The influence of plasma on the amplification of traveling slow waves

Summary form only given, as follows. The performance of traveling wave tube amplifiers is limited by the need to keep the electron beam close to the wall of the slow wave structure. We investigate the possibility of relaxing this constraint by propagating the beam through a magnetized plasma channel. This approach has already found success in the case of a coupled cavity TWT. The role of the plasma is to modify the transverse structure of the amplified wave so that the axial electric field of the wave peaks on the axis of the device. This effect is most dramatic when a so called ´hybrid mode´ representing a coupled electromagnetic slow wave and a Trivelpiece-Gould mode is formed. The theory addresses the linear gain of a sheath helix TWT driven by a solid beam and filled with a plasma of the same radius as the beam. Numerical results of gain and bandwidth for a variety of parameters are presented.