Non L.T.E. Properties of Quasistationary Oxygen Plasmas

1976 ◽  
Vol 31 (3-4) ◽  
pp. 362-368 ◽  
Author(s):  
M. Cacciatore ◽  
M. Capitelli
Keyword(s):  
Excited States ◽  
Cross Sections ◽  
Ground State ◽  
Radiative Recombination ◽  
Local Thermodynamic Equilibrium ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Ionization Coefficients ◽  
Selection Of ◽  
The Continuum

The non L.T.E. (local thermodynamic equilibrium) properties of optically thin and thick quasistationary oxygen plasmas have been calculated for the temperature range k T = 0.5 - 1.5 eV and for the electron density interval 108 - 1016 cm-3 , by using the collisional-radiative model of Bates, Kingston and McWhirther. The results include1 the coefficients r0(i) and r1(i), which represent the contribution to the population density of the ith quantum level from the continuum and from the ground state, respectively2 the values of α and S, which are the collisional-radiative recombination and ionization coefficients, respectively. The accuracy of the present results is discussed in connection with the adopted plasma model and with the selection of the collisional cross sections for forbidden and allowed transitions. A discussion is also presented of the influence of the two low lying excited states of oxygen atoms (i.e. the states 2p41D, 2p41S) on the non L.T.E. properties of these plasmas. A satisfactory agreement is found with the calculations of Julienne et al. and with the experimental results of Jones.

Collisional radiative model for the evaluation of the Thermal Helium Beam diagnostic at ASDEX Upgrade

2022 ◽  
Author(s):  
Daniel Wendler ◽  
Ralph Dux ◽  
Rainer Fischer ◽  
Michael Griener ◽  
Elisabeth Wolfrum ◽  
...  
Keyword(s):  
Excited States ◽  
Ultra Violet ◽  
Plasma Edge ◽  
Excitation Mechanism ◽  
Computationally Efficient ◽  
Injection Point ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Measured Line ◽  
Vacuum Ultra Violet

Abstract The thermal helium beam diagnostic at ASDEX Upgrade is used to infer the electron density ne and temperature Te in the scrape-off layer and the pedestal region from the emission of visible lines of the locally injected helium. The link between ne and Te and the emission is provided by a collisional radiative model, which delivers the evolution of the populations of the relevant excited states as the He atoms travel through the plasma. A computationally efficient method with just three effective states is shown to provide a good approximation of the population dynamics. It removes an artificial rise of Te at the plasma edge when using a simple static model. Furthermore, the re-absorption of the vacuum ultra-violet resonance lines has been introduced as additional excitation mechanism being mainly important in the region close to the injection point. This extra excitation leads to a much better fit of the measured line ratios in this region for larger puff rates.

scholarly journals Investigation of a Collisional Radiative Model for Laser-Produced Plasmas

Atoms ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 52
Author(s):  
Nicholas L. Wong ◽  
Fergal O’Reilly ◽  
Emma Sokell
Keyword(s):  
Radiative Recombination ◽  
Rate Coefficients ◽  
Ion Distribution ◽  
Ion Distributions ◽  
Nist Database ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Collisional Ionization ◽  
Three Body ◽  
Body Recombination

Plasmas of a variety of types can be described by the collisional radiative (CR) model developed by Colombant and Tonan. From the CR model, the ion distribution of a plasma at a given electron temperature and density can be found. This information is useful for further simulations, and due to this, the employment of a suitable CR model is important. Specifically, ionization bottlenecks, where there are enhanced populations of certain charge states, can be seen in these ion distributions, which in some applications are important in maintaining large amounts of a specific ion. The present work was done by implementing an accepted CR model, proposed by Colombant and Tonon, in Python and investigating the effects of variations in the ionization energy and outermost electron subshell occupancy term on the positions of ionization bottlenecks. Laser Produced Plasmas created using a Nd:YAG laser with an electron density of ∼ne = 1021 cm−3 were the focus of this work. Plots of the collisional ionization, radiative recombination, and three-body recombination rate coefficients as well as the ion distribution and peak fractional ion population for various elements were examined. From these results, it is evident that using ionization energies from the NIST database and removing the orbital occupancy term in the CR model produced results with ionization bottlenecks in expected locations.

Photoluminescence Study of Radiative Recombination in Porous Silicon

1993 ◽  
Vol 298 ◽  
Author(s):  
Chun Wang ◽  
Franco Gaspari ◽  
Stefan Zukotynski
Keyword(s):  
Porous Silicon ◽  
Excited States ◽  
Ground State ◽  
Radiative Recombination ◽  
Single Electron ◽  
Photoluminescence Study ◽  
Recombination Centre ◽  
Electron Center ◽  
Recombination Centers

AbstractPhotoluminescence has been studied in porous silicon. Two types of radiative recombination centers have been identified. One gives rise to luminescence at about 820 nm and is believed to be related to Si-H bonds. The second gives rise to luminescence at about 770 nm and is likely associated with S-O bonds. Above about 20K radiative recombination is assisted by excited states of the recombination centre located about 10 meV above the ground state. The Si-H recombination centre is a single electron center whereas the Si-O center appears to be a multi-electron center.

