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To examine the influence of radiative transitions on the performance of nonequilibrium seed-free argon plasma magnetohydrodynamic (MHD) generators, we developed MHD numerical simulation technique with a collisional-radiative (C-R) model, where neutral argon atoms with 45 discrete effective electronic excitation levels, singly ionized argon ions, and free electrons were considered under a two-temperature, low-magnetic Reynolds number MHD approximation. Furthermore, a so-called escape factor was implemented in the C-R model to consider the effects of radiation trapping by ground-state neutral atoms. Using the developed technique, we computed the performance characteristics of a nonequilibrium seed-free argon plasma MHD generator. The numerical results showed that the generator performance gets higher as the escape factor decreases, i.e., the optical thickness for radiative transitions to the ground state of neutral atoms increases. The numerical results also suggested that when the escape factor is $1.0\times 10^{-3}$ or less, the generator performance is almost the same as that for the escape factor of 0 corresponding to completely optical-thick plasma case for the radiative transitions to the ground state of neutral atoms. Furthermore, realistic escape factor values for resonance lines in the power generation channel were evaluated using a well-known estimation model. Consequently, the estimated values had the order of $10^{-4}$ . We also showed that under such relatively optically thick plasma cases, a collisional (C) model and a widely used global ionization-recombination rate model with no explicit consideration of electronically excited-state neutral atoms can reproduce the generator performance predicted by the C-R model with relatively good accuracy.

Тонкі плівки використовуються в різних галузях промисловості, а саме у виробництві сонячних елементів, плоских екранів та для поліпшення фізичних властивостей поверхонь матеріалів. У процесах осадження тонких плівок ступінь рівноваги та інші характеристики плазми, такі як природа, густина і температура, повинні бути визначені, щоб зрозуміти появу різних явищ. У роботі основна увага приділяється вивченню просторових розподілів густин збуджених станів Ar* (3p54s (1sx: x = 2-5)), а також відносних внесків таких процесів, як бомбардування електронами, випромінювальне дезбудження, явища дифузії метастабільних станів та іонізація Пеннінга в популяції та депопуляції різних станів атомів аргону. Для цього радіаційну модель зіткнень (CRM), яка включала 41 стан, було застосовано з використанням заданих параметрів у плазмі високочастотного магнетронного розпилення. Ці параметри включають температуру електронів, густини електронів та іонів аргону. Кінетичні рівняння густин станів привели до матричної системи, яка була розв'язана чисельно за допомогою ітераційного методу Гауса-Зейделя. Результати показують, що осьові розподіли різних збуджених станів та станів на катоді трохи більші, ніж на аноді; вони також показують, що обидві густини менші, ніж у центрі реактора. Іонізація Пеннінга важлива для метастабільних станів 3p54s (1s5, 1s3), але не важлива для резонансних станів 3p54s (1s4, 1s2). Різні густини збуджених станів не є симетричними відносно центру реактора через наявність магнітного поля на катоді. Thin films are used in various industrial fields, namely in the manufacture of solar cells, flat screens and in improving the physical properties of material surfaces. In thin film deposition processes, the degree of equilibrium and other plasma characteristics such as the nature, density and temperature must be identified in order to understand the occurrence of various phenomena. In this work, the main focus is on studying the spatial distributions of densities of excited states of Ar* (3p54s (1sx: x = 2-5)), as well as the relative contributions of processes such as the electron impact effect, the radiative de-excitation, the diffusion phenomena of metastable states and the Penning ionization in the population and depopulation of different argon atoms states. For this purpose, a Collisional-Radiative Model (CRM) including 41 states was applied using specified parameters in RF magnetron sputtering plasma. These parameters include electron temperature, electron and ion densities of argon. The rate equations of the state densities led to a matrix system that was solved numerically by iterative Gauss-Seidel Method. The results show that the axial distributions of different excited states and those on the cathode side are slightly larger than those found on the anode side, and they show also that both densities are less than at the reactor center. For metastable states 3p54s (1s5, 1s3), the Penning ionization is important, but it is not important for resonant states 3p54s (1s4, 1s2). Different densities of the excited states are not symmetrical with respect to the center of the reactor due to the existence of a magnetic field at the cathode.

