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Hydrogen retention and erosion of carbon–tungsten mixed material
Fusion Engineering and Design 49 – 50 (2000) 213 – 216 www.elsevier.com/locate/fusengdes
Hydrogen retention and erosion of carbon–tungsten mixed material T. Hino *, F. Hirano, Y. Yamauchi, Y. Hirohata Department of Nuclear Engineering, Hokkaido Uni6ersity, Kita-13, Nishi-8, Kita-ku, Sapporo 060 -8628, Japan
Abstract Upon machine operation, the wall surface in the divertor region of ITER results to be covered by a mixture of carbon and tungsten, due to erosion and re-deposition of CFC and tungsten wall materials. Thus, it is necessary to evaluate the fuel hydrogen retention and the erosion of such mixed materials. In the present study, the deuterium desorption spectra were examined upon deuterium ion irradiation for the materials with tungsten concentrations of 6, 13 and 32 at.%. Two desorption peaks appeared at approximately 150 and 700°C. The peaks at 150 and 700°C correspond to the desorptions from tungsten and carbon, respectively. The peak height at 150°C increased and that at 700°C decreased as the tungsten concentration increased. The total amount of deuterium retained was reduced by the addition of tungsten, as compared with a case of graphite. The desorption of CD4 largely decreased with the tungsten concentration increase. The present data show that both the hydrogen retention and the chemical erosion of carbon–tungsten mixed material were reduced, as compared to graphite. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Divertor; Graphite; Tungsten; Carbon–tungsten mixed material; Deuterium retention; Chemical erosion
1. Introduction In the divertor region of an experimental reactor, several plasma facing materials such as CFC and tungsten (W) will be used. The properties of these materials such as hydrogen retention and erosion have been investigated so far [1 – 9]. As the discharge shot number increases after the machine operation, these materials will be mixed at the
* Corresponding author. Tel. + 81-11-7067195; fax: +8111-7096413. E-mail address: [email protected] (T. Hino).
divertor wall surface by numerous erosion and re-deposition processes due to the high particle and heat fluxes [10]. Thus, the material at the divertor wall surface becomes a mixture of carbon and tungsten, when CFC and tungsten are employed as the divertor materials. The hydrogen retention and erosion of the carbon–tungsten mixed material have not been systematically investigated so far. On the tungsten or carbon wall, carbon and tungsten are deposited in forms of atom, cluster and micro particle. This surface is annealed during discharge shots. The surface temperature rise exceeds 2000°C in the case of disruptions. Then, it is of interest to
0920-3796/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 0 ) 0 0 3 4 7 - 1
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Fig. 1. ECR ion irradiation apparatus.
evaluate the fuel hydrogen retention and the erosion of such the mixed material. The mixing material was fabricated from carbon and tungsten powders by means of hot pressing in Toyo Tanso. The hot pressing temperature was approximately 2000°C. Three samples with tungsten concentrations of 6, 13 and 32 at.% were prepared. In the XRD analysis, peaks of tungsten carbide and graphite were observed. The material consists of tungsten carbide and graphite. The peak profile remained the same even after the annealing at 1000°C. For these materials, deuterium ion irradiation was conducted in an ECR ion source, and followed by that the retained amount of deuterium was measured by a thermal desorption spectroscopy (TDS). The chemical erosion was also measured based upon the TDS data. The obtained data were compared with cases of isotropic graphite and polycrystalline tungsten.
and the fluence were 5 keV and 3× 1018 D cm − 2, respectively. The deuterium ion flux was 5×1014 D cm − 2 s − 1. The vacuum pressure before the irradiation was 10 − 5 Pa, and the pressure during the irradiation was 10 − 3 Pa. The major residual gas species was D2. After the implantation, the sample was heated without breaking the vacuum from RT to 1000°C with a ramp rate of 50°C min − 1. Then, the thermal desorption spectrum for the retained deuterium was obtained. For the comparison, a similar experiment was conducted for isotropic graphite (PD-330S) [2] and polycrystalline tungsten (Nilaco) [1].
