Studies On Controllable Technology And Application Of Dielectric Barrier Discharge At Atmospheric Pressure

Atmospheric non-equilibrium plasma, which can be produced and controlled without vacuum equipments, has demonstrated environmental advantages in several application fields, including material processing, biomedical engineering and gas purification. Now one of the most common methods to produce atmospheric non-equilibrium plasma is dielectric barrier discharges (DBDs). DBDs could be driven non-equilibrium plasma without rigorous conditions with frequencies in the hertz range to megahertz range. Many DBDs'experiments and simulations have been done. However, due to the lack of diagnosis which is useful for low pressure plasma, the discharge dynamics and mechanism of plasma during ignition and extinguishment could not been understood thorough. In this study, we investigate the dynamics and mechanism of atmospheric dielectric barrier discharges, including:1. An experimental study of discharge dynamics of pin-to-plate dielectric barrier discharge in atmospheric helium at 20 kHz was carried out. With the optical and electrical diagnosis, it found that the discharge was predominately ignited in positive half cycle of applied voltage with sinusoidal waveform. The temporal evolution of the discharge was investigated vertically along the discharge gap and radically on the dielectric surface by time resolved imaging. It is found that firstly a discharge column with a diameter of 2 mm was ignited above the pin electrode and then expanded toward a plate electrode. On the dielectric surface, plasma ring was formed with radius up to 25 mm. The expansion velocity of plasma ring can reach a hypersonic speed of 3.0 km/s. The ionization wave due to electron diffusion is considered to be the mechanism for plasma ring formation and dynamics.2. An experimental study of sub-microsecond high voltage pulse excited discharges in atmospheric helium is carried out. We study and compare the discharges of dielectric barrier and barrier free, respectively. The discharge is generated between powered copper electrode and ground electrode covered with or without ceramic sheet. The results showed that these two types of discharge have different mechanism. The time-resolved imaging is used to demonstration the evolution of discharge. It shows that there are two discharge events in each voltage pulse with dielectric barrier and only one discharge event without barrier. It is found that the first discharge depends markedly on pulse voltage magnitude and space charges accumulation on ceramic sheet surface plays an important role on ignition of second discharge. However, without barrier means no reverse electrical field to restrict the avalanche. Hence, it is necessary to reduce the applied voltage to avoid transition from diffuse plasma to filamentary plasma.3. An experimental study of plasma surface modification on polyethylene terephthalate (PET) is carried out. We analysis the physical and chemical processes on the interface between material surface and atmospheric plasma phase with different pulse duration and positions by water contact angle and optical emission spectrum.