Effect of admixture of metal vapor on cathode surface temperature of plasma torch

An arc current in Gas Tungsten Arc (GTA) is originated mainly from thermionic electron emission on the high temperature cathode surface. Therefore it is significantly important to understand the temperature distribution on the cathode surface to realize required properties of GTA. In material processing such as arc welding, it has been experimentally confirmed that a large quantity of metal vapor evaporated from a weld pool of the material drastically changes the physical property such as electrical conductivity of the arc plasma and changes the plasma temperature distribution. Therefore, it is expected that the cathode surface temperature during material processing is influenced by the mixture of the metal vapor. This paper presents experimental results of the cathode temperature measurement during argon and helium arc welding. Consequently, it was found that during arc welding, cathode temperature increases by several hundred Kelvin in comparison with the cases of pure argon and helium arc.