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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:100(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.

JAEA Reports

Storage management of disassembled and radioactive components of JT-60 tokamak device; Storage of radioactive components by containers

Nishiyama, Tomokazu; Miyo, Yasuhiko; Okano, Fuminori; Sasajima, Tadayuki; Ichige, Hisashi; Kaminaga, Atsushi; Miya, Naoyuki; Sukegawa, Atsuhiko; Ikeda, Yoshitaka; Sakasai, Akira

JAEA-Technology 2014-006, 30 Pages, 2014/03

JAEA-Technology-2014-006.pdf:4.87MB

JT-60 tokamak device and the peripheral equipment were disassembled so as to be upgraded to the superconducting tokamak JT-60SA. The disassembled components were stored into storage and airtight containers at the radioactive control area. The total weight and the total number of those components are about 1,100 tons and about 11,500 except for large components. Radiation measurements and records of the radioactive components were required one by one under the law of Act on Prevention of Radiation Disease Due to Radioisotopes, etc. for the control of transport and storage from the radioactive control area to the other area. The storage management of the radioactive components was implemented by establishing the work procedure and the component management system by barcode tags. The radioactive components as many as 11,500 were surely and effectively stored under the law. The report gives the outline of the storage of JT-60 radioactive components by the storage containers.

Journal Articles

Modifications to the edge radial electric field by angular momentum injection in JT-60U and their implication for pedestal transport

Kamiya, Kensaku; Honda, Mitsuru; Miyato, Naoaki; Urano, Hajime; Yoshida, Maiko; Sakamoto, Yoshiteru; Matsunaga, Go; Oyama, Naoyuki; Koide, Yoshihiko; Kamada, Yutaka; et al.

Nuclear Fusion, 52(11), p.114010_1 - 114010_12, 2012/10

 Times Cited Count:9 Percentile:55.06(Physics, Fluids & Plasmas)

Depending on the direction of the external tangential momentum input, substantial changes in not only toroidal but also poloidal flows for the carbon impurity ions are observed at around the $$E$$$$_{r}$$-well region. The shear in the edge $$E$$$$_{r}$$ becomes wider in the co-NBI case, while the edge $$E$$$$_{r}$$-well becomes deeper in the counter-NBI case.

Journal Articles

The Unified effect of counter-toroidal rotation and power across separatrix on type-I ELMs in JT-60U

Urano, Hajime; Oyama, Naoyuki; Kamiya, Kensaku; Aiba, Nobuyuki; Kamada, Yutaka; Fujita, Takaaki; JT-60 Team

Nuclear Fusion, 52(10), p.103012_1 - 103012_7, 2012/10

 Times Cited Count:2 Percentile:88.91(Physics, Fluids & Plasmas)

The unified effect of counter toroidal rotation and heating power on type-I ELMs was investigated in JT-60U tokamak. ELM frequency $$f_mathrm{ELM}$$ increased monotonically together with the power across the sepratrix $$P_mathrm{sep}$$ for all the cases of tangential NBs. However, dependence of $$f_mathrm{ELM}$$ on $$P_mathrm{sep}$$ was explicitly stronger than a proportional relation when the perpendicular NBs were injected. The toroidal rotation velocity at the H-mode pedestal $$V$$$$rm_T^{rm PED}$$ shifted continuously in counter direction when the perpendicular NBs were applied. At fixed values of $$V$$$$rm_T^{rm PED}$$, $$f_mathrm{ELM}$$ increased clearly in proportion to $$P_mathrm{sep}$$.

Journal Articles

Report on ITPA (International Tokamak Physics Activity) meeting, 36

Oyama, Naoyuki; Shinohara, Koji; Isayama, Akihiko; Yoshida, Maiko; Kamiya, Kensaku

Purazuma, Kaku Yugo Gakkai-Shi, 88(5), p.282 - 285, 2012/05

no abstracts in English

Journal Articles

Edge pedestal characteristics in JET and JT-60U tokamaks under variable toroidal field ripple

Urano, Hajime; Saibene, G.*; Oyama, Naoyuki; Parail, V.*; de Vries, P.*; Sartori, R.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; L$"o$nnroth, J.*; et al.

