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Journal Articles

Liquid divertor

Shimada, Michiya; Miyazawa, Junichi*

Purazuma, Kaku Yugo Gakkai-Shi, 92(2), p.119 - 124, 2016/02


Actively convected liquid metal divertor is promising for providing a solution for issues of DEMO reactors including heat removal and disruptions. This chapter gives an overview of the motivation, research history, recent development, future perspective and issues to be resolved.

Journal Articles

Analysis of the direction of plasma vertical movement during major disruptions in ITER

Lukash, V.*; Sugihara, Masayoshi; Gribov, Y.*; Fujieda, Hirobumi*

Plasma Physics and Controlled Fusion, 47(12), p.2077 - 2086, 2005/12

 Times Cited Count:9 Percentile:31.61(Physics, Fluids & Plasmas)

Vertical directions of plasma movement after the thermal quench (TQ) of major disruptions in ITER are investigated using the predictive mode of the DINA code. Three dominant parameters in determining the direction of plasma movement are identified; (1) the rate of plasma current quench, (2) change of the internal plasma inductance li associated with the TQ and (3) the initial vertical position of plasma column before the TQ. It is shown that the reference ITER plasma moves upward after the TQ, if the current quench rate is higher than 200kA/ms and the drop of li does not exceed 0.2 for the present reference initial vertical position (55.5 cm above the center of machine).

Journal Articles

Neural-net predictor for beta limit disruptions in JT-60U

Yoshino, Ryuji

Nuclear Fusion, 45(11), p.1232 - 1246, 2005/11

 Times Cited Count:37 Percentile:74.45(Physics, Fluids & Plasmas)

Prediction of major disruptions observed at the $$beta$$-limit for tokamak plasmas has been investigated in JT-60U with developing neural networks. A sub-neural network is trained to output a value of the $$beta$$$$_