Nonlinear Plasma Waves Research Articles

Coherent, Short-Pulse X-ray Generation via Relativistic Flying Mirrors

Coherent, Short X-ray pulses are demanded in material science and biology for the study of micro-structures. Currently, large-sized free-electron lasers are used; however, the available beam lines are limited because of the large construction cost. Here we review a novel method to downsize the system as well as providing fully (spatially and temporally) coherent pulses. The method is based on the reflection of coherent laser light by a relativistically moving mirror (flying mirror). Due to the double Doppler effect, the reflected pulses are upshifted in frequency and compressed in time. Such mirrors are formed when an intense short laser pulse excites a strongly nonlinear plasma wave in tenuous plasma. Theory, proof-of-principle, experiments, and possible applications are addressed.

New method for rekindling the nonlinear solitary waves in Maxwellian complex space plasma

Our interest is to study the nonlinear wave phenomena in complex plasma constituents with Maxwellian electrons and ions. The main reason for this consideration is to exhibit the effects of dust charge fluctuations on acoustic modes evaluated by the use of a new method. A special method (G′/G) has been developed to yield the coherent features of nonlinear waves augmented through the derivation of a Korteweg-de Vries equation and found successfully the different nature of solitons recognized in space plasmas. Evolutions have shown with the input of appropriate typical plasma parameters to support our theoretical observations in space plasmas. All conclusions are in good accordance with the actual occurrences and could be of interest to further the investigations in experiments and satellite observations in space. In this paper, we present not only the model that exhibited nonlinear solitary wave propagation but also a new mathematical method to the execution.

Towards compact Free Electron–Laser based on laser plasma accelerators

The laser invention more than fifty years ago was a major scientific revolution. Among the different possible gain media, the Free Electron–Lasers (FEL) uses free electrons in the period permanent magnetic field of an undulator, covering wavelengths from far infrared to X-ray, with easy tuneability and high peak power. Nowadays, the advent of tuneable intense (mJ level) short pulse FELs with record peak power (GW level) in the X-ray domain sets a major step in laser development, and enables to explore new scientific areas, such as deciphering molecular reactions in real time, understanding functions of proteins. Besides, lasers have also been considered for driving plasma electron acceleration. A high-power femtosecond laser is focused into a gas target and resonantly drives a nonlinear plasma wave in which plasma electrons are trapped and accelerated with high energy gain of GeV/m. Nowadays, laser wakefield acceleration became reality and electron beams with multi-GeV energies, hundreds of pC charge, sub-percent energy spread and sub-milliradian divergence can be produced. It is relevant to consider a FEL application to quality these laser plasma produced electrons. After having described the FEL panorama, the strategies towards laser plasma based acceleration based FELs will be discussed, including the mitigation of the large energy spread and divergence of these beams should be mitigated.

The effects of finite mass, adiabaticity, and isothermality in nonlinear plasma wave studies

The propagation of arbitrary amplitude ion-acoustic solitons is investigated in a plasma containing cool adiabatic positive ions and hot electrons or negative ions. The latter can be described by polytropic pressure-density relations, both with or without the retention of inertial effects. For analytical tractability, the resulting Sagdeev pseudopotential needs to be expressed in terms of the hot negative species density, rather than the electrostatic potential. The inclusion of inertia is found to have no qualitative effect, but yields quantitative differences that vary monotonically with the mass ratio and the polytropic index. This result contrasts with results for analogous problems involving three species, where it was found that inertia could yield significant qualitative differences. Attention is also drawn to the fact that in the literature there are numerous papers in which species are assumed to behave adiabatically, where the isothermal assumption would be more appropriate. Such an assumption leads to quantitative errors and, in some instances, even qualitative gaps for “reverse polarity” solitons.

