Linear and nonlinear investigation of a coaxial-waveguide cyclotron autoresonance maser amplifier

A different concept of gyrodevices in the form of a coaxial-waveguide cyclotron autoresonance maser (CARM) is proposed. Embodying the salient features of large cross-sectional area, low guiding magnetic field, and good mode selectivity as compared to the gyrotron and to the conventional CARM, the proposed device is well suited for operation at both high power and ultrahigh gain in the millimeter wave and far infrared regions. Gyrokinetic analysis and nonlinear simulation are given in detail for a coaxial configuration—with outer and inner radii of 1.83 and 0.50 cm—designed to operate in the $TE28,16$ mode at 335 GHz, yielding a gain of 64 dB on using a 90 keV and 50 A electron beam confined by a 9.35 T magnetic field. Nonlinear simulation demonstrates the possibility of power enhancement via a tapered magnetic field. The competition of the degenerate mode and the excitation of the absolute instability are discussed.