A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures

Abstract

A finite-difference algorithm was developed to calculate several RF breakdown parameters, for example, the formative delay time that is observed between the initial application of a RF field to a dielectric surface and the formation of field-induced plasma interrupting the RF power flow. The analysis is focused on the surface being exposed to a background gas pressure above 50 Torr. The finite-difference algorithm provides numerical solutions to partial differential equations with high resolution in the time domain, making it suitable for simulating the time evolving interaction of microwaves with plasma; in lieu of direct particle tracking, a macroscopic electron density is used to model growth and transport. This approach is presented as an alternative to particle-in-cell methods due to its low complexity and runtime leading to more efficient analysis for a simulation of a microsecond scale pulse. The effect and development of the plasma is modeled in the simulation using scaling laws for ionization rates, momentum transfer collision rates, and diffusion coefficients, as a function of electric field, gas type and pressure. The incorporation of plasma material into the simulation involves using the Z-transform to derive a time-domain algorithm from the complex frequency-dependent permittivity of plasma. Therefore, the effect of the developing plasma on the instantaneous microwave field is calculated. Simulation results are compared with power measurements using an apparatus designed to facilitate surface flashover across a polycarbonate boundary in a controlled N2, air, or argon environment at pressures exceeding 50 Torr.

Short-pulse high-power microwave breakdown at high pressures

“…The high-power microwave (HPM) has important applications in military and civilian fields, such as directed energy weapons, creation of artificial plasma mirrors, long distance wireless energy transport, and so on. [1] In recent years, the peak electric field of the HPM has reached several MV/m, [2,3] which is close to or exceeds the gas breakdown threshold at high pressures. Once the gas breakdown occurs, the generated plasma strongly hinders the radiation and propagation of the HPM.…”

Effect of aperture field distribution on the maximum radiated power at atmospheric pressure

“…[1] In recent years, the electric field radiated from the aperture antenna reaches several MV/m that can exceed the breakdown electric field at atmospheric pressure. [2,3] Once the air breakdown occurs, the attendant plasma strongly hinders the microwave radiation. This suggests that the radiated power reaches the maximum (or critical) value when the maximum electric field in the near-field region is equal to the breakdown electric field.…”

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components

“…In recent years, many scholars have studied the air breakdown caused by the high-power microwave. [7][8][9][10] Nam et al introduced the pressure-independent enhanced electron energy distribution function into the global model, and improved fidelity for modeling the gas breakdown. [7] The twodimensional model coupling Maxwell equations with plasma fluid equations was developed by Boeuf et al to simulate the patterns of breakdown plasma, in which the accurate diffusion coefficient was adopted.…”

“…[8] Ford et al used the finitedifference time-domain method to solve a one-dimensional model similar to that of Boeuf et al, and predicted the breakdown formation time and the microwave transmission in the breakdown plasma. [9] The Poisson and Boltzmann equations were utilized by Zhu et al to describe the air breakdown near the dielectric window, and the results showed that the range can be roughly divided into at least two regions, sheath region and plasma region. [10] Most of these studies above focused on the case in which the microwave has one electric field com-ponent or two mutually orthogonal and inphase electric field components.…”