Präzisionsmessungen am Spektrum des Wasserstoffplasmas

Detailed and precise investigations on the Balmer spectrum of a hydrogen arc have been made in order to compare the measured absolute values of the spectral emission coefficients with the existing theories, the results being of special interest with respect to line broadening calculations and to the lowering of the ionization energy. The plasma is generated in a stationary high power cascade arc at atmospheric pressure. The experiment covers the temperature range between 12000 and 20000 K, where all emission coefficients show maxima in their temperature dependence. To keep self-absorption within the plasma as low as possible, the investigations have been carried out in side-on observation. The extended gas layer of almost constant intensity surrounding the maxima ensures very accurate results of the side-on measurements. For the necessary precise calibration of the optical system both a standard carbon arc and tungsten strip lamps have been used. As the intensity of these different radiation standards only shows a few percent deviation, a very high accuracy can also be established for the measured hydrogen emission coefficients. After evaluating an average radial temperature distribution at first the absolute emission coefficients of five selected wavelengths are plotted vs. temperature and compared with theory, whereby a very good agreement is found. The emission coefficients of the continuous radiation thus confirm the lowering of the ionisation energy according to Griem used in the calculations. In the following the spectral intensities for 16250 K, i.e. the temperature in the neighbourhood of which all the maxima occur, are represented vs. wavelength to investigate the spectral dependence of the emission coefficients. Again an excellent agreement with theories of continuous radiation and line profiles is found. The experimental line shape ofH _α, however, is described much better by Vidal's ‘Unified Theory” than by Griem's standard profile. When the maxima of the emission coefficients appear appr. at half the tube radius, the side-on distributions of the intensity show a flat top in the center and their value is almost independent of the arc current. Because of these qualities and of the reliability of the theoretical calculations of the spectrum finally the hydrogen arc is recommended for a radiation standard both for the visible and the UV region.     

Spectral distribution of radiation from the cascade arc plasma

A mathematical model has been developed for radiation emission and absorption in the cascade arc plasma, and calculations have been performed to determine the complete spectral distribution of radiation emerging from the argon arc. Although self-absorption effects are negligible for the continuum radiation, they are significant for much of the line radiation. The radiation flux emerging from the arc, as well as the efficiency for conversion from electrical to radiant energy, increase with increasing arc current and pressure and decreasing arc radius. The relative contribution of line radiation to the total arc radiation decreases with increasing current and pressure and decreasing radius.     

电弧增材成形中熔积层表面形貌对电弧形态影响的仿真

电弧增材成形常采用单道多层或多道搭接的熔积方式,不同的熔积方式下对应的熔积层表面形貌不同,从而影响电弧的形态及其传热传质过程.本文建立了纯氩保护电弧增材成形的电弧磁流体动力学三维数值模型,以及不同表面形貌的熔积层模型,并在保持阳极与阴极之间距离和熔积电流不变的条件下,通过模拟计算获得增材成形特有的单道和多道搭接熔积条件下的不同表面形貌对应的电弧形态以及相应的温度场、流场、电流密度、电磁力、电弧压力分布.数值模拟结果表明:平面基板上起弧情况下电弧中心具有较高的温度、速度、电流密度以及压强;单道多层熔积情况下熔积层数对电弧的各个参量影响较小;多道搭接熔积情况下电弧呈非对称分布,电弧中心温度较前两者低,电流密度、电磁力和电弧压强的分布偏向熔积层一侧.     

Why vacuum arc cathode spots can appear larger than they are

The visual appearance of arc cathode spots in vacuum is studied experimentally and theoretically. Emission photographs of the spots taken with line radiation have a broad light profile with a rather flat slope (proportional to r^-β with β≈2, r being the distance from the spot center), while photographs taken in absorption are small, having a sharp edge with a steep slope of the profile (β⩾4). Emission photographs from the continuum are similar to absorption photographs. Theoretical analysis shows that the emitted line radiation cannot stem from the locus of excitation. As a consequence, the particles are excited at the edge of the dense spot core, but they radiate at a greater distance due to the finite lifetime of the excited levels and the plasma expansion. Thus, emission photographs from line radiation indicate a greater spot size (about 100 μm) than corresponding to the active spot radius which amounts to ⩽10 μm. This statement holds for discharge durations from 10 ns up to at least 100 μs. The spots exist not only at ignition but during the whole time of the discharge, the location varying due to the spot movement. Absorption photographs show a small size of 10-20 μm still 200 μs after ignition     

