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Journal Articles

Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku*; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*

Scientific Reports (Internet), 7(1), p.14971_1 - 14971_8, 2017/11

 Times Cited Count:13 Percentile:15.73(Multidisciplinary Sciences)

Journal Articles

Experimental identification of electric field excitation mechanisms in a structural transition of tokamak plasmas

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.

Scientific Reports (Internet), 6, p.30720_1 - 30720_7, 2016/08

 Times Cited Count:11 Percentile:28.67(Multidisciplinary Sciences)

In this Letter, we report model verifications for a key physics for the L-H transition. Radial electric field excitation, using discharges having a two-step transition. Examining time derivative of Poissons equation, it is found that the sum of the loss cone loss current and neoclassical bulk viscosity current agrees the experimentally observed current in the order of magnitude at the first transition. Following second transition and an ambipolar condition in the L-mode cannot be explained by the models.

Journal Articles

Infinity, complex system and super computer

Miura, Yukitoshi

RIST News, (61), p.1 - 2, 2016/07

no abstracts in English

Journal Articles

Dynamics of edge limit cycle oscillation in the JFT-2M tokamak

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.

Nuclear Fusion, 54(7), p.073017_1 - 073017_14, 2014/07

 Times Cited Count:21 Percentile:18.52(Physics, Fluids & Plasmas)

In the JFT-2M tokamak, limit-cycle oscillation among several variables is observed before L-to-H transition. Spatiotemporal dynamics of the LCO is analyzed in detail. Zonal fows are not seen, and modulation in edge-localized poloidal flow and density gradient is observed. Modulation is also seen in Reynolds stress, caused by that in turbulence intensity and turbulence wavenumber. However, flow acceleration is not able to be explained by the modulation in the Reynolds stress. Rapid inward propagation in density gradient and turbulence packet is also observed. Characteristics of the propagation are veried by means of turbulence spreading theory and diffusion theory.

Journal Articles

Spatiotemporal structures of edge limit-cycle oscillation before L-to-H transition in the JFT-2M tokamak

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.

Physical Review Letters, 111(3), p.035002_1 - 035002_5, 2013/07

 Times Cited Count:72 Percentile:5.37(Physics, Multidisciplinary)

In this Letter, we report analyses of spatiotemporal dynamics of turbulence and structure in the limit cycle oscillation that precedes L-to-H transition. Zonal flows are not observed during LCO, and the oscillation is the periodic generations/decays of barrier with edge localized mean flow. Oscillatory Reynolds stress is found too small to accelerate the LCO flow. Changes of the density gradient and turbulence amplitude are found to propagate into the core in a ballistic manner, suggesting a cause of fast change of core transport after H-mode transition.

Journal Articles

Current status of research and development at Japan Atomic Energy Agency

Tajima, Yasuhide; Miura, Yukitoshi; Ieda, Yoshiaki

Denki Hyoron, 98(2), p.45 - 60, 2013/02

no abstracts in English

Journal Articles

Current status of research and development at Japan Atomic Energy Agency

Tajima, Yasuhide; Miura, Yukitoshi; Umeki, Hiroyuki

Denki Hyoron, 97(2), p.66 - 85, 2012/02

no abstracts in English

Journal Articles

Response of fusion gain to density in burning plasma simulation on JT-60U

Takenaga, Hidenobu; Kubo, Hirotaka; Sueoka, Michiharu; Kawamata, Yoichi; Yoshida, Maiko; Kobayashi, Shinji*; Sakamoto, Yoshiteru; Iio, Shunji*; Shimomura, Koji*; Ichige, Hisashi; et al.

Nuclear Fusion, 48(3), p.035011_1 - 035011_6, 2008/03

 Times Cited Count:2 Percentile:89.64(Physics, Fluids & Plasmas)

A burning plasma simulation scheme has been developed with consideration for temperature dependence of the DT fusion reaction rate in JT-60U. The heating power for the simulation of alpha particle heating was calculated using real-time measurements of density and ion temperature. Response of a simulated fusion gain to the density was investigated in this scheme with constant heating power for the simulation of external heating, in order to understand burn controllability by the fuel density in a fusion reactor. When temperature dependence of the fusion reaction rate was assumed as square of ion temperature, density dependence of the simulated fusion gain stronger than square of density was observed. Transport analysis using a 1.5 dimension transport code indicated that the strong density dependence is induced due to both change in a confinement improvement factor and change in a pressure profile.