Response to “Comment on ‘Solitonic and chaotic behaviors for the nonlinear dust-acoustic waves in a magnetized dusty plasma’” [Phys. Plasmas 24, 094701 (2017)

On our previous construction [H. L. Zhen et al., Phys. Plasmas 23, 052301 (2016)] of the soliton solutions of a model describing the dynamics of the dust particles in a weakly ionized, collisional dusty plasma comprised of the negatively charged cold dust particles, hot ions, hot electrons, and stationary neutrals in the presence of an external static magnetic field, Ali et al. [Phys. Plasmas 24, 094701 (2017)] have commented that there exists a different form of Eq. (4) from that shown in Zhen et al. [Phys. Plasmas 23, 052301 (2016)] and that certain interesting phenomena with the dust neutral collision frequency ν0>0 are ignored in Zhen et al. [Phys. Plasmas 23, 052301 (2016)]. In this Reply, according to the transformation given by the Ali et al. [Phys. Plasmas 24, 094701 (2017)] comment, we present some one-, two-, and N-soliton solutions which have not been obtained in the Ali et al. [Phys. Plasmas 24, 094701 (2017)] comment. We point out that our previous solutions in Zhen et al. [Phys. Plasmas 23, 052301 (2016)] are still valid because of the similarity between the two dispersion relations of previous solutions in Zhen et al. [Phys. Plasmas 23, 052301 (2016)] and the solutions presented in this Reply. Based on our soliton solutions in this Reply, it is found that the soliton amplitude is inversely related to Zd and B0, but positively related to md and α, where α refers to the coefficient of the nonlinear term, Zd and md are the charge number and mass of a dust particle, respectively, B0 represents the strength of the external static magnetic field. We also find that the two solitons are always in parallel during the propagation.

Simulation study of the sub-terawatt laser wakefield acceleration operated in self-modulated regime

Laser wakefield acceleration (LWFA) can be accomplished by introducing a sub-terawatt (TW) laser pulse into a thin, high-density gas target. In this way, the self-focusing effect and the self-modulation that happened on the laser pulse produce a greatly enhanced laser peak intensity that can drive a nonlinear plasma wave to accelerate electrons. A particle-in-cell model is developed to study sub-TW LWFA when a 0.6-TW laser pulse interacts with a dense hydrogen plasma. Gas targets having a Gaussian density profile or a flat-top distribution are defined for investigating the properties of sub-TW LWFA when conducting with a gas jet or a gas cell. In addition to using 800-nm laser pulses, simulations are performed with 1030-nm laser pulses, as they represent a viable approach to realize the sub-TW LWFA driven by high-frequency, diode-pumped laser systems. The peak density which allows the laser peak power PL∼2Pcr of self-focusing critical power is favourable for conducting sub-TW LWFA. Otherwise, an excessively high peak density can induce an undesired filament effect which rapidly disintegrates the laser field envelope and violates the process of plasma wave excitation. The plateau region of a flat-top density distribution allows the self-focusing and the self-modulation of the laser pulse to develop, from which well-established plasma bubbles can be produced to accelerate electrons. The process of electron injection is complicated in such high-density plasma conditions; however, increasing the length of the plateau region represents a straightforward method to realize the injection and acceleration of electrons within the first bubble, such that an improved LWFA performance can be accomplished.

Characterisation of beam driven ionisation injection in the blowout regime of plasma acceleration

Beam driven ionisation injection is characterised for a variety of high-Z dopant. We discuss the region of extraction and why the position where electrons are captured influences the final quality of the internally-injected bunch. The beam driven ionisation injection relies on the capability to produce a high gradient fields at the bubble closure, with magnitudes high enough to ionise by tunnelling effect the still bounded electrons (of a high-Z dopant). The ionised electrons are captured by the nonlinear plasma wave at the accelerating and focusing wake phase leading to high-brightness trailing bunches. The high transformer ratio guarantees that the ionisation only occurs at the bubble closure. The quality of the ionisation-injected trailing bunches strongly and non-linearly depends on the properties of the dopant gas (density and initial ionisation state). We use the full 3D PIC code ALaDyn to consider the highly three-dimensional nature of the effect. By means of a systematic approach we have investigated the emittance and energy spread formation and the evolution for different dopant gases and configurations.