Absorption line profile recovery based on TDLS and MEMS micro-mirror for photoacoustic gas sensing

A novel and efficient absorption line recovery technique is presented. A micro-electromechanical systems (MEMS) mirror driven by an electrothermal actuator is used to generate laser intensity modulation through the mirror reflection. Tunable diode laser spectroscopy (TDLS) and photoacoustic spectroscopy (PAS) are used to recover the target absorption line profile which is compared with the theoretical Voigt profile. The target gas is 0.01% acetylene (C2H2) in a nitrogen host gas. The laser diode wavelength is swept across the P17 absorption line of acetylene at 1535.4 nm by a current ramp, and an erbium-doped fibre amplifier (EDFA) is used to enhance the optical intensity and increase the signal-to-noise ratio (SNR). A SNR of about 35 is obtained with 100 mW laser power from the EDFA. Good agreement is achieved between the experimental results and the theoretical simulation for the P17 absorption line profile.     

Computer diagnostics of an optically dense plasma from absorption spectra

An algorithm is constructed for solving the problem of diagnostics of an optically dense plasma from the absorption spectra of isolated self-reversed spectral lines. The basic parameters taken are the width of the absorption line at the level 0.8J_o, where J_o is the intensity of the transmitted radiation, and the asymmetry of the absorption profile. The problem is solved by computer with the iteration method on the basis of the transverse pattern of the spectra. The radial variation of the concentration of absorbing atoms, of the electron concentration, and of the thin layer profile is determined. The method is applied to a low-voltage pulsed discharge, 2 msec in length, with a time resolution of 0.10 msec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 11–16, July, 1981.     

A new approach to determination of the asymmetry parameter of Stark-broadened isolated spectral lines

A new approach to evaluation of asymmetry parameters of Stark-broadened isolated spectral lines is presented. The procedure is discussed on the example of the N I line at λ = 9822.75 Å. Line shape measurements were performed using a wall-stabilized arc, operated at atmospheric pressure. The radiation of the plasma, emitted from homogeneous plasma layers in end-on direction, was measured using a grating spectrometer equipped with a two-dimensional CCD detector. Griem-like profiles, convoluted with the corresponding Doppler and apparatus profiles, were fitted to experimental data. In this way the Stark broadening parameters (electron impact widths, shifts and asymmetry) have been determined. Detailed analysis of the line shapes shows that the standard Griem-like profile does not explain the observed line asymmetry satisfactorily. The results of preliminary studies indicate that including collision-duration effects in profile calculations provides a better agreement between experiment and calculations. PACS. 32.70.Jz Line shapes, width, and shift – 52.70.Kz Optical (ultraviolet, visible, infrared) measurements.     

基于Stark展宽的TIG焊接电弧三维电子密度测量研究

焊接电弧三维电子密度的测量对于焊接质量控制具有重要意义,通过光谱仪采集电弧弦方向特征谱线轮廓,利用多项式拟合对径向采集数据进行降噪及平滑处理,通过Abel逆变换法重新构建径向光谱发射系数谱线轮廓,采用傅里叶变换从重建光谱轮廓中分离出Lorentz线形,获得Stark展宽,最终计算了TIG焊电弧等离子体电子密度的三维空间分布。     

Determination of the Local Parameters of a Cascade‐Arc Plasma by the Profiles of the Lines in the Radiation Spectrum

The transverse distribution of the plasma temperature in the positive column of a d.c. cascade arc in argon at atmospheric pressure has been measured. The measurements have been carried out by the conventional method involving the determination of the emissivity of plasma as well as directly from the radiation spectrum of the arc without recourse to the Abelian inversion. A theoretical and model justification of the applicability of the second method is given. The results of the determination of the temperature profile in the observation direction by the width and shift of the ArI 425.9nm line selected for the diagnostics are presented. An analysis of the data obtained supports the possibility of determining the temperature of an inhomogeneous, optically thin plasma from the profiles of lines in the emission spectrum.     

