Coupled cavities by rods (TWTs)

The average power capability of conventional coupled cavity TWTs (traveling-wave tubes) is limited by the maximum amount of heat transfer from the ferrules to the cooling walls. An unconventional structure, allowing a remarkable improvement in the thermal capability of such tubes, is proposed. It operates in the fundamental backward wave mode. The structure uses two conducting rods: one rod connects alternate pole pieces and the other connects the other pole pieces. Heat transfer capability is improved because of the small dimensions of coupling holes compared to the kidney iris. A preliminary thermal analysis showed that the maximum temperature of the ferrules was decreased by 50-70 degrees C against the more conventional structure (X-band 1.5-kW average power TWT). The performance of an eight-cavity experimental structure is in good agreement with the equivalent model studied; 10% bandwidth and 700-W minimum interaction impedance have been obtained.<
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