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 &sim, ne = 1021 cm&minus, 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.

This paper describes the use of Optical Emission Spectroscopy (OES) to measure electron densities and temperatures in non-equilibrium plasmas. The ways to interpret relative line-intensities of neutral argon atoms are evaluated based upon a collisional-radiative model including atomic collisional processes. A conversion from an excitation temperature determined from relative line intensities assuming a Boltzmann population distribution to the thermal electron temperature in the electron temperature range 1–4 eV and electron density range 1010–1012 cm–3 is given. Procedures to obtain electron temperature Te and density Ne of non-equilibrium argon plasma by OES measurement with collisional radiative model.

Hall Effect thrusters (HET) have demonstrated its applicability on satellites for the Low earth orbit (LEO), Geo-stationary earth orbit (GEO) and long duration missions. High thrust density and long lifetimes are attractive parameters of the HET. In order to improve the thruster performance and lifetimes, decades of efforts are made to understand the plasma physics.Several intrusive and non-intrusive diagnostics techniques are employed for HET investigation. Simple and precise diagnostics technique is attractive to delineate the characteristics of the thruster. Optical emission spectroscopy provides several advantages over the other methods which are used for the HET diagnostics. Using this diagnostics tool in correlation with the collisional radiative model, the information of electron kinetics is extracted instantaneously.Collisional radiative model is developed by using the xenon near-infrared emission lines. This kinetic model can be used to determine the local electron temperature with error less than 15 % for investigating the HET physics., Холловские двигателя являются перспективным типом плазменного двигателя, который нашел свое применение в космосе. Несмотря на это, с каждым годом отмечается рост требований к xолловской двигателей. Разработка современных моделей холловской двигатели нуждается в совершенствовании теоретической и диагностической базы, Холлівські двигуни є перспективним типом плазмового двигуна, який знайшов своє застосування в космосі. Незважаючи на це, з кожним роком відбувається зростання вимог до холлівських двигунів. Розробка нових сучасних моделей холлівських двигунів потребує вдосконалення теоретичної і діагностичної бази

A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X 1 Σ g + population distribution in a SlimCS fusion demo detached divertor plasma is investigated by solving the model time dependently with an initial 300 K Boltzmann distribution. The effective reaction rate coefficients of molecular assisted recombination and of other processes in which atomic hydrogen is produced are calculated using the obtained time-dependent population distribution.

Hall Effect thrusters (HET) have demonstrated its applicability on satellites for the Low earth orbit (LEO), Geo-stationary earth orbit (GEO) and long duration missions. High thrust density and long lifetimes are attractive parameters of the HET. In order to improve the thruster performance and lifetimes, decades of efforts are made to understand the plasma physics. Several intrusive and non-intrusive diagnostics techniques are employed for HET investigation. Simple and precise diagnostics technique is attractive to delineate the characteristics of the thruster. Optical emission spectroscopy provides several advantages over the other methods which are used for the HET diagnostics. Using this diagnostics tool in correlation with the collisional radiative model, the information of electron kinetics is extracted instantaneously. Collisional radiative model is developed by using the xenon near-infrared emission lines. This kinetic model can be used to determine the local electron temperature with error less than 15 % for investigating the HET physics.

A method for determining the electron temperature and electron density in a plasma is proposed that is based on minimization of the difference between the experimental relative intensities of the spectral argon (Ar) lines and those same intensities calculated with the aid of the collisional-radiative model. The model describes the kinetics of the ground state and 40 excited states of the Ar atom and takes into account the following processes: excitation and deactivation of the states of the atom by electron impact, radiative decay of the excited states, self-absorption of radiation, ionization of excited states by electron impact, and quenching of metastable states as a consequence of collisions with the chamber walls. Using the given method, we have investigated the plasma of a magnetron discharge on a laboratory setup for intermediate-frequency magnetron sputtering for a few selected operating regimes.