Hyperfine structure in Iodine at the 612-nm and 640-nm helium-neon laser wavelengths

The hyperfine structure of iodine-127 at 612 nm and 640 nm is observed by saturated absorption in a gas cell placed within a He-Ne laser cavity modified to operate at these wavelengths. At 612 nm, all the 21 components of the strong R 47 9-2 line lie within the laser gain profile, and the resulting saturated absorption peaks have a contrast of 10% at a gas pressure of 3 Pa.     

Calculation of radiative heat transfer in argon arc plasmas

Radiation emission and absorption in arc plasmas are important energy transfer processes. Exact calculations, though possible in principle, are usually impossible in practice because of the need to treat a large number of spectral lines and also the continuum radiation in the whole spectrum range. Recently, we have used an approximate method of partial characteristics to evaluate the radiation intensities, radiation fluxes and the divergence of radiation fluxes for SF₆ arc plasma with cylindrical symmetry. In this paper, we have extended our calculations toargon arc plasmas for the plasma pressures of 0.1, 0.5 and 1.0 MPa. We have calculated the coefficients of absorption for Ar plasmas at temperatures from 300 to 35 000 K, and have used these coefficients to calculate the partial characteristics. Both the continuum and the line spectra have been included in calculations. We have taken into account the radiative photo-recombination and bremsstrahlung for the continuous spectrum, and over 500 spectral lines for the discrete spectra.The method of partial characteristics has been applied to three-dimensional calculations of radiative heat transfer — i.e. radiation intensity, radiation flux and its divergence — in simplified temperature profiles. Conclusions have been made concerning validity and utilization of the method of partial characteristics in general gas dynamics problems.     

A Spectroscopic Investigation of Spatial Symmetry of Radiation in the U-shaped DC Argon Plasma with Aerosol Supply

Radial distributions of plasma parameters, temperature, and electron number density, together with radial distribution of analyte absorption and emission, were investigated in order to obtain insight into the radial symmetry of low-current (≤ 10 A), atmospheric pressure, argon stabilized arc with tangential introduction of the aerosol. For plasma diagnostics, several methods were used: measurements of H_β line profile, absolute intensity measurements of the argon 430.01-nm line, and of the spectrally adjacent continuum and power interruption technique. It was found that the inevitable asymmetry in aerosol introduction has negligible influence on basic plasma parameters but influences considerably the spatial distribution of the analyte particle spectral absorption and emission.     

Ba原子6s6p1P1←6s6s1S0跃迁的光腔衰荡光谱

建立了一套光腔衰荡原子束吸收光谱测量装置,并对Ba原子的6s6p¹P₁←6s6s¹S₀吸收谱线用光腔衰荡光谱方法进行了测量,得到了Ba原子在553.548nm不同温度下的吸收谱线线型.实验结果表明,该装置测量吸收灵敏度达到6×10^-7. 关键词： 光腔衰荡 吸收光谱 Ba原子     

Investigation of the 2-0 pressure-induced vibrational absorption spectrum of hydrogen at temperatures below ambient

A theoretical fit has been made to oue laboratory measurements of the 2-0 collisionally induced H₂ absorption band for temperatures of 122 and 273.3 K and at a density of 20 amagats. A Lennard-Jones 6–12 intermolecular potential and a Birnbaum-Cohen line profile have been used. The fit resulted in a chi-square of 0.2%. Line widths have also been derived as a function of temperature. The lifetimes of the states have been calculated.     

High resolution emission spectra of laser-excited molecular iodine as the excitation frequency is tuned through and away from resonance

We have studied the ΔJ = 2 rotationally shifted emission lines in the region of the strong absorption of molecular iodine which occurs within the 5145 Å argon ion laser line. We used an etalon tuned, single frequency argon ion laser with a linewidth of 20 MHz to excite the iodine emission and recorded the spectra of the rotational lines with Fabry-Perot spectrometers having resolutions up to 70 MHz (0.0023 cm^-1). To overcome Doppler linewidth limitations we took spectra of the emission at small angles to the exciting beam and found the lines to have widths less than our instrumental resolution and frequencies which accurately tuned with the incident laser frequency. We recorded the emission lines for laser frequencies in the absorption line center and out into the absorption wing. Our spectra show that the intensity of the emission lines follows the absorption line profile while the frequency of the emission lines is determined by the laser frequency; the intensity is maximum at the absorption line center, falling by 10⁴ as the laser frequency is moved off the line center, while the line position maintains a constant frequency shift from the laser frequency.     

