Plasma and Fusion Research

Volume 21, 1402025 (2026)

Regular Articles

Transient Suppression of Pulsed Ion Flux Induced by Dynamic Recycling in the Upgraded Linear Plasma Device TPD-II
Yuki HAYASHI1), Yukinori HAMAJI2,3), Noriyasu OHNO4), Naomichi EZUMI5), Shinichi NAMBA6), Shin KAJITA1), Akira TONEGAWA7), Makoto TAKAGI4), Goro NOMURA2), Sakuji KOBAYASHI8), Suguru MASUZAKI2,3)
1)
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan
2)
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
3)
The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
4)
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
5)
Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
6)
Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima 739-8527, Japan
7)
Global Research Institute of Nuclear Energy, Tokai University, Hiratsuka 259-1292, Japan
8)
Kyoto Fusioneering Ltd., Tokyo 143-0006, Japan
(Received 17 November 2025 / Accepted 29 January 2026 / Published 31 March 2026)

Abstract

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.

Keywords

linear plasma device, direct current arc discharge, pulse plasma, recycling particles

DOI: 10.1585/pfr.21.1402025

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