Effect of helium pressure and flow rate on microplasma propagation along hollow-core fibers

The effect of helium pressure and flow rate on the propagation of microplasmas obtained inside hollow-core fibers (HCFs) with their inner diameters of 100-2000μm has been reported in this study. Measurements show that microplasma length, breakdown voltage, pulse durations, and pulse current are strongly dependent on He flow rate and He pressure ranging from 50 Pa to 1.0 atm. Comparison between experimental results and analytical mode shows that Townsend's model is valid for understanding the discharge process of microplasmas inside HCFs, where the wall effect has to be considered. Analysis indicates that long-lived metastable species (He_m&z.ast) from one previous discharge period can greatly contribute to the propagation of microplasmas along the microns-thick HCFs. An avalanche discharge model combined with the surface recombination of charged species has been used to explain the propagation of microplasma inside HCFs.