Damping Of Ion Acoustic Waves Research Articles

Heating and Acceleration of the Solar Wind by Ion Acoustic Waves—Parker Solar Probe

The heating of the solar wind has been shown to be correlated with certain ion acoustic waves. Here calculations of the heating are made, using the methods used previously for STEREO observations, which show that the strong damping of ion acoustic waves rapidly delivers their energy to the plasma of the solar wind. It is shown that heating by the observed waves is not only sufficient to produce the observed heating but can also provide much or all of the outward acceleration of the solar wind.

The competing effects of wave amplitude and collisions on multi-ion species suppression of stimulated Brillouin scattering in inertial confinement fusion Hohlraums

Reduction in stimulated Brillouin scattering (SBS) from National Ignition Facility Hohlraums has been predicted through the use of multi-ion species materials on Hohlraum walls. This approach to controlling SBS is based upon introducing a lighter ion species to the heavier ion species Hohlraum wall in order to greatly increase the ion Landau damping of ion acoustic waves (IAWs). In a collisionless plasma, if the IAWs driven by SBS reach sufficient amplitudes, this increased damping is reduced or even eliminated by ion trapping in the IAWs. Here, the nonlinear behavior of IAWs is simulated with a multi-ion species Vlasov code, including interspecies ion–ion collisions, self-collisions, and electron–ion pitch-angle collisions. The effect of collisions on the trapping of ions and electrons in a large-amplitude IAW is studied in a regime of relevance to current Inertial Confinement Fusion experiments. Our simulations show that collisions can scatter trapped particles out of resonance with the IAW, suppressing trapping and helping to maintain an effective Landau damping of the IAW. The IAW amplitude required to trap particles in the presence of strong collisions is estimated analytically. These estimates are tested for strongly damped IAWs in tantalum oxide and pure helium plasmas. Our simulations show that, above a threshold amplitude, the damping is reduced by an amount inversely proportional to the wave amplitude. Thus, the success of controlling SBS using a multispecies plasma may depend sensitively on laser power and pulse length.

Cascading parametric decay coupling between whistler and ion acoustic waves: Darwin particle-in-cell simulations

We present the results of numerical studies of the whistler wave parametric decay instability in the system with the suppressed Landau damping of ion acoustic waves (IAWs) based on the self-consistent Darwin particle-in-cell (PIC) model. It has been demonstrated that a monochromatic whistler wave launched along the background magnetic field couples to a counter-propagating whistler mode and co-propagating ion acoustic mode. The coupling of the electromagnetic mode to the electrostatic mode is guided by a ponderomotive force that forms spatio-temporal beat patterns in the longitudinal electric field generated by the counter-propagating whistler and the pump whistler wave. The threshold amplitude for the instability is determined to be δBw/B0 = 0.028 and agrees with a prediction for the ion decay instability: δBw/B0 = 0.042 based on the linear kinetic damping rates, and δBw/B0 = 0.030 based on the simulation derived damping rates. Increasing the amplitude of the pump whistler wave, the secondary and tertiary decay thresholds are reached, and cascading parametric decay from the daughter whistler modes is observed. At the largest amplitude (δBw/B0 ∼ 0.1) the primary IAW evolves into a short-lived and highly nonlinear structure. The observed dependence of the IAW growth rate on the pump wave amplitude agrees with the expected trend; however, quantitatively, the growth rate of the IAW is larger than expected from theoretical predictions. We discuss the relevant space regimes where the instability could be observed and extensions to the parametric coupling of whistler waves with the electron acoustic wave (EAW).

