Papers by Keyword: Gas Discharge

Abstract: Electron transport data been calculated numerically in mixture of molecular nitrogen and oxygen, using Monte Carlo simulation technique and a multi-term theory for solving the Boltzmann equation to investigate and obtaining the exact transport coefficients. It may serve the basis for modeling physical and chemical processes in streamer plasma discharges. Transport data influenced by the amount of O₂ in the mixture. The values of mean energy drift velocity reported.

Abstract: Based on fractal theory and WZ model of gas discharge, The spacial temporal behavior in discharge process from Thundercloud to Ground was simulated efficiently. Moreover, we discussed the probability index and the field intensity of the discharge path and their influence on the fractal dimension and the discharge path., and pointed out that the research should focus on the relation between the probability index and the fractal dimension.

Abstract: Although intensified charge coupled device (ICCD) is conventionally used to investigate the breakdown mechanism in gas discharge. ICCD can not be used to study the long plasma column because it is hard to be imaged. For solving this problem, a novel optical system is proposed which consists of several elements. Each element is composed of one collimator and a photomultiplier tube. Using this system, spatial resolved emission signal can be obtained. Results show that the light emission signal from each area shows a pulse with a width of about 3μs. It is interesting that the time lag in each half cycle increases with the increase of distance away from the dielectric barrier discharge (DBD). This phenomenon implies that the plasma bullet always leaves DBD at the rising edge of the applied voltage. The time lag versus the distance from DBD is used to calculate the propagation velocity of the discharge.

Abstract: A planar micro triggered spark gap switch with three electrodes was designed and fabricated based on non-silicon surface micromachining technology. It consists of two main electrodes, the shape of which is semicircle, and a triggering electrode which is a thin strip. The gap distance between two main electrodes is 800μm. Benefitting from MEMS technology, the switch is integratable and its cost has the potential to be reduced. The designed switch has been optimized and tested. It gives out a pulse current with peak of 5165.21A and 129.6ns rise time. The test data has an agreement with the simulation results.

Abstract: A new type of cathode gas sensor based on carbon nanotube film is presented to analyze CO and CH4 mixed gas. The structure and measuring principle of breakdown voltages are proposed to build support vector machine nonlinear model. As a result, the max relative error of CO and CH4 is 3.8% and 6.0%, respectively. This hints the sensor acts an accuracy measurement.

Abstract: Diamond saw is generally used to make the silicon carbide (SiC) wafers from ingots, but it takes long time for cutting. We have used the electric discharge machining (EDM) to cut SiC. The cutting speed of EDM for SiC is almost 10 times faster than the diamond saw, and the surface roughness is 1/10 for the diamond saw. EDM cut SiC by the plasma produced between the wire and SiC material. The emissions from EDM plasma may involve much information for EDM cutting. We monitored the total light intensity by a photodiode, and observed the spectrum of the emission from EDM plasma by a visible spectroscopy. The discharge gas used helium and argon. In both discharges, the light emission was observed when the current was not zero. Also, many lines were observed Si I, Si II and C I from the SiC sample, and Cu I and Zn I from the wire. And, the electron temperature of EDM plasma was estimated to be under several eV because the observed lines were almost the emission from atoms. Also, the scars, which show the copper-alloy wire was hurt by discharge, were observed from the wire.

Abstract: In order to cut the ingots and slabs of the silicon carbide (SiC), we developed the new method of electric discharge machining (EDM). EDM is usually used for the machining of the metals, and if it is electric conductive material, it is effective for the machining. However, if the electrical resistivity of SiC is high, the electric current cannot be large enough for and the EDM, and we failed the machining of SiC. Therefore, we use three methods to keep higher electric conduction. One is photoconductive, the second is high electric field effect and it is called avalanche effect, and the third is high temperature effect because usually the resistivity is low when the semiconductor or insulation materials are in high temperature. Thus, we applied three method, and finally can cut the SiC slabs of the resistivity of the order of 10 Ωm, which is almost 1000 times higher than that of the ordinary EDM at least. The flatness of the cutting surface is the same of the metals’ and the cutting rate for the SiC ingots is 10 times higher than that of diamond saw. This technique will be effective for the related materials of SiC, such as diamonds and GaN.

Abstract: The photon emission accompanying fracture of a polycrystalline MgO was investigated at room temperature under N2 gas pressures from 10-4 to 105 Pa. At fracture, the ultraviolet, visible and infrared photon emissions instantaneously increased, and then rapidly decreased in most of the experimental conditions. However, in a N2 gas pressure of around 100 Pa, their peak counts lasted for about 10 milliseconds, and the amount of the UV photon emission was fifteen times larger than those obtained in the other N2 gas pressures. This abrupt increment in the emission was explained by the luminescence due to N2 gas discharge according to the classical Townsend’s theory. In conclusion, the photon emission accompanying fracture of a polycrystalline MgO mainly originated from the excited defects as reported by the authors previously, but the N2 gas discharge had a supplementary effect on the emission around a specific N2 gas pressure.

Abstract: The electrical and optical signal waveforms of nitrogen/hydrogen glow discharges used for plasma nitriding process were recorded and analyzed. The shape of the discharge voltage and current signals is dependent on the process parameters, pulse plasma generator properties and cathode geometry. It has been found that the dynamic parameters of the electrical signal waveforms contain information related to the charged particles generation, which is relevant to the homogeneity of different gas discharge surface treatment processes. On the other hand, information related to the active species generation responsible for thermochemical processes at the cathode surface is stored in the optical emission waveforms. The generation and quenching of the active ingredients during the voltage pulses switch on and off influence the shape of the emitted light signals. From the optical signal analysis it was found that the thermochemical processes are influenced by the plasma generator properties such as pulse duty cycle, frequency, applied discharge voltage level and process parameters like working gas composition, operating temperature and pressure.