2. Experiment Carbon–tungsten mixed material sample with a size of 50× 5 ×0.1 mm was irradiated at RT by deuterium ions in the ECR ion irradiation apparatus [5,11] as shown in Fig. 1. The implanting deuterium ion species was D+ 3 , and the energy
Fig. 2. Desorption spectra of D2 after deuterium ion irradiation.
T. Hino et al. / Fusion Engineering and Design 49–50 (2000) 213–216
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3. Results
Fig. 3. Desorption spectra of HD after deuterium ion irradiation.
Fig. 4. Desorption spectra of CD4 after deuterium ion irradiation.
Fig. 5. Deuterium retention amount versus tungsten concentration.
Before the deuterium ion irradiation, the sample was annealed at 1000°C for 60 min. After this outgassing, the sample was exposed to deuterium ion with the fluence of 3 × 1018 D cm − 2. After that, the sample was resistively heated from RT to 1000°C. During this heating, D2, HD and CD4 were observed as major outgassing species. Fig. 2 shows the thermal desorption spectra of D2 for three samples. Here, samples A, B and C correspond the carbon–tungsten mixed materials with tungsten concentration of 6, 13 and 32 at.%, respectively. Major peaks are observed at 150 and 700°C. Fig. 3 shows the thermal desorption spectra of HD for the samples, A, B and C. The peak positions were similar to those of D2. In the case of polycrystalline tungsten irradiated by He ions, major desorption peak was observed at around 200°C [5]. As the increase of tungsten concentration, this peak height increased. Then, it is regarded that the deuterium desorption in the low temperature regime is due to the detrapping of deuterium from tungsten. In the case of graphite, the desorption peak appeared at around 800°C [11,12]. Then, the desorption in the high temperature regime is due to the detrapping of deuterium from carbon. Fig. 4 shows the thermal desorption spectra of CD4 for the samples, A, B and C. The peak temperature of CD4 desorption for three samples was about 600°C, which was the same as that of the graphite. The desorption amounts for samples A, B and C were 1.54 × 1016, 1.27× 1016, 6.71 × 1015 CD4 cm − 2, respectively. The desorption amount of CD4 for sample A was comparable with that of the graphite. For samples, B and C with higher tungsten concentration, the desorption amounts of CD4 were considerably small. Then, the mixing of tungsten into carbon reduces the chemical erosion. Total deuterium retention was obtained from the desorption spectra of D2, HD and CD4. Fig. 5 shows the deuterium retention as a function of tungsten concentration. As the references, the data of the graphite and the polycrystalline tung-
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sten are also plotted. As the increase of tungsten concentration, the deuterium retention slightly decreased, but the decreasing amount was not large, compared with the case of the tungsten. This reason is the increase of deuterium trapped by tungsten, which is desorbed at 150°C.
Acknowledgements The authors deeply appreciate Drs T. Sogabe and K. Kuroda, Toyo Tanso, for fabrications of carbon–tungsten mixed materials.
References 4. Summary For carbon – tungsten mixed materials, the deuterium retention and the chemical erosion were examined, and these were compared with those of isotropic graphite and polycrystalline tungsten. The deuterium retention was reduced by the mixing of tungsten into carbon. However, the decreasing amount was not large compared with the case of tungsten, since the deuterium is well trapped in the tungsten content. The chemical erosion was largely reduced by the mixing of tungsten into carbon. In the tokamak divertor, the material mixing takes place due to erosion and re-deposition. During disruptions, this mixed material is annealed at the temperature higher than 2000°C. Thus, the present data on the carbon –tungsten material produced at 2000°C may simulate the tokamak conditions. In the tokamak divertor with carbon – tungsten mixing, it is expected that both the hydrogen retention and the chemical erosion are reduced, compared with the case of carbon divertor plate.
