Trapping of Langmuir waves in Ion Holes

Abstract

We present analytical and numerical studies of a new electron plasma wave interaction mechanism which reveals trapping of Langmuir waves in ion holes associated with non-isothermal ion distribution functions. This Langmuir-ion hole interaction is a unique kinetic phenomenon, which is governed by two second-order nonlinear differential equations in which the Langmuir wave electric field and ion hole potential are coupled in a complex fashion. Numerical analyses of our nonlinearly coupled differential equations exhibit trapping of localized Langmuir wave envelops in ion holes which are moving with sub- or super ion thermal speeds. The resulting ambipolar potential of the ion hole is essentially negative, giving rise to bipolar slow electric fields. The theoretical predictions are investigated numerically with a fully kinetic Vlasov code, and are found to be in qualitative agreement with the numerical results. Furthermore, a process for the generation of Langmuir waves by colliding ion holes is studied numerically.