Modulational instability of the coupled waves between fast magnetosonic wave and slow Alfvén wave in the laser–plasma interaction

By performing modulational instability analysis of the the nonlinear coupled dimensionless equations between a fast magnetosonic wave(FMSW) propagating obliquely with the magneticfield and a low-frequency slow Alfvén wave(SAW), we obtain the dispersion relation of the perturbation wave. The growth rate of the perturbation wave is obtained. It is found that the growth rate increases as background magnetic field increases, which is in agreement with that reported by Tiwary et al(2016 Phys. Plasmas 23 122307). A critical perturbation wave number is found. When the perturbation wave number is greater than or equal to the critical value, the growth rate is positive and it increases as the perturbation wave number increases, while the wave is stable. The maximum growth rate is reached when the frequency of the FMSW is half of the ion cyclotron frequency. The minimum growth rate is reached when the propagation direction of the perturbation wave is the same as that of the FMSW.     

Dispersion Equation of Low-Frequency Waves Driven by Temperature Anisotropy

The plasma temperature (or the kinetic pressure) anisotropy is an intrinsic char-acteristic of a collisionless magnetized plasma.In this paper,based on the two-fluid model,a dispersion equation of low-frequency (ω<<ωci,ωci the ion gyrofrequency) waves,including the plasma temperature anisotropy effect,is presented.We investigate the properties of low-frequency waves when the parallel temperature exceeds the perpendicular temperature,and especially their dependence on the propagation angle,pressure anisotropy,and energy closures.The results show that both the instable Alfv’en and slow modes are purely growing.The growth rate of the Alfv’en wave is not affected by the propagation angle or energy closures,while that of the slow wave depends sensitively on the propagation angle and energy closures as well as pressure anisotropy.The fast wave is always stable.We also show how to elaborate the symbolic calculation of the dispersion equation performed using Mathematica Notebook.     

Solitary kinetic Alfvén waves in a dense electron–positron–ion plasma with degenerate electrons and positrons

Through the use of a reductive perturbation technique, solitary kinetic Alfvén waves(KAWs) are investigated in a low but finite b(particle-to-magnetic pressure ratio) dense electron–positron–ion plasma where electrons and positrons are degenerate. The degenerate plasma model considered here permits the existence of sub-Alfvénic compressive solitary KAWs. The influence of r(equilibrium positron-to-ion density ratio), sF(electron-to-positron Fermi temperature ratio), b and obliqueness parameter lzon various characteristics of solitary KAWs are examined through numerical plots. We have shown that there exists a critical value of lzat which a soliton width attains its maximum value which decreases with an increase in r and sF.It is also found that solitons with a higher energy propagate more obliquely in the direction of an ambient magnetic field. The results of the present investigation may be useful for understanding low frequency nonlinear electromagnetic wave propagation in magnetized electron–positron–ion plasmas in dense stars. Specifically, the relevance of our investigation to a pulsar magnetosphere is emphasized.     

Fuel compression in the magnetized cylindrical implosion driven by a gold tube heated by heavy ion beams

A magnetized cylindrical target composed of a gold tube filled with deuterium-tritium fuel plasma at low density is studied numerically in the present paper. A shock wave is produced when a heavy ion beam heats the gold along the direction of the magnetic field. The density peak of the shock wave increases with the increase in time and it propagates in the-r direction in the cylindrical tube. It seems that this wave is the supermagnetosonic wave. It is found that the Mach number M is between 6.9...     

