In accordance with one embodiment of the present invention, the
hollow-cathode apparatus comprises a small-diameter tantalum tube with a
plurality of tantalum-foil radiation shields, wherein the plurality of
shields in turn comprise one or more spiral windings external to that
tube and approximately flush with the open end from which electron
emission takes place. The axial length of at least one of the inner
windings (closer to the tantalum tube) is equal to or less than
approximately half the length of the tantalum tube. An enclosed keeper
surrounds the cathode. To start the cathode, a flow of ionizable inert
gas, usually argon, is initiated through the cathode and out the open
end. An electrical discharge is then started between the keeper and the
hollow cathode. When heated to operating temperature, electrons exit from
the open end of the hollow cathode.