Experimental investigation on the sensitivity of parameters in a Ku-band permanent magnet packaged relativistic backward wave oscillator

This paper presents the design and experimental investigation of a Ku-band highly overmoded relativistic backward wave oscillator under a 74 kg, 0.4 T permanent magnet package. The experiments reveal that the phase of the electron beam envelope oscillation deviates significantly from the simulated value under a low magnetic field, leading to marked differences between the experimentally optimized values and simulations for the anode–cathode gap (LAK), the cathode endplate distance (LCE), and the anode head length (LAnode). Meanwhile, to compensate for the upward shift in the extraction cavity resonant frequency induced by the collector plasma, the extraction cavity width was increased from the simulation-optimized value of 3.5 to 3.7 mm. After extensive parameter scanning involving 822 combinations, stable high-power microwave output was achieved at 515 kV and 10 kA, with a frequency of 15.08 GHz, a power of 1.1 GW, a repetition rate of 20 Hz, and a pulse width of 27 ns. This study reveals the intrinsic reasons for the deviation of parameter sensitivity from simulations under a low magnetic field and provides an important reference for the experimental optimization of similar devices.