Efficient Beam–Wave Conversion in an X-Band Coaxial Dual-Mode Relativistic Cherenkov Oscillator Under Low Magnetic Field

In order to reduce the volume and energy consumption of high-power microwave (HPM) systems, HPM sources with low guiding magnetic fields have become one of the most important trends. However, the beam-wave conversion efficiency of such devices is typically low due to the divergence of the electron beam, which lacks the constraint of a high magnetic field. Here, we investigate a coaxial dual-mode relativistic Cherenkov oscillator (RCO) that exhibits efficient beam-wave interaction at a low guiding magnetic field. On the one hand, the space charge effect of electrons can be reduced by increasing the radius of the device; on the other hand, dual-mode operation can be achieved for efficient beam-wave conversion, while the competition of higher order modes from large radii can be avoided by introducing a coaxial inner conductor to the slow wave structure (SWS). In particle simulations, a guiding magnetic field of only 0.33 T has been demonstrated to confine the electron beam, resulting in an output microwave power of 1.98 GW and a beam-wave conversion efficiency of approximately 43% when the diode voltage and diode current are 510 kV and 9 kA, respectively. Moreover, preliminary validation experiments were conducted, wherein microwaves with a power of 1.71 GW were generated with a beam-wave conversion efficiency of 36%. The experimental results obtained under low magnetic fields provide a high degree of confidence that the size and weight of HPM systems utilizing this device will be significantly reduced.