Science Seminars

5/4/2016- Konrad Sauer; Current-driven Langmuir oscillations and wave packet formation in plateau plasmas: Relevance to type III bursts

Speaker: Konrad Sauer (Univ. of Alberta)
Date: Monday, May 04, 2020
Time: 11:00 AM
Location: SPSC N100

Seminar Abstract:

Instead of starting with an unstable electron beam, the excitation of Langmuir waves is considered in the stable two-electron plasma after beam stabilization in which the velocity distribution function of the second population forms a plateau (p) with a more or less extended region of ¶fp/¶v=0. As shown by PIC simulations, this so-called plateau plasma is stable over long times without remarkable change of the distribution function and drives two types of Langmuir waves by its associated current: 1) Langmuir oscillations at w=we and 2) Langmuir waves with finite wave number whose phase velocity is correlated with the point where according to ¶fp/¶v=0 Landau damping disappears. Both current-driven electrostatic waves have nearly the same amplitude which is simply given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in good agreement with space observations if Doppler frequency shifts are taken into account. Higher-order effects, as second harmonic and ion-acoustic wave generation are considered, too.