Investigation of a low energy alkali ion gun.
Haskell, Hugh B.
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A design used by Simpson and Kuyatt for a multistage electron gun has been modified for use with ions. In the work reported here a thermal emitter of Lithium ions using the mineral ß-eucryptite was employed as a source of ions. While the electron gun yielded a space charge limited beam, practical and theoretical considerations held the obtainable Lithium ion currents to less than 10% of the space charge limit in most cases. Currents of 10⁻⁷ to 10⁻¹⁰ amps were obtained at nominal energies of 2 to 100 eV. Minimum beam radii occurred a few cm. from the end of the lens and were less than one mm. at higher energies and less than two mm. at all energies. Well colllmated beams of up to 16 cm. in length have been obtained. Beam profiles were measured and analyzed assuming the radial current density to be Gaussian. Theoretical calculations of space charge dispersion are presented along with the Information necessary for design and use of the gun. Detailed measurements of the energy distribution of the ions are in progress but no conclusive results are available at this time.