Nonlinear Dynamics of Beam–Plasma Instability in a Finite Magnetic Field

Abstract—The nonlinear dynamics of beam–plasma instability in a finite magnetic field is investigated numerically. In particular, it is shown that decay instability can develop. Special attention is paid to the influence of the beam−plasma coupling factor on the spectral characteristics of a plasma relativistic microwave accelerator (PRMA) at different values of the magnetic field. It is shown that two qualitatively different physical regimes take place at two values of the external magnetic field: B₀ = 4.5 kG (${{\Omega }_{B}} \simeq {{\omega }_{p}}$) and 20 kG (${{\Omega }_{B}} \gg {{\omega }_{p}}$). For B₀ = 4.5 kG, close to the actual experimental value, there exists an optimal value of the gap length between the relativistic electron beam and the plasma (and, accordingly, an optimal value of the coupling factor) at which the PRMA output power increases appreciably, while the noise level decreases.