Performance characteristics of a hyperthermal oxygen atom generator

Abstract

The design and operating characteristics of a hyperthermal oxygen atom generator are presented and described. In this source oxygen atoms permeate through a Ag/0.5% Zr membrane at 550 degrees C from a high-pressure region (200 Torr) to the vacuum side of the membrane. There they are emitted toward the target by electron stimulated desorption (ESD). The average O neutral kinetic energy is about 5 eV, and a flux of 4.5*1012 neutrals cm-2 s-1 has been attained using a circular filament/reflector assembly to generate the primary electrons responsible for ESD. The primary electron current required to generate this O neutral flux is 3 mA. The flux produced is very high purity but does contain a relatively small number of O+ and possibly H2O+ or F+. A computer simulation of the charged particle trajectories was used to design the filament/reflector assembly. The simulation studies indicate that a uniform primary electron flux is attained across the membrane, that the secondary electrons are trapped by the source, and that positive ions can be removed from the neutral flux by placing a negative potential on the membrane. Over the range examined, the O neutral flux increases linearly with primary electron current indicating that the overall process is ESD limited rather than limited by the O permeation rate.