On the large variability of streamer discharges

Streamer discharges are a basic phenomenon in electric breakdown of gases; they appear in lightning, sparks, and numerous application fields. They are 3-dimensional dynamic multiscale phenomena, with high electron energies up to possible run-away, and with growth velocities that can reach fractions of the speed of light. Our review [Nijdam, Teunissen, Ebert, PSST 29, 103001 (2020)] also summarizes open questions, and I will address results found since. First, we have studied single positive streamers in air under the same conditions both in experiments and in simulations, and we found quantitative agreement without fitting parameters. But second, positive streamers in air at fixed temperature and pressure can also have very different modes of propagation, with velocities much larger or much smaller than the electron drift velocity, accelerating, decelerating or propagating in a solitary manner. The solitary streamers propagate with constant shape and velocity after having lost the conductive connection to the electrode; this behavior matches the original definition of the stability field. But third, due to the long-range photoionization, positive streamers in air are by no means generic; in air with a stoichiometric admixture of 9.5% methane (for combustion) or in CO2 dominated gas mixtures (for high voltage engineering) positive streamer discharges behave very differently, as we illustrate with 3D MCC-PIC models for the electrons in the discharge. Fourth, we also investigate negative streamers in air, they are particular interesting in lightning due to possible electron run away, and because the radio telescope LOFAR now can detect negative streamers in thunderstorms on the meter scale that is also reached by simulations. Finally, I won’t have much time left to comment on recent model reduction approaches to complete streamer corona’s, and on processes before and after the streamer phase. Results are due to the MD-group at CWI and to the EPG-group at TU/e.