  Particle accelerations by a 1D, EM, dispersive pulse in an external magnetic
field are investigated. It is found that the well-known cyclotron resonance may
be classified into three regimes as the length and/or the amplitude of the
pulse are varied. Namely, as the pulse amplitude increases, the transit-time
cyclotron-resonance acceleration [CRA] evolves to phase trapping, and reflect
particles. The amplitude and wave dispersion as well as the pulse length
strongly affect those accelerations. The interesting phenomena of quantization
of resonance velocities in between the two regimes are also investigated. This
new mechanism may lead to wave amplification at some discrete frequencies other
than the cyclotron frequency.