Messung von Temperaturverteilungen im H2-Kaskadenbogen bis 27000°K

On a stationary, flowless, and cylindrical hydrogen arc, the radial temperature distributions are measured spectroscopically at a pressure of 1 at and up to a current of 150 amps. By reducing the diameter of the improved high power cascade arc chamber (4) to 2 mm, the instabilities of this can be overcome. For the measurements the hydrogen lineH _β is used, relative overall intensity of which is derived from the line profile by means of a new method. As the line emission coefficient ofH _β has a maximum at approximately 16,000 °K, the temperature can be determined using the Larenz method which yields quite reliable results by normalizing the relative line intensity measured in the arc to that maximum. For the measurement, the “end-on” observation is adopted, since at high currents, i.e. at axial temperatures in the arc of more than 16,000 °K, the intensity in the axis of the arc is considerably lower than outside the axis, i.e. in the edge of the arc. To avoid any perspective distortions of the arc image at the slit, a telecentric optical array is used. The error caused by the inhomogeneous layers of the electrode regions is eliminated by determining the intensity difference ofH _β on two arcs of very different lengths. For the employed current range, radial temperature profiles in the range of 11,000–27,000 °K with ionization degrees of up to 98% are obtained.     

Effects of layers of different dust particles on propagation characteristics of millimeter wave

In the present paper theoretical investigation has been carried out to evaluate the effect of layers of different shapes of dust particles (ellipsoidal and spheroidal) on the propagation of millimeter wave. For this purpose a length of communication link has been considered, which contains layers of dust particles blown to the height of the link due to dust storms. Further, each layer of dust particles has been assumed as a section of transmission line and entire link as number of transmission line sections in a cascade. Hence using the concept of transmission line the reflection coefficient, transmission coefficient and absorption loss have been calculated. It is found that propagation parameters depend on frequency and visibility. Brewster’s phenomenon is clearly observed by the system which is at around 75° of angle of incidence.     

Vacuum ultraviolet measurements of the emission profiles of the argon 1435.93A˚Ar(II) line

The profile of the 1435.93A?Ar(II) line has been measured by using vacuum ultraviolet spectroscopic diagnostics for an argon plasma generated in a 300 amp, atmospheric free-burning arc, over a temperature range of 8000-18000°K. From the line profiles were obtained the Stark shifts and the Stark semi-half widths. Temperature measurements were made using the line 7635.1A?Ar(I) and its adjacent continuum.     

FMR studies in compositionally modulated Co-Nb and Co films

Compositionally modulated (CM) films of Co-Nb have been prepared by sequential evaporation onto Si substrates using two E-guns fitted in an UHV system. The thickness of the Co sublayer was varied in the range 50 to 105 Å and that of Nb in the range 18 to 90 Å. A single layer Co film of about 850 Å was also prepared and studied. Magnetization was measured using a VSM at 290 K. FMR was observed at about 9.8 GHz in the range 3 to 290 K. For Co a layer thickness of 50 Å the magnetization in CM film is about 12% lower at 4.2 K, as compared to the bulk value. The FMR spectrum of single layer Co film shows a single absorption in the perpendicular configuration with a narrow line width of 40 Oe. Other properties of this film agree with those published in the literature. In CM films, multiple absorption modes are observed. A small perpendicular anisoropy is also measured. The magnetization in all the samples varies at T^3/2. The Curie temperature of CM films is lower than that of bulk Co. The resonance line width in CM films at lower temperatures, increases much faster than in Co film.     

Measurements of O2-broadening and -shifting parameters of water vapor spectral lines in the second hexad region

Oxygen pressure induced broadening and shifting coefficients for water vapor absorption lines in the 8600–9010 cm⁻¹ region have been measured and calculated. The spectra were recorded with a Bruker IFS 125HR spectrometer at a spectral resolution of 0.01 cm⁻¹ for lines with angular moment of the upper states up to 10. Calculations of line broadening and shifting coefficients are performed using a semi-empirical approach. The method is based on the impact theory of broadening, and includes the correction factors whose parameters can be determined by fitting the broadening or shifting coefficients to the experimental data. The comparison of our calculations with the experimental values argues that the semi-empirical method is quite acceptable for the determination of the water vapor absorption line profile parameters.