[1] T. Hino, Y. Takasugi, T. Yamashina, Tanso 150 (1991) 266 – 270 In Japanese. [2] K. Nakamura, A. Nagase, M. Dairaku, M. Akiba, M. Araki, Y. Okumura, J. Nucl. Mater. 220-222 (1995) 890– 894. [3] A.P. Zakharov, A.E. Gorodetsky, V.Kh. Alimov, S.L Kanashenko, A.V. Markin, J. Nucl. Mater. 241-243 (1997) 52 – 67. [4] K. Tokunaga, M. Takayama, T. Muroga, N. Yoshida, J. Nucl. Mater. 220-222 (1995) 800 – 804. [5] T. Hino, K. Koyama, Y. Yamauchi, Y. Hirohata, Fusion Eng. Des. 39-40 (1998) 227 – 233. [6] Y. Hirooka, M. Bourham, J.N. Brooks, R.A. Causey, G. Chevalier, R.W. Conn, W.H. Eddy, J. Gilligan, M. Khandagle, Y. Ra, J. Nucl. Mater. 196-198 (1992) 149 – 158. [7] T. Tanabe, N. Noda, H. Nakamura, J. Nucl. Mater. 196-198 (1992) 11 – 27. [8] D.G. Whyte, J.N. Brooks, C.P.C. Wong, W.P. West, R. Bastasz, W.R. Wampler, J. Rubenstein, J. Nucl. Mater. 241-243 (1997) 660 – 665. [9] A.A. Haasz, M. Poon, J.W. Davis, J. Nucl. Mater. 266-269 (1999) 520 – 525. [10] A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889 – 895. [11] Y. Yamauchi, Y. Hirohata, T. Hino, Fusion Eng. Des. 39-40 (1998) 427 – 432. [12] Y. Gotoh, T. Yamaki, T. Ando, R. Jimbou, N. Ogiwara, M. Saidoh, K. Teruyama, J. Nucl. Mater. 196-198 (1992) 708 – 712.
Hydrogen retention and erosion of carbon–tungsten mixed material T. Hino *, F. Hirano, Y. Yamauchi, Y. Hirohata Department of Nuclear Engineering, Hokkaido Uni6ersity, Kita-13, Nishi-8, Kita-ku, Sapporo 060 -8628, Japan
Abstract Upon machine operation, the wall surface in the divertor region of ITER results to be covered by a mixture of carbon and tungsten, due to erosion and re-deposition of CFC and tungsten wall materials. Thus, it is necessary to evaluate the fuel hydrogen retention and the erosion of such mixed materials. In the present study, the deuterium desorption spectra were examined upon deuterium ion irradiation for the materials with tungsten concentrations of 6, 13 and 32 at.%. Two desorption peaks appeared at approximately 150 and 700°C. The peaks at 150 and 700°C correspond to the desorptions from tungsten and carbon, respectively. The peak height at 150°C increased and that at 700°C decreased as the tungsten concentration increased. The total amount of deuterium retained was reduced by the addition of tungsten, as compared with a case of graphite. The desorption of CD4 largely decreased with the tungsten concentration increase. The present data show that both the hydrogen retention and the chemical erosion of carbon–tungsten mixed material were reduced, as compared to graphite. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Divertor; Graphite; Tungsten; Carbon–tungsten mixed material; Deuterium retention; Chemical erosion
1. Introduction In the divertor region of an experimental reactor, several plasma facing materials such as CFC and tungsten (W) will be used. The properties of these materials such as hydrogen retention and erosion have been investigated so far [1 – 9]. As the discharge shot number increases after the machine operation, these materials will be mixed at the
* Corresponding author. Tel. + 81-11-7067195; fax: +8111-7096413. E-mail address: [email protected] (T. Hino).
