Study of the LTE departure in a low pressure supersonic plasma jet in Ar-H/sub 2/ and in Ar-N/sub 2/-H/sub 2/ mixture

Summary form only given. Plasma torches at low pressure and controlled atmosphere are used in major applications for the production and processing of materials due to their potential for high performance, and low contamination. A good knowledge of the plasma parameters is necessary, particularly for the design of high-performance mathematical models that avoid the building of expensive prototypes for performance assessment. The present work is undertaken on a DC plasma torch operating over a wide pressure range (8 kPa to 100 kPa) at an arc power fixed at 17.5 kW. Emission spectroscopy diagnostics was carried out for determining temperature, electron and particle density profiles in two gas mixtures: Ar-N/sub 2/-H/sub 2/ with flow rates of 40, 10, and 1 slpm respectively, and Ar-H/sub 2/ with input flow rates of 35 and 7 slpm respectively. The electron temperature was determined by using a Boltzmann diagram of Ar spectral lines. The absolute values of the intensity of these lines, of the molecular bands and of the continuum was obtained by using a standard tungsten filament lamp. Local values were obtained by Abel transform. For the rotational temperature measurement, the first negative system of N/sub 2//sup +/ was used using a method that consists in comparing the experimental spectra and the simulated molecular bands. The N/sub 2//sup +/ population density as calculated by using the band head intensity (the integrated 1-26 P-branch lines). To measure the electron density, we used the broadening of the H/sub /spl beta// line of hydrogen by the Stark effect. The local profile of H/sub /spl beta// was obtained by Abel inversion of the integrated profiles for 25 wavelengths on either side of the peak.