M.H. Chen

A new detailed term accounting opacity code for mid-Z elements: TOPAZ

A new opacity code, TOPAZ, that explicitly includes the detailed configuration term structure for mid-Z elements is under development and preliminary results are presented. The main purpose is to extend the current capabilities of opacity codes such as OPAL, which are limited to elements of astrophysical interest, towards heavier elements. Results from the new code are compared to several past experiments.

ESTIMATING PLASMA TEMPERATURES FROM TRANSMISSION SPECTRA

Abstract Recent laser-produced plasma experiments have relied on spectroscopic comparisons with models to infer plasma temperatures. The models use an experimentally determined value for the matter density as input and treat the temperature as an adjustable parameter to obtain a best fit to the experimental absorption spectrum. However, uncertainties in the ionization balance theories lead to inferred temperatures that are model dependent. We report results of a new approach which combines high-quality atomic data with an ionization balance obtained from systematic expansions of the grand canonical ensemble. The latter avoids the ad hoc cutoffs required in free energy minimization schemes and includes Coulomb corrections usually neglected in other models. Comparisons to experimental spectra show excellent agreement.

Spectroscopic measurements of Rosseland mean opacity

Abstract The first quantitative measurement of photoabsorption in the region determining Rosseland and Planck mean opacity, is obtained for an x-ray heated iron plasma, using novel techniques and instrumentation. The plasma density of 0.0113 ± 0.0013 g/cm3 and temperature of 59 ± 3 eV are accurately constrained experimentally by imaging plasma expansion and observing and modeling absorption in sodium dopant ions. The measured iron absorption spectrum is compared with several newly developed opacity models. The data constrains Rosseland and Planck group means with of order 15% precision. This is the first quantitative experimental certification of opacity models germane to radiative transfer in LTE plasmas.

A REVISED ALGORITHM FOR THE COMPUTATION OF SUPER-TRANSITION ARRAY SPECTRA OF HOT DENSE PLASMAS

Abstract The formula for computing bound–bound X-ray absorption from unresolved ‘Super’-transition arrays is reformulated in terms of correlated occupation numbers, averaged over subensembles of the ideal grand canonical ensemble. These can be expressed as generalized Fermi factors which depend on the ratio of partition functions. A new algorithm for the computation of this ratio is presented, hybridizing recursion relations starting from full or empty super-shells with an exact relation numerically stable about the average occupation of the supershell.

A New Detailed Term Accounting Opacity Code: TOPAZ

A new opacity code, TOPAZ, which explicitly includes configuration term structure in the bound‐bound transitions is being developed. The goal is to extend the current capabilities of detailed term accounting opacity codes such as OPAL that are limited to lighter elements of astrophysical interest. At present, opacity calculations of heavier elements use statistical methods that rely on the presence of myriad spectral lines for accuracy. However, statistical approaches have been shown to be inadequate for astrophysical opacity calculations. An application of the TOPAZ code will be to study the limits of statistical methods. Comparisons of TOPAZ to other opacity codes as well as to experiments are presented.