Results of testing a 3 MW, 140 GHz coaxial gyrotron

Summary form only given. We present experimental results of a high-power, high-frequency coaxial gyrotron. The inner conductor of a coaxial cavity influences the spectral density of the resonant modes and their corresponding quality factors. The operating mode is then chosen to remain essentially unaffected by the presence of the inner conductor, whereas competing modes see their Q lowered. As a result, multimode competition is avoided and an operating mode with a high radial index can be chosen, leading to a potentially higher output power with the same level of average ohmic losses. A coaxial gyrotron designed to produce 3 MW at 140 GHz has been built and tested at MIT. The main parameters of the tube are summarized.