Thermal equilibrium criteria in a nitrogen plasma

A method for obtaining the lower electron density limit for LTE in a nitrogen plasma is described, whereby the experimentally determined ratio of the collisional-radiative ionization and recombination coefficients (S/α) is compared with the corresponding LTE value (Saha ratio). It is argued that if the electron density is increased from values of about 10¹⁶cm^-3, S/α should tend to the Saha ratio as LTE is approached. For NII and NIII spectral lines, this is found to happen at an electron density of a few times 10¹⁶cm^-3 when the electron temperature is about 3 eV, in good agreement with the LTE criterion of Griem.     

Collisional-radiative volume recombination and ionization coefficients for quasi-stationary helium plasmas

Collisional-radiative recombination and ionization coefficients, α andS, have been calculated on the basis of a non-hydrogen-like collisional-radiative model for atomic helium. The singlet and triplet systems have been considered as two individual systems coupled to each other through a set of elementary processes for collisions and radiation. Auto-ionization states have not been taken into account. Therefore the computations of the coefficient α have been limited to the range 125≦T _e [°K]≦64000. (AboveT _e=64 000 °K the auto-ionizing states considerably influence the recombination rates (di-electronic recombination).) The results show that the α- andS-coefficients for helium are more sensitive to radiative trapping than those for hydrogen under comparable absorption conditions. Concerning the α-values: For low electron densities one obtains approximately α_helium≈2α_hydrogen, whereas at high electron densities one finds approximately α_helium≈1/2α_hydrogen (to 1/10 α_hydrogen at high electron temperatures). Collisional-radiative ionization coefficients for atomic helium have not yet been published in the past. In the present paper one finds for the first time a complete set ofS-coefficients for different degrees of radiative trapping.     

Al等离子体辐射损失的数值研究

建立了一个用于研究Al等离子体中的离子丰度和辐射损失的碰撞辐射模型,模型考虑了碰撞电离和复合,碰撞激发和退激发,辐射复合和自发辐射跃迁等原子过程,在恒离子密度和光性薄近似下,讨论了该模型给出的离子丰度和辐射损失的动态结果。 关键词：     

Population inversion in recombining hydrogen plasma

The collisional-radiative model is applied to a recombining hydrogen plasma in order to investigate plasma conditions in which a population inversion between the energy levels of hydrogen can be generated. Population inversion is expected in plasmas for which three-body recombination makes a large contribution to the recombining processes and the effective recombination rate is larger than a critical value for a given electron density and temperature. Calculated results are presented in figures and tables.     

Influence of Laser radiation on the collisional-radiative recombination and ionization coefficients

It is shown that irradiation of a plasma by a Laser beam lowers the collisional-radiative coefficient for recombination (α) and increases the one for ionization (S) compared to unirradiated plasmas. Numerical values ofα andS are given for a hydrogen plasma irradiated by CO₂, Ruby, and Ar-Ion Lasers. The calculations are based on a collisional-radiative model in which photoionization and stimulated recombination intervene. Stimulated recombination has an important effect and can lead to saturation of free-bound transitions at high power density of the Laser beam as long as multiphoton ionization effects and plasma heating by inverse bremsstrahlung remain negligibly small.     

Collisional-radiative volume recombination and ionization coefficients for He+-He2+-e plasmas

Coefficients have been calculated for collisional-radiative recombination of doubly ionized helium atoms with electrons and collisional-radiative ionization of singly into doubly ionized helium atoms due to electronic collisions and radiative absorption. Up to one hundred coupled equations have been solved which corresponds to a level system in which levels up to principal quantum number one hundred have been taken into account. The numerical results are presented in form of curves for a large number of parameters corresponding to very different experimental situations. Comparison of our values with those experimentally determined by Mosburg and by Gippiuset al. is made.     

Influence of atom-atom collisions on the collisional-radiative ionization and recombination coefficients of helium plasmas

Coefficients for volume recombination and ionization have been calculated for a dense helium plasma of low degree of ionization. The calculations are based on a collisional-radiative model in which electron-atom, electron-electron-ion, atom-atom, and electron-atom-ion collisions intervene. Molecular species such as He ₂ ^* and He ₂ ⁺ have not been taken into account. The essential results are: At low temperatures and high neutral gas densities the recombination coefficient is proportional to the number density of neutral helium atoms. At high temperatures the presence of neutral particles practically does not influence the recombination process compared to pure ion-electron-electron recombination. At high neutral particle densities, high atom temperatures and low electron densities the ionization process is mainly due to atom-atom collisions. In this point our calculations are in relatively good agreement with recent shock tube measurements of Kalra and Measures (Phys. Fluids14, 2544 (1971)). It is emphasized that the simple two-step model for ionization by shock waves in the noble gases should be replaced by a more general collisional-radiative model in which the atomic level structure intervenes in more detail.     

