ePLAS modeling of laser induced lightning streamers

The ePLAS code is a derivative of ANTHEM\footnote{R. J. Mason, J. Comp. Phys. 71, 429 (1987)} originally developed to model long pulse laser interactions. The code has been enhanced to treat opening switch plasmas, plasma jets, and short pulse laser interactions with cones and wires.\footnote{R. J. Mason, et al., Bull. Am. Phys. Soc. 53, 152 (2008).} We address new features for application to lightning and guided arcs. ePLAS models collisional background plasma with cold electron and ion components. Self-consistent \textit{E- and B-}fields are determined implicitly for time steps well beyond the plasma period; hybridization permits spatial scales exceeding the Debye length. For lightning studies an initial start-up potential in a strongly ionized region has been added, plus ``air chemistry'' to create additional plasma in intense, propagating $E-$field regions at the leading edge of ``streamers.'' We discuss the motion of both positive and negative streamers in nitrogen on nanosecond time scales, showing streamer guidance in added plasma seeded by a laser. $B$-field inclusion permits the study of return strikes.