X-Band TM 02 Klystron-Like Relativistic Backward-Wave Oscillator Design via Tree-Encoding-Based Hierarchical Parameter Optimization

This article presents a tree-encoding-based multiobjective optimization algorithm (TMOA) for the hierarchical parameter (HP) optimization of high-power vacuum electronic devices (HPVEDs). The TMOA considers the structural parameter correlations of the HPVEDs, enabling integrated optimization of both the number of periods in the device’s high-frequency structure and the parameters of each unit. An efficient X-band TM${}_{\mathbf {{02}}}$klystron-like relativistic backward-wave oscillator (KL-RBWO) is designed using the TMOA. Particle-in-cell (PIC) simulations show that the TM${}_{\mathbf {{02}}}$KL-RBWO achieves an output power of 2.5 GW at a diode voltage of 736 kV, a current of 9.2 kA, and a guiding magnetic field of 2.8 T, with a frequency of 9.6 GHz and a beam-to-microwave conversion efficiency improved to 36.9%. Mechanism analysis indicates that the efficient KL-RBWO exhibits improved phase matching between the axial electromagnetic field and electron current, more reasonable energy spread in the electron beam, and more favorable harmonic current distribution.