Thick Plasma Layer Research Articles

Reflection and transmission characteristics of frequency selective surface embedded within a thick plasma layer

In this paper, the reflection and transmission characteristics of frequency selective surface (FSS) embedded within a thick plasma is studied. The plasma layer is lossy and dispersive medium and the embedding of the FSS will change the electromagnetic wave propagation very much. The reflection and transmission coefficients of a square patch FSS layer embedding in plasma is calculated utilizing finite-difference time-domain (FDTD) method. Auxiliary differential equation (ADE) is utilized to simulate the dispersion of the plasma. The influence of the plasma and slab's parameter to the reflection and transmission coefficients is investigated. Various parameters of collision frequency, plasma frequency and thickness of plasma are involved to study the influence of these factors. The reflection and transmission coefficient values of different parameters are plotted to compare their effects. The results show that collision frequency reduces the reflection and transmission coefficient. Plasma frequency changes the FSS from low pass filter to band pass filter. Thick plasma slab makes the transmission coefficient oscillate as the variation of incident frequency.

Unexpected impact of radiation friction: enhancing production of longitudinal plasma waves

We study the penetration of ultra-intense (intensity Isimeq 1023–24 W/cm2) circularly polarized laser pulses into a thick subcritical plasma layer with accounting for radiation friction. We show that radiation pressure is enhanced due to radiation friction in the direction transverse to the laser pulse propagation, and that for stronger and longer laser pulses this mechanism dominates over the ordinary ponderomotive pressure, thus resulting in a substantionaly stronger charge separation than anticipated previously. We give estimates of the effect and compare them with the results of one and two dimensional particle-in-cell simulations. This effect can be important for laser-based acceleration schemes.

Stability of finitely incompressible magnetized plasma layer through porous fluids

The combined effect of horizontal and vertical magnetic fields on the instability of the incompressible plasma layer of finite thickness through porous medium is investigated. The layer is confined between two rigid boundaries. The basic Magnetohydrodynamics set of equations have been constructed and linearized. The dispersion relation is obtained by applying the appropriate boundary conditions and solved numerically. The results show that the presence of both magnetic field components besides the resistive and convective terms will bring about more stability on the considered system.

Reflection and transmission of an ultrashort electromagnetic pulse incident normal to a flat plasma layer

The process of reflection and transmission of ultrashort pulses incident normal to a flat plasma layer of finite thickness and on a step barrier is calculated within an exact mathematical approach for various parameters (barrier width and duration and carrier frequency of a corrected Gaussian pulse) of the problem.

Radially polarized terahertz radiation in laser-induced linear plasma wake

The radially polarized terahertz radiation from laser-induced oscillating current is investigated by employing a two-dimensions plasma wakefield analytical model. It is shown that in linear plasma wake the currents have a periodical change along laser axis, and the current directions in potential well and potential barrier are opposite. The radial currents vanish at laser axis, which is different from longitudinal current, thus leading to a angle deviation of peak radiated power of radially polarized THz wave from laser axis. The deviation is more significant in thick plasma layer. The dependance of peak radiated power and total power of THz emission on thickness of plasma layer and laser intensity is discussed.

Equivalent Circuit Model for Frequency-Selective Surfaces Embedded Within a Thick Plasma Layer

In this paper, an equivalent circuit model for a frequency-selective surface (FSS) embedded in a thick plasma layer is introduced. The plasma layer is a lossy and dispersive medium, and therefore, the equivalent model is not purely imaginary and consists of resistive elements as well as inductance and capacitance elements. First, a square patch FSS is simulated in a wide frequency range from 1 to 25 GHz by a full-wave electromagnetic software, and then all the circuit elements are calculated by genetic algorithm optimization to achieve reflection coefficient similar to the one obtained by simulation. It is shown that this model can mimic the simulated behavior with good approximation. Then values of different elements of the model through practical variations of cold plasma parameters are plotted, and the effects of electron density and collision frequency are investigated on circuit elements.

Monoatomically thin polarizable sheets

We consider a flat lattice of dipoles modeled by harmonic oscillators interacting with the electromagnetic field in the dipole approximation. Eliminating the variables from the coupled equations of motion, we come to effective Maxwell equations. These allow for taking the lattice spacing $a$ to zero. As a result, we obtain reflection coefficients for the scattering of electromagnetic waves off the sheet. These are a generalization of that known from the hydrodynamic model. For instance, we get a nontrivial scattering for polarizability perpendicular to the sheet. Also, we show that the case of polarizability parallel to the sheet can be obtained in a natural way from a plasma layer of finite thickness. As an alternative approach, we discuss the elimination of the electromagnetic fields resulting in effective equations for the oscillators. These are shown, for $a\ensuremath{\rightarrow}0$, divergent behavior, resulting from the electrostatic interaction of the dipoles.

