Mean Opacity Research Articles

Eddy evolution during large dust storms

The evolution of eddy kinetic energy during the development of large regional dust storms on Mars is investigated using the Mars Analysis Correction Data Assimilation (MACDA) reanalysis product and the dust storm data derived from Mars Global Surveyor Mars Daily Global Maps. Transient eddies in MACDA are decomposed into different components according to their eddy periods: P≤1 sol, 1<P≤8 sols, 8<P≤60 sols. This paper primarily focuses on the Mars year 24 pre-solstice ”A” storm that starts with many episodes of frontal/flushing dust storms from the northern hemisphere and attains its maximum global mean opacity after dust expansion in the southern hemisphere. During the development of this storm, the dominant eddies in terms of eddy kinetic energy progress from the 1<P≤8 sol eddies in the northern mid/high latitudes to the P≤1 sol eddies (dominated by thermal tides) in the southern mid latitudes, and the 8<P≤60 sol eddies show a prominent peak with the increased global-mean dust opacity. The peaks of the 1<P≤8 sol eddies are found to best correlate with the average area of textured frontal/flushing dust storms within 40∘N–60∘N. The region where the 1<P≤8 sol eddies increase the most corresponds to the main flushing channel. The eddy kinetic energy of the P≤1 eddies, dominated by P = 1 and its harmonics, increases with the global mean dust opacity both before and after the winter solstice in Mars year 24. The 8<P≤60 sol eddies briefly spike during large, regional dust storms but remain weak if dust storm sequences do not lead to a major dust storm. Zonal wavenumber analysis of eddy kinetic energy shows that the peaks of the 1<P≤8 eddies often result from combinations of zonal wavenumbers 1 to 3, while the P≤1 eddies and 8<P≤60 sol eddies are each dominated by zonal wavenumber 1.

Non-LTE radiation hydrodynamics in PLUTO

Context. Modeling the dynamics of most astrophysical structures requires an adequate description of the interaction of radiation and matter. Several numerical (magneto-) hydrodynamics codes were upgraded with a radiation module to fulfill this request. However, those that used either the flux-limited diffusion (FLD) or the M1 radiation moment approaches are restricted to local thermodynamic equilibrium (LTE). This assumption may not be valid in some astrophysical cases. Aims. We present an upgraded version of the LTE radiation-hydrodynamics (RHD) module implemented in the PLUTO code, which we have extended to handle non-LTE regimes. Methods. Starting from the general frequency-integrated comoving-frame equations of RHD, we have justified all the assumptions that were made to obtain the non-LTE equations that are implemented in the module under the FLD approximation. An operator-split method with two substeps was employed: the hydrodynamics part was solved with an explicit method by the solvers that are currently available in PLUTO, and the non-LTE radiation diffusion and energy exchange part was solved with an implicit method. The module was implemented in the PLUTO environment. It uses databases of radiative quantities that can be provided independently by the user: the radiative power loss, and the Planck and Rosseland mean opacities. In our case, these quantities were determined from a collisional-radiative steady-state model, and they are tabulated as functions of temperature and density. Results. Our implementation has been validated through different tests, in particular, radiative shock tests. The agreement with the semi-analytical solutions (when available) is good, with a maximum error of 7%. Moreover, we have proved that a non-LTE approach is of paramount importance to properly model accretion shock structures. Conclusion. Our radiation FLD module represents a step toward a general non-LTE RHD modeling.

