大气压等离子体炬电子密度的光谱诊断

利用空心针-板放电装置产生了大气压等离子体炬,采用光谱法测量了其内部及表面的电子密度. 向空心针中通入氩气,在大气环境中产生了长度为1cm的等离子体炬.实验分别测量了Hα谱线和ArⅠ(696.54nm)谱线,通过反卷积方法分离出其相应的Stark展宽,并由此计算了电子密度.结果发现,采用Hα谱线和ArⅠ(696.54nm)谱线Stark展宽计算得到的等离子体的电子密度分别为1.0×10¹⁵cm^－3和3.78×10^{15关键词： 等离子体炬 电子密度 气体温度 Stark展宽}     

A shock tube study of line broadening in a temperature range of 6100 to 8300 K

Line widths of the Ca(II) 3968 Å and Na(I) 5890 Å resonance lines broadened by electric microfields in a plasma were measured. A pressure-driven shock tube was used as the light source. Radiation from the equilibrium region behind the reflected shock wave was studied using a rapid scanning Fabry-Perot interferometer. Electron and argon atom densities of about 8 x 10¹⁶ and 1 x 10¹⁹ per cm³, respectively, were achieved at the relatively low temperature of around 7500 K by vaporizing a cesium powder that had been added to the shock tube as a solid aerosol in argon gas. The measured line widths were predominantly Stark broadened by the electrons and ions in the plasma, although Doppler, van der Waals, instrument function and optical depth effects had to be taken into account. The electron broadened line width of Na(I) 5890 Å was lower by about 16% than the predicted value from a semiclassical calculation, in agreement with a recently reported measurement, while for Ca(II) 3968 Å the results agree with previous reliable experiments and are lower than two calculated values by 20 and 36% respectively. The van der Waals broadening by argon was also determined and showed qualitative agreement with other results.     

Determination of the Electron Density in an Argon Laser Plasma by Spectroscopy of the Hydrogen Hα and Hβ Lines

From measurements of the H_α and H_β spectral line profiles in a plasma, a method is developed which allows to separate the contributions of Doppler and Stark broadening. This method is superior to the deconvolution of Voigt profiles, in particular, when the lines are of low intensity. The electron density in the plasma can be calculated from the Stark broadening. An example is the low pressure (p ≈ 1 hPa) arc discharge of argon ion lasers which is characteristised by electron densities of approximately 10¹⁴ cm^?3 at heavy particle temperatures of about 10⁴ K. These plasma parameters lead to a broadening of the Balmer H_α and H_β spectral lines of hydrogen, which has a low concentration within the discharge area. The spectral lines are broadened due to the electron density dependent Stark effect and the temperature responsive Doppler effect. The results are consistent with predictions of the argon ion laser modelling.     

Line broadening studies in low energy plasma focus

Optical emission spectroscopic studies were carried out to characterise the plasma leading to the estimation of two plasma parameters, electron density and temperature. These experiments were conducted on a 2 kJ plasma device which is equipped with squirrel cage electrode configuration enclosed in a glass vacuum chamber filled with hydrogen at a pressure of 5 mbar. Spectral emissions obtained from each flash were photographed in the region of 4000–6000 Å using one metre Czerny-Turner spectrograph cum monochromator. Detailed examination of the observed features showed that theH _β andH _λ lines of hydrogen showed significant broadening of the order of 35 Å FWHM which is due to Stark effect expected in high density plasmas. Further several atomic lines of Cu and Zn from the electrode material (brass) showed broadening which was due to quadratic Stark effect. A comparative study of the broadening of lines obtained in DC arc, hollow cathode and plasma focus was made. Electron density from Stark broadened hydrogen lines and quadratic Stark Coefficient C₄ for the CuI and ZnI lines were evaluated. The excitation temperature was determined from the line intensity ratio method using CuI lines.     

Measurement of Stark broadened profile of He(II) 4686A

Stark broadened profiles of the He(II) 4686A line were measured using a Z-pinch plasma as source. The electron density was determined from the halfwidth of the He(I) 3889 line and the temperature from the intensity ratio of the He(II) 4686 and the He(I) 3889 lines. The electron densities covered the range 0.5?2.3×10¹⁷ cm³ and the electron temperature was 4 eV. The plasma homogeneity was checked by varying the length of the column observed. The experimental profiles are in better agreement with the recent calculations of Greene than with the earlier calculations of Keeple.     

High density measurements of the Stark broadened profile of the He(II)4686 Å line

The Stark broadened profile of the He(II)4686 Å line has been scanned in the electron density range of 1–3 × 10¹⁸ cm^-3. The electron temperature, as determined from the line to continuum ratio, ranged from 9.4 to 19.9 eV. The plasma which emitted the He(II)4686 Å line was created in a 60-kJ theta pinch operated with a high fill pressure (3 and 5 torr) of pure helium. Electron densities were calculated from the half-half widths of the He(II)4686 Å line using two Stark broadening theories. These electron densities are compared with the electron densities determined from the absolute value of the continuum intensity and a total sweep up compressional model. The two theoretical models predict electron densities in good agreement with the electron densities from the absolute value of the continuum intensity.     

