Rarefactive ion-acoustic electrostatic solitary structures in nonthermal plasmas

An investigation has been made of ion-acoustic solitary waves in an unmagnetized nonthermal plasma whose constituents are an inertial ion fluid and nonthermally distributed electrons. The properties of stationary solitary structures are briefly studied by the pseudo-potential approach, which is valid for arbitrary amplitude waves, and by the reductive perturbation method which is valid for small but finite amplitude limit. The time evolution of both compressive and rarefactive solitary waves, which are found to coexist in this nonthermal plasma model, is also examined by solving numerically the full set of fluid equations. The temporal behaviour of positive (compressive) solitary waves is found to be typical, i.e., the positive initial disturbance breaks up into a series of solitary waves with the largest in front. However, the behaviour of negative (rarefactive) solitary waves is quite different. These waves appear to be unstable and produce positive solitary waves at a later time. The relevancy of this investigation to observations in the magnetosphere of density depressions is briefly pointed out. Received 12 October 1999     

Electron acoustic solitary waves in unmagnetized nonthermal plasmas

Electron acoustic(EA) solitary waves(SWs) are studied in an unmagnetized plasma consisting of hot electrons(following Cairns-Tsalli distribution), inertial cold electrons, and stationary ions.By employing a reductive perturbation technique(RPT), the nonlinear Korteweg–de Vries(KdV) equation is derived and its SW solution is analyzed. Here, the effects of plasma parameters such as the nonextensivity parameter(q), the nonthermality of electrons(α), and the cold-to-hot electron density ratio(β) are investigated.     

Damped dust-ion-acoustic solitons in collisional magnetized nonthermal plasmas

A multispecies magnetized collisional nonthermal plasma system, containing inertial ion species, noninertial electron species following nonthermal -distribution, and immobile dust particles, is considered to examine the characteristics of the dissipative dust-ion-acoustic soliton modes, theoretically and parametrically. The electrostatic solitary modes are found to be associated with the low-frequency dissipative dust-ion-acoustic solitary waves (DIASWs). The ion-neutral collision is taken into account, and the influence of ion-neutral collisional effects on the dynamics of dissipative DIASWs is investigated. It is reported that most of the plasma medium in space and laboratory are far from thermal equilibrium, and the particles in such plasma system are well fitted via the -nonthermal distribution than via the thermal Maxwellian distribution. The reductive perturbation approach is adopted to derive the damped KdV (dKdV) equation, and the solitary wave solution of the dKdV equation is derived via the tangent hyperbolic method to analyse the basic features (amplitude, width, speed, time evolution, etc.) of dissipative DIASWs. The propagation nature and also the basic features of dissipative DIASWs are seen to influence significantly due to the variation of the plasma configuration parameters and also due to the variation of the supethermality index in the considered plasma system. The implication of the results of this study could be useful for better understanding the electrostatic localized disturbances, in the ion length and time scale, in space and experimental dusty plasmas, where the presence of excess energetic electrons and ion-neutral collisional damping are accountable.     

New method for polarization measurements of magnetic fields indense plasmas

Measurements of magnetic fields based on observations of the Zeeman splitting ω_B of spectral lines is a virtually impossible task in dense plasmas of powerful Z-pinches where the Stark splitting in the ion microfields ω_F is much greater than ω_B. In this situation, much better diagnostics of magnetic fields can be achieved through polarization difference contours obtained by subtracting profiles of the same spectral line observed in two orthogonal linear polarizations. In this way the obscuring role of the Stark effect is significantly diminished. In the present paper it is shown that the most sensitive and accurate measurements of the magnitude and the direction of the magnetic field in a dense plasma can be conducted employing central Stark components of hydrogen or hydrogen-like spectral lines. The polarization contour of a central Stark component turned out to be much more sensitive to the magnetic field than the polarization contour of a lateral component of the same line, namely by a factor of (ω_F/ω_B) ³≫1. This constitutes a drastic enhancement of the previously suggested method that had used the polarization contour of a lateral Stark component because in dense plasmas a typical value of the above factor is (ω_F/ω_B)³⩾10³ . The new method can also be used for laser fusion plasmas and for some astrophysical objects such as magnetic white dwarfs     

