LANGMUIR TURBULENCE IN MODERATELY MAGNETIZED SPACE PLASMAS

Beam-driven Langmuir turbulence is studied in two moderately moderatel y magnetized (OMEGA(e) almost-equal-to omega(e)) space-plasma regimes: regions of the lower solar corona and the Earth's auroral ionosphere. The turbulence is modeled using modified Zakharov equations, which ar e employed in two-dimensional numerical simulations. For coronal param eters, highly anisotropic coherent wave packets form and collapse when OMEGA(e) < omega(e). By contrast, the turbulence is phase incoherent when OMEGA(e) > omega(e), as a result of change in the topology of the Langmuir dispersion relation. In the auroral ionosphere, intense Lang muir waves (up to 500 mV/m) have been measured, in conjunction with fi eld-aligned electron streams and nonthermal electron tails. Approximat e agreement with high-time-resolution electric-field measurements, is found in the simulations. However, because of strong damping on nonthe rmal electrons, wave collapse is inhibited, irrespective of the orderi ng of OMEGA(e) and omega(e).