Calculations Of Level Populations Research Articles

X-Ray Photoabsorption of Density-sensitive Metastable States in Ne vii, Fe xxii, and Fe xxiii

Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify Kα transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 1010.5 cm−3.

CHIANTI—An Atomic Database for Emission Lines. XV. Version 9, Improvements for the X-Ray Satellite Lines

Abstract CHIANTI contains a large quantity of atomic data for the analysis of astrophysical spectra. Programs are available in IDL and Python to perform calculation of the expected emergent spectrum from these sources. The database includes atomic energy levels, wavelengths, radiative transition probabilities, rate coefficients for collisional excitation, ionization, and recombination, as well as data to calculate free–free, free–bound, and two-photon continuum emission. In Version 9, we improve the modeling of the satellite lines at X-ray wavelengths by explicitly including autoionization and dielectronic recombination processes in the calculation of level populations for select members of the lithium isoelectronic sequence and Fe xviii–xxiii. In addition, existing data sets are updated, new ions are added, and new total recombination rates for several Fe ions are included. All data and IDL programs are freely available at http://www.chiantidatabase.org or through SolarSoft, and the Python code ChiantiPy is also freely available at https://github.com/chianti-atomic/ChiantiPy.

The CHIANTI database, a consistency check on the accuracy of the stored cross-section values in He i to O i isoelectronic sequence ions

CHIANTI is an atomic database with software for calculating emission properties. It is extensively used in deriving the atomic properties of spectra recorded from astrophysical and low density laboratory plasmas. In order to obtain an insight into the accuracy of the CHIANTI calculated level populations, a consistency check was conducted along the He i, Be i, B i, C i, N i, and O i isoelectronic sequences. In the evaluation process, levels of the ground configuration and the first and second excited configurations were considered. These are the levels responsible for most of the spectral lines used when deriving the plasma properties of astrophysical objects. As is documented below, the accuracy of the CHIANTI level population calculations depends on the particular ion, level and on the electron density. Under some conditions the calculations appear quite robust while in others they are not.

NLTE simulation of spectrum for Z-pinch Al plasma with the effects of opacity

In this article,the emission coefficients and absorption coefficients of a Z-pinch Al plasma are calculated in nonlocal- thermodynamic-equilibrium model (NLTE) under detailed level accounting model (DLA) base on the calculation of level populations at first.Then,we calculate the detail spectrum of Al plasma and analyze the opacity effects on plasma elementary using a simple 1-D slate radicalization-transition model.The calculation results indicate that the effect of absorption is very strong to Z-pinch plasma especially on resonance lines (It influenced the figure of plasma spectrum obviously).Yet it’s effect slightly on satellite lines.The Z-pinch Al plasma is optical thick to resonance lines but thin to satellite lines.In more detail the calculation results show that the effective absorption radius of K-shell lines in the Z-pinch Al plasma is about 100–200μm.

High-resolution solar spectral irradiance from extreme ultraviolet to far infrared

[1] This paper presents new extremely high-resolution solar spectral irradiance (SSI) calculations covering wavelengths from 0.12 nm to 100 micron obtained by the Solar Irradiance Physical Modeling (SRPM) system. Daily solar irradiance spectra were constructed for most of Solar Cycle 23 based on a set of physical models of the solar features and non-LTE calculations of their emitted spectra as function of viewing angle, and solar images specifying the distribution of features on the solar disk. Various observational tests are used to assess the quality of the spectra provided here. The present work emphasizes the effects on the SSI of the upper chromosphere and full-non-LTE radiative transfer calculation of level populations and ionizations that are essential for physically consistent results at UV wavelengths and for deep lines in the visible and IR. This paper also considers the photodissociation continuum opacity of molecular species, e.g., CH and OH, and proposes the consideration of NH photodissociation which can solve the puzzle of the missing near-UV opacity in the spectral range of the near-UV. Finally, this paper is based on physical models of the solar atmosphere and extends the previous lower-layer models into the upper-transition-region and coronal layers that are the dominant source of photons at wavelengths shorter than ∼50 nm (except for the He II 30.4 nm line, mainly formed in the lower-transition-region).

