Vacuum breakdown from nanostructured fuzzy surfaces

Abstract

Studying of initial steps of unipolar arc ignition process is important for reduction of probability of arcing between the plasma and the wall in thermonuclear devices. Tungsten nano-fuzz surface formed by helium plasma irradiation at high fluences and temperatures is a perfect material for easy arc ignition. Snowflake-like craters were detected on the fuzzy surfaces after short micro-breakdowns. Such sort of craters have not been observed before on any other metallic surfaces. These specific traces are formed due to unique properties of the fuzz structure. The nano-fuzz could be easily melted and vaporized by micro-breakdown current, due to it porosity and bad thermal conductivity, and formation of low conducting metallic vapor cause discharge movement to the nearest place. Thus, even low current arc can be generated and leave traces, which could be easily observed by a optic or secondary electron microscopes.