*3.4. Discharge Life Characteristics of Planar Spark Gap Switch*

The service life of the high-voltage switch seriously affects the working reliability of the exploding foil initiation system. The performance of the three-electrode planar sparkgap high-voltage switch based on copper foil was reduced after several discharge tests. Under the same input voltage condition, the working reliability is reduced, the conduction time is longer, and the trigger voltage needs to be increased. Moreover, it was found that the trigger electrode of the switch had traces of burns, as shown in Figure 12.

**Figure 12.** Photo of ablation after switch discharge.

After analysis, this is because the electrode gap is filled with air, so that the threeelectrode planar spark gap switch can withstand a specific high voltage, but when the switch needs to be triggered and turned on, it needs to form a sufficient electric field strength in the trigger gap. Since the thickness of the copper foil-based three-electrode plane spark gap high-voltage switch is only 4.0 μm, a large amount of ions or electrons will be generated in the instant when the switch is turned on, and the narrow pulse strong current generated by the discharge circuit will be turned on, causing burns to the switch electrodes.

The electrode thickness of the three-electrode plane spark gap switch has a certain influence on the field strength, and ultimately affects the service life of the switch. The electrostatic field of the three-electrode plane switch is analyzed with the help of finite element simulation software. In the simulation, copper was selected as the electrode material, and air was selected as the dielectric material. The excitation source was electrostatic field solver excitation source, and the boundary condition is balloon boundary condition. The diameter of positive and negative main electrodes is 4.0 mm, the distance *b* is 2.0 mm and the width of trigger electrode *a* is 1.2 mm. The setting negative voltage is 0 V, the positive voltage is 1.3 kV, the trigger voltage is 1.5 kV, the number of calculation steps is 10, and the allowable error is 0.1%. Figure 13 shows the overall field intensity distribution cloud diagram of the three-electrode plane spark gap high voltage switch, Figure 14 shows the electric field distribution before triggering, and Figure 15 shows the electric field distribution after triggering.

**Figure 13.** Cloud diagram of the overall field intensity distribution of the three-electrode plane spark gap high-voltage switch.

**Figure 14.** Electric field distribution before triggering.

As shown in Figure 14, when a high voltage of 1.3 kV is provided between the two main electrodes of the switch, the electric field is evenly distributed between the two main electrodes, and the field strength near the edge of the trigger electrode is the largest at 22.9 kV/cm. At this time, the maximum field strength is lower than the breakdown strength of air by 30 kV/cm, so the switch cannot self-breakdown. Considering that the air in the test environment is a non-ideal environment, the breakdown strength of the air will be lower than the ideal 30 kV/cm due to factors such as humidity and temperature. In order to improve the safety of the switch, it is necessary to reserve a certain distance to ensure the insulation effect and avoid false triggering. As shown in Figure 15, the trigger electrode was applied with a voltage of 1.5 kV, and the maximum electric field strength between the trigger electrode and the cathode reached 52.5 kV/cm, which was 30 kV/cm higher than the breakdown strength of air. At this time, the gas between the trigger electrode and the cathode will be ionized, and electrical breakdown will occur, so that the main electrodes will be broken down, and the conduction loop will discharge. In order to improve the working reliability of the switch, when the trigger voltage is loaded, the minimum electric field strength between the two main electrodes and the trigger electrode must be higher than the breakdown strength of air by 30 kV/cm.

The maximum static operating voltage of the three-electrode planar switch is simulated by the established simulation model. In the simulation, the dielectric material is air, no trigger voltage is applied, the negative voltage is 0 V, and the anode voltage constantly increases from 0 V. When the electric field strength of the main electrode gap is greater than the air breakdown strength, the switch is considered to be broken down. Since the breakdown strength of ideal air is 30 kV/cm, the lower limit of the field strength is set to 30 kV/cm in the simulation results; only the electric field strength greater than the breakdown strength of air is displayed, so that the self-breakdown process of the switch can be visually observed, and the self-breakdown voltage can be obtained, as shown in Figure 16.

Figure 17 is a partial enlarged view of the field strength of the switch gap. It can be seen from Figure 17 that the field strength of the trigger gap has increased significantly, and the field strength is greater as it is closer to the trigger electrode. The electrostatic field simulation results show that the discharge first occurs in the trigger gap, and then extends to the entire main electrode gap, but the field strength is the highest around the main electrode closest to the trigger electrode, and a high concentration of electron clouds appears. However, since the thickness of the switch electrode is only 4 μm, a burning phenomenon occurs.

**Figure 16.** Electric field distribution of integrated components under different charging voltages (**a**) electric field distribution at 1500 V, (**b**) electric field distribution at 1500 V, (**c**) electric field distribution at 2500 V, (**d**) electric field distribution at 2500 V, (**d**) Electric field distribution at 2558 V.

**Figure 17.** Simulation results of the field strength distribution in the trigger gap of the three-electrode plane spark gap high-voltage switch.