A detailed fine-structure resolved collisional radiative model is developed to investigate the laser-produced Mg plasma. The dominant processes linked with the electron impact excitation and de-excitation have been considered explicitly in a very reliable and consistent manner in the present model. The required electron impact excitation cross-sections of Mg for the large number of transitions from the ground state 3s2 (J = 0) to the 3s3p, 3s4s, 3s3d, 3s4p, 3s5s, 3s4d, 3s5p, 3s6s, 3s5d, and 3s6p excited states and from 3s3p manifolds to the other fine-structure levels of 3s4s, 3s3d, 3s5s, 3s4d, 3s6s, and 3s5d configurations are obtained using the fully relativistic distorted wave approach. To ensure the accuracy of our calculations, where available, the oscillator strengths and cross-sections are compared with previous measurements and other calculations. Further, plasma diagnostics are carried out by coupling the present collisional radiative model with the laser-induced breakdown spectroscopy measurements reported by Delserieys et al (2009 J. Appl. Phys., 106, 083304). Five measured intense emission lines of Mg viz 383.3, 470.3, 517.8, 552.8, and 571.1 nm are used and corrected through the self-absorption to extract the plasma parameters i.e. electron temperature and electron density. The obtained plasma parameters at different delay times ranging from 100–700 ns are compared with the results of Delserieys et al (2009 J. Appl. Phys., 106, 083304) that were estimated using the Thomson scattering and Boltzmann plot approaches.

In this work, an optimization algorithm was proposed for plasma diagnostic modeling based on a statistical analysis of reduced population density distribution. The algorithm generates a diagnostic equation, whose input parameters are the radiant flux of the multi-optical emission lines, and output parameters are electron temperature T e, electron density N e, and electron energy distribution function (EEDF), based on the dependence of reduced population density onT e, N e, and EEDF. The argon collisional-radiative model and the generalized EEDF were applied for the analysis of the excitation-kinetics. In this study, the diagnostic error for the low-pressure inductively coupled plasma, the low-pressure microwave discharge surface wave plasma, and the atmospheric dielectric barrier discharge plasma were simulated. The simulated diagnostic errors were smaller than those of the previously reported model.

It is crucial to measure the electron density (ne) and temperature (Te) for applications such as developing small helicon sources in plasma thrusters. Hence, this study developed a method based on an optical emission spectroscopic (OES) measurement without disturbance or contamination for helicon plasma produced using argon gas. The argon collisional-radiative (CR) model was used to describe the excitation number density in plasma as a function of ne and Te. Each number density ratio was surveyed as a function of ne and Te. From these results, contours of two number densities, i.e., two excitation energy levels, were drawn on an ne–Te plane. By applying various contour pairs, ne and Te were determined from the intersection point of two contours whose values were taken from the experimental intensities. Finally, we compared the new OES measurements with the CR model for various intensity ratios and found a way to select a valid intensity ratio that is in good agreement with the ne and Te derived by the probe method.

To increase the accuracy of a particle, momentum, and energy source terms in the detached helium plasma simulation, rate coefficients with the collisional-radiative model were introduced into the fluid code LINear Divertor Analysis (LINDA). Obtained effective rate coefficients and related source terms were compared with those from the conventional empirical databases. It is shown that a high-density condition in future fusion devices causes larger deviation between the effective and the empirical source terms. One-dimensional detached plasma simulation indicated that the peak amplitude of the plasma density during the rollover is sensitive to the source term difference related to the recombination. This study additionally revealed that the heating effect in the three-body recombination process strongly affects the detached plasma formation and downstream plasma parameters., ファイル公開：2021/10/07

Optical emission spectroscopy technique with Bayesian probability theory is used to infer electron temperatures and densities of low density helium plasmas. Helium plasmas are generated in a newly developed DC multi-dipole chamber, MAXIMUS (Magnetic X-point sIMUlator System). Plasma parameters are varied by adjusting neutral pressure, bias voltage and heating current. Likelihoods are calculated based on a helium collisional-radiative model consistent with the measured signal and noise level. With a uniform prior probability, we obtain the posterior which are compared with the simultaneous and independent measurements of the electron temperature and density by Langmuir probes.