Journal Articles

Density limit in discharges with high internal inductance on JT-60U

Yamada, Hiroshi*; Takenaga, Hidenobu; Suzuki, Takahiro; Fujita, Takaaki; Takizuka, Tomonori; Kamada, Yutaka; Asakura, Nobuyuki; Tsuda, Takashi; Takechi, Manabu; Matsunaga, Go; et al.

Nuclear Fusion, 47(11), p.1418 - 1424, 2007/11

 Times Cited Count:1 Percentile:95.94(Physics, Fluids & Plasmas)

High densities exceeding the Greenwald limit by a factor of 1.7 have been obtained in discharges with high internal inductances of ${it l$_{rm i}$}$ as high as 2.8 in JT-60U L-mode plasmas. The internal inductance, which is an index of the edge magnetic shear, is controlled by ramping down the plasma current. In addition to the extension of the operational regime, confinement performance remains as good as an H89PL factor of 1.5 even above the Greenwald limit. While the earlier work of a high ${it l$_{rm i}$}$ study has indicated that core confinement improvement, the additional improvement of the tolerance against the high density is turned out to be correlated with high edge temperature. The normalized density when the detachment characterized by the decrease in a D$$_alpha$$ signal at the divertor occurs is even higher in the case with no disruption than the case with a disruption. These comparisons have indicated that the improvement in thermal and particle transport does exist in the periphery and the edge in the high ${it l$_{rm i}$}$ plasmas, and mitigation of the density limit is observed coincidently. Although the high ${it l$_{rm i}$}$ discharge studied here lies outside of the usual parameter space for a steady-state operation of tokamak, demonstration of a stable discharge with good confinement beyond the Greenwald limit suggest the magnetic shear at the edge is one key parameter to uncover physical element of the operational density limit.

Journal Articles

Design optimization for plasma performance and assessment of operation regimes in JT-60SA

Fujita, Takaaki; Tamai, Hiroshi; Matsukawa, Makoto; Kurita, Genichi; Bialek, J.*; Aiba, Nobuyuki; Tsuchiya, Katsuhiko; Sakurai, Shinji; Suzuki, Yutaka; Hamamatsu, Kiyotaka; et al.

Nuclear Fusion, 47(11), p.1512 - 1523, 2007/11

 Times Cited Count:22 Percentile:35.33(Physics, Fluids & Plasmas)

Design of modification of JT-60U, JT-60SA, has been optimized in viewpoint of plasma control, and operation regimes have been evaluated. Upper and lower divertors with different geometry are prepared for flexibility of plasma shape control. The beam lines of negative-ion NBI are shifted downward for off-axis current drive, in order to obtain a weak/reversed shear plasma. The feedback control coils along the port hole in the stabilizing plate are found effective to suppress the resistive wall mode (RWM) and sustain high $$beta$$$$_{rm N}$$ close to the ideal wall limit. The regime of full current drive operation has been extended with upgraded heating and current drive power. Full current drive operation for 100 s with reactor-relevant high values of normalized beta and bootstrap current fraction ($$I$$$$_{rm p}$$ = 2.4 MA, $$beta$$$$_{rm N}$$ = 4.4, $$f$$$$_{rm BS}$$ = 0.70, $$bar{n}$$$$_{rm e}$$/$$n$$$$_{rm GW}$$ = 0.86, H$$_{rm H98y2}$$ = 1.3) is expected in a highly-shaped low-aspect-ratio configuration ($$A$$ = 2.65). High $$beta$$$$_{rm N}$$, high-density ELMy H-mode is also expected.

Journal Articles

Prospective performances in JT-60SA towards the ITER and DEMO relevant plasmas

Tamai, Hiroshi; Fujita, Takaaki; Kikuchi, Mitsuru; Kizu, Kaname; Kurita, Genichi; Masaki, Kei; Matsukawa, Makoto; Miura, Yukitoshi; Sakurai, Shinji; Sukegawa, Atsuhiko; et al.

