Stark broadening of neutral helium lines and spectroscopic diagnostics of pulsed helium plasma

Stark broadening parameters (widths and shifts) of two He I isolated spectral lines are measured in a plasma of a low-pressure pulsed arc. Plasma electron densities, determined by spectroscopic method based on previously calibrated He I lines, ranges from 1 x 10¹⁶ cm^-3 to 6 x 10¹⁶ cm^-3. The plasma electron temperature acquired by a Boltzmann plot of several He I lines, lies in the interval 8 000-30 000 K. Results of this work are compared with theoretical predictions and with other experimental data.Received: 30 April 2003, Published online: 29 July 2003PACS: 52.70.-m Plasma diagnostic techniques and instrumentation - 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Jz Line shapes, widths, and shiftsR. Santamarta: Present address: DESY/ZEUS Hamburg, Germany.     

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.     

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.     

Stark broadening of S(III) and S(IV) lines

Measurements of the Stark widths of doubly and triply ionized sulfur lines were made in a low pressure, pulsed arc plasma of electron density 5.1 × 10¹⁶ cm^-3 at an electron temperature of 28, 500°K. The experimental S(III) and S(IV) Stark-profile halfwidths were compared with calculated values obtained with Griem's semiempirical and approximate semiclassical approach. The experimental results agree better with the semiclassical results.     

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.     

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.     

Stark broadening and shift measurements of two doubly excited NI multiplets

Experimental Stark-broadening studies of two selected doubly excited NI multiplets from the infrared wavelength range are presented. One of them is very sensitive to interactions with charged particles in plasmas and the other exhibits — at the same plasma conditions — only very small broadening and shift. A high current wall-stabilized arc operated in helium with admixture of nitrogen and hydrogen was applied as the excitation source. The radiation of the plasma was detected by applying a grating spectrometer equipped with a CCD detector. Measurements were performed at electron densities of the plasma between 3×10¹⁵ and 7×10¹⁵ cm^-3, corresponding to temperatures from the range 8000–10500 K. Electron impact widths (w_e) and shifts (d_e) of fine structure components of these multiplets were determined. The evaluated Stark broadening parameters (w_e, d_e) are compared with other experimental data and with calculated Stark effect constants.     

Experimental Stark widths and shifts of two ultraviolet C(II) lines

Photoelectric measurements of Stark widths and shifts of the components of the C(II) multiplet UV13 at 2837 Å were made with a wall-stabilized arc in a gas mixture of argon, hydrogen and carbon dioxide. Plasma diagnostics have been carried out to determine the electron density and the temperature. For experiments performed under two different physical conditions, the values n_e(1) = 4.95 × 10¹⁶ cm^?3, T(1) = 11,430 K and n_e(2) = 6.78 × 10¹⁶ cm^?3, T(2) = 12,080 K were obtained. Agreement between our widths and experimental data of Plati?a et al. is within error limits; a discrepancy of a factor of 4 appears in a comparison of our data with those of Kusch.     

Stark broadening and displacement of isolated He I lines

Experimental results for Stark broadened He I lines emitted by a helium plasma jet (N_e≈3×10¹⁶ cm^-3) are compared with theory; agreement is well enough for widths whereas shifts calculations present generally large discrepancies with experimental data.     

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.     

Calculated Stark widths of isolated S(III) and S(IV) lines

Calculations have been performed on the electron-impact broadening of isolated lines from doubly-ionized and triply-ionized sulphur emitted from a plasma of electron density 10¹⁷ cm^-3 and temperature 28,500°K. These have been compared with results of measurements performed by Plati?a, Popovi?, Dimitrijevi?, and Konjevi? on a low-pressure, pulsed arc. Good overall agreement has been obtained for both ionization stages, in confirmation of our earlier conclusions based on a similar comparison for oxygen ion lines. The present calculations have been compared with calculations based upon two simplified models of Griem and the classical-path approximation of Sahal-Bréchot. Our calculated widths are in better agreement with experiment than with values obtained from the first two models; for the two multiplets, where comparison is possible, good agreement is found with the widths obtained by Sahal-Bréchot. We conclude that the present model, whereby the effective Gaunt factor is calculated, is capable of predicting reliable values for the Stark widths of isolated ion lines. Comparison with experiment [for S(III) indicates that, provided a sufficiently complete set of perturbing levels is used in the calculations, the present formula for ? may also be used for below-threshold energies in the determination of the elastic contribution to the broadening. For S(IV), an ambiguity remains in this regard, owing chiefly to a scarcity of available experimental data.     

Measured Cd III Stark widths

The Stark FWHM (Full-Width at Half of the Maximal line intensity, W) have been measured for 16 doubly ionized cadmium (Cd III) spectral lines in a pulsed helium discharge in the wavelength interval between 200 nm and 304 nm. The helium discharge was created in the linear low pressure pulsed arc operated at 19 000 K electron temperature and 5.0×¹⁰²² m−3 electron density. The cadmium atoms were sputtered from the cadmium (99.9% purity) cylindrical plates located in the linear part of the discharge tube. The high density of the Cd III ions is boosted by cascade ionization processes via the well populated Cd II energy levels due to the Penning and charge exchange effects. The shapes of the Cd III lines are recorded using a spectrograph (McPherson model 209, 1.33 m focal-length with 2400 grooves/mm holographic grating) and intensified CCD camera (Andor DH740-18F-03) as a high-sensitive detection system. The Stark parameters introduced in this Letter are the first published experimental Cd III Stark widths.     

