Spectroscopic determination of temperature and density spatial profiles and mix in indirect-drive implosion cores

Abstract

In the field of inertial confinement fusion (ICF), work has been consistently progressing in the past decade toward a more fundamental understanding of the plasma conditions in ICF implosion cores. The research presented here represents a substantial evolution in the ability to diagnose plasma temperatures and densities, along with characteristics of mixing between fuel and shell materials. Mixing is a vital property to study and quantify, since it can significantly affect implosion quality. We employ a number of new spectroscopic techniques that allow us to probe these important quantities. The first technique developed is an emissivity analysis, which uses the emissivity ratio of the optically thin Lybeta and Hebeta lines to spectroscopically extract temperature profiles, followed by the solution of emissivity equations to infer density profiles. The second technique, an intensity analysis, models the radiation transport through the implosion core. The nature of the intensity analysis allows us to use an optically thick line, the Lyalpha, to extract information on mixing near the core edge. With this work, it is now possible to extract directly from experimental data not only detailed temperature and density maps of the core, but also spatial mixing profiles.

Inference of ICF implosion core mix using experimental dataand theoretical mix modeling

“…The constant ζ in front of the mixing coefficient γ is a factor related to the fill pressure of the gas [2]. The L represents the length of a chord, as shown in Fig.…”

“…For each of the six zones, there exists a system of two equations which link theoretical and experimental intensities and emissivities. The equations include a term which represents, for each zone, the local mixing coefficient γ, which in this case is the ratio of the atom number densities of plastic shell to fuel material [2]. The simplest set of equations is for the outer zone 0, which has only a selfemission term in the intensity equation:…”

“…The spectroscopic analysis begins with the extraction of a temperature spatial profile using an emissivity ratio technique [2]. The analysis uses the sensitivity of the Lyβ/Heβ emissivity ratio to temperature.…”

“…In previous work, we have demonstrated that it is possible to extract information on mixing directly from experimental data using spectroscopic techniques [2][3][4]. The development was first carried out based on a set of indirect drive implosions at the Laboratory for Laser Energetics' OMEGA laser [5].…”

“…[2]. The data-derived spatial mixing profiles were evaluated to determine the corresponding width of the mixing region, for direct comparison to the mix modeling results.…”