The physics of radiation transport in dense plasmas

Abstract

Radiation transport redistributes energy within a medium through the emission and reabsorption of photons. These processes also have a pronounced effect on the spectrum of radiation that escapes the medium. As the deliverable energies of plasma drivers such as lasers and pulsed-power generators steadily increase, denser and/or more massive plasmas can be created. Such plasmas are more absorptive to their own emitted radiation, with portions of the line spectrum frequently being highly opaque. Thus, radiation transport becomes more important, along with the need to consider its impact on the design of experiments and their diagnosis. This tutorial paper covers the basic theory and equations describing radiation transport, its physical effects, experimental examples of transport phenomena, and current challenges and issues. Among the specific topics discussed are requirements for local thermodynamic equilibrium (LTE), conditions for diffusion and the use of the diffusion approximation, the formation of emission and absorption lines, the approach of an emitted spectrum to the Planck limit, and diagnostic applications of transport effects.

Modeling of K-shell Al and Mg radiation from compact single, double planar and cylindrical alloyed Al wire array plasmas produced on the 1 MA Zebra generator at UNR

“…A diagnostic method for studying radiation from such wire array implosions was suggested and successfully applied by Apruzese et al [5]. It is based on the use of the alloyed Al 5056 wires, which have 95% Al þ 5% Mg.…”

“…4a) are Al Hea, Heb, an Lya lines which are usually optically thick. Therefore, we use the optically thinner Mg Hea and Heb lines, as well as the shorter wavelength Al Hed and Al Lyb lines from higher-n states to diagnose the plasma electron temperature and density [5,6].…”

“…The analysis of the K-shell emission requires the introduction of opacity effects and therefore radiation transport modeling (see, for example [4],). Another diagnostic approach was to use alloyed Al-5056 wires to produce low opacity line emission [5,6].…”

The effect of unresolved transition arrays on plasma opacity calculations

“…The description of radiation is an essential component of the description in many areas of physics, not least in high energy density and plasma physics where the self-generated photon field can contain a significant portion of the system's total energy [1,2]. In this case the processes by which photons are absorbed and emitted play an important part in energy transport.…”

Opacity calculations on plasmas with open M and N shell configurations

“…The accurate calculation of plasma opacity is essential to many areas of plasma physics [1,2]. In particular, radiative-hydrodynamic simulations require values for the Rosseland mean opacity as input [3,4], and as a result opacity calculations have seen continual development for many years [5][6][7].…”