The Design of Megawatt Gyrotrons

The design parameters of a 120-GHz gyromonotron capable of output powers in excess of 1 MW are determined through a nonlinear model that assesses the interaction between the beam and RF field, emphasizing the efficiency as a function of three normalized variables. Factors such as ohmic heating, voltage depression, and beam thickness are carefully incorporated into the framework to calculate permissible design parameters that ensure high efficiency operations. A notable design achieving an 80-kV 29-A output with a total efficiency of 44% is presented, alongside the challenges posed by parasitic modes that may affect power delivery and performance. The analysis reveals that, while lower-order modes offer options at reduced voltages, the current constraints complicate their application. Furthermore, it is shown that operations exceeding 20 MW are within reach if single-mode performance is realized with very-high-order modes. The methodology showcased is not restricted to the specific parameters of the gyromonotron discussed; it can be adapted for various frequencies and power outputs, providing a comprehensive approach to gyrotron design and operation.