Nuclear Fusion, 51(11), p.113004_1 - 113004_10, 2011/11

 Times Cited Count:7 Percentile:63.81(Physics, Fluids & Plasmas)

The effect of TF ripple on the edge pedestal characteristics are examined in JET and JT-60U. By the installation of ferritic inserts, TF ripple was reduced from $$1%$$ to $$0.6%$$ in JT-60U. In JET, TF ripple was varied from $$0.1%$$ to $$1%$$ by feeding different currents to TF coils. The pedestal pressure was similar with reduced ripple in JT-60U. In JET, no clear difference of the pedestal characteristics was also observed. The edge toroidal rotation clearly decreased in counter direction by increased TF ripple. However, in JT-60U, the ELM frequency decreased by $$sim 20%$$ and the increased ELM loss power by $$30%$$ with reduced ripple. In JET, ELM frequency increases only slightly with increased TF ripple. From this inter-machine experiment, TF ripple less than $$1%$$ does not strongly affect the pedestal pressure. The effect of TF ripple on pedestal characteristics at lower collisionality close to ITER should be investigated as a next step study.

Journal Articles

Management of radioactive materials for the disassembly of JT-60U fusion tokamak device

Sukegawa, Atsuhiko; Miya, Naoyuki; Oikawa, Akira

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 8 Pages, 2011/10

The radioactivities on the materials of JT-60U fusion device, which decommissioning is underway toward the upgraded superconducting tokamak machine, have been evaluated by calculation and measurements on the specimens of the structure materials and the components. In the induced activities on those materials, the highest activation on the material was stainless steel. The essential nuclide was $$^{60}$$Co in the stainless steels. The stainless steel 316 of about 35 tons constitutes the base of interiorities as a first wall on the vacuum vessel in JT-60U. For the management of radioactive materials, the evaluation for the steels with the activated nuclides is important. The activated structure materials are kept in the controlled area in the JT-60 facilities, according to the criteria for handling activated materials by the defined domestic government.

Journal Articles

Spatio-temporal structure of the edge radial electric field during H-mode in JT-60U

Kamiya, Kensaku; Sakamoto, Yoshiteru; Matsunaga, Go; Kojima, Atsushi; Urano, Hajime; Oyama, Naoyuki; Koide, Yoshihiko; Kamada, Yutaka; Ida, Katsumi*; Kurki-Suonio, T.*; et al.

Nuclear Fusion, 51(5), p.053009_1 - 053009_3, 2011/05

 Times Cited Count:12 Percentile:45.68(Physics, Fluids & Plasmas)

We revisited to measure the edge impurity ion dynamic with new CXRS in the hot ion H-mode regime at the high magnetic field having two steps transition where a jump of Ti gradient precedes a jump of impurity Vp. Two discrete phases with different magnitude of Er in the H-phase have been observed. One is the intermediate H-phase having a large Ti gradients without significant Vp of impurity species with moderate magnitude of Er, and the other is the complete H-phase characterized by a large Er.

Journal Articles

Storage and safety management of radioactive components for disassembly of JT-60 tokamak device

Nishiyama, Tomokazu; Okano, Fuminori; Miyo, Yasuhiko; Kubo, Hirotaka; Miya, Naoyuki; Oikawa, Akira; Sasajima, Tadayuki; Sakasai, Akira

Heisei-22-Nendo Kumamoto Daigaku Sogo Gijutsu Kenkyukai Hokokushu (CD-ROM), 5 Pages, 2011/03

no abstracts in English

Journal Articles

Interactions between MHD instabilities in the wall-stabilized high-$$beta$$ plasmas

Matsunaga, Go; Aiba, Nobuyuki; Shinohara, Koji; Sakamoto, Yoshiteru; Takechi, Manabu; Suzuki, Takahiro; Asakura, Nobuyuki; Isayama, Akihiko; Oyama, Naoyuki; Yoshida, Maiko; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

