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J. Oreg

Bio: J. Oreg is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Ionization & Autoionization. The author has an hindex of 14, co-authored 24 publications receiving 1362 citations.

Papers
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Journal ArticleDOI
TL;DR: H ULLAC as mentioned in this paper, an integrated code for calculating atomic structure and cross sections for collisional and radiative atomic processes, is based on relativistic quantum mechanical calculations including configuration interaction.
Abstract: We describe H ULLAC , an integrated code for calculating atomic structure and cross sections for collisional and radiative atomic processes. This code evolved and has been used over the years, but so far, there was no coherent, comprehensive, and in-depth presentation of it. It is based on relativistic quantum mechanical calculations including configuration interaction. The collisional cross sections are calculated in the distorted wave approximation. The theory and code are presented, emphasizing the various novel methods that has been developed to obtain accurate results very efficiently. In particular we describe the parametric potential method used for both bound and free orbitals, the factorization–interpolation method applied in the derivation of collisional rates, the phase amplitude approach for calculating the continuum orbitals and the N JGRAF graphical method used in the calculation of the angular momentum part of the matrix elements. Special effort has been made to insure the simplicity of use, which is demonstrated in an example.

437 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: A theory for calculating a many-transition spectrum of electron-ion collisional excitations in the distorted-wave approximation (DWA) and the computationally involved radial part is shown to be a smooth function of transition energies over a very wide range, allowing easy interpolation.
Abstract: A theory for calculating a many-transition spectrum of electron-ion collisional excitations in the distorted-wave approximation (DWA) is presented. First, it is shown that the collision strength including exchange can be factorized into (i) a radial part, involving one-electron wave functions only, and the summation over partial waves of the continuum electron; and (ii) an angular part, involving the coupling between bound electrons in the target states only, specific to each transition. Factorized representations of the collision strengths are derived in various coupling schemes. Second, the computationally involved radial part is shown to be a smooth function of transition energies over a very wide range, allowing easy interpolation. These two results enable one to obtain a complete collisional-excitation array with a drastic reduction of the number of time-consuming radial calculations compared with standard methods. This allows the solution of problems which were heretofore considered impractical. As an illustration, the whole array of excitation rate coefficients for Ni-like Gd xxxvii including the lowest 107 levels (5671 transitions) was calculated in the DWA, and used in a steady-state collisional-radiative model. Resulting population inversions are presented versus plasma density.

206 citations

Journal ArticleDOI
TL;DR: The factorization-interpolation model, developed to compute collisional excitation rate coefficients efficiently in dense plasma, is applied here to autoionization and radiationless electron capture and results are compared to multiconfigurational Dirac-Fock calculations.
Abstract: The factorization-interpolation model, developed to compute collisional excitation rate coefficients efficiently in dense plasma, is applied here to autoionization and radiationless electron capture. Results using a parametric atomic central potential and factorization interpolation for autoionization rates and dielectronic recombination rate coefficients in Ne-like Fe are compared to multiconfigurational Dirac-Fock calculations. Agreement is very good. As a further application, we treat the problem of indirect ionization via collisional excitation followed by autoionization in Zn-like Mo.

62 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of configuration interaction (CI) between relativistic subconfigurations of an electron configuration in the calculation of emission and absorption spectra of plasmas in local thermodynamic equilibrium (LTE) are presented.
Abstract: We present a method for including the effects of configuration interaction (CI) between relativistic subconfigurations of an electron configuration in the calculation of emission and absorption spectra of plasmas in local thermodynamic equilibrium (LTE). Analytical expressions for the correction to the intensities, owing to CI, of an unresolved transition array (UTA) and of a supertransition array (STA) are obtained when the correction is small compared to the spin-orbit splitting, bypassing the need to diagonalize energy matrices. These expressions serve as working formulas in the STA model and, in addition, reveal a priori the conditions under which CI effects are significant. Examples of the effect are presented.

