Starting currents of modes in cylindrical cavities with mode-converting corrugations for second-harmonic gyrotrons - Tetiana I. Tkachova; Vitalii I. Shcherbinin; Viktor I. Tkachenko; Ioannidis, Zisis C.; Thumm, Manfred; Jelonnek, John (Journal of Infrared, Millimeter, and Terahertz Waves, 2021)