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Supplementary Material 4

Supplementary Material 1

Supplementary Material 6

Supplementary Material 5

Supplementary Material 2

Summary form only given. The evolution of single-wire and dual-wire Z-pinch of 8μm-W were investigated by X-ray backlighting using the X-pinch which radiated a soft X-ray source. The experiments were carried out on the pulsed power generator PPG-I (400kA/500kV/100ns) which was designed and constructed by Department of Electrical Engineering of Tsinghua University. In order to scale the mass distribution at different explosion time, a mass step wedge including eight tungsten layers was fabricated and inserted between the object Z-pinch and the X-ray film. By a large number of imaging experiments, the physical images of the plasma merging, the coronal plasma formation and development of the instabilities of Z-pinch and some important parameters like mass ablation ratio and core expansion ratio were obtained. The mass density distributions at different explosion time were drawn based on the x-ray photos of 8μm-W and step wedge. The conductance curve of time-dependence of 8μm-W was also calculated using waveform of voltage and current.

The axial backlighting of two-wire Z-pinch using an X-pinch as an X-ray source was conducted on PPG-1, a pulsed power generator with a current of 400 kA in amplitude and 100 ns in pulse width. Its time-resolved axial backlighting images are obtained. In the backlighting images all the physical processes similar to those occurring in the early stage of the wire-array Z-pinch are observed, including the expansion of the high-density wire core surrounded by low-density coronal plasmas, the motion of the coronal plasma toward the axis of the wire-array, and the formation of precursor plasma. The areal mass density of the plasma shown in the backlighting images is calibrated with step-wedge filters. And the time-resolved radial distributions of the areal mass density of the plasma from the two-wire Z-pinch are obtained.

The energy deposition process of electrical wire explosion under vacuum or low gas pressure circumstances is usually terminated prematurely, owing to the flashover along the surfaces of wires. Therefore energy deposited into wires can be far less than the amount needed to fully vaporize them. In this paper, a parallel connection method of wire is introduced in order to improve the energy deposition of the concerned wire before flashover takes place. Wire explosion driven by a current with a rise time of tens of ns and an amplitude of about 1 kA is studied numerically, and the simulation results show that by connecting a wire of a certain size in parallel with both ends of the exploding wire, the voltage rising rate is suppressed and the flashover is delayed; therefore the energy deposited into the concerned wire is increased effectively.