Collisional-Radiative Recombination in Argon Plasmas

On the basis of the realistic argon atom model consisting of 65 discrete effective levels numerical results for the collisional-radiative volume recombination, ionization and decay coefficients are obtained. The computations are carried out without any approximations of integral functions. The presented comparison of theoretical and experimental results for the decay coefficient shows that the values calculated by us are in much better agreement with experimental values than those obtained by Desai and Corcoran on the assumption that the argon atom is hydrogen-like.     

Collisional-radiative ionization and recombination coefficients for quasi-stationary homogeneous hydrogen and hydrogenic ion plasmas

The recombination and ionization coefficients have been re-calculated on the basis of the collisional-radiative model. The numerical results obtained deviate from those published byBates, Kingston, andMcWhirter. The deviations reach a factor of about four for the recombination and a factor ten for the ionization coefficients. The smallest deviations occur in the recombination coefficients when the plasma is assumed to be optically thin in all transitions. The conditions for the applicability of the collisional-radiative model are discussed.     

Kinetics of electron tunneling transfer in KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> and NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> crystals with hydrogen bonds

A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) on a wide temporal scale (10⁻⁸–10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and other experimental conditions have been considered.     

Theoretical and Experimental Investigations of the Suitability of Low‐Current Z‐Pinch Plasma as an Absorption Medium for Laser Radiation

In this study the electron density of z‐pinch plasmas driven at relatively low currents (ca. 2‐5 kA) was determined using only emission spectroscopy. The suitability of a hollow‐cathode‐triggered z‐pinch plasma as an absorption medium for laser radiation was investigated. The temporal and spatial behaviors of electron temperature and density profiles were estimated using magnetohydrodynamic (MHD) simulations to evaluate the experimental results. Temperature measurements were performed according to the Boltzmann plot method in the visible spectrum range, using the fact that, in low‐current z‐pinch plasma, a local thermodynamic equilibrium prevails for states at high principal quantum numbers (partial local thermodynamic equilibrium). In this case, the Saha equation can be used to determine the electron density. The results demonstrate that this method of determining the electron temperature and density of z‐pinch plasmas is only applicable during the pinching phase. However, in this case the experimentally determined values are in fairly good agreement with the values determined using the MHD model. A user‐oriented 1‐D radiation MHD code was used to simulate the dynamic evolution of the plasma. The experimentally determined maximum electron temperature of approximately 12 eV is in fairly good agreement with the simulated value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

“碰撞-辐射”模型在Z箍缩等离子体K壳层线辐射谱分析中的应用

介绍了由K壳层谱线强度比估算等离子体状态参数的"碰撞-辐射"模型的基本原理.详细描述了自行研制的基于该模型的Z箍缩等离子体K壳层线辐射谱分析程序——ZSPEC的基本情况.给出了氖等离子体的计算结果,包括不同电离态离子的相对含量随电子温度的变化曲线和K壳层谱线强度比在"电子密度-电子温度"平面内的等高线分布图.该程序已在"阳"加速器Z箍缩实验结果分析中得到应用,将椭圆晶体谱仪测得的氖等离子体K壳层谱线强度比与ZSPEC程序计算结果相比较,得出在该发实验 关键词： 碰撞-辐射模型 K壳层线辐射谱')" href="#">K壳层线辐射谱 氖气喷气Z箍缩 阳加速器     

Lowering of the Populations of Excited Hydrogen and Helium Atoms in Plasmas Irradiated by a Laser Beam

The populations of excited hydrogen and helium atoms in non-L.T.E. plasmas have been calculated for two different physical situations, namely (i) no external radiation field present, and (ii) strong superposed radiation originating from a CO₂, Ruby or Argon Ion Laser. The radiation field intervenes in the collisional-radiative model via two new terms: Photoionization and stimulated recombination induced by the Laser radiation field. The solutions of the rate equations yield a lowering of the populations when a plasma is irradiated by a Laser beam. The lowering is different for cold recombining and hot diffusion-dominated plasmas. At high radiation densities a saturation effect occurs, since the photoionization rate becomes equal to the rate of stimulated recombination. Measurements of the populations of excited H and He atoms in a glow discharge irradiated by a CO₂ Laser beam of power density 10⁵ W/cm² are in broad agreement with the theoretical predictions.     