Plasmas Computed with ATMED CR of the 3rd Non-LTE Code Comparison Workshop Database

In this paper, there are presented some results calculated with ATMED CR of the 3rd Non-LTE Code Comparison Workshop held in December 2003, when this software didn’t exist, having been released in 2017. NLTE population kinetics codes were tested of steady-state cases for C, Al, Ar, Ge, Xe and Au plasmas selected for detailed comparisons. The scope of the meeting consisted of analyzing steady-state dense plasma cases of carbon, low temperature plasmas of aluminium and argon, X-ray laser experiments of germanium also with imposing a Planckian radiation field, medium- and high-Z multicharged ions of hot “experiment-related” plasmas of xenon, using real electron temperature and density parameters inferred from electronic and ionic Thomson scattering spectra and finally plasmas of gold. Being motivated by germanium X-ray laser experiments, the time history of electronic temperature Te and density Ne for a temporal dependent case is provided in Workshop NLTE-3. The calculation with ATMED CR has been carried out to t = 1.975 ns considering the non-uniform time grid along with the corresponding values of Te and Ne presented, being the initial condition LTE at low temperature. &#x0D; The results for plasma properties can be considered as relatively precise and optimal, being checked fundamentally the high sensitivity of calculations to changes in regime, local thermodynamic equilibrium (LTE) or non-LTE (NLTE), electronic and radiation temperatures, electronic density and the percentage of hot electrons. Frequency resolved and mean opacities are also displayed computed with ATMED CR using UTA (Unresolved Transition Array) or Mixed UTA formalisms.

Simultaneous X-ray and XUV absorption measurements in nickel laser-produced plasma close to LTE

We present an experiment performed in 2016 at the LULI2000 laser facility in which X-ray and XUV absorption structures of nickel hot plasmas were measured simultaneously. Such experiments may provide stringent tests of the accuracy of plasma atomic-physics codes used to the modeling of plasmas close to local thermodynamic equilibrium. The experimental set-up relies on a symmetric heating of the sample foil by two gold hohlraums in order to reduce the spatial gradients. The plasma conditions are characterized by temperatures between 10 and 20 eV and densities of the order of 10−3 g/cm3–10−2 g/cm3. For the X-ray part, we investigate the 2p-3d and 2p-4d transitions, and for the XUV part, we recorded the Δn = 0 (n = 3) transitions, which present a high sensitivity to plasma temperature. These latter transitions are of particular interest because, in mid-Z plasmas, they dominate the Planck and Rosseland mean opacities. Measured spectra are compared to calculations performed using the hybrid opacity code SCO-RCG and the Flexible Atomic Code (FAC). The influence of a spectator electron on the calculated spectra is analyzed using the latter code.

Seismic modelling of early B-type pulsators observed by BRITE – I. θ Ophiuchi

We analyse time-series observations from the BRITE-Constellation of the well known $\beta$ Cephei type star $\theta$ Ophiuchi. Seven previously known frequencies were confirmed and nineteen new frequency peaks were detected. In particular, high-order g modes, typical for the SPB (Slowly Pulsating B-type star) pulsators, are uncovered. These low-frequency modes are also obtained from the 7-year SMEI light curve. If g modes are associated with the primary component of $\theta$ Oph, then our discovery allows, as in the case of other hybrid pulsators, to infer more comprehensive information on the internal structure. To this aim we perform in-depth seismic studies involving simultaneous fitting of mode frequencies, reproducing mode instability and adjusting the relative amplitude of the bolometric flux variations. To explain the mode instability in the observed frequency range a significant increase of the mean opacity in the vicinity of the $Z$-bump is needed. Moreover, constraints on mass, overshooting from the convective core and rotation are derived. If the low-frequency modes come from the speckle B5 companion then taking into account the effects of rotation is enough to explain the pulsational mode instability.

Extended Calculations of Energy Levels and Transition Rates of Nd ii-iv Ions for Application to Neutron Star Mergers

Abstract The coalescence of a binary neutron star gives rise to electromagnetic emission, known as a kilonova, that is powered by radioactive decays of r-process nuclei. Observations of a kilonova associated with GW170817 provide a unique opportunity to study heavy element synthesis in the universe. However, the atomic data of r-process elements are not yet complete enough to decipher the light curves and spectral features of kilonovae. In this paper, we perform extended atomic calculations of neodymium (Nd, Z = 60) to study the impact of the accuracy in atomic calculations on astrophysical opacities. By employing multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods, we calculate the energy levels and transition data of electric dipole transitions for Nd ii, Nd iii, and Nd iv ions. Compared with previous calculations, our new results provide better agreement with the experimental data. The energy level accuracies achieved in the present work are 10%, 3%, and 11% for Nd ii, Nd iii, and Nd iv, respectively, compared to the NIST database. We confirm that the overall properties of the opacity are not significantly affected by the accuracies of the atomic calculations. The impact on the Planck mean opacity is up to a factor of 1.5, which affects the timescale of kilonovae by at most 20%. However, we find that the wavelength-dependent features in the opacity are affected by the accuracies of the calculations. We emphasize that accurate atomic calculations, in particular for low-lying energy levels, are important to provide predictions of kilonova light curves and spectra.