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.

Two-period model for calculation of level populations in subbands of multi-period quantum-cascade superlattice structures

For two periods of quantum-cascade laser structures, we propose a system of closed balance equations that make it possible to calculate the occupancy of the energy levels, the quasi-Fermi levels, and also the injection current density taking into account different charge carrier scattering mechanisms.

A study of the ac Stark effect in doped photonic crystals

In this paper we present calculations of level populations and susceptibility for an ensembleof five-level atoms doped in a photonic crystal, using the master equation method. Theatoms in the ensemble interact with the crystal which acts as a reservoir and are coupledwith two strong pump fields and a weak probe field. It is found that, by manipulating theresonance energy associated with one of the decay channels of the atom, the system can beswitched between an inverted and a non-inverted state. We have also observed theac Stark effect in these atoms and have shown that due to the role played bythe band structure of the photonic crystal, it is possible to switch between anabsorption state and a non-absorption state of the atomic system. This is a veryimportant finding as techniques of rendering material systems transparent to resonantlaser radiation are very desirable in the fabrication of novel optical and photonicdevices.

Line photon transport in a non-homogeneous plasma using radiative coupling coefficients

We present a steady-state collisional-radiative (CR) model for the calculation of level populations in non-homogeneous plasmas with planar geometry. The line photon transport is taken into account following an angle- and frequency-averaged escape probability model. Several models where the same approach has been used can be found in the literature, but the main difference between our model and those ones is that the details of geometry are exactly treated in the definition of coupling coefficients and a local profile is taken into account in each plasma cell.

Feasibility studies of two-dimensional edge turbulence measurements by laser induced fluorescence

Edge turbulence is a key factor in the performance of fusion devices but is not well understood even after many years of research. We assess the feasibility of using laser induced fluorescence to obtain two-dimensional images of turbulent structures in the plasma. Based on theoretical expectations of density fluctuations arising from turbulence and calculations of level populations in He-like and noble gas ions we show that high signal/noise ratios (S/N>100) may be expected for experimental conditions in the magnetic reconnection experiment and on the National Spherical Torus Experiment at PPPL. Schemes include exciting the ion emission lines such as B IV 282.3 nm or Kr II 441.8 nm by a tunable laser.

OIII] Electron temperatures in planetary nebulae

Relative level populations for O III, derived using electron impact excitation rates calculated with the R-matrix code, are used to deduce the electron-temperature-sensitive emission-line ratioR=I(2s 22p2 1D–2s22p21S)/I(2s2 2p23P1,2–2s22p2 1D) =I(4363 A)/I(4959 + 5007 A) for a range ofTe = (7500–20000 K) applicable to planetary nebulae. Electron temperatures deduced from the observed values ofR in several planetary nebulae are in excellent agreement with those determined fromTe-sensitive line ratios in other species, including CIII]/C [II], [NII] and [ArIII], which provides support for the accuracy of the atomic data adopted in the level population calculations.

EFFECT ON DEUTERON TEMPERATURE ON IRON FORBIDDEN LINE INTENSITIES IN RF-HEATED TOKAMAK PLASMAS

Two line ratios, the forbidden line at 845.5 A (2s/sup 2/2p /sup 2/P/sub 1/2/ - 2s/sup 2/2p /sup 2/P/sub 3/2/) to the allowed line at 135.7 A (2s/sup 2/2p /sup 2/P/sub 1/2/ - 2s2p/sup 2/ /sup 2/D/sub 3/2/) in Fe XXII and the forbidden line at 592.1 A (2s/sup 2/2p/sup 4/ /sup 3/P/sub 2/ - 2s/sup 2/2p/sup 4/ /sup 1/D/sub 2/) to the forbidden line at 1118.2 A (2s/sup 2/2p/sup 4/ /sup 3/P/sub 2/ - 2s/sup 2/2p/sup 4/ /sup 3/P/sub 1/) in Fe XIX, have been measured as the ion temperature-sensitive line ratios during rf heating in the Princeton Large Torus. The results indicate that deuteron collisions in plasmas of high deuteron temperature have a noticeable effect on the intensity of the forbidden lines. Measured relative intensities are compared with values from level population calculations, which include deuteron collisional excitation between the levels of the ground configuration. The agreement between the observed and calculated ratios is within 30%. A method for deuteron (or proton) temperature measurement in tokamak plasmas is discussed. 37 refs.

