ABSTRACT
Considered in this chapter, classical vacuum electron devices based on “electron beam-slow-wave” synchronism, such as backward wave oscillator (BWO) [1], Carcinotron [2], clinotron [3], orotron [4], and diffraction radiation oscillator (DRO) [5, 6], have been widely used in microwaves due to outstanding performances combining high levels of output power and wide frequency tuning range. Therefore, at present many research and development activities are focused on filling the THz gap with the help of mentioned above devices. However, there are several reasons for a drastic output power drop in those devices with the wavelength shortening that results in small efficiency of those tubes in the THz frequency range and, therefore, it limits their practical applications. Among these reasons, the most special ones are as follows: (1) technological constraints in the manufacturing of small-scale slow-wave circuits and other components of the tubes; (2) requirements in generation and transportation of the intense electron beams including the problems of fabrication of magnetic system; (3) increase in electromagnetic wave attenuation caused by ohmic losses due to metal surface roughness and skin layer effects; (4) problems of electromagnetic energy extraction from the small-scaled slow-wave circuits, as well as mode competitions, etc.
