Investigation of Fluid and Thermal Analysis in the Interaction Circuit for Ka-Band Sheet Beam Traveling Wave Tube

Achieving perfect sheet beam transmission through the interaction circuit remains a critical challenge in the sheet beam traveling wave tube (SB-TWT). Particle-in-cell (PIC) simulations reveal that electron interception predominantly concentrates at the terminal region of the interaction circuit, generating highly localized heat fluxes. This nonuniform power density induces temperature spikes ( $\gt 350~^{\circ }$ C) and vacuum degradation due to outgassing, necessitating advanced thermal management strategies. This article proposes a novel embedded heat sink unit (EHSU) for Ka-band SB-TWTs, which integrates a staggered grid structure of the interaction circuit and boundary layer suppression to address localized overheating. A model of the heat sink unit, as well as its thermal resistance network was constructed and analyzed for its thermal and fluid behavior. The EHSU framework resulted in a maximum temperature reduction of about 40%. The prototype was fabricated, and the hot test showed it operated stably for long periods of time at an average power of 3 kW. The titanium pump current (Ti-current) was stabilized at approximately 60 nA for over an hour.