In the present work, we develop a collisional radiative (CR) model for the Ar-CO2 mixture plasma. The model is applied to the diagnostics of a recently reported low-pressure DC generated Ar-CO2 plasma of Rodriguez et al. [Phys. Plasmas 25, 053512 (2018)] utilizing their spectroscopic measurements who reported the plasma parameters at different concentrations of CO2 in Ar at various pressures and powers. Our CR model includes various population transfer mechanisms between the fine structure levels, viz., electron-impact excitation, radiative decay, and ionization, as well as their reverse processes, e.g., electron-impact de-excitation as well as two- and three-body recombination. The effects of radiation trapping and diffusion are also taken into account. The plasma parameters viz. electron density (ne) and electron temperature (Te) are obtained as a function of different pressures (0.2, 0.3, and 0.6 mbars) and discharge powers at 25 and 50% concentrations of CO2 in argon. These results are determined using measured intensities of seven intense emission lines out of 3p54p (2pi) → 3p54s (1si) fine-structure transitions. It is observed that both the electron density and electron temperature increase with the increase of CO2 concentration, which is in confirmation with experimental predictions. The populations obtained for 1si and 2pi levels from our CR model are also reported and compared respectively with the corresponding available values from the simple CR model and experiment of Rodriguez et al. [Phys. Plasmas 25, 053512 (2018)]. A significant difference in the populations is observed from the two models.

Plasma diagnostics in magnetic confinement fusion plasmas by using visible spectrum strongly depends on the knowledge of fundamental atomic properties. A detailed collisional-radiative model of W 26+ ions has been constructed by considering radiative and electron excitation processes, in which the necessary atomic data had been calculated by relativistic configuration interaction method with the implementation of Flexible Atomic Code. The visible spectrum observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm to 392 nm was reproduced by present calculations. Some transition pairs of which the intensity ratio is sensitive to the electron density were selected as potential candidates of plasma diagnostics. Their electron density dependence is theoretically evaluated for the cases of EBIT plasmas and magnetic confinement fusion plasmas.

A zero-dimensional collisional–radiative (CR) model, coupled self-consistently with the electron Boltzmann equation, has been applied to the description of a metallic-laser induced plasma at experimental conditions typical of LIBS experiment. To take in account expansion effects, the experimental temperature and total number density as function of time have been used as input data. Plasma composition and the simultaneous time evolution of both heavy particle level distributions and the electron energy distribution function have been calculated by taking into account the most relevant collisional and radiative processes. This approach estimates the hierarchy of the elementary processes during the expansion and possible deviations from LTE conditions. The comparison of the experimental and theoretical results shows a good agreement, but at the same time new questions arise on the analysis of spectroscopic results and on the assumption generally made in LIBS.

A helicon thruster was developed to research a diagnostic technique for determining plasma parameters using emission spectroscopy and helium line ratios. Conventional plasma diagnostics consisting of conductive components which contact the plasma directly can have measurement errors in the presence of radio frequency, electric, or magnetic fields. A non-invasive diagnostic technique is sought to eliminate these problems. A collisional radiative model is needed to determine the electron density and temperature that result in the measured emission line ratios. This research describes a quasi-steady state collisional radiative model used to determine the electron temperature and density in a helium helicon thruster.

We have constructed a collisional-radiative (CR) model for W27+ ions including 226 configurations with n ≤ 9 and ł ≤ 5 for spectroscopic diagnostics. We newly include recombination processes in the model and this is the first result of extreme ultraviolet spectrum calculated for recombining plasma component. Calculated spectra in 40–70 Å range in ionizing and recombining plasma components show similar 3 strong lines and 1 line weak in recombining plasma component at 45–50 Å and many weak lines at 50–65 Å for both components. Recombination processes do not contribute much to the spectrum at around 60 Å for W27+ ion. Dielectronic satellite lines are also minor contribution to the spectrum of recombining plasma component. Dielectronic recombination (DR) rate coefficient from W28+ to W27+ ions is also calculated with the same atomic data in the CR model. We found that larger set of energy levels including many autoionizing states gave larger DR rate coefficients but our rate agree within factor 6 with other works at electron temperature around 1 keV in which W27+ and W28+ ions are usually observed in plasmas.

