Kinetic study of instability growth rate in a helicon plasma discharge source

In this work, a kinetic model is developed to study the effects of the radio frequency antenna wavenumber, helicon plasma electron density, as well as their drift velocity and temperature on the instability increment rate of the helicon wave in both longitudinal and transverse directions. The ion acoustic (IA) wave frequencies and wavenumbers of the helicon waves are obtained when the maximum wave energy is deposited on the plasma ions. Moreover, it is shown that, at the IA wavenumber and frequencies, while the longitudinal instability increment rates for both the helicon and IA waves are ignorable, the transverse instability increment rate for both the helicon and IA wave increases. Besides, the longitudinal instability increment rate for the helicon or IA wave has non‐zero resonant frequencies. On the other hand, the transverse instability increment rate of helicon or IA wave can be neglected. Furthermore, it is observed that, while both the imaginary part of longitudinal permittivity and longitudinal instability increment rate are not influenced by the electron temperature, their transverse component increases linearly with the electron temperature. In addition, the imaginary part of transverse permittivity increases almost linearly with the drift velocity of the plasma electrons.     

The parallel permittivity of magnetized toroidal plasmas with elliptic magnetic surfaces

The asymptotic solution of the Vlasov equation under the drift approximation, for an axially symmetric toroidal plasma configuration with an elliptic cross section of magnetic surfaces, is presented. The analytical expressions for the parallel component of the dielectric permittivity tensor are obtained. These expressions are used for theoretical analyses of the trapped and untrapped electron influence on the collisionless wave dissipation. The evaluated dielectric tensor components can be used for computer calculations of the radio frequency field structure and the collisionless dissipated power related to trapped and untrapped electrons in tokamak plasmas.This work was supported by the State University of Rio de Janeiro (UERJ), Rio de Janeiro Research Foundation (FAPERJ) and Brazilian National Council of Research (CNPq).     

A study of the microwave dielectric permittivity of liquid crystals in electric and magnetic fields

A microwave detector based on a self-sustained oscillator circuit is proposed as a means to investigate the real and imaginary components of the dielectric permittivity of liquid crystals in external electric and magnetic fields. Results are given for measurements of a 500 MHz oscillator frequency for two types of nematic crystals, 5CBP and MBBA. Fundamental regularities are identified in the behavior of the microwave dielectric permittivity of samples in electric and magnetic fields. It is shown that the minimum of the high-frequency dielectric loss in liquid crystals correspond to a situation in which the long axes of the molecules are oriented parallel to the direction of the microwave electric field. Zh. Tekh. Fiz. 68, 117–121 (January 1998)     

Analysis of long wavelength electromagnetic scattering by a magnetized cold plasma prolate spheroid

Abstract

Using dielectric permittivity tensor of the magnetized prolate plasma, the scattering of long wavelength electromagnetic waves from the mentioned object is studied. The resonance frequency and differential scattering cross section for the backward scattered waves are presented. Consistency between the resonance frequency in this configuration and results obtained for spherical plasma are investigated. Finally, the effective factors on obtained results such as incident wave polarization, the frequency of the incident wave, the plasma frequency and the cyclotron frequency are analyzed.     

Generation and amplification of terahertz electromagnetic waves in a plasma waveguide with a dielectric rod and an annular degenerate plasma

The theoretical investigation of terahertz waves and their excitation by electron beam injection in a cylindrical metallic plasma waveguide is investigated. This metallic waveguide includes a cold collisionless unmagnetized annular degenerate plasma and a dielectric rod. The dispersion characteristics of these waves, the frequency spectra of fast and slow E-modes waves (transverse magnetic field), are studied. Also, the effects of the dielectric permittivity, the radius of the dielectric rod and the radius of the plasma on the frequency spectra and the time growth rate of waves are simulated. In addition, the electric field profiles in this waveguide are plotted.     