Alfvén Wave Current Drive in Tokamak Rotating Plasma with Negative Magnetic Shear

The current drive due to Alfvén wave in Tokamak rotating plasma with negative magnetic shear is studied in this paper. In cylindrical geometry, an expression for driving current density J_z is given by means of the single-fluid magneto-hydrodynamic (MHD) model taking plasma rotation and magnetic shear into account. Furthermore, a set of differential equations in r for the perturbed fields E_r, E_θ and E_z is derived. The current drive due to the compressional Alfv(?)n wave and the shear Alfv(?)n wave is considered, respectively. It is found that the efficiency of     

Experimental studies on the propagation of whistler-mode waves in a magnetized plasma structure with a non-uniform density

Propagation of whistler-mode waves in a magnetized plasma structure is investigated in the Keda linear magnetized plasma device. The magnetized plasma structure has its density peak in the center, and the background magnetic field is homogeneous along the axial direction. A whistlermode wave with a frequency of 0.3 times of electron cyclotron frequency( fce) is launched into the plasma structure. The wave normal angle(WNA) is about 25°, and the wavefront exhibits a wedge structure. During propag...     

Generation of Alfvén wave energy during magnetic reconnection in Hall MHD

The effect of the reconnection rate on the generation of Alfvén wave energy is systematically investigated using Hall magnetohydrodynamics(MHD). It is well known that a decrease in magnetic energy is proportional to the reconnection rate. It is found that an instantaneous increase in Alfvén wave energy in unit Alfvén time is the square dependence on the reconnection rate. The converted Alfvén wave energy is strongly enhanced due to the large increase in the reconnection rate in Hall MHD. For solar-terrestrial plasmas, the maximum converted Alfvén wave energy in unit Alfvén time with the Hall effect can be over 50 times higher than that without the Hall effect during magnetic reconnection.     

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(S_H) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and S_H. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of S_H suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which S_His calculated with respect to various plasma parameter settings. The results show that S_H can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. S_H measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when n_e≈1.9×10~(13) cm~(-3), which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.     

FDTD Analysis of Reflection of Electromagnetic Wave From a Conductive Plane Covered with Inhomogeneous Time-Varying Plasma

A finite-difference time-domain (FDTD) algorithm is applied to study the electromagnetic reflection of conduction plane covered with inhomogeneous time-varying plasma, homogeneous plasma and inhomogeneous plasma. The collision frequency of plasma is a function of electron density and plasma temperature. The number density profile follows a parabolic function. A discussion on the effect of various plasma parameters on the reflection coefficient is presented. Under the one-dimensional case, transient electromagnetic propagation through various plasmas has been obtained, and the reflection coefficients of EM wave through various plasmas are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave.     

Characteristics of dust acoustic waves in dissipative dusty plasma in the presence of trapped electrons

The formation and propagation of nonlinear dust acoustic waves(DAWs) as solitary and solitary/shock waves in an unmagnetized, homogeneous, dissipative and collisionless dusty plasma comprising negatively charged micron sized dust grains in the presence of free and trapped electrons with singly charged non-thermal positive ions is discussed in detail. The evolution characteristics of the solitary and shock waves are studied by deriving a modified Korteweg–de Vries–Burgers(mKdV–Burgers) equation using the reductive perturbation method. The mKdV–Burgers equation is solved considering the presence(absence) of dissipation. In the absence of dissipation the system admits a solitary wave solution, whereas in the presence of dissipation the system admits shock waves(both monotonic and oscillatory) as well as a combination of solitary and shock wave solutions. Standard methods of solving the evolution equation of shock(solitary) waves are used. The results are discussed numerically using standard values of plasma parameters. The findings may be useful for better understanding of formation and propagation of waves in astrophysical plasma.     

The Self-Consistent Nonlinear Theory of Charged Particle Beam Acceleration by Slowed Circularly Polarized Electromagnetic Waves

The relativistic interaction of charged particle beams with a circularly polarized electromagnetic wave propagating along a uniform guiding magnetic field in the tunneling of a dielectric medium is analyzed. The acceleration mechanism and a self-consistent nonlinear theory are presented for the interaction of relativistic charged particle beams with electromagnetic waves. Numerical results show that the beam particle can be efficiently accelerated in the interaction process.     

