1. I. L. Korenev, L. A. Yudin, and Kh. Kh. Mustafin, Izv. Vyssh. Uchebn. Zaved., Radiofiz.,22, No. 12, 1523 (1979).
2. V. M. Lopukhin, Excitation of Electromagnetic Oscillations and Waves by Electron Streams [in Russian], Gostekhizdat, Moscow (1953).
3. M. L. Sloan and W. E. Drummond, Phys. Rev. Lett.,31, No. 20, 1234 (1973).
4. B. I. Ivanov, D. V. Gorozhanin, and V. A. Miroshnichenko, Pis'ma Zh. Tekh. Fiz.,5, No. 18, 1112 (1979).
5. Dzh. Pirs, Traveling Wave Lamps [in Russian], Sov. Radio, Moscow (1952).