A QUANTITATIVE LASER SCHLIEREN METHOD FOR MEASUREMENT OF NEUTRAL GAS-DENSITY IN HIGH-PRESSURE GAS SWITCHES

A quantitative laser schlieren technique has been developed to measure the changes in neutral gas density inside a spark gap switch after br eakdown. The measurement system incorporates an array of narrow laser beams which are used to probe the inter-electrode gas volume at discre te distances from the spark axis. Changes in the refractive index grad ient within the switch, caused by variations in neutral gas density, r esult in beam deflection, which is measured using a neutral density we dge/photodiode combination. The resulting Schlieren profiles yield bot h spatially and temporally resolved refractive index data, which enabl e calculation of the gas density. The use of four averaged trials to o btain the final neutral gas density profiles minimizes errors caused b y the turbulent nature of the cooling gas. A typical set of results is presented for SF6 at a pressure of 0.5 bar.