Spectroscopic Mapping of the Nonequilibrium between Electron and Excitation Temperatures in a 1 ATM Helium ARC

The thermostatic states of a 100 amp, 1.016 bar, free-burning helium short arc with a 10 mm electrode gap are mapped from spectroscopic measurements at eight cross sections. The theoretical model used is a multifluids model extended to consider nonequilibrium between electron and excitation temperatures, as well as simple nonequilibrium among excited electronic levels. Seven helium lines are used to determine population densities and upper level excitation temperatures. The electron density is calculated from continuum intensity measurements at C4690. Electron temperatures are found from an astrophysical method suggested by Athay and Menzel. The effective total excitation temperature is obtained by iteration using the multifluids model. The results indicate total excitation temperature values close to the usually calculated "LTE" temperatures, but electron temperatures up to three times larger than the total excitation temperature on the arc centerline near the electrodes. The ratio is approximately 1.5 in the middle of the arc. The heavy particle kinetic temperatures appear to follow the electron temperature, except near the anode, where they drop to values smaller than the total excitation temperatures.     

Relative transition probabilities of F(I) spectral lines in the visible

The relative transition probabilities of 36 neutral fluorine lines were determined by photoelectric measurements of the spectral lines emitted from a wall-stabilized arc operated in argon-fluorine mixtures. The arc current was varied from 50–70 A, the electron concentration from 1.25 to 1.55 x 10²³m^-3, and the temperature from 13,600 to 14,300 K. The assumption of LTE was used for optically thin spectral lines. The electron concentration was measured by introducing a small quantity of hydrogen, and the temperature was determined from the relative intensities of Ar lines. Close agreement was found with other experimental data obtained from arc sources.     

Temporal follow up of the LTE conditions in aluminum laser induced plasma at different laser energies

In order to analyze the emission spectrum of a laser-induced plasma for obtaining quantitative information on the abundance of the species present in the plasma it is necessary to study the local thermodynamic equilibrium (LTE) conditions in the plasma and determine the best conditions at which they are satisfied. In the present work Nd:YAG laser light pulses (λ=?1064 nm, 6 ns) of different energies (25, 50, 75 and 100 mJ) are focused using a quartz lens (focal length 10 cm) onto certified aluminum alloy samples in air under atmospheric pressure. The emitted spectra are collected and analyzed using an echelle spectrometer coupled with an intensified charge coupled device camera. The temporal history of the plasma is obtained by recording the emission features at predetermined delays and at a fixed gate width (2500 ns). For each spectrum both electron density and excitation temperature are calculated for each delay time and laser pulse energy; we found that the values of the electron density are decreasing from 10¹⁸ to 10¹⁷ cm^-3. The corresponding excitation temperatures were between 30000 and 4000 K depending on the laser pulse energy and the sample used. The LTE conditions were followed up for the different delays and different energies to determine the temporal range in which they are satisfied. It has been found that in the cases of 25- and 50-mJ laser energies, the LTE conditions were satisfied in the chosen delay range (500–5000 ns). On the other hand, for higher laser energies, the LTE conditions were critical at delay times less than 1500 ns and are satisfied for longer delays.     

Saha decrements and collisional-radiative recombination and ionization coefficients for a nonequilibrium oxygen plasma

Using a time-dependent approach, a collisional-radiative model is developed for an oxygen plasma. Effective recombination and ionization coefficients are calculated for two specific cases, optically thin and optically thick in bound-bound u.v. radiation. The steady-state population densities for neutral and ionic states are presented in terms of their deviations from Saha equilibrium predictions. These results show the approach of the plasma to a state of local thermodynamic equilibrium (LTE) as a function of electron temperature and density. The computations are for temperatures between 1.0 and 3.0 eV and electron densities between 10¹⁶ and 10¹⁹ cm^-3.     

Non-LTE diagnostic of an argon arc plasma

The plasma of an argon arc has been investigated by applying the partial LTE model (overpopulation of the ground state) and accounting for different kinetic temperatures of electrons and atoms. The plasma analysis is performed without making use of atomic constants (e.g. transition probabilities) from the literature. The experimental results show that LTE is obtained in the 4mm arc at atmospheric pressure for electron densities above 6×10¹⁶cm^-3. Below this value, increasing under-population of the excited levels with decreasing arc current can be observed. This deviation from LTE may explain some not understood results from previously published spectroscopic observations of argon plasmas.     