Type Ia supernovae have two physical width–luminosity relations and they favour sub-Chandrasekhar and direct collision models - II. Colour evolution

While the width-luminosity relation (WLR) among type Ia supernovae (slower is brighter) is one of the best studied properties of this type of events, its physical basis has not been identified convincingly. The 'luminosity' is known to be related to a clear physical quantity -- the amount of $^{56}$Ni synthesized, but the 'width' has not been quantitatively linked yet to a physical time scale. We show that the recombination time of $^{56}$Fe and $^{56}$Co from doubly to singly ionized states causes the typical observed break in the color curve B-V due to a cliff in the mean opacities, and is a robust width measure of the light curve, which is insensitive to radiation transfer uncertainties. A simple photospheric model is shown to predict the recombination time to an accuracy of $\sim5$ days, allowing a quantitative understanding of the color WLR. Two physical times scales of the width luminosity relation are shown to be set by two column densities -- the total column density which sets the gamma-ray escape time $t_0$ (previous Paper I) and the $^{56}$Ni column density which sets the recombination time (this Paper II). Central detonations of sub-$\rm M_{ch}$ WDs and direct WD collision models have gamma-ray escape times and recombination times which are consistent with observations across the luminosity range of type Ia's. Delayed detonation Chandrasekhar mass models have recombination times that are broadly consistent with observations, with tension at the bright end of the luminosity range and inconsistent gamma-ray escape times at the faint end.

Influence of metallicity on the near-surface effect on oscillation frequencies

Context. The CoRoT and Kepler missions have provided high-quality measurements of the frequency spectra of solar-like pulsators, enabling us to probe stellar interiors with a very high degree of accuracy by comparing the observed and modelled frequencies. However, the frequencies computed with 1D models suffer from systematic errors related to the poor modelling of the uppermost layers of stars. These biases are what is commonly named the near-surface effect. The dominant effect is thought to be related to the turbulent pressure that modifies the hydrostatic equilibrium and thus the frequencies. This has already been investigated using grids of 3D hydrodynamical simulations, which also were used to constrain the parameters of the empirical correction models. However, the effect of metallicity has not been considered so far. Aims. We aim to study the impact of metallicity on the surface effect, investigating its influence across the Hertzsprung-Russell diagram, and providing a method for accounting for it when using the empirical correction models. Methods. We computed a grid of patched 1D stellar models with the stellar evolution code CESTAM in which poorly modelled surface layers have been replaced by averaged stratification computed with the 3D hydrodynamical code CO5BOLD. It allowed us to investigate the dependence of both the surface effect and the empirical correction functions on the metallicity. Results. We found that metallicity has a strong impact on the surface effect: keeping Teff and log g constant, the frequency residuals can vary by up to a factor of two (for instance from [Fe/H] = + 0.0 to [Fe/H] = + 0.5). Therefore, the influence of metallicity cannot be neglected. We found that the correct way of accounting for it is to consider the surface Rosseland mean opacity. It allowed us to give a physically grounded justification as well as a scaling relation for the frequency differences at νmax as a function of Teff, log g and κ. Finally, we provide prescriptions for the fitting parameters of the most commonly used correction functions. Conclusions. We show that the impact of metallicity through the Rosseland mean opacity must be taken into account when studying and correcting the surface effect.

Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds

Context. Clumping in the radiation-driven winds of hot, massive stars severly affects the derivation of synthetic observables across the electromagnetic spectrum. Aims. We implement a formalism for treating wind clumping – focusing in particular on the light-leakage effects associated with a medium that is porous in physical and velocity space – into the global (photosphere + wind) NLTE model atmosphere and spectrum synthesis code FASTWIND. Methods. The basic method presented here assumes a stochastic, two-component wind consisting of a mixture of optically thick and thin clumps embedded in a rarefied inter-clump medium. We have accounted fully for the reductions in opacity associated with porosity in physical and velocity-space (the latter due to Doppler shifts in an accelerating medium), as well as for the well-known effect that opacities depending on ⟨ρ2⟩ are higher in clumpy winds than in smooth ones of equal mass-loss rate. By formulating our method in terms of suitable mean and effective opacities for the clumpy wind, we are able to compute atmospheric models with the same speed (∼15 min on a modern laptop or desktop) as in previous generations of FASTWIND. Results. After verifying important analytic limits (smooth, optically thin, completely optically thick), we present some first, generic results of the new models. These include: i) Confirming earlier results that velocity-space porosity is critical for analysis of UV wind resonance lines in O-stars; ii) for the optical Hα line, we show that optically thick clumping effects are small for O-stars, but potentially very important for late B and A-supergiants; iii) in agreement with previous work, we show that spatial porosity is a marginal effect for absorption of high-energy X-rays in O-stars, as long as the mean-free path between clumps are kept at realistic values ≲R*; iv) whereas radio absorption in O-stars shows strong spatial porosity effects in near photospheric layers, it is negligible at their typical radio-photosphere radii ∼100R*; v) regarding the wind ionization balance, a general trend is that increased rates of recombination in simulations with optically thin clumps lead to overall lower degrees of ionization than in corresponding smooth models, but that this effect now is counteracted by the increased levels of light-leakage associated with porosity in physical and velocity space (i.e., by an increase of ionization rates). We conclude by discussing future work and some planned applications for this new generation of FASTWIND models.

Novel radiomics evaluation of bone formation utilizing multimodal (SPECT/X-ray CT) in vivo imaging.

Although an extensive research is being undertaken, the ideal bone graft and evaluation method of the bone formation draw still a warranted attention. The purpose of this study was to develop a novel multimodal radiomics evaluation method, utilizing X-ray computed tomography (CT) and single photon emission computed tomography (SPECT) with Tc-99m-Methyl diphosphonate (Tc-99m-MDP) tracer. These modalities are intended to provide quantitative data concerning the mineral bone density (after evaluation it is referred to as opacity) and the osteoblast activity, at the same time. The properties of bone formation process within poly (methyl methacrylate)-based bone cement graft (PMMA) was compared to that of albumin coated, sterilized, antigen-extracted freeze-dried human bone grafts (HLBC), in caudal vertebrae (C5) of rats. The animals were scanned at 3 and 8 weeks after surgery. In both groups, the mean opacity increased, while the mean Tc-99m-MDP activity decreased. The later parameter was significant (n = 4, p = 0.002) only in HLBC group. The linear regression analysis of PMMA-treated group variables (mean opacity increase; mean Tc-99m-MDP activity decrease), revealed a negative correlation with the medium strength (r = 0.395, p = 0.605). Whereas, it showed strong positive correlation when HLBC group variables were analyzed (r = 0.772, p = 0.012). These results indicate that using HLBC grafts is advantageous in terms of the osteoblast activity and bone vascularization over PMMA cement. Using this regression analysis method, we were able to distinguish characteristics that otherwise could not be distinguished by a regular data analysis. Hence, we propose utilizing this novel method in preclinical tests, and in clinical monitoring of bone healing, in order to improve diagnosis of bone-related diseases.

