Spectroscopic measurements in a titanium vacuum arc with different ambient gases

Spectral emission lines from a low pressure d-c arc discharge with a Ti cathode were studied in various ambient gases; N2, O2, and Ar. Light from the plasma was detected by an optical spectrometer multichannel analyzer (OSMA). The spectral intensities of Ti, Ti+, Ar and N2 were measured as a function of the gas pressure in the range 5 × 10-3 - 0.5 mbar. The measurements were performed in the inter-electrode region at different distances from the cathode. For N2 and O2 as the filling gases, the intensities of Ti and Ti+ increase with the gas pressure up to pressure values of the order of 0:2¡0:4 mbar, while they decrease for higher pressure values. With Ar gas, a different behavior of the Ti+ intensity was found; it presents an increasing general trend. The behavior of the lines was qualitatively analyzed in terms of the most relevant atomic processes that take place in the metallic plasma - gas structure (charge-exchange, electron impact excitation and ionization, etc.). It is found that the behavior of the observed spectral lines can be satisfactorily explained in terms of the relevance of these processes as functions of the neutral gas density and electron temperature