Journal Articles

Observation of a complex multistage transition in the JT-60U $$H$$-mode edge

Kamiya, Kensaku; Ida, Katsumi*; Sakamoto, Yoshiteru; Matsunaga, Go; Kojima, Atsushi; Urano, Hajime; Oyama, Naoyuki; Koide, Yoshihiko; Kamada, Yutaka

Physical Review Letters, 105(4), p.045004_1 - 045004_4, 2010/07

 Times Cited Count:30 Percentile:18.42(Physics, Multidisciplinary)

Journal Articles

Effects of edge collisionality on ELM characteristics in the grassy ELM regime

Oyama, Naoyuki; Kojima, Atsushi; Aiba, Nobuyuki; Horton, L. D.*; Isayama, Akihiko; Kamiya, Kensaku; Urano, Hajime; Sakamoto, Yoshiteru; Kamada, Yutaka; JT-60 Team

Nuclear Fusion, 50(6), p.064014_1 - 064014_10, 2010/06

 Times Cited Count:19 Percentile:34.04(Physics, Fluids & Plasmas)

The effect of the edge collisionality on ELM characteristics has been investigated in the grassy ELM regime on JT-60U. Both in high and low $$q$$ regimes ($$q_{95} > 6$$ and $$q_{95} sim 4.3$$), ELM amplitude becomes higher in plasmas with high edge collisionality. This collisionality dependence is opposite to the dependence observed in type I ELM regime, where the ELM amplitude decreases with increasing the edge collisionality. This collisionality dependence is favorable for next step devices such as ITER.

Journal Articles

29th report of ITPA topical group meeting

Isayama, Akihiko; Sakakibara, Satoru*; Furukawa, Masaru*; Matsunaga, Go; Yamazaki, Kozo*; Watanabe, Kiyomasa*; Idomura, Yasuhiro; Sakamoto, Yoshiteru; Tanaka, Kenji*; Tamura, Naoki*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 86(6), p.374 - 377, 2010/06

no abstracts in English

Journal Articles

Development of a lithium beam probe and measurement of density pedestal in JT-60U

Kojima, Atsushi; Kamiya, Kensaku; Fujita, Takaaki; Kubo, Hirotaka; Iguchi, Harukazu*; Oyama, Naoyuki; Suzuki, Takahiro; Kamada, Yutaka; JT-60 Team

Plasma and Fusion Research (Internet), 5, p.015_1 - 015_7, 2010/04

A lithium beam probe (LiBP) has been developed for the measurement of electron density profiles with high spatial and temporal resolutions in JT-60U. Using an electron beam heating ion source with a capability of 10 mA extraction, a 5.5 mA beam has been injected to the plasmas. Using the LiBP, time evolutions of pedestal density profiles during type I and grassy edge localized modes (ELMs) have been obtained for the first time. After a type I ELM crash, the drop of the line-integrated density measured by an interferometer delays by 2 ms later than that of the pedestal density. Comparing the line-integrated density to the line integration of the edge density profile measured by the LiBP, it is found that the recovery from the type I ELM crash is correlated with the reduction of core plasma density. Compared with the type I ELM, grassy ELMs have smaller density crashes than that of type I ELMs, which is mainly derived from the narrower ELM affected area.

Journal Articles

27th report of ITPA topical group meeting

Osakabe, Masaki*; Shinohara, Koji; Toi, Kazuo*; Todo, Yasushi*; Hamamatsu, Kiyotaka; Murakami, Sadayoshi*; Yamamoto, Satoshi*; Idomura, Yasuhiro; Sakamoto, Yoshiteru; Tanaka, Kenji*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 85(12), p.839 - 842, 2009/12

no abstracts in English

Journal Articles

Fast dynamics of type I and grassy ELMs in JT-60U

Kojima, Atsushi; Oyama, Naoyuki; Sakamoto, Yoshiteru; Kamada, Yutaka; Urano, Hajime; Kamiya, Kensaku; Fujita, Takaaki; Kubo, Hirotaka; Aiba, Nobuyuki; JT-60 Team

