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Journal Articles

Suppression of vacancy formation and hydrogen isotope retention in irradiated tungsten by addition of chromium

Wang, J.*; Hatano, Yuji*; Toyama, Takeshi*; Suzudo, Tomoaki; Hinoki, Tatsuya*; Alimov, V. Kh.*; Schwarz-Selinger, T.*

Journal of Nuclear Materials, 559, p.153449_1 - 153449_7, 2022/02

 Times Cited Count:2 Percentile:71.05(Materials Science, Multidisciplinary)

To study the effect of the content of chromium (Cr) in the tungsten (W) matrix on the vacancy formation and retention of hydrogen isotopes, the samples of the W-0.3Cr alloy were irradiated with 6.4 MeV Fe ions in the temperature range of 523-1273 K. These displacement-damaged samples were exposed to D$$_{2}$$ gas at a temperature of 673 K. The addition of 0.3% Cr into the W matrix resulted in a significant decrease in the retention of deuterium compared to pure W after irradiation especially at high temperature. Positron lifetime for W-0.3Cr alloy irradiated at 1073 K was almost similar to that for non-irradiated one. These facts indicate the suppression of the formation of vacancy-type defects by 0.3% Cr addition.

Journal Articles

Behavior of tritium in the vacuum vessel of JT-60U

Kobayashi, Kazuhiro; Torikai, Yuji*; Saito, Makiko; Alimov, V. Kh.*; Miya, Naoyuki; Ikeda, Yoshitaka

Fusion Science and Technology, 67(2), p.428 - 431, 2015/03

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Disassembly of the JT-60U torus was started in 2010 after 18 years deuterium operations. In the disassembly of the JT-60U torus, tritium retention in the vacuum vessel of the JT-60U is one of the most important safety issues for the fusion reactor. It was very important to study the tritium behavior in Inconel 625 from viewpoint of the clearance procedure in the future plan. After the tritium release for about 1 year at 298 K, the residual tritium in the specimen was released by heating up to 1073 K, and then the residual tritium in the specimen was measured by chemical etching method. Most of the chemical form of the released tritium was HTO. The contaminated specimen by tritium was released continuously the diffusible tritium under the ambient condition. In the tritium release experiment, most of tritium in the specimen was released during 1 year.

Journal Articles

Tritium distribution on the tungsten surface exposed to deuterium plasma and then to tritium gas

Isobe, Kanetsugu; Alimov, V. Kh.*; Taguchi, Akira*; Saito, Makiko; Torikai, Yuji*; Hatano, Yuji*; Yamanishi, Toshihiko

Journal of Plasma and Fusion Research SERIES, Vol.10, p.81 - 84, 2013/02

The distribution of hydrogen trapping sites on W surface exposed with D plasma was examined by the techniques of imaging plate and autoradiography. Recrystallized W specimens were exposed with D plasma at around 495 and 550 K to the same fluence of 10$$^{26}$$ D/m$$^{2}$$. Then, tritium was introduced into specimen by the exposure to tritium gaseous at 473 K. After that, the tritium distribution on W surface was examined by the techniques of imaging plate and autoradiography. From the results of the imaging plate, tritium was found to be highly concentrated within the area exposed with D plasma and the concentration of tritium was slightly varied even in that area. In the autoradiograph of W surface, it was found that tritium concentrated on the grain boundary and blisters.

Journal Articles

Temperature dependence of surface topography and deuterium retention in tungsten exposed to low-energy, high-flux D plasma

Alimov, V.; Shu, Wataru*; Roth, J.*; Lindig, S.*; Balden, M.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Journal of Nuclear Materials, 417(1-3), p.572 - 575, 2011/10

 Times Cited Count:75 Percentile:98.58(Materials Science, Multidisciplinary)

Blistering and deuterium retention in re-crystallized tungsten exposed to a low energy (38 eV/D) and high deuterium ion flux (10$$^{22}$$ D/m$$^{2}$$s) D plasma at ion fluences of 10$$^{26}$$ and 10$$^{27}$$D/m$$^{2}$$ at temperatures in the range from 320 to 800 K have been examined with scanning electron microscopy, thermal desorption spectroscopy (TDS), and the nuclear reaction. During exposure to the D plasma blisters with various shapes and sizes depending on the exposure temperature are formed on the W surface. At the temperatures above 700 K the blisters disappear. The deuterium retention increases with the exposure temperature, reaching its maximum value of about 7$$times$$10$$^{21}$$ D/m$$^{2}$$ at 530 K and about 1$$times$$10$$^{22}$$ D m$$^{2}$$ at 480 K for ion fluences of 10$$^{26}$$ and 10$$^{27}$$ D/m$$^{2}$$, respectively. As the temperature grows further, the D retention decreases to about 10$$^{19}$$ D/m$$^{2}$$ at 800 K.

