Experimental investigation of opacity models for stellar interior, inertial fusion, and high energy density plasmas

Abstract

Theoretical opacities are required for calculating energy transport in plasmas. In particular, understanding stellar interiors, inertial fusion, and Z pinches depends on the opacities of mid-atomic-number elements over a wide range of temperatures. The 150–300 eV temperature range is particularly interesting. The opacity models are complex and experimental validation is crucial. For example, solar models presently disagree with helioseismology and one possible explanation is inadequate theoretical opacities. Testing these opacities requires well-characterized plasmas at temperatures high enough to produce the ion charge states that exist in the sun. Typical opacity experiments heat a sample using x rays and measure the spectrally resolved transmission with a backlight. The difficulty grows as the temperature increases because the heating x-ray source must supply more energy and the backlight must be bright enough to overwhelm the plasma self-emission. These problems can be overcome with the new generation of high energy density (HED) facilities. For example, recent experiments at Sandia’s Z facility [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)] measured the transmission of a mixed Mg and Fe plasma heated to 156±6 eV. This capability will also advance opacity science for other HED plasmas. This tutorial reviews experimental methods for testing opacity models, including experiment design, transmission measurement methods, accuracy evaluation, and plasma diagnostics. The solar interior serves as a focal problem and Z facility experiments illustrate the techniques.

Investigation of iron opacity experiment plasma gradients with synthetic data analyses

“…where I ν, i [erg/(cm 2 s str eV)] is the intensity for photon frequency ν at layer i,κ j ν, i [cm 2 /g] are the local opacity per mass density of element j in layer i, and (ρL) j i [g/cm 2 ] are areal density of element j in layer i. By letting I ν, 0 be the incident radiation flux on the first layer of the sample provided by the backlighter, the pure transmission, T ν , becomes…”

“…2 Dynamic hohlraum x-rays heat an iron sample and an abrupt radiation power increase at stagnation provides the strong backlight required for accurate transmission spectra measurements. K-shell line absorption from Mg uniformly doped into the iron sample provides the independent temperature and density measurements, which are required to benchmark opacity models.…”

Plasma screening effects on the electronic structure of multiply charged Al ions using Debye and ion-sphere models

“…Other crucial spectral properties of atomic systems that are of immense interest are excitation energies (EEs), spectral line shifts, line broadenings, energy level crossings etc. Accurate knowledge of these quantities is essential in describing equation of state of plasma [16], finding out opacity of an element in the astrophysical plasma [17,18], in understanding dynamics of atomic systems in the laser cooling and trapping of ions [19], inertial confinement fusion studies [20] etc.…”

Primary experimental results of wire-array Z-pinches on PTS

“…Z-pinch plasma is the most powerful x-ray radiation sources [1] that created in laboratories at present and has wide applications in inertial confinement fusion (ICF), laboratory astrophysics, radiation science and other high energy density sciences [2][3][4][5]. In this paper, the results of Z-pinch experiments carried out on PTS using tungsten high-wire-number array loads are presented.…”