Three-dimensional patterns with <italic>C</italic>_{6<italic>v</italic>} symmetry in dielectric barrier discharge with a double-layer gas gap

In this work, several three-dimensional patterns with C6v symmetry are observed in the discharge of a mixture of air and argon by using a specially designed double-layer gas gap dielectric barrier discharge device for the first time. The formation mechanism of one of these 3D patterns, which is named a quasi hex-bolts lattice pattern, is studied experimentally and theoretically. It is composed of three interleaved discharge lattices: the axial points in a narrow gas gap, the axial points in a wide gas gap, and the column points in a narrow gas gap. The former two kinds of points are located at the same (x, y) positions on opposite sides of the quartz dielectric that separates the two gaps, forming the axis of each cell of the hex-bolts. The quasi hex-bolts lattice pattern can be observed within the range of argon content from 10% to 60% and pressure from 15.2 to 25.3 kPa. The spatiotemporal dynamics of the quasi hex-bolts lattice pattern are studied using a photomultiplier tube. It is found that the axial points in a wide gas gap discharge before the column points in a narrow gas gap in each half cycle of the applied voltage. By solving the Poisson equation using COMSOL, the effects of the inserted quartz dielectric on charge transport and its influence on the electric fields in two gas gaps are studied for the first time. The spatial distribution of the electric field in two gas gaps after each substructure discharge is simulated. It shows that the discharge in any gas gap (wide or narrow) will guide the discharge in the corresponding (x, y) position in the other gas gap (narrow or wide), and the following discharges occur at other locations in the narrow gap. It gives a good explanation for the experimental result that the axial point in a wide gas gap always discharges before the column point in a narrow gas gap. This work not only advances the research on three-dimensional patterns but also has significant implications for the fundamental and application studies on DBDs with inserted dielectric material.