New Ion-Wave Path in the Energy Cascade (original) (raw)
Related papers
A new branch of electrostatic fluctuations: the ion-bulk waves
2011
We present the results of kinetic numerical simulations that demonstrate the existence of a novel branch of electrostatic nonlinear waves driven by particle trapping processes. These waves have an acoustic-type dispersion with phase speed comparable to the ion thermal speed and would thus be heavily Landau damped in the linear regime. At variance with the ion-acoustic waves, this novel electrostatic branch can exist at a small but finite amplitude even for low values of the electron to ion temperature ratio. Our results provide a new interpretation of observations in space plasmas, where a significant level of electrostatic activity is observed in the high frequency region of the solar-wind turbulent spectra.
Nonlinear Low Frequency Wave Phenomena in Space Plasmas
Space is endowed with a rich variety of electrodynamic phenomena. Much of known matter in the universe exists as plasmas. Plasmas occur naturally, predominantly occupy the Sun, Stars, Auroras and Interstellar space. The solar wind is a stream of energized, charged particles (i.e., electrons and protons, along with few heavier ions), flowing outward from the Sun, through the solar system at a very high speed and temperature. Once the solar wind has blown into space, the particles travel all the way past planet Pluto and do not slow down until they reach the termination shock within the heliosphere. Because of the author's interest in space electrodynamics phenomena, the focus of this thesis is " Nonlinear low frequency wave phenomena in space plasmas". In the name of Allah, the Beneficent and the Merciful. I would like to express my sincere appreciation and gratitude to the following people, departments and institutions, without whose involvement this work would not been possible. • My supervisor, Prof. Ramesh Bharuthram for his expert guidance, fatherly advice and encouragement.
New features of ion acoustic waves in inhomogeneous and permeating plasmas
Astronomy & Astrophysics, 2013
Context. It is generally accepted that the ion acoustic (IA) wave in plasmas containing ions and electrons with the same temperature is of minor importance due to strong damping of the wave by hot resonant ions. Aims. In this work it will be shown that the IA wave is susceptible to excitation even in hot-ion plasmas when both an electromagnetic transverse wave and a background density gradient are present in the plasma and, in addition, the wave is unstable (i.e., growing) in the case of permeating homogeneous plasmas. Methods. The multi-component fluid theory is used to describe the IA wave susceptibility for excitation in inhomogeneous plasmas and its coupling with electromagnetic waves. The growing IA wave in permeating homogeneous plasmas is described by the kinetic theory. Results. In plasmas with density and temperature gradients, the IA wave is effectively coupled with the electromagnetic waves. In comparison to the ordinary IA wave in homogeneous plasma, the Landau damping of the present wave is much smaller; to demonstrate this effect, a simple but accurate fluid model is presented for the Landau damping. In the case of permeating plasmas, a kinetic mechanism for the currentless IA wave instability is presented; it has a very low threshold for excitation compared with ordinary electron-current-driven kinetic instability. Such growing IA waves can effectively heat plasma in the upper solar atmosphere by a stochastic heating mechanism presented in the work. Conclusions. The results presented in the work suggest that the role of the IA wave in the heating of the solar atmosphere (chromosphere and corona) should be reexamined.
Nonlinear ion-acoustic waves with Landau damping in non-Maxwellian space plasmas
Scientific Reports, 2024
The dynamics of nonlinear ion-acoustic solitary waves in the presence of kinetic (Landau type) damping have been investigated in a collisionless, non-magnetized electron-ion plasma. A cold ion fluid model, coupled to a Vlasov-type kinetic equation for the electron dynamics, has been adopted as a starting point. The electron population was assumed to be in a kappa-distributed state, in account of the non-Maxwellian behavior of energetic (suprathermal) electrons often observed in Space. A multiscale perturbation technique has led to an evolution equation for the electrostatic potential, in the form of a modified Korteweg-de Vries (KdV) equation, incorporating a non-local term accounting for Landau damping (associated with the electron statistics). Exact analytical solutions have been obtained, representing solitary waves undergoing amplitude decay over time. The combined effect of Landau damping and non-Maxwellian electron statistics (via the kappa parameter) on the characteristics of IASWs has been examined. Numerical integration of the evolution equation has been undertaken, to elucidate the importance of kinetic Landau damping on a shock-shaped initial condition. The results of this investigation aim to improve our understanding of the dynamics of nonlinear electrostatic waves under the influence of Landau damping in various space plasma environments.
