Investigation Of Two Kinds Of Hexagonal Superlattice Pattern In Dielectric Barrier Discharge At Atmosphere Pressure

Two types of hexagonal superlattice pattern are observed firstly by using a dielectric barrier discharge device with water electrode at atmosphere pressure. The formation, evolvement and spatial-temporal dynamics about each hexagonal superlattice pattern are experimented.Firstly, to the harmonic hexagonal superlattice pattern, the bifurcation scenario of it with the applied voltage increasing is given, which follows as traveling hexagonal pattern, harmonic hexagonal superlattice pattern, spiral pattern, and hexagonal pattern. The correlation measurements indicate that the hexagonal superlattice pattern is an interleaving of two different transient sublattices, both of them are harmonic. The spatial power spectrum demonstrates that the harmonic hexagonal superlattice pattern has two separate wave vectors, The sequence of two transient sublattices is S-L-L-S-L-L in one cycle of the voltage. Both the small wave vector qh and the big wave vector Kh belong to the harmonic mode, and they obey a triad resonant interaction qh1+qh2=Kh. The selection of pattern formation in quadrangular boundary with different area is studied. It is found that the hexagonal superlattice pattern is a typical type of nonlinear self-organized pattern, and the formation of square superlattice pattern is dependent upon the boundary condition.Secondly, the vibrating hexagonal superlattice pattern is studied, The bifurcation scenario of vibrating hexagonal superlattice pattern with the applied voltage increasing is shown as traveling hexagonal pattern, vibrating hexagonal superlattice pattern, spiral pattern (or stripe pattern), and hexagonal pattern. It is found that the small spot of vibrating hexagonal superlattice pattern vibrates periodically between two large spots. The spatial intensity distributions and the vibration mode of vibrating hexagonal superlattice pattern with a fast exposure time of 10 ms are obtained. The correlation measurements indicate that the vibrating hexagonal superlattice pattern is an interleaving of four different transient sublattices.The contractive analysis between harmonic hexagonal superlattice pattern and the vibrating hexagonal superlattice pattern is obtained. Large spot of two hexagonal superlattice patterns result from two times ignition in each half cycle of applied voltage. The first ignition takes the shape of a wide column, which looks like a big homogeneous spot from the cross-sectional view. However the second ignition takes the shape of a funnel, which looks like a small shinning spot with a circle of gleam around it from the cross-sectional view. A time integral of the two ignitions forms the large spot, which is are a shining central point and a gleam circle around it. It is found that, the formation of these two hexagonal superlattice patterns is influenced by the relative humidity of air.