Stability Analysis of a Planar Multiple-Beam Circuit for W-Band High-Power Extended-Interaction Klystron

Circuit analysis of a multiple-beam version of a high-power extended-interaction klystron is performed. The circuit is based on the barbell cavity with five coplanar electron beams across the transverse section of the cavity. Although the basic circuit design is straightforward, stable operation is challenging due to the mode competition and the self-oscillation in an oversized multiple-gap cavity driven by multiple beam sources. The 3-D particle-in-cell (PIC) simulation technology and the space-charge wave theory were exploited to analyze the stability. The physical design of the interaction system was accomplished with the beam parameters of voltage 19 kV and of overall current 4 A (0.8 A x 5). PIC results show that a power of 11.28 kW can be achieved at a frequency of 94.48 GHz with an instantaneous 3-dB bandwidth of 160 MHz. The corresponding gain and electric efficiency are 55.75 dB and 14.84%, respectively.