Study on pseudospark switch triggered by weakly focused 266 nm ultraviolet laser
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摘要: 当前对于光触发伪火花开关的研究主要集中在使用紫外激光触发，触发物理机制普遍认为是光电发射。然而，当紫外弱聚焦激光在低电场环境中照射光电材料（靶材）时，由光电发射产生的种子电子非常有限。为了进一步揭示紫外弱聚焦激光触发物理机制，利用266 nm紫外弱聚焦激光，搭建了开关测试实验平台和种子电子测试实验平台，研究了激光能量、开关电压、气压、靶材料、触发位置对开关触发特性的影响，分析了种子电子的来源和对触发开关的贡献。研究结果表明，在阴极背面孔边缘触发时，光电发射产生的瞬发电子不是种子电子的主要来源，与烧蚀等离子有关的超快电子才是。因此，当在阴极背面孔边缘触发时，密度和熔沸点低，易烧蚀的材料更适合作为紫外弱聚焦激光触发伪火花开关的靶材。经测试，当在阴极背面孔边缘触发，工作电压为−15 kV，气压为80 Pa（氦气）时，以镁为靶材的开关能实现稳定触发导通的最低激光能量为2 mJ，远低于铜（6 mJ）和钼（8 mJ）。此外，在上述相同条件下，激光在开关阴极孔内壁触发时，触发时延和抖动分别为36.9 ns和1.41 ns，远低于在阴极背面孔边缘触发时的时延和抖动（116.4 ns和5.39 ns）。Abstract: Currently, the research on pseudospark switches triggered by laser mainly focuses on triggering by ultraviolet laser, and the physical triggering mechanism is generally considered to be photoemission. However, when the weakly focused ultraviolet laser irradiates the photoelectric material (target) in a low electric field environment, the seed electrons generated by the photoemission are very limited. To further reveal the physical mechanism of the switches triggered by the weakly focused ultraviolet laser, we established the test experimental platform for discharge of pseudospark switches triggered by weakly focused 266 nm ultraviolet laser. On this basis, the emission characteristics of seed electrons irradiated by laser were tested. The effects of laser energy, switch voltage, gas pressure, target material and irradiation position on the trigger characteristics of the switch were studied, and the source of seed electrons and their contribution to trigger were analyzed. The results show that when the laser is irradiated on the edge of the hole on the back of the cathode, the prompt electrons generated by the photoemission are not the main source of the seed electrons, and the ultrafast electrons related to the ablation plasma are the main source. Therefore, when the laser is irradiated on the edge of the hole on the back of the cathode, the material with low density and melting boiling point is more suitable as the target material for pseudospark switch triggered by weakly focused ultraviolet laser. According to the testing result, in this case, the operating voltage is −15 kV, and the pressure is 80 Pa (helium), the minimum laser energy of the switch with magnesium as the target can achieve stable trigger conduction is 2 mJ, which is much lower than that of copper (6 mJ) and molybdenum (8 mJ). In addition, under the same conditions, when the laser is irradiated on the inner wall of the cathode hole of the switch, the trigger delay and jitter are 36.9 ns and 1.41 ns, which are much lower than those when the laser is irradiated on the edge of the hole on the back of the cathode (116.4 ns and 5.39 ns).
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图 5 激光能量和气压对开关触发时延的影响
Figure 5. Influence of laser energy and gas pressure on trigger delay of the switch
图 6 激光能量和气压对开关触发时延抖动的影响
Figure 6. Influence of laser energy and gas pressure on trigger delay jitter of the switch
图 7 激光能量和工作电压对开关触发时延的影响
Figure 7. Influence of laser energy and working voltage on trigger delay of the switch
图 8 激光能量和工作电压对开关触发时延抖动的影响
Figure 8. Influence of laser energy and working voltage on trigger delay jitter of the switch
图 9 靶材料对开关触发时延和抖动的影响
Figure 9. Influence of target materials on trigger delay and jitter of the switch
图 10 镁、铜、钼发射电子电流波形
Figure 10. Emitted electron current waveform of magnesium, copper and molybdenum
图 11 不同偏置电压下，镁发射电子电流波形
Figure 11. Emitted electron current waveform of Mg under different bias voltages
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