Thermal Nonequilibrium of a Free-Burning Argon Arc Plasma

The axial distributions of the electron temperature and number density of a free-burning atmospheric argon arc plasma at 15 Amps have been measured using a Thomson scattering technique. In addition, the excitation temperature of singly ionized argon has been found spectroscopically by relative line intensity method. The results are presented in terms of the degree of electron temperature nonequilibrium as compared with the calculated Saha equilibrium temperature and with the measured ionic excitation temperature along the axis of the arc. The observed temperatures are discussed with respect to the theoretical ion-like particle temperature and to the effect of electrode geometry.     

Spectroscopical Observation of a Relaxing High Speed Nitrogen Plasma Jet

A near sonic nitrogen plasma jet operating at pressures between 100 Torr and 1 atm has been investigated spectroscopically. From the absolute emission coefficient of a NI spectral line, local values for the electron temperature T_e have been derived. For pressures above 200 Torr, T_g was found to coincide within the limits of experimental error with the gas temperature T_g. The latter quantity has been determined via the relative emission coefficient of selected rotational line components of the N₂⁺ molecular band at 3914 Å. The results of these measurements together with control data for the electron density derived from the continuous emission coefficient indicate that at pressures above 200 Torr the existence of a thermal equilibrium between the degrees of freedom corresponding to particle translation, electron excitation, and ionization can be accepted, at least for the inner zone of the plasma jet. To the contrary, the data for the absolute emission coefficient of N₂⁺ molecular band lines show that the degree of dissociation in the plasma jet is much in excess of that corresponding to equilibrium. This phenomenon can be explained as a result of the rapid temperature decay in the plasma from initially 13000 K in the arc heating zone to T ≦ 9000 K in the plasma jet zone proceeding in a time interval of 10^?5 s which is much shorter than the time necessary for adjustment of dissociation equilibrium. In the outer cool zone of the plasma jet, an unusual high intensity of the N₂⁺ radiation was found thus indicating the existence of a nonequilibrium excitation mechanism typical for a decaying nitrogen plasma. From the supernormal high degree of dissociation in the high-speed subatmospheric nitrogen plasma jet, conclusions are drawn with respect to its applicability as source of reactive particles in plasma-chemical experiments.     

An experimental investigation of partial LTE for lower excited levels of Ar(I) in a wall-confined,argon arc plasma

This paper contains experimental results on partial LTE in the lower excited levels of Ar(I). The experiments were performed in a well-confined argon arc source. The population densities were obtained from self-absorption measurements of the lines. Plasma parameters were determined spectroscopically; measurements included the electron density (from the H_β line width) and the electron temperature (from the Boltzmann plot for higher excited levels of Ar(I)). The results show that the levels 1s₅ to 1s₅ are in Saha-Boltzmann equilibrium for electron densities above 3 × 10¹⁶ cm^-3.     

大气压直流氩等离子体射流工作特性研究

介绍了一种新型大气压直流双阳极等离子喷枪,并对其电特性参数和发射光谱进行了测量.通过对氩等离子体射流的电信号进行时域和频域分析,研究了载气流量和弧电流的变化对射流脉动的影响,结果表明氩等离子体电弧的伏安特性呈上升趋势,射流脉动属于接管模式,电源特性中的交流分量引起的电压波动是影响氩等离子体射流脉动的主要因素. 通过光谱法测量了氩等离子体射流在弧室内和弧室出口的发射光谱,利用玻尔兹曼曲线斜率法计算了射流的激发温度,根据Ar I谱线的斯塔克展宽得到了射流的电子密度,并对等离子体射流满足局域热力学平衡(LTE) 关键词： 等离子喷枪 射流脉动 激发温度 局域热力学平衡     

Critical Review of Plasma Spectroscopic Diagnostics via MTE

The often used absolute, ratio, and off-axis peaking methods of LTE spectroscopy are examined using the Multithermal Equilibrium (MTE) multifluid model. The partial MTE model distinguishes between the upper level and total excitation temperatures of atom and ion (Tex?a or Tex?i and Texa or Texi, respectively) as well as different valued electron (Te) and heavy particle (Ta = Ti) temperatures. In complete MTE, all excitation temperatures are equal valued but may differ from kinetic temperature values. In this paper, the particular temperature approximated by common diagnostic methods is identified. The probable errors in the temperature values are presented in a figure as a function of probable errors in data, temperature and level energy difference. The results indicate that the ratio methods (neutral-neutral, ion-neutral, and continuumneutral) yield upper level excitation temperature values; the absolute neutral line and absolute continuum (at low Texa) yield total atom excitation temperatures; and the off-axis peaking method for the neutral line yields the total excitation temperature. Application of the methods are more complex than in LTE spectroscopy. Probable errors are smallest for the absolute and off-axis peaking methods. The electron temperature may be determined from the continuum-neutral ratio at very high excitation temperatures (Texa >> E?/10k). The paper also comments on MTE diagnostic methods.     

