Jieshu Jia

Propagation of electromagnetic waves in a weakly ionized dusty plasma

Propagation properties of electromagnetic (EM) waves in weakly ionized dusty plasmas are the subject of this study. Dielectric relation for EM waves propagating at a weakly ionized dusty plasma is derived based on the Boltzmann distribution law while considering the collision and charging effects of dust grains. The propagation properties of EM energy in dusty plasma of rocket exhaust are numerically calculated and studied, utilizing the parameters of rocket exhaust plasma. Results indicate that increase of dust radius and density enhance the reflection and absorption coefficient. High dust radius and density make the wave hardly transmit through the dusty plasmas. Interaction enhancements between wave and dusty plasmas are developed through effective collision frequency improvements. Numerical results coincide with observed results by indicating that GHz band wave communication is effected by dusty plasma as the presence of dust grains significantly affect propagation of EM waves in the dusty plasmas. The results are helpful to analyze the effect of dust in plasmas and also provide a theoretical basis for the experiments.

Propagation of electromagnetic waves in a weak collisional and fully ionized dusty plasma

The propagation properties of electromagnetic (EM) waves in fully ionized dusty plasmas is the subject of this study. The dielectric relationships for EM waves propagating in a fully ionized dusty plasma was derived from the Boltzmann distribution law, taking into consideration the collision and charging effects of the dust grains. The propagation properties of the EM waves in a dusty plasma were numerically calculated and studied. The study results indicated that the dusty grains with an increased radius and charge were more likely to impede the penetration of EM waves. Dust grains with large radii and high charge cause the attenuation of the EM wave in the dusty plasma. The different density of the dust in the plasma appeared to have no obvious effect on the transmission of the EM waves. The propagation of the EM waves in a weakly ionized dusty plasma varies from that in a fully ionized dusty plasma. The results are helpful to analyze the effects of dust in dusty plasmas and also provide a theoretical basis for future studies.

Investigation of Low-Pressure Glow Discharge in a Coaxial Gridded Hollow Cathode

This paper contains results of numerical and experimental investigation of glow discharge plasma created in a chamber of a new-type large-volume coaxial gridded hollow cathode. The discharge is created in argon at 25 Pa by applying time-varying power with frequency 20 kHz on electrodes. A 2-D model of the discharge was built using COMSOL Multiphysics. Self-consistent description of the discharge was obtained using the extended fluid approach, which couples continuity equations for charged particles and electron energy balance with Poissons equation for electric potential. Electron transport coefficients and rates of electron-impact reactions were calculated using the electron energy distribution function. The spatial and radial distributions of plasma potential (Vp), electron density (ne), and electron temperature (Te) were obtained. It is shown that the plasma inside the chamber is similar to the negative glow of a dc glow discharge. Comparison of numerical results with the Langmuir probe measurements of electron density and electron temperature is presented and showed a good agreement.

Broadband microwave propagation in a novel large coaxial gridded hollow cathode helium plasma

The broadband microwave propagating characteristics of a novel, large volume, coaxial gridded hollow cathode helium plasma is reported in this paper. The basic plasma parameters were determined using an Impedans Ltd. Langmuir probe under a variety of conditions. The transmission attenuation was recorded by using Scattering Parameters (S-parameters) of a vector network analyzer with the frequency range from 2 GHz to 18 GHz and a propagation model was established using the Z transform finite-difference time-domain method for simulating the transmission of microwave. The effects of both the gas pressure and the input power on the electromagnetic wave propagation are analyzed. The results showed that the computational and experimental results of transmission attenuation were in good agreements. Moreover, the electron density ne and the effective collision rate νc were found to play important roles in the propagation of microwave.

Properties of a large volume glow discharge helium plasma by measuring the broadband microwave phase shift in different pressures

A novel type of large cylindrical glow discharge helium plasma with a 50 cm diameter and a 40 cm thickness is presented, which is powered by dual reticular electrodes under an AC source with frequency 20 kHz. Microwave characteristics are studied using vector network analyzer with two broadband antennae ranging from 2 GHz to 18 GHz to measure the phase shift. The phase shift under varying gas pressure is used to calculate the electron density ne, which varies from 2.36 × 1016 m−3 to 11.2 × 1016 m−3 under different discharge conditions. The measured results provide a method to diagnose helium plasma with large volume, high pressure, and high collision rate, especially for the condition which the probe is not suitable.

