Two-dimensional simulation studies of the electron beam-plasma instability

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Abstract
Two-dimensional simulations of the electron-beam plasma instability with large system size are carried out and are compared with recent one-dimensional simulations for plasma parameters appropriate to the electron foreshock. It is found that wave propagation and diffusion perpendicular to the beam drift are significant at all times. Because a plateau cannot be maintained in this case, the wave level decreases much more rapidly than in one-dimensional simulations. The nonlinear wave scattering process which occurs at late times also differs in that it generates a broad secondary spectrum rather than a condensate. The two-dimensional model, in addition, allows the investigation of the effects of increasing magnetic field strength (e.g., along auroral field lines). For intermediate magnetic fields Langmuir waves and a highly oblique spectrum belonging to the lower hybrid branch are simultaneously excited. The oblique wave spectrum for strong magnetic fields can be explained by mapping from the magnetic field direction.