It has been discovered that a cold gas flow parallel to the anode surface can lead to a stable attachment with an enlarged non-equilibrium region between the luminous arc plasma and the anode surface. The current flow to the anode appears to be distributed over a relatively large area, thus drastically reducing the anode heat flux. In this study, this type of arc attachment, in which a constrictor-stabilized arc attaches to an anode perpendicular to the arc axis with a cold gas flow parallel to the anode surface, is investigated. The enlarged non-equilibrium region between the anode and the arc column is characterized with a newly developed data analysis technique using Thomson scattering of laser radiation to determine the electron temperature and density distributions. Measurements with a Langmuir probe imbedded in the anode provide values for the same quantities at the anode surface allowing determination of the current density distribution, and heat-flux probe measurements give the heat-flux distribution at the anode surface. A parallel modeling effort using a three-dimensional finite-volume code for a non-equilibrium plasma provides insight into the physical processes in this non-equilibrium region including a mapping of the electric field strength. Both kinetic and composition non-equilibrium are considered, and a self-consistent treatment for diffusion is used.
Broader impact
High intensity arcs have attracted considerable interest for materials processing because they can provide high fluxes of electrons, ions, or other radicals. However, because the arc plasma is usually close to equilibrium, these fluxes are usually coupled with high heat fluxes, limiting their usefulness for processing applications. Furthermore, electric arcs frequently operate in an unstable manner, and the high heat fluxes lead to erosion of the electrodes, limiting the life of arcing devices. This study addresses the problems of the high heat fluxes associated with the benefits of high electron densities in electric arcs. Two aspects of this investigation are expected to lead to results of practical importance. One is the generation of larger non-equilibrium plasma volumes that can be used for surface treatment or bulk chemical processing. The second is the existence of a wide-area diffuse attachment for high-intensity arcs with apparently low heat-flux densities and, consequentl
