STUDY AND ANALYSIS OF PARASITIC OSCILLATIONS IN GYROTRONS

Abstract

Gyrotrons (gyromonotrons) are best suitable high power microwave devices for generation of high powers at microwave and millimeter regimes when comparing with conventional microwave tubes, used for plasma/fusion experiments. In present work, we focus on the problem of parasitic oscillations in the high power gyrotrons. Their origin can be anywhere in the whole geometry either in the region after the gyrotron interaction cavity or before. They can lead to a dynamic modulation of the output power or degrade the efficiency of the gyrotron. The major question which arises is, at which position these parasites are generated and which modes other than cavity mode are excited. The spurious frequencies generated by the parasitic oscillations are the most valuable and direct source of information about the parasites. To analyze such measured frequencies, a new tool called "Brillouin Analysis Tool" was developed in MATLAB. This tool is applied to different Ineasureniemit data from the KIT step-tunable gyrotron and some also from the W7-X 140 GHz gyrotron to Bud the position and mode of measured parasitic oscillations. The investigation of the coupling coefficient variation is a key feature to find the suitable modes of the parasites. The Coupled dispersion relation is also included in the tool to observe the brillouin diagrams. It can be applied to both the cavity mode and the parasites. The tool is also capable to observe the distraction from the uncoupled interaction frequency of the analysing mode (as observed experimentally also).