Small ultrahigh vacuum compatible hyperthermal oxygen atom generator

Abstract

The development of a compact, ultrahigh vacuum (UHV) compatible instrument for generating a flux of pure hyperthermal oxygen atoms for NASA applications has been achieved. The instrument combines the mechanisms of O2 dissociation and transport through a hot Ag membrane to provide a continuous source of O atoms to a vacuum interface where they are subsequently emitted into the vacuum space by electron-stimulated desorption (ESD). A flux of neutral O atoms 4.5 X 10(exp 13) cm(exp-2) s(exp-l)(P-3) with a mean ion kinetic energy of approximately 5eV and a full width at half maximum of 4eV was detected at a quadrupole mass spectrometer located 10 cm away. The geometry of the instrument is such that it is mounted on a 7 cm flange and can be tailored in length and orientation to fit most UHV systems. The data presented here are for ESD-controlled conditions where increases in the flux are strictly linear with electron bombardment current. Calculation shows that transport-controlled conditions can be achieved at temperatures as low as 350 C with membrane thicknesses on the order of 10 micron.