Electron and ion kinetic effects on non-linearly driven electron plasma and ion acoustic waves
Physics of Plasmas, 2013
Fully non-linear kinetic simulations of electron plasma and ion acoustic waves (IAWs) have been carried out with a new multi-species, parallelized Vlasov code. The numerical implementation of the Vlasov model and the methods used to compute the wave frequency are described in detail. For the first time, the nonlinear frequency of IAWs, combining the contributions from electron and ion kinetic effects and from harmonic generation, has been calculated and compared to Vlasov results. Excellent agreement of theory with simulation results is shown at all amplitudes, harmonic generation being an essential component at large amplitudes. For IAWs, the positive frequency shift from trapped electrons is confirmed and is dominant for the effective electron-to-ion temperature ratio, Z T e =T i տ 10 with Z as the charge state. Furthermore, numerical results demonstrate unambiguously the dependence [R. L. Dewar, Phys. Fluids 15, 712 (1972)] of the kinetic shifts on details of the distribution of the trapped particles, which depends in turn on the conditions under which the waves were generated. The trapped particle fractions and energy distributions are derived and, upon inclusion of harmonic effects, shown to agree with the simulation results, completing a consistent picture. Fluid models of the wave evolution are considered but prove unable to capture essential details of the kinetic simulations. Detrapping by collisions and sideloss is also discussed.
Ion-acoustic waves in non-Maxwellian magnetospheric electron-positron-ion plasma
Using Boltzmann-Vlasov kinetic model for non-thermal distributed electron-positron-ion plasma of our Earth's magnetosphere and the solar wind streaming plasma can drive ion-acoustic waves unstable. It is found that the growth rate increases with the decrease of spectral index and increases with the streaming velocity of the solar wind. The numerical results are also presented by choosing some suitable parameters of magnetospheric plasma.
Linear and nonlinear waves in space plasmas
2014
The work presented in this thesis is about a study of some linear and nonlinear plasma waves. Firstly, a kinetic-theoretical approach is used to study ion Bernstein waves in an electron-proton plasma with a kappa velocity distribution. The effects of the parameter kappa on the dispersion relation of ion Bernstein waves are discussed in detail, considering various values of the ratio of the ion plasma frequency to the ion cyclotron frequency, ωpi/ωci, allowing application of the results to various space environments. For a fixed value of ωpi/ωci, we have found that the dispersion relation depends significantly on the parameter kappa of the ions, κi, but is independent of the electron kappa. Over all cyclotron harmonics, the dispersion curves are shifted to higher wavenumbers (k) if κi is reduced. When the value of ωpi/ωci is increased, the fall-off of the wave frequency, ω, at large k is smaller for lower κi, and curves are shifted towards larger wavenumbers. For large values of ωpi/...
The Astrophysical Journal, 2014
Pickup ions (PUIs) in the outer heliosphere and the local interstellar medium are created by charge exchange between protons and hydrogen (H) atoms, forming a thermodynamically dominant component. In the supersonic solar wind beyond >10 AU, in the inner heliosheath (IHS), and in the very local interstellar medium (VLISM), PUIs do not equilibrate collisionally with the background plasma. Using a collisionless form of Chapman-Enskog expansion, we derive a closed system of multi-fluid equations for a plasma comprised of thermal protons and electrons, and suprathermal PUIs. The PUIs contribute an isotropic scalar pressure to leading order, a collisionless heat flux at the next order, and a collisionless stress tensor at the second-order. The collisionless heat conduction and viscosity in the multi-fluid description results from a non-isotropic PUI distribution. A simpler one-fluid MHD-like system of equations with distinct equations of state for both the background plasma and the PUIs is derived. We investigate linear wave properties in a PUI-mediated three-fluid plasma model for parameters appropriate to the VLISM, the IHS, and the solar wind in the outer heliosphere. Five distinct wave modes are possible: Alfvén waves, thermal fast and slow magnetoacoustic waves, PUI fast and slow magnetoacoustic waves, and an entropy mode. The thermal and PUI acoustic modes propagate at approximately the combined thermal magnetoacoustic speed and the PUI sound speed respectively. All wave modes experience damping by the PUIs through the collisionless PUI heat flux. The PUI-mediated plasma model yields wave properties, including Alfvén waves, distinctly different from those of the standard two-fluid model.
The invariant ion-acoustic waves in the plasma
We have formulated the invariant ion-acoustic waves (IAWs) in the astrophysical plasmas including the pure thermodynamic features of the background particles. Here, we have used the modern version of the kappa distribution formalism, where it is labeled with an invariant kappa index as of the zero dimensionality spectral index, κ0. Two contexts for studying the invariant IAWs have been employed, i.e., the kinetic theory formalism and the hydrodynamic fluid description. At first, we have employed the Vlasov-Poisson equations at the low frequency band of the weakly damped ion waves, where the most generalized formalism of the ion-sound speed has been confirmed in terms of the extended polytropic indices of the plasma species, γj. Furthermore, the Landau damping of IAWs has been formulated in terms of κ0, the wavelength, and the temperatures of the plasma species. In the hydrodynamic description, we have normalized the fluid parameters by using the extended quantities, including the ge...