Apparatus for Electron Optical Study of Low-density Gas Flow

Abstract

An apparatus has been developed and built at the National Bureau of Standards to study low-density (~4014particles/cm3or 40-4 mm Hg) gas flow.1, 2This is an electron—optical schlieren technique which depends on the scattering of electrons in collision with individual gas molecules or atoms to form a dark field image of the gas. The apparatus consists of a bakeable stainless steel low-pressure chamber and other chambers containing brass and glass electron optical components which are not baked. The low-pressure chamber (~10-8 mm Hg) is connected to three other chambers (~10-6 mm Hg) through two small apertures and a slit. Metal gaskets are used on the bakeable chamber. The system is pumped by four oil diffusion pumps each with a liquid nitrogen trap. A small liquid helium trap (~1 1.) will be used to decrease the residual pressure from 10-7 mm Hg to 10-8 mm Hg or better.