A plasma column with a length of about 65 cm is generated in the upstream region of a plasma jet using dielectric barrier discharge configurations. The effects of experimental parameters such as the amplitude of the applied voltage and the driving frequency are investigated in aspects of the plasma column by the optical method. Results show that both the plasma length and the propagating velocity, as well as the discharge current, increase with the increase in the applied voltage or its frequency. The discharge mechanism is analysed qualitatively based on streamer theory, where photo-ionization is important. Furthermore, optical emission spectroscopy is used to investigate the electric field intensity of the upstream region.
A large-gap uniform discharge is ignited by a coaxial dielectric barrier discharge and burns between a needle anode and a plate cathode under a low sustaining voltage by feeding with flowing argon. The basic aspects of the large-gap uniform discharge are investigated by optical and spectroscopic methods. From the discharge images, it can be found that this discharge has similar regions with glow discharge at low pressure except a plasma plume region. Light emission signals from the discharge indicate that the plasma column is invariant with time, while there are some stochastic pulses in the plasma plume region. The optical emission spectra scanning from 300 nm to 800 nm are used to calculate the excited electron temperature and vibrational temperature of the large-gap uniform discharge. It has been found that the excited electron temperature almost keeps constant and the vibrational temperature increases with increasing discharge current.Both of them decreases with increasing gas flow rate.
Atmospheric pressure glow discharges were generated in an air gap between a needle cathode and a water anode.Through changing the ballast resistor and gas gap width between the electrodes,it has been found that the discharges are in normal glow regime judged from the currentvoltage characteristics and visualization of the discharges.Results indicate that the diameter of the positive column increases with increasing discharge current or increasing gap width.Optical emission spectroscopy is used to calculate the electron temperature and vibrational temperature.Both the electron temperature and the vibrational temperature increases with increasing discharge current or increasing gap width.Spatially resolved measurements show that the maxima of electron temperature and vibrational temperature appeared in the vicinity of the needle cathode.
In this study, a dielectric barrier discharge device with needle-plate electrodes wasused to investigate the characteristics of the micro-discharge in argon at one atmospheric pressureby an optical method. The results show that there are two discharge modes in the dielectric barrierdischarge, namely corona mode and filamentary mode. The corona discharge only occurs in thevicinity of the needle tip when the applied voltage is very low. However, the filamentary dischargemode can occur, and micro-discharge bridges the two electrodes when the applied voltage reachesa certain value. The extended area of micro-discharge on the dielectric plate becomes largerwith the increase in applied voltage or decrease in gas pressure. The variance of the light emissionwaveforms is studied as a function of the applied voltage. Results show that very narrow dischargepulse only appears at the negative half cycle of the applied voltage in the corona discharge mode.However, broad hump (about several microseconds) can be discerned at both the negative halfcycle and the positive half cycle for a high voltage in the filamentary mode. Furthermore, theinception voltage decreases and the width of the discharge hump increases with the increase inapplied voltage. These experimental phenomena can be explained qualitatively by analyzing thedischarge mechanism.
The dielectric barrier discharge characteristics in helium at atmospheric pressure are simulated based on a one-dimensional fluid model. Under some discharge conditions, the results show that one discharge pulse per half voltage cycle usually appears when the amplitude of external voltage is low, while a glow-like discharge occurs at high voltage. For the one discharge pulse per half voltage cycle, the maximum of electron density appears near the anode at the beginning of the discharge, which corresponds to a Townsend discharge mode. The maxima of the electron density and the intensity of electric field appear in the vicinity of the cathode when the discharge current increases to some extent, which indicates the formation of a cathode-fall region. Therefore, the discharge has a transition from the Townsend mode to the glow discharge mode during one discharge pulse, which is consistent with previous experimental results.
A direct current(DC) source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using optical and electrical methods,the discharge characteristics are investigated for the diffuse plasma plume.Results indicate that the discharge has a pulse characteristic,under the excitation of a DC voltage.The discharge pulse corresponds to the propagation process of a plasma bullet travelling from the anode to the cathode.It is found that,with an increment of the gas flow rate,both the discharge plume length and the current peak value of the pulsed discharge decrease in the laminar flow mode,reach their minima at about1.5 L/min,and then slightly increase in the turbulent mode.However,the frequency of the pulsed discharge increases in the laminar mode with increasing the argon flow rate until the argon flow rate equals to about 1.5 L/min,and then slightly decreases in the turbulent mode.
