Design of a 3D field emission electron source with improved emission current density and cathode life

Field emission electron sources have been increasingly investigated and practiced as cold electron sources for many Xray generation mechanisms especially in certain medical imaging applications, such as computed tomography (CT). In a field emission electron source, the emission current and cathode life are the two key performance parameters of interests. Conventional field emission electron source in the form of a 2-dimensional single surface cathode design is often undergoing the bottleneck of limited emission current. Higher current can be obtained by increasing the strength of driving electric field. However this is at the expense of a reduced cathode life. In this paper we present a novel field emission electron source design based on a 3-dimensional semi-enclosed cavity structure, by utilizing the cavity’s multiple inner faces as electron emission surfaces. The cavity has one bottom inner face open for electron ejection, the area of which was kept the same as a conventional single surface cathode to maintain the same initial electron beam cross section. The extended emission area of the new cathode design due to its 3-dimensional structure provides a higher electron emission current while maintaining the same beam cross section, resulting in an improved effective emission current density. We have demonstrated a significantly increased electron emission current from this 3-dimensional cathode under a constant electric field, without over-driving the cathode field emitters. Alternatively this new cathode design can also achieve the same total emission current with a lower electric field compared with a conventional 2- dimensional cathode, which will significantly extend its life.