Analysis of the trigger characteristics for a pseudospark switch triggered by nanosecond focused laser

Abstract

Clarifying the trigger characteristics of pseudospark switch triggered by laser (backlight thyratron, BLT) is crucial for optimizing the trigger performance under different conditions. This paper investigates the electron and ion emission characteristics of metal irradiated by nanosecond focused laser, and tests the trigger characteristics of BLT triggered from the back of the cathode (CBLT) and the back of anode (ABLT) with different targets (Mg, Ti, Cu, Mo, W), and discusses the trigger mechanism. The trigger characteristics of CBLT depends on the emission of prompt electrons e1 and the expansion of ultrafast electrons e2. When the laser energy ε is less than 0.3 mJ, there will be no e1 emission, and low-density metals (e.g. Mg and Ti) are prone to ablation, resulting in large e2 amplitude and short trigger delay td. Due to the slow speed of e2, td of CBLT has an exponential relationship with the laser irradiation position. When ε is increased to above 1 mJ, different metals can be fully heated, and the emission of e1 will be enhanced and play a major role in trigger. In this case, metals with high melting and boiling points will produce more e1, so the trigger performance of Mg is the worst and W is the best. Due to the fast speed of e1, the sensitivity of td of CBLT triggered by e1 to the laser irradiation position is low, and the trigger lifetime can be improved by fine-tuning the laser irradiation position. The trigger of ABLT depends on the expansion of fast ions i2, and heavy metal ions diffuse easily in the background gas, so the laser irradiation area where ABLT can be stably triggered is larger, and the corresponding trigger performance of ABLT is better.