Stoß-Strahlungsmodelle (SSM) werden in der Niedertemperatur-Plasmaphysik verwendet, um die Eigenschaften der Elektronen des Plasmas aus optischen Emissionsspektren zu bestimmen. In dieser Dissertation wurde ein SSM für Argon-Plasmen entwickelt und evaluiert. Verschiedene Prozesse wie Elektronenstoß-Anregung und Elektronenenergieverteilung, Strahlungsreabsorption und Diffusion von metastabilen Atomen wurden im Detail untersucht. Parameter und Inputdaten wie Elektronenstoß-Wirkungsquerschnitte und Einsteinkoeffizienten werden diskutiert und ihr Einfluss auf die Ergebnisse der Modellierung wird explizit gezeigt. Um die Ergebnisse des SSM zu evaluieren, werden experimentelle Daten verschiedener Entladungen bei unterschiedlichen Bedingungen herangezogen. Das Argon-SSM wird zudem zur Analyse reaktiver Plasmen eingesetzt, indem Argon in kleinen Mengen beigemischt wird. Bei höherem Druck verändert sich das SSM deutlich, wie anhand eines Wasserstoff-Silan-Argon-Plasmas gezeigt wird. In low-temperature plasma physics collisional-radiative models (CRMs) are used to extract information on the plasma electrons from optical emission spectra. In this dissertation a collisional-radiative model for argon plasmas is developed and evaluated. A detailed discussion of different processes such as electron impact excitation and the electron energy distribution, radiation trapping and diffusion of metastable atoms is given. Parameters and input data such as electron impact cross sections and Einstein coefficients are discussed in detail and their impact on the modelling results is shown. To evaluate the CRM the modelling results are compared with experimental data from several kinds of discharges under different conditions. The argon CRM is also applied to evaluate gas mixture plasmas using argon as a trace gas. At higher pressures the CRM is found to change fundamentally, as the analysis of a hydrogen-silane-argon plasma shows.

Energy levels, transition probabilities, collision sections, and collision excitation rate coefficients of NII ion have been calculated using Flexible Atomic Code, which is based on the multiconfiguration Dirac–Fock method. The ratios of line intensity, I567.96 nm/I500.52 nm, where the 567.96 and 500.52 nm are two strong spectral lines from the core current channel of lightning, have been calculated by using the collisional-radiative model, in which the line intensity is proportional to the collision excitation rate coefficients from the ground state to the excited state and the transition probability from the high excited state to the low excited state. The temperatures of six lightning plasma channels were then obtained, and they are consistent with temperatures obtained by diagnosing the actual spectrum with the multispectral line method.

We present a collisional-radiative approach of the theoretical analysis of laser-induced breakdown spectroscopy (LIBS) plasmas. This model, which relies on an optimized effective potential atomic structure code, was used to simulate a pure aluminum plasma. The description of aluminum involved a set of 220 atomic levels representative of three different stages of ionization (Al 0 , Al + and Al ++ ). The calculations were carried for stationary plasmas, with input parameters ( n e and T e ) ranging respectively between 10 13–18 cm − 3 and 0.3–2 eV. A comparison of our atomic data with some existing databases is made. The code was mainly developed to address the validity of the local thermodynamic equilibrium (LTE) assumption. For usual LIBS plasma parameters, we did not reveal a sizeable discrepancy of the radiative equilibrium of the plasma towards LTE. For cases where LTE was firmly believed to stand, the Boltzmann plot outputs of this code were used to check the physical accuracy of the Boltzmann temperature, as it is currently exploited in several calibration-free laser-induced breakdown spectroscopy (CF-LIBS) studies. In this paper, a deviation ranging between 10 and 30% of the measured Boltzmann temperature to the real excitation temperature is reported. This may be due to the huge dispersion induced on the line emissivities, on which the Boltzmann plots are based to extract this parameter. Consequences of this fact on the CF-LIBS procedure are discussed and further insights to be considered for the future are introduced.

The electron temperature in atmospheric argon plasmas created by a DBD jet is determined using a combination of Absolute Line Intensity (ALI) measurements and a collisional radiative model (CRM). The ALI measurements have been performed to determine the densities of the states in the 4p level. In addition, the ground state density is taken into account, which is found via the pressure and the gas temperature. The density ratio of the ground state and 4p state gives a value of the excitation temperature, which by means of the CRM is transformed into the electron temperature. With this method, the electron temperature in the active zone of a pure argon plasma is found to be 1.27 eV which is significantly higher than the experimental value reported by others. An error analysis shows that the relative error in the electron temperature obtained in this way is about 5%. In the afterglow, the temperature decreases gradually to about 0.88 eV. The addition of 2% O-2 leads to a decrease in electron temperature of about 5%.

