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Author

A Decoster

Bio: A Decoster is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 75 citations.

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TL;DR: In this article, the first "virtual workshop" designed to compare NLTE emissivities produced by widely differing types of atomic physics codes is presented, and a small set of significant results illustrate the progress that is still to be achieved.
Abstract: We review the first “virtual workshop” designed to compare NLTE emissivities produced by widely differing types of atomic physics codes. A small set of significant results, illustrating the progress that is still to be achieved, is presented. We conclude with some lessons learned and possible avenues for future progress.

77 citations


Cited by
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TL;DR: In this paper, a simple screened-hydrogenic model was proposed to calculate ionization balance with sufficient accuracy, at a low enough computational cost for routine use in radiation-hydrodynamics codes.

166 citations

Journal ArticleDOI
TL;DR: The High Flux Model (HFM) as discussed by the authors was used in the National Ignition Campaign (NIC) gas-filled/capsule-imploding hohlraum energetics campaign.

148 citations

08 Jul 2009
TL;DR: In this paper, a simple screened-hydrogenic model was proposed to calculate ionization balance with surprising accuracy, at a low enough computational cost for routine use in radiation-hydrodynamics codes.
Abstract: The last few years have seen significant progress in constructing the atomic models required for non-local thermodynamic equilibrium (NLTE) simulations. Along with this has come an increased understanding of the requirements for accurately modeling the ionization balance, energy content and radiative properties of different elements for a wide range of densities and temperatures. Much of this progress is the result of a series of workshops dedicated to comparing the results from different codes and computational approaches applied to a series of test problems. The results of these workshops emphasized the importance of atomic model completeness, especially in doubly excited states and autoionization transitions, to calculating ionization balance, and the importance of accurate, detailed atomic data to producing reliable spectra. We describe a simple screened-hydrogenic model that calculates NLTE ionization balance with surprising accuracy, at a low enough computational cost for routine use in radiation-hydrodynamics codes. The model incorporates term splitting, {Delta}n = 0 transitions, and approximate UTA widths for spectral calculations, with results comparable to those of much more detailed codes. Simulations done with this model have been increasingly successful at matching experimental data for laser-driven systems and hohlraums. Accurate and efficient atomic models are just one requirement for integrated NLTE simulations. Coupling the atomic kinetics to hydrodynamics and radiation transport constrains both discretizations and algorithms to retain energy conservation, accuracy and stability. In particular, the strong coupling between radiation and populations can require either very short timesteps or significantly modified radiation transport algorithms to account for NLTE material response. Considerations such as these continue to provide challenges for NLTE simulations.

141 citations

Journal ArticleDOI
TL;DR: The Los Alamos suite of relativistic atomic physics codes is a robust, mature platform that has been used to model highly charged ions in a variety of ways The suite includes capabilities for calculating data related to fundamental atomic structure, as well as the processes of photoexcitation, electron-impact excitation and ionization, photoionization and autoionization within a consistent framework as discussed by the authors.
Abstract: The Los Alamos suite of relativistic atomic physics codes is a robust, mature platform that has been used to model highly charged ions in a variety of ways The suite includes capabilities for calculating data related to fundamental atomic structure, as well as the processes of photoexcitation, electron-impact excitation and ionization, photoionization and autoionization within a consistent framework These data can be of a basic nature, such as cross sections and collision strengths, which are useful in making predictions that can be compared with experiments to test fundamental theories of highly charged ions, such as quantum electrodynamics The suite can also be used to generate detailed models of energy levels and rate coefficients, and to apply them in the collisional-radiative modeling of plasmas over a wide range of conditions Such modeling is useful, for example, in the interpretation of spectra generated by a variety of plasmas In this work, we provide a brief overview of the capabilities within the Los Alamos relativistic suite along with some examples of its application to the modeling of highly charged ions

130 citations

10 Jan 2011
TL;DR: The High Flux Model (HFM) was used in the National Ignition Campaign (NIC) gas-filled/capsule-imploding hohlraum energetics campaign as discussed by the authors.
Abstract: Abstract In 2009 the National Ignition Campaign (NIC) gas-filled/capsule-imploding hohlraum energetics campaign showed good laser-hohlraum coupling, reasonably high drive, and implosion symmetry control via cross-beam transfer. There were, however, discrepancies with expectations from the standard simulation model including: the level and spectrum of the Stimulated Raman light; the tendency towards pancake-shaped implosions; and drive that exceeded predictions early in the campaign, and lagged those predictions late in the campaign. We review here the origins/development path of the “high flux model” (HFM). The HFM contains two principal changes from the standard model: 1) It uses a detailed configuration accounting (DCA) atomic physics non-local-thermodynamic-equilibrium (NLTE) model, and 2) It uses a generous electron thermal flux limiter, f = 0.15, that is consistent with a non-local electron transport model. Both elements make important contributions to the HFM’s prediction of a hohlraum plasma that is cooler than that predicted by the standard model, which uses an NLTE average atom approach, and a value of f = 0.05 for the flux limiter. This cooler plasma is key in eliminating most of the discrepancies between the NIC data and revised expectations based on this new simulation model. The HFM had previously been successfully deployed in correctly modeling Omega Laser illuminated gold sphere x-ray emission data, and NIC empty hohlraum drive. However, when the HFM was first applied to this energetics campaign, the model lacked some credibility/acceptance compared to the standard model, because it actually worsened the discrepancy between the observed hohlraum drive for the 1 MJ class experiments performed late in the campaign and the revised expectation of higher drive based on the HFM. Essentially, the HFM was making a prediction that the laser-hohlraum coupling was less than that assumed at that time. Its credibility was then boosted when a re-evaluation of the laser light losses from the hohlraum due to laser plasma interactions matched its prediction.

127 citations