Journal Articles

Deuterium retention in porous vacuum plasma-sprayed tungsten coating exposed to low-energy, high-flux pure and helium-seeded D plasma

Alimov, V.; Tyburska, B.*; Ogorodnikova, O. V.*; Roth, J.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Journal of Nuclear Materials, 415(Suppl.1), p.S628 - S631, 2011/08

 Times Cited Count:15 Percentile:74.1(Materials Science, Multidisciplinary)

Deuterium retention in porous vacuum plasma spraying tungsten coating exposed at various temperatures to a low-energy, high flux (10$$^{22}$$ D/m$$^{2}$$s) pure D and helium-seeded D plasmas was examined by thermal desorption spectroscopy and the nuclear reaction. Under exposure to pure D plasma (76 eV D$$_{2}$$$$^{+}$$) at 340-560 K, the D concentration reaches 1$$sim$$2 at.% at depths of several micrometers, while at temperatures above 700 K the D concentration is below 10$$^{-2}$$ at.% and deuterium is retained over the whole thickness of the coating. Seeding of 76 eV He$$^{+}$$ into the D plasma reduces the D retention at temperatures of 400-600 K. However, at temperature above 700 K, the D retention becomes comparable to that for pure D plasma exposure.

Journal Articles

Tritium concentration in tungsten surface exposed to low-energy, high-flux D plasma

Isobe, Kanetsugu; Alimov, V. Kh.*; Yamanishi, Toshihiko; Torikai, Yuji*

Toyama Daigaku Suiso Doitai Kagaku Kenkyu Senta Kenkyu Hokoku, 31, p.49 - 57, 2011/00

The limits on tritium inventory in the vacuum vessel and the need for prevention of impurity ingress into plasma, make plasma-surface interaction on tungsten an important issue. It is well known that plasma exposure on tungsten makes some kinds of blisters on the surface and increases the hydrogen inventory. On the other hands, there is a possibility that plasma exposure would change the characteristic of surface and surface region in tungsten and cause the increase of tritium inventory. Tritium concentration in tungsten exposure by low-energy, high-flux D plasma with was examined with BIXS after thermal exposure of tritium gas. The tritium concentration was measured with BIXS. The tritium concentration in surface and surface region was found to be increased by plasma exposure. And its concentration of tungsten exposed at 495 K was estimated to be twice higher than that of as-received tungsten.

Journal Articles

Deuterium trapping in tungsten deposition layers formed by deuterium plasma sputtering

Alimov, V.; Roth, J.*; Shu, Wataru*; Komarov, D. A.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Journal of Nuclear Materials, 399(2-3), p.225 - 230, 2010/04

 Times Cited Count:30 Percentile:89.22(Materials Science, Multidisciplinary)

A study of the influence of the deposition conditions on the surface morphology and deuterium concentration in tungsten deposition layers formed by magnetron sputtering and in the linear plasma generator has been carried out. Adhesion of the W layer to substrate is shown to depend on the coefficients of thermal expansion for tungsten and substrate material, thickness of the W layer, and the substrate temperature during layer deposition. A decreased D concentration for increased substrate temperatures and deposition rate are observed.

Journal Articles

Surface morphology and deuterium retention in tungsten exposed to low-energy, high flux pure and helium-seeded deuterium plasmas

Alimov, V.; Shu, Wataru*; Roth, J.*; Sugiyama, Kazuyoshi*; Lindig, S.*; Balden, M.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Physica Scripta, T138, p.014048_1 - 014048_5, 2009/12

 Times Cited Count:121 Percentile:95.31(Physics, Multidisciplinary)

Blistering and deuterium retention in re-crystallized tungsten exposed to low-energy, high flux (10$$^{22}$$ D/m$$^{2}$$s) pure and helium-seeded D plasmas to a fluence of 10$$^{27}$$ D/m$$^{2}$$ have been examined with scanning electron microscopy, thermal desorption spectroscopy (TDS), and the D($$^{3}$$He,p)$$^{4}$$He nuclear reaction at a $$^{3}$$He energy varied from 0.69 to 4.0 MeV. In the case of exposure to pure D plasma (38 eV/D), blisters with various shapes and sizes depending on the exposure temperature are found on the W surface. No blisters appear at temperatures above 700 K. The deuterium retention increases with the exposure temperature, reaching a maximum value of about 10$$^{22}$$ D/m$$^{2}$$ at 480 K, and then decreases as the temperature rises further. Seeding of helium into the D plasma to the He ion concentration of 0.2 and 5% significantly reduces the D retention at elevated temperatures and prevents formation of the blisters.

