MoD-PMI 2019 June 18 th – 20 th at NIFS Presentation No. O-16 Development of functional material for deuterium permeation observation under divertor plasma exposures T. Takimoto a , N. Ashikawa b,c , D. Mori d , K. Katayama d , V. Rohde e , Y. Matsumura a , A. Tonegawa a , K.N. Sato f , and K. Kawamura a a Tokai University (Japan), b NIFS (Japan), c SOKENDAI (Japan), d Kyushu University (Japan), e IPP (Germany), f Tokyo University of Science (Japan) 1
Table of Contents ◆ Background & Motivation Observation of D permeation amount in PFCs ◆ New method to observe D permeation amount Concept of new method Design of W-Pd-Ti sample ◆ Plasma exposures in the linear plasma device Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface ◆ Summary & Future Plans 2
Table of Contents ◆ Background & Motivation Observation of D permeation amount in PFCs ◆ New method to observe D permeation amount Concept of new method Design of W-Pd-Ti sample ◆ Plasma exposures in the linear plasma device Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface ◆ Summary & Future Plans 3
Background ➢ In DEMO, control of tritium (T) amounts is critical issue because of its radioactivity and necessity of reuse. ➢ Although hydrogen isotopes diffuse into plasma-facing components (PFCs) under high heat flux and particle flux, its amounts have not been measured. ➢ Therefore, it is necessary to directly evaluate the retention and permeation amount of hydrogen isotopes in PFCs. High temperature region ➢ During plasma exposure, hydrogen retention desorption DD D permeation isotopes in plasma-facing materials D D DD D D (PFM) are desorbed or permeates. D plasma D D ➢ After plasma exposure, it can be D DD observed retention of hydrogen D D D DD isotopes in materials by TDS, and PFM PFM During plasma exposure After plasma exposure so on. 4
Background ⚫ Hydrogen isotope permeation has been investigated in laboratory-scale plasma devices and fusion devices by using quadrupole mass analyzer (QMA) installed behind a membrane. For example: I. Takagi et al ., J. Nucl. Mater. 415 (2011) S692-S695. H.S. Zhou, Plasma and Fusion Research, 8 (2013) 2402065. ⚫ However, QMA method is difficult to perform at PFCs under high heat flux and particle flux such as High temperature region retention desorption divertor regions due to limited spaces, strong DD D permeation magnetic fields, high heat loads, and so on. D D DD D D D ⚫ It is required to develop a new method to measure plasma D D D D amounts of permeation in PFCs. DD D D D DD PFM PFM During plasma exposure After plasma exposure 5
Motivation & Aim There is no precedent for direct evaluation of hydrogen permeation in PFCs under high flux plasma exposures in fusion devices. ⚫ A new method have been proposed that titanium (Ti) and palladium (Pd) are combined with tungsten (W) to store permeated deuterium (D). ⚫ It is planed that hydrogen isotopes amount of permeation in PFCs of current fusion devices such as ASDEX-U is measured by this method. ⚫ It is expected that characteristics of hydrogen isotopes obtained by the method will contribute to T handling in DEMO. In this work, W-Pd-Ti combined samples has been developed and improved in order to use in tokamaks. 6
Table of Contents ◆ Background & Motivation Observation of D permeation amount in PFCs ◆ New method to observe D permeation amount Concept of new method Design of W-Pd-Ti sample ◆ Plasma exposures in the linear plasma device Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface ◆ Summary & Future Plans 7
Concept of new method It has been considered that Ti and Pd are combined with W to store the permeated D. ⚫ In order to store permeated D, we used Ti which is a hydrogen storage metal. Pd ⚫ Ti is installed behind W. desorption DD D permeation D ⚫ Pd enhances the D transport from W to Ti. D D D D D ⚫ Pd is used at contact surfaces of W and Ti as a plasma D D D catalyst. D D D DD W D Ti During plasma exposure 8
