Thin Plasmas Research Articles

Observation of EUV spectra from gadolinium and neodymium ions in the Large Helical Device

We have observed extreme ultraviolet (EUV) spectra from highly charged gadolinium and neodymium ions in optically thin plasmas produced in the Large Helical Device at the National Institute for Fusion Science. Time evolutions of EUV spectra in the 6–9 nm region following injection of a solid pellet into a hydrogen plasma were measured by a grazing incidence spectrometer with a frame rate of 0.2 s. Three different types of spectral features have been observed depending on the electron temperature. Discrete spectral lines of Ni- and Cu-like gadolinium and neodymium ions were identified when the peak electron temperature was around 2 keV, while some lines of Ag-like gadolinium ions were found in the plasma with temperatures below 240 eV when an unusual hollow plasma was formed. Under the intermediate temperature, a quasi-continuum spectral feature arising from an unresolved transition array from open 4p/4d subshell ions is predominant.

CHANDRAANDSUZAKUOBSERVATIONS OF THE Be/X-RAY STAR HD110432

We present an analysis of a pointed 141 ks Chandra high resolution transmission gratings observation of the Be X-ray emitting star HD110432, a prominent member of the gamma Cas analogs. The Chandra lightcurve shows a high variability but its analysis fails to detect any coherent periodicity up to a frequency of 0.05 Hz. The analysis of the Chandra HETG spectrum shows that, to correctly describe the spectrum, three model components are needed. Two of those components are optically thin thermal plasmas of different temperatures (kT~8-9 and 0.2-0.3 keV respectively). Two different models seem to describe well the third component. One possibility is a third hot optically thin thermal plasma at kT=16-21 keV with an Fe abundance Z~0.3Zo, definitely smaller than for the other two thermal components. Alternatively, the third component can be described by a powerlaw with a photon index Gamma=1.56. In either case, the Chandra HETG spectrum establishes that each one of these components must be modified by distinct absorption columns. The analysis of a non contemporaneous 25 ks Suzaku observation shows the presence of a hard tail extending up to at least 33 keV. The Suzaku spectrum is described with the sum of two components: an optically thin thermal plasma at kT ~ 9 keV and a very hot second plasma with kT ~33 keV or, alternatively, a powerlaw with photon index Gamma=1.58. The analysis of the Si XIII and S XV He like triplets present in the Chandra spectrum point to a very dense (n_e ~ 10^13 cm^-3) plasma located either close to the stellar surface (r<3R_*) of the Be star or, alternatively, very close (r ~1.5R_WD) to the surface of a (hypothetical) WD companion. We argue, however, that the available data supports the first scenario.

Modeling of Analysis ICP Torch at Atmospheric Pressure With Applied Voltage

In this paper, a new 2-D nonlinear direct-coupled model for the simulation of inductively coupled plasma torches working at atmospheric pressure is presented. Steady fluid flow and temperature equations are simultaneously solved (direct method) using a finite-element formulation for optically thin argon plasmas under the assumptions of local thermodynamic equilibrium and laminar flow. The electromagnetic field equations are formulated in terms of potential vector with applied voltage source.

Diagnostic Challenges of Asymmetrically Burning Arcs

Asymmetric arcs may cause some complications in the evaluation of optical emission spectroscopy for optically thin plasmas. Even a slight asymmetry can result in increased experimental uncertainties or erroneous conclusions.

Optical Emission Spectroscopy Measurements and Simulation of Radioelement Volatility During Radioactive Waste Treatment by Plasma

An optical emission spectroscopy (OES) method has been used to measure the concentration above the melt of some radioelements, 137Cs, 60Co and 106Ru during the vitrification of radioactive wastes by thermal plasma. This method allows the study of non homogeneous optically thin plasmas exhibiting a symmetry plane without sophisticated tomographic systems. Local plasma temperatures above the melt have been evaluated using measured relative intensities of spectral lines of the plasma-forming gas. Radioelement concentrations in the plasma are deduced from the intensity ratio of the radioelement–gas spectral lines. A computer model is used to simulate the volatility of 137Cs, 60Co and 106Ru, during the treatment of radioactive wastes by thermal plasma. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. In this study, the OES measurements and the computer model allowed the determination of this radioelement volatility depending on the parameters like plasma current, and the nature of atmosphere furnace. The results of the model are compared to those obtained by OES measurements.