divertor wall surface by numerous erosion and re-deposition processes due to the high particle and heat fluxes [10]. Thus, the material at the divertor wall surface becomes a mixture of carbon and tungsten, when CFC and tungsten are employed as the divertor materials. The hydrogen retention and erosion of the carbon–tungsten mixed material have not been systematically investigated so far. On the tungsten or carbon wall, carbon and tungsten are deposited in forms of atom, cluster and micro particle. This surface is annealed during discharge shots. The surface temperature rise exceeds 2000°C in the case of disruptions. Then, it is of interest to
0920-3796/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 0 ) 0 0 3 4 7 - 1
214
T. Hino et al. / Fusion Engineering and Design 49–50 (2000) 213–216
Fig. 1. ECR ion irradiation apparatus.
evaluate the fuel hydrogen retention and the erosion of such the mixed material. The mixing material was fabricated from carbon and tungsten powders by means of hot pressing in Toyo Tanso. The hot pressing temperature was approximately 2000°C. Three samples with tungsten concentrations of 6, 13 and 32 at.% were prepared. In the XRD analysis, peaks of tungsten carbide and graphite were observed. The material consists of tungsten carbide and graphite. The peak profile remained the same even after the annealing at 1000°C. For these materials, deuterium ion irradiation was conducted in an ECR ion source, and followed by that the retained amount of deuterium was measured by a thermal desorption spectroscopy (TDS). The chemical erosion was also measured based upon the TDS data. The obtained data were compared with cases of isotropic graphite and polycrystalline tungsten.
and the fluence were 5 keV and 3× 1018 D cm − 2, respectively. The deuterium ion flux was 5×1014 D cm − 2 s − 1. The vacuum pressure before the irradiation was 10 − 5 Pa, and the pressure during the irradiation was 10 − 3 Pa. The major residual gas species was D2. After the implantation, the sample was heated without breaking the vacuum from RT to 1000°C with a ramp rate of 50°C min − 1. Then, the thermal desorption spectrum for the retained deuterium was obtained. For the comparison, a similar experiment was conducted for isotropic graphite (PD-330S) [2] and polycrystalline tungsten (Nilaco) [1].
2. Experiment Carbon–tungsten mixed material sample with a size of 50× 5 ×0.1 mm was irradiated at RT by deuterium ions in the ECR ion irradiation apparatus [5,11] as shown in Fig. 1. The implanting deuterium ion species was D+ 3 , and the energy
Fig. 2. Desorption spectra of D2 after deuterium ion irradiation.
T. Hino et al. / Fusion Engineering and Design 49–50 (2000) 213–216
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3. Results
Fig. 3. Desorption spectra of HD after deuterium ion irradiation.
Fig. 4. Desorption spectra of CD4 after deuterium ion irradiation.
Fig. 5. Deuterium retention amount versus tungsten concentration.
Before the deuterium ion irradiation, the sample was annealed at 1000°C for 60 min. After this outgassing, the sample was exposed to deuterium ion with the fluence of 3 × 1018 D cm − 2. After that, the sample was resistively heated from RT to 1000°C. During this heating, D2, HD and CD4 were observed as major outgassing species. Fig. 2 shows the thermal desorption spectra of D2 for three samples. Here, samples A, B and C correspond the carbon–tungsten mixed materials with tungsten concentration of 6, 13 and 32 at.%, respectively. Major peaks are observed at 150 and 700°C. Fig. 3 shows the thermal desorption spectra of HD for the samples, A, B and C. The peak positions were similar to those of D2. In the case of polycrystalline tungsten irradiated by He ions, major desorption peak was observed at around 200°C [5]. As the increase of tungsten concentration, this peak height increased. Then, it is regarded that the deuterium desorption in the low temperature regime is due to the detrapping of deuterium from tungsten. In the case of graphite, the desorption peak appeared at around 800°C [11,12]. Then, the desorption in the high temperature regime is due to the detrapping of deuterium from carbon. Fig. 4 shows the thermal desorption spectra of CD4 for the samples, A, B and C. The peak temperature of CD4 desorption for three samples was about 600°C, which was the same as that of the graphite. The desorption amounts for samples A, B and C were 1.54 × 1016, 1.27× 1016, 6.71 × 1015 CD4 cm − 2, respectively. The desorption amount of CD4 for sample A was comparable with that of the graphite. For samples, B and C with higher tungsten concentration, the desorption amounts of CD4 were considerably small. Then, the mixing of tungsten into carbon reduces the chemical erosion. Total deuterium retention was obtained from the desorption spectra of D2, HD and CD4. Fig. 5 shows the deuterium retention as a function of tungsten concentration. As the references, the data of the graphite and the polycrystalline tung-
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T. Hino et al. / Fusion Engineering and Design 49–50 (2000) 213–216
sten are also plotted. As the increase of tungsten concentration, the deuterium retention slightly decreased, but the decreasing amount was not large, compared with the case of the tungsten. This reason is the increase of deuterium trapped by tungsten, which is desorbed at 150°C.