Fusion Engineering and Design, 82(5-14), p.541 - 547, 2007/10

 Times Cited Count:9 Percentile:40.6(Nuclear Science & Technology)

JT-60SA is positioned as the ITER satellite tokamak to conduct research elements to support and supplement ITER towards DEMO under the joint collaboration of Japan and EU. After the discussions in JA-EU Satellite Tokamak Working Group in 2005, the heating power is increased up to 41MW, 100s to ensure the ITER support research. With such increased heating power, the prospective plasma performances are analysed by the equilibrium and transport analysis codes. Operation window of a fully non-inductive current drive is extended to high density region. Simultaneous achievement of high equivalent Q$$_{DT}$$ and high normalised beta is also expected in wide operational margin. Those prospects strongly indicate that JT-60SA is suitable machine to conduct the advanced research orienting to ITER and DEMO.

Journal Articles

Burn control simulation experiments in JT-60U

Shimomura, Koji*; Takenaga, Hidenobu; Tsutsui, Hiroaki*; Mimata, Hideyuki*; Iio, Shunji*; Miura, Yukitoshi; Tani, Keiji; Kubo, Hirotaka; Sakamoto, Yoshiteru; Hiratsuka, Hajime; et al.

Fusion Engineering and Design, 82(5-14), p.953 - 960, 2007/10

 Times Cited Count:2 Percentile:79.35(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Iguchi, Harukazu*; Hamada, Yasuji*; Nakano, Haruhisa*; Oshima, Shinsuke*; Ito, Kimitaka*; et al.

Nuclear Fusion, 47(10), p.S718 - S726, 2007/10

 Times Cited Count:85 Percentile:4.38(Physics, Fluids & Plasmas)

Present status of experiments on zonal flows is overviewed. Innovative use of modern diagnostics has revealed the existence of zonal flows, their spatio-temporal characteristics, their relationship with turbulence, and their effects on confinement. Particularly a number of observations have been accumulated on the oscillatory branch of the zonal flow, dubbed as geodesic acoustic modes suggesting necessity of theories to give their proper description. Several new methods have elucidated the zonal flow generation processes from the turbulence. Further investigation of relationship between the zonal flows and confinement is strongly encouraged as cross-device activity.

Journal Articles

In search of zonal flows by using direct density fluctuation measurements

Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Yagi, Masatoshi*; Hoshino, Katsumichi; Shinohara, Koji; Ejiri, Akira*; Takase, Yuichi*; Ido, Takeshi*; et al.

Plasma Physics and Controlled Fusion, 49(10), p.1611 - 1625, 2007/10

 Times Cited Count:41 Percentile:16.22(Physics, Fluids & Plasmas)

It was found that the envelope of the ambient density fluctuation of the drift wave turbulence has spectral peaks aroound zonal flow frequencies. A method to detect the zonal flow using this characteristic was considered using the JFT-2M density fluctuation data. There is a possibility that the zonal flow will be able to be detected in the future burning plasmas by using the density fluctuations measured by some density fluctuation measurement by such as the microwave reflectometer and so on.

Journal Articles

Ferritic insertion for reduction of toroidal magnetic field ripple on JT-60U

Shinohara, Koji; Sakurai, Shinji; Ishikawa, Masao; Tsuzuki, Kazuhiro*; Suzuki, Yutaka; Masaki, Kei; Naito, Osamu; Kurihara, Kenichi; Suzuki, Takahiro; Koide, Yoshihiko; et al.

Nuclear Fusion, 47(8), p.997 - 1004, 2007/08

 Times Cited Count:35 Percentile:20.18(Physics, Fluids & Plasmas)

Ferritic steel plates have been installed to improve the energetic ion confinement through reducing a toroidal magnetic field ripple. Aiming at cost-effective installation, orbit following calculations of energetic ions were performed for a design of ferritic installation on JT-60U by using the Fully three Dimensional magnetic field Orbit-Following Monte-Carlo (F3D OFMC) code. The installed ferritic steel adds the non-linear magnetic field on magnetic sensors for a plasma control and an equilibrium calculation. The code for a real-time control has been modified to take into account the magnetic field by ferritic steel. The plasma operation was successfully resumed and a real-time plasma control was successfully carried out after usual preparation processes. The heat load measurement indicates the improved confinement of energetic ions. These results are important for practical application of ferritic steel which is a leading candidate of a structural material on a demo reactor.