Modeling of population kinetics of plasmas that are not in local thermodynamic equilibrium, using a versatile collisional-radiative model based on analytical rates

We discuss the modeling of population kinetics of nonequilibrium steady-state plasmas using a collisional-radiative model and code based on analytical rates (ABAKO). ABAKO can be applied to low-to-high Z ions for a wide range of laboratory plasma conditions: coronal, local thermodynamic equilibrium or nonlocal thermodynamic equilibrium, and optically thin or thick plasmas. ABAKO combines a set of analytical approximations to atomic rates, which yield substantial savings in computer running time, still comparing well with more elaborate codes and experimental data. A simple approximation to calculate the electron capture cross section in terms of the collisional excitation cross section has been adapted to work in a detailed-configuration-accounting approach, thus allowing autoionizing states to be explicitly included in the kinetics in a fast and efficient way. Radiation transport effects in the atomic kinetics due to line trapping in the plasma are taken into account via geometry-dependent escape factors. Since the kinetics problem often involves very large sparse matrices, an iterative method is used to perform the matrix inversion. In order to illustrate the capabilities of the model, we present a number of results which show that the ABAKO compares well with customized models and simulations of ion population distribution. The utility of ABAKO for plasma spectroscopic applications is also outlined.

Mechanisms of forward laser harmonic emission from thin overdense plasmas

As a high-intensity laser pulse impinges a thin solid foil, high-order harmonics of the incident frequency can be observed at the rear (non-illuminated) side of this foil. Using numerical simulations, we show that these harmonics can be generated either at the front or at the rear side of the target. We analyze the mechanisms responsible for these two types of emission, and discuss their connection with those involved in the generation of harmonics detected on the front side. The combined measurements of spectra on both sides of the target constitute a powerful, but often nontrivial, probe of the ultrafast plasma dynamics.

Grmonty: A MONTE CARLO CODE FOR RELATIVISTIC RADIATIVE TRANSPORT

We describe a Monte Carlo radiative transport code intended for calculating spectra of hot, optically thin plasmas in full general relativity. The version we describe here is designed to model hot accretion flows in the Kerr metric and therefore incorporates synchrotron emission and absorption, and Compton scattering. The code can be readily generalized, however, to account for other radiative processes and an arbitrary spacetime. We describe a suite of test problems, and demonstrate the expected N−1/2 convergence rate, where N is the number of Monte Carlo samples. Finally, we illustrate the capabilities of the code with a model calculation, a spectrum of the slowly accreting black hole Sgr A* based on data provided by a numerical general relativistic MHD model of the accreting plasma.

The X-ray spectrum of the classical TTauri star TW Hydrae observed by LETGS aboard Chandra

Aims. I present the analysis of the X-ray spectrum of the classical TTauri star TW Hydrae, and determine emission measure distributions, elemental abundances, electron temperatures, densities, and line fluxes. Methods. TW Hya was observed in the wavelength range 5–175 A by CHANDRA-LETGS . I performed a multi-temperature fit, based on a collisional ionisation equilibrium (CIE) model for optically thin plasmas. I measured line fluxes by fitting a Gaussian line profile, folded through the response matrix, to the observed line features and I applied these values to establish plasma properties. Results. No line features were established in the spectrum above 40 A. Due to the absence of line features above 40 A N H is calculated to be somewhat higher than assumed so far. The observed “coronal” temperature covers a range from about 1.5 to 20 MK. The abundance pattern shows a very strong enhancement of Ne and some enhancement of N. From forbidden-intercombination line ratios of $\ion{O}{\sc vii}$ and of $\ion{Ne}{\sc ix}$ I obtain a value for the electron density of $n_{\rm e}\simeq 10^{12}~{\rm cm}^{-3}$. This is higher than the value for electron densities in coronal plasmas of older late type main-sequence stars. A blackbody component was added to describe the shape of the continuum around 15 A better. The emitted X-ray luminosity is in the order of 10 30 erg/s.

