Modeling study on pressure dependence of plasma structure and formation in 110 GHz microwave air breakdown

Recent experimental studies of 110 GHz microwave air volume breakdown have shown that as pressure is decreased from atmosphere to a few torr, the discharge transitions from a well-defined array to a smeared-out array and finally to a diffuse plasma. In this letter, a two-dimensional model coupling plasma fluid equations and Maxwell equations is used to simulate the pressure dependence of plasma structure and formation under conditions similar to the experiments. The modeling pressure dependence of plasma structures in H plane and E plane is qualitatively consistent with the experimental observation. The quantitative discrepancy between modeling and experimental results is explained. The simulations allow a good understanding of plasma structure at different pressures in microwave volume breakdown. (C) 2011 American Institute of Physics. [doi:10.1063/1.3583452]