Spectra of neutral helium in the visible wavelength range are measured for a discharge in the Large Helical Device (LHD). The electron temperature ( T e ) and density ( n e ) are derived from the intensity distribution of helium emission lines. For that purpose, a collisional-radiative model developed by Sawada et al. [Plasma and Fusion Res. 2010;5:001] which takes the reabsorption effect into account is used. It is found that incorporation of the reabsorption effect is necessary to obtain a set of T e and n e giving consistent line intensity distribution with the measurement, and that those parameters obtained vary as the line-averaged n e changes in the course of time. The position where the helium line emission dominantly takes place is located with the help of T e and n e profiles measured by the Thomson scattering system. The result indicates that the emission position is almost fixed at the place where the connection length of the magnetic field lines to the divertor plate leaps beyond 10 m. Because intense neutral atom line emission suggests the vigorous ionization of neutral atoms, the helium line emission location determined here can be regarded as the effective boundary of the plasma.

Plasma spectroscopy is a common method for diagnosing the radiative behaviour and predicting the key properties of a plasma. Plasma spectroscopy may be merged with plasma modelling and simulation to perform numerical diagnostics. A new Collisional Radiative (CR) model is developed for argon plasma at low temperature and low pressure. In the developed model, rather than grouping the energy levels into lumped sets, all the energy levels up to a maximum level were modeled for both the argon neutrals and the argon single ions. With the gathered data of collisional and radiative rate coefficients from LANL (Los Alamos National Laboratory) and NIST (National Institute of Standards and Technology), this model calculates the time-varying population densities of 101 atomic and 222 ionic energy levels. The model considers the emissions of 146 Ar-I lines (in 86.68–2397.3 nm range) and 303 Ar-II lines (in 71.8–6985.3 nm range), and gives the simulated spectra over the optical and near-optical region. The simulated radiation emission spectra were then compared with the measured spectra of a laboratory helicon plasma source for the prediction of the plasma parameters such as electron temperature and electron density.

A method of constructing a compact and complete collisional radiative model of multiple charged ions of mid- to high-Z elements is proposed, for studying radiative properties of the plasmas. The proposed tungsten model, which is based on atomic data calculated by the HULLAC code, incorporates a computer algorithm to identify well-populated atomic states and dielectronic recombination channels that have a significant effect on the ionization balance. The model is validated by investigating the convergence of the mean charge and radiative power loss with respect to the size of the model, and by comparing results with other calculations presented at the nLTE kinetics workshop.

A Maxwellian electron energy distribution function (EEDF) is often assumed when using the optical emission line-ratio method to determine the electron temperature in low-temperature plasmas. However, in many cases, non-Maxwellian EEDFs can be formed due to the non-local electron heating or the inelastic-collisional energy loss processes. In this work, with a collisional-radiative model, we propose an approach to obtain the non-Maxwellian EEDF with a 'two-temperature structure' from the emission line-ratios of Paschen 2p levels of argon and krypton atoms. For applications of this approach in reactive gas (CF4, O2, etc) discharges that contain argon and krypton, recommendations of some specific emission line-ratios are provided, according to their sensitivities to the EEDF variation. The kinetic processes of the relevant excited atoms are also discussed in detail.

This work is focused on diagnostics of electron temperature (1.0 eV–3.8 eV) and electron density (1.0 × 109 cm−3–5.0 × 1012 cm−3) of lowpressure (133 Pa) discharge argon plasma by optical emission spectroscopic (OES) measurement. The diagnostic method using multi-emission lines was analyzed. First, the excitation-kinetic models were obtained by extracting dominant kinetic processes based on the collisional-radiative model. Then, the diagnostic equations for wide range of electron temperature and density were proposed to describe the approximate excitation kinetic balance of several excited levels. 15 optical emission lines (wavelength range: 340.7 nm–912.3 nm) were selected for OES measurement. RMS of the theoretical relative error was found to be 5.96% for electron temperature, while 32.6% for electron density. The diagnostics of 2.45 GHz microwave plasma was demonstrated by the proposed method and by the probe method. The electron density results by the proposed method were in good agreement with the probe method.

