## 3 Results and Discussion
### The Morphology Analysis  
After the electric explosion of the above three samples under a driving voltage of 2.0 kV, the photographs of the bridge area were taken and are shown in Figure 10.  
Figure 9: The flyer speed of three samples under different driving voltages. As shown in Figure 10, the electric explosion occurred locally in the center of the bridge area of Sample A, and there were traces of electric explosion in the center of the bridge area. However, a large number of metal bridge foils still existed. In the bridge area of Sample B, the electric explosion occurred completely, except that some metal copper slag existed. In the bridge area of Sample C, the electric explosion was relatively complete, with only a small amount of residue, and the explosion trace was obvious. During the electrical explosion of the metal bridge foil, due to the size of the bridge area being small and the loaded pulse current being kA level, the current density flowing through the bridge area is relatively concentrated. When the grains of the bridge foil are not uniform and there are many pores and cracks in the Cu microparticles, the reaction in the middle area of the bridge foil is not concentrated and the current density is not uniform, which leads to an incomplete electrical explosion. After the electric explosion at a driving voltage of 2.0 kV, the flyers of the bridge foils for the three samples were collected. SEM was also used for morphology analysis. The morphology of the collected flyer was observed. The results are shown in Figure 11.  
In Figure 11, it can be observed that for Sample A, the center of the flyer after the electric explosion has been broken and a perforation formed. For Sample B, the surface of the flyer after the electric explosion has a large curvature, and the shape of the flyer is like a bowl. Moreover, there is an irregular shape that appears in the center, which is critical to the broken shape. For Sample C, the flyer is relatively complete and the shape of the flyer is like a cap. The surface of the flyer is relatively flat. After the measurement, the diameter of the three kinds of flyers is consistent with that of the accelerating chamber. According to the electric explosion process of the metal bridge foil, when the narrow pulse and large current output by a high voltage pulse power source pass through the Cu foil, the bridge area of the bridge foil generates a lot of heat due to the Joule effect and will instantly experience the phase transition process of solid-liquid-gas-plasma, resulting in an electric explosion and generating a lot of high-temperature and high-pressure plasma. Under the constraint of the accelerating chamber, the polyimide film is sheared to form the flyer. It can be seen from the above results that in the sputtering process of the Cu film, the quality of the metal film is determined by the sputtering power. When the sputtering power becomes higher, the metal grain size becomes smaller and the grain distribution is more uniform. A complete morphology of the Cu foil without voids will be obtained. At the moment, when a current at a high-energy density passes through and is heated, the distribution of the premelting temperature in each part of the bridge region is relatively consistent. The compactness of the foil is poor, due to the phenomenon of delamination and voids in the micromorphology of the bridge foil. During the electric explosion, the problem of an inconsistent temperature distribution in the premelting heating process of the metal bridge zone is bound to occur, which will cause the possibility that a part of the metal crystal will form plasma while another part of the metal crystal will still be in the previous station. Thus, the electric explosion is incomplete, and the plasma produced is not uniform, leading to a decrease in the formation efficiency of plasma.