Dust charge fluctuation and ion acoustic wave propagation in dusty plasma with q-nonextensive hot and Maxwellian cold electrons

We have employed the self-consistent kinetic theory to study the linear dispersion relation of ion acoustic waves in a four-component plasma consisting of nonextensive hot electrons, Maxwellian cold electrons, positive ions, and dust particles. The dust charging process with the modified ion acoustic wave damping, as well as its unstable mode, has been graphically illustrated. It is found that the dust charging mechanism depends on the density of hot electrons, the degree of nonextensive electron distribution, and the temperature ratio of hot to cold electrons. It is shown that the damping and instability rates of ion acoustic waves due to dust charge fluctuations explicitly depend on the choice of electron distribution and the magnitude of dusty plasma parameters. In addition, we have studied the ion acoustic Landau damping in the absence of dust particles. It is found that the weak damping region broadens, while the strong damping region shrinks and is shifted toward the short wavelength region for the increase in the temperature ratio of hot to cold electrons.

Beam Spray Thresholds in ICF-Relevant Plasmas.

Beam spray measurements suggest thresholds that are a factor of ≈2 to 15× less than expected based on the filamentation figure of merit often quoted in the literature. In this moderate-intensity regime, the relevant mechanism is forward stimulated Brillouin scattering. Both weak ion acoustic wave damping and thermal enhancement of ion acoustic waves contribute to the low thresholds. Forward stimulated Brillouin scattering imparts a redshift to the transmitted beam. Regarding the specific possibility of beam spray occurring outside the laser entrance holes of an indirectly driven hohlraum, this shift may be the most concerning feature owing to the high sensitivity of crossed-beam energy transfer to the interacting beam wavelengths in the subsequent overlap region.

Absolute stimulated Brillouin side scattering in an inhomogeneous flowing plasma.

Theory of absolute stimulated Brillouin side scattering in an inhomogeneous flowing plasma is presented and verified numerically. The linearized coupling equations are transformed into a Schrödinger equation in k space and solved as an eigenvalue problem. Analytic threshold, growth rate, and scattering geometry are obtained for the pump laser with arbitrary incidence angle. Numerical solutions of the coupling equations show good agreements between the theoretical and numerical absolute thresholds when ion-acoustic wave damping is not too large, and thus an old but famous threshold in [Phys. Fluids 17, 1211 (1974)PFLDAS0031-917110.1063/1.1694867] is corrected. It also indicates that the theoretical analysis is not accurate for strong dampings, since it will overestimate the absolute threshold. Possibility of finding such instability in the current experiments is also discussed.

SRS-SBS competition and nonlinear laser energy absorption in a high temperature plasma

Stimulated Raman and Brillouin scattering of laser radiation in a plasma corona are outstanding issues for the inertial confinement fusion. Stimulated Raman scattering may produce absorption of a significant fraction of laser energy near the plasma quarter critical density associated with plasma cavitation and generation of hot electrons. By contrast, stimulated Brillouin scattering operates in a lower density plasma and prevents the laser light access to the absorption region. In the present paper, we report the results of analysis of competition of these two parametric instabilities with a series of one-dimensional kinetic simulations of laser-plasma interactions. We revised several flexible methods for controlling the SRS-SBS competition in inertial fusion plasmas. Suppression of SBS favors SRS excitation, electron acceleration and cavitation. The latter process makes an important contribution to the laser absorption by trapping the backscattered light. Consequently, by controlling the Brillouin backscattering through variation such plasma parameters as ion acoustic wave damping, divergence of the plasma expansion velocity or the laser bandwidth, we demonstrate the possibility of controlling the level of nonlinear laser absorption and scattering in a hot, weakly collisional plasma.

Dispersion and damping of ion acoustic wave in deuterium–tritium fusion plasmas with slowing-down distributed α particles

The dispersion and damping rate of the ion acoustic waves (IAWs) in deuterium–tritium (D–T) fusion plasmas with slowing-down distributed α particles are investigated within the framework of kinetic theory. It is shown that the concentration of α particles has an important effect on IAWs. The frequency of IAWs decreases as the α concentration increases. Inversely, the damping rate increases as the α concentration increases. The results for slowing-down distributed α particles are compared with those obtained when α particles are assumed to have an equivalent Maxwellian distribution.

