Research of the Binding of an Argon Arc to the Cathode in a DC Plasma Torch

Experiments were carried out to study the stable attachment of an atmospheric pressured argon dc arc to the surface of pure, thoriated and lanthanated tungsten. Using spectroscopic methods electron temperatures and concentrations were obtained in the positive plasma column near the cathode. With a current of 200 A and a plasma gas flow rate of 1.5 g/s, the average values of temperatures were T-e similar to 2.6 eV for pure tungsten, T-e similar to 2 eV for thoriated and lanthanated tungesten, and concentrations n(e) similar to 10(17) cm(-3). In these experiments, the cathode with an insert of lanthanated tungsten (3100 K) had the lowest working surface temperature due to the lower effective work function, while for thoriated and pure tungsten surface temperatures were 3300 and 3800 K, respectively. It was found that at a current of 200 A, the tip of the pure tungsten cathode was in the liquid phase, in contrast to thoriated and lanthanated tungsten that remained in solid phase.