A." Sagara

M. Takagi

M. Tokitani

M. Yamagiwa

N. "Ohno

N. Matsunami

S. Kajita

S. Masuzaki

T. Kaneko

Y. Nakamura

National Institute for Fusion Science (NIFS-Repository)

In-situ measurement of hydrogen retention inplasma-facing materials under plasma exposure, so calleddynamic retention has been one of the most importanttopics in plasma-wall interaction because the dynamic re-tention has a strong eﬀect on a particle balance in fusiondevices, associated with fueling. However, because of thediﬃculty of the in-situ measurement of hydrogen reten-tion under plasma exposure, only static hydrogen reten-tion was measured after plasma exposure termination.In this study, we have investigated deuterium retentionin graphite under and after plasma exposure by using adevice of PS-DIBA (Plasma Surface Dynamics with IonBeam Analysis) as shown in Fig. 1, which makes it pos-sible to carry out in-situ ion beam analysis of deuteriumretention1).Fig. 1: Schematic top view of PS-DIBA device.The steady state deuterium plasma was producedwith a DC arc discharge using a zigzag-shaped LaB6cathode. Electron density ne was above 1 × 1018m−3.The incident ion energy can be controlled by electricallybiasing the sample. D(3He, p)α nuclear reaction analy-sis (NRA) was used to measure retained deuterium. Aprimary energy of a mass-separated 3He ion beam gen-erated by a Van de Graaﬀ accelerator was 1.0 MeV.Deuterium retention in isotropic graphite (ETU-10) sample was investigated by using PS-DIBA device2).Figure 2 shows the time evolution of deuterium retentionmeasured with NRA. The sample temperature was con-trolled from 350 K to 550 K with a step of 50K by usingair cooling and electron heating. The sample was irra-diated to deuterium plasma at three diﬀerent ﬂuxes upto 1.0× 1018cm−2s−1 with the incident ion energy of 33eV. Dynamic deuterium retention were clearly observed.The dynamic retention decreased with the sample tem-perature and increased with the plasma ﬂux. However,fraction of the dynamic retention normalized by totalretention on each sample temperature was almost con-stant.Figure 3 shows dependence of the dynamic deu-terium retention on deuterium ion ﬂux. It shows thatthe dynamic retention was proportional to the ion ﬂuxand the release time τ was estimated. Therefore, wefound the sample temperature dependence of the releasetime τ (84 ms at 350 K, 59 ms at 400 K and 48 ms at 450K, respectively) and it is needed to control fuel particleswith a time scale of τ to maintain stable plasma in futurefusion devices.Fig. 2: Time evolution of deuterium retention inisotropic graphite measured by NRA under plasma ex-posure.Fig. 3: Dependence of dynamic retention Nd on deu-terium ion ﬂux ΓD .1) M. Yamagiwa, Y. Nakamura, N. Matsunami, N.Ohno, et.al., Physica Scripta T145 (2011) 010432.2) Y. Nakamura, M. Yamagiwa, T. Kaneko, et.al., to bepublished in J. Nucl. Mater.152§1. In-situ Measurement of Hydrogen Isotope Retention under Plasma Exposure by Using Ion Beam AnalysisOhno, N., Yamagiwa, M., Nakamura, Y., Kaneko, T., Matsunami, N., Takagi, M., Kajita, S. (Nagoya Univ.), Masuzaki, S., Tokitani, M., Sagara, A.

In-situ Measurement of Hydrogen Isotope Retention under Plasma Exposure by Using Ion Beam Analysis

In-situ Measurement of Hydrogen Isotope Retention under Plasma Exposure by Using Ion Beam Analysis

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