Shizuoka University Conducts World's First Plasma-Driven Permeation Experiment on W-Re Alloys for Fusion Reactors

A research group led by Associate Professor Yasuhisa Oya of the Faculty of Science at Shizuoka University conducted plasma irradiation experiments using the Plasma-Driven Permeation (SUMPPU) device at Shizuoka University. They elucidated the effects of Re and irradiation defects on physical constants related to the plasma permeation and retention behavior in tungsten-tungsten-rhenium (W-Re) alloy samples.

This research achievement was published on May 30, 2026, in the international academic journal "Fusion Engineering and Design" published by Elsevier.

[Research Background] Fusion power generation, expected to be a next-generation clean energy source, utilizes the energy obtained from the fusion reaction of deuterium (D) and tritium (T). Since the fusion reaction is maintained in a high-temperature plasma state, tungsten (W), with its high melting point and low sputtering yield, is considered a leading candidate for plasma-facing materials that form the reactor wall. During operation, W is exposed not only to high-energy D and T but also to neutrons generated by the D-T reaction. For the realization of fusion reactors, long-term plasma sustainment and strict management of scarce T are indispensable. Therefore, it is necessary to clarify the hydrogen isotope permeation behavior in W under conditions close to actual operation.

However, in W subjected to neutron irradiation, some of it transmutes into rhenium (Re), and irradiation defects are simultaneously introduced. Thus, evaluating the impact of Re and irradiation defects on hydrogen isotope behavior is crucial. Neutron-irradiated samples are radioactive and can only be handled in a limited number of facilities worldwide. By installing the Plasma-Driven Permeation (SUMPPU) device within a controlled area, this research group has been conducting plasma permeation experiments on neutron-irradiated samples, a capability unique globally. In this study, we aimed to elucidate the effects of Re addition by evaluating not only permeation but also retention behavior through D plasma irradiation using SUMPPU.

[Research Results] In this study, W and W–10%Re alloys were used as samples. To simulate irradiation defects, Fe²⁺ ion irradiation was performed at the Ion Irradiation Research Facility (TIARA), after which the samples were introduced into Shizuoka University's SUMPPU. D plasma permeation experiments were conducted on W and W–Re alloys to evaluate the permeation behavior in W–Re. Furthermore, post-D plasma irradiation, Temperature Programmed Desorption (TPD) was performed to assess the effects of Re and irradiation defects on hydrogen isotope retention behavior.

The results showed that the permeation flux increased in W–10%Re compared to W. Calculating the recombination constant based on the parameters obtained from the experiments revealed that the recombination constant for W–10%Re is smaller than that for W. A decrease in the recombination constant suppresses the release of D from the surface, increasing the D concentration within the sample. This indicates that the increased internal D diffuses to the back surface, leading to a larger permeation flux in W–10%Re.

Furthermore, it was found that Re addition significantly reduces the amount of D retained by suppressing the generation of irradiation defects and reducing D trapping sites. The effects of Re addition were clarified to decrease the recombination constant and suppress the generation of irradiation defects.

[Future Prospects and Ripple Effects] The insights gained from this research deepen the understanding of hydrogen isotope migration dynamics in W–Re alloys under irradiation environments and will greatly contribute to building the fundamental data required for the development of fusion reactor materials.

[Publication Information] Journal: Fusion Engineering and Design Paper Title: Hydrogen isotope permeation and desorption dynamics in W-Re alloys Authors: Yuzuka Hoshino, Robert Kolasinski, Yasuhisa Oya DOI: https://doi.org/10.1016/j.fusengdes.2026.115841

Image: SUMPPU device and D plasma irradiation.