Investigation of the Anode Boundary Layer of an Atmospheric Pressure Argon Arc

This paper is concerned with the thermodynamic state of the plasma in the anode region of a high intensity arc. Spectrometric studies of the boundary layer in front of a plane anode perpendicular to the axis of a wall-stablized, high-intensity arc in argon atmosphere indicate substantial deviations from LTE. Data taken at distances of 0.5 to 2 mm from the anode surface are evaluated with two different but not entirely independent non-equilibrium data reduction techniques in order to obtain radial distributions of electron temperature and electron density. The electron temperature distribution displays an off-axis peak which increases in magnitude with decreasing distance from the anode. Both electron temperatures and electron densities are considerably higher than the corresponding LTE values.     

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.     

Spectroscopic Diagnostics of Pulsed arc Plasmas for Particle Generation

Pulsed arc plasmas were diagnosed by means of emission spectroscopy. A capacitor was discharged through argon and hydrogen leading to a few cycles of damped current oscillation with ≈120 μs period and 5‐12 kA maximum current. Spectroscopic measurements in the visible range were carried out in order to characterise the electron temperature and density in the arc channel as well as electron and gas temperatures in the afterglow plasmas. Spectra were integrated over 10 μs time windows and shifted in time from pulse to pulse. The plasmas also contained substantial fractions of electrode material (brass), namely copper and zinc. The electron density was measured in the conventional way from the broadening of H_β or from the Ar I Stark width. In the arc channel, it ranged from about 3 · 10²² to 2 · 10²³ m^–3. The broadening of Zn II lines could also be used. Ratios of Ar I to Ar II and of Zn I to Zn II line intensities were analysed for the electron temperature. Line pairs were found which lay conveniently close in one frame of the spectrometer allowing automatic on‐line analysis without relying on reproducibility. Atomic physics models including opacity were developed for Ar II and Zn II in order to check the existence of a Boltzmann distribution of their excited states. These calculations showed that the observed levels were in fact close to thermodynamic equilibrium, in particular, if the resonance lines were optically thick. Electron temperature measurements yielded values between 14000 K and 21000 K. The gas temperature in the afterglow, where particles should have formed, was derived from the rotational and vibrational temperatures of C₂ molecular bands. Ratios between Cu I line intensities yielded the electron temperatures. Both were found to be a few 1000 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zur Asymmetrie der Reaktion139La(n,α)136Cs mit polarisierten Neutronen

Experimental and theoretical investigations have been performed to determine the thermal conductivity of hydrogen in the temperature range between 2000 and 7000 °K. For this purpose the radial temperature distributions for various currents and theE-I-characteristic of a low current wall-stabilized hydrogen arc have been measured. In the dark region of the arc outside the bright core the temperature and the thermal conductivity between 2000 and 4500 °K were found by means of the schlieren technique. The electron temperature in the core of the arc results from spectroscopic measurements. The gas temperature has been calculated with a formula, derived from the kinetic theory of gases. Assuming a constant collision integralQ _eH ¹¹ the radial distribution of electric conductivity has been calculated according to Langevin's formula. The valueQ _eH ¹¹ =30·10^?16 cm₂ results by comparing the integrated conductance with the measured one. Since now the radial distribution of power input and the temperatures are known, the thermal conductivity between 4500 and 7000 °K can be determined as well. The total course of the heat conductivity shows a strong peak at the temperature of 3740 °K characteristic for the dissociation process.     

Photoinduced electron transfer and spin dynamics in mixed porphyrin-quinone solutions studied by time-resolved EPR

From time-resolved direct detection cw EPR with pulsed laser excitation, the photoinduced electron transfer and spin dynamics (CIDEP) in mixed zinc-tetraphenylporphyrin (ZnTPP)/benzo-1,4-quinone (BQ) ethanol solutions were determined as functions of temperature and BQ concentration. At lower temperatures the EPR spectra reveal that mixing of the S and T_?1 states in the charge separated radical pair gains in importance relative to the ST₀ mixing. Furthermore, at lower temperatures, the EPR spectra of the spin-correlated radical pairs of ZnTPP⁺ and BQ⁷ could also be observed. From the temperature/viscosity dependence of the electron transfer rates and of the polarization contributions from the triplet and radical pair mechanisms, deviations from a macroscopic diffusion behaviour are inferred at lower temperatures.     

