Absorption experiments on x-ray-heated mid-Z constrained samples.
TL;DR: 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.
Abstract: 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.
Citations
More filters
TL;DR: Measurements of wavelength-resolved iron opacity at electron temperatures and electron densities at the solar radiation/convection zone boundary show that wavelength-dependent opacity is 30–400 per cent higher than predicted, which represents roughly half the change in the mean opacity needed to resolve the solar discrepancy.
Abstract: Laboratory measurements of iron opacity made under conditions similar to those inside the Sun reveal much higher opacity than predicted, helping to resolve inconsistencies within stellar models of the internal temperatures of stars. Internal temperature profiles of the Sun and other stars are controlled in large part by the rate at which radiation is absorbed by stellar matter. Until now it has not been possible to determine the opacity of matter in star-like conditions in the laboratory, but James Bailey et al. have now achieved that feat using the Sandia National Laboratories' Z facility, the world's most powerful X-ray generator. The experiments reveal a wavelength-resolved iron opacity that is 30 to 400 times greater than predicted in conditions very similar to those at the radiation/convection zone boundary in the Sun. Previous measurements of stellar interiors have been based on observations of surface waves, and there were serious discrepancies between theoretical predictions and observations. The new measurements account for about half of adjustment in opacity figures required to restore agreement between standard solar models and observations. Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2,3,4,5. A particular problem arose2,3,6,7,8 when refined photosphere spectral analysis9,10 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted2,3,6,7,8, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity2,12 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.
354 citations
TL;DR: The 80-TW "Z" pulsed power facility at Sandia National Laboratories as discussed by the authors is the largest pulsed-power device in the world today, and it can discharge up to 22'MJ of energy stored in its capacitor banks into a current pulse that rises in 100'ns and peaks at a current as high as 30 MA in low-inductance cylindrical targets.
Abstract: Pulsed power accelerators compress electrical energy in space and time to provide versatile experimental platforms for high energy density and inertial confinement fusion science. The 80-TW “Z” pulsed power facility at Sandia National Laboratories is the largest pulsed power device in the world today. Z discharges up to 22 MJ of energy stored in its capacitor banks into a current pulse that rises in 100 ns and peaks at a current as high as 30 MA in low-inductance cylindrical targets. Considerable progress has been made over the past 15 years in the use of pulsed power as a precision scientific tool. This paper reviews developments at Sandia in inertial confinement fusion, dynamic materials science, x-ray radiation science, and pulsed power engineering, with an emphasis on progress since a previous review of research on Z in Physics of Plasmas in 2005.
127 citations
TL;DR: Theoretical opacities for calculating energy transport in plasmas are required for calculating stellar interiors, inertial fusion, and Z pinches as mentioned in this paper, which depends on the Opacities of mid-atomic-number elements over a wide range of temperatures.
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...
115 citations
Journal Article•
TL;DR: Theoretical opacities for calculating energy transport in plasmas are required for calculating stellar interiors, inertial fusion, and Z pinches as discussed by the authors, which depends on the Opacities of mid-atomic-number elements over a wide range of temperatures.
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...
105 citations
TL;DR: The fourth international LTE opacity workshop and code comparison study, WorkOp-IV, was held in Madrid in 1997 as mentioned in this paper, with a focus on iron opacities, and the astrophysically important photon absorption region between 50 and 80 eV was emphasized for a sequence of iron plasmas at densities and temperatures that produce nearly the same average ionization stage (Z ∗ ∼8.6).
Abstract: The fourth international LTE opacity workshop and code comparison study, WorkOp-IV, was held in Madrid in 1997. Results of this workshop are summarized with a focus on iron opacities. In particular, the astrophysically important photon absorption region between 50 and 80 eV is emphasized for a sequence of iron plasmas at densities and temperatures that produce nearly the same average ionization stage (Z ∗ ∼8.6) . Experimental data that addressed this spectral region is also reviewed.
