Beam-plasma instability in inhomogeneous magnetic field and second order cyclotron resonance effects

A new analytical approach to cyclotron instability of electron beams with s harp gradients in velocity space (step-like distribution function) is devel oped taking into account magnetic field inhomogeneity and nonstationary beh avior of the electron beam velocity. Under these conditions, the convention al hydrodynamic instability of such beams is drastically modified and secon d order resonance effects become important. It is shown that the optimal co nditions for the instability occur for nonstationary quasimonochromatic wav elets whose frequency changes in time. The theory developed permits one to estimate the wave amplification and spatio-temporal characteristics of thes e wavelets. (C) 1999 American Institute of Physics. [S1070-664X(99)02003-0] .