Broadband microwave characteristics of a novel coaxial gridded hollow cathode argon plasma

The interaction between microwave and large area plasma is crucially important for space communication. Gas pressure, input power, and plasma volume are critical to both the microwave electromagnetic wave phase shift and electron density. This paper presents a novel type of large coaxial gridded hollow cathode plasma having a 50 cm diameter and a 40 cm thickness. Microwave characteristics are studied using a microwave measurement system that includes two broadband antennae in the range from 2 GHz to 18 GHz. The phase shift under varying gas pressure and input power is shown. In addition, the electron density ne, which varies from 1.2 × 10(16) m(-3) to 8.7 × 10(16) m(-3) under different discharge conditions, is diagnosed by the microwave system. The measured results accord well with those acquired by Langmuir Probe measurement and show that the microwave properties in the large volume hollow cathode discharge significantly depend on the input power and gas pressure.

Absolute continuum intensity diagnostics of a novel large coaxial gridded hollow cathode argon plasma

This paper reports a novel coaxial gridded hollow discharge during operation at low pressure (20 Pa–80 Pa) in an argon atmosphere. A homogeneous hollow discharge was observed under different conditions, and the excitation mechanism and the discharge parameters for the hollow cathode plasma were examined at length. An optical emission spectrometry (OES) method, with a special focus on absolute continuum intensity method, was employed to measure the plasma parameters. The Langmuir probe measurement (LPM) was used to verify the OES results. Both provided electron density values (ne) in the order of 1016 m−3 for different plasma settings. Taken together, the results show that the OES method is an effective approach to diagnosing the similar plasma, especially when the LPM is hardly operated.

Transmission characteristics of microwave in a glow-discharge dusty plasma

In this study, the propagation characteristics of electromagnetic wave in a glow discharge plasma with dust particles are experimentally investigated. A helium alternating current glow discharge plasmas have been successfully generated. Measurements of the plasma parameters using Langmuir probes, in the absence of dust particles, provide plasma densities (ne) of 1017 m−3 and electron temperatures (Te) ranging from 2 to 4 eV. Dusty plasmas are made by adding 30 nm radius aluminum oxide (Al2O3) particles into the helium plasma. The density of the dust particle (nd) in the device is about 1011–1012 m−3. The propagation characteristics of electromagnetic waves are determined by a vector network analyzer with 4–6 GHz antennas. An apparent attenuation by the dust is observed, and the measured attenuation data are approximately in accordance with the theoretical calculations. The effects of gas pressure and input power on the propagation are also investigated. Results show that the transmission attenuation incre...

Propagation characters of multi-Gaussian beam with large eccentric displacement in collisionless plasma: Higher order paraxial theory

The multiple coherent identical Gaussian beams with symmetry distribution are abbreviated as multi-Gaussian beam, of which the propagation characters in collisionless plasma are studied with the WKB method and higher order paraxial theory. The initial beam profile presents the flat top like or hollow like distribution when the eccentric displacement is large enough. Based on the derived nonlinear propagation equations, the initial condition analyses are performed, and the impact of eccentric displacement on the free propagation effect and ponderomotive nonlinearity is thoroughly discussed. The propagation characters of dimensionless beam width parameter, spot intensity, and spatial distribution of plasma electron density are presented. Results show that the initial spot intensity is expanding outwards along the propagation and the ring structure of electron evacuation in plasmas is generated.

Broadband microwave propagation in a novel large volume glow discharge argon plasma

The broadband microwave propagating characteristics of a novel, large volume, glow-discharge argon plasma is reported in this paper. A large volume, glow-discharge argon plasma was designed and the basic plasma parameters were determined using an Impedans Ltd. Langmuir probe under a variety of conditions. The transmission attenuation was recorded by using S parameters of a vector network analyzer with the frequency range from 2GHz to 18GHz and a propagation model was established using the Z transform FDTD method for simulating the attenuation of microwave. The effects of both the gas pressure and input power on the EM wave propagation are analyzed. The results showed that the theoretical and experimental results of transmission attenuation were in good agreement. Moreover, the electron density ne and the effective collision rate vc were found to play important roles in the propagation of microwave.