Transient Suppression of Pulsed Ion Flux Induced by Dynamic Recycling in the Upgraded Linear Plasma Device TPD-II

The linear plasma device TPD-II was reactivated and upgraded to enable pulsed plasma and liquid-metal flow experiments. As an initial study, we performed pulsed plasma experiments using a capacitor bank system, focusing on the influence of transient recycling particles. Time-resolved measurements showed that the ion current at the target responded on a time scale longer than that of the pulse duration, attributed to slower transport of ions compared to that of electrons. In contrast, floating potentials responded on the same time scale as the pulse, reflecting the behavior of fast electrons. At higher pulse power, a transient drop in ion current and an increase in floating potential were observed after the input of pulse to the target, suggesting a rapid decrease in electron temperature and the onset of electron-ion recombination. Filtered high-speed imaging revealed enhanced He I emissions due to the recombination processes at the period. These results demonstrate the utility of the upgraded TPD-II in exploring transient plasma-neutral interactions relevant to divertor physics in future fusion reactors.