Destruction of organophosphorus compounds in flames and nonthermal plasmas

The available results of experimental and theoretical studies of the chemistry and mechanism of the destruction of organophosphorus compounds (OPCs) in a flame and corona discharge plasma are systematized. The experimental methods, instrumentation, and methodological approaches used in determining the flame structure and identifying the products of OPC destruction are described. The published kinetic models capable of describing the decomposition of OPCs and the mechanisms of the promoting and inhibiting action of OPCs on combustion are considered. Common and distinctive features of the mechanisms of OPC destruction in various processes are examined. Practical aspects of the processed studied, including toxic waste disposal, chemical weapon elimination, and fire safety problems, are briefly overviewed.     

A method of analysis of distributions of local electric fields in composites

A method of prediction of distributions of local electric fields in composite media based on analysis of the tensor operators of the concentration of intensity and induction is proposed. Both general expressions and the relations for calculating these operators are obtained in various approximations. The analytical expressions are presented for the operators of the concentration of electric fields in various types of inhomogeneous structures obtained in the generalized singular approximation.     

Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas

Unlike α- and γ-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF(4). Mode transitions induced by voltage and pressure variations are studied.     

Frequency shift and anomalous resistivity of turbulent plasmas in external electric and magnetic fields

Accounting for the modified orbits of plasma particles due to constant external electric and magnetic fields, a general expression for the velocity space diffusion tensor of a turbulent plasma is derived. The nonlinear frequency shift and the anomalous resistivity in the presence of external fields are calculated. It is shown that the effect of a strong external electric field on the frequency shift is to reduce its magnitude. Furthermore, the dependence of the anomalous resistivity on the external magnetic field is obtained.     

Propagation properties of dust-electron-acoustic waves in weakly magnetized dusty nonthermal plasmas

The linear and nonlinear properties of dust-electron acoustic waves (DEAWs) propagating in magnetized, collisionless, dusty plasma system containing inertial cold electrons, Maxwellian hot electrons, nonthermal ions, and arbitrarily (positively or negatively) charged stationary dust are investigated. The reductive perturbation technique is employed to reduce the basic set of fluid equations to the modified Korteweg-de Vries equation or Ostrovsky's equation, which governs the dynamics of small amplitude DEAWs in a weakly magnetized dusty nonthermal plasma. The approximate analytical as well as numerical solutions reveal that the basic characteristics of DEA nonlinear structures are found to be significantly modified by the key plasma configuration parameters. It is found that the leading compressive or rarefactive solitary wave structure separates from a trailing wave packet during a considerable time under the influence of magnetic field-induced Lorentz force.     

Stationary equilibria of two fluid plasmas having significant, internal, static electric fields

New steady-state equilibria of two-species, collisionless plasmas have been found for symmetrical systems by varying the total energy subject to Maxwell's equations, momentum moment equations, and adiabatic equations of state, without imposing a quasineutrality condition. Electrons are confined by magnetic forces and ions by internal, electrostatic forces due to charge separation. The scale length for one-dimensional plasmas is characterized by the electron skin depth. Minimum average beta values are approximately one-half. Space and laboratory applications are discussed.     

Renormalized diffusion coefficients for electron-hole plasmas in crossed fields

The diffusion and drift of an excess plasma in a semiconductor is described with magnetohydrodynamic two-fluid equations including the fluctuating electric field produced by the equilibrium plasma in the sample. Using the weak coupling limit an equation of motion for the mean density of the excess plasma is established with renormalized drift and diffusion coefficients. With the aid of the fluctuation dissipation theorem these coefficients are expressed in terms of the dielectric function and discussed in detail for stable systems. The renormalized diffusion coefficient differs from the bare one by an additional term with thet ^–3/2-long time dependence. It is shown that this term in addition represents an anomalous diffusion rate proportionalB ^–1 which overweights the classical ambipolar diffusion for sufficiently strong fields, but decreases with increasing external electric field. The results are compared with experimental data.     