Nuclear Fusion, 49(11), p.115008_1 - 115008_8, 2009/11

 Times Cited Count:16 Percentile:41.25(Physics, Fluids & Plasmas)

In order to understand the physics of the ELM trigger and determining the ELM size, the fast ELM dynamics of type I and grassy ELMs have been studied in JT-60U, using new fast diagnostics with high spatial and temporal resolutions. The evolution of the ion pressure profile in the pedestal region is evaluated for the first time by detailed edge profile measurements. Type I ELMs observed in co-rotating plasmas exhibited larger and wider ELM affected area than ctr-rotating plasmas. Just before type I ELM crash, the pedestal ion pressure and its maximum gradient in co-rotating plasmas are 20% and 12% higher than those in ctr-rotating plasmas, respectively. It is found that the radial extent of the ion pressure gradient at the pedestal region in co-rotating plasmas is 14% wider than that in ctr-rotating plasmas. The experimental results suggest that the ELM size is determined by the structure of the plasma pressure in the whole pedestal region.

Journal Articles

The Impact of the current density profile on heat transport and pedestal structure in JT-60U

Urano, Hajime; Sakamoto, Yoshiteru; Suzuki, Takahiro; Fujita, Takaaki; Kamiya, Kensaku; Isayama, Akihiko; Kamada, Yutaka; Takenaga, Hidenobu; Oyama, Naoyuki; Matsunaga, Go; et al.

Nuclear Fusion, 49(9), p.095006_1 - 095006_7, 2009/09

 Times Cited Count:3 Percentile:85.57(Physics, Fluids & Plasmas)

H-modes operated at higher $$l_mathrm{i}$$ with the current ramp down have shown higher energy confinement with higher density in JT-60U. The $$H$$-factor evaluated for the core plasma depends strongly on $$l_mathrm{i}$$ with the relation of $$H_mathrm{89core} propto l_mathrm{i}^{0.8}$$ for the case without sawtooth activities. Center peaked profiles of electron density and electron temperature are obtained in high $$l_mathrm{i}$$ H-modes. The pedestal pressure is not significantly changed. The enhanced energy confinement in high $$l_mathrm{i}$$ H-modes is attributed to the core improvement with the peaked profiles of electron density and temperature. The electron heat diffusivity is reduced at the plasma core in high $$l_mathrm{i}$$ case, resulting in the center peaked $$T_mathrm{e}$$ profile while the $$T_mathrm{i}$$ profiles are approximately unchanged.

Journal Articles

Balance of the stored energies sustained by the internal and edge transport barriers and effects of ELMs and L-H transitions in JT-60U

Kamada, Yutaka; Yoshida, Maiko; Sakamoto, Yoshiteru; Koide, Yoshihiko; Oyama, Naoyuki; Urano, Hajime; Kamiya, Kensaku; Suzuki, Takahiro; Isayama, Akihiko; JT-60 Team

Nuclear Fusion, 49(9), p.095014_1 - 095014_9, 2009/09

 Times Cited Count:2 Percentile:90.39(Physics, Fluids & Plasmas)

