Simulation and theory for two-dimensional beam-plasma instability

A comparative study of the dynamics of the electron beam-plasma system in two spatial dimensions is carried out by means of particle-in-cell (PIC) simulation and quasilinear theory. In the literature, the beam-plasma instability is usually studied with one-dimensional assumption. Among the few works that include higher-dimensional effects are two-and three-dimensional quasilinear theory and two-dimensional PIC simulations. However, no efforts were made to compare the theory and simulation side by side. The present paper carries out a detailed comparative study of two-dimensional simulation and quasilinear theory. It is found that the quasilinear theory quite adequately accounts for most important features associated with the simulation result. For instance, the particle diffusion time scale, the maximum wave intensity, dynamical development of the electron distribution function, and the change in the wave spectrum all agree quantitatively. However, certain nonlinear effects such as the Langmuir condensation phenomenon are not reproduced by the quasilinear theory. Nevertheless, the present paper verifies that the simple quasilinear theory is quite effective for the study of beam-plasma instability for the present choice of parameters. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3529359]open1155Nsciescopu

MULTIPLE HARMONIC PLASMA EMISSION

Electromagnetic radiation at the plasma frequency and/or its second harmonic, the so-called plasma emission, is widely accepted as the fundamental process responsible for solar type II and III radio bursts. There have also been occasional observations of higher-harmonic plasma emissions in the solar-terrestrial environment. This paper presents the first demonstration of multiple harmonic emission by means of two-dimensional electromagnetic particle-in-cell simulation. This finding indicates that under certain circumstances the traditional mechanism of fundamental-harmonic pair emission might also be accompanied by higher-harmonic components. Consequently, the present findings are highly relevant to in situ observations of third- and/or higher-harmonic plasma emission in astrophysical and solar-terrestrial environments.open111313sciescopu

A low frequency coherent structure driven by turbulence in a Hanbit mirror plasma

Ion saturation currents in a Hanbit mirror plasma have been analyzed by using the wavelet bispectral method. From this bicoherence analysis, an interesting phase coherent mode has been found at a very low frequency. This mode seems to be generated by the low frequency turbulence which could be identified as either ion drift waves or interchange modes. The wave coupling process leading to this coherent structure is found to follow the resonant three-wave coupling with an exact frequency match. A brief review is given on this coherent turbulence structure in a Hanbit mirror plasma.X111sciescopu

1D PIC simulation study of nonlinear beam plasma interaction

Since the early days of plasma simulation studies, superthermal electrons having energies much greater than the injected beam electrons have been widespreadly observed. The origin of such superthermal tail in the electron velocity distribution is generally believed due to the second order Fermi acceleration, i.e. the acceleration due to turbulence. In this paper, generation of superthermal electrons is studied by using a 1D PIC simulation code. (C) 2007 Elsevier B.V. All rights reserved.X113sciescopu

Simulation Study of Plasma Emission in Beam-Plasma Interactions

A two-dimensional electromagnetic particle-in-cell simulation of the beam-plasma interaction process is carried out to study the electromagnetic radiation at the plasma frequency and its second harmonic. In the simulation, a homogeneous plasma background with a periodic boundary condition is assumed. Electromagnetic radiation at the plasma frequency and its higher harmonics are widely believed to be responsible for solar type-II and type-III radio bursts. Traditional theory based upon weak turbulence of three-wave and nonlinear wave-particle interaction processes predicts radiation emission primarily at the fundamental and second harmonic of the plasma frequency. Electrostatic modes and electromagnetic radiation corresponding to this expectation at the fundamental and the second harmonics plasma frequencies are found. The radiation patterns of the fundamental and second harmonic electromagnetic modes are examined in detail.X115sciescopuskc

Radiation pattern of plasma emission in beam-plasma interaction

The physical process of type-III solar radio bursts by an electron beam in a plasma involves electromagnetic radiation at the plasma frequency and its second harmonic. Recently, multiple-harmonic radiation of plasma frequency has drawn renewed interests in electromagnetic radiation in theoretical and numerical studies. The radiation pattern of electromagnetic waves in nonlinear beam-plasma interaction at the plasma frequency and its multiple harmonics is presented, by using a 2-D electromagnetic particle-in-cell simulation.X111sciescopu

Particle-in-cell simulation study of the parametric instabilities and turbulence of Alfven-ion-cyclotron waves in a low-beta plasma

Parametric instabilities of Alfven-ion-cyclotron (AIC) waves and the turbulence driven by them are investigated using a particle-in-cell simulation technique. By introducing anisotropic ion temperature, a broad spectrum of AIC wave is excited. In addition to the normal AIC waves, their harmonic modes and upper sideband modes are found. Through the interaction of these Alfvenic waves and longitudinal electrostatic waves, Alfvenic turbulence is developed. Excitation of density and electromagnetic waves and their mode coupling structures are investigated using the omega-k spectrum and bicoherence analysis. It is found that the ion-acoustic wave is excited by the modulational instability, and that the ion density mode with a negative group velocity is excited in the high-k region by the decay instability. In addition, a longitudinal mode whose phase velocity behaves similarly to that of the ion-acoustic mode with a shifted wave number is found. This mode is identified as the second harmonic ion-acoustic wave. The inverse cascade structures of the electromagnetic and density fluctuations exhibit an interesting behavior that the density fluctuation shows a dual spectrum, whereas the electrostatic field E-x shows a single spectrum.X111sciescopu