高气压微波氢等离子体发射光谱诊断

在2.45GHz,800W级的高气压微波等离子体放电系统中,通过测量不同微波功率和放电气压下氢等离子体的Balmer线系的发射光谱,从测量的谱线总展宽中卷积去掉具有高斯线形的Doppler展宽和仪器展宽得到谱线的Stark展宽,并通过Stark展宽测量氢等离子体的电子数密度和电场强度。结果表明:等离子体的电子数密度和电场强度随着放电气压的升高都是先增大后减小,随着微波功率的增加呈现逐渐增大的趋势。微波功率为800W时,气压在25kPa时电子数密度和电场强度都达到最大值,等离子体的电子数密度和内部的电场强度分别为3.55×1012cm-3及4.01kV/cm。     

仪器展宽对大气压等离子体电子密度测量的影响

实验使用两台不同的单色仪,采用光谱线型法测量了大气压氩气介质阻挡放电中的电子密度.诊断结果表明,由于不同的单色仪其仪器加宽不同,仪器加宽对总的光谱线型有较大影响.通过考虑等离子体中的各种加宽机制,采用卷积和反卷积的方法对氩原子发射谱线线型进行了分析,从整个光谱线型中分离出Stark线型,排除了仪器加宽对最终诊断结果的影响.从而最终测量了大气压氩气介质阻挡放电中的电子密度.测量得到在大气压氩气介质阻挡放电中单个放电丝存在时,电子温度为10000K时,电子密度约为3.05-3.26×1021 m-3.此方法不仅可以应用在大气压介质阻挡放电中,还可以用于测量其它大气压等离子体电子密度.     

Experimental Stark broadening studies of the CI transition 3s1P1o ? 3p1S0 at 833.5 nm

Experimental Stark broadening studies of the infrared CI transition 3s ¹ P ₁ ^o − 3p ¹ S ₀ at 833.5 nm are reported for the first time. A high-current wall-stabilized arc, operated in a mixture of helium, argon, carbon dioxide and hydrogen, was applied as the plasma source. Radiation emitted from homogeneous and optically thin plasma layers was analyzed. Stark broadening studies of the selected CI transition and the hydrogen Balmer β line were performed. As expected from theoretical considerations, the CI line width depends linearly on the electron density of the plasma. Applying theoretical Stark broadening data for the H _gb line, the measured Stark widths of the CI line were calibrated for the purpose of electron density determination in low temperature plasmas.     

Spectroscopic diagnostics of carbon and aluminum laser-produced plasmas

VUV emission spectra of plasmas produced by focusing laser radiation with intensity of 10¹⁰–10¹¹ W/cm² on carbon and aluminum targets were studied. Using the partial local thermodynamic equilibrium model for an electron density exceeding 10¹⁷ cm^?3, the spectroscopic diagnostics and the analysis of ion composition of plasmas were carried out. The electron temperatures determined for carbon and aluminum plasmas from the ratio of intensities of ionic lines were found to be 8±3 eV and 11±4 eV, respectively. Stark broadening of aluminum lines was measured and parameters of electron broadening were determined. Using the spatially resolved measurement of Stark line broadening, the spatial density distribution and the law of electron gas expansion were found. The electron gas in the hot region of size 5 mm with an average density of (5±2) 10₁₇cm ^?3 experienced one-dimensional expansion according to the law 1/z ^1.1 with increasing distance z from the target.     

Stark broadening and shift of some isolated spectral lines of singly ionised earth alkaline metals

Using aZ pinch discharge as a plasma source the profiles and shifts of some prominent ion lines of earth alkaline metals were measured and compared with Stark broadening theories and other experimental results. An electron density of 3.1 to 10.3×10¹⁶ cm^?3 was determined by the laser interferometry, while the electron temperature in the range 25100 to 34800 °K were measured from relative intensities of spectral lines. Comparison of reported experimental shifts and widths with the theories both semi-classical and quantum mechanical shows good agreement. It was also found that Griem's semi-empirical formula is useful and accurate for line widths evaluation.     

