One-Dimensional Studies of Positive Streamer Discharges Using Empire

Atmospheric streamer discharges are simulated using EMPIRE, a SANDIA National Laboratories electromagnetic/electrostatic particle-in-cell (PIC), Direct Simulation Monte Carlo (DSMC) code used for plasma modeling. This work focuses on the early onset of positive streamers in an electrostatic environment and are studied in detail to demonstrate EMPIRE capabilities. Geometry considered is a one-dimensional geometry with an electrode gap size of 1 cm and varying applied voltages. A custom gas consisting of only elastic, excitation, and ionization cross section is used to provide collision rates at atmospheric pressure. Simulation is seeded with an initial plasma density near the anode and allowed to propagate towards the cathode via photoionization mechanisms. The role of photoionization length scales on the positive streamer behavior is studied (e.g. the photoionization mean free path is varied to observe the influence on streamer velocity and formation). Mean free path is varied from micron scale to the entire gap size (1 cm). Results demonstrate the influence of photoionization length scales on streamer formation behavior and could point to the cause of observed behavior in fully three-dimensional simulations.