Microwave plasma chemical vapor deposition diamond output window for 3 mm gyro-traveling wave tube

The sapphire window for 3 mm gyro-traveling wave tube(TWT) can not meet the design requirement of power capacity. To solve the problem, comparisons of several materials in power capacity and thermal shock resistance are carried out. A microwave plasma chemical vapor deposition(MPCVD) diamond window of low reflectivity and absorption for 3 mm high power gyro-TWT is designed by using numerical calculation and simulation. The results indicate that the designed MPCVD diamond window is appropriate for outputting TE01 mode, the bandwidth in which S11 is less than -20 dB is about 6 GHz. In addition, the thermal shock resistance of the window is good and the power capacity is about 61 kW in the condition of natural convection heat dissipation.