Focusing properties of an anode‐controlled telefocus keV electron gun

摘要

A new design of a triode telefocus keV electron gun is presented, of which the focal distance can be varied during operation of the gun by axially adjusting the anode. The dependence of the maximum beam current density on geometrical and electrical quantities has been investigated in the neighborhood of the beam crossover, yielding the basic data for optimizing the gun performance under given experimental boundary conditions. At a crossover distance of 0.27 m a beam width (FWHM) of 65 μm corresponding to a current density of 3.1×104 A m-2 was attained at an acceleration voltage of 17.5 kV.