FDTD Simulation on Power Absorption of Terahertz Electromagnetic Waves in Dense Plasma

A finite difference time domain （FDTD） method is used to numerically study the power absorption of broadband terahertz （0.1 - 1.5 THz） electromagnetic waves in a partially ionized uniform plasma layer under low pressure and atmosphere discharge conditions. The power absorption spectra are calculated numerically and the numerical results are in accordance with the analytic results. Meanwhile, the effects on the power absorption are calculated with different applied magnetic fields, collision frequencies and electron number densities, which depend strongly on those parameters. Under the dense strongly magnetized plasma conditions, the absorption gaps appear in the range of 0.3 - 0.36 THz, and are enlarged with the increasing electron number density.     

Numerical and Experimental Investigation on Electromagnetic Attenuation by Semi-Ellipsoidal Shaped Plasma

Some reports presented that the radar cross section(RCS) from the radar antenna of military airplanes can be reduced by using a low-temperature plasma screen. This paper gives a numerical and experimental analysis of this RCS-reduction method. The shape of the plasma screen was designed as a semi-ellipsoid in order to make full use of the space in the radar dome.In simulations, we discussed the scattering of the electromagnetic(EM) wave by a perfect electric conductor(PEC) covered with this plasma screen using the finite-difference-time-domain(FDTD)method. The variations of their return loss as a function of wave frequency, plasma density profile, and collision frequency were presented. In the experiments, a semi-ellipsoidal shaped plasma screen was produced. Electromagnetic attenuation of 1.5 GHz EM wave was measured for a radio frequency(RF) power of 5 k W at an argon pressure of 200-1150 Pa. A good agreement is found between simulated and experimental results. It can be confirmed that the plasma screen is useful in applications for stealth of radar antenna.     

Experimental Study on the Interaction of Electromagnetic Waves and Glow Plasma

An experimental system was established in order to study the interaction between electromagnetic waves, with a frequency of 300 kHz to 3 GHz, and DC glow discharge plasma. The results show that the DC glow discharge plasma affects the transmission properties of electromagnetic waves, while the waves can change both temperature and density of electrons.     

Influences of Turbulent Reentry Plasma Sheath on Wave Scattering and Propagation

The randomness of turbulent reentry plasma sheaths can affect the propagation and scattering properties of electromagnetic waves.This paper developed algorithms to estimate the influences.With the algorithms and typical reentry data,influences of GPS frequency and Ka frequency are studied respectively.Results show that,in terms of wave scattering,the scattering loss caused by the randomness of the turbulent plasma sheath increases with the increase of the ensemble average electron density,ensemble average collision frequency,electron density fluctuation and turbulence integral scale respectively.Also the scattering loss is much smaller than the dielectric loss.The scattering loss of Ka frequency is much less than that of the GPS frequency.In terms of wave propagation,the randomness arouses the fluctuations of amplitude and phase of waves.The fluctuations change with altitudes that when the altitude is below 30 km,fluctuations increase with altitude increasing,and when the altitude is above 30 km,fluctuations decrease with altitude increasing.The fluctuations of GPS frequency are strong enough to affect the tracking,telemetry,and command at appropriate conditions,while the fluctuations of Ka frequency are much more feeble.This suggests that the Ka frequency suffers less influences of the randomness of a turbulent plasma sheath.     

Full-wave Analyses of Scattering of Electromagnetic Wave from the Weakly Ionized Plasma in Plane Geometry

The purpose of the present work is to present a full-wave analysis of scattering from the weakly ionized plasma in the plane geometry. We have yielded an approximate solution in an analytic form to the electromagnetic wave scattering from the weakly ionized plasma. In the normal and oblique incidence, the analytic solution works well, as compared with the exact solution and the solution based on the Wenzell-Kramers-Brillouin-Jeffreys (WKBJ) approximation to the uniform density profile.     

Propagation Properties of Electromagnetic Wave in a Plasma Slab

In this paper, the calculated results about the propagation properties of electromag-netic wave in a plasma slab are described. The relationship of the propagation properties with frequencies of electromagnetic wave, and parameters of plasma (electron temperature, electron density, dimensionless collision frequency and the size of the plasma slab) is analyzed.     