For understanding of the physics processes determining the radial profiles of the kinetic plasma parameters in the advanced tokamak plasmas, correlation between the edge and the internal transport barriers (ETB and ITB) has been studied. We fond that the edge pedestal beta, $$beta$$$$_{p-ped}$$, increases almost linearly with the total $$beta$$$$_{p}$$, over a wide range of the plasma current for the type I ELMing H-mode, and the dependence becomes stronger with increasing triangularity. This dependence is not due to the profile stiffness. However, with increasing the stored energy inside the ITB radius (W$$_{ITB}$$), the total thermal stored energy (W$$_{th}$$) increases and then the pedestal stored energy (W$$_{p-ped}$$) increases. With increasing W$$_{p-ped}$$, the ELM penetration depth expands more inward and finally reaches the ITB-foot radius. At this situation, the ITB radius cannot move outward and the ITB strength becomes weak. Then the fractions of W$$_{ITB}$$ and W$$_{p-ped}$$ to W$$_{th}$$ become almost constant. We also found that the type I ELM expels/decreases edge toroidal momentum larger than ion thermal energy. The ELM penetration radius for toroidal rotation tends to be deeper than that for ion temperature, and can exceeds the ITB radius. The ELM affected area is deeper for CO rotating plasmas than CTR rotating ones. The ELM affected area is deeper in the order of the toroidal rotation (V$$_{t}$$), the ion temperature (T$$_{i}$$) and then the electron temperature (Te). The L-H transition also changes the V$$_{t}$$-profile more significantly than the Ti-profile. After the L-H transition, in the ELM-free phase, the pedestal V$$_{t}$$ sifts into the CTR direction deeply and suddenly, and after that the pedestal V$$_{t}$$ and T$$_{i}$$ evolves in the similar timescale. The change in V$$_{t}$$ by ELM and L-H transition may affect degradation / evolution of ITBs.

Journal Articles

The Characteristics of the internal transport barrier under reactor relevant conditions in JT-60U weak shear plasmas

Takenaga, Hidenobu; Oyama, Naoyuki; Urano, Hajime; Sakamoto, Yoshiteru; Asakura, Nobuyuki; Kamiya, Kensaku; Miyo, Yasuhiko; Nishiyama, Tomokazu; Sasajima, Tadayuki; Masaki, Kei; et al.

Nuclear Fusion, 49(7), p.075012_1 - 075012_11, 2009/07

 Times Cited Count:8 Percentile:65.01(Physics, Fluids & Plasmas)

Characteristics of internal transport barrier (ITB) have been investigated under reactor relevant condition with edge fuelling and electron heating in JT-60U weak shear plasmas. High confinement was sustained at high density with edge fuelling by shallow pellet injection or supersonic molecular beam injection (SMBI). The ion temperature (T$$_{i}$$) in the central region inside the ITB decreased due to cold pulse propagation even with edge fuelling. By optimizing the injection frequency and the penetration depth, the decreased central T$$_{i}$$ was recovered and good ITB was sustained with enhanced pedestal pressure. The T$$_{i}$$-ITB also degraded significantly with electron cyclotron heating (ECH), when stiffness feature was strong in the electron temperature (T$$_{e}$$) profile. The ion thermal diffusivity in the ITB region increased with the electron thermal diffusivity, indicating existence of clear relation between ion and electron thermal transport. On the other hand, T$$_{i}$$-ITB unchanged or even grew, when stiffness feature was weak in the T$$_{e}$$ profile. Density fluctuation level at ITB seemed to be unchanged during ECH, however, correlation length became longer in the T$$_{i}$$-ITB degradation case and shorter in the T$$_{i}$$-ITB unchanging case.

Journal Articles

Pedestal characteristics of ELMy H-mode plasmas in JT-60U

Urano, Hajime; Sakamoto, Yoshiteru; Oyama, Naoyuki; Kamiya, Kensaku; Kojima, Atsushi; Hayashi, Nobuhiko; Aiba, Nobuyuki; Kamada, Yutaka; JT-60 Team

Proceedings of 36th European Physical Society Conference on Plasma Physics (CD-ROM), 4 Pages, 2009/07

In JT-60U, the physics basis and control of the H-mode pedestal have been studied. Frequency of type-I ELMs becomes higher with increasing counter toroidal rotation. Fast recovery of density pedestal was observed after the ELM crash. ELM perturbation profile of density and temperature extends inward with co-NBI. In grassy ELM regime, ELM frequency increases with counter-toroidal rotation independently of $$beta_p$$. The amplitude of grassy ELM decreases as edge collisionality decreases. QH-mode was obtained at nearly zero or slightly co-toroidal rotation at the plasma edge. Scaling of pedestal width was examined by using hydrogen/deuterium discharges. It was found that dependence of pedestal width on the Larmor radius is weak.

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