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<p>Transitions between plasma modes in pulsed discharges have a strong influence on plasma properties, and thus, they impact many plasma-based applications. The streamer-to-spark transition has been extensively studied in gases; however, it is far less explored in liquids, with only few reports published in the literature. Herein, we investigate the streamer-to-spark transition in water using a liquid–liquid interface configuration, in which a pin electrode is placed at the heptane–water interface to enhance the electric field and generate 4&#xa0;mm-long discharges at 20&#xa0;kV with 100% occurrence probability. Using 1-ns ICCD imaging, it is revealed that the transition occurs within 14 ns, from the moment the streamer reaches the cathode to the moment the plasma channel resistivity drops. Gaussian Process analysis shows that two successive anode-directed ionization waves are issued in the residual streamer channel upon streamer contact with the cathode. The first potential wave is identified as a return streamer due to the resistive nature of the primary streamer channel, and it propagates at 1000–4000&#xa0;km/s. Comparatively, the second wave is slower (150–600&#xa0;km/s) and thus, is identified as a filament. This filament is induced by progressive channel heating, which eventually leads to reduced resistivity and the formation of a thermalized spark.</p>

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Investigation of the Streamer-to-spark Transition in Nanosecond in-liquid Discharges

  • 期刊论文

  • 发表日期：

    2026年1月17日

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  • Audren Dorval,
  • Luc Stafford,
  • Ahmad Hamdan

摘要

Transitions between plasma modes in pulsed discharges have a strong influence on plasma properties, and thus, they impact many plasma-based applications. The streamer-to-spark transition has been extensively studied in gases; however, it is far less explored in liquids, with only few reports published in the literature. Herein, we investigate the streamer-to-spark transition in water using a liquid–liquid interface configuration, in which a pin electrode is placed at the heptane–water interface to enhance the electric field and generate 4 mm-long discharges at 20 kV with 100% occurrence probability. Using 1-ns ICCD imaging, it is revealed that the transition occurs within 14 ns, from the moment the streamer reaches the cathode to the moment the plasma channel resistivity drops. Gaussian Process analysis shows that two successive anode-directed ionization waves are issued in the residual streamer channel upon streamer contact with the cathode. The first potential wave is identified as a return streamer due to the resistive nature of the primary streamer channel, and it propagates at 1000–4000 km/s. Comparatively, the second wave is slower (150–600 km/s) and thus, is identified as a filament. This filament is induced by progressive channel heating, which eventually leads to reduced resistivity and the formation of a thermalized spark.