Journal Articles

Deuterium retention, blistering and local melting at tungsten exposed to high-fluence deuterium plasma

Shu, Wataru; Nakamichi, Masaru; Alimov, V.; Luo, G.-N.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Journal of Nuclear Materials, 390-391, p.1017 - 1021, 2009/06

 Times Cited Count:49 Percentile:95.14(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Surface modification and deuterium retention in tungsten and molybdenum exposed to low-energy, high flux deuterium plasmas

Alimov, V.; Shu, Wataru; Roth, J.*; Komarov, D. A.*; Lindig, S.*; Isobe, Kanetsugu; Nakamura, Hirofumi; Yamanishi, Toshihiko

Advanced Materials Research, 59, p.42 - 45, 2009/00

 Times Cited Count:0 Percentile:0.12

Journal Articles

Deuterium depth profiling in JT-60U tiles using the D($$^{3}$$He, p)$$^{4}$$He resonant nuclear reaction

Hayashi, Takao; Sugiyama, Kazuyoshi*; Krieger, K.*; Mayer, M.*; Alimov, V. Kh.*; Tanabe, Tetsuo*; Masaki, Kei; Miya, Naoyuki

Journal of Nuclear Materials, 363-365, p.904 - 909, 2007/06

 Times Cited Count:11 Percentile:61.24(Materials Science, Multidisciplinary)

The absolute concentrations and the depth profiles of deuterium in plasma-facing graphite tiles used in JT-60U were determined by means of the D($$^{3}$$He, p)$$^{4}$$He resonant nuclear reaction. The highest deuterium concentration was found at a plasma-facing surface near the outer pumping slot on the outer dome wing tile, where redeposited layers with thicknesses in the micron or submicron range were observed, indicating deuterium codepostion with carbon. In addition, a high flux of high energy deuterium originating from NBI is expected on the outer dome wing as well as on the dome top tile, and could have some contribution to this area of highest deuterium retention. The deuterium content integrated up to about 16 $$mu$$m was $$approx$$2.5$$times$$10$$^{22}$$ D/m$$^{2}$$. The depth profile has a broad peak in the atomic ratio of D/C$$approx$$0.05 at a depth of about 2.5 $$mu$$m. This is mainly because D retained in the top surface was replaced by H due to isotope exchange during H discharges, which were carried out to remove tritium from the plasma-facing wall before air ventilation. In erosion dominated areas such as the outer divertor tiles, the amount of deuterium was one order of magnitude lower than that on the outer dome wing tile. In the first wall area, the highest amount of deuterium with a content of $$approx$$1.0$$times$$10$$^{22}$$ D/m$$^{2}$$ was found in the upper region, nearest to the plasma. Again implantation of high energy deuterium due to NBI could have some contribution to the high deuterium retention.

Oral presentation

Study for blistering mechanism of tungsten exposed with D plasma

Isobe, Kanetsugu; Alimov, V.; Yamanishi, Toshihiko; Torikai, Yuji*; Hatano, Yuji*

no journal, , 

no abstracts in English

Oral presentation

Tritium distribution of tungsten exposed with low energy, high flux D plasma

Isobe, Kanetsugu; Alimov, V.; Yamanishi, Toshihiko; Torikai, Yuji*

no journal, , 

To understand these plasma surface interactions, tritium distribution of tungsten exposed with low energy (38 eV), high flux D plasma was examined with BIXS. D plasma exposures were carried out at around 495 and 550 K of specimen. After that, specimen was exposed with gaseous tritium diluted with deuterium at 473 K in 5 hours. Amount of tritium in surface layer was measured with BIXS and tritium distribution of surface. The amount of tritium in surface layer was different of each exposure condition and tungsten exposed at 495 K shows highest amount of tritium. This result quite agrees with D inventory examination with thermal desorption spectrometer.

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