Simulating positive streamer discharges in air

December 21, 2023

Zhen Wang defended her PhD thesis at the Department of Applied Physics and Science Education on December 21st.

Image: iStockPhoto

For her PhD research, Zhen Wang focused on positive streamer discharges in atmospheric air, starting with detailed comparisons between different computational models. As part of her research, she also explored the role of photoionization in streamer branching using simulations and experiments. Added to that, Wang looked at the propagation of positive streamers in strong external magnetic fields. Her work contributes to the validation of streamer discharge models, as well as the explanation of streamer morphology under certain conditions.

For the computational part of her research, Zhen Wang performed the validation and verification of classical models for streamer discharges and investigated the source of instabilities in streamer propagation.

The studies were done using a drift-diffusion-reaction fluid model and a PIC-MCC (particle-in-cell, Monte Carlo collision) particle model. The comparison between fluid and particle model was performed, considering both axisymmetric and 3D Cartesian coordination, and good agreements were found.

2D vs. 3D

By using the fluid model, Wang analyzed the difference between 2D and 3D Cartesian coordination under the same condition which helped in the interpretation of the simulation results from 2D Cartesian model into 3D settings.

The 3D fluid model was combined with stochastic photoionization to quantitatively predict the branching behavior of positive streamer discharges in air, and the consistency with dedicated experiments proved that photoionization is the main mechanism that causes streamer branching.

In addition, Wang also studied how strong external magnetic fields influence positive streamers using the 3D PIC-MCC model. This helped in deciphering the complex spatial structure, which is currently difficult to observe using experimental methods. The results could be scaled to different pressures and corresponding field strength.

Title of PhD thesis: Simulating Positive Streamer Discharges in Air - branching and model validation. Supervisors: Ute Ebert, Anbang Sun, and Jannis Teunissen.