Analysis of High-Power Microwave Propagation in a Magnetized Plasma Filled Waveguide

Plasma filling can dramatically improve the performance of high power microwave devices.The characteristics of high-power microwave propagation along plasma filled waveguides in an axial magnetic field are analyzed in this paper,and the ponderomotive force effect of high power microwave is taken into consideration.Theoretical analysis and preliminary numerical calculations are performed.The analyses show that the ponderomotive effect would change the plasma density,distribution of microwave field intensity,and dispersion of wave propagation.The higher the microwave power,the stronger the ponderomotive effect.In different magnetic fields,the ponderomotive effect is different.     

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.     

Relativistic Filamentation of Intense Laser Beam in Inhomogeneous Plasma

In the paper, relativistic filamentation of intense laser beam in inhomogeneous plasma is investigated based on the nonparaxial region theory. The results show that, relativistic nonlinearity plays a main role in beam filamentation, and plasma inhomogeneity further reinforces the beam filamentation. The combination effects of relativistic nonlinearity and plasma inhomogeneity can generate particularly intense and short pulse laser. However, plasma inhomogeneity leads to obvious filamentation instability.     

Influence of Plasma Pressure Fluctuation on RF Wave Propagation

Pressure fluctuations in the plasma sheath from spacecraft reentry affect radiofrequency(RF) wave propagation.The influence of these fluctuations on wave propagation and wave properties is studied using methods derived by synthesizing the compressible turbulent flow theory,plasma theory,and electromagnetic wave theory.We study these influences on wave propagation at GPS and Ka frequencies during typical reentry by adopting stratified modeling.We analyzed the variations in reflection and transmission properties induced by pressure fluctuations.Our results show that,at the GPS frequency,if the waves are not totally reflected then the pressure fluctuations can remarkably affect reflection,transmission,and absorption properties.In extreme situations,the fluctuations can even cause blackout.At the Ka frequency,the influences are obvious when the waves are not totally transmitted.The influences are more pronounced at the GPS frequency than at the Ka frequency.This suggests that the latter can mitigate blackout by reducing both the reflection and the absorption of waves,as well as the influences of plasma fluctuations on wave propagation.Given that communication links with the reentry vehicles are susceptible to plasma pressure fluctuations,the influences on link budgets should be taken into consideration.     

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.     

Study on Propagation Characteristics of Plasma Surface Wave in Medium Tube

Axial propagation characteristics of the axisymmetric surface wave along the plasma in the medium tube were studied. The expressions of electromagnetic field inside and outside the medium tube were deduced. Also, the impacts of several factors, such as plasma density, signal frequency, inner radius of medium tube, collision frequency, etc., on plasma surface wave propa- gation were numerically simulated. The results show that, the properties of plasma with higher density and lower gas pressure are closer to those of metal conductor. Furthermore, larger radius of medium tube and lower signal frequency are better for surface wave propagation. However, the effect of collision frequency is not obvious. The optimized experimental parameters can be chosen as the plasma density of about 10^17 m^-3 and the medium radius between 11 mm and 19 mm.     

Propagation of Surface Wave Along a Thin Plasma Column and Its Radiation Pattern

Propagation of the surface waves along a two-dimensional plasma column and the far-field radiation patterns are studied in thin column approximation. Wave phase and attenuation coefficients are calculated for various plasma parameters. The radiation patterns are shown. Results show that the radiation patterns are controllable by flexibly changing the plasma length and other parameters in comparison to the metal monopole antenna. It is meaningful and instructional for the optimization of the plasma antenna design.     

The Characteristics of Columniform Surface Wave Plasma Excited Around a Quartz Rod by 2.45 GHz Microwaves

A novel surface wave plasma(SWP) source excited with cylindrical Teflon waveguide has been developed in our previous work. The plasma characteristics have been simply studied.In this work, our experimental device has been significantly improved by replacing the Teflon waveguide with a quartz rod, and then better microwave coupling and higher gas purity can be obtained during plasma discharge. The plasma spatial distributions, both in radial and axial directions, have been measured and the effect of gas pressure has been investigated. Plasma density profiles indicate that this plasma source can produce uniform plasma in an axial direction at low pressure, which shows its potential in plasma processing on a curved surface such as an inner tube wall. A simplified circular waveguide model has been used to explain the principle of plasma excitation. The distinguishing features and potential application of this kind of plasma source with a hardware improvement have been shown.     

Damping Solitary Wave in a Three-Dimensional Rectangular Geometry Plasma

The solitary waves of a viscous plasma confined in a cuboid under the three types of boundary condition are theoretically investigated in the present paper.By introducing a threedimensional rectangular geometry and employing the reductive perturbation theory,a quasi-Kd V equation is derived in the viscous plasma and a damping solitary wave is obtained.It is found that the damping rate increases as the viscosity coefficient increases,or increases as the length and width of the rectangle decrease,for all kinds of boundary condition.Nevertheless,the magnitude of the damping rate is dominated by the types of boundary condition.We thus observe the existence of a damping solitary wave from the fact that its amplitude disappears rapidly for a → 0and b → 0,or ν→ +∞.     

Solutions to mKdV Eequation of Electromagnetic Wave Propagation in Cold Collisionless Plasma

The equation of electromagnetic wave propagation through cold collisionless plasma can be reduced to the modified Kortweg-de Vries （mKdV） equation. Using a new technique, whose keys are the trial solution in terms of the exponential function and the ideas of the like-terms＇ balance, some groups of accurate analytical solutions for this mKdV equation, such as solitary wave solutions, can be obtained. It is successfully shown that this method may be still valid for solving other nonlinear plasma equations.     