Dielectric tensor elements for the description of waves in rotating inhomogeneous magnetized plasma spheroids

The dielectric permittivity tensor elements of a rotating cold collisionless plasma spheroid in an external magnetic field with toroidal and axial components are obtained. The effects of inhomogeneity in the densities of charged particles and the initial toroidal velocity on the dielectric permittivity tensor and field equations are investigated. The field components in terms of their toroidal components are calculated and it is shown that the toroidal components of the electric and magnetic fields are coupled by two differential equations. The influence of thermal and collisional effects on the dielectric tensor and field equations in the rotating plasma spheroid are also investigated. In the limiting spherical case, the dielectric tensor of a stationary magnetized collisionless cold plasma sphere is presented.     

The perpendicular permittivity of magnetized toroidal plasmas with elliptic magnetic surfaces

The Vlasov equation for charged particles is analyzed in an axially symmetric toroidal plasma configuration with an elliptic cross section of magnetic surfaces. The asymptotic solution of the Vlasov equation is found. The analytical expressions for the perpendicular component of the dielectric permittivity tensor are obtained. These expressions are used for theoretical analyses of the trapped and untrapped ion influence on the collisionless cyclotron wave dissipation. The evaluated dielectric tensor components can be used for computer calculations of the radio frequency field structure and the collisionless dissipated power related to trapped and untrapped ions in tokamak plasmas. It is shown that ion cyclotron resonance dissipation in tokamaks depends on toroidicity and ellipticity parameters and does not depend on plasma temperature. This work was supported by the State University of Rio de Janeiro (UERJ), Rio de Janeiro Research Foundation (FAPERJ) and Brazilian National Council of Research (CNPq).     

Anomalous absorption of TM electromagnetic waves by an ultrathin layer: optical analog of liquid friction

A strong maximum of absorption (as much as 100%) of bulk TM electromagnetic waves by an ultrathin film with imaginary dielectric permittivity is shown to exist at some optimal film thickness. This typical thickness is usually much smaller than the wavelength and the wave penetration depth in the material of the film. The absorptivity maximum increases and the typical thickness decreases with increasing dielectric permittivity of the layer. An optical analog of linear (liquid) friction is discussed. A frictional contact approximation for TM electromagnetic waves is analyzed, and relevant boundary conditions with an optical coefficient of friction are derived.     

Surface wave propagation at the interface between lossy metamaterials medium and nonlinear media with arbitrary nonlinearity

The dispersion relation in a system that consists of a lossy metamaterials (MTMs) film surrounded by a linear substrate and a nonlinear cladding with an arbitrary nonlinearity is derived. The surface plasmonic (SP) wave at the interfaces between metamaterials (MTMs) and the nonlinear cover is recovered by taking certain limits. Lossy MTMs have simultaneously complex-negative permeability μ and complex-negative permittivity ε. Results are presented by plotting the SP frequency as a function of the nonlinearity at chosen damping factors. Both the real and imaginary parts are studied. Results also display the wave frequency as a function of plasma frequency. For comparison, the imaginary part is set to zero and curves are reproduced.     

单轴各向异性异向介质平板波导中的导模特性

 推导了介电常数张量和磁导率张量中各分量带有不同符号的单轴各向异性异向介质平板波导的导行条件。根据分量符号的正负组合，分情况讨论了导行TE波的偶模特性，画出了平板波导中为实横波数时的布里渊图。结果表明，在特定条件下此平板波导中有无穷多导模，这与传统介质波导及各向同性异向介质平板中只有有限数量模式存在有很大不同。此外，还发现当分量参数满足一定条件时，出现了多个虚横波数的传输模式解，并且该模式存在高频截止。     

Absorption losses in periodic arrays of thin metallic wires

We analyze the transmission and reflection of electromagnetic waves calculated from transfer matrix simulations of periodic arrangements of thin metallic wires. The effective permittivity and the absorption of the arrangements of wires are determined. Their dependence on the wire thickness and the conductance of the metallic wires is studied. The cutoff frequency, or effective plasma frequency, is obtained and compared with analytical predictions. It is shown that the periodic arrangement of wires exhibits a frequency region in which the real part of the permittivity is negative while its imaginary part is very small. This behavior is seen for wires with thickness as small as 17 microm with a lattice constant of 3.33 mm.     