Particle-in-cell simulation of the effect of dust charge fluctuation on ion acoustic waves in a dusty plasma

A new hybrid-particle-in-cell (PIC)-Monte Carlo Collision (h-PIC-MCC) algorithm is presented here. The code correctly simulates the damping of ion acoustic wave due to dust charge fluctuation in a dusty plasma along with other kinetic effects such as Landau damping. In the model, on event of a collision between a charged particle and a dust particle, a randomised probability determines whether the charged particle is absorbed by the dust with the collision cross section being determined dynamically by the overall interaction scenario. We find that this method is versatile enough as it can also include the size and mass distribution for the dust particles, in addition to the charged species dynamics. As such, it can be adopted to study numerous phenomena that occur in diverse dusty plasma environments. We believe that the damping of the ion acoustic wave through dust charge fluctuation is being demonstrated, for the first time, with a PIC code, in this work.

Laser propagation in a subcritical foam: Ion and electron heating

We develop a model for laser propagation and heating in a subcritical foam (homogeneous electron density as a fraction of critical ne,0/nc<1). Our model describes the partition of energy between ions and electrons in an expanding foam element irradiated by a laser, and we solve for the plasma conditions generated by burning down the foam microstructure. We find that a substantial fraction of laser energy goes into breaking down and homogenizing the foam microstructure, which slows down the laser heat front. We also find that the ion temperature in a plasma generated by burning down a foam can exceed the electron temperature. This is because laser energy is deposited into the expansion kinetic energy of ions as the foam microstructure burns down explosively. The higher ion temperature increases ion-acoustic wave damping which reduces stimulated Brillouin scattering (SBS). We test our model against data from an experiment that shot a subcritical foam with a high intensity laser pulse on the Janus laser facility at LLNL. We find that by modeling the effect of the foam microstructure, we can explain both the experimentally measured laser propagation velocity and the backscattered SBS power.

Anti-Langmuir decay instability in Langmuir decay instability cascade

Backward stimulated Raman scattering (BSRS) with Langmuir decay instability (LDI) and anti-Langmuir decay instability (ALDI or anti-LDI) has been researched by Vlasov simulation. The decay productions of anti-LDI in LDI cascade and their evolution with time are demonstrated for the first time. The BSRS reflectivity will be decreased largely through LDI cascade and ALDI in the small wave-number region. Different mechanisms to saturate BSRS in CH (or H) and C plasmas have been demonstrated. The dominant saturation mechanism of BSRS in CH (or H) plasmas is LDI cascade and ALDI. However, in C plasmas, due to very weak Landau damping of ion acoustic waves, LDI cascade will promote stimulated Brillouin scattering (SBS) excitation, then SBS will compete with BSRS and saturate BSRS in the later stage. The proportion of the hot electrons is decreased largely through LDI cascade and ALDI. These results give an effective mechanism to suppress BSRS and hot electron generation in the small wave-number region, which are of important significance in the inertial confinement fusion.

Enhanced hot-electron production and strong-shock generation in hydrogen-rich ablators for shock ignition

Experiments were performed with CH, Be, C, and SiO2 ablators interacting with high-intensity UV laser radiation (5 × 1015 W/cm2, λ = 351 nm) to determine the optimum material for hot-electron production and strong-shock generation. Significantly more hot electrons are produced in CH (up to ∼13% instantaneous conversion efficiency), while the amount is a factor of ∼2 to 3 lower in the other ablators. A larger hot-electron fraction is correlated with a higher effective ablation pressure. The higher conversion efficiency in CH is attributed to stronger damping of ion-acoustic waves because of the presence of light H ions.

Ion acoustic wave damping in a non-Maxwellian bi-ion electron plasma in the presence of dust

In this work, we investigate the properties of ion acoustic waves generated by negative heavy ions in a multi-component non-Maxwellian electrostatic plasma, consisting of electrons, positive and negative heavy ions, and a background population of dust particles. In the absence of external energy source and collisions, the ion acoustic waves are subject to Landau damping. We perform a collisionless linear instability analysis within a slow damping approximation and study the effect of various plasma conditions on the damping rate. Our model is highly relevant to multi-ion laboratory plasmas and has been applied to K+– SF6− and K+– C7 F14− mixtures in particular.

