Study of Coulomb collisional effects on the propagation of electromagnetic waves in a turbulent plasma

The presence of Weibel instability in laser-irradiated fuel could be detrimental to the process of ablative implosion, which is necessary for achieving thermonuclear fusion reactions. In this paper, the effect of the Coulomb collisional within the turbulent plasma on the Weibel instability growth rate has been investigated for linear and circular polarization. The results indicate that the Weibel instability growth rate at circular polarization near the ignition centre of the fuel fusion (collisional plasma) is about 10⁵ times higher than the collisional Weibel instability growth rate at linear polarization. The Weibel instability growth rate is observed near the critical density of the fuel fusion (collisionless plasma) at linear polarization and enhancement near the foot of the heat in front of the fuel fusion. By increasing the steps of the density gradient plasma in the low-density corona, electromagnetic instability occurs at a higher stress flow. Therefore, the deposition condition of electron beam energy in circular polarization of turbulent plasma can be shifted to the fuel core for suitable ignition.     

The ion streaming effect on Weibel instability in the relativistic dense plasma

The Weibel instability plays an important role in stopping hot electrons and energy deposition mechanism in fast ignition of inertial fusion process. In this paper, the ion Weibel instability in counter propagating electron‐ion plasmas is investigate. The obtained results show that the growth rate of Weibel instability will be decreased about 40% with the anisotropy velocity as v_xe = 2v_ze = 20; the ion density ratio, b = n _{0i 1}/n _{0i 2}, and density gradient, are increasing 50 and 90% respectively. The ion streaming in density gradient of dense plasma leads to increasing the Weibel instability growth rate and its amplification through ion streaming in the large wavenumber. The maximum unstable wavenumber has been decreased with decreasing the ion beam density ratio. For fixed ion density ratio, increasing 90% of the density gradient in the near of fuel plasma corona leads to reducing growth rate and unstable wavenumber about 43 and 42% respectively.     

Weibel instability in plasma produced by a superintense femtosecond laser pulse

The Weibel instability increment is analytically derived for plasma produced at the barrier-suppression ionization of atoms and atomic ions by a superintense femtosecond laser pulse. The cases of linear and circular polarization are considered. Relativistic effects are discussed. It is found that the instability increment is larger for the circular polarization than for the linear polarization. This increment can attain the plasma frequency. Barrier-suppression ionization decreases the increment compared with the case of tunneling ionization. Relativistic effects also decrease the value of the increment. Estimates of the produced maximum quasistatic magnetic field are given.     

The effect of the plasma density gradient on current filamentation instability

The filamentation instability is one of the basic beam-plasma instabilities that play a significant role in the energy deposition mechanism of the relativistic electrons generated by the laser-plasma interaction in the fast ignition scenario. In this paper, the effect of the density gradient into plasma on the filamentation instability was investigated in the Weibel unstable plasma, where the plasma temperature anisotropy can play an important role. Results indicated that the density gradient enhances the instability growth rate so that decreasing the density gradient from the critical surface to the core of fuel leads to instability for longer regions in k space. Also, investigations in the region close to the critical surface showed that for decreasing the beam number density n_b ≤ 0.01n₀, the instability occurs for while this can be different for higher values. Increasing the beam relativistic factor causes a decreasing peak of instability growth rate because of a reduction in beam current, whereas the initial thermal spread of plasma amplifies the filamentation instability.     

Saturation of relativistic Weibel instability and the formation of stationary current sheets in collisionless plasma

We have studied the features of formation and the possible stationary structures of a self-consistent magnetic field in a relativistic collisionless plasma, which are characteristic of a simple geometry of the Weibel instability that is well known in the nonrelativistic case. The universal condition is established, the growth rate is determined, and the criteria of saturation of the Weibel instability are analyzed for a broad class of anisotropic particle distribution functions (for definiteness, in application to an electron-positron plasma). A nonlinear equation of the Grad-Shafranov type describing the potential current structures is derived and its solutions are analytically studied. Special attention is paid to spatially harmonic, nonlinear current configurations with parameters determined by the properties of the initial homogeneous plasma subject to the Weibel instability. It is demonstrated that the magnetic field energy density in the obtained solutions (both harmonic and nonharmonic) can be comparable with the kinetic energy density of plasma particles.     

