Study on structural characteristics of Ka-band high power millimeter wave radial transit time oscillator

High power coherent electromagnetic radiation of a millimeter waveband is a tough research topic of plasma physics. In axial millimeter wave electromagnetic radiation devices, low power capacity and mode competition limited the output power. The radial structure is a promising candidate to realize high power millimeter wave radiation. Structural characteristics of a radial Ka-band high power millimeter wave transit time oscillator (TTO) are studied in this paper. Analysis without an electron beam indicates that if the average radius of radial cavities is increased, the mode of the stimulated field will not change, the power capacity will be improved, and the quality factor due to ohmic loss will remain unchanged. Particle-in-cell simulation proves that, for radial millimeter wave TTO, increasing the radius of the cathode and keeping sizes of the other parts unchanged, the output power will be increased, the efficiency will remain the same, and electric field growth will be slower than that in axial devices. Besides, taking ohmic loss into consideration, the efficiency will increase to a stable value. Therefore, by this method, high power coherent electromagnetic radiation in a millimeter wave can be realized.