The effects of geometrical configurations on the head collision on nonlinear solitary pulses in a quantum semiconductor plasma: A case study on GaAs semiconductor

An investigation is presented to examine nonlinear electrostatic waves in a quantum semiconductor plasma. A quantum semiconductor plasma model consisting of electrons and holes is going to be used, which includes exchange–correlation potentials, the quantum recoil effect, and degenerate pressures of electrons and holes. Actually, a nonlinear solitary pulse can be used to represent the intrinsic coherent electrostatic wave in a quantum semiconductor plasma. The propagation and the collision of nonlinear solitary pulses are examined by the extended Poincaré-Lighthill-Kuo method. Typical values for the GaAs semiconductors are employed to investigate the basic characteristics of solitary pulses. The numerical studies show that the energies and then the trajectories of nonlinear solitary pulses after the collision are significantly changed due to the effects of the exchange and correlation potentials and the variety in the studied system's geometry. The results obtained here may be useful for gaining a better understanding of the basic features of the nonlinear solitary pulses in quantum semiconductor plasmas.

Stability of electron wave spectra in weakly magnetized plasmas

Analytical models for nonlinear electron plasma waves in weakly magnetized plasmas are developed for single as well as multi-mode conditions, with continuous wave spectra being a limiting case. The conditions for wave decay as well as modulational instabilities are analysed. Our results demonstrate that slow or nearly stationary plasma density variations can be found for weakly magnetized plasmas even for weakly nonlinear electron plasma waves without involving cavitation of large amplitude plasma waves. A reduction of the growth rates for decay as well as modulational instabilities are found when the spectral width of the wave spectrum is increased. Some of our results are relevant for the interpretation of the nonlinearly enhanced ion acoustic lines often observed in non-equilibrium ionospheres.

Strongly Mismatched Regime of Nonlinear Laser–Plasma Acceleration: Optimization of Laser-to-Energetic Particle Efficiency

Laser electron accelerators utilize a bubble regime of nonlinear plasma waves driven as laser wakefields that, from theoretical considerations, require a matched laser spot size incident on plasma. A strongly mismatched regime of nonlinear laser–plasma acceleration in the bubble regime, favored by experiments, is introduced and modeled for optimization of laser-to-particle energy efficiency with application to the recently proposed laser positron accelerator. Strong mismatch, in contrast with the matched condition, arises from the incident laser spot size being much larger than that needed for equilibration of the laser ponderomotive and electron-ion charge-separation forces in the nonlinearly driven density structure of a plasma bubble. This is shown to be favorable for optimization of large self-injected electron charge and ultralow transverse emittance without precluding beam spectral shaping. It is shown that there are prominent signatures of the mismatched regime, strong optical-shock excitation, and bubble elongation, which are validated using multidimensional particle-in-cell simulations. This paper thus uncovers a generalized regime that apart from being used in many laser–plasma acceleration experiments also opens a novel pathway for a wide range of future applications.

Large amplitude ion-acoustic solitons in warm negative ion plasmas with superthermal electrons

Large amplitude ion-acoustic solitons are investigated in a plasma consisting of warm adiabatic positive and negative-ions and hot superthermal electrons having kappa distributions. Using Pseudo-potential method an energy integral equation is derived for the system. The latter is analysed to examine the existence regions of the solitary waves. It is found that negative ion concentration (α), spectral index (k) and ionic temperature ratio (σ1 or σ2) significantly influence the characteristic of the solitons. Our numerical analysis shows that the system also supports rarefactive solitons for some selected set of plasma parameters. It is also found that large amplitude ion-acoustic compressive and rarefactive solitons exist simultaneously for the same values of plasma parameters. Further an increase in the superthermality (i.e. decreasing the value of spectral index k) leads to shrinking the existing domain of the large amplitude ion-acoustic solitons. The amplitude of the compressive/rarefactive solitons increases with the increase in negative ion concentration (α). Whereas, on increasing ionic temperature ratio (σ1 or σ2) the amplitude of the compressive/rarefactive soliton decreases. The effect of negative-ion concentration (α), temperature ratio of two ion species (σ1 and σ2), Mach number (M) and spectral index (k) on the characteristics of solitons are discussed in detail. The results of the present investigation may be helpful to understand the nonlinear ion-acoustic solitary waves in space plasma and laboratory plasmas, where two distinct groups of ions and non-Boltzmann distribution electrons are present.