任意纵向磁场中等离子体-腔漂移通道电磁波的解析解

 从麦克斯韦方程和双成分等离子体粒子在外部轴向磁场的线性化运动方程出发，推导出了任意纵向磁场中等离子体介电张量和等离子体-腔漂移通道的电磁波的解析解。结果表明在一般情形下，在位于外部均匀纵向磁场的等离子体波导中，不存在分离的轴对称E波和H波。在此基础上进一步得到轴对称波的具体解析式。单波近似下的结果和俄罗斯全俄电技术研究所M.A.Zavjalov等的结果一致。     

Ion surface cyclotron waves at plasma-metal interfaces

The dispersion properties of slow electromagnetic surface waves propagating across a constant external magnetic field and along a plane plasma-metal interface at harmonics of the ion cyclotron frequency are studied. The motion of the plasma particles is described by a Vlasov-Boltzmann kinetic equation. The effects of the plasma size, the dielectric permittivity of the transition region between the plasma and metal, and the magnitude of the constant external magnetic field on the dispersion characteristics of ion surface cyclotron waves are studied. Zh. Tekh. Fiz. 69, 83–89 (October 1999)     

Light collimation and focusing by a thin flat metallic slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a point source. The effect is optimized when the radiation is around the bulk, not at the surface, plasma frequency. Also, the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of Al, whose imaginary part of permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

Attenuation of electromagnetic waves in a semiconductor superlattice in a magnetic field

Magnetoplasma waves and inhomogeneous (complex) waves in an infinite semiconductor superlattice in a magnetic field are studied, and dispersion curves are obtained. It is shown analytically and numerically that, in periodic structures, among inhomogeneous waves, there are many complex waves for which the imaginary part of the wave vector is greater than the real part. The effect of dissipation in a medium on the dispersion curves of magnetoplasma waves is examined. The dependence of the minimum phase velocity on the collision frequency and the magnetic field strength is studied.     

Effect of nickel nanofillers on the dielectric and magnetic properties of composites based on rubber in the X-band

Nickel–rubber nanocomposites were synthesized by incorporating ferromagnetic nickel nanoparticles in a natural rubber as well as neoprene rubber matrix. Complex dielectric permittivity and magnetic permeability of these composites were evaluated in the X-band microwave frequencies at room temperature using cavity perturbation technique. The dielectric loss in natural rubber is smaller compared to neoprene rubber. A steady increase in the dielectric permittivity is observed with increase in the content of nickel in both the composites. The magnetic permeability exhibits a steady decrease with increase in frequency and magnetic loss shows a relaxation at 8 GHz. The suitability of these composites as microwave absorbers is modeled based on the reflection loss which is dependant on the real and imaginary components of the complex dielectric permittivity and magnetic permeability.     

Traveling Internal Plane-wave Synthesis (TIPS) for uniform B1 in high field MRI

A new target-field approach to generating uniform radio frequency (RF) fields within the human body for high field MRI is described. The method involves producing a set of external fields which, after interaction with a dielectric object, superimpose to produce a traveling plane wave, exposing all spins to the same RF amplitude (B1) over a cycle of the harmonic field. Conceptually this is similar to conventional RF shimming, but uses a different RF source design, input data, and objective function. The method requires a detailed knowledge of the coupling between exterior field modes, produced by an array of RF sources, and field modes within the body. Given an estimate of the coupling matrix, the linear superposition of external modes that produces a desired internal target field can be determined. The new method is termed Traveling Internal Plane-wave Synthesis (TIPS). A simple design of a coil array is described that can, in principle, generate the required field modes. Simulations demonstrate that radio frequency magnetic fields of nearly uniform (< 1% variation) magnitude can be produced within dielectric objects larger than a wavelength in size. If the dielectric medium has non-zero conductivity, traveling waves are attenuated as they traverse the object, but field uniformity within planar slices is preserved. For general 3D imaging, a superposition of plane waves can provide field focusing to balance conductive losses, thereby achieving nearly uniform-magnitude B1+ magnetic fields over a volume of interest.