Identifying parasitic oscillations at 570 and 600 MHz in a 170-GHz gyrotron collector

Parasitic oscillations cause undesirable electromagnetic wave emissions from gyrotrons. In a recent study using a 170-GHz gyrotron, waves with a frequency of approximately 570 MHz were observed, which potentially indicated the occurrence of parasitic oscillations in the gyrotron. However, the site of this excitation was not likely at well known gyrotron components such as the beam tunnel and cathode. This study examined parasitic oscillations in a 170-GHz gyrotron to identify the site of their excitation. Frequency measurements showed that waves with a frequency of approximately 570 and 600 MHz were generated. In addition, the wave excitations were observed only at certain collector coil currents, potentially indicating that the parasitic oscillations were excited at the collector. Therefore, resonance frequencies around the collector (including window and DC break sections) were calculated and measured. The calculated and measured resonant frequencies were consistent with the frequencies of the parasitic oscillations. Thus, this study determined that the parasitic oscillations were excited at the collector and the resonance frequencies were determined by the inner shape around the collector. The findings of this study enhance the understanding of unintended wave-generation mechanisms in high-power gyrotrons, which is essential for improving their operational reliability.