Investigation of Power Capacity in the Output Window for a High-Power W-Band Gyro-TWT

To further enhance the average output power of the W -band gyrotron traveling-wave tube (gyro-TWT), the power capacity of the output window is investigated in this article. In the case of the original meta-surface dielectric window (MSDW), the primary factors leading to window failure and air leakage under high-power conditions are the high residual thermal stress at the weld surface. Based on the experimental phenomenon, the derived reference threshold for braze surface fracture is 113 MPa. Then, the idea of a multiwavelength window and the addition of boundary heat transfer channels are proposed. Thermal analysis results show that the maximum temperature and side thermal stress are 102 ^{\circ} C and 61 MPa, respectively. The novel cooling system demonstrates a 28% improvement in cooling efficiency compared to the initial structure. The power capacity of the thickened MSDW is 26 kW and increased by 44%. The output window is fabricated and experimented. The mechanical strength and the vacuum seal of the window are guaranteed by the new assembly technology. Cold test results validate that \textit{S}_{\text{11}} is lower than - 15 dB in the operating bandwidth and are in good agreement with the simulation results. These investigations provide insights for achieving the stable operation of high-frequency gyro-TWTs at high power levels.