Characterization of temporal and spatial distribution of hydrogen gas density in capillary tubes for laser-plasma experiments

Abstract

Measurements of the time evolution of neutral hydrogen gas filling capillary tubes were performed by interferometry. Time-resolved gas density evolution was observed by following the temporal variation of the interference pattern, while the spatial distribution of gas in the stationary state was obtained by numerical fluid simulation. It was found that for a 178 μm diameter and 30 mm long capillary tube, the gas flow reaches a stable state at around t=34 ms regardless of the value of the reservoir pressure in the range of 100–500 mbar. The gas density filling the capillary tube is measured to be 81±3% of the reservoir density; the density drop is attributed to losses along the filling line and gas leaks from the capillary in the background vacuum.