Atomic helium (He I) optical emission spectroscopy was carried out in a MAP-II divertor simulator to investigate the applicability of He I collisional-radiative (CR) model for the measurement of electron temperature ( T e ) and density ( n e ) in He–H 2 mixture plasmas. The result was compared with Langmuir probe measurements. The excited population distribution of the He–H 2 mixture plasma was not reproduced by the He I CR model, although it was reproduced well for pure He and He–Ar mixture plasma. Specifically, the deviation of the population ratio of singlet to triplet states became more evident as the concentration of H 2 increased. This fact implies that the measurement of T e for He–H 2 plasma using the He I CR model could lead to a significant error under a certain condition, such that T e

Morel, V. Bultel, A. Cheron, B. G.; A OD numerical approach including a Collisional-Radiative model is elaborated in the purpose of describing the behavior of the nascent plasma resulting from the interaction between a 4 ns/65 mJ/532 nm Q-switched Nd:YAG laser pulse and an aluminum sample in vacuum. The heavy species considered are Al, Al(+), Al(2+) and Al(3+) on their different excited states and free electrons. The translation temperatures of free electrons and heavy species are assumed different (T(e) and T(A) respectively). Numerous elementary processes are accounted for as electron impact induced excitation and ionization, elastic collisions, multiphoton ionization and inverse Bremsstrahlung. Atoms passing from the sample to gas phase are described by using classical vaporization theory so that the surface temperature is arbitrarily limited to values less than the critical point one at 6700 K. The laser flux density considered in the study is therefore moderate with a fluence lower than 7J cm(-2). This model puts forward the major influence of multiphoton ionization in the plasma formation, whereas inverse Bremsstrahlung turns out to be quasi negligible. The increase of electron temperature is mainly due to multiphoton ionization and Te does not exceed 10,000 K. The electron induced collisions play an important role during the subsequent phase which corresponds to the relaxation of the excited states toward Boltzmann equilibrium. The electron density reaches its maximum during the laser pulse with a value approximate to 10(22), 10(23) m(-3) depending highly on the sample temperature. The ionization degree is of some percents in our conditions. (C) 2010 Elsevier B.V. All rights reserved.

A collisional–radiative model (CRM) is developed to study nitrogen arc plasma. The model is based on solution of the rate equations of ν species chosen for the study. The species chosen are: electrons e, atomic ions N+, atoms N, diatomic molecules N2, and molecular ions N 2 + , we have then ν=5 species. The CRM is applied to homogeneous and quasi-stationary state (HQSS) plasma for electron temperature Te upto 12 000 K. All heavy particles are assumed to have the same kinetic temperature Tg such that Tg=Te, this means the temperature of the all five species is identical and is called plasma temperature T. The total pressure of the plasma is considered between 1 and 4 atm. The plasma composition is calculated taking into account all significant collisional and radiative mechanisms. The local effect of radiation absorption is described by the optical escape factors Λj and Λjk for free–bound and bound–bound transitions. Results show significant deviation from local thermodynamic equilibrium (LTE). It was also shown that the plasma pressure p has a strong influence on deviation from LTE. To assess the relative speeds of recombination reactions in nitrogen arc plasma we have calculated the relaxation time τ (or time constant) as a function of temperature.

A simple collisional?radiative model for low-pressure argon discharges is proposed. Using this model and the measured cross section data from recent literature, the relationship between the electron density and some emission line intensities is investigated, resulting in a semi-empirical formula relating the electron density and the emission intensity ratio of argon lines (from levels 3p and 4p). The electron density determined from this model is compared with that from a Langmuir probe in an inductively coupled argon plasma. The application and validity of this model in other kinds of low-pressure argon plasmas, such as capacitively coupled and helicon plasmas, or in discharges containing both argon and other gases are discussed.

