A Particle-in-Cell Simulation of Double Layers and Ion-Acoustic Waves

Double layers and ion-acoustic waves are investigated by using a one-dimensional electrostatic particle-in-cell simulation code. Our results show that double layers can be formed even when the drift velocity between electrons and ions is less than the electron thermal velocity. Electron and ion density depressions were clearly seen. Electrons gradually developed a distribu- tion comprising both background and beam components. In fact, as the initial electron-ion drift velocity was less than the electron thermal velocity, intense ion-acoustic waves could be found only at the places where the electron beam was located, suggesting that they are excited by the self-consistently developed electron beam. Besides the Langmuir waves and ion-acoustic waves, the beam mode excited by electron beams produced in our simulation has been clearly found.

Kinetic Electron-Ion Two Streams Instability in Space Dusty Plasma with Temperature Gradient

The excitation, growing and damping of current instability is an important and vital subject for a lot of studies through its importance in communication for instance and in understanding the nature of space and the interpretation of many phenomena in space and astrophysics. Recent analytical and numerical works are presented to describe and investigate the excitation and growing of kinetic electron-ion two streams instability in anisotropic inhomogeneous dusty space plasmas. We elucidated the thermal effects of plasma species on the characteristics of such instability. It is found that the gradient of space plasma temperature, , is a cause of interesting physical phenomena. Besides, different parameters, such as electron to ion temperature ratio , magnetized plasma and dust grains, are also found to play a crucial role in the growth and depression of such instability.

Two Stream Instability as a Source of Coronal Heating

Recent observation of oscillating the two stream instability (TSI) in a solar type III radio bursts and spatial damping of Langmuir oscillations has made this instability as an important candidate to understand the coronal heating problem. This instability has been studied by several authors for cold plasma found to be stable for high frequencies (greater than plasma frequency ωp). In this paper, we prove that this instability is unstable for warm plasma for higher frequencies (greater than plasma frequency ωp) and much suitable to study the solar coronal heating problem. We have derived a general dispersion relation for warm plasma and discussed the various methods analyzing the instability conditions. Also, we derived an expression for the growth rate of TSI and analyzed the growth rate for photospheric and coronal plasmas. A very promising result is that the ion temperature is the source of this instability and shifts the growth rate to high frequency region, while the electron temperature does the reverse. TSI shows a high growth rate for a wide frequency range for photosphere plasma, suggesting that the electron precipitation by magnetic reconnection current, acceleration by flares, may be source of TSI in the photosphere. But for corona, these waves are damped to accelerate the ions and further growing of such instability is prohibited due to the high conductivity in coronal plasma. The TSI is a common instability;the theory can be easily modifiable for multi-ion plasmas and will be a useful tool to analyze all the astrophysical problems and industrial devices, too.

Propagation dynamics of relativistic electromagnetic solitary wave as well as modulational instability in plasmas

By one-dimensional particle-in-cell(PIC) simulations, the propagation and stability of relativistic electromagnetic(EM) solitary waves as well as modulational instability of plane EM waves are studied in uniform cold electron-ion plasmas.The investigation not only confirms the solitary wave motion characteristics and modulational instability theory, but more importantly, gives the following findings. For a simulation with the plasma density 10^(23) m^(-3) and the dimensionless vector potential amplitude 0.18, it is found that the EM solitary wave can stably propagate when the carrier wave frequency is smaller than 3.83 times of the plasma frequency. While for the carrier wave frequency larger than that, it can excite a very weak Langmuir oscillation, which is an order of magnitude smaller than the transverse electron momentum and may in turn modulate the EM solitary wave and cause the modulational instability, so that the solitary wave begins to deform after a long enough distance propagation. The stable propagation distance before an obvious observation of instability increases(decreases) with the increase of the carrier wave frequency(vector potential amplitude). The study on the plane EM wave shows that a modulational instability may occur and its wavenumber is approximately equal to the modulational wavenumber by Langmuir oscillation and is independent of the carrier wave frequency and the vector potential amplitude.This reveals the role of the Langmuir oscillation excitation in the inducement of modulational instability and also proves the modulational instability of EM solitary wave.

The Evolution of Instabilities Driven by a Drift Between Ions and Electrons in Nonmagnetized Plasma

The electron-ion beam instability is studied by one-dimensiong electrostatic particle-in-cell simulation. When the relative drift velocity between the electron and ion is suf- ficiently less than the electron thermal speed, the dominant mode is the Langmuir wave; the ion-acoustic instability is very weak; the Buneman instability is not excited. When the relative drift speed is equal to the electron thermal speed, the Langmuir wave, the ion-acoustic and the Buneman instability nearly exist simultaneously. The three instabilities now appear to have al- most equal intensities. When the relative drift speed exceeds the electron thermal speed, the ion-acoustic instability turns into the Buneman instability which appears to have much higher intensity than the Langmuir wave.