Emergence of self-organized patterns in arc discharges by anode cooling

Summary form only given. The spontaneous formation of self-organized patterns is a captivating phenomenon found in numerous physical systems. Self-organized electrode patterns have been observed experimentally in diverse types of electrical discharges, but rarely captured in general-purpose computational plasma dynamics simulations. Simulations using a thermodynamic nonequilibrium (two-temperature) model have revealed for the first time the spontaneous formation of self-organized anode attachment spot patterns in the free-burning arc, a canonical dc discharge. The model is implemented using a monolithic second-order-accurate variational multiscale finite element method. The simulations show the gradual emergence of spot patters with increasing levels of anode cooling: from a single diffuse spot for low cooling levels to the eventual coverage of the anode region by small spots for intense cooling. Additionally, the patterns transition from steady to dynamic with decreasing total current for high cooling levels. The pattern dynamics show the formation of new spots occurring in the center of the plasma, as well as the eventual extinction of spots at the plasma boundaries. The different types of anode patterns (from diffuse to self-organized spots) have a significant effect on the total voltage drop across the plasma column, but a minor effect on other plasma characteristics away from the anode region. The obtained patterns qualitatively agree with experimental observations and confirm the hypothesis that the attachment spots originate at the fringes of the arc - anode interface.