Average Opacity Calculation for Core-collapse Supernovae

Abstract Supernovae (SNe) are among the most intensely studied objects of modern astrophysics, but due to their complex physical nature, theoretical models are essential to better understand these exploding stars, as well as the properties of the variation of the emitted radiation. One possibility for modeling SNe light curves (LCs) is the construction of a simplified semianalytic model, which can be used for getting order-of magnitude estimates of the SN properties. One of the strongest simplifications in most of these LC models is the assumption of the constant Thomson-scattering opacity that can be determined as the average opacity of the ejecta. Here we present a systematic analysis for estimating the average opacity in different types of core-collapse supernovae that can be used as the constant opacity of the ejecta in simplified semianalytic models. To use these average opacities self-consistently during LC fit, we estimate their values from hydrodynamic simulations. In this analysis, we first generate MESA stellar models with different physical parameters (initial mass, metallicity, and rotation), which determine the mass-loss history of the model star. Then we synthesize SN LCs from these models with the SNEC hydrodynamic code and calculate the Rosseland mean opacity in every mass element. Finally, we compute the average opacities by integrating these Rosseland mean opacities. As a result, we find that the average opacities from our calculations show adequate agreement with the opacities generally used in previous studies.

Computation of Atomic Astrophysical Opacities

The revision of the standard Los Alamos opacities in the 1980–1990s by a group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) consortium was an early example of collaborative big-data science, leading to reliable data deliverables (atomic databases, monochromatic opacities, mean opacities, and radiative accelerations) widely used since then to solve a variety of important astrophysical problems. Nowadays the precision of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is a recurrent topic in a hot debate involving stringent comparisons between theory, laboratory experiments, and solar and stellar observations in sophisticated research fields: the standard solar model (SSM), helio and asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear reaction rates, solar neutrino observations, computational atomic physics, and plasma experiments. In this context, an unexpected downward revision of the solar photospheric metal abundances in 2005 spoiled a very precise agreement between the helioseismic indicators (the radius of the convection zone boundary, the sound-speed profile, and helium surface abundance) and SSM benchmarks, which could be somehow reestablished with a substantial opacity increase. Recent laboratory measurements of the iron opacity in physical conditions similar to the boundary of the solar convection zone have indeed predicted significant increases (30–400%), although new systematic improvements and comparisons of the computed tables have not yet been able to reproduce them. We give an overview of this controversy, and within the OP approach, discuss some of the theoretical shortcomings that could be impairing a more complete and accurate opacity accounting.

The Carnegie Supernova Project I

Stripped-envelope (SE) supernovae (SNe) include H-poor (Type IIb), H-free (Type Ib), and He-free (Type Ic) events thought to be associated with the deaths of massive stars. The exact nature of their progenitors is a matter of debate with several lines of evidence pointing towards intermediate mass (Minit&lt; 20 M⊙) stars in binary systems, while in other cases they may be linked to single massive Wolf-Rayet stars. Here we present the analysis of the light curves of 34 SE SNe published by the Carnegie Supernova Project (CSP-I) that are unparalleled in terms of photometric accuracy and wavelength range. Light-curve parameters are estimated through the fits of an analytical function and trends are searched for among the resulting fit parameters. Detailed inspection of the dataset suggests a tentative correlation between the peak absolute B-band magnitude and Δm15(B), while the post maximum light curves reveals a correlation between the late-time linear slope and Δm15. Making use of the full set of optical and near-IR photometry, combined with robust host-galaxy extinction corrections, comprehensive bolometric light curves are constructed and compared to both analytic and hydrodynamical models. This analysis finds consistent results among the two different modeling techniques and from the hydrodynamical models we obtained ejecta masses of 1.1–6.2M⊙, 56Ni masses of 0.03–0.35M⊙, and explosion energies (excluding two SNe Ic-BL) of 0.25–3.0 × 1051 erg. Our analysis indicates that adopting κ = 0.07 cm2 g-1 as the mean opacity serves to be a suitable assumption when comparing Arnett-model results to those obtained from hydrodynamical calculations. We also find that adopting He i and O i line velocities to infer the expansion velocity in He-rich and He-poor SNe, respectively, provides ejecta masses relatively similar to those obtained by using the Fe ii line velocities, although the use of Fe ii as a diagnostic does imply higher explosion energies. The inferred range of ejecta masses are compatible with intermediate mass (MZAMS ≤ 20M⊙) progenitor stars in binary systems for the majority of SE SNe. Furthermore, our hydrodynamical modeling of the bolometric light curves suggests a significant fraction of the sample may have experienced significant mixing of 56Ni, particularly in the case of SNe Ic.

