BEAM-GENERATED PLASMA TURBULENCE DURING SOLAR-FLARES

We develop a simple theoretical model to analyze the harmonic plasma r adiation produced by an electron beam injected in a flaring loop and t raveling along its magnetic field lines. For a given atmospheric model , we consistently consider collisional effects and the generation of L angmuir waves as a function of the atmospheric depth. Langmuir wave ge neration is assumed to saturate by quasilinear relaxation, which in tu rn causes the electron distribution function to develop a plateau at i ts low-energy end. We formulate an iterative procedure to integrate th e coupled equations for the electron distribution function and the wav e energy density, taking advantage of the fact that quasilinear relaxa tion occurs on times much shorter than the collisional timescale. From the wave energy density as a function of depth, we computed the micro wave flux generated by second harmonic radiation, taking into account the optical thickness due to the reverse process. Previous studies yie ld microwave fluxes much larger than those derived from observations. The smaller levels of turbulence obtained from this model, and the low er emissivity due to the relaxation of the head-on approximation, cont ribute to reduce significantly the predicted microwave emission. We su ggest that the simplicity of the present model makes it suitable for t he quantitative analysis of spatially resolved radio observations in t he GHz range.