Electrical and Thermal Design of a $W$ -Band Gyrotron Interaction Cavity

In this paper, the design of an interaction cavity for a W-band gyrotron with a 55-kV, 5-A beam has been presented. For the above purpose, a parametric design code has been developed. The mode of interaction has been selected as TE6,2. The large-signal analysis was carried out using the code Gyro-K for four differed lengths of the cavity, such as 24, 25, 26, and 27 mm to estimate the output power. The diffractive quality factor and ohmic loss have also been computed for all these four lengths of cavity. For the sake of cooling the cavity, 16 numbers of cooling channels are proposed surrounding the cavity with deionized water flowing through the channels at an ambient temperature of 20 °C with the flow-rate of 8 L/min. As the cavity length increases, the diffractive quality factor and the output power increase. However, with the increase of cavity length, the ohmic loss and thermal load also increase. And this eventually leads to higher cooling requirements. The steady-state temperature distribution for the cavity of four different lengths is computed using FloEFD software. Also, the transient analysis was carried out for a pulselength of 100 ms and 10% duty with and without cooling. In view of these results, the cavity length of 26 mm is proposed as the optimum length of the cavity.