Level populations in plasmas RF discharges and sonic channel

An absolute intensity calibration has been made to previously reported spectrographic measurements in an extensively studied argon rf discharge downstream of the exciting coil, and sonic afterglow. This calibration allows calculation of neutral argon atom density and of individual level population. Neutral atom densities were calculated from the electron density, the electron temperature, and Saha's equation, assuming that the electron temperatures were equal to the excitation temperatures. The densities calculated by these methods were far higher than those obtained from the perfect gas law, the gas temperature, and the pressure. The observed under- population of the ground level is shown to correspond to the “terminal non-equilibrium” defined by PARK.⁽³⁾ The present data are compared with two existing experiments to show that agreement exists among seemingly inconsistent and confusing reports, provided the non-equilibrium phenomena are properly accounted for.     

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.     

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.     

Effect of temperature on the luminescence processes of SrAl2O4:Eu

The UV excited and persistent luminescence properties as well as thermoluminescence (TL) of Eu²⁺ doped strontium aluminates, SrAl₂O₄:Eu²⁺ were studied at different temperatures. Two luminescence bands peaking at 445 and 520 nm were observed at 20 K but only the latter at 295 K. Both Sr-sites in the lattice are thus occupied by Eu²⁺ but at room temperature efficient energy transfer occurs between the two sites. The UV excited and persistent luminescence spectra were similar at 295 K but the excitation spectra were different. Thus the luminescent centre is the same in both phenomena but excitation processes are different. Two TL peaks were observed between 50 and 250 °C in the glow curve. Multiple traps were, however, observed by preheating and initial rise methods. With longer delay times only the high temperature TL peak was observed. The persistent luminescence is mainly due to slow fading of the low temperature TL peak but the step-wise feeding process from high temperature traps is also probable.     

Spectroscopic measurements in nitrogen arcs with respect to local thermodynamic equilibrium

A wall-stabilized nitrogen arc at atmospheric pressure was studied spectroscopically in the current range from 20 to 70 A with the aim of detecting departures from LTE. Measurements of the relative intensity of several N(I) lines showed that the populations of the upper excited states are in equilibrium for currents greater than approx. 25 A. Comparisons of the excitation temperatures obtained from relative intensities with the electron temperature and with the temperature curves calculated for different departures from LTE show that deviations from equilibrium are small at the arc center for electron densities above approx. 4 × 10¹⁶ cm^-3. Deviations between the radial profiles of the electron and excitation temperatures were observed for currents between 35 and 55 A.     

Excitation energies of barium oxide bands measured in flames

Experiments are described that yield additional information about the excitation energy of visible barium oxide bands appearing in flames. Excitation energy differences are derived directly from the ratios of thermal band intensities as a function of temperature and agree with the value calculated from the known (relative) energy-level diagram. Absolute excitation energies are derived from the temperature dependence of the ratio of band-to-line intensity under thermal equilibrium conditions and under the assumption of a most probable value for the dissociation energy of BaO. Flames with temperatures ranging from 1911 to 2886 K were used. The excitation energy values found can be reconciled with the assumption that the lower ¹∑ state of the optical transitions is the electronic ground state only if there are low-lying electronic levels that contribute at least a factor of 6 to the electronic partition function.     

The MTE continuum relation with application to an argon arc at atmospheric pressure

The continuum emission coefficient relation for a plasma in Multithermal Equilibrium (MTE) is derived using the partial-MTE ionization equation. The results are presented in a form using the nonhydrogenic free-bound Gaunt factors of Schlüter. Measurements on a 200 A, 1 atm, constricted argon arc indicate that electron densities calculated from the MTE continuum relation and Schlüter's ξ_fb values exceed electron densities from the Stark broadening of H_β by 15–30%. Experimental values of ξ_fb are up to 3 times larger than Schlüter's values, but are in agreement with the values of Morris and Krey at 5 atm, which is probably one of the few similar experiments actually in or near complete LTE. In the present experiment at the arc axis: N_e(H_β) = 1.00 × 10¹⁷cm^-3 (±8%); T_e = 34,000 K (±20%); T_exa = 12,000 K (±3%); T_exβ = 9000 K (±5%); and T_a = T_i = 10,000 K (±68%). The probable errors reflect the need for more accurate transition probabilities which had an uncertainty of 25%.     