Langmuir Wave Scattering Induced by Electrons in a Single Collisionless Plasma

New calculations of the kinetics of Langmuir wave scattering induced by plasma electrons are performed, with refraining from traditional substitution of real plasma by plasma probabilistic ensemble. The equations developed are compared with those suggested by Tsytovich in the Theory of Turbulent Plasma (Consultants Bureau, New York, 1977) and also in Uspehi Fiz. Nauk 90 (3), 435 (1966) (Sov. Phis. Uspekhi 9, 805 (1967)). It is shown that Tsytovich's calculations do not account properly for the Compton wave scattering on plasma electrons.     

Electromagnetic Wave Attenuation in Atmospheric Pressure Plasma

When an electromagnetic （EM） wave propagates in an atmospheric pressure plasma （APP） layer, its attenuation depends on the APP parameters such as the layer width, the electron density and its profile and collision frequency between electrons and neutrals. This paper proposes that a combined parameter -the product of the line average electron density n and width d of the APP layer （i.e., the total number of electrons in a unit volume along the wave propagation path） can play a more explicit and decisive role in the wave attenuation than any of the above individual parameters does. The attenuation of the EM wave via the product of n and d with various collision frequencies between electrons and neutrals is presented.     

Power Absorption of High Frequency Electromagnetic Waves in a Partially Ionized Plasma Layer in Atmosphere Conditions

We have studied the absorption, reflection, and transmission of electromagnetic waves in an unmagnetized uniform plasma layer covering a metal surface in atmosphere conditions. Instead of the absorption of the electromagnetic wave propagating only once in previous work on the plasma layer, a general formula of total power absorption by the plasma layer with an infinite time of reflections between the atmosphere-plasma interface and the metal surface has been derived for the first time. Effects of plasma parameters, especially the dependence of the fraction of positive lons, negative ions and electrons in plasmas on the power absorption processes are discussed. The results show that the existence of negative ions significantly reduces the power absorption of the electromagnetic wave. Absorptions of electromagnetic waves are calculated.     

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.     

The Oblique Incident Effects of Electromagnetic Wave in Atmospheric Pressure Plasma Layers

The propagating behaviours, i.e. phase shift, transmissivity, reflectivity and absorp- tivity, of an electromagnetic （EM） wave in a two-dimensional atmospheric pressure plasma layer are described by the numerical solutions of integral-differential Maxwell＇s equations through a generalized finite-difference-time-domain （FDTD） algorithm. These propagating behaviours are found to be strongly affected by five factors： two EM wave characteristics relevant to the oblique incident and three dimensionless factors. The two EM wave factors are the polarization mode （TM mode or TE mode） and its incident angle. The three dimensionless factors are： the ratio of the maximum electron density to the critical density no/nor, the ratio of the plasma layer width to the wave length d/λ, and the ratio of the collision frequency between electrons and neutrals to the incident wave frequency veo/f.     

Interaction of Electromagnetic Waves with Two-Dimensional Metal Covered with Radar Absorbing Material and Plasma

A two-dimensional metal model is established to investigate the stealth mechanisms of radar absorbing material （RAM） and plasma when they cover the model together. Using the finite-difference time-domain （FDTD） method, the interaction of electromagnetic （EM） waves with the model can be studied. In this paper, three covering cases are considered： a. RAM or plasma covering the metal solely; b. RAM and plasma covering the metal, while plasma is placed outside; e. RAM and plasma covering the metal, while RAM is placed outside. The calculated results show that the covering order has a great influence on the absorption of EM waves. Compared to case a, case b has an advantage in the absorption of relatively high-frequency EM waves （HFWs）, whereas case c has an advantage in the absorption of relatively low-frequency EM waves （LFWs）. Through the optimization of the parameters of both plasma and RAM, it is hopeful to obtain a broad absorption band by RAM and plasma covering. Near-field attenuation rate and far-field radar cross section （RCS） are employed to compare the different cases.     

