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Plasma Driven Permeation of Hydrogen in Tungsten Deposition Layer under Co-Deposition of Tungsten and Hydrogen

Kentaro MASUTA¹⁾, Kazunari KATAYAMA²⁾

1)

Kyushu University, Interdisciplinary Graduate School of Engineering Science, Kasuga, Fukuoka 816-8580, Japan

2)

Kyushu University, Faculty of Engineering Science, Kasuga, Fukuoka 816-8580, Japan

(Received 25 July 2025 / Accepted 5 October 2025 / Published 16 December 2025)

Abstract

This study investigates the influence of tungsten (W) deposition on hydrogen plasma-driven permeation (PDP) behavior by examining co-deposition of W and hydrogen on a nickel (Ni) substrate. Experiments were performed using RF plasma sputtering at a substrate temperature of 693 K. The measured hydrogen permeation flux exhibited a transient peak followed by a steady-state phase, even as the W deposition layer continued to grow. Additionally, doubling the Ni substrate thickness had no effect on the steady-state flux, indicating that the permeation was limited by surface recombination processes rather than bulk diffusion. The numerical model was developed to simulate hydrogen diffusion and surface recombination processes in both the Ni substrate and the growing W layer. As W deposition changes the surface condition, the recombination coefficient (K_r) was expressed as a function of time, which successfully reproduced the transient peak observed in the experiment. The temporal suppression of K_r was attributed to the initial deposition of W atoms on the Ni surface. Further validation through repeated discharge experiments with pre-deposited W confirmed that the initial transition from Ni to W was responsible for the peak. These results show that surface changes such as W deposition strongly affect surface recombination, thereby influencing PDP behavior.

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

hydrogen permeation, tungsten, co-deposition, recombination coefficient

DOI: 10.1585/pfr.20.1405054

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