The Importance of VUV-Radiation in the Anode Region of High-Current Plasma Generators with Diverging Anode Channel

It is demonstrated that a region of a stable laminar mode of arc burning with diffuse flow of current to the anode exists in high-current $(I \ge 250$ A, $I/d \ge 40$ A/mm$)$ plasma generators with a self-adjusting arc length and diverging anode channel. The most important mechanism providing for the volume ionization of the "plasma-anode wall" transition layer is the photoionization of the cold surface layer of gas by dense VUV-radiation transferred to the periphery from the arc core where the fully ionized plasma has a temperature above $20\,000$ K. The presence of high-intensity resonance radiation of singly charged nitrogen ions and its absorption at the periphery of the energy release region of the nitrogen arc enable one to explain the experimentally observed nonthermal pattern of distribution of intensity in the radiation spectrum of molecular ion of nitrogen.