Simulation and modeling of alignment-free field emission X-ray tubes

A new hemispherical-geometry cathode for field emission (FE) X-ray tubes was designed and simulated in this study. The electric field strength distribution on the hemispherical-geometry cathode was calculated and used to predict the emission current. Because of their unique FE properties, carbon nanocoils were used as the electron emitters for simulation and modeling. The results show that a large tolerance is permitted, and the performance attained with ±20° cathode misalignment was nearly identical to that without misalignment. The maximum emission current can be achieved using a hemispherical-geometry cathode with a radius of 1 mm. Additional advantages of FE X-ray tubes with hemispherical-geometry cathodes are higher FE currents, shorter response times, and smaller X-ray spot sizes. In addition, lower power consumption, longer lifetimes, and higher resolutions are expected with this simple and low-cost design.