Diffractive Quality Factor Research Articles

Scattering in a corrugated-wall cavity

It is shown from theory and experiment that the spectrum and structure for the radiation from a corrugated cylindrical cavity in a relativistic uhf generator are determined in particular by the reradiation (scattering) at the corrugations. The diffraction quality factor for a cavity having length L can in principle be less than ~L/vli, while the emission from the cavity may include waves having transverse indices differing from those for the working mode. In a relativistic uhf electron-beam oscillator, it is comanon to use an electrodynamic system in the form of a cylindrical guide segment having corrugated walls [1-3]o A resonant system of that type usually has a large cross section, and the radiation is extracted by diffraction. A typical example is provided by the cavity in a relativistic orotron [2, 3], which is a segment of a slightly irregular corrugated waveguide (Fig. i), where the working mode consists of a set of spatial harmonics, of which the main one (largest in amplitude) is formed by rays propagating almost transverse to the guide, while the other and relatively weak retarded harmonics include one synchronous with the electrons. The radiation is usually extracted from such a cavity bY means of a smoothly expanding conical horn; it is assumed that the transverse output structure (higher-type wave) is close to the fundamental field in the cavity. However, in some hot experiments it has been found that the output radiation from a relativisitc orotron may contain some other waveguide waves, one reason being scattering directly in the cavity at the corrugations having a finite number of periods (N = i0) comparable with the wavelength.