O--ion radiation in the spectrum of an oxygen arc plasma

The radiation emitted from the axis of a wall-stabilized, low-current cylindrical arc in pure oxygen at temperatures around 9000 K was measured quantitatively in the wavelength range from 2000 to 9000 A. In the near i.r. region, the two first thresholds of the affinity continuum appear at 8615 and 8465 A, respectively, yielding an electron affinity (EA) of 1.465 eV and a ground-state splitting Δ = 26 meV for the negative oxygen ion. Another threshold occurs in the u.v. region at 3630 A and involves a transition to O^- from the first exited state of atomic oxygen. The continuous spectrum can be shown (Fig. 17) to be dominated in the u.v. and visible regions by the affinity continuum due to the negative oxygen ion. Additional contributions, which become increasingly important towards longer wave-lengths, are the Kramers-Unsöld continuum and O₂⁺-association radiation. In the u.v., the recombination of two neutral oxygen atoms forms a small contribution. A broad peak structure centered around 7000 A cannot be definitely explained. Applying Kirchhoff's law, the photodetachment cross section of O^- is obtained as a function of photon energy. Deviations from local thermodynamic equilibrium (LTE) are accounted for.     

Energetic Characteristics of Oxygen Plasma

A low-temperature oxygen plasma is studied using the thermocouple, probe and spectral method in the range of 2–8 Torr pressure, 30–100 mA discharge currents, 0, 5, 10 m/s pumping velocity. The gas temperature, concentrations of electrons and oxygen atoms in the 3 p⁵P state, and the longitudinal electric field are measured. Radial distributions of gas temperature and electron concentration are obtained. Ranges of pressures and currents are found in which considerable increases in electric field, discharge voltage, temperatures of gas and electrons are observed at pumping switched on. An estimate of the rate constant of the steplike ionization through the O₂(a¹Δg) state is given. The concentration of atomic oxygen in the ground state and excitation constant of the triplet O(3p⁵P) by electron impact are obtained from the solution of the balance equations and our experimental data.     

Transition probabilities for sulfur lines from wall-stabilized arc measurements

A new type of analysis has been developed to determine transition probabilities of spectral lines emitted from optically thin, multi-element, arc plasmas in local thermodynamic equilibrium (LTE). Provided the ionization energy of the element of interest is considerably lower than that of the other elements, this method is independent of demixing effects for a fairly wide temperature range. The technique has been applied to spectroscopic data obtained from wall-stabilized arcs operated at atmospheric pressure, first in a mixture of argon and sulfur hexafluoride (SF₆), and second in SF₆. A trace of hydrogen is added in both experiments in order to determine the electron density from the measuredHβ hydrogen line width. The experimental data do not contradict the assumption of LTE. The transition probabilities for the SI 4695 Å, SI 5279 Å, SII 5320 Å, and SII 5454 Å lines are in good agreement with those listed in the NBS critical data compilation.     

1064 nm Nd:YAG激光诱导铁等离子体特征参数的研究

利用1064 nm Nd:YAG激光器研究了激光诱导铁条等离子体的特征参数。为了减小测量误差和谱线自发辐射跃迁几率不确定性带来的计算误差,采用改进的迭代Boltzmann方法精确求解铁等离子体的电子温度为8058 K。Lorentz函数拟合Fe I 376.553 nm得到等离子体的电子数密度为8.71017 cm-3。分析表明等离子体的加热机制主要是逆轫致过程,其吸收系数是0.14 cm-1。实验数据证实激光诱导铁等离子体处于局部热力学平衡状态和光学薄状态。     

Examination of the LTE model for the sputtering process with spectroscopy of ion induced photons (SIIP)

With the help of SIIP the distribution of excited states of sputtered particles and the excitation temperature are determined using two different equations for the relationship between intensity and energy. A comparison of the evaluation of spectra of Ti and V with the results of arc spectra obtained with the same apparatus and a comparison of the temperatures of the elements in the Ti-V alloy LT 31 give new arguments in favour of the LTE model.