Effect on Deuteron Temperature on Iron Forbidden Line Intensities in RF-Heated Tokamak Plasmas

AbstractTwo line ratios, the forbidden line at 845.5 Å to the allowed line at 135.7 Å in Fe XXII and the forbidden line at 592.1 Å to the forbidden line at 1118.2 Å in Fe XIX, have been measured as ion temperature-sensitive line ratios during rf heating in the Princeton Large Torus. The results indicate that deuteron collisions in plasmas of high deuteron temperature have a noticeable effect on the intensity of the forbidden lines. Measured relative intensities are compared with values from level population calculations which include deuteron collisional excitation between the levels of the ground configuration. The agreement between the observed and calculated ratios is within 30%. A method for deuteron (or proton) temperature measurement in tokamak plasmas is discussed.1More details about this experiment can be found in Ref. 2.

Effect of deuteron temperature on iron forbidden-line intensities in rf-heated tokamak plasmas.

Two line ratios, the forbidden line at 845.5 A\r{} (2s${}^{2}$2p ${}^{2}$${P}_{1/2}$--2s${}^{2}$2p ${}^{2}$${P}_{3/2}$) to the allowed line at 135.7 A\r{} (2s${}^{2}$2p ${}^{2}$${P}_{1/2}$--2s2${p}^{2}$ ${}^{2}$${D}_{3/2}$) in Fe xxii and the forbidden line at 592.1 A\r{} (2s${}^{2}$2${p}^{4}$ ${}^{3}$${P}_{2}$--2s${}^{2}$2${p}^{4}$ ${}^{1}$${D}_{2}$) to the forbidden line at 1118.2 A\r{} (2s${}^{2}$2${p}^{4}$ ${}^{3}$${P}_{2}$--2${s}^{2}$2${p}^{4}$ ${\mathrm{}}^{3}$${P}_{1}$) in Fe xix, have been measured as ion-temperature-sensitive line ratios during rf heating in the Princeton Large Torus. The results indicate that deuteron collisions in plasmas of high deuteron temperature have a noticeable effect on the intensity of the forbidden lines. Measured relative intensities are compared with values from level-population calculations, which include deuteron collisional excitation between the levels of the ground configuration. The agreement between the observed and calculated ratios is within 30%. A method for deuteron (or proton) temperature measurement in tokamak plasmas is discussed.

Theoretical Ne v emission line ratios compared to solar observations

The recent level population calculations for Ne v by Aggarwal are used to determine the theoretical emission line ratios R1 = I(2s2p31Do - 2s22p21De)/I(2s2p33D20- 2s22p23P1e) and R2 = I(2s2p31Do-2s22p21De)/I(2s2p33D30-2s22p23P2e). A comparison of these with observational data for a solar flare and erupting prominence obtained with the NRL XUV spectrograph on board Skylab reveals that R1 and R2 are in their predicted high density limits. Although the ratios cannot be used as density diagnostics for values of ne typical of the solar transition region, it is shown that they are temperature sensitive and hence may be employed to determine the electron temperatures of Ne v line emitting regions.

