A rich variety of spiral patterns such as single-armed spiral, dipole spirals, target pattern, multiarmed spiral, and spiral defect chaos state have been observed in ac-driven atmospheric pressure gas discharge. The confined and free boundary conditions are defined by means of whether there is a sidewall in the discharge domain or not, respectively. In the free boundary condition, the spiral pattern arises when the stripe pattern undergoes core instability or notching instability. In the confined boundary condition, the spiral pattern is formed by sidewall forcing. The spiral drifts upward in the free boundary condition and meanders in the confined boundary condition. The topological charge of the spiral pattern can be changed when the spiral interacts with the dislocations. The spiral wavelength (average distance between two consecutive rolls) is a function of gas composition and decreases rapidly with increase of air concentration in discharge gas.
We report the observation of a square superlattice pattern in a dielectric barrier discharge system. The correlation measurements indicate that the square superlattice pattern is an interleaving of two different transient square sublattices. The interplay between the charge pattern and the discharge filament pattern is discussed.
An atmospheric glow discharge controlled by a dielectric barrier is realized in a coaxial electrode geometry in argon. The discharge characteristics are studied by the electrical method and optical emission spectroscopy. The experimental results indicate that there is only one discharge pulse per half cycle when the applied voltage is very low, and the rise time of the discharge pulses at the positive half cycle is much shorter than that at the negative one. With an increase in applied voltage, the width of the discharge pulse increases, while the inception voltage at which breakdown occurs decreases. The rise time at positive half cycle almost equals that at negative half cycle when the applied voltage is high enough. The research results pertaining to gas gap voltage indicate that the critical electric field for breakdown decreases with increasing applied voltage. The electron temperature is estimated from the Einstein relation, and the result indicates that the electron temperature and the electron density are functions of the applied voltage and the gas flow rate. The electron temperature is also studied by emission spectroscopy and a similar result is obtained.
Hexagon and square patterned air discharges are realized by using a dielectric barrier discharge device with two water electrodes. With increasing voltage, the filaments (plasma columns) tend to be dense and regularly arranged, and the current in each half cycle changes from several peaks to one leading peak followed by a broad hump of current peaks. It shows that the spatiotemporal correlation between filaments is enhanced with increasing voltage. A phase diagram of hexagon patterned air discharge with different gas gap widths as a function of air pressure and applied voltage is presented.
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