Influence of Langmuir Turbulence on Plasma Electron Distribution During the Induced Wave Scattering

An equation is derived of the electron distribution evolution during the scattering of Langmuir waves by the plasma electrons. Calculation is performed with refraining from traditional substitution of a real plasma by a plasma probabilistic ensemble. The picture of the electron distribution evolution is compared with one suggested by Tsytovich (Refs. 12 and 19). The Tsytovich's idea of the respective electron kinetics is shown to underestimate substantially the intensity of the phenomenon and thus to evidence once more for the scientific inconsistency of the nonequilibrium statistical mechanics.Other former calculations of the particle kinetic equations are also discussed.     

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.     

FDTD Analysis of Reflection of Electromagnetic Wave From a Conductive Plane Covered with Inhomogeneous Time-Varying Plasma

A finite-difference time-domain (FDTD) algorithm is applied to study the electromagnetic reflection of conduction plane covered with inhomogeneous time-varying plasma, homogeneous plasma and inhomogeneous plasma. The collision frequency of plasma is a function of electron density and plasma temperature. The number density profile follows a parabolic function. A discussion on the effect of various plasma parameters on the reflection coefficient is presented. Under the one-dimensional case, transient electromagnetic propagation through various plasmas has been obtained, and the reflection coefficients of EM wave through various plasmas are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave.     

Experimental Investigation of Surface Wave Plasma Excited by a Cylindrical Dielectric Rod

An improved surface wave plasma source equipped with a cylindrical quartz rod has been developed, which has great potential in processing inner wall of cylindrical workpieces. A cylindrical quartz rod not only excites the plasma around the rod, but also guides surface wave plasma along the rod. The distributions of plasma density and plasma temperature under different incident microwave powers and pressures are diagnosed by a Langmuir probe. The electron density near the rod is around the order of 10^11cm^-3. When the incident power is 450 W, the length of surface wave plasma column can reach up to 420 mm at 20 Pa.     

Gravitational Effects on Plasma Waves in Environment of Sun and Neutron Star

Local plasma phenomena in environment of Sun are observed closely by spacecrafts in recent years. We provide a new method to apply general relativity to astro-plasma physics in small local area. The relativistic dispersion relations of Langmuir, electromagnetic and cyclotron waves are obtained. The red shifts of Langmuir and cyclotron frequencies are given analytically. A new equilibrium velocity distribution of particles soaked in local gravitational field is suggested. The gravitational effect of a neutron star is also estimated.     

Numerical Modelling Point-to-Plane of Negative Corona Discharge in N_2 Under Non-Uniform Electric Field

The paper presents a simulation model of the negative corona discharge in N_2 under various pressures.The simulated discharge is of a negative point-to-plane mass type,with an inter-electrode separation distance of 20 mm and a symmetry about the axis of discharge.This simulation investigates the behavior of the neutral density and temperature for different pressures in the range of 0.1-10.0 bar.The spatial and temporal evolution of the neutral gas is analyzed based upon the equations of continuity,momentum and energy in a two-dimensional cylindrical geometry model.For that geometry of the system,the FCT(Flux Corrected Transport) technique was adopted.The results show that the pressure plays a significant role of the neutrals dynamics.     

Effect of Gas Velocity on the Dust Sediment Layer in the Coupled Field of Corona Plasma and Cyclone

A dust sediment layer was found on the outer tube wall when the ESCP （electrostatic centrifugal precipitator） trapped diesel particulates or ganister sand. The Compton back scatter method was used to measure the sediment thickness during the experiment. The effect of the inlet gas velocity on the dust sediment layer was investigated. PIV （Particle Image Velocimetry） was used to measure the velocity field between the inner barb tube wall and the outer tube wail. Experiments showed that the thickness of the sediment increased with time, and the sediment layer at the lower end was much thicker than that at the upper end. The agglomeration on the outer tube wall could be removed when the inlet gas velocity was increased to a certain value.     

Experimental Study of the Movement of Particles in the Coupled Field of Low Temperature Plasma and Cyclone

An investigation was made of the movement of particles in the coupled field of a low temperature plasma and cyclone with PIV in order to study the moving trace of particles‘ movement in an electrostatic cyclonic collector. The experimental results show that the plasma field had little effect on the tangential velocity of particles, but had an obvious influence on the radial velocity. The tangential velocity of airflow had a great impact on particles‘ tangential movement. With the particles going down the cyclone tube, their tangential velocity dropped.Their radial velocity dropped as the radius enlarged from the center to the collecting wall of the tube. The plasma field could improve the radial velocity of particles by 5%-10%, but the motionalong the radius was determined by the cyclone.     

Discharge Characteristics of SF6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses

The characteristics of high pressure sulphur hexafluoride (SF ₆ ) discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper. The influencing factors on discharge process, such as gas pressure, pulse repetition frequency (PRF), and number of applied pulses, are analyzed. Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses. Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current. The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure. The reduced electric field (E/p) decreases with the increase of PRF in all circumstances. The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.     

Effect of Plasma Density on Proton Acceleration in a Rectangular Waveguide

Analytical studies are made for the proton acceleration during its motion in thefields of the fundamental mode excited by a high-intensity microwave in a rectangular waveguide,when the proton is injected along the propagating direction of the mode. The trajectory of theproton is calculated and the expressions are obtained for the energy gain and acceleration gradienttogether with the effects of plasma density, microwave frequency and waveguide width. Energygain of 181 keV is attained by a 50 keV proton in a 0.015m×0.020 m evacuated waveguide when0.5×10～(10)W/m～2 microwave intensity is used. However, this gain increases to 1387 keV whenthe waveguide is filled with a plasma having a density of 1.0×10～(19) m～(-3). Higher accelerationgradients are achieved when the proton is injected with a higher initial energy and also when themicrowave intensity increases. The effects of the microwave frequency and width of the waveguideare found to decrease the acceleration gradient.