The first measured Mn I Stark widths

The shapes of the astrophysically interesting neutral manganese (Mn I) resonance spectral lines (403.075, 403.306, 403.448, 279.481, 279.826 and 280.108 nm) have been observed together with six other prominent Mn I lines in the laboratory helium plasma at a 47 000 K electron temperature and electron density. With these plasma parameters the Stark broadening has been found to be an important mechanism in the Mn I line shape formation. Our measured Mn I Stark widths (W) are the first data in the literature. Stark widths are compared with line hyperfine structure splittings (Δ_hfs). At above mentioned helium plasma conditions the line broadening due to hyperfine structure splitting of the lines is less than that of the Stark and Doppler broadening for the case of the Mn I lines under investigation. We estimate that at electron densities below and electron temperatures below 4000 K the components in the hyperfine structure play an important role in the mentioned Mn I line shape formation.     

Stark widths and transition probabilities of some multiplets of singly ionized carbon

Photoelectric measurements of lines emitted by a helium-carbon d.c. arc plasma of n_e = 1.9 × 10¹⁶cm^-3 at T = 12,800 K have been performed. Stark widths of 6 C(II) lines and transition probabilities for components of 3 C(II) multiplets were determined and compared with other experimental and theoretical data. Good agreement was generally observed except for the C(II) multiplets UV13 and UV14, where the results of Kusch deviate notably from others.     

Stark-Effekt-Verbreiterung der Neon I-Übergänge mit schwacher Feldstärkeabhängigkeit (2p 5 3s-2p 5 3p)

The half widths of Stark-broadened Ne I spectral lines (2p ⁵ 3s-2p ⁵ 3p) were measured in wall stabilized arc plasmas (pressurep=1 atm, andp=3 atm) consisting of several gas components (Ar 68%, Ne 27%, He 3%, H₂ 2%). The theoretical half widths of two spectral lines (λ=6,266.50 Å,λ=6,163.59 Å) with known calculated broadening parameters according to Griem differ by a factor 1.8 to 1.9 from the measured widths. Within the errors of Griem's line broadening calculations of about 20% there was agreement between experimental and theoretical half widths regarding two other spectral lines (λ=5,881.90 Å,λ=5,852.49 Å). Calculated adiabatic widths are smaller than the widths according to Griem. Therefore in some cases the deviation of the adiabatic widths from the measured widths is smaller than the difference between Griem widths and experimental ones. Static quadratic coefficients of NeI transitions 2p ⁵ 3s-2p ⁵ 3p calculated from measured Stark-broadened lines showed wavelength displacements in the order of 0.005 Å referring to an electrical field of 100 kV/cm. The determined coefficients are 10² times smaller than those values measurable by known methods of emission spectroscopy.     

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.     

Variation of the ion dynamics parameter in stark-broadened helium lines

Stark broadening of quasidegenerate He lines at λ = 447 nm and 492 nm hasbeen investigated at low electron densities (N_e = 10²¹ and 3 x 10²¹ m^-3). The perturber mass was varied by using H⁺, He⁺ and Ar⁺ ions. Variation of the parameter (T₀/μ)^1/2 by a factor of 3 is accompanied by marked ion-dynamical effects in the forbidden component. The results are compared with calculations according to the unified theory and the model microfield method. Characteristic deviations are observed and critically discussed.     

在等离子体中镁离子谱线MgⅡλ4481?的宽度和位移

本工作测量了MgIIλ4481?(3²D—4²F)在电子数密度为7×10¹⁶—3.1×10¹⁷电子数/cm³范围内的谱线轮廓和位移。采用振荡型电容放电作为光谱光源。在光源中引入水汽,由测量H_β谱线宽度来定电子数密度。观测结果指出,H_β的实验轮廓和Griem-Kolb-Shen的计算结果符合颇好。实验发现MgIIλ4481?谱线向紫方位移,并正比于微观电场的平方;由此定出一个经验上的二级斯塔克效应常数C₄=5.0×10^-14cm⁴/sec。该谱线的轮廓宽度和标准微观电场之间也有平方正比的关系。发现在本实验条件范围内,宽度和位移的比值γ/△保持为常数,其值为γ/△=10.4±0.6。由于谱项4²D的二级斯塔克效应的干扰而产生上能级4²F位移的理论计算虽能说明谱线位移和微观电场间的平方正比关系,但数值偏小于实验结果,指出还有电子贡献的部分。把光谱线的宽度和Lindholm理论公式及Griem等的近似公式作了比较;简单的估计指出,实验结果和后者符合较好。     

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.     

SiH4激光等离子体内H谱线的线型研究

本工作利用光学多道分析仪(OMA Ⅲ)测量了脉冲TEA CO₂激光诱发的SiH₄等离子体内H Balmer系的H_α,H_σ和H_γ线的线型。结果表明,三条谱线的FWHM(半值全宽度)随跃迁上能级的主量子数的增加而增加,即△λ_1/2(H_α)<△λ_1/2(H_β)<△λ_1/2(H_γ)。通过对等离子体内各类加宽机制的讨论,得出等离子体内谱线的主要加宽机制为Stark加宽。由H_α线的实验线型与Stark加宽理论线型的拟合,得到等离子体的两个重要参量,平均电子密度N≈10¹⁷cm^-3,电子温度T≈40 000K。由H_β线的时间分辨测量得到等离子体的电子密度随时间的演变曲线。 关键词：