Simulation of plasma dynamics in a keyhole during laser welding of metal with deep penetration

Physical processes occurring in the keyhole during the deep-penetration laser welding of aluminium, where evaporation, ionization and formation of near-surface low-temperature plasma can take place, are studied theoretically. Equations of radiation gas dynamics including the equilibrium model of plasma, description of laser radiation transport and absorption are solved. Numerical calculations of plasma cloud propagation processes in aluminium vapour are performed in a one-dimensional approach. The minimum radiation power necessary to maintain this cloud is found. The effect of radiation trapping by plasma due to self-absorption in the optically thick plasma layer is revealed. The simulation results are of interest for a qualitative understanding of the processes in the keyhole plasma.

Reflection of Electromagnetic Waves by a Nonuniform Plasma Layer Covering a Metal Surface

Reflection coefficients of electromagnetic waves in a nonuniform plasma layer with electrons, positive ions and negative ions, covering a metal surface are investigated by using the finite-difference-time-domain method. It is shown that the reflection coefficients are influenced greatly by the density gradient on the layer edge, layer thickness and electron proportion, i.e., the effect of the negative ions. It is also found that low reflection or high attenuation can be reached by properly choosing high electron proportion, thick plasma layer, and smooth density gradient in the low frequency regime, but sharp density gradient in the high frequency regime.

Applications of low-density foams for x-ray source studies and laser beam smoothing

Layers of low density porous materials offer various applications in laser plasma interaction experiments. Two experimental studies of laser-foam interaction are presented. Firstly, time-integrated and time-resolved transmission of the laser beam through a layer of underdense plastic TAC (C12H16O8) foam was measured. The data are required for the design of dynamic smoothing of inhomogeneities inside a laser beam by its propagation through an underdense foam. Secondly, emission of K-shell lines from TMPTA (C15H20O6) foams of density 10 and 20 mg/cc doped by 10 or 20 weight % of chlorine was measured with a high spectral (>5000) and spatial (<10 μm) resolution. The demonstrated formation of a relatively thick homogenous plasma layer close to the foam surface may be used for atomic physics studies of multiply ionized dense plasmas.

Vasculoprotective properties of the endothelial glycocalyx: effects of fluid shear stress

The endothelial glycocalyx exerts a wide array of vasculoprotective effects via inhibition of coagulation and leucocyte adhesion, by contributing to the vascular permeability barrier and by mediating shear stress-induced NO release. In this review, we will focus on the relationship between fluid shear stress and the endothelial glycocalyx. We will address the hypothesis that modulation of glycocalyx synthesis by fluid shear stress may contribute to thinner glycocalyces, and therefore more vulnerable endothelium, at lesion-prone sites of arterial bifurcations. Finally, we will discuss the effects of known atherogenic stimuli such as hyperglycaemia on whole body glycocalyx volume in humans and its effect on endothelial function.

Removal of volatile organic compounds in atmospheric pressure air by means of direct current glow discharges

A nonthermal plasma with an electron density on the order of 10/sup 12/ cm/sup -3/ and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a /spl sim/1 mm/sup 3/ micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure glow discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure glow discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.

Measurement of Frictional Characteristics of Red Blood Cells Moving on a Plate in Plasma due to Inclined Centrifugal Force.

As a fundamental equipment for studying blood flow in microcirculation, the inclined centrifuge microscope enables us to measure frictional characteristics of cells moving on a plate in a medium under the effect of inclined centrifugal force. Specifically, this paper deals with measurement for red blood cells moving on a glass plate in plasma. First, accuracy of the manual measurement of cell velocity through the microscope was confirmed in comparison with the image processing method. Measurement was then performed confirming frictional characteristics of red blood cells were properly modeled as the sum of the Coulomb friction with friction coefficient of 0.206 and the linear viscous friction applied on a simplified circular disk with a plasma layer of thickness of 0.176 μm in the present condition.

