Spectroscopic investigations of the cathode region of the free-burning copper arc

A free-burning electric arc between copper electrodes is convenient to use in studies of electrode regions of a vacuum arc. The reason is that the plasma formed gas is the copper vapour in this case. The cathode region plasma of electric arcs has been repeatedly investigated. The ionization nonequilibrium due to diffusion processes as well as the deviation of the electron temperature from that of heavy particles is usually taken into account in this region. It was previously discussed by the authors that the plasma nonequilibrium of the electric arc in copper vapours is caused by the resonance radiation transfer. In this paper such an approach as applied to the plasma of arc cathode region is developed. The investigations were carried out by the spectroscopic method. It was shown that the nonequilibrium population of not only resonance level, but more highly excited levels takes place due to significant gradients of plasma parameters in this region. Thus, phenomena associated with the radiation transfer of separate spectral lines should be taken into account when the plasma condition in electrode regions is analyzed