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

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 can be accelerated. When θ<; 0.1π (θ is the angle between two wavevectors), the plasma structure and formation of intersecting beams are similar to those of single beam. For θ > 0.5π and high pressures (v_c >> ω), at the initial stage of discharge, the filamentary plasma propagates along the field maxima and forms 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. 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 0.5 λ/sin (θ/2).