J. Abdallah

The Los Alamos suite of relativistic atomic physics codes

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.

A NEW GENERATION OF LOS ALAMOS OPACITY TABLES

We present a new, publicly available set of Los Alamos OPLIB opacity tables for the elements hydrogen through zinc. Our tables are computed using the Los Alamos ATOMIC opacity and plasma modeling code, and make use of atomic structure calculations that use fine-structure detail for all the elements considered. Our equation of state model, known as ChemEOS, is based on the minimization of free energy in a chemical picture and appears to be a reasonable and robust approach to determining atomic state populations over a wide range of temperatures and densities. In this paper we discuss in detail the calculations that we have performed for the 30 elements considered, and present some comparisons of our monochromatic opacities with measurements and other opacity codes. We also use our new opacity tables in solar modeling calculations and compare and contrast such modeling with previous work.

X-RAY TRANSMISSION CALCULATIONS FOR AN ALUMINUM PLASMA

Computer programs developed recently at Los Alamos have been used to calculate the transmission of x rays through an aluminum plasma. Theoretical energy levels, oscillator strengths, and photoionization cross sections were combined with the local thermodynamic equilibrium population model to calculate the plasma absorption coefficient as a function of photon energy. The transmission spectrum is simulated by accounting for the plasma depth and spectrometer characteristics. These results are compared to spectra observed during recent experiments; excellent agreement is obtained.

Mixed UTA and detailed line treatment for mid-Z opacity and spectral calculations

We developed a method to mix detailed and statistical treatments within the same transition array and for a set of transition arrays entering the spectral or opacity calculations of light and mid-Z elements. By retaining the strongest lines within a given transition array, the method provides a spectral description comparable in accuracy to a detailed treatment approach, where all the lines are explicitly included in the spectral calculation. The remaining weak lines are represented by a UTA-like functional form. Overall, we show that the computational cost approaches the statistical UTA method. The method has been implemented in the Cowan atomic structure code and applied to the calculation of the LTE and non-LTE spectra of two mid-Z elements, xenon and iron.

Calculations of energy losses due to atomic processes in tokamaks with applications to the International Thermonuclear Experimental Reactor divertor

Reduction of the peak heat loads on the plasma facing components is essential for the success of the next generation of high fusion power tokamaks such as the International Thermonuclear Experimental Reactor (ITER) [Rebut et al., Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, in press)]. Many present concepts for accomplishing this involve the use of atomic processes to transfer the heat from the plasma to the main chamber and divertor chamber walls and much of the experimental and theoretical physics research in the fusion program is directed toward this issue. The results of these experiments and calculations depend upon a complex interplay of many processes. In order to identify the key features of these experiments and calculations and the relative role of the primary atomic processes, simple quasianalytic models and the latest atomic physics rate coefficients and cross sections have been used to assess the relative roles of central radiation losses ...

Generation of X rays and energetic ions from superintense laser irradiation of micron-sized Ar clusters

AbstractHigh-resolutionK-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters havebeen measured with an intensity above 10 19 W0cm 2 and a pulse duration of 30 fs. The total photon flux of 2310 8 photons0pulse was achieved for He a1 resonant line of Ar ~l 5 3.9491 A, 3.14 keV !. In parallel with X-raymeasurements,energydistributionsofemittedionshavebeenmeasured.Themultiplychargedionswithkineticenergiesup to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoricheating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield ofthe He-like argon ion and the ion kinetic energy.Keywords: Cluster; High power laser; Isochoric heating; Multiply charged ion; X ray 1. INTRODUCTIONRecent development of ultrashort, high peak-power lasersystems, based on the chirped pulse amplification ~CPA!technique, opens up a new regime of laser–matter inter-action ~Perry & Mourou, 1994!. Nowadays a focusing ofsuch laser pulses produces laser peak intensities well above10

Exotic dense-matter states pumped by a relativistic laser plasma in the radiation-dominated regime

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of KK hollow atoms (atoms without n = 1 electrons) from thin Al foils was observed at pulse intensities of 3 × 10(20) W/cm(2). The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the KK hollow atom production. We estimate that this x-ray field has an intensity of >5 × 10(18) W/cm(2) and is in the 3 keV range.

K-shell spectra from hot dense aluminum layers buried in carbon and heated by ultrashort laser pulses

Ultrashort laser pulses allow for the generation of hot plasmas near solid state densities. For this purpose a Ti:Sapphire laser was used, which delivers after frequency doubling, pulses of high contrast with an energy of about 60mJ and a duration of 150fs at 395nm. The typical intensity on the target was a few 1017W/cm2. To achieve a high degree of uniformity we used targets consisting of a 25nm thin Al tracer layer buried at different depths up to 400nm in solid carbon. Time-integrated Al K-shell spectra are presented. Characteristic features of the spectra are significant high-order satellite line emission, strong line broadening and a center-of-mass line shift to the red, which was observed in transitions from principal quantum number n=2 or 3 to 1. Accurate measurement of the shift was made possible by using the cold Si Kα line as an absolute wavelength calibration. In addition to time-integrated measurements, we used an ultrafast X-ray streak camera to obtain time and spectrally resolved spectra. Typical durations of the Lyα and Heα lines are in the range 2–4 ps. The experimental results are compared with a time-dependent model, which combines hydrodynamic simulations, time-dependent atomic kinetics, detailed spectral line shapes including line shifts, and radiation transport.

Radiative Losses of Solar Coronal Plasmas

A comprehensive set of calculations of the radiative losses of solar coronal plasmas is presented. The Los Alamos suite of atomic structure and collision codes is used to generate collisional data for 15 coronal elements. These data are used in the Los Alamos plasma kinetics code ATOMIC to compute the radiative power loss as a function of electron temperature. We investigate the sensitivity of the loss curves to the quality of the atomic data and changes in the coronal elemental abundances, and we compare our results with previous work.

Los Alamos Opacities: Transition from LEDCOP to ATOMIC

This paper discusses the development of the ATOMIC code, a new low to mid Z opacity code, which will replace the current Los Alamos low Z opacity code LEDCOP. The ATOMIC code is based on the FINE code, long used by the Los Alamos group for spectral comparisons in local thermodynamic equilibrium (LTE) and for non‐LTE calculations, utilizing the extensive databases from the atomic physics suite of codes based on the work of R. D. Cowan. Many of the plasma physics packages in LEDCOP, such as line broadening and free‐free absorption, are being transferred to the new ATOMIC code. A new equation of state (EOS) model is being developed to allow higher density calculations than were possible with either the FINE or LEDCOP codes. Extensive modernization for both ATOMIC and the atomic physics code suites, including conversion to Fortran 90 and parallelization, are under way to speed up the calculations and to allow the use of expanded databases for both the LTE opacity tables and the non‐LTE calculations. Future pl...