Theoretical study on air breakdown by two intersecting high power microwave beams

Summary form only given. There is an extensive literature on air breakdown by single microwave beam^1-4, but relatively few studies on that by intersecting beams. In this paper, air breakdown in the region of two intersecting high power microwave (HPM) beams is investigated by numerical solution of fluid-based plasmas equations coupled with the Maxwell equations. For two coherently intersecting HPM beams, interference field maxima and minima are created in the intersecting region. The collisional cascade breakdown occurs only if the initial free electron appears or arrives in the vicinity of field maxima, where the free electron is accelerated. When θ<; 0.1π (θ is the angle between two beams), the plasma structure and formation of intersecting beams are similar to those of single beam. For θ> 0.25π and high pressure (ν_c >>ω), at the initial stage of discharge, the filamentary plasma propagates along the field maxima and forms a plasma filament band. After the plasma-filament band growing long enough, the two HPM beams are separated in the vicinity of plasma due to scattering and absorption by plasma. The new plasma-filament bands continue to appear on both sides of plasma region as time increases. When θ> 0.5π, the distance between adjacent plasma filament bands is about 0.25λ/ sin(θ/ 2). However, if θ in the range of π/4 to π/3, the distance between adjacent plasma filament bands is about 0.5λ/ sin(θ/ 2). It is also found that, under the same condition, the plasma region produced by two incoherent beams is smaller than that by two coherent beams.