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Study of instabilities in a double-staggered waveguide sheet beam TWT

The instabilities in a Ka-band double- staggered grating waveguide sheet beam TWT is studied in this paper based on CST particle-in-cell (PIC) simulation. The geometrical parameters are optimized to realize the broadband operation. Through the stability analysis of the slow wave structure (SWS), the regenerative oscillation is not only induced by outside port reflection produced by output and input coupler but also caused by inside refection (SWS).As for the outside reflection, it can be suppressed well by carefully design of the input and output coupler. An input signal with a continuous frequency sweep is employed in PIC simulation for studying this inside regenerative oscillation. At last, two methods for suppressing the oscillation have been put forward and proven effective.