Kinetic theory of fully degenerate electrons in the long scale limit

The kinetic theory of fully degenerate electrons in a weakly coupled plasma is considered. We derive an evolution equation for a generalized Fermi surface that also depends on the electron spin state. The equation allows for the study of weakly nonlinear modifications of the Fermi surface within perturbation theory. We apply the theory to Landau damping of ion-acoustic waves. The transition to the nonlinear stage and the nonlinear modification of the Fermi surface are investigated.

Causality and Collisionless Damping in Plasma

We derive the collisionless Landau damping in a plasma by satisfying the causal requirement that the susceptibility function of the plasma for time t should be nil. The causality condition should be satisfied by the susceptibility function of a plasma no matter what equations we employ to describe the plasma. Thus we conclude that the fundamental reason of the collisionless damping can be traced to the causality. As an example, we derive the collisionless damping of ion acoustic wave in a plasma by employing fluid equations.

Enhanced damping of ion acoustic waves in dense plasmas

A theory for the ion-acoustic wave damping in dense plasmas and warm dense matter, accounting for the Umklapp process, is presented. A higher decay rate compared to the prediction from the Landau damping theory is predicted for high-Z dense plasmas, where the electron density ranges from 1021 to 1024 cm−3 and the electron temperature is moderately higher than the Fermi energy.

Ion acoustic waves in the plasma with the power-law q-distribution in nonextensive statistics

We investigate the dispersion relation and Landau damping of ion acoustic waves in the collisionless magnetic-field-free plasma when the plasma is described by the nonextensive q -distributions of Tsallis statistics. We show that the increased numbers of superthermal particles and low velocity particles can explain the strengthened and weakened modes of Landau damping, respectively, with the q -distribution. When the ion temperature is equal to the electron temperature, the weakly damped waves are found to be the distributions with small values of q .

Viscosity estimates of liquid metals and warm dense matter using the Yukawa reference system

A practical method of computing the viscosity of liquid metals and warm dense matter over wide ranges in parameters is proposed. The method is based on mapping the system of interest onto the Yukawa model, for which the viscosity is well known and can be written in a quasiuniversal form. Comparisons are made with quantum molecular dynamics results for compressed iron relevant to the Earth's core, experimental data for many liquid metals, and simulation results for dense deuterium relevant to inertial confinement fusion experiments. Finally, the dispersion and damping of ion-acoustic waves in warm dense matter are considered in this context.

Formulation of the relativistic moment implicit particle-in-cell method

A new formulation is presented for the implicit moment method applied to the time-dependent relativistic Vlasov-Maxwell system. The new approach is based on a specific formulation of the implicit moment method that allows us to retain the same formalism that is valid in the classical case despite the formidable complication introduced by the nonlinear nature of the relativistic equations of motion. To demonstrate the validity of the new formulation, an implicit finite difference algorithm is developed to solve the Maxwell’s equations and equations of motion. A number of benchmark problems are run: two stream instability, ion acoustic wave damping, Weibel instability, and Poynting flux acceleration. The numerical results are all in agreement with analytical solutions.

Electrostatic waves in a Maxwellian dusty plasma with variable charge on dust particles

A kinetic formulation developed to analyze wave propagation in dusty plasmas, which takes into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions, is utilized to study the propagation and damping of electrostatic waves with wave number exactly parallel to the external magnetic field and Maxwellian distributions for the electrons and ions in the equilibrium. It is shown that, due to the presence of the dust, the damping of Langmuir waves in the region of large wavelengths is increased as compared to conventional Landau damping. Langmuir waves in the occurrence of collisional charging of dust particles also feature weak damping for small wavelengths, which vanishes if the effect of collisional charging of the dust particles is neglected in the dispersion relation. It is also shown that the damping of ion-acoustic waves is modified by the presence of the dust, and that some damping effect due to the dust particles remains even if the effect of collisional charging of dust particles is neglected in the dispersion relation.