Evaluation of hydrogen retention behavior in tungsten exposed to hydrogen plasma in QUEST. (March 2021)

• Record Type: Journal Article
• Authors: Koike, Ayaka; Nakata, Moeko; Yamazaki, Shota; Wada, Takuro; Sun, Fei; Zhao, Mingzhong; Yoshida, Naoaki; Hanada, Kazuaki; Oya, Yasuhisa
• Is Part Of: Nuclear materials and energy. Volume 26(2021)
• Publication Date: 2021-03
• Subjects: Hydrogen isotope retention -- Tungsten -- Deposition layer -- Plasma exposure -- QUEST; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2020.100856
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: To evaluate hydrogen isotope retention, W was exposed by plasma of QUEST 2017A/W. Deuterium desorption was different from sample position of wall. H was mainly accumulated in the deposition layer and trapped as C–H bonds. Abstract: The W (tungsten) samples were placed at Top, Equator and Bottom plasma facing walls of QUEST (Q-shu University Experiment with Steady-State-Spherical Tokamak) device and exposed to 754 shots of hydrogen plasma during 2017A/W (Autumn/Winter) campaign. Thereafter, their surface morphologies and chemical states were evaluated by TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy). The XPS results showed that a thick carbon layer about 3–18 nm has formed throughout the wall surface. Among them, the Bottom wall had the deposition layer with the thickness of 2 nm, which was thinner than the top wall, namely erosion-dominated. On the other hand, a thick C layer about 18 nm was deposited on the Equator wall. The additional 1 keV D2 + was implanted into these samples and the D (deuterium) retention enhancement was estimated. The D2 TDS (Thermal Desorption Spectroscopy) spectra for all the samples had two major desorption stages at 400 K and 650 K, namely the desorption of D trapped by irradiation damages and deposition layer. The erosion/deposition profile would be caused by wall position and plasma condition, like a current start-up experiment. The desorption temperature of H2 (hydrogen) was shifted toward higher temperature side compared to that exposed to previous plasma campaign (2016 A/W), suggesting that H was mainly accumulated in the deposition layer with forming C–H bonds.