Propagation of plasma bullet in U-shape tubes

In this work, to better understand the propagation mechanism of plasma bullets in capillary tubes, the propagation of plasma stream in a special designed U-shape tube is investigated. First, it’s observed that the smaller the distance d between the bended tubes is, the shorter the total length of the plasma stream is. Second, when d is reduced to 1 mm, the plasma stream in the lower part of the tube propagates along the upper inner surface of the tube rather than propagating in the whole tube uniformly. Third, high-speed photographs show that the plasma bullet starts to accelerate as soon as the secondary discharge is ignited, and propagating along the upper inner surface of the lower part of the tube. Such behavior is totally different with the propagation of plasma streams in straight tube. According to these results, we can conclude that the surface discharge plays an important role in the propagation of the plasma bullet and the conductivity of the plasma channel is relatively low, which is important for understanding the plasma bullet behavior.