Dielectric Cherenkov maser as a powerful amplifier with superwide bandwidth

Abstract

An important feature of dielectric Cherenkov masers (DCM), distinguishing them from other FEL kinds is emphasized. So far practically all DCM experiments were carried out with rather thin dielectric liners or films. Meanwhile, when the coefficient of waveguide filling by the dielectric is not small, the beam wave coupling doesn't depend on frequency, and, hence, superwide bandwidth is possible. The value of bandwidth is significantly determined also by the current and velocity of electron beam. In this context DCM dispersion relations have been analysed: analytically in simplest of total waveguide filling and numerically, for a hollow beam in a wavequide with dielectric liner. It has been shown that maximum value of bandwidth is achieved at a certain optimal value of the beam current for fixed velocity (and vice versa). Numerical results demonstrate the -3 dB bandwidth of 40-50% at a peak gain of 40 dB for usual electron energies (300-600 keV) and beam currents (1-10 kA). Also, an effect of discontinuous gain disappearance at a lower boundary of the band has been found.