59 citations


Cited by
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Journal ArticleDOI
TL;DR: The Astrophysical Plasma Emission Code (APEC) as mentioned in this paper uses atomic data from the companion ASTPED database to calculate spectral models for hot plasmas, such as collisional and radiative rates, recombination cross sections, dielectronic recombination rates, and satellite line wavelengths.
Abstract: New X-ray observatories (Chandra and XMM-Newton) are providing a wealth of high-resolution X-ray spectra in which hydrogen- and helium-like ions are usually strong features. We present results from a new collisional-radiative plasma code, the Astrophysical Plasma Emission Code (APEC), which uses atomic data in the companion Astrophysical Plasma Emission Database (APED) to calculate spectral models for hot plasmas. APED contains the requisite atomic data such as collisional and radiative rates, recombination cross sections, dielectronic recombination rates, and satellite line wavelengths. We compare the APEC results to other plasma codes for hydrogen- and helium-like diagnostics and test the sensitivity of our results to the number of levels included in the models. We find that dielectronic recombination with hydrogen-like ions into high (n = 6-10) principal quantum numbers affects some helium-like line ratios from low-lying (n = 2) transitions.

2,124 citations

Journal ArticleDOI
TL;DR: In this paper, an approach to fusion that relies on either electron conduction (direct drive) or x rays (indirect drive) for energy transport to drive an implosion is presented.
Abstract: Inertial confinement fusion (ICF) is an approach to fusion that relies on the inertia of the fuel mass to provide confinement. To achieve conditions under which inertial confinement is sufficient for efficient thermonuclear burn, a capsule (generally a spherical shell) containing thermonuclear fuel is compressed in an implosion process to conditions of high density and temperature. ICF capsules rely on either electron conduction (direct drive) or x rays (indirect drive) for energy transport to drive an implosion. In direct drive, the laser beams (or charged particle beams) are aimed directly at a target. The laser energy is transferred to electrons by means of inverse bremsstrahlung or a variety of plasma collective processes. In indirect drive, the driver energy (from laser beams or ion beams) is first absorbed in a high‐Z enclosure (a hohlraum), which surrounds the capsule. The material heated by the driver emits x rays, which drive the capsule implosion. For optimally designed targets, 70%–80% of the d...

2,121 citations

Journal ArticleDOI
TL;DR: The 1990 National Academy of Science final report of its review of the Inertial Confinement Fusion Program recommended completion of a series of target physics objectives on the 10-beam Nova laser at the Lawrence Livermore National Laboratory as the highest priority prerequisite for proceeding with construction of an ignition-scale laser facility as mentioned in this paper.
Abstract: The 1990 National Academy of Science final report of its review of the Inertial Confinement Fusion Program recommended completion of a series of target physics objectives on the 10-beam Nova laser at the Lawrence Livermore National Laboratory as the highest-priority prerequisite for proceeding with construction of an ignition-scale laser facility, now called the National Ignition Facility (NIF). These objectives were chosen to demonstrate that there was sufficient understanding of the physics of ignition targets that the laser requirements for laboratory ignition could be accurately specified. This research on Nova, as well as additional research on the Omega laser at the University of Rochester, is the subject of this review. The objectives of the U.S. indirect-drive target physics program have been to experimentally demonstrate and predictively model hohlraum characteristics, as well as capsule performance in targets that have been scaled in key physics variables from NIF targets. To address the hohlrau...

1,601 citations

Journal ArticleDOI
TL;DR: In this paper, a complete software package for the computation of various atomic data such as energy levels; radiative transition; collisional excitation; ionization by electron impact, photoionizatio...
Abstract: We describe a complete software package for the computation of various atomic data such as energy levels; radiative transition; collisional excitation; ionization by electron impact, photoionizatio...

1,055 citations

Journal ArticleDOI
TL;DR: High energy density (HED) laboratory astrophysics as discussed by the authors is a new class of experimental science, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory.
Abstract: With the advent of high-energy-density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, millimeter-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors, equations of state relevant to planetary interiors, strong shock-driven nonlinear hydrodynamics and radiative dynamics relevant to supernova explosions and subsequent evolution, protostellar jets and high Mach number flows, radiatively driven molecular clouds and nonlinear photoevaporation front dynamics, and photoionized plasmas relevant to accretion disks around compact objects such as black holes and neutron stars.

650 citations