Design and Performance Analyses of a Ka-Band Radial Transit Time Oscillator With Low Magnetic Field and High Efficiency

The traditional axial high-power microwave (HPM) generator in the Ka-band requires high-intensity magnetic field due to the strong space charge effect, which hinders the development of devices toward lightweight. When the electron beam in the radial drift tube radiates outward, the charge density decreases gradually, and the space charge effect weakens. Weakening the spatial potential well is beneficial for improving the efficiency of beam-wave interactions. At the same time, the demand for guiding magnetic field strength will also be reduced. Considering the characteristics of high power, high efficiency, and single mode for the transit time oscillator, a low magnetic field radial transit time oscillator (RTTO) is presented by theoretical analysis and simulation. With the 450-keV, 9-kA beam guided by the magnetic field of about 0.8 T, the 1.22-GW microwave pulse at 31.13 GHz is generated, yielding the conversion efficiency of 40.6%. The research in this article lays the foundation for the development of radial HPM devices toward millimeter wave and higher frequency bands.