A phase field method for simulating morphological evolution of vesicles in electric fields

A phase field method is developed to investigate the morphological evolution of a vesicle in an electric field, taking into account coupled mechanical and electric effects such as bending, osmotic pressure, surface tension, flexoelectricity, and dielectricity of the membrane. The energy of the system is formulated in terms of a continuous phase field variable and the electric potential. The governing equations of the phase field and the electric field are solved using the Galerkin weighted residual approach. The validation and robustness of the algorithm are verified by direct comparisons of the obtained numerical solutions with relevant experimental results. The morphological evolution of an axisymmetric vesicle under an electric field is studied in detail. The results demonstrate that the present method can simulate complex morphological evolutions of vesicles under coupled mechanical–electrical fields.     

激光烧蚀Cu靶产生等离子体紫外段发射光谱的研究

利用波长532nm,脉宽15ns的Nd:YAG 激光器作用于Cu靶上,研究了产生等离子体的紫外段（180 nm～300 nm）发射光谱。在局部热力学平衡条件下,采用Boltzmann图表法估算了等离子体的电子温度,得到了电子温度随时间和空间的变化,以及电子温度随激光能量密度的变化。结果显示,随着激光能量的变化,电子温度有一个极大值。随着时间的发展,电子温度先减小,而后增大,接着缓慢减小。随着距靶面距离的增加,电子温度呈下降趋势。     

激光烧蚀Cu靶产生等离子体紫外段发射光谱的研究

利用波长532nm,脉宽15ns的Nd:YAG 激光器作用于Cu靶上,研究了产生等离子体的紫外段（180 nm～300 nm）发射光谱。在局部热力学平衡条件下,采用Boltzmann图表法估算了等离子体的电子温度,得到了电子温度随时间和空间的变化,以及电子温度随激光能量密度的变化。结果显示,随着激光能量的变化,电子温度有一个极大值。随着时间的发展,电子温度先减小,而后增大,接着缓慢减小。随着距靶面距离的增加,电子温度呈下降趋势。     

Dust acoustic solitary and shock waves in strongly coupled dusty plasmas with nonthermal ions

The Korteweg-de Vries-Burgers (KdV-Burgers) equation and modified Korteweg-de Vries-Burgers equation are derived in strongly coupled dusty plasmas containing nonthermal ions and Boltzmann distributed electrons. It is found that solitary waves and shock waves can be produced in this medium. The effects of important parameters such as ion nonthermal parameter, temperature, density and velocity on the properties of shock waves and solitary waves are discussed.     

Superradiation from non-ideal plasmas in electric field

An effect of external static electric field on emission of radiation from non-ideal plasmas of erosion focus has been experimentally observed. An order-of-magnitude increase in radiation intensity for spectral interval hv = 40 ? 350 eV with electric field increasing up to 10³V/cm has been found for plasmas with $\text{ξ}\text{Z}\text{?1}$, where ξ is the number of electrons in Debye sphere, Z = 2 ? 3 is the stage of ionization. The energy emitted has been several times higher than the black body energy for the same spectral interval at maximum electric field achieved. The effect vanishes at $\text{ξ}\text{Z}\text{?10}$.     

Diagnostics for radial electric field measurements in hot magnetized plasmas

Measurements of the radial electric field profile in magnetically confined plasmas have yielded important new insights in the physics of L-H transitions, edge biasing and/or the active control of Internal and Edge Transport Barriers. The radial electric field is not an easy plasma parameter to diagnose. Techniques to measure the radial electric field in the plasma core are the Heavy Ion Beam Probe and the Motional Stark Effect. An indirect method that is quite often applied is to derive the electric field from measurements of the poloidal and toroidal rotation velocities via the radial ion force balance. This paper will first briefly explain the need for detailed measurements of the radial electric field profile. Subsequently, the various diagnostics to measure this parameter will be reviewed. The emphasis will be especially put on recent trends, rather than on an exhaustive overview. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24, 2002. Partner in the Trilateral Euregio Cluster