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Title: (U) Utility of Average Particle Diameter Diagnostic in Ejecta Physics Experiments

Abstract

This report documents particle size distribution use in ejecta physics experiments presented by an LANL working group.

Authors:
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1351167
Report Number(s):
LA-UR-17-22159
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Wood, William Monford. (U) Utility of Average Particle Diameter Diagnostic in Ejecta Physics Experiments. United States: N. p., 2017. Web. doi:10.2172/1351167.
Wood, William Monford. (U) Utility of Average Particle Diameter Diagnostic in Ejecta Physics Experiments. United States. doi:10.2172/1351167.
Wood, William Monford. Tue . "(U) Utility of Average Particle Diameter Diagnostic in Ejecta Physics Experiments". United States. doi:10.2172/1351167. https://www.osti.gov/servlets/purl/1351167.
@article{osti_1351167,
title = {(U) Utility of Average Particle Diameter Diagnostic in Ejecta Physics Experiments},
author = {Wood, William Monford},
abstractNote = {This report documents particle size distribution use in ejecta physics experiments presented by an LANL working group.},
doi = {10.2172/1351167},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Mar 14 00:00:00 EDT 2017},
month = {Tue Mar 14 00:00:00 EDT 2017}
}

Technical Report:

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  • The goal of this work is to determine the feasibility of extracting the size of particles ejected from shocked metal surfaces (ejecta) from the angular distribution of light scattered by a cloud of such particles. The basis of the technique is the Mie theory of scattering, and implicit in this approach are the assumptions that the scattering particles are spherical and that single scattering conditions prevail. The meaning of this latter assumption, as far as experimental conditions are concerned, will become clear later. The solution to Maxwell’s equations for spherical particles illuminated by a plane electromagnetic wave was derived bymore » Gustav Mie more than 100 years ago, but several modern treatises discuss this solution in great detail. The solution is a complicated series expansion of the scattered electric field, as well as the field within the particle, from which the total scattering and absorption cross sections as well as the angular distribution of scattered intensity can be calculated numerically. The detailed nature of the scattering is determined by the complex index of refraction of the particle material as well as the particle size parameter, x, which is the product of the wavenumber of the incident light and the particle radius, i.e. x = 2rπ= λ. Figure 1 shows the angular distribution of scattered light for different particle size parameters and two orthogonal incident light polarizations as calculated using the Mie solution. It is obvious that the scattering pattern is strongly dependent on the particle size parameter, becoming more forward-directed and less polarizationdependent as the particle size parameter increases. This trend forms the basis for the diagnostic design.« less
  • This document describes LANL's source model for RMI-based ejecta.
  • The Los Alamos Physics and Engineering Models (PEM) program has developed a model for Richtmyer-Meshkov instability (RMI) based ejecta production from shock-melted surfaces, along with a prescription for a self-similar velocity distribution (SSVD) of the resulting ejecta particles. We have undertaken an effort to validate this source model using data from explosively driven tin coupon experiments. The model’s current formulation lacks a crucial piece of physics: a method for determining the duration of the ejecta production interval. Without a mechanism for terminating ejecta production, the model is not predictive. Furthermore, when the production interval is hand-tuned to match time-integrated massmore » data, the predicted time-dependent mass accumulation on a downstream sensor rises too sharply at early times and too slowly at late times because the SSVD overestimates the amount of mass stored in the fastest particles and underestimates the mass stored in the slowest particles. The functional form of the resulting m(t) is inconsistent with the available time-dependent data; numerical simulations and analytic studies agree on this point. Simulated mass tallies are highly sensitive to radial expansion of the ejecta cloud. It is not clear if the same effect is present in the experimental data but if so, depending on the degree, this may challenge the model’s compatibility with tin coupon data. The current implementation of the model in FLAG is sensitive to the detailed interaction between kinematics (hydrodynamic methods) and thermodynamics (material models); this sensitivity prohibits certain physics modeling choices. The appendices contain an extensive analytic study of piezoelectric ejecta mass measurements, along with test problems, excerpted from a longer work (LA-UR-17-21218).« less
  • This system consists of three major components, namely: (1) time resolving neutron counters, (2) neutron threshold activation detectors, and (3) the total neutron yield monitors. These three components when taken together enable a thorough description of target produced neutrons. In particular, the system is capable of giving an indication of the neutron spectrum produced, the total number of neutrons produced, and the neutron formation time. The system is designed to maintain as high an overall detection efficiency as possible since it is expected that initial pellet implosion experiments will have low thermonuclear neutron yields. A novel feature of the systemmore » is the use of gated photomultiplier tubes capable of operating in the presence of the intense bremsstrahlung background characteristic of electron and some ion beam experiments.« less