Resonance structure of doubly-charged-ion production during laser dielectronic ionization of atoms

The resonance structure of doubly-charged-ion production during the ionization of Ba atoms by infrared radiation (color-center laser radiation) is identified. It is shown that this structure is due to the excitation of states of the neutral Ba atom which are strongly perturbed as a result of the Stark effect under conditions such that the dynamic polarizability has large absolute values and depends strongly on the frequency of the radiation. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 796–800 (10 December 1998)     

空气—氩气混合气冷却ICP中镁,铬,镉,锰四种元素的谱线强度和信背比的 …

The dependence of net analyte emission intensity and signal-background ratio on coolant gas composition and observation heights for 8 lines of four elements (Mg, Cr, Cd and Mn) in Ar-air mixed coolant gas ICP was measured under the similar condition as that in the low power Ar-ICP with a commercial sequential plasma spectrometer. Further, the detection limits under compromise conditions were estimated. The results show that ion lines and neutral atom lines with high excitation energy have maximum intensity and are more intense than those in the Ar-ICP, when 5-10% air is added to the coolant flow. The intensity of neutral atom lines with low excitation energy drops gradually as air is added to coolant flow. The signal-background ratio of analyte lines depends upon excitation energy and wavelength.     

Influence of electron-density variation on the population distributions of excited atoms in a plasma

The effects of electron-density variations on population distributions of excited atomic states in a plasma have been studied. For specified conditions, an analytic expression is derived between excitation and electron temperatures. It has been found that the ratio of the ionization rate of the excited atom to the rate of electron-density variation plays an important role in the temperature difference. When this ratio is of order unity, the temperature difference is significant. However, when this ratio is large or small compared with unity, the two temperatures are nearly equal. These predictions are investigated experimentally.     

基于激光诱导击穿光谱的化验室水泥质量检测设备研制

研制了一套基于激光诱导击穿光谱(LIBS)的化验室水泥质量检测设备,可对水泥生熟料成分及率值进行快速检测。对该设备的总体结构、光学系统、样本制备、光谱处理方法等几方面进行了介绍。通过内标法建立定标模型,将LIBS测量结果与X射线荧光光谱分析(XRF)结果进行了对比分析,该套LIBS设备对水泥生熟料中CaO,SiO₂,Al₂O₃和Fe₂O₃测量的平均绝对误差分别为0.46%,0.25%,0.13%和0.05%,对水泥熟料率值KH,SM,IM测量的平均绝对误差分别为0.02,0.05和0.04;通过计算激发产生的等离子体温度和电子密度,验证了激光诱导水泥等离子体处于局部热平衡(LTE)态。     

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.     

Measurements of plasma temperature and electron density in laser-induced copper plasma by time-resolved spectroscopy of neutral atom and ion emissions

Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300–2000 ns. An echelle spectrograph coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu I lines. It is found to be 700–1000 ns.     

Characteristics of an argon rf plasma: Active discharge and laminar sonic flow region

The electron density, the excitation and the gas temperatures have been obtained from optical spectrometric, microwave interferometric and thermocouple measurements in an argon rf plasma. The investigation was carried out in an active discharge and a channel region characterized by sonic laminar flow. Optical measurements of the excitation temperature were made in the 4000–5000 Å range for discharge pressures of ∼ 63–644 torr and input rf power of 42–60 kW. Excitation temperatures in the discharge ranged between ∼ 7000–10,000 K. Electron densities measured by optical and microwave techniques showed good agreement. Thermocouple measurements in the channel and N₂ rotational spectra from traces of N₂ injected in the argon, as well as gas dynamic considerations, indicated that the gas temperature in the discharge and the channel regions were 2900–4400K and 1900–3300K, respectively. These values were substantially lower than the excitation temperatures corresponding to these regions, indicating that the plasma was in a two-temperature state in both regions. Standard tests for local thermal equilibrium (LTE) showed that the first excited level of argon constituted the bottleneck level.     