91 citations
References
More filters
TL;DR: In this paper, the authors present new radiative Rosseland mean opacity tables calculated with the OPAL code developed independently at LLNL, which allow accurate interpolation in temperature, density, hydrogen mass fraction, as well as metal mass fraction.
Abstract: For more than two decades the astrophysics community has depended on opacity tables produced at Los Alamos. In the present work we offer new radiative Rosseland mean opacity tables calculated with the OPAL code developed independently at LLNL. We give extensive results for the recent Anders-Grevesse mixture which allow accurate interpolation in temperature, density, hydrogen mass fraction, as well as metal mass fraction
594 citations
TL;DR: A method is presented for calculating the bound-bound emission from a local thermodynamic equilibrium plasma and it is shown that under certain plasma conditions the contributions of low-probability transitions can accumulate into an important component of the emission.
Abstract: A method is presented for calculating the bound-bound emission from a local thermodynamic equilibrium plasma. The total transition array of a specific single-electron transition, including all possible contributing configurations, is described by only a small number of super-transition-arrays (STA's). Exact analytic expressions are given for the first few moments of an STA. The method is shown to interpolate smoothly between the average-atom (AA) results and the detailed configuration accounting that underlies the unresolved transition array (UTA) method. Each STA is calculated in its own, optimized potential, and the model achieves rapid convergence in the number of STA's included. Comparisons of predicted STA spectra with the results of the AA and UTA methods are presented. It is shown that under certain plasma conditions the contributions of low-probability transitions can accumulate into an important component of the emission. In these cases, detailed configuration accounting is impractical. On the other hand, the detailed structure of the spectrum under such conditions is not described by the AA method. The application of the STA method to laser-produced plasma experiments is discussed.
319 citations
TL;DR: In this article, an algorithm is presented to calculate electronic levels and the equation of state of atoms suitable for arbitrary matter density and temperature, using the self-consistent field treatment.
Abstract: An algorithm is presented to calculate electronic levels and the equation of state of atoms suitable for arbitrary matter density and temperature. The self-consistent-field treatment starts with relativistic Thomas-Fermi-Dirac model in the iterative procedure. The Fermi statistics and the central-field approximation are maintained, giving an average atom representation. The broadening of upper electronic levels into bands is taken into account in a simple approximation. Calculations are presented for the ${\mathrm{Fe}}^{26}$ and ${\mathrm{Rb}}^{37}$ atoms at several temperatures and matter densities.
282 citations
TL;DR: In this article, measurements of the absorption of X-rays by 1 to 2 transitions in Al XII through Al VIII have been made in a laser-heated slab plasma at the measured temperature and density of 58 ^ 4e V and 0.020 g cm~3.
Abstract: Measurements of the opacity of aluminum in a well characterized, hot, dense, laser produced plasma are reported. Measurements of the absorption of X-rays by 1 to 2 transitions in Al XII through Al VIII have been made in a laser-heated slab plasma at the measured temperature and density of 58 ^ 4e V and 0.020 ^ 0.007 g cm~3. Separate measurements of the temperature and density were made. The con- ditions in the plasma were determined to be reproducible, spatially uniform, and in nearly complete local thermodynamic equilibrium. The absorption spectra and the temperature-density data obtained provide an improved means for comparison with detailed atomic physics and opacity calculations. Subject headings: atomic datamethods: laboratoryplasmasX-rays: general
150 citations
TL;DR: The results of an experiment measuring the photoabsorption in the spectral region from 50 to 120 eV of x-ray-heated iron are reported which corroborate these new opacity calculations, providing an indirect validation of the theory.
Abstract: Novel opacity calculations, which treat in detail the spectra of medium-Z ions [Rogers and Iglesias, Astrophys. J. Suppl. Ser. 79, 507 (1992)], produce results that are substantially different from opacity calculations extant in the literature. These new opacities provide solutions to a number of outstanding problems in astrophysics, thus providing an indirect validation of the theory. We report the results of an experiment measuring the photoabsorption in the spectral region from 50 to 120 eV of x-ray-heated iron which corroborate these new opacity calculations.
134 citations