Electromagnetic Particle-in-Cell Simulations of Electron Holes Formed During the Electron Two-Stream Instability

Previous electrostatic particle-in-cell (PIC) simulations have pointed out that electron phase-space holes (electron holes) can be formed during the nonlinear evolution of the electron two-stream instability. The parallel cuts of the parallel and perpendicular electric field have bipolar and unipolar structures in these electron holes, respectively. In this study, two-dimensional (2D) electromagnetic PIC simulations are performed in the x y plane to investigate the evolution of the electron two-stream instability, with the emphasis on the magnetic structures associated with these electron holes in different plasma conditions. In the simulations, the background magnetic field (Bo= Boex ) is along the x direction. In weakly magnetized plasma (Ωe < ωpe , whereΩe and ωpe are the electron gyrofrequency and electron plasma frequency, respectively), several 2D electron holes are formed. In these 2D electron holes, the parallel cut of the fluctuating magnetic field δBx and δBz has unipolar structures, while the fluctuating magnetic field δB y has bipolar structures. In strongly magnetized plasma (Ωe > ωpe ), several quasi-1D electron holes are formed. The electrostatic whistler waves with streaked structures of E y are excited. The fluctuating magnetic field δB x and δBz also have streaked structures. The fluctuating magnetic field δBx and δB y are produced by the current in the z direction due to the electric field drift of the trapped electrons, while the fluctuating magnetic field δBz can be explained by the Lorentz transformation of a moving quasielectrostatic structure. The influences of the initial temperature anisotropy on the magnetic structures of the electron holes are also analyzed. The electromagnetic whistler waves are found to be excited in weakly magnetized plasma. However, they do not have any significant effects on the electrostatic structures of the electron holes.     

Relativistic Filamentation of Intense Laser Beam in Inhomogeneous Plasma

In the paper, relativistic filamentation of intense laser beam in inhomogeneous plasma is investigated based on the nonparaxial region theory. The results show that, relativistic nonlinearity plays a main role in beam filamentation, and plasma inhomogeneity further reinforces the beam filamentation. The combination effects of relativistic nonlinearity and plasma inhomogeneity can generate particularly intense and short pulse laser. However, plasma inhomogeneity leads to obvious filamentation instability.     

The effect of substrate holder size on the electric field and discharge plasma on diamond-film formation at high deposition rates during MPCVD

The effect of the substrate holder feature dimensions on plasma density(ne), power density(Qmw) and gas temperature(T) of a discharge marginal plasma(a plasma caused by marginal discharge) and homogeneous plasma were investigated for the microwave plasma chemical vapor deposition process. Our simulations show that decreasing the dimensions of the substrate holder in a radical direction and increasing its dimension in the direction of the axis helps to produce marginally inhomogeneous plasma. When the marginal discharge appears, the maximum plasma density and power density appear at the edge of the substrate. The gas temperature increases until a marginally inhomogeneous plasma develops. The marginally inhomogeneous plasma can be avoided using a movable substrate holder that can tune the plasma density, power density and gas temperature. It can also ensure that the power density and electron density are as high as possible with uniform distribution of plasma. Moreover, both inhomogeneous and homogeneous diamond films were prepared using a new substrate holder with a diameter of 30 mm. The observation of inhomogeneous diamond films indicates that the marginal discharge can limit the deposition rate in the central part of the diamond film. The successfully produced homogeneous diamond films show that by using a substrate holder it is possible to deposit diamond film at 7.2 μm h~(–1)at 2.5 kW microwave power.     

