Temporal evolution of atmosphere pressure diffuse discharges sustained by micros econd and nanosecond pulses in a blade knife-to-plate gap

Diffuse discharge could achieve glow-like discharge at atmospheric pressure1,2. It is important to understand the physics of the diffuse discharge due to the need for plasma surface treatment and the pure scientific merit. In this paper, characteristics of diffuse discharges in a blade knife-to-plate gap under different power sources and different discharge gap distances are investigated. Two homemade power supplies, microsecond power supply (CMPC-40D) and nanosecond power supply (MPC-50D), are used to produce diffuse discharges. In the experiments, diffuse discharges are generated in a blade knife-to-plate gap. The blade knife has a length of 20 cm, and the gap spacing ranges from 2 cm to 3 cm. Temporal evolution of atmosphere pressure diffuse discharges is conducted by ICCD (Andor-DH334T). Both positive and negative pulses under the conditions of gap spacing of 2 cm, 2.5 cm and 3 cm, power frequencies of 500 Hz, 1000 Hz and 1500 Hz are investigated. The discharge images taken by digital camera shows that the discharge is a diffuse mode in atmospheric pressure. Furthermore, discharge images taken by ICCD with an expose time of 2 ns are used to analyze the temporal evolution process of the diffuse discharge. The experimental results show that the diffuse in a large gap is more intense than that in a small gap. Moreover, the ICCD images present that the initial radiant area emerged near high voltage electrode, and it costs about 40 ns for forming a strip form plasma channel. The plasma channel moves forward and arrives at the negative electrode at 60 ns. It is calculated from the ICCD images that the velocity of the plasma channel is about 3×105 m/s.