Investigation of a low energy alkali ion gun.
Abstract
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.