Level population by recombination in a pulsed plasma jet in an He-Xe mixture

Measurements have been made on the spatial and time characteristics of the radiation from an He-Xe plasma jet emerging from a discharge channel through a nozzle with a speed of about 10⁵ cm/sec. A recombination mechanism is indicated for the line excitation by the delay between the current pulse and the production of the radiation, as well as by the substantial differences in time course for the intensities of the atomic and ionic lines and by the increase in intensity with pressure. Measurements have been made of the electron temperature and concentration, and estimates have been made of the recombination coefficients, which reflect the performance of the collisional-radiative recombination in a decaying He-Xe plasma jet.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 12–17, March, 1984.     

Numerical analysis of chemical reaction processes in different anode attachments of a high-intensity argon arc

The attachment mode of arc on anode is closely related to the non-equilibrium chemical kinetics process of the anode region of arc. In this paper, the detailed chemical reaction mechanisms in the flow-affected region for both diffuse and constricted argon arc attachments are investigated by means of one-dimensional discharge coupled with a single-fluid, two-temperature model. The collisional-radiative model is used to examine the chemical reaction processes occurring in the anode region, including the arc centreline and fringe region. The numerical results are validated by comparison with available experimental data. The obtained radial distributions of electron temperature, electron density, excited states densities, ionization, and recombination processes reveal that different mechanisms dominate the diffuse and constricted arc-anode attachments.     

Mechanisms of resonant laser ionization

An experimental investigation and numerical simulation of resonant laser breakdown are performed. As a result, quantitative agreement between the experimental data on the parameters of a dense resonant plasma (the electron density and the electron temperature) and the results of calculations in the range of detunings of the laser radiation from resonance Δλ>2–2.5 nm, in which the spatial instability of the intense resonant laser beam and the absorption of radiation are minimal, is obtained for the first time. It is shown that the previously proposed mechanism of resonant breakdown associated with laser-induced associative ionization introduces only a small correction to the final extent of ionization of the resonant plasma and scarcely alters its temperature. The influence of quantum stimulated inverse bremsstrahlung processes, which are usually described as collisions of the second kind in the resonance case, on the energy gain by electrons is analyzed for the first time in reference to specific experimental findings. The numerical calculations show that at detunings of the order of the Rabi frequency, the mechanism by which electrons gain energy through the resonant system does not reduce to collisions of the second kind and can significantly increase the density of the resonant plasma. However, in this range of detunings the laser beam is still strongly perturbed by instability processes, precluding a proper comparison of the theory with experiment. At large Δλ the classical and quantum cases differ from one another only slightly, and the values of N _e calculated for both mechanisms lie within the measurement error. Zh. éksp. Teor. Fiz. 111, 1274–1296 (April 1997)     

Kinetics of the transient optical absorption in Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> and LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> lithium borate crystals

This paper reports on a study of the kinetics of electron tunneling transport between electron and hole centers in Li₂B₄O₇ and LiB₃O₅ lithium borate crystals under the conditions where the mobility of one of the partners in the recombination process is thermally stimulated. A mathematical model has been proposed to describe all specific features in the relaxation kinetics of the induced optical density observed in Li₂B₄O₇ (LTB) and LiB₃O₅ (LBO) nonlinear optical crystals within a broad time interval of 10⁻⁸−1 s after a radiation pulse. The results of calculations have been compared with experimental data on transient optical absorption (TOA) of LTB and LBO crystals in the visible and ultraviolet spectral regions. The nature of the radiation defects responsible for TOA and the dependence of the TOA decay kinetics on temperature, excitation power, and other experimental conditions have been discussed.     

Analysis of Ar line spectra from indirectly-driven implosion experiments on SGII facility

This paper reports on the indirectly-driven implosion experiments on SGII laser facility in which Ar emission spectrum from Ar-doped D-filled plastic capsule is recorded with the crystal spectrometer. Spectral features of Ar Heβ line and its associated satellites are analysed to extract the electron temperature and density of the implosion core. Non local thermal equilibrium (NLTE) collisional-radiative atomic kinetics and Strark broadening line shape are included in the present calculation. By comparing the calculated spectrum with the measured one, the core electron temperature and density are inferred to be 700 eV and 2.5×10²³ cm^-3 respectively. With these inferred values of electron temperature and density, neutron yield can be estimated to agree with the measured value in magnitude despite of the very simple model used for the estimation.     

Population densities of He(I) and He(II) excited states in plasmas

Reduced population coefficients for He(I) and He(II) levels, both for optically thin and partially optically thick conditions, have been calculated from a collisional-radiative model using recent experimental and theoretical cross sections. The calculated population densities are compared with experimental results on helium plasmas. Agreement with experimental results is better at low electron temperatures.