Nonlinear Plasma Phenomena Research Articles

Introduction to high temperature plasma physics

Most of the matter in the Universe is in the plasma state. A plasma will be defined and the concepts of quasi-neutrality and Debye distance introduced. The subject has its historical roots in gas discharge, astrophysics and ionospheric physics. Key theoretical concepts were developed in the context of those subjects. However, only in the last two decades, under the pressures of the controlled thermonuclear and space exploration programmes, have these concepts been tested experimentally. The theory of collisions in plasma has special features owing to the Coulomb nature of the interaction. Magnetized plasma is a medium in which a rich variety of small signal waves can propagate. Charged particle—wave interactions lead to collisionless (Landau) damping and growth mechanisms. Finally, nonlinear phenomena in plasma can and do change its transport properties by orders of magnitude. Our lack of detailed understanding of these nonlinear phenomena applies equally to natural plasmas and to plasmas in both inertially and magnetically confined fusion systems. This feature provides the challenge and the fascination of high temperature plasma physics.

Active stimulation of the ionospheric plasma

Laboratory experiments in which high power, pulsed electromagnetic waves interact with an inhomogeneous plasma indicate that the generated nonlinear plasma phenomena depend on peak incident power and not on pulse length. The electromagnetic waves can penetrate beyond the cutoff and produce large, enhanced electrostatic fields at the critical layer within 100 electron plasma periods. The enhanced electric field pressure can be comparable to the thermal pressure and can accelerate ions and electrons to velocities much greater than their thermal speed. Large density cavities (with δn/n ≳ 10%) can be created in a time shorter than the usual ion response time because of the accelerated ion dynamics. These laboratory results have been extended to create a new and generalized concept to actively stimulate space plasmas with high power pulses of short duration. A field experiment will be used for the stimulation of auroral ionospheric plasma. The ground-based system is modular, each module consisting of a 2 MW pulsed HF transmitter designed at UCLA and a crossed-dipole antenna element. Incoherent scatter radar and optical diagnostic methods are discussed.

Nonlinear phenomena in plasma with relativistic high-frequency electron motion

Considering the influence of relativistic effects on the plasma motion in a HF field, we show that even small relativistic terms qualitatively change the propagation character of nonlinear longitudinal and transverse waves. We also find new regions and branches for the modulational instability.

Plasma instabilities in the solar wind: A theoretical review

I present here a review of recent theoretical progress in the possible role of microturbulence in the solar wind. The solar wind is anticipated to excite plasma microinstabilities because of its transition from collision‐dominated to collisionless behavior. The applications of linear plasma theory that have been made in this field are extensively reviewed and discussed, along with our present understanding of nonlinear plasma phenomena. The solar wind is an excellent laboratory for studying many aspects of solar and plasma physics and may soon provide some answers to several fundamental questions.

Topics on Solitons in Plasmas

Solitons can be regarded as "nonlinear normal modes", in terms of which dynamical properties of a given physical system could be analyzed. The author, however, points out firstly that the cnoidal wave is also the genuine nonlinear wave playing important roles in nonlinear phenomena in plasmas and other dispersive media. Explicit analysis for the ion acoustic cnoidal wave is carried out up to the second order on the basis of Kodama-Taniuti's renormalized reductive perturbation theory. The nonlinear ion flux associated with the cnoidal wave is shown to have different dependence on the wave amplitude as compared with the quasi-linear ion flux. At the same time, it should be noticed that the nonlinear ion flux also exhibits profound frequency dependence, which is not predicted by the quasi-linear treatment. Secondly Bogoliubov-Mitropolsky perturbation analysis of the perturbed envelope soliton is briefly discussed referring to Karpman-Maslov's perturbation approach based on the inverse scattering method. Thirdly, brief summaries on plasma waves in magnetized plasmas are followed by a report on the new inverse scattering scheme for the derivative nonlinear Schrödinger equation. In concluding remark, the potential importance of researches on solitons in strong plasma turbulence has been emphasized.

Collision-Induced Nonlinear Excitations

We demonstrate that a velocity-dependent collision frequency can introduce significant nonlinearities in the theory of a homogeneous, unmagnetized plasma. By means of a practical collision model which allows us to obtain useful information on nonlinear plasma phenomena without involving the mathematical complexity usually associated with collision operators, we investigate the problems of self-focusing, parametric excitation, and third-order frequency mixing. Our results are compared with those of previous authors. It is shown that the collision-induced nonlinear excitations considered here may be more important than those due to other mechanisms.

Contribution of computer simulation to plasma theory

Recent advances in computers and in techniques for simulating plasmas have made it possible to investigate rather complicated nonlinear and turbulent phenomena in plasmas. Quite a number of problems have been investigated in recent years. Among them, anomalous absorption of intense electromagnetic waves due to the turbulence associated with parametric instabilities created by the electromagnetic wave, the diffusion of plasma across strong magnetic fields due to thermally exerted convective motion. Sampling amplitudes of ion waves, and the coupling of intense plasma oscillations due to ion density fluctuations. From the simulation one can generally gain a pretty good idea of the mechanisms involved and construct theories for the observed effects. The present status of simulation and a few examples of how it has been used to aid theory will be given.

Some Investigations of Nonlinear Behavior in One-Dimensional Plasmas

Numerical experiments on a one-dimensional electron plasma were used to obtain an insight into nonlinear plasma phenomena. Three experiments were carried out. The first dealt with the damping of a large-amplitude wave which is found to be much stronger than that predicted by linear theory. A rough theory for the damping is presented. The second experiment examined mode-mode coupling. Quantitative agreement was found with theory after precautions were taken to avoid other effects, in particular, “trapped” particles. A rough theory for “trapping” is given. The third experiment examined the weak turbulence produced by a small bump in the tail of the distribution function, and present theory appears inadequate to describe this behavior. After initial growth, the unstable modes fluctuate on a time scale of 10ωp−1. The bump in the tail of the velocity distribution flattens out in a short time (20ωp−1), and then evolves into a hot Gaussian tail which coexists with the main plasma for a long time (≳ 1000 ωp−1). Particles in the tail have been observed with four times the initial average energy of the beam electron. A discussion of the physical effects which appear to be involved in this experiment is given, and estimates of their importance for three-dimensional plasmas are presented.

Wave interaction and dynamic nonlinear phenomena in plasmas

Wave interaction and dynamic nonlinear phenomena in plasmas

Нелинейные явления в плазме, находящейся в переменном электромагнитном поле

Нелинейные явления в плазме, находящейся в переменном электромагнитном поле

Нелинейные явления в плазме, находящейся в переменном электромагнитном поле

Нелинейные явления в плазме, находящейся в переменном электромагнитном поле