The ecton model of unipolar arcing at fine-structured surface

The initiation of the explosive electron emission pulses - ectons being responsible for the ignition and burning of a vacuum discharge, in particular, - unipolar arcs. The latter being a common feature of intense plasma-surface interactions in fusion devices. A fusion devices first wall with a strongly non-uniform surface, as well as an intense power load onto the surface in the edge localized modes (ELMs) form, intensely promotes explosive emission ignition. Furthermore, the thin-film metallic surfaces define the arcing properties, such as the erosion rate. This agrees with a novel detailed experiments on unipolar arcing at linear simulator NAGDIS-II, the Asdex-Upgrade tokamak, and the Large Helical Device. Such fine-structured - film-like surfaces, are as follows: a micron-scale layer of tungsten nanowires (so called “W-fuzz”) that had been grown at the bulk tungsten; a liquid lithium coating of capillary porous system made from tungsten or molybdenum; and tungsten layers deposited on a carbon tiles. We are considering the ecton processes (ecton current, its life-time, spot-cell motion velocity, erosion rate) depending on the film thickness and its thermo-physical and explosive properties.