Design and Experiment of Sapphire Output Window for 170 GHz Gyrotron

In order to satisfy the energy transmission requirements of 170GHz gyrotron, sapphire output window with low reflectivity of 100mm in diameter and 1.44mm in thickness was selected. Through the experimental test, the output power of 170 GHz gyrotron is approximately 0.3MW under the condition of 0.25% duty ratio. Under the pulse width of 2.5ms and pulse repetition frequency of 1Hz, the sapphire output window is broken and damaged. According to the thermal and structure simulation, the reason for the damage of the window is that the temperature difference between the centre and the edge exceeds the bearing limit of sapphire material. By comparing theoretical analysis with experimental phenomenon, it provides a reliable theoretical basis for the gyrotron experiment and the optimization of the structure of the output window.