Computational modeling of gas heating mechanism during high power microwave breakdown in air

High Power Microwave (HPM) breakdown at high pressure involving complex plasma dynamics and gas heating is a challenging problem to study theoretically, experimentally as well as computationally. Early experimental research focused on the guided microwave exposure on freely located discharge for different pressure and field conditions. The discharge is the outcome of the enhancement of the microwave electric field at the focus of the converged microwave radiation thereby enabling an efficient way to couple the radiated EM energy into a gas. Intermediate to high pressure is required for observing proper gas heating phenomenon like streamer formation. Of late, researchers have renewed their interest to investigate this phenomena computationally to replicate those experimental results, and properly understand the EM wave plasma interaction, plasma formation, subsequent energy exchanges between wave and plasma, and finally between gas and plasma. The renewed interest is primarily because of potential applications of above discharges in aerodynamic flow control, combustion ignition, flame stabilization and space propulsions. The phenomenon is non-linear in nature, involves complex plasma/ gas chemistry and necessitates multiscale modeling for computational investigations. The modeling and simulation of coupled high frequency EM waves and plasma requires synchronization between multiple time and space scales involved in the problem. The plasma and EM wave physical interaction (nanoseconds timescale) model consists of Maxwell's equations that are coupled to the plasma continuity equation via electron current density that further couples to gas dynamics (microseconds timescale) equation using gas density. Several numerical works have been done in the past to look into this problem till hundreds of nanoseconds timescale. In this work, we describe how to tackle the numerical challenges of multiscale modeling and simulation of complex Plasma Dynamics during HPM breakdown in air particularly focusing on the gas heating phenomena at longer time scales (microseconds). (author)