Generation of quasi‐isotropic electron population during nonlinear beam‐plasma interaction

Abstract

The nonlinear interaction of a single or a bidirectional electron beam and a background plasma is analyzed on the basis of electrostatic weak turbulence theory. It is found that for a sufficiently high electron beam density, the nonlinear interaction produces quasi‐isotropic electron population. This is in contrast to our previous finding in which a relatively low electron beam density was adopted, and for which complete isotropization was not achieved. The present finding may thus provide a possible explanation for the observed isotropic solar wind electron distribution within the context of electrostatic nonlinear theory involving Langmuir and ion‐sound turbulence, without the resorting to additional mechanisms such as the pitch angle scattering by electromagnetic whistler turbulence.