Weak dissipative ion-acoustic solitons in relativistically degenerate collisional plasma

Using the quantum hydrodynamical model, we study the effect of collisions on the dynamics of nonlinear ion-acoustic waves in a superdense degenerate electron-ion plasma. The electrons are assumed to be moving with relativistic velocities. The standard reductive perturbation technique leads to a dissipative KdV equation, for small amplitude electrostatic potential disturbances. The dynamics of these solitary waves is studied both analytically as well as numerically. It is observed that the system supports both positive as well as negative potential ion-solitary waves. The interplay between the relativistic degeneracy parameter and the ion-neutral collision frequency gives rise to both dispersion and dissipation, such that the soliton energy, amplitude, and velocity decrease exponentially with time, whereas its width increases.

Nonplanar dissipative ion acoustic waves in electron-ion plasmas

The properties of nonlinear ion acoustic waves (IAWs) in a two-component electron-ion dissipative plasma are investigated by using a nonlinear perturbation method in bounded nonplanar geometries. The dissipation is introduced by taking into electron-ion elastic collisions. It is found that the nonlinear IAW is governed by nonplanar Kakutani-Kawahara equations. The temporal evolutions of the nonlinear structures for nonplanar geometries are investigated numerically. The collisions are found to significantly affect the basic features of the IAWs. The results are useful for the understanding of the properties of general nonlinear structures in space and laboratory plasmas.

Deformed Korteweg-de Vries equation of two solitons in a quantum semiconductor plasma in the presence of electron-phonon collision frequency and exchange-correlation potential

The effect of electron-phonon collision frequency, exchange-correlation potential, quantum term and degenerate pressure on the nature of solitary waves in a quantum semiconductor plasma is investigated. It is observed that the width of the solitary waves change with variation of different parameters for the GaAs semiconductor. A deformed Korteweg-de Vries equation is obtained for propagation of nonlinear waves in a quantum semiconductor plasma, and the effect of different parameters on the two-soliton solution of the equation are also presented.

Clonal populations of effector regulatory T cell increase in human decidua of late pregnancy

The laser invention more than fifty years ago was a major scientific revolution. Among the different possible gain media, the Free Electron–Lasers (FEL) uses free electrons in the period permanent magnetic field of an undulator, covering wavelengths from far infrared to X-ray, with easy tuneability and high peak power. Nowadays, the advent of tuneable intense (mJ level) short pulse FELs with record peak power (GW level) in the X-ray domain sets a major step in laser development, and enables to explore new scientific areas, such as deciphering molecular reactions in real time, understanding functions of proteins. Besides, lasers have also been considered for driving plasma electron acceleration. A high-power femtosecond laser is focused into a gas target and resonantly drives a nonlinear plasma wave in which plasma electrons are trapped and accelerated with high energy gain of GeV/m. Nowadays, laser wakefield acceleration became reality and electron beams with multi-GeV energies, hundreds of pC charge, sub-percent energy spread and sub-milliradian divergence can be produced. It is relevant to consider a FEL application to quality these laser plasma produced electrons. After having described the FEL panorama, the strategies towards laser plasma based acceleration based FELs will be discussed, including the mitigation of the large energy spread and divergence of these beams should be mitigated.