Concept of new method It has been considered that Ti and Pd are combined with W to store the permeated D. ➢ When molecules diffuse into ⚫ In order to store permeated D, we used Ti which is materials, they must be dissociated a hydrogen storage metal. Pd at the surface. ⚫ Ti is installed behind W. ⚫ Dissociative energies of hydrogen desorption ➢ A dissociation needs high energy. DD D permeation molecules for the diffusion into D ⚫ Pd enhances the D transport from W to Ti. D D D materials are lower than most of D D ⚫ Pd is used at contact surfaces of W and Ti as a plasma D metals. D D catalyst. For example: E. B. Maxted et al., J. Chem. Soc. 1959, 3130. D D H. Nakatsuji et al., J. Am. Chem. Soc. 1985, 107, 26. D DD W D Ti ⚫ Due to Pd layer, it is expected that During plasma exposure D permeates to base materials as atoms without recombination. ⚫ Pd is one material of the hydrogen- permselective membranes. 9
Concept of new method It has been considered that Ti and Pd are combined with W to store the permeated D. ⚫ In order to store permeated D, we used Ti which is a hydrogen storage metal. Pd ⚫ Ti is installed behind W. desorption DD D permeation D ⚫ Pd enhances the D transport from W to Ti. D D D D D ⚫ Pd is used at contact surfaces of W and Ti as a plasma D D D catalyst. D D D DD W D Ti ⚫ W is a candidate of PFMs. During plasma exposure 10
Concept of new method It has been considered that Ti and Pd are combined with W to store the permeated D. ⚫ From these reasons, the combination of the Pd materials was selected. desorption ⚫ In the previous study, D amounts of permeation DD D permeation D D D D had been observed as D retention in Ti. [1] D D ⚫ In these samples [1], Ti and W were separating, plasma D D D and the contact between W and Ti via Pd was as D D D DD only touching. W D Ti During plasma exposure [1] T. Hayashi, T. Takimoto, et.al ., FED, 136 (2018) 545. However, in order to experiments in tokamaks, it is necessary to modify the samples from separating structure. In this work, integrated-type samples have been newly developed. 11
Design of integrated samples Coated Pd Ti plate (15 mm x 15 mm) has been applied mirror polish. (~400nm) Magnetron sputtering Pd has been coated (~400 nm) on Ti plate Magnetron sputtering W has been coated (~1 μm ) on Pd layer Coated W Ti Plate ➢ Comparing D permeation time (~1μm) (0.5mm) Provided by K. Schmid at ASDEX-U in private communications through W and a pulse length of Time [h] discharges of ASDEX-U (<0.01h), W thickness must be less than 100 μm at least. 1 ➢ In order to produce such thin W 0.5 layer, coated W was selected. 0.1 Thickness [ μm ] 12 200 100
Design of integrated samples Coated Pd Before exposure (~400nm) Blisters 10μm Surface morphology by Scanning Electron Microscope (SEM). ➢ Surface observations were performed on produced W-Pd-Ti samples ⚫ Blisters (several μm ) were observed on the surface. Coated W Ti Plate (~1μm) (0.5mm) 13
Design of integrated samples Coated Pd Before exposure (~400nm) Pore W Pd Ti 2μm Before exposure 10μm Cross-sectional images after Focused Ion Beam (FIB). ➢ Surface observations were performed on produced W-Pd-Ti samples ⚫ Blisters (several μm ) were observed on the surface. Coated W Ti Plate (~1μm) (0.5mm) ➢ Cross-sectional observations were performed on same samples. ⚫ Pores (width of several μm ) were observed around the boundary between Pd and Ti. ⚫ It is not satisfied a good contact between Pd and Ti required to smoothly permeation due to Pd. It is necessary to enhance the contact between Pd and Ti. 14
Preparation of samples Coated Pd Ti plates (15 mm x 15 mm) have been applied mirror polish (~400nm) Magnetron sputtering Pd has been coated (~400 nm) on Ti plates Infrared heating Heat treatment to Pd-Ti samples has been performed Magnetron sputtering Coated W Ti Plate (~1μm) (0.5mm) W has been coated (~1 μm ) on Pd layer Pd-Ti mixture layer Heat treatments have been performed to enhance the diffusion contact between these layers by promoting the diffusion Pd diffusion of metal particles into each other layer. Ti Ti Pd 15
Preparation of samples Coated Pd w/ heat treatment @ 900 ℃ , 1h w/o heat treatment (~400nm) 10μm 10μm W W Pd Pd? Coated W Ti Plate Ti Ti (~1μm) (0.5mm) 2μm 2μm 1000 1000 Cross-sectional images after FIB. 800 800 ➢ Surface and cross-sectional observations were performed on Temperature[℃] 600 600 also W-Pd-Ti sample with a heat treatment. 400 400 ⚫ After heat treatment, blisters were not observed on the 200 200 surface. 0 ⚫ Also, pores were not observed between W and Ti after heat 0 1 2 3 4 5 Time [ [h] 16 treatment. Heating characteristic
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