Spectral analysis of arc radiation with high optical thickness

High-pressure arcs in copper vapor with peak currents up to 3.2 kA are studied by optical emission spectroscopy. The arc experiments are operated in air at atmospheric pressure, and copper vapor is generated by erosion of the copper electrodes (cathode and anode). The latter is caused by high current densities and high power flux densities at the electrode due to a restriction of the electrode area. The arc radiation in the visible part of the spectrum is dominated by line radiation of copper atoms and ions. Depending on arc current and copper evaporation the lines show quite different line width and optical thickness up to self-reversal. The spectroscopic study is aimed at the determination of plasma temperatures and the copper densities in these arcs. It is demonstrated, that well-known methods of line analysis like the Boltzmann plot of optical thin lines and the Bartels method to analyze lines with self-reversal cannot be applied under the specific arc operating conditions. Thus, temperature determination requires an explicit consideration of the radiation absorption by means of radiation transport simulations. The analysis is focused on the comparison of the arc properties near to the cathode. Temperatures in the range from 10000 to 18000 K were obtained.