The paper discusses the relation between streamer velocity and diameter that follows from an analytical approach to description of the streamer head structure. It is shown that using measured data for streamer velocity and diameter one can evaluate the electric field in the streamer head. The analytical approach predicts that for positive streamers a minimum diameter exists, inversely proportional to the gas density.

• Received 27 January 2009

DOI:https://doi.org/10.1103/PhysRevE.79.057401