A method for the determination of the reduced electric field strength (E/N) in a neon discharge from the optical emission spectra was developed. This method is based on a collisional–radiative model, which was used to calculate the emission spectra of the neon plasma. In the model, populations of 30 excited levels of the neon atom were studied. Various elementary collision processes were taken into account: electron impact excitation, de-excitation and ionization of neon atoms, emission and absorption of radiation, metastable–metastable collisions, metastable and radiative dimer production, Penning ionization, etc. To determine the rates of electron collisions, the Boltzmann kinetic equation for the electron distribution function (EDF) was solved for given E/N, and thus the dependence of the emission spectra on E/N could be determined. The EDF was expanded in terms of Legendre polynomials and the first two terms of this approximation were taken into account. The theoretical emission spectra were fitted by the non-linear least-squares method to the measured spectra with respect to the unknown parameter E/N.The method was applied to the study of low pressure dc glow discharge in neon. In such a discharge the calculated reduced electric field strength could be compared with the independent results of simultaneously performed electric probe measurements of E/N. Generally, close agreement of the calculated values with the experimental data was achieved.

Optical diagnostics for plasmas has many advantages that allow for the determination and understanding of plasma parameters. A method employing the line intensity ratio (LIR), combined with the collisional-radiative (CR) model considering the radiation trapping effect (RTE), was developed to analyze the recombining helium plasmas. The recombining plasma component and the ionizing plasma components in the He CR-model were evaluated, and the RTEs for from the ground state to n1P states were analyzed. The electron temperature and density of the helium recombining plasmas were determined using seven LIRs with the He CR-model, considering the RTEs of 11S–31P, 11S–41P, and 11S–51P. When the He gas pressure was above 100 mTorr, the electron temperature was less than 0.8 eV and the electron density was more than 1012 cm−3. The determined plasma parameters were compared with those obtained by the continuum method and in reasonable agreement with those by the continuum method.Optical diagnostics for plasmas has many advantages that allow for the determination and understanding of plasma parameters. A method employing the line intensity ratio (LIR), combined with the collisional-radiative (CR) model considering the radiation trapping effect (RTE), was developed to analyze the recombining helium plasmas. The recombining plasma component and the ionizing plasma components in the He CR-model were evaluated, and the RTEs for from the ground state to n1P states were analyzed. The electron temperature and density of the helium recombining plasmas were determined using seven LIRs with the He CR-model, considering the RTEs of 11S–31P, 11S–41P, and 11S–51P. When the He gas pressure was above 100 mTorr, the electron temperature was less than 0.8 eV and the electron density was more than 1012 cm−3. The determined plasma parameters were compared with those obtained by the continuum method and in reasonable agreement with those by the continuum method.

Optical diagnostics of plasma by a collisional-radiative model combined with optical emission spectroscopy is simple and has many advantages. However, the radiation trapping effect (RTE) disturbs the spectra of plasma and becomes an obstacle to determine the exact electron temperature and density. In order to take into account RTE, the radiative excitation rate coefficient (RERC) was introduced and the analytical expression of RERC was proposed. The hot filament discharge system was constructed and helium spectra were analyzed by the collisional-radiative model with RERC. The characteristics of RERC were discussed against the discharge power and gas pressure.

A collisional-radiative model for the ground state and fifty effective excited levels of atomic iron, and one level for singly-ionized iron, is set up for technological plasmas. Attention is focused on the population of excited states of atomic iron as a result of excitation, de-excitation, ionization, recombination and spontaneous emission. Effective rate coefficients for ionization and recombination, required in non-equilibrium plasma transport models, are also obtained. The collisional-radiative model is applied to a thermal arc plasma. Input parameters for the collisional-radiative model are provided by a magnetohydrodynamic simulation of a gas-metal welding arc, in which local thermodynamic equilibrium is assumed and the treatment of the transport of metal vapour is based on combined diffusion coefficients. The results clearly identify the conditions in the arc, under which the atomic state distribution satisfies the Boltzmann distribution, with an excitation temperature equal to the plasma temperature. These conditions are met in the central part of the arc, even though a local temperature minimum occurs here. This provides assurance that diagnostic methods based on local thermodynamic equilibrium, in particular those of optical emission spectroscopy, are reliable here. In contrast, deviations from the equilibrium atomic-state distribution are obtained in the near-electrode and arc fringe regions. As a consequence, the temperatures determined from the ratio of line intensities and number densities obtained from the emission coefficient in these regions are questionable. In this situation, the collisional-radiative model can be used as a diagnostic tool to assist in the interpretation of spectroscopic measurements.