Segmented gate drive for dynamic beam shape correction in field emission cathodes

摘要

A field emission cathode providing for dynamic adjustment of beam shape is disclosed. Beam shape adjustment is accomplished by segmenting the gate electrode of a gated field emission cathode and independently driving the various gate segments to form the desired beam shape. Segments can be turned on and off as the beam is deflected allowing dynamic correction of aberrations in the beam. A focus lens can be placed on the gated cathode to produce a parallel electron beam. In addition, a hollow cathode can be produced to minimize space charge repulsion in a beam.