This Rapid Communication reports on the observation of an interesting phenomenon: the shape, especially the length, of a microwave plasma jet (MPJ) can be clearly influenced by simply placing a conductor near the plasma source, particularly when the nearby conductor is in contact with the external conductor of the coaxial microwave plasma generator, accompanied by a significant change in microwave reflection power from the terminal. To further investigate this discovery, the relationships between the length of the plume and some important factors, such as the conductivity and length of the nearby conductor, microwave input power, and gas flow velocity, are analyzed, and we find nonlinear rules of influence of these factors on the jet. Measurements of the electric potential around the jet reveal the nonuniform and non-neutral charge distribution inside the visible plasma plume, which plays a vital role in uncovering the mechanism underlying this phenomenon. The results are helpful for providing a deeper understanding of microwave plasma jet characteristics. More importantly, it provides guidelines to control the MPJ using simple structures.

• Received 3 January 2020
• Revised 17 July 2020
• Accepted 27 July 2020

DOI:https://doi.org/10.1103/PhysRevE.102.031201