Predicting Rosseland mean opacities of Aluminum using a difference converging method

A difference converging method for opacity (DCMo) calculation is suggested to predict opacities and transmissions of metal plasmas at other photon energies that were not measured. The applications of the DCMo to the opacity and transmission calculations of Aluminum plasmas, in the spectral range of 73.5eV ≤ hν ≤ 245eV with Te = 20eV, and of 1475eV ≤ hν ≤ 1540eV with Te = 19eV, show that: 1) the DCMo correctly reproduce all important absorption structures of the Al plasmas and their corresponding intensities; 2) the agreement between the experimental and the DCMo transmissions is notably better than that between the experimental and some other computational transmissions like the ones obtained using OPAL and ATOMIC models.

Efficiency of thermal relaxation by radiative processes in protoplanetary discs: constraints on hydrodynamic turbulence

Hydrodynamic, non-magnetic instabilities can provide turbulent stress in the regions of protoplanetary discs, where the MRI can not develop. The induced motions influence the grain growth, from which formation of planetesimals begins. Thermal relaxation of the gas constrains origins of the identified hydrodynamic sources of turbulence in discs. We estimate the radiative relaxation timescale of temperature perturbations and study the dependence of this timescale on the perturbation wavelength, the location within the disc, the disc mass, and the dust-to-gas mass ratio. We then apply thermal relaxation criteria to localise modes of the convective overstability, the vertical shear instability, and the zombie vortex instability. Our calculations employed the latest tabulated dust and gas mean opacities and we account for the collisional coupling to the emitting species. The relaxation criterion defines the bulk of a typical T Tauri disc as unstable to the development of linear hydrodynamic instabilities. The midplane is unstable to the convective overstability from at most $2\mbox{ au}$ and up to $40\mbox{ au}$, as well as beyond $140\mbox{ au}$. The vertical shear instability can develop between $15\mbox{ au}$ and $180\mbox{ au}$. The successive generation of (zombie) vortices from a seeded noise can work within the inner $0{.}8\mbox{ au}$. Dynamic disc modelling with the evolution of dust and gas opacities is required to clearly localise the hydrodynamic turbulence, and especially its non-linear phase.

Pre-nebular Light Curves of SNe I

Abstract We compare analytic predictions of supernova light curves with recent high-quality data from SN2011fe (Ia), KSN2011b (Ia), and the Palomar Transient Factory and the La Silla-QUEST variability survey (LSQ) (Ia). Because of the steady, fast cadence of observations, KSN2011b provides unique new information on SNe Ia: the smoothness of the light curve, which is consistent with significant large-scale mixing during the explosion, possibly due to 3D effects (e.g., Rayleigh–Taylor instabilities), and provides support for a slowly varying leakage (mean opacity). For a more complex light curve (SN2008D, SN Ib), we separate the luminosity due to multiple causes and indicate the possibility of a radioactive plume. The early rise in luminosity is shown to be affected by the opacity (leakage rate) for thermal and non-thermal radiation. A general derivation of Arnett’s rule again shows that it depends upon all processes heating the plasma, not just radioactive ones, so that SNe Ia will differ from SNe Ibc if the latter have multiple heating processes.

Radiative properties of matter based on quantum statistical method

We present the preliminary results of our code OPAQS (opacity calculation using quantum statistical model) that is based on the self consistent Hartree–Fock–Slater model for the average atom. The code is capable of performing robust calculations of average charge state, frequency-dependent and mean opacities. The accuracy of the atomic model is verified by comparing the calculations of average charge state with various published results. The monochromatic opacities for iron computed at different sets of temperatures and densities are compared with LEDCOP. The Rosseland and Planck opacities for iron and aluminum are validated with some state-of-the-art codes. The results are in good agreement with the published data.

