Atmospheric air diffuse plasmas have enormous application potential in various fields of science and technology. Without dielectric barrier, generating large-scale air diffuse plasmas is always a challenging issue. This paper discusses and analyses the formation mechanism of cold homogenous plasma. It is proposed that generating stable diffuse atmospheric plasmas in open air should meet the three conditions: high transient power with low average power, excitation in low average E-field with locally high E-field region, and multiple overlapping electron avalanches. Accordingly, an experimental configuration of generating large-scale barrier-free diffuse air plasmas is designed. Based on runaway electron theory, a low duty-ratio, high voltage repetitive nanosecond pulse generator is chosen as a discharge excitation source. Using the wire-electrodes with small curvature radius, the gaps with highly non-uniform E-field are structured. Experimental results show that the volume-scaleable, barrier-free, homogeneous air non-thermal plasmas have been obtained between the gap spacing with the copper-wire electrodes. The area of air cold plasmas has been up to hundreds of square centimeters. The proposed formation conditions of large-scale barrier-free diffuse air plasmas are proved to be reasonable and feasible.
The solution resistive divider is often used considering its excellent high-frequency and withstanding voltage characteristics. This paper develops a nanosecond pulse measurement system based on the CuSO4 solution resistive divider, which can be used to measure high voltage impulses with rise time of 50 ns and amplitude of 300 kV. The low-voltage arm of the newly designed solution resistive divider is composed of noninductive metal film resistors. The newly designed resistive divider combines the advantages of the conventional solution resistive divider and metal film resistive divider. The stray parameters of the resistive divider are theoretically calculated and the circuit simulation is studied. Besides, the square wave response characteristics of the resistive divider are studied in the experiments. Considering the effect of frequency on the surge impedance of the cable, a matching cable of the same type with the transmission cable instead of a common matching resistor is used to improve the matching effects. In order to reduce the effects of electromagnetic interference on the measurement results, some shielding measures are taken. The experimental results show that the measurement system has good response characteristics in the practical application.
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