Simulation of collective ion acceleration in a slow cyclotron beam mode

Slow cyclotron beam waves provide an attractive means for accelerating ions in intense relativistic electron beams.^1-3 There are several characteristics of this mode which lend themselves directly to collective acceleration. First and most important is the field magnitude which can be generated in current electron beams (I = 10-50 kA; γ = 6 - 10) with cyclotron waves. Fields between 10⁵ - 10⁶ V/cm seem achievable in the near term. These can never reach the levels of beam front mechanisms, such as virtual cathodes, but easily exceed conventional ion acceleration sources. Second, the cyclotron phase velocity can be controlled externally and can be reduced far below that of the other collective mode, the slow space-charge beam wave. This facilitates ion loading and permits operation in low velocity regimes that are difficult even for conventional accelerators. An extreme limit of this is the commonly observed zero-frequency cyclotron wave, which possesses a phase velocity of zero in the laboratory frame. Use of this mode has been explored by us and will be discussed later. Finally, the slow cyclotron wave is moderately insensitive to transverse beam spread, or scatter. This relaxes a constraint on beam quality.