A departure from local thermodynamic equilibrium within a freely burning arc and asymmetrical Thomson electron features

Spectrally resolved measurements of Thomson scattering were made in a freely burning arc in argon at a pressure of 1 atm. The radial and axial profiles in electron temperature and number density exhibited extensive regions of departure from local thermodynamic equilibrium, so confirming the findings of Snyder et al in E 48 4124 - 7, 1993. Electron temperatures at least 4000 K above those of the gas were found. Asymmetry in the Thomson electron feature was found and shown to depend on which segment of the laser-profile scattering data was sourced. This arises from an asymmetry in the arc - laser interaction. Also described is a simple technique for accurately defining the position of the cathode tip once an arc has been ignited.