Synchrotron maser emission in the saturated regime

Using the method of Einstein coefficients, we derive a quasi-linear kinetic equation for relativistic electrons, in which synchrotron emission of the particles is taken into account. We discuss the evolution of the electron distribution taking into account the effect of weak radiative diffusion of the particles over pitch angles. We analyze a solution of the quasi-linear kinetic equation for electrons and the radiation transfer equation in a stationary thick plasma layer in which maser amplification of the synchrotron radiation takes place. In this case, we assume that population inversion in the electron distribution and, thus, stationary synchrotron emission occur due to an external (nonsynchrotron) acceleration mechanism. The efficiency of this acceleration mechanism is assumed to have a power-law dependence of the electron energy. Under these conditions, we find the spectra of synchrotron maser emission, which are entirely determined by the external acceleration.

Rayleigh-Taylor Instability of a Compressible Plasma with Finite Larmor Radius Effects

Abstract The Rayleigh-Taylor instability of a compressible plasma in the presence of a horizontal magnetic field is investigated, taking into account the effects of finite Larmor radius. Only transverse perturbations are considered. The problem is shown to be characterized by a variational principle. Using it, the dispersion relation is obtained for a plasma layer of finite thickness and having an exponentially varying density. It is found that the finite Larmor radius effects can thoroughly stabilize unstable configurations. For configurations which are not completely stabilized, the compressibility stabilizes some of the disturbances which are unstable for an incompressible plasma.

Comments on ‘‘Finite Larmor radius effects on thermosolutal instability of a plasma’’ [Phys. Fluids 2 4, 2242 (1981)

The effects of the finite Larmor radius on the thermosolutal instability of an incompressible plasma layer of finite thickness are discussed in the presence of a uniform vertical magnetic field. A sufficient condition for the principle of exchange of stabilities is established.

Effect of finite Larmor radius on the gravitational instability of a conducting plasma layer of finite thickness surrounded by a non-conducting matter

The gravitational instability of an incompressible, infinitely conducting plasma layer of finite thickness surrounded a non-conducting matter has been investigated taking into account the effect of the finite Larmor radius. The magnetic field is assumed to be directed parallel to the interfaces. Only the perturbations transverse to the magnetic field are considered, though both the symmetric and asymmetric nature of the perturbations are taken into account. Using the normal mode technique, dispersion relations are obtained.

Double stimulated Raman scattering in a plasma

An analysis is made of the simultaneous stimulated scattering of the incident and reflected components of a pump wave by electron density perturbations in a plasma. It is shown that this double stimulated Raman scattering (DSTRS) effect results in an absolute instability of the scattered component. A model of a homogeneous plasma layer of finite thickness is used to find the DSTRS reflection coefficient allowing both for the pump wave depletion and for the plasma wave nonlinearity. It is shown that the DSTRS effect is retained also in a plasma with an inhomogeneous density distribution. In this case the width of the wave interaction region is governed either by electron collisions or by convective transport of plasma waves. The angular and spectral characteristics of DSTRS in an inhomogeneous plasma are considered.

Low-frequency surface waves on bounded warm magneto-active plasma

The spectra of low-frequency surface waves propagating along a warm magneto- plasma layer bounded by dielectric are investigated, using a two-fluid hydrodynamic plasma model. It is shown that such propagation is possible only for some definite directions of the external magnetic field B0, with respect to the plasma-dielectric interfaces. The spectra obtained for a thick plasma layer correspond to the well-known results for a magneto-active plasma, bounded on one side by a vacuum, derived in the limit of one-fluid hydrodynamics.

Coherent Emission from Indium Antimonide with Closely Spaced Coplanar Contacts

A new versatile, coplanar-contact device configuration has been developed for generation of coherent emission from indium antimonide. The devices, which generate coherent emission at frequencies from 6.5–30 GHz, exhibit three types of operation. Emission is generated (1) in a thin-layer plasma formed by a strong transverse magnetic field, (2) in a thin-layer plasma formed as a result of the coplanar-contact configuration (zero magnetic field) and (3) in a thick-layer plasma formed by forcing carriers away from the contact surface with a strong transverse magnetic field. For a resonance condition between the coplanar-contacts, the emission frequency generated in a thin-layer plasma is related to the contact spacing in accordance with two-stream theory. The emission from the thin-layer plasma in zero magnetic field and the noise emission generated at room temperature by the coplanar-contact samples in a 10-kG transverse magnetic field give further confirmation of the two-stream theory. In the first and second types of operation, instantaneous power levels of 1 to 10 μW are emitted for input power levels of 0.2 to 1.5 W. In the third type of operation, with an input power level of 2 W, peak output power levels of 80 to 170 μW at X-band frequencies have been measured. The low input power level, which is required for emission from the coplanar-contact devices, permits cw operation in several samples. Low-frequency instabilities generated in a thick plasma layer are frequency-locked by a 160-MHz external signal with a −3 dBm power level.