Molecular Dynamics Simulation for Emission and Propagation of Electrons in Cathode Nano-Structures

This research resulted in the successful development of simulation code for modeling field, thermionic, and photo electron emission cathodes using a molecular dynamics formalism. This work examined and performed verification testing of many different critical electron emission phenomenology of critical importance to high power microwave (HPM) and radio frequency (RF) amplifiers for electronic warfare, radar, and communication. The software code was provided to AFRL/RDH personnel and now being used to research cathodes and cathodes in HPM devices. The Grant research using the software code investigated mutual space charge effects on field emission from finite emitters embedded in a planar cathode of an infinite diode. It was shown how separation of the emitters can affect the equilibrium current to a significant degree depending on the applied electric field and material parameters of the emitters. Another cathode limiting phenomenon is the classic form of the two-dimensional Child Langmuir law developed by Y.Y. Lau and J.W. Luginsland, which was known not to be valid for emitters of very small diameter or for large ratios of diode spacing to emitter width (large aspect ratio). This FE MD code allowed investigation into how the large aspect ratio emitters of a large cathode exceeded the 2D space-charge limited emission for this regime. In addition, they investigated the effect of non-homogenous work function on the emission current and emittance of a thermionic-field emission cathode. They demonstrated how these parameters are dependant on both the granularity of the cathode structure and its degree of disorganization. A very interesting result was that the emittance improved by almost 30 with large numbers of in-homogenous emitters.