Results of a niobium absorption experiment are presented that represent a major step in the development of techniques necessary for the quantitative characterization of hot, dense matter. The general requirements for performing quantitative analyses of absorption spectra are discussed. Hydrodynamic simulations are used to illustrate the behavior of tamped x-ray-heated matter and to indicate potential two-dimensional problems inherent in the technique. The absorption spectrum of a low-Z material, in this case aluminum, mixed with niobium provides a temperature diagnostic, which together with radiography as a density diagnostic fully characterizes the sample. A discussion is presented of opacity calculations and a comparison to the measurements is given that illustrates the need for experiments to provide a critical test of theory. The experimental technique is placed in context with a review of previous measurements using absorption spectroscopy to probe hot, dense matter. It is shown that the overall experimental concepts, although understood, were not always achieved in previous experiments. \textcopyright{} 1996 The American Physical Society.

Absorption experiments on x-ray-heated mid-Z constrained samples.

Several thin foils have been heated by X-ray radiation emitted by a small gold cavity irradiated with the LULI facility Nd glass laser. The foils were heated to moderate temperatures (10–25 eV) in conditions near local thermodynamic equilibrium. Measurements of the absorption of Kα transitions of aluminum, of the K-shell transitions of boron, and of the n=2–3 and 4 transitions of nickel are reported. A 5000 l/mm transmission grating spectrograph recorded the boron data, and a flat thallium hydrogen phthalate (TlAP) crystal was used for aluminum and nickel absorption measurements. The nickel and aluminum spectra indicate a higher temperature (22–25 eV) than the boron case (14 eV), explained by a difference in the absorption spectra of these elements. In the Ni case the measured 2p-3d spin–orbit–split absorption structures compared well with theoretical spectra obtained with the SCO superconfiguration code using the spin orbit split transition arrays formalism (SOSA). The heating of the foils as calculated with radiative hydrodynamic simulations is very similar to the experimental data.

Radiative heating of B, Al and Ni thin foils at 15–25 eV temperatures

We present measurements of the samarium $(Z=62)$ $M$-shell absorption band around 11 \AA{} (1.1 keV) at electron temperatures between 5 and 20 eV. Using point projection absorption spectroscopy, we measured the absolute transmission of an x-ray probe beam through a radiatively heated samarium plasma at different drive temperatures. The measurements show two principal absorption features corresponding to the spin-orbit-split $3d\ensuremath{-}4f$ transitions of Sm IV--Sm X ions. The influence of the heating on the spectral opacity shape was characterized by a shift of the absorption features to higher energy for a hotter plasma. The data are compared with calculations done with the superconfiguration code SCO for different plasma temperatures. The temperature and average ionization inferred from the analysis of the experiment are compared to radiative hydrodynamic simulations.

Absorption spectroscopy of a radiatively heated samarium plasma

Absorption spectra of magnesium and germanium plasma were measured in the 8–11 A range. The experiments used the Phebus laser (CEA-Centre d’Etudes de Limeil-Valenton) to irradiate a gold hohlraum, within which a CH-tamped Mg or Ge sample was radiatively heated. A 200-ps duration Pr backlight probed the sample at different delayed times to produce spectral absorption features. Temperature was monitored using Mg K-shell absorption measurement that was cross-checked with radiative-hydrodynamic calculations. The experimental technique was used to measure Ge L-shell absorption data. The interpretation of Ge spectral opacity data shows that the orbital relaxation treatment has a strong impact on theoretical results. This is confirmed by detailed-line accounting calculations.

Absorption experiments on X-ray-heated magnesium and germanium constrained samples

The density, temperature and charge state distribution are accurately determined in a highly ionized non-LTE Au sample. Laser heated Au microdots buried in a thin Be foil, reach temperatures of 2 keV and ionize into the M-shell. During expansion, the tamped Au samples remain uniform and in near steady-state ionization equilibrium. The electron temperature is measured with time and space resolved Thomson scattering while the density is determined from time-gated X-ray imaging the expanded Au sample. The charge state distribution is obtained from analysis of emission measurements of Au 5f–3d transition arrays in the wavelength range 3.3–3.9 A, allowing the average charge to be determined to within ∼1% accuracy.

Accurate determination of the charge state distribution in a well characterized highly ionized Au plasma

We have extended the technique of absorption spectroscopy to study the ion charge distribution and the areal mass density variations of expanding laser-produced and radiationdriven plasmas. Specifically, we will present space and time-resolved absorption spectroscopy measurements for K and L -shell ions (Mg and Ge) in the 8–11 A spectral range. The nanosecond plasmas were created either by direct laser irradiance in the case of Mg (up to 10 13 W/cm 2 ) or by indirect x-ray heating (at a few 10 12 W/cm 2 x-ray irradiance). The ion population and areal mass of the expanding plasmas were deduced from the agreement between the experimental optical depths and the theoretical modelling of absorption derived from atomic data calculated either in a detailed configuration MCDF (Mg and Ge) or in a statistical UTA approach (Ge), both analysis being in good agreement. We will also present comparisons of the Mg and Ge data to space and time predictions of the hydrodynamical code CHIVAS.

Space and time resolved absorption spectroscopy of directly and indirectly driven expanding plasmas

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Space and time resolved absorption spectroscopy of directly and indirectly driven expanding plasmas