Diffusion-Surface Ionization Alkali Metal Ion Source

摘要

An ion source is described wherein alkali metal atoms diffuse through a thinmembrane emitter of nonporous refractory metal operating at temperatures in excess of 800 C. The ion source is a double-oven configuration containing potassium metal. The first oven is a low-temperature cell, operating at 300 C or higher, which controls the pressure of the alkali metal vapor in the source. The second oven of the configuration has, as part of its surface, a membrane of refractory metal of thickness 0.050 cm or less. This cell, when heated to 800 C or higher, yields ion currents in the range of 0.001 to 10 to the -7th A/cm2. The neutral flux, in the direction normal to the emitter, is in the range of 10 to the 11th to 10 to the 13th atoms/sr/sec. Both neutral and ion emission are measured as a function of emitter temperature and saturated potassium metal vapor pressure for potassium diffusing through Ta, W, and Mo. (Author)