Relativistic electron beam cyclotron wave growth in helical slow wave structures

One of the more promising and thoroughly studied proposals for high energy collective ion acceleration is Autoresonant Acceleration: Ions trapped in the electrostatic wells of large amplitude slow cyclotron waves in an unneutralized intense relativistic electron beam are accelerated by the increase of wave phase velocity as the beam propagates along a magnetic guide field of decreasing strength. A critical component of this scheme is growth of coherent, large amplitude waves. Here, we consider wave growth by interaction of the beam with a helical slow wave structure. Specific topics include (1) equilibrium charge and current distributions on the helix, (2) linear wave growth spectra including the effects of radial inhomogeneity, (3) wave growth and saturation, and (4) extraction of cyclotron waves from the amplifier cavity. Movies of two-dimensional computer simulations are presented. We find that waves of amplitude adequate for planned feasibility experiments can indeed be obtained.