Fig. 2-7 Method of Nuclear Reaction Analysis (NRA) Charged particles are produced by nuclear reactions between a deuteron beam and target atoms. The energy and yield of these particles are measured using a detector to obtain an energy spectrum. Depth profiles of D, T, etc., are calculated with the energy spectrum. The measurable depth is limited due to the incident beam energy, the incident angle, the geometrical layout of the detector, etc. In the present condition, the measurable range is from the surface to a depth of 2 micrometer in the sample.

Fig. 2-8 D and T depth profiles in plasma facing components of JT-60U and TFTR evaluated from NRA energy spectra (a) D existed only near the surface in JT60U, whereas it was distributed well below the surface in TFTR. Negative values of depth arose from the finite depth resolution of the detector system. (b) T existed only around a depth of 2.0 micrometer in JT-60U, whereas the T used as fuel in TFTR was distributed well below the surface of the sample.

Deuterium (D) and tritium(T) used as fusion reactor fuel accumulate inside the vacuum vessel (plasma facing components) of fusion devices. The accumulation induces undesirable effects for plasma controls, T safety, etc. Thus, the amounts of these hydrogen (H) isotopes must be estimated to understand their behavior in plasma facing components (PFC). Depth profiles of H isotopes in PFCs of the experimental facilities "JT-60U and the TFTR (Princeton Plasma Physics Laboratory)" were measured by deuteron-induced nuclear reaction analysis, which allows absolute measurements of atomic densities in matter (Fig. 2-7) [1]. As is shown in Fig. 2-8 (a) and (b), both D and T depth profiles of the TFTR sample were different from that of the JT-60U sample. The H isotopes were distributed over a deeper region in the profiles of the TFTR sample because of the co-deposition of H isotopes with eroded carbon particles that resulted from TFTR operations of plasmas in contact with an inner bumper limiter made of carbon-based materials. In the D-D plasmas used in JT-60U, T is produced only by D(d,t)H reactions. Since such T penetrates more deeply in a PFC due to its kinematic energy, T was not distributed in the surface region [2]. Although the H isotope depth profile of some PFCs has been obtained in the present analysis, we expect additional important information will be obtained to reveal the H isotope behavior by continued systematic PFC analysis.

References [1] K. Ochiai et al., Measurement of Deuterium and Tritium Retentions on the Surface of JT-60 Divertor Tiles by Means of Nuclear Reaction Analysis, J. Nucl. Mater., 329-333, 836 (2004). [2] N. Kubota et al., Depth Profile Measurements of Hydrogen Isotopes near the Surface of the TFTR Plasma Facing Component Using Nuclear Reaction Analysis, Purazuma, Kaku Yugo Gakkai-shi, 81(4), 296 (2005) (in Japanese).

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