The Enhanced Effect of Optical Emission from Laser Induced Breakdown Spectroscopy of an Al-Li Alloy in the Presence of Magnetic Field Confinement

In this paper,the influence of magnetic field strength on laser-induced breakdown spectroscopy(LIBS) has been investigated for various pressures.The plasma plume was produced by employing Q-switch Nd:YAG laser ablation of an Al-Li alloy operating at a 1064 nm wavelength.The results indicated that the LIBS intensity of the Al and Li emission lines is boosted with an increase of magnetic strength.Typically,the intensity of the Al Ⅰ and Li Ⅰ spectral emissions can be magnified by 1.5-3 times in a steady magnetic field of 1.1 T compared with the field-free case.Also,in this investigation we recorded time-resolved images of the laser-produced plume by employing a fast ICCD camera.The results show that the luminance of the plasma is enhanced and the time of persistence is increased significantly,and the plasma plume splits into two lobes in the presence of a magnetic field.The probable reason for the enhancement is the magnetic confinement effect which increases the number density of excited atoms and the population of species in a high energy state.In addition,the electron temperature and density are also augmented by the magnetic field compared to the field-free case.     

Numerical and Experimental Investigation on the Attenuation of Electromagnetic Waves in Unmagnetized Plasmas Using Inductively Coupled Plasma Actuator

The attenuation of electromagnetic(EM) waves in unmagnetized plasma generated by an inductively coupled plasma(ICP) actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square flat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.     

Numerical Research of Mode Conversion in an Inhomogeneous Plasma

The linear mode conversion of electromagnetic waves in the hot, unmagnetized inhomogeneous plasma is studied numerically for different density profiles, and the dependence of the absorption coefficient on the incident angles and the wave frequencies are obtained for different electrons＇ temperature. The results show that the shapes of the density profiles and the electron＇s temperature create a certain effect on the coefficients of absorption, which reaches its peak value （about 50%） for appropriate parameters. Effective absorption occurs in a limited range of parameter q.     

Theoretical Analysis on Propagation of Electromagnetic Wave in Preformed Narrow Plasma Channel

In the plasma sheath a narrow plasma channel generated by ultraintense laser pulses is simplified as a special cylindrical and hollow plasma waveguide with the infinite thickness of the plasma cladding.The electromagnetic wave (EM) propagation properties of the plasma channel near the cutoff and far from the cutoff are considered.Theoretical analysis shows that TE 0m and TM 0m and hybrid modes emerge in the plasma channel,which is influenced by the normalized frequency parameter B and numerical aperture NA.The cutoffs of the various modes are approximated.Single-mode operation is possible without a high-frequency limitation in the channel.     

The Efficiency of Ion Stochastic Heating by a Monochromatic Obliquely Propagating Low-Frequency Alfven Wave

Abstract The process of ion heating by a monochromatic obliquely propagating low-frequency Alfven wave is investigated. This process can be roughly divided into three stages： at first, the ions are picked up by the Alfven wave in several gyro-periods and a bulk velocity in the transverse direction is achieved; then, the ions are scattered in the transverse direction by the wave, which produces phase differences between the ions and leads to ion heating, especially in the perpendicular direction; and finally, the ions are stochastically heated due to the sub- cyclotron resonance. In this paper, with a test particle method, the efficiency and time scale of the ion stochastic heating by a monochromatic obliquely propagating low-frequency Alfven wave are studied. The results show that with the increase of the amplitude, frequency, and propagation angle of the AlDen wave, the efficiency of the ion stochastic heating increases, while the time scale of the ion stochastic heating decreases. With the increase of the plasma beta β, the ions are stochastically heated with less efficiency, and the time scale increases. We also investigate the heating of heavy ion species （He2＋ and O5＋）, which can be heated with a higher efficiency by the oblique Alfven wave.     

Three dimensional nonlinear shock waves in inhomogeneous plasmas with different size dust grains and external magnetized field

The evolution of three dimensional nonlinear shock waves is investigated in a dusty plasma with inhomogeneous particles’density,nonadiabatic dust charge variation,external magnetized field and power law dust size distribution.For this purpose,a modified nonlinear Korteweg-de Vries Burgers equation containing variable coefficients is obtained by reductive perturbation method.The effects of inhomogeneity,dust size distribution,external magnetized field,dust charge variation and obliqueness parameter on shock structures are numerically examined in great detail.Furthermore,research results show that oscillatory shock waves and monotone shock waves exist and transform each other in this system.