Velocity Analysis of Shock-Heated Molecular Beams by a Time-of-Flight Method

Abstract

Measurements of the mean velocities u_∞ and the velocity distributions of the molecular beams from a shockheated source have been carried out by a conventional time-of-flight method, and their translational temperatures T^∞_// parallel to the flow direction have been determined. The speed ratios, S^∞_// = (mu_∞/2kT^∞_//) ^1/2, of 6-20 have been obtained in the source temperature range of T₀ =1, 400-10, 800K and its pressure range of P₀=1.3-6.8atm for argon. They have been less than the theoretical terminal speed ratios for a free jet. In the present apparatus with a convergentdivergent conical nozzle, the boundary layer from the nozzle wall limits the expansion and results in a decrease of the speed ratio. Although the flow is strongly affected by the background gas in the far downstream from the nozzle exit, higher speed ratios have been obtained.