Qingming Chen

The effect of various magnetic field configurations on a hollow-cathode discharge

A Monte Carlo model was used to describe the behaviour of electrons and ions in an argon hollow-cathode discharge under the influence of a transverse or longitudinal magnetic field. The model included calculating the energy distribution of electrons and ions, the electron excitation and ionization rate spatial distributions and the flux and density distribution of electrons and ions. Comparisons were made between these two kinds of magnetic field to primarily distinguish their effects on the hollow-cathode effect and the sputtering process. The results show that the applied magnetic fields influence the characteristics of discharge in the negative glow more efficiently than that in the cathode dark space, and the transverse magnetic field (parallel to the sheath electric field) is more suitable to enhance the hollow-cathode effect and sputtering process than the longitudinal one (parallel to the electrode).

Numerical modeling of RF-excited plasma in coaxial CO2 lasers

Abstract Theoretical investigations have been performed to describe the discharges in coaxial RF-excited CO 2 lasers, in which the formation of a boundary layer has been considered. Characteristic parameters such as the spatial distributions of electron density, electric field, RF power density and excitation efficiency have been evaluated, which are used to explain the electrical properties of the discharges.

Coupling efficiencies and mode discrimination in coaxial waveguide laser resonators

An approach of calculating coupling efficiencies of waveguide modes in a coaxial waveguide laser resonator is developed by which the computational time is considerably reduced. The coupling efficiency is expressed in terms of the structural parameters of the resonator, which indicates that there exist three special configurations to provide low coupling losses. Mode discrimination can be achieved by appropriately choosing resonator parameters. The influences of the ratio of the outer radius to the inner radius of the waveguide on coupling losses and mode properties are also discussed.

Coupling losses in coaxial waveguide laser resonators

In this paper an approach of calculating the coupling losses in a coaxial (or annular) waveguide laser resonator is developed by which the computational time is considerably reduced. Computations of the coupling losses for some TE modes of an annular waveguide, as a function of mirror curvature and position, are presented in the limit of large mirror aperture. It is shown that there exist three special configurations to provide low coupling losses. The resonator properties are discussed. The calculating results are useful for design of annular waveguide laser resonators.

Theoretical treatment of rf discharges in annular CO2 lasers with diffusion cooling

In this paper, the theoretical studies, considering the formation of boundary layer, have been performed to describe RF discharges in annular CO2 lasers with diffusion-cooling. Such characteristic parameters as spatial distributions of electron density, electric field, RF power density and discharge mixture temperature have been evaluated, which can be used to explain some experimental properties of RF discharges very well.

Thermal effects of a coaxial rf-excited CO2 laser

This paper describes the thermal effect of coaxial RF- excited CO2 lasers, based on the equations of electron density and energy balance, current continuity, and heat conduction. The formation of the boundary layers and their influences are analyzed. Dependence of the spatial distributions of gas temperature on some discharge parameters is discussed. The calculating results are consistent with the experiments well.

Preparation and structure characterization of CeO 2 films on stainless steel substrates deposited by laser ablation with Ar + ion beam assistance

The CeO2 films were deposited by pulsed laser ablation on stainless steel substrates at room temperature with the Ar+ ion beam assistance. The results show that when the CeO2 films were deposited directly on the stainless steel substrates, the desired (001)-normal textured were achieved, but there was no evidence for alignment of in- plane crystal axes. Further experimental results indicate that CeO2/YSZ (Yttria-Stabilized Zirconia)/stainless steel films deposited under the same conditions are not only normal orientation to the substrates surface but also highly in-plane textured.

Large-area thin film preparation by a hybrid scanning laser ablation

In this paper an improved approach of large area superconducting thin film deposition by a hybrid scanning laser ablation is proposed, in which the pulsed laser radiates a target along a specially designed track just like planet-movement trajectory. The calculation results show that the thickness distribution of films is more homogeneous than that with the simple circle scanning ablation, and an optimum dependence of film thickness homogeneity on such parameters as scanning track, and scanning speed etc. is presented. The tentative experimental study indicates the effectiveness of this method.

In-plane aligned YBCO tape on textured YSZ buffer layer deposited on NiCr alloy substrate by laser ablation with only O+ ion beam assistance

High critical current density and in-plane aligned YBa2Cu3O7-x (YBCO) films on textured yttria- stabilized zirconia (YSZ) buffer layers deposited on NiCr alloy (Hastelloy c-275) substrates by laser ablation with only O+ ion beam assistance were fabricated. The X- ray Phi-scan full width at half-maximums for YSZ (202) and YBCO (103) were 18 degree(s) and 11 degree(s) respectively. A critical current density of 7.9 X 105 A/cm2 of YBCO films was obtained at liquid nitrogen temperature and zero field. The critical temperature of the YBCO tape was 90 K.

Simulation of magnetic effects on electron and ion behavior in hollow cathode discharge

A Monte Carlo model is used to describe electron and ion transport in argon hollow cathode discharge. The model includes calculating the electron excitation and ionization rate spatial distributions, the flux and density distribution of electrons and the ion flux distribution for two kinds of cross field configuration. The simulation results are normalized by taking into account the experimental total current. The magnetic effects on the hollow cathode effect is discussed.