Electrostatic Getter-Ion-Pump Design

Abstract

The theory and design of a nonmagnetic, multicelled, triode, getter-ion pump capable of attaining pressures of less than 3 × 10−11 Torr and a pumping speed for air of 1700 liter/sec using a 6-in.-diam orifice is described. A quantitative theory is presented for maximizing the ionizing efficiency of electrons trapped in the electrostatic potential of a cylindrical diode. The experimentally verified theory predicts that for optimum results, electrons must be injected in a well-defined range of angular momenta from an injector whose potential is nearly that of the outer cylindrical electrode. The theory also predicts the optimum axial and radial position for injection. In the new pump, each cell consists of an open cylindrical grid within which is a central anode and two electron injectors. All cells are surrounded by a common cathode which also serves as the pump housing. A new-design, large-area, resistance-heated sublimator with pressure-controlled sublimation rate is located on the axis of the cylindrical cathode. Because the ionizing and gettering functions have been effectively separated it has been possible to optimize each function separately.