On the contribution of active galactic nuclei to the high-redshift metagalactic ionizing background

Motivated by the claimed detection of a large population of faint active galactic nuclei (AGN) at high redshift, recent studies have proposed models in which AGN contribute significantly to the z > 4 H I ionizing background. In some models, AGN are even the chief sources of reionization. If correct, these models would make necessary a complete revision to the standard view that galaxies dominated the high-redshift ionizing background. It has been suggested that AGN-dominated models can better account for two recent observations that appear to be in conflict with the standard view: (1) large opacity variations in the z ~ 5.5 H I Lyman-alpha forest, and (2) slow evolution in the mean opacity of the He II Lyman-alpha forest. Large spatial fluctuations in the ionizing background from the brightness and rarity of AGN may account for the former, while the earlier onset of He II reionization in these models may account for the latter. Here we show that models in which AGN emissions source >~ 50 % of the ionizing background generally provide a better fit to the observed H I Lyman-alpha forest opacity variations compared to standard galaxy-dominated models. However, we argue that these AGN-dominated models are in tension with constraints on the thermal history of the intergalactic medium (IGM). Under standard assumptions about the spectra of AGN, we show that the earlier onset of He II reionization heats up the IGM well above recent temperature measurements. We further argue that the slower evolution of the mean opacity of the He II Lyman-alpha forest relative to simulations may reflect deficiencies in current simulations rather than favor AGN-dominated models as has been suggested.

Opacity Structure of Glass Ablator in ICF Target Design

Opacity is dependent on the radiation temperature, material temperature and density of the material. The collisional ionization and the excitation rate can have direct effect on the temperature and the electron density of plasma. The plasma density can be determined by measurements of Stark-broadened K-shell spectral lines. Because Silicon may be used as dopant in the ablator of ignition target, the knowledge of their opacities is very important. The purpose of this work is to obtain a more detailed structure of opacity in regards with broadening effects in the form of Voigt profile. For this aim the opacity frequency dependency and the mean opacity of mixed plasmas are calculated under local thermodynamic equilibrium conditions. The final results show that the Stark-broadened line shape is dependent on the density. Also it is shown that the resonance peak and spectrum broadening of opacity spectrum of mixed plasma such as the \(\hbox {SiO}_2\)-plasma is larger than a single atom plasma such as Silicon, Si. Eventually these results can be used in the design of fuel pellets in Inertial Confinement Fusion.

Influence of atomic kinetics in the simulation of plasma microscopic properties and thermal instabilities for radiative bow shock experiments.

Numerical simulations of laboratory astrophysics experiments on plasma flows require plasma microscopic properties that are obtained by means of an atomic kinetic model. This fact implies a careful choice of the most suitable model for the experiment under analysis. Otherwise, the calculations could lead to inaccurate results and inappropriate conclusions. First, a study of the validity of the local thermodynamic equilibrium in the calculation of the average ionization, mean radiative properties, and cooling times of argon plasmas in a range of plasma conditions of interest in laboratory astrophysics experiments on radiative shocks is performed in this work. In the second part, we have made an analysis of the influence of the atomic kinetic model used to calculate plasma microscopic properties of experiments carried out on magpie on radiative bow shocks propagating in argon. The models considered were developed assuming both local and nonlocal thermodynamic equilibrium and, for the latter situation, we have considered in the kinetic model different effects such as external radiation field and plasma mixture. The microscopic properties studied were the average ionization, the charge state distributions, the monochromatic opacities and emissivities, the Planck mean opacity, and the radiative power loss. The microscopic study was made as a postprocess of a radiative-hydrodynamic simulation of the experiment. We have also performed a theoretical analysis of the influence of these atomic kinetic models in the criteria for the onset possibility of thermal instabilities due to radiative cooling in those experiments in which small structures were experimentally observed in the bow shock that could be due to this kind of instability.