The spatial structure of a nonthermal electron beam - Conditions for stabilization via strong turbulence

The stability and propagation of nonthermal electron beams that produce type III solar radio bursts is studied. A model for the spatial structure of such a beam, based on the physics of strong Langmuir turbulence, is presented. In this model it is assumed that the beam-generated waves reach the threshold for nonlinear (modulation) instability over a narrow spatial region. This region, denoted the beam "front", moves at a velocity that corresponds to the velocity deduced from the type III drift rate. Assuming a steady state, the wave and particle distributions, as functions of velocity and distance ahead of the front, are computed self-consistently, using quasi-linear theory in a frame that moves with the front.