## 3 Experimental Results  
### Gap Withstand  
The typical experimental observation results when the gap withstood the voltage are shown in Figure 2. Specifically, Figure 2a illustrates the waveform of discharge voltage and discharge current, whereas Figure 2b presents partial high-speed optical photographs capturing the initiation and development process of the leader. In order to highlight the characteristics of important electrical parameters, only the first 800 \(\upmu\)s of the voltage and current waveforms are presented in Figure 2a. When the switching voltage was applied to the gap, the positive electrode generated an initial corona discharge at t = 19.71 \(\upmu\)s, with a pulse amplitude of 2.45 A. Subsequently, under the suppression effect of the positive space charge in the streamer region near the electrode tip, the discharge ceased. After a dark period of approximately 23 \(\upmu\)s, the leader initiated at t = 42.35 \(\upmu\)s and continuously propagated toward the middle of the gap. However, the continuous-development current of the leader at this time was relatively low, approximately 0.1-0.2 A. Starting from t = 136.65 \(\upmu\)s, the leader began to enter the discontinuous development stage. Thereafter, seven typical restrikes occurred. Among the restrikes that occurred, the current pulse amplitudes of the two restrikes at t = 373.74 \(\upmu\)s and t = 499.33 \(\upmu\)s reached 8.32 A and 11.6 A, respectively. Thereafter, before the front time of the voltage wave ended, the development of the leader channel had already ceased, and the gap withstood the voltage. As can be seen from the current waveform presented in Figure 2, all of the restrikes appearing during the discharge development process were of the \"steep rise\" type. During the discharge relaxation stage between every two restrike current pulses, the discharge current was ultimately zero, and the duration of the relaxation process varied. Among the relaxation stages, the relaxation time between the fifth and sixth restrike pulses was the longest, at 71 \(\upmu\)s and 100 \(\upmu\)s, respectively, and the corresponding current pulse amplitudes were also the highest. In order to clearly observe the current characteristics and the luminous characteristics of the leader channel before and after the occurrence of the restric, photographs captured by the high-speed camera and current waveform corresponding to the fifth (t = 373.74 \(\upmu\)s) and sixth (t = 499.33 \(\upmu\)s) restricle presented in Figure 2 were extracted, as illustrated in Figure 3. The six high-speed photographs taken before and after the occurrence of these two restrikes were labeled F1-F6 and F7-F12, respectively, with the start and end moments of the exposure of each frame corresponding to the time axis of the discharge current waveform with dashed lines. Figure 2: The typical experimental results when the gap withstood the voltage. (**a**) Waveforms of applied voltage and discharge current and (**b**) optical morphology during leader development. Due to the limited resolution of the high-speed photographs presented in Figure 3, in order to highlight the details of the optical characteristics of the leader channel before the occurrence of restrike, the high-speed optical photographs in Figure 3 were processed with the image pseudo-color algorithm [22]. In more detail, as the grayscale value of the image increases, its color gradually changes from blue to red, and it turns white when the grayscale value is extremely high. In addition, the area where the leader channel is located in the photograph is marked with a white dotted frame, and the area within the white dotted frame was magnified three times and is placed below the photograph.