Acknowledgements The authors deeply appreciate Drs T. Sogabe and K. Kuroda, Toyo Tanso, for fabrications of carbon–tungsten mixed materials.
References 4. Summary For carbon – tungsten mixed materials, the deuterium retention and the chemical erosion were examined, and these were compared with those of isotropic graphite and polycrystalline tungsten. The deuterium retention was reduced by the mixing of tungsten into carbon. However, the decreasing amount was not large compared with the case of tungsten, since the deuterium is well trapped in the tungsten content. The chemical erosion was largely reduced by the mixing of tungsten into carbon. In the tokamak divertor, the material mixing takes place due to erosion and re-deposition. During disruptions, this mixed material is annealed at the temperature higher than 2000°C. Thus, the present data on the carbon –tungsten material produced at 2000°C may simulate the tokamak conditions. In the tokamak divertor with carbon – tungsten mixing, it is expected that both the hydrogen retention and the chemical erosion are reduced, compared with the case of carbon divertor plate.
[1] T. Hino, Y. Takasugi, T. Yamashina, Tanso 150 (1991) 266 – 270 In Japanese. [2] K. Nakamura, A. Nagase, M. Dairaku, M. Akiba, M. Araki, Y. Okumura, J. Nucl. Mater. 220-222 (1995) 890– 894. [3] A.P. Zakharov, A.E. Gorodetsky, V.Kh. Alimov, S.L Kanashenko, A.V. Markin, J. Nucl. Mater. 241-243 (1997) 52 – 67. [4] K. Tokunaga, M. Takayama, T. Muroga, N. Yoshida, J. Nucl. Mater. 220-222 (1995) 800 – 804. [5] T. Hino, K. Koyama, Y. Yamauchi, Y. Hirohata, Fusion Eng. Des. 39-40 (1998) 227 – 233. [6] Y. Hirooka, M. Bourham, J.N. Brooks, R.A. Causey, G. Chevalier, R.W. Conn, W.H. Eddy, J. Gilligan, M. Khandagle, Y. Ra, J. Nucl. Mater. 196-198 (1992) 149 – 158. [7] T. Tanabe, N. Noda, H. Nakamura, J. Nucl. Mater. 196-198 (1992) 11 – 27. [8] D.G. Whyte, J.N. Brooks, C.P.C. Wong, W.P. West, R. Bastasz, W.R. Wampler, J. Rubenstein, J. Nucl. Mater. 241-243 (1997) 660 – 665. [9] A.A. Haasz, M. Poon, J.W. Davis, J. Nucl. Mater. 266-269 (1999) 520 – 525. [10] A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889 – 895. [11] Y. Yamauchi, Y. Hirohata, T. Hino, Fusion Eng. Des. 39-40 (1998) 427 – 432. [12] Y. Gotoh, T. Yamaki, T. Ando, R. Jimbou, N. Ogiwara, M. Saidoh, K. Teruyama, J. Nucl. Mater. 196-198 (1992) 708 – 712.