LINEAR-THEORY OF A WIDE-BAND GYRO-TWT AMPLIFIER USING SPIRAL WAVE-GUIDE

A novel electrodynamic system to realize high efficiency and a broad f requency band in a gyro-TWT amplifier at millimeter and microwave freq uencies is described. A cylindrical waveguide having a helically groov ed wall selectively couples an electromagnetic waveguide mode at a fre quency close to cutoff to the forward travelling wave of a lower mode, resulting in an eigenwave with a constant positive group velocity and approximately zero axial wavenumber over a wide frequency band. For a travelling-wave gyroamplifier, such a dispersion characteristic permi ts operation with significantly increased bandwidth and reduced sensit ivity to electron-beam axial velocity spread. Numerical calculations w ill be presented to show the beam-coupled dispersion characteristics, stability, and gain profiles of a simple amplifier, based upon a linea rized coupled-wave theory.