Karol Musiol

A spectroscopic diagnostic method using UV OH band spectrum

Noisy and spectrally poorly resolved molecular emission spectra of the 306.357 nm OH band were employed for evaluation of the rotational temperature in different plasma sources, in the temperature range 300 - 6000 K, when an apparatus function of a recording system is unknown. The described method is based on a comparison of experimental data with a theoretical spectrum. The following plasma sources are examined: a recombining jet of plasma torch, an atmospheric pressure glow discharge, a surface ionized wave device and a gliding arc. The temperatures of these weakly ionized plasmas, measured from the OH spectra, are in good agreement with temperatures obtained by using other techniques: thermocouples, tungsten wire resistance measurements and other spectroscopic methods. The results show that the OH spectra are very useful for temperature measurements of non-equilibrium plasmas.

N2+/N2 ratio and temperature measurements based on the first negative N2+ and second positive N2 overlapped molecular emission spectra

The and molecular emission spectra are frequently observed simultaneously in plasmas containing nitrogen. Relative band intensities of these systems are very sensitive to a variation of the ratio and temperature. The spectrum, emitted between 3800 and 4000 A, has been used to measure rotational and vibrational temperatures, and to estimate the ratio when the electron temperature is known, in different plasma sources (Glidarc, ac discharge between tips). The proposed method is based on a point-to-point comparison of an experimentally measured spectrum with the computer-simulated one.

Application of the (0,0) Swan band spectrum for temperature measurements

Emission spectra of the 516.611 nm Swan band of the molecule were employed for evaluation of the rotational temperature in different plasma sources. This diagnostic method may be applied in the temperature range from 300 - 6000 K and is especially useful for noisy and spectrally not well-resolved spectra when the apparatus function of a recording system is unknown. The described method is based on a comparison of experimental data with the theoretically calculated spectrum. The numerical minimization procedure is started with the temperature value obtained from the Boltzmann plot or the intensity ratio of two selected spectrum components. An analysis of a theoretically calculated spectrum is presented. Two plasma sources were examined, a plasma torch recombining jet and high-voltage-triggered dielectric barrier discharge (DBD).

Investigations of GMAW plasma by optical emission spectroscopy

We report on investigations of gas metal arc welding plasma operated in pure argon and in a mixture of argon and CO2 at a dc current of 326?A. The spatially resolved electron densities and temperatures were directly obtained by measuring the Stark widths of the Ar?I 695.5?nm and Fe?I 538.3?nm spectral lines.Our experimental results show a reduction of the plasma conductivity and transfer from spray arc to globular arc operation with increasing CO2 concentration. Although the electron density ne increases while approaching the core of the plasma in the spray-arc mode, a drop in the electron temperature Te is observed. Moreover, the maximum Te that we measure is about 13?000?K. Our experimental results differ from the Haidar model where Te is always maximum on the arc axis and its values exceed 20?000?K. These discrepancies can be explained as a result of underestimation of the amount of metal vapours in the plasma core and of the assumption of local thermal equilibrium plasma in the model.

The temperature of a plasma used in electrical discharge machining

The temperature in an electrical discharge machining (EDM) plasma was determined from measurements of relative intensities of the 411.85 and 413.29 nm Fe I spectral lines. The time-dependence of the plasma temperature was measured for individual electrical machining pulses. Under our experimental conditions (electrodes of C6(+) and M1E(-), cosmetic paraffin as the dielectric liquid) the measured plasma temperature ranged from 8000 to 10 000 K for different current pulses. We observed higher temperature values during the initial phase of the discharge. Temporal characteristics of discharge electric parameters, light emission and the plasma temperature are presented.

Investigation of a cathode region of an electric arc

Investigations of the near-cathode region of the atmospheric pressure, 200 A arc burning in pure argon have been performed using spectroscopic techniques. Several slices at different distances from the cathode tip have been observed side-on. In order to perform diagnostic measurements of the plasma, the profiles of the Ar I and Ar II lines have been recorded. Phenomena inexplicable in terms of the model based on assumption of a local thermodynamic equilibrium state and constant pressure in the plasma have been observed and are shown on an Olsen-Richter diagram.

Stark width of - Ar I transition (696.543 nm)

The full width at half maximum (FWHM) of the 696.5 nm Ar I spectral line profiles was measured in the plasma temperature range from 13 500 K to 24 000 K and free electron density from 1.2 to . Results were obtained for this line emitted from the near-cathode region of an atmospheric pressure, 200 A arc burning in pure argon. Our results are compared with data existing up to now. In the electron density range of our experiment, the 696.543 nm Ar I line Stark FWHM is linearly proportional to the electron density. The observed dependence of the FWHM on the plasma temperature and electron density is in qualitative agreement with Griems theory; however, the ratio of calculated and measured FWHM was equal to 1.55, for the dependence on electron density and temperature. The dependence of FWHM on electron density, obtained by weighted least squares fitting of all our data with the constraint that the curve passes through the origin, is well represented by the following equation: , with in nm and in , for the temperature .

Spectroscopic investigation of the equilibrium state in the electric arc cathode region

Several thin layers of an arc plasma column were observed side-on at different distances from the cathode. The arc was operated in argon at atmospheric pressure with the arc current equal to 200 A. As the basic diagnostic method we used the Olsen - Richter diagrams. For determination of temperature the Larenz - Fowler - Milne and Boltzmann plot methods were applied. Electron density was measured from the Stark width of the ArII line and continuum intensity. The plasma near the cathode tip shows axial and radial dependence of its physical equilibrium state. In the hot core, the plasma is in LTE. Toward outer zones, the plasma state deviates from LTE. For plasma layers closer to the cathode, this deviation begins at smaller distances from the axis and for higher temperatures it vanishes for h > 3 mm. It is caused after all by the ArI ground state overpopulation. Theoretical estimations of the ArI ground state overpopulation give results consistent with experiment. Calculations show that this overpopulation is caused by inward transport of ground state atoms into the plasma column.

Measurement of atomic Stark parameters of many Mn I and Fe I spectral lines using GMAW process

The particular character of the welding arc working in pure argon, whose emission spectrum consists of many spectral lines strongly broadened by the Stark effect, has allowed measurement, sometimes for the first time, of the Stark parameters of 15 Mn I and 10 Fe I atomic spectral lines, and determination of the dependence on temperature of normalized Stark broadening in Ne = 1023 m−3 of the 542.4 nm atomic iron line. These results show that special properties of the MIG plasma may be useful in this domain because composition of the wire-electrode may be easily adapted to the needs of an experiment.

Experimental investigations of the arc MIG‐MAG welding

The type of the applied shielding gas has a strong influence on quality of the welding process. In particular, increase of the percentage of carbon dioxide in argon, causes increase of the transition current value from the globular to spray mode of metal transfer. Observations by fast camera allows to better characterize the arc column shape in the different working modes. The spectroscopic diagnostic of the welding arc is also necessary to understand the observed changes in the mode of droplet transfer. The use of an original diagnostic method allows to estimate the temperature and the electronic density distributions in the plasma without hypothesis on its equilibrium state. Results of this work seem to show that the observed effects could be linked to the microstructural modifications of the anode tip during the MIG‐MAG welding process as a function of the gas composition, and especially to the existence and disappearance of an insulating oxide “gangue” at the wire extremity.