As an emerging technology for flexibly generating large-area atmospheric plasma, jet arrays are facing an urgent problem to control discharge modes caused by jet-to-jet interactions, apart from issues of stability and uniformity. Here, two modes in one-dimensional ns-pulsed He plasma jet arrays are reported, namely coupling and collimated modes. Discharge characteristics and transition rules of the two modes are explored by optical, electrical, spatial-temporal resolved and Schlieren methods. Results reveal that the coupling mode appears only when multiple conditions are satisfied, including low gas flow rate, high voltage frequency and small jet separation. Fluid dynamics and intensified charged-coupled device images prove that the mode transition mainly depends on the hydrodynamic interaction, which exceeds the effect of electrostatic repellence between ionization waves. Shrinkage of He flows is visualized to be enhanced at coupling mode, contributing to inward deflection of outmost plasma jets. Eddies on both sides of jet array and low-pressure regions near nozzles are generated by electric winds, promoting the transversal momentum transfer and gas fusion among adjacent He flows, thus tending to jet couplings. Some fresh insights are provided in this work about jet coupling and generation of controllable large-area plasma sources. The results could help to understand the importance of hydrodynamic interaction among proximal plasma jets, and plasma action on adjacent gas flows.

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Surface flashover of insulating materials induced by pollution and moisture environment is one of the main reasons for the damage of power system and electrical equipment. The improvement of the insulating materials surface hydrophobicity is key important, which can prevent the pollutants and water attachment, and enhance the insulating performance. In this paper, the super-hydrophobic film is formed on the surface of epoxy resin by a one-dimensional (1D) argon (Ar) jet array driven by nanosecond pulse power supply with hexamethyldisiloxane (HMDSO) addition. The influences of the processing time and HMDSO content on the epoxy resin surface hydrophobicity are investigated. It shows that with 0.04 % HMDSO, the jet array achieves a best hydrophobic treatment effect on the epoxy resin surface. After 60 s treatment, the apparent contact angle (ACA) of the epoxy resin surface increases from 60.3°of the untreated surface to 150.0°. The wettability of epoxy resin surface does not change too much as the treatment time beyond 60 s. The maximum ACA value 153.4°appears at 120 s processing time, which is just slightly higher than that of 60 s treatment time. The epoxy resin surface morphology and chemical feature before and after plasma processing are characteristics by the scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infra-red spectroscopy and X-ray photoelectron spectroscopy. It shows that the treated epoxy resin surface is covered with dense coral like particles in nanoscales, the original C=O、C-H and other organic functional groups are replaced by Si-(CH 3 ), Si-O-Si and other silicon containing groups, and the Si content increases from 0.4% to 28.0%. The experimental results provide important references to develop jet array as an efficient tool to enhance the surface hydrophobicity and insulating performance of insulating materials.

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