Spectral line shapes modeling in laboratory and astrophysical plasmas

An overview of several spectral line shapes studies of common interest in astrophysical and laboratory plasmas is presented. For lines dominated by Stark broadening, approaches taking into account the dynamics of numerous perturbers are sometimes required. We briefly recall ab initio simulation techniques and model microfield methods used for such conditions. Together with the impact approximation, such models may also be used for studying the effects on a line profile of a magnetic field of the order of the tesla, allowing the diagnostic of stellar objects or magnetic fusion devices. The problem of the apparent spectral line emitted in a plasma affected by strong fluctuations of the plasma parameters is discussed for the case of optically thin plasmas.

Turbulence and line shape formation in plasmas

We investigate the role of turbulent fluctuations on line shape formation in optically thin plasmas. A general expression, valid if the turbulent scales are much larger than the atomic scales, is obtained for the profile measured using a passive spectroscopy set up. Well-known limiting cases for Doppler and Stark broadening are identified. Then, the role of temperature fluctuations on Doppler line shapes, and the effect of density fluctuations on Stark broadened lines in the quasi-static regime are investigated.

Distribution of Excited Species in a Helium Plasma Flame During the Destruction of Carbon Tetrachloride at Atmospheric Pressure

The distribution of excited species in a helium plasma torch is studied during the introduction of carbon tetrachloride in the main gas. This paper provides information on the processes occurring in the plasma. The method uses a fast high-resolution acquisition setup, as well as a new data processing procedure based on the Abel inversion technique that provides the radial profile of thin plasmas.

RAPCAL code: A flexible package to compute radiative properties for optically thin and thick low and high-Z plasmas in a wide range of density and temperature

AbstractRadiative properties are fundamental for plasma diagnostics and hydro-simulations. For this reason, there is a high interest in their determination and they are a current topic of investigation both in astrophysics and inertial fusion confinement research. In this work a flexible computation package for calculating radiative properties for low and high Z optically thin and thick plasmas, both under local thermodynamic equilibrium and non-local thermodynamic equilibrium conditions, named RAPCAL is presented. This code has been developed with the aim of providing accurate radiative properties for low and medium Z plasmas within the context of detailed level accounting approach and for heavy elements under the detailed configuration accounting approach. In order to show the capabilities of the code, there are presented calculations of some radiative properties for carbon, aluminum, krypton and xenon plasmas under local thermodynamic and non-local thermodynamic equilibrium conditions.

Soft X‐Ray Spectroscopy of Highly Charged Silicon Ions in Dense Plasmas

Rich soft X-ray emission lines of highly charged silicon ions (Si VI--Si XII) were observed by irradiating an ultra-intense laser pulse with width of 200 fs and energy of $\sim$90 mJ on the solid silicon target. The high resolution spectra of highly charged silicon ions with full-width at half maximum (FWHM) of $\sim$0.3--0.4\AA is analyzed in wavelength range of 40--90 \AA . The wavelengths of 53 prominent lines are determined with statistical uncertainties being up to 0.005 \AA . Collisional-radiative models were constructed for Si VI -- Si XII ions, which satisfactorily reproduces the experimental spectra, and helps the line identification. Calculations at different electron densities reveal that the spectra of dense plasmas are more complicate than the spectra of thin plasmas. A comparison with the Kelly database reveals a good agreement for most peak intensities, and differences for a few emission lines.

ABAKO: A new code for population kinetics and radiative properties of plasmas under NLTE conditions

In this work we present ABAKO, a new computational code based on analytical models and developed to study the population kinetics of steady-state plasmas. The tool ABAKO can be applied to low-to-high Z ions under a wide range of laboratory plasma conditions: coronal, LTE or NLTE, optically thin or thick plasmas. Autoionizing states are explicitly included. The results obtained with ABAKO are competitive with more elaborated, but also time-consuming codes. Our code provides satisfactory charge state distributions (CSD) and reasonable estimations of spectroscopic observables of high-Z plasmas, as it can be seen through comparison with experimental data.

