Hydrogen content in divertor baffle tiles in Wendelstein 7-X. (March 2021)

• Record Type: Journal Article
• Authors: Oelmann, Jannis; Wüst, Erik; Brezinsek, Sebastijan; Li, Cong; Zhao, Dongye; Rasinski, Marcin; Dhard, Chandra Prakash; Mayer, Matej; Naujoks, Dirk; Gao, Yu
• Is Part Of: Nuclear materials and energy. Volume 26(2021)
• Publication Date: 2021-03
• Subjects: Plasma-facing components -- Hydrogen retention -- Deposition pattern -- Laser Induced Breakdown Spectroscopy (LIBS) -- Wendelstein 7-X -- Divertor component; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2021.100943
• Languages: English
• ISSNs: 2352-1791

Abstract

Abstract: Plasma–wall interactions play a crucial role for the performance of fusion devices and the lifetime of plasma-facing components. In this work the results of some plasma–wall interaction processes, namely the erosion/deposition pattern and the fuel content of divertor baffle tiles exposed in Wendelstein 7-X in the initial phase of island divertor, are presented. Net-deposition of carbon with co-deposited oxygen and hydrogen is determined on the graphite tiles after about 1 hour of plasma operation in hydrogen and helium in operation phase OP 1.2a. C is predominately a result of net-erosion of the graphite target plates and oxygen is the strongest intrinsic impurity in Wendelstein 7-X in OP 1.2a. The hydrogen content distribution on a set of tiles exposed in equivalent positions in three of the five modules of the stellarator was quantified for the first time. Ex-situ performed laser-induced breakdown spectroscopy measurements show the depth-resolved fuel content in deposited layers as well as implantation and diffusion in the base material. Complementary, gas analysis after laser-induced ablation offers quantitative hydrogen content determination in the deposited layers up to 10 18 hydrogen atoms/cm 2 that is non-uniformly distributed over the 95 mm × 125 mm sized tiles. The results show a toroidal asymmetry with 60% more hydrogen in the stellarator module 2 with respect to module 1 as well as a slight top-down asymmetry for the baffle tiles in upper and lower half modules. A clear dependence of the hydrogen content on the surface temperature during plasma exposition in stellarator discharges in standard magnetic divertor configuration with edge transformation 5/5 was not observed. Graphical abstract: Highlights: Analyses of divertor baffle tiles exposed in Wendelstein 7-X OP1.2a are presented. The H content distribution for equivalent positions in 4 of 5 modules was quantified. The depth-resolved fuel contents show erosion/deposition pattern and fuel retention. Non-uniformly distributed deposition layers with up to 10 18 H atoms/cm 2 are analyzed. 60% more hydrogen in W7-X module 2 with respect to module 1 baffle tiles is observed.