A nonlinear theory of premodulated electron beam propagating through a helix-loaded waveguide

Abstract

Summary form only given, as follows. One of the most important issues in the charged particle beam physics is evolution of prebunched beam during propagation. The prebunched charged particle beams have various applications, including accelerator physics, relativistic klystron amplifiers, and high-power traveling wave tubes. Particularly, the prebunched beam train may provide a compact devices for these applications. It is therefore important to investigate evolution of beam profile during propagation in downstream. In this presentation, we develop a self-consistent nonlinear theory of prebunched electron beam propagating through a helix-loaded waveguide. The prebunched beam particles move downstream with traveling waves of electric potential caused by non-uniform charge distribution along the propagation direction. A closed integrodifferential equation for the beam current is obtained in terms of time and propagation distance. The equation consists of the space-charge force caused by the self-electric field and of the helix effects. Properties of the current and energy modulations are investigated from this equation for a broad range of system parameters. Linearization of the integrodifferential equation leads to the mode evolution of individual mode during propagation. It is observed from the linear theory that the mode grows exponentially when the helix effects dominate. On the other hand, for an intense beam, the space charge oscillation occurs at the beginning of the propagation. However, all the modes grow exponentially in a long range propagation regardless of the beam intensity.