A Fully Coupled Nonlinear Scheme for Time-Domain Modeling of High-Power Microwave Air Breakdown

In this paper, the air breakdown problem encountered with high-power microwave operation is modeled using a fully coupled nonlinear Newton scheme in the time domain. As a highly nonlinear process, the air breakdown is resulted from the complicated electromagnetic-plasma interactions, which can be described by a coupled system where Maxwell's equations govern the electromagnetic fields, and a simplified plasma fluid equation governs the plasma current. The resulting nonlinear Maxwell's equations are solved by the time-domain finite-element method with a proposed Newton's method, while the simplified plasma fluid equation is solved with another point-wise Newton's method. These two sets of equations are coupled together using a proposed inner-outer iterative scheme to guarantee the convergence and accuracy of the numerical solution. Numerical examples are presented to characterize the nonlinear phenomenon of the breakdown process and the self-sustaining property of the plasma current.

I. Introduction

High-power microwave (HPM) devices and systems have very important military and civilian applications. To design better HPM devices that generate higher electromagnetic power and longer pulsewidth, extensive research effort has been devoted to the development of microwave sources [1], [2], the design of output windows [3], [4], and the optimization of advanced cathodes. However, as the power density increases, the air breakdown can be triggered in the HPM devices and systems, which is usually hazardous and can become a limiting factor for the high-power radiation to be generated and transmitted.