Experimental study of stark broadening of nitrogen ion lines in a theta pinch plasma

We have studied the Stark broadening of the 3s-3p, 3p-3d and 3d-4f emission lines of the nitrogen II, III, and IV ions emitted from a hot plasma. The plasma was created by a 60 kJ, 60 kV single turn coil theta pinch, where the fill gas was 3 torr of (49%He+51%N₂). The plasma was diagnosed by measuring the Stark-broadened profile of the He(II) 4686 Å line and by taking shadowgrams of the plasma development. It was found that the ionization stage distribution and thus the electron density departed from that predicted by Saha-Boltzmann equilibrium relations. The analysis of the plasma parameters gave an electron density of 1.4 x 10¹⁸ cm^-3. The electron temperature was measured from the relative intensities of emission lines as well as from the line-to-continuum ratio and was found to be 5.0 eV. The line profiles have been fitted to Lorentzian profiles and the thus measure line widths are compared with earlier experimental data as well as with simple theoretical calculations. We find that our line widths are broader than earlier data taken at lower densities if we assume a linear scaling of the half width with the density. A simple Lorentzian profile fits in most cases quite well to the observed line profile. The simple calculations can predict the linewidths within 20% for the low lying levels of both the singly and doubly ionized nitrogen while the predictions are far too narrow for the higher lying levels from the multiply ionized atoms.     

Stark profiles of some ion lines of alkaline earth elements

The widths and shifts of Mg⁺, Ca⁺, Sr⁺ and Ba⁺ lines broadened by electron and ion Stark effects have been measured in an argon welding type plasma. The electron density is about 1.3×10¹⁷ cm^-3 and the temperature is about 13,000°K. Special care was taken to avoid self-absorption of resonance lines. Injection of alkaline earth elements into the cold region of the plasma edge permitted reliable measurements of the signs of line-shifts. Experimental results are compared with semi-classical theories and a new-classical computation of Sahal-Bréchot in which resonances of elastic cross sections are taken into account. Good agreement is observed between experiment and the later calculations.     

Stark broadening measurements of some N(II) and N(III) lines

The Stark widths of seventeen N(II) and ten N(III) spectral lines, emitted from a wall-stabilized arc plasma with electron densities in the range 0.9-2.9 × 10¹⁷ cm^-3, were measured. The arc was run with a 1:1N₂:He mixture, and the electron densities were determined from the Stark widths of He(I) 5876 and 6678 A. The Stark widths of the N lines were found to scale approximately linearly with electron density.     

Measurement of stark broadened Lyman-lines

Stark broadened profiles of the hydrogen Lyman-lines Ly-α to Ly-? have been measured in a wall-stabilized argon arc, providing a plasma of an electron density of 7·2 X 10¹⁶ cm^-3 and a temperature of 12,200 K. In the cases of Ly-α and Ly-β, detailed investigations of the profiles are performed including absolute measurements, measurements of line shifts and asymmetries and comparisons with modern theories. Moreover, a comprehensive discussion of experimental errors is given and some important features of the radiation source are outlined.     

Measurements of electron density and Stark width of neutral helium lines in a helium arc plasma

Electron densities in an atmospheric helium arc plasma have been measured with the Stark broadening parameters of helium spectral lines. The spatially distributed radiation intensities are converted to plasma emission coefficients at every wavelength by means of Abel inversion. From the inverted profiles of He I lines of 4713 ?, 5016 ?, and 6678 ? electron density has been calculated, which ranges from 0.5 ×10¹⁶ to 4 ×10¹⁶ cm^-3 for a helium arc with current 200 A. Stark widths of He I lines of 3889 ? and 7065 ? are determined based on the measurements and compared with existing data.     

Axial variation of electron number density in thermal plasma spray jets

The electron number density has been measured in a plasma spray torch using Stark broadening of H and Ar-I (430 nm) line. A small amount of hydrogen (1% by volume in argon gas) was introduced to study the H line profile. Axial variation of electron number density has been determined up to a distance of 20 mm from the nozzle exit point of spray torch. The plasma torch was operated at 5 and 10 kW power level and flow of argon was kept at 25 liters per minute. Using the measured excitation temperature data under same experimental conditions, the electron number density has also been calculated using Saha equation. Comparison of electron number densities measured from Stark broadening with those derived from excitation temperature measurements under the assumption of local thermodynamic equilibrium (LTE) in thermal plasma jets indicate about the deviation from LTE in thermal plasma jets. The electron number density measurement using Stark broadening of Ar-I (430 nm) line will be particularly useful when only argon gas is used in thermal plasma jets.Received: 6 January 2003, Published online: 22 July 2003PACS: 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 52.77.-j Plasma applications - 52.25.-b Plasma properties     

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)     

Experimental stark parameters of carbon C II 2993 Å line

Total Stark profiles of the C II 2993 Å line of a plasma jet of a slit discharge with an evaporating wall. In the interval of electron densities of 10¹⁷ to 6 × 10¹⁷ cm^?3, the electron impact width, the ionic broadening and the shift of the intensity maximum of the line are measured. It is found that, at an inversely quadratic dependence of the electron impact width on the electron concentration, the Stark shift and the ionic contribution to the total width of the profile are linear. It is noted that calculated values of the shift regularly exceed measured values, while the signs of the measured and calculated shifts coincide. The method of approximating experimental data is proposed, which takes into account the interrelation of the main Stark parameters in plasma with a strong interparticle interactions.