Journal Articles

Conceptual design of magnet system for JT-60 super advanced (JT-60SA)

Kizu, Kaname; Tsuchiya, Katsuhiko; Ando, Toshinari*; Sborchia, C.*; Masaki, Kei; Sakurai, Shinji; Sukegawa, Atsuhiko; Tamai, Hiroshi; Fujita, Takaaki; Matsukawa, Makoto; et al.

IEEE Transactions on Applied Superconductivity, 17(2), p.1348 - 1352, 2007/06

 Times Cited Count:4 Percentile:68.55(Engineering, Electrical & Electronic)

no abstracts in English

Journal Articles

Recent progress on the development and analysis of the ITPA global H-mode confinement database

McDonald, D. C.*; Cordey, J. G.*; Thomsen, K.*; Kardaun, O. J. W. F.*; Snipes, J. A.*; Greenwald, M.*; Sugiyama, L.*; Ryter, F.*; Kus, A.*; Stober, J.*; et al.

Nuclear Fusion, 47(3), p.147 - 174, 2007/03

 Times Cited Count:38 Percentile:73.68(Physics, Fluids & Plasmas)

This paper describes the updates to and analysis of the International Tokamak Physics Activity (ITPA) Global H-node Confinement Database version 3 (DB3) over the period 1994-2004. Global data, for the energy confinement time and its controlling parameters, have now been collected from 18 machines of different sizes and shapes: ASDEX, ASDEX Upgrade, C-Mod CoMPASS-D, DIII-D, JET, JFT-2M, JT-60U, MAST, NSTX, PBX-M, PDX, START, T-10, TCV, TdeV, TFTR and TUMAN-3M. A wide range of physics studies has been performed on DB3 with particular progress made in the separation of core and edge behavior, dimensionless parameter analyses and the comparison of the database with one-dimensional transport code. A key aim of the database has always been to provide a basis for estimating the energy confinement properties of next step machines such as ITER, and so the impact of the database and its analysis on such machines is also discussed.

Journal Articles

Ferritic insertion for reduction of toroidal magnetic field ripple on JT-60U

Shinohara, Koji; Sakurai, Shinji; Ishikawa, Masao; Tsuzuki, Kazuhiro*; Suzuki, Yutaka; Masaki, Kei; Naito, Osamu; Kurihara, Kenichi; Suzuki, Takahiro; Koide, Yoshihiko; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Ferritic steel plates have been installed to improve the energetic ion confinement through reducing a toroidal magnetic field ripple. Aiming at cost-effective installation, orbit following calculations of energetic ions were performed for a design of ferritic installation on JT-60U by using the Fully three Dimensional magnetic field Orbit-Following Monte-Carlo (F3D OFMC) code. The installed ferritic steel adds the non-linear magnetic field on magnetic sensors for a plasma control and an equilibrium calculation. The code for a real-time control have been modified to take into account the magnetic field by ferritic steel. The plasma operation was successfully resumed and a real-time plasma control was successfully carried out after usual preparation processes. The heat load measurement indicates the improved confinement of energetic ions. These results are important for practical application of ferritic steel which is a leading candidate of a structural material on a demo reactor.

Journal Articles

Density limit in discharges with high internal inductance on JT-60U

Yamada, Hiroshi*; Takenaga, Hidenobu; Suzuki, Takahiro; Fujita, Takaaki; Takizuka, Tomonori; Kamada, Yutaka; Asakura, Nobuyuki; Tsuda, Takashi; Takechi, Manabu; Matsunaga, Go; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

no abstracts in English

Journal Articles

Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Hamada, Yasuji*; Hoshino, Katsumichi; Nagashima, Yoshihiko*; Shinohara, Koji; Nakano, Haruhisa*; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 12 Pages, 2007/03

Present status of experiments on zonal flows is overviewed. Innovative use of traditional and modern diagnostics has revealed unambiguously the existense of the zonal flows, their spatio-temporal caracteristics, their relationship with turbulence, and their effects on confinement. Particularly, a number of observations have been accumulated on the oscillatory branch of zonal flows, dubbed geodesic acoustic modes, suggesting necessity of theories to give their proper description. Furthur investigation of relationship between zonal flows and confinement is strongly encouraged as cross-device activity.

251 (Records 1-20 displayed on this page)