MASS SEPARATION DURING MOLECULAR-BEAM SAMPLING PROCESS

In a molecular beam sampling process, if the stagnation gas is a mixture, heavier species are concentrated onto the axis of the molecular beam, while lighter ones are diffused away from it. This phenomenon is generally called “mass separation.” Mass separation is caused mainly by three phenomena: (1) pressure diffusion, (2) Mach-number focusing and (3) skimmer interference. Pressure diffusion has already been analyzed by Sherman. In the present work, the mass separation for a binary mixture of Ar and He was experimentally measured by means of a molecular beam-mass filter system, and its kinetic analysis was carried out with regard to Mach-number focusing taking into consideration of the non-equilibrium of translational temperatures. The experimental results and the theoretical prediction agree well except in the cases of a shorter nozzle-skimmer distance, where skimmer interference is dominant, and in the cases of a higher Ar content. © 1979 The Japan Society of Applied Physics.