Effect of a concave grid mesh in a carbon nanotube-based field emission X-ray source

[Display omitted] •Successful design using a concave grid mesh for the focusing electron.•Much better X-ray image due to the concave grid mesh.•Higher anode current efficiency using the concave grid mesh versus a flat grid mesh. This study introduces a simple approach to improve the X-ray image quality produced by the carbon nanotube (CNT) field emitter X-ray source by altering the geometrical shape of the grid mesh from the conventional flat shape to a concave one in a typical triode structure. The concave shape of the grid electrode increases the effective number of the grid cells in the mesh, which exerted an electric field in the direction of the emitted electrons, thereby increasing the emission current reaching the anode. Furthermore, the curved mesh (concave grid mesh), which was responsible for the extraction of electrons from the field emitter, exhibited a focusing effect on the electron beam trajectory thereby, reducing the focal spot size impinging on the anode and resulted in a better spatial resolution of the X-ray images produced.