDV) has been a valuable diagnostic, measuring reliably particles and free surface velocities in the single scattering regime. Here we present ejecta experiments in gas and how, in this context, PDV allows one to retrieve additional information on the ejecta, i.e. information on the particles' size. We explain what governs ejecta transport in gas and how it can be simulated. To account for the multiple scattering of light in these ejecta, we use the Radiative Transfer Equation (RTE) that quantitatively describes PDV spectrograms, and their dependence on the velocity but also on the size distribution of the ejecta. We remind how spectrograms can be simulated by solving numerically this RTE and we show how to do so on hydrodynamic ejecta simulation results. Finally, we use this complex machinery in different ejecta transport scenarios to simulate the corresponding spectrograms. Comparing these to experimental results, we iteratively constrain the ejecta description at an unprecedented level. This work demonstrates our ability to recover particle size information from what is initially a velocity diagnostic, but more importantly it shows how, using existing simulation of ejecta, we capture through simulation the complexity of experimental spectrograms.