Interaction Mechanism of a THz Wave Generator using a Field Emission Cathode

In the previous meeting held at MIT (IVNC2004), we proposed a vacuum electronic device based on field emission mechanism for the generation of THz waves. A preliminary result was obtained. However, the detail interaction mechanisms were under study to improve the efficiency. In the present work, the MAGIC code is used to investigate the interactions between the electrons and the THz waves. To understand the interaction mechanism, the cathode has been trimmed to emit electrons. The simulation results show that the efficiency of the case corresponding to the trimmed cathode is higher than that of the original planar cathode. The phase space diagram of the case corresponding to the original cathode has been observed. The downstream current is oscillating with the THz radiation. The bunching electrons between the gaps contribute most of the generation of THz waves. The phase space diagram of the case corresponding to the trimmed cathode shows almost no downstream current but the corresponding efficiency is higher than that of the untrimmed case. This indicates that the interaction mechanism is strongly related to the gaps. The AC electric fields of the THz waves not only velocity-modulate the electron beam but also cause the density modulation of the field emission current. This pre-bunching effect provides the feedback loop as required by an oscillator