Two modes of cathode spot operation at high-current high pressure arc

Summary form only given. According to the currently most accepted model, current density at the refractory cathode of a high current arc is directly proportional to the gas pressure, and does not depend on the arc current. In the theoretical part of the present work, it is shown that at higher currents, and/or higher gas pressures, the cathode spot exists in another mode. In this mode, current density does not depend on the gas pressure and is inversely proportional to the arc current. In the experimental part of the work, the current density was measured using two methods: by analysis of the arc footprints at the cathode surface after the arc extinguishes and by measuring Q, the heat load of the cathode. Experiments were conducted with Argon and Nitrogen in the 1 atm. to 6 atm. pressure range. The cathodes were made of pure and 2% thoriated tungsten. The arc current was 50 A to 500 A. The experiments confirmed the existence of the second mode and current density dependencies on the arc current and the gas pressure. The arc current density, obtained by the footprint method, was approximately two times higher than that obtained by the cathode heat load method.