Improved theoretical line ratios for Ciii in the Sun

The recent twelve-state R-matrix calculations of electron excitation rates in Ciii by Berrington are used to derive level populations applicable to the solar transition region. Line ratios R = I(2p2 3Pe - 2s2p3P°)/I(2s2p1P° - 2s2 1Se) and R2=I(2p2 1Se - 2s2p1P°)/I(2p2 3Pe - 2s2p3P°) deduced from these data in conjunction with the relevent transition probabilities are found to be in much better agreement with the observed quiet Sun values than those determined from the level population calculations of Keenan et al.

Relative intensities of 2s22pk-2s2pk+1 transitions in F

Measured relative intensities of a number of allowed 2${s}^{2}$2${p}^{k}$-2s2${p}^{k+1}$ transitions (60--200 A\r{}) in the F i-- to B i--like ions of titanium, chromium, iron, nickel, and germanium are compared with values from level-population calculations. The measurements are from Princeton Large Torus (PLT) tokamak plasmas with electron densities of \ensuremath{\sim}2.5\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. For titanium and chromium, data from plasmas with densities of \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ are also presented; a number of density-dependent line-intensity ratios are found. The spectra were obtained with use of a grazing-incidence time-resolving spectrograph which was radiometrically calibrated with use of synchrotron radiation from the National Bureau of Standards Synchrotron Ultraviolet Radiation Facility (SURF II). The measured relative intensities are therefore reliable. For the majority of the observed lines, agreement between the measured and calculated relative intensities is within 30%, the estimated accuracy of the measurements; significant discrepancies are found in the titanium ions at the low density. The discrepancies, some of which are due to blends, are discussed. Thus, the level-population calculations may be used with some confidence for spectroscopic plasma diagnostics. In the C i--like ions, there is some evidence that calculations which include proton-collisional excitation and deexcitation between the levels of the ground configuration are in better agreement with the measurements than those that do not, indicating that proton collisions should be included in the calculations for these ions.

Interstellar O2. I - Abundance, excitation, and prospects for detection of O-16O-18 at radio frequencies

Molecular oxygen, O2, is predicted to be an important constituent of the interstellar gas, but it has not yet been detected in interstellar clouds. In this paper, the gas phase production and destruction of O2 are reconsidered, a non-LTE calculation of level populations at cloud temperatures is presented, and O2 column densities in diffuse and dark clouds are predicted. Ground-based detection of the 234 GHz line of O-16O-18 is shown to be feasible; if CO and O2 are comparable in abundance in clouds similar to the Taurus molecular cloud or in giant molecular clouds, the brightness temperature is predicted to be 0.1 K.

Relative Intensities of Lines in F I- B I-Like Ti, Cr, Fe, Ni, and Ge: A Comparison of Theory and Experiment

Allowed 2s22pk − 2s2pk+1 transitions in the F I- B I-like ions of elements with Z ≥ 20 are often observed in spectra of high-temperature (Te ≥ 107 K) laboratory and astrophysical plasmas. Calculations of level populations in these ions are important in the interpretation of measured intensities of these lines for plasma diagnostics. Impurity ion densities and radiated power losses in tokamak plasmas, and the emission measure of astrophysical sources, can be derived from spectroscopic measurements using level population calculations. Certain line-intensity ratios can be used to measure the electron density in astrophysical plasmas; this technique may also be useful in some low-density laboratory plasmas. It is therefore important to experimentally check the level populations in high-Z ions using spectra from a well-diagnosed laboratory plasma, such as that of a tokamak. This has been previously done only for some transitions in Fe XVIII - Fe XXII (Suckewer and Hinnov 1979).

Spectroscopy and atomic physics of highly ionized krypton for tokamak plasmas

We present calculations of electron-impact collision strengths and spontaneous radiative decay rates for krypton ions of the Li I through F I isoelectronic sequences for transitions between levels of the 2s22pk, 2s2pk+1, and 2pk+2 configurations. From these atomic data, excitation rate coefficients are calculated, as well as populations of levels within the three configurations mentioned above. The calculations of level populations are carried out at three electron temperatures—2×107, 3×107, and 5×107 K (1.7, 2.6, and 4.4 keV)—which are expected to be typical for future tokamak plasmas.