Spectroscopic study of microwave discharge as a radiation source for transition probability measurements

The optical properties of a discharge in a mixture of helium (200 torr) and hydrogen (0.1 torr) were investigated. Line intensities were measured photoelectrically. Partial LTE is demonstrated by the linearity of plots of log(Iλ/gA) vs E. The temperatures T_He = 3300 and T_H = 3400 K are obtained from the slopes of the plots for He and H, respectively. Relative A-values for the hydrogen Balmer lines derived from the helium temperature agree with theoretical values within ±20 per cent. The uncertainties (≤ 7 per cent) estimated from the discrepancy between the temperatures are smaller than those (±10 per cent) due to errors in the observed line intensities.     

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.     

Density and temperature in heavy-ion collisions: A test of classical and quantum approaches

Different methods to extract the temperature and density in heavy-ion collisions (HIC) are compared using a statistical model tailored to reproduce many experimental features at low excitation energy. The model assumes a sequential decay of an excited nucleus and a Fermi-gas entropy. We first generate statistical events as a function of excitation energy but stopping the decay chain at the first step. In such a condition the “exact” model temperature is determined from the Fermi-gas relation to the excitation energy. From these events, using quantum fluctuation (QF) and classical fluctuation (CF) methods for protons and neutrons, we derive temperature and density (quantum case only) of the system under consideration. Additionally, the same quantities are also extracted using the double ratio (DR) method for different particle combinations. A very good agreement between the “exact” model temperatures and quantum fluctuation temperatures is obtained. The role of the density is discussed. Classical methods give a reasonable estimate of the temperature when the density is very low, as expected. The effects of secondary decays of the excited fragments are discussed as well.     

蒙特卡罗模拟四极阱中原子的参变激发

在中性原子的磁囚禁实验中,磁阱线圈的电流噪声会激发磁阱中的原子运动,势必对原子团的温度和寿命产生不可忽视的影响。对于非简谐阱,这种激发具有能量选择特性,它又取决于电流噪声的频谱分布。选择了实验中常用的四极阱为研究对象,用直接模拟蒙特卡罗方法来模拟四极阱中原子运动的参变激发现象,得到了原子温度与原子数损失随激发频率的变化关系,并进一步计算了两个共振峰处原子温度随调制时间和调制深度的变化曲线。此外,还研究了弹性碰撞速率对参变激发过程中原子温度上升的影响。这些结果对四极阱参变激发的实验有较好的参考价值。     

Caloric curves of small fragmenting clusters

The kinetic energy release distribution of neutral atoms emitted from photoexcited clusters Sr(+)(n) with n=4-15, has been obtained by time-of-flight velocity dispersion. The deduced temperature is plotted as a function of the excitation energy. For small sizes n<7 a general increase is observed. For cluster sizes larger than n=9, the deduced caloric curves first increase, and then show evidence of a plateau regime as excitation energy increases. This limiting temperature in neutral atom ejection is consistent with a bound cluster-vapor phase transition in a microcanonical system.     

Dissociative excitation cross sections of the lead atom in collisions between electrons and PbI2 molecules

Dissociative excitation of the lead atom in e-PbI₂ collisions has been studied experimentally. 27 excitation cross sections were measured for an energy of the exciting electrons equal to 100 eV. Nine optical excitation functions were recorded with variation of the electron energy in the range 0–100 eV. The most probable reaction channels for low electron energies are discussed, as well as the ratio of the dissociative excitation cross sections for the lead atom in e-PbI₂ and e-PbCl₂ collisions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 701–706, November–December, 2006.