Effects of dust-charge gradient and polarization forces on the waves and Jeans instability in strongly coupled dusty plasma

The effects of dust charge gradient (DCG) force and polarization force have been investigated on the properties of dust acoustic wave (DAW) and linear Jeans instability in strongly coupled dusty plasma. In the kinetic regime, DCG and polarization forces modify the DAW mode and couple with compressional viscoelastic wave mode. The Jeans instability criterion and critical wavenumber have been modified due to DCG force, polarization force and strong coupling effects. The results have been discussed in the warm photodisassociation region and in the laboratory complex plasmas. The strong correlation effect and the charge variation parameter stabilize the growth rate of Jeans instability. But, the polarization parameter stabilize the growth rate for positively charged dust grains and destabilize for negatively charged dust grains. The implications of charge gradient and polarization parameters are discussed for lower and higher charges in the laboratory complex plasma which decreases the growth of the propagating DAW.     

相对论电子束在等离子体中的能量沉积

 用3维粒子模拟程序LARED-P研究了束-等离子体不稳定性, 不稳定性激发的强电磁场使电子束在非常短的距离内沉积能量。对于10 MeV的单能电子束,束电子数目占总电子数目5％的情况下,最终约损失14％的束能量。推导了等离子体的色散关系,得出了增长率。     

Stabilization effect of Weibel modes due to inverse bremsstrahlung absorption in laser fusion plasma using Krook collisions model

In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma has been investigated. The stabilization effect due to the coupling of the self-generated magnetic field by Weibel instability with the laser wave field is explicitly showed. The main result obtained in this work is that the inclusion of self-generated magnetic field due to Weibel instability to the inverse bremsstrahlung absorption causes a stabilizing effect of excited Weibel modes. We found a decrease in the spectral range of Weibel unstable modes. This decrease is accompanied by a reduction of two orders in the growth rate of instability or even stabilization of these modes. It has been shown that the previous analyses of the Weibel instability due to inverse bremsstrahlung have overestimated the values of the generated magnetic fields. Therefore, the generation of magnetic fields by the Weibel instability due to inverse bremsstrahlung should not affect the experiences of an inertial confinement fusion.     

Collisional Effect on Weibel Instability with Semi-Relativistic Maxwellian Distribution Function

In this paper, the Coulomb collisional effect of electron-ion on the growth rate of Weibel instability is investigated based on the semi-relativistic Maxwellian distribution function in dense and unmagnetized plasma. An analytical expression was derived for the dispersion relation of Weibel instability for two limit cases [ξ = ω＇/k‖T‖ 〉〉 1 and ｜ξ｜ 〈〈 1. In limit ｜ξ｜ 〉〉 1 the dispersion relation only includes a real part and in limit ｜ξ｜ 〈〈 1 the imaginary part of the frequency of waves＇ instability plays a role in the dispersion relation. In limit ｜ξ｜ 〈〈 1, the two quantities μ and η, that are due to the relativistic and collisional effects, will appear in the growth rate of Weibel instability. The growth rate of Weible istability will be increased through decreasing the Coulomb collisional frequency and also increasing the temperature anisotropic parameter in strong relativistic limit.     

Nonlocal theory of stimulated Raman backscattering in a strongly magnetized plasma

A nonlocal theory of stimulated Raman backscattering (BSRS) parametric instability of a large amplitude electromagnetic (EM) mode in a strongly magnetized plasma e.g., one encountered in a plasma filled backward wave oscillator, is reported. The EM mode is unstable to parametric instability in a magnetized plasma and decays into a Trivelpiece-Gould (TG) mode and a sideband EM mode. The growth rate of instability (Γ) scales proportional to three-fourth power of plasma density. For a typical BWO the growth rate is ∼10⁸ s^-1     

Kinetic Current-Convective Instability in Hot Electron Plasma

The kinetic current-convective instability excited in a hot electron plasma, i.e. for T_e ? T_i, is investigated in the linear stage. Density and temperature of plasma components have gradients along the x-direction. In the absence of longitudinal current (u = 0) and homogeneous temperature the instability is also excited with maximum growth rate much exceeding that obtained in the case of u ≠ 0. Gradual increasing of the ion temperature over that of the electrons and a large density gradient leads to reduce the instability in the linear stage.     

On the electric activity of superfluid systems

The Keldysh theory of the superfluidity of a diluted electron-hole gas has been generalized to the case of the possible polarization of the pairs. It has been shown that the inhomogeneity of the system induces the dipole moment, which appears near the system boundaries and is proportional to the gradient of the particle density. It has been found that the quantized vortices in the magnetic field carry a real electric charge. The charge density in He II rotating at a rate of 10²s⁻¹ in a magnetic field of 10 T is about 10⁴ e cm⁻³, where e is the elementary charge.     

