The Generation And Characteristics Of Dielectric Barrier Uniform Glow Discharge At High Pressure

Uniform glow discharge at atmospheric pressure is widely used in surface modification and plasma sterilization. The history and status of research on the uniform glow discharge at atmospheric pressure are summarized in Chapter 1, where also includes a comparison for some different electrode modes such as metal panel electrodes, multi-pin-panel electrodes, mesh electrodes, and water electrodes.Chapter 2 describes three types of discharge instruments with panel electrodes, comb electrodes and water electrodes. Experiments of sterilization were conducted in plasmas that were produced by volume discharge with panel electrodes and surface discharge with comb electrodes. A water electrode was used to realize dielectric barrier uniform glow discharge at sub-atmospheric pressure in a vacuum glass cavity.In Chapter 3, the waveform of discharge voltage, current and intensity of emission spectrum for uniform glow discharge and filamentary discharge at high pressure (15-760 Torr) are compared. A criterion of uniform glow discharge is proposed. A pulse appears in the half cycle of current in uniform glow discharge of helium and argon. But with the increase of voltage, the numbers of current pulses increase and pulse amplitude decrease. The same phenomenon was observed in filamentary discharge. It was shown that there is no necessary relationship between current waveform and discharge uniformity. The single current pulse in a half cycle can't be treated as criterion of uniform discharge in high frequency operation. The fluctuation of grey scale of discharge picture was proposed to be a quantitative parameter for judgment of discharge uniformity. The emission spectrum of argon discharge at different pressure was measured. The results show the intensity of spectral lines within 750-850 nm decreases because the absorption of low-lying energy levels increases at higher pressure.The influence factors such as pressure, discharge gap, water vapor and oxygen molecular in uniform discharge are analyzed in Chapter 4. The mechanism and pressure threshold for the transition from filamentary discharge to uniform glow discharge are discussed. It's more difficult to obtain a uniform discharge at high pressure. The up limits of pressure for uniform discharge are: argon, 760 Torr; mixture of argon and 5% oxygen, 600 Torr; nitrogen, 525 Torr; mixture of nitrogen and 20% oxygen, 375 Torr; air, 300 Torr. The electronegative oxygen and water molecular will absorb free electrons that lead to the increase of breakdown voltage and un-uniformity.