This paper presents the findings on the streamer development and propagation of streamers energized using a subnanosecond rise-time high voltage pulse in a specially designed wire-cylinder plasma reactor. Two U-shaped reactors with a width of 50mm and a length of 1m are created. A polycarbonate window is placed over an open slot in the reactor, making it airtight. It uses a pre-existing subnanosecond rise time pulse source to create streamers [1]. The streamer's length, width, velocity and number of streamers and the effect of reactor length, pulse repetition rate and gas flow is investigated using an ICCD camera. An automation system is designed to control the position of the camera and pulse source and it processes the data generated by the camera and oscilloscope without human interference. It is found that generally the maximum streamer length is larger on the edges than in the middle of the 2m reactor. Also a positive streamer propagates further than a negative streamer. Furthermore, the mean of the streamer's width becomes 1.5mm when it has enough energy and time to develop. When the streamers reach the reactor wall, the mean width decreases because the residual streamers have a smaller width. The next investigated parameter is the streamer velocity. The streamers accelerate after their inception until a stable velocity of 1.5m s-1 is reached. When the streamers reach the reactor wall, their velocity increases quickly. If their velocity drops to zero before reaching the reactor wall, they extinguish. Next, it has been found that the number of streamers initially climbs to 293m-1 and slowly decreases when the streamers reach the reactor wall or reduces to zero quickly if the streamers extinguish. Finally, also the effect of flow, repetition rate and reactor length have been investigated. The effect of a 5 standard litres per minute (slm) flow of synthetic air at 3 Hz repetition rate is insignificant, but it is needed to prevent sparks at 100 Hz. A high repetition rate causes the streamers to propagate less far, but they are more evenly distributed across the reactor. Decreasing the length of the reactor to 1m creates a higher overall voltage level in the reactor due to overlapping pulse reflections. This causes the streamers to propagate further. Lastly, a summary is given concerning design constraints for an optimal reactor. A reactor is considered optimized when the total volume is filled with active plasma. When the same pulse source is used, this optimal reactor has a length of 1m and uses pulses with a high repetition rate and a positive polarity. A gas flow is mandatory to prevent spark and to be able to clean air.
Streamer development and propagation through a coaxial reactor using a sub-nanosecond rise-time pulse source
Sengers, W. (Author). 31 Dec 2014
Student thesis: Master