飞秒激光与等离子体相互作用中自生磁场的热电机制

采用理论分析和数值模拟研究了考虑相对论效应的自生磁场及其产生机制,给出了自生磁场的解析表达式,得到了温度梯度和密度梯度的非共线性所引起的自生磁场空间分布的时间演化关系。数值结果表明,当峰值强度为1019 W/cm2的激光作用于凹形靶前表面时,在等离子体表面领域观察到的自生磁场最大值为51102 T量级,与实验测量结果相符合。     

A simple analytical model for the Weibel instability in the non-relativistic regime

The Weibel instability is prompted by a temperature anisotropy within a plasma. We present an analytical model based on a non-relativistic two temperatures waterbag distribution function. The model is exactly solvable in terms of the stability condition, the growth rate for any wave vector and temperature parameters, the maximum growth rate and the wave number for which it is reached.     

Influence of Negative Ions on Drift Waves in a Low‐Density Ar/O2‐Plasma

The effect of negative ions on the drift wave instability has been studied in detail in a linear device by means of Langmuir probes and cross‐correlation analysis. Drift waves are excited in low‐density (5 × 10¹⁴ m^–3) and strongly magnetized (0.5 T) pure argon plasmas and in the presence of an oxygen admixture. The radial density profile of negative ions is hollow. For increasing concentration of negative ions the wave frequency decreases by about 25%. Despite of an axial density gradient, a global wave frequency is established for the entire column length. While for the noble gas case the drift wave frequency is given by the equilibrium plasma parameters in the mid‐plane, there is no such relationship for the argon plasma with oxygen admixture. This different finding is attributed to the inhomogeneous distribution of the negative ions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Weibel instability associated with inverse bremsstrahlung absorption of intense electromagnetic radiation

We investigate the Weibel instability in a plasma with a nonstationary three-temperature electron distribution generated by inverse bremsstrahlung of an intense elliptically polarized electromagnetic wave. We show that electron-ion collisions in this strong high frequency field are simultaneously the cause of the development of the instability and the reason it is suppressed. We find plasma and radiation parameters for which spontaneous quasistationary solenoidal electromagnetic fields can increase by many times. Zh. éksp. Teor. Fiz. 111, 1245–1257 (April 1997)     

Quasi Exact Model for the Anisotropy Driven Weibel Instability all over Fourier Space

The Weibel instability is prompted by a temperature anisotropy within a plasma. We investigate its growth rate for wave vectors making an arbitrary angle with the high temperature axis. We use a two temperatures waterbags model and derive stability conditions depending on both temperatures and wave vector orientation. It is found that the growth rate is maximum for wave vectors normal to the high temperature axis. Also, a critical angle is evidenced in the k space in which direction modes are unstable at high k although the growth rate decreases quickly in this direction. Exact results are derived in most cases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Amplification of electromagnetic radiation by a nonequilibrium plasma unstable against the development of Weibel instability

The reflection of an electromagnetic pulse by a nonequilibrium plasma in which the development of Weibel instability is possible has been studied. An exponentially strong amplification of the reflected signal at the stage of instability development has been found to be possible. The amplification maximum takes place at a radiation frequency comparable to the instability growth rate. A nonequilibrium plasma is shown to be a generator of radiation even after the switch-off of the incident pulse. The described effect of amplification of the reflected signal points, in particular, to a new possibility in mastering the terahertz frequency band.     

Snake instability in the plasma of the Globus-M spherical tokamak

Experiments with the limiting density of a plasma generated in the Globus-M spherical tokamak operating in the ohmic heating regime show that, when the plasma density reaches a certain value at the center of the plasma filament, snake-type strong magnetohydrodynamic instability exciting the m/n = 1/1 mode arises. A further rise in the density causes an internal disruption of the plasma. Numerical simulation of the instability dynamics is performed, and the results of simulation are compared with experimental and theoretical data. Experimental and theoretical data are in good agreement. It is shown that the instability is associated with an increased amount of impurities in the plasma and that the limit in density is of a “technological,” rather than of a fundamental, character. With the vacuum chamber cleaned more thoroughly, this limit disappears and the snake instability is not observed. Accordingly, a plasma filament density of 1 × 10^{20 m?3} was attained with a Greenwald number as high as 95%.