Solitons, Lie Group Analysis and Conservation Laws of a (3+1)-Dimensional Modified Zakharov-Kuznetsov Equation in a Multicomponent Magnetised Plasma

Abstract In this paper, we investigate a (3+1)-dimensional modified Zakharov-Kuznetsov equation, which describes the nonlinear plasma-acoustic waves in a multicomponent magnetised plasma. With the aid of the Hirota method and symbolic computation, bilinear forms and one-, two- and three-soliton solutions are derived. The characteristics and interaction of the solitons are discussed graphically. We present the effects on the soliton’s amplitude by the nonlinear coefficients which are related to the ratio of the positive-ion mass to negative-ion mass, number densities, initial densities of the lower- and higher-temperature electrons and ratio of the lower temperature to the higher temperature for electrons, as well as by the dispersion coefficient, which is related to the ratio of the positive-ion mass to the negative-ion mass and number densities. Moreover, using the Lie symmetry group theory, we derive the Lie point symmetry generators and the corresponding symmetry reductions, through which certain analytic solutions are obtained via the power series expansion method and the (G′/G) expansion method. We demonstrate that such an equation is strictly self-adjoint, and the conservation laws associated with the Lie point symmetry generators are derived.

Nonlinear plasma waves driven by short ultrarelativistic electron bunches

We advance a theory of quasistatic approximation and investigate the excitation of nonlinear plasma waves by the driving beam of ultrarelativistic electrons using a novel electrostatic-like particle-in-cell code. Assuming that the beam occupies an infinitesimally small volume, we find the radius and the length of the plasma bubble formed in the wake of the driver for varying values of the beam charge. The mechanism of bubble formation is explained by developing simple models of the bubble at large charges. Plasma electrons expelled by the driver charge excite secondary plasma waves, which complicate the plasma electron flow near the bubble boundary.

Kinetic treatment of nonlinear ion-acoustic waves in multi-ion plasma

By applying the kinetic theory of the Valsove-Poisson model and the reductive perturbation technique, a Korteweg-de Vries (KdV) equation is derived for small but finite amplitude ion acoustic waves in multi-ion plasma composed of positive and negative ions along with the fraction of electrons. A correspondent equation is also derived from the basic set of fluid equations of adiabatic ions and isothermal electrons. Both kinetic and fluid KdV equations are stationary solved with different nature of coefficients. Their differences are discussed both analytically and numerically. The criteria of the fluid approach as a limiting case of kinetic theory are also discussed. The presence of negative ion makes some modification in the solitary structure that has also been discussed with its implication at the laboratory level.

Solitary wave solutions of two-dimensional nonlinear Kadomtsev–Petviashvili dynamic equation in dust-acoustic plasmas

Nonlinear two-dimensional Kadomtsev–Petviashvili (KP) equation governs the behaviour of nonlinear waves in dusty plasmas with variable dust charge and two temperature ions. By using the reductive perturbation method, the two-dimensional dust-acoustic solitary waves (DASWs) in unmagnetized cold plasma consisting of dust fluid, ions and electrons lead to a KP equation. We derived the solitary travelling wave solutions of the two-dimensional nonlinear KP equation by implementing sech–tanh, sinh–cosh, extended direct algebraic and fraction direct algebraic methods. We found the electrostatic field potential and electric field in the form travelling wave solutions for two-dimensional nonlinear KP equation. The solutions for the KP equation obtained by using these methods can be demonstrated precisely and efficiency. As an illustration, we used the readymade package of Mathematica program 10.1 to solve the original problem. These solutions are in good agreement with the analytical one.

Nonlinear Electrostatic Waves in PIE and PI Plasmas With Field-Aligned Shear Flow

Nonlinear low-frequency ion acoustic (IA) wave and pair plasma convective cell (PPCC) mode are investigated in pair-ion (PI) plasmas with and without electrons in the presence of sheared flows. IA wave forms both KdV solitons and dipolar vortices in PI-electron plasma, and their amplitude depends upon electron density and sheared flow. But when electron density is too low, the structures disappear, because IA does not exist in pure PI plasma. On the other hand, PPCC mode cannot form pulse-type solitary structures in the pair plasma, while it forms dipolar vortices due to finite vorticity. The nonlinear analysis has been performed assuming the presence of electrons in fullerene PI plasma and limit of zero electron density is also considered for a comparison.