Experimental study of the near-electrode plasma-tungsten cathode system in high-current atmospheric-pressure nitrogen arcs

Results of spectroscopic and pyrometric studies of the near-electrode plasma-tungsten cathode system are presented. The $\mathrm{2D}$-spectra of radiation of the multiply ionized nitrogen plasma of electric-arc discharge under atmospheric pressure are obtained at different current values. The axial electron temperature in this plasma is determined depending on the distance from the cathode tip, and the temperature distribution over the current-collecting surface of the cathode is found. The high-speed visualization of the cathode-near-cathode plasma region made it possible to observe phase transitions on the cathode surface and processes of crack formation and detachment of its fragments. The power released at the cathode is analyzed including the contribution of the arc column resonance emission, and the peculiarities of phase transitions on the cathode surface are revealed. The densities of the electron emission current at the cathode are estimated theoretically and compared with the data obtained in the experiment. Possible causes of the difference between the theoretical values of the emission current density and those found experimentally are discussed.