Effects Of A Bias Electrode On Discharge Characteristics Of A Plasma Jet At Atmosphere Pressure

Using a dielectric barrier discharge(DBD)jet,a uniform and stable argon plasma plume is generated at atmospheric pressure outside the jet nozzle.In order to increase volume of the generated plasma plume,a plate electrode with a bias voltage is poised in the downstream region of the DBD jet to form a plasma jet with three electrodes.Using the tri-electrode jet,a large volume plasma plume is generated downstream of flowing argon or helium at atmospheric pressure.Then effects of the biased electrode on discharge characteristics of the tri-electrode plasma jet are investigated.The main contents of the thesis are given as follows:A stable argon plasma plume is generated at atmospheric pressure by a DBD jet in a coaxial geometry.The discharge current and the light emission signal of the plasma plume are pulsed.Length of the plasma plume increases with increasing peak value of the applied voltage,which increases firstly and then decreases with increasing the gas flow rate.High-speed images captured by an intensified charge-coupled device(ICCD)indicate that the plasma plume is composed of successive fast-moving plasma bullets.The line intensity ratio,vibrational temperature and the rotational temperature are investigated by optical emission spectroscopy and the electron density is studied by the collisional-radiative model.It is found that all of them increase with increasing the applied voltage or the gas flow rate,and decrease with increasing the driving frequency.A large volume plasma plume is generated downstream of flowing argon or helium at atmospheric pressure by a tri-electrode jet.With increasing the bias voltage applied on the plate electrode,it is found that the plume length increases until it bridges the tube opening and the plate electrode.By using ICCD,it is found that the transition from the guided streamer to the branching one can be attributed to the electric field and the air content.By optical emission spectroscopy,the plasma parameters such as the line intensity ratio,the vibrational temperature,the rotational temperature and the excited electron temperature are investigated.Results indicate that all of them increase with increasing the bias voltage,which are symmetric perpendicular to the gas flow.