Terahertz Plasma Waves in Two Dimensional Quantum Electron Gas with Electron Scattering

We investigate the Terahertz(THz) plasma waves in a two-dimensional(2D) electron gas in a nanometer field effect transistor(FET) with quantum effects, the electron scattering,the thermal motion of electrons and electron exchange-correlation. We find that, while the electron scattering, the wave number along y direction and the electron exchange-correlation suppress the radiation power, but the thermal motion of electrons and the quantum effects can amplify the radiation power. The radiation frequency decreases with electron exchange-correlation contributions, but increases with quantum effects, the wave number along y direction and thermal motion of electrons. It is worth mentioning that the electron scattering has scarce influence on the radiation frequency. These properties could be of great help to the realization of practical THz plasma oscillations in nanometer FET.     

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.     

Microwaves Scattering by Underdense Inhomogeneous Plasma Column

The scattering characteristics of microwaves(MWs) by an underdense inhomogeneous plasma column have been investigated.The plasma column is generated by hollow cathode discharge(HCD) in a glass tube filled with low pressure argon.The plasma density in the column can be varied by adjusting the discharge current.The scattering power of X-band MWs by the column is measured at different discharge currents and receiving angles.The results show that the column can affect the properties of scattering wave significantly regardless of its plasma frequency much lower than the incident wave frequency.The power peak of the scattering wave shifts away from 0°to about ±15odirection.The finite-different time-domain(FDTD) method is employed to analyze the wave scattering by plasma column with different electron density distributions.The reflected MW power from a metal plate located behind the column is also measured to investigate the scattering effect on reducing MW reflectivity of a metal target.This study is expected to deepen the understanding of plasma-electromagnetic wave interaction and expand the applications concerning plasma antenna and plasma stealth.     

Preliminary Results of Drift Instability by Fast Optical Images in KT-5D Toroidal Plasma

Drift instability in plasma generated by electron cyclotron resonance （ECR） in KT- 5D device was investigated by using a fast camera and Langmuir probes. The similarity between the distribution of light intensity from the images and the plasma pressure indicates a nearly linear relationship. The discharge images taken by the camera and the plasma parameters measured by the probes also indicate the existence of low frequency turbulent events with a time scale less than a few mini-seconds.     

Relativistic Electromagnetic Soliton in Electron-Positron-Ion Plasma

Considering the limiting weak nonlinearity, we obtained the solution of the coupled equations describing the interaction of ultraintense laser with cold transparent multicomponent plasma. It was indicated that the ions tend to accumulate at the center of the soliton and have large velocity when we consider the mobile ions in the multicomponent plasma, which shows that the result is different from that of the Berezhiani＇s analysis. The change of proportion of ions in the plasma has effects on the amplitude of vector potential and the maximum velocity of the soliton.     

Observation of Vortex Patterns in a Magnetized Dusty Plasma System

Vortex patterns of dust particles have been observed in a magnetized dusty plasma system. The formation mechanism of two-dimensional （2D） vortex patterns has been investigated by analysing the forces acting on dust particles and molecular dynamics （MD） simulations in a 2D confined magnetized dusty plasma. It has been found that with a weak confining electric field and a strong magnetic field, the particles＇ trajectories will form a vortex shape. The simulation results agree with our experimental observations. In our experiments, vortex patterns can be induced via circular rotation of particles by changing the rf （radio-frequency） power in a magnetized dusty plasma.     

Numerical Study on Microwave Scattering by Various Plasma Objects

The scattering features of microwave(MW) by planar plasma layer, plasma column and plasma-column array under different parameters have been numerically studied by the finitedifference time-domain(FDTD) method. The effects of the plasma frequency and electron collision rate on MW's reflectance, transmittance and absorptance are examined. The results show that for the planar plasma layer, the electron collision plays an important role in MW absorption and the reduction of wave reflection. In the plasma column condition, strong scattering occurs in certain directions. The scattering pattern depends on the plasma frequency, electron collision rate and column radius. A collisional, non-planar shaped plasma object like the plasma-column array can reduce significantly the wave reflection comparing with the planar plasma layer.     

Electromagnetic Resistive Drift Instability in Current Carrying Low Temperature Tokamak Edges

It is shown that the purely growing electrostatic rippling mode can couple with the shear Alfven wave to give rise to an oscillatory electromagnetic instability in tokamak edge regions. This mechanism can be one of the causes of electromagnetic fluctuations observed near plasma edges. This instability can occur only in the very low temperature regions where resistivity fluctuations can become important due to large electron-ion collision frequency.