High-Power Microwave Oscillation of a 94 GHz Gyrotron for Air-Breakdown Plasma Observations in Microwave Rocket

We report high-power microwave oscillation of a 94 GHz gyrotron, contributing to the study on air breakdown plasma in Microwave Rocket. The gyrotron is demountable, adopting a diode magnetron injection gun and a built-in quasi-optical mode converter, installed in a compact superconducting magnet with a bore diameter of 100 mm. In this study, microwave signal was detected using a pyroelectric detector and a liquid thermograph sheet at the beam voltage of 40 kV and beam current of about 20 A. Besides, air breakdown plasma, useful for the thrust generation of Microwave Rocket, was successfully ignited at atmospheric pressure. The observed plasma's filamentary structure at the propagation velocity of 720 m/s was different from 170 GHz, which indicates a frequency dependence of the plasma structure.