Investigation of Excited States of Helium Atoms in a Stationary PIG-Discharge

1971 ◽  
Vol 26 (2) ◽  
pp. 186-197 ◽  
Author(s):  
H. W. Drawin ◽  
F. Klan ◽  
H. Ringler
Keyword(s):  
Excited States ◽  
Theoretical Calculations ◽  
Principal Quantum Number ◽  
Population Densities ◽  
Boltzmann Plot ◽  
Line Intensities ◽  
Quantum Numbers ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Large Experimental Error

AbstractSpectral line intensities emitted by a quiescent PIG-discharge have been measured and the population densities up to a principal quantum number n = 24 have been derived from them. The experimentally determined population densities have been compared with theoretical ones calculated on the basis of a collisional-radiative model in which one accounts for electron and atom collisions. I t is shown that even in the case of different electron and atom temperatures, Te and Ta, an evaluation of the Boltzmann plot at medium and moderately high quantum numbers always leads to the electron temperature, whereas the Saha-Eggert equation for the same states may yield incorrect electron densities. The theoretical calculations predict an inflection of the slope of the Boltzmann plot from Te to Ta for very highly excited states. For the plasma para­ meters under which the PIG-discharge was operated (ne ≅ 2.5 × 1012 cm-3, Te ≅ 1200°K, n0 ≅ 1.5 × 1015 cm-3, 300°K) the change of the slope should become visible for states having principal quantum numbers n > 18. Due to the large experimental error bars it was not possible to check this behaviour.

scholarly journals Intensities in Complex Spectra of Highly Ionized Atoms

1984 ◽  
Vol 86 ◽  
pp. 44-44
Author(s):  
M. Klapisch ◽  
A. Bar-Shalom ◽  
A. Cohen
Keyword(s):  
Cross Sections ◽  
Wave Functions ◽  
Coupling Scheme ◽  
Distorted Wave ◽  
Intermediate Coupling ◽  
Potential Wave ◽  
Excitation Cross Sections ◽  
Collisional Radiative Model ◽  
Radiative Model ◽  
Efficient Program

We describe a package of programs for the implementation of the collisional-radiative model to complex configurations. The number of levels taken into account may be several hundreds. The heart of the package is a very efficient program for excitation cross sections in the Distorted Wave framework, using the Relativistic Parametric Potential wave functions. The basic jj coupling scheme actually simplified the computations, enabling a useful factorization into radial and angular parts. Intermediate coupling and configuration interactions are accounted for. We computed ratios of intensities of 3d9 − 3d84s (E2) to 3d9 −3d84p (El) transitions as functions of ne and Te in Xe XXVIII and other Co-like spectra. The atomic model involves all the levels of configurations (3p6)3d9; −3d84s, −3d84p, −3d84d, −3d84f, and (3p5) −3d10, −3d94p. (275 levels) and all the transitions between them. Results compare very well with experimental spectra from TFR.

Excited states of positronium in positron–hydrogen charge exchange

1978 ◽  
Vol 56 (5) ◽  
pp. 565-570 ◽  
Author(s):  
V. S. Kulhar ◽  
C. S. Shastry
Keyword(s):  
Excited States ◽  
Charge Exchange ◽  
Cross Sections ◽  
Ground State ◽  
Born Approximation ◽  
Energy Region ◽  
Hydrogen Charge ◽  
Positronium Formation ◽  
State Approximation ◽  
Higher Excited States

The two state approximation method for the study of the rearrangement collisions is applied to the process of positronium formation in excited states for positron–hydrogen charge exchange collisions. Differential and integrated cross sections are computed for positronium formation in 2S, 2P, and 3S excited states. The results obtained in the energy region 2 to 10 Ry are compared with positronium formation cross sections in ground state. Total positronium formation cross sections including the contributions of capture into all the higher excited states of positronium are also computed in the first Born approximation and the two state approximation in the energy region considered.

scholarly journals Simplified DWBA for Heavy Ion Induced Transfer at High Energies

1979 ◽  
Vol 32 (3) ◽  
pp. 173 ◽  
Author(s):  
LR Dodd
Keyword(s):  
Excited States ◽  
Cross Sections ◽  
Ground State ◽  
Optical Model ◽  
Heavy Ion ◽  
Transfer Reactions ◽  
Angular Distributions ◽  
High Energies ◽  
Scattering States ◽  
Exact Calculations

The treatment of the distorted wave Born approximation (DWBA) for transfer reactions at high energies between complex nuclei due to Braun-Munzinger and Harney (1974) is simplified by introducing eikonal-like representations for the elastic scattering states. Simple expressions for the differential cross sections are derived. The model includes recoil approximately and takes into account the strong absorption of the nuclear cores. Reasonable values for the parameters of the model wavefunctions are determined by comparison with the usual optical model wavefunctions. Angular distributions calculated for the model are compared with the results of exact finite-range DWBA calculations and experimental data for transitions to the ground state and excited states of 13C in the reaction 12C(14N,13N)13C at several energies. The model reproduces the general features of the exact calculations, giving reasonable fits for the transitions to the ground state and the 1ds/2 (3�85 MeV) state. The transition to the 2S1/2 (3 �09 MeV) state appears to be anomalous as in the case of the full DWBA theory.

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