H2 AND RARE GAS FIELD ION SOURCE WITH HIGH ANGULAR CURRENT.

Abstract

A field ion source that has been designed to operate at very low temperatures with a physisorbed surface supply to the ionization region has been constructed, and initial tests have been carried out. This mode has been found to give beams of high angular current density and is expected to have low energy spread in the beam. The UHV system allows processing of the field emitter under clean, high vacuum conditions. A liquid He cooled finger raintains the tip at controlled temperatures from that of liquid He to room temperature. Observations on the characteristics of the field ionization pattern are made under varying conditions of pressure, temperature, field and tip processing, and orientation.