Multifrequential and mean opacity calculation of carbon plasmas in a wide range of density and temperature

The purpose of this work is to calculate the multifrequential and mean opacity of optically thin carbon plasmas in a wide range of density and temperature, where corona equilibrium, local thermodynamic equilibrium and non-local thermodynamic equilibrium regimes are present.

X-Ray Spectroscopy of SN 1006 with Suzaku

We report on observations of SN 1006 with Suzaku. We firmly detected K-shell emission from Fe, for the first time, and found that the Fe ionization state is quite low. The broad-band spectrum extracted from southeast of the remnant was well-fitted with a model consisting of three optically thin thermal non-equilibrium ionization plasmas and a power-law component. Two of the thermal models are highly overabundant in heavy elements, and hence are likely due to ejecta. These components have different ionization parameters, $n_{\rm e}t \sim 1.4\times 10^{10}$cm$^{-3}$s and $n_{\rm e}t \sim 7.7\times 10^8$cm$^{-3}$s; it is the later one that produces Fe-K emission. This suggests that Fe has been heated by reverse shock more recently than the other elements, consistent with a picture where the ejecta are stratified by composition with Fe in the interior. On the other hand, the third thermal component is assumed to be solar abundance, and we associate it with emission from the interstellar medium. The electron temperature ($kT_{\rm e} \sim$0.5keV) is lower than that expected from the shock velocity, which suggests a lack of collisionless electron heating at the forward shock. The extremely low ionization parameter and extreme non-equilibrium state are due to the low density of the ambient medium.

Determination of corona, LTE, and NLTE regimes of optically thin carbon plasmas

AbstractIn this work is accomplished the determination of the corona, local and non-local thermodynamic equilibrium regimes for optically thin carbon plasmas in steady state, in terms of the plasma density and temperature using the ABAKO code. The determination is made through the analysis of the plasma average ionization and ion and level populations. The results are compared whit those obtained applying Griem's criterion. Finally, it is made a brief analysis of the effects of the calculation of level populations assuming different plasma regimes in radiative properties, such as emissivities and opacities.

Self-compression and splitting of laser pulse in plasmas

We study the self-compression and splitting of a circularly polarized laser pulse propagating in plasmas with density window from 1/4 critical to slightly below critical density by solving the nonlinear Schrdinger equation numerically. It is demonstrated by the numerical calculation that the effective self-compression of laser pulse can be achieved in even shorter distance by increasing both the background plasma density and intensity of the laser pulse, or decreasing the width of pulse. The full-width at half maximum of the compressed pulse can reach 1/35 of the initial one's or even smaller. It has been found that this kind of self-compression occurs in the process of formation of a high-order soliton when a laser pulse propagates in a plasma, so that we can obtain greats compression ratio than in thin plasmas. We also obtained the splitting of a high-order soliton formed after self-compression of a laser pulse propagating in plasmas from the result of the numerical calculation in this situation. The phenomenon of self-compression and splitting is also observed by using one-dimensional particle-in-cell simulations and the result was consistent with the numerical calculation.

Comparative study on mechanical properties of MoSiN multilayer films deposited on Si(100) and Ti-covered Si(100) substrates

We deposited MoSiN multilayer films using a MoSi2 target via pulsed-DC and radio-frequency (RF) magnetron sputtering methods. For the fabrication of the Ti-covered Si(100) substrate, we also grew Ti layers via the RF magnetron sputtering method. To improve the mechanical properties of the as-grown MoSiN thin films, argon and nitrogen plasmas ignited by RF and pulse DC under vacuum conditions were also used with a total pressure of 0.7 Pa, a substrate bias of −100 V, and a substrate ion current density of 1.5 mA/cm2. The as-grown MoSiN films were investigated for hardness (Gpa) and macro-stress(s) properties, and the relationship between film composition and micro-structures was analyzed using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The maximum hardness and stress values of the MoSiN films were 32 GPa and −2.5 GPa, respectively, depending on variations of substrates and reactive gas.