B. "Pegourie

E. Bernard

R." Sakamoto

National Institute for Fusion Science (NIFS-Repository)

Understanding the dynamics of in-depth migrationand retention of hydrogen isotopes in Carbon FiberComposites (CFCs) used as plasma facing material hasfor long time been complicated by the lack on in situ ana-lyzing tools. A dedicated experimental setup coupling anECR ion source to the Saclay nuclear microprobe (CEA,France) was developed to expose CFC NB31 samples todeuterium implantation at 200 − 300 eV and ﬂuencesfrom 1022 to 1024 D/m2, and then to perform in situµ−NRA analysis for 3D deuterium proﬁles.Main result was that when deuterium concentrationat the surface is homogeneous and ﬂuence-independent,the in-bulk deuterium is concentrated in the porositiesand increases in quantity with the incident ﬂuence, up tovery large depth (500 µm). Moreover, these two distinctmechanisms are simultaneous to the implantation andD proﬁles evolve very little with in-vacuum storage time[1].These measurements were complemented by TDSand micro-porosimetry experiments, for characterizingthe energy distribution of the deuterium traps and thesize distributions and eﬀective surface of the porous net-work. It was shown that the energy distribution oftraps is diﬀerent in the near surface and porous net-work, the former been characterized by a much largerratio of bounds associated to sp3 carbons with respectto those associated to sp2 carbons, and that matrix (1 >diameter (µm) > 0.1) and interfacial ﬁber/matrix poresFig. 1 Simulated deuterium con-centration proﬁle of CFC NB31 ir-radiated by 200 eV D+ ions as afunction of incident ﬂuence. Sam-ples are at a temperature of 50 ◦C.Fig. 2 Simulated deuterium con-centration proﬁle of CFC NB31 ir-radiated by 200 eV D+ ions asa function of sample temperature(middle), for a ﬂuence of 2 × 1024D/m2.Fig. 3 Retained ﬂuence as a func-tion of the incident ﬂuence: thedashed black line corresponds to100 % retention, the dashed pinkcurve to a massive sample, the fulllines to porous CFC NB31 (the pinkcurve is the near surface retention;the blue curve is the total retention,including the porous network).(0.1 > diameter (µm) > 0.01) dominate the porous net-work, both with an eﬀective surface of ∼ 0.1 m2/g.This ensemble of results suggests a picture wherethe deuterium concentration saturates in the near sur-face - partly amorphized due to ion bombardment, whenthe retention in the porous network increases on a longertimescale, the deuterium atoms penetrating along thepores up to a depth ≥ 100 µm.For interpreting the measurements, a model wasbuilt according to the picture described above. It isbased on a Monte Carlo method and calculates the prop-agation of D atoms in a network of pores assumed to berectilinear. At each impact, the reﬂection/absorptioncoeﬃcient and direction/energy of the reﬂected particle(atom or molecule) are estimated through TRIM simula-tions [2]. Input parameters are the diameter, volume, ef-fective surface and average inclination of the pores withrespect to the sample macroscopic surface. The threeformer are deduced of porosimetry measurements, thelatter is partly constrained by SEM images.Preliminary results are displayed in Fig. 1 − 3,showing the variation of the deuterium concentrationproﬁle with incident ﬂuence (Fig. 1), implantation tem-perature (Fig. 2) and the increase of the retained ﬂuenceas a function of the incident ﬂuence (Fig. 3). Corre-sponding measurements are displayed in Figs. 1 and 2of Ref. [3]. It is found that the simulations reproducesatisfactorily the main trends of the measurements, butthat the porous network contribution to deuterium re-tention is underestimated. This has been identiﬁed to bedue to the fact that D-rich deposits form in the pores,increasing their retention capability. Work for includingthis eﬀect in the code is ongoing.[1] E. Bernard et al., J. Nucl. Mat. 438 (2013) S975[2] J. F. Ziegler, Nucl. Instr. Meth. B. 219-220 (2004) 1027[3] J. Roth et al., J. Nucl. Mat. 363-365 (2007) 822212§3. Modeling of Deuterium Retention in Carbon Fiber Composite NB31Pégourié, B. (IRFM/CEA Cadarache, NIFS),  Bernard, E. (NIFS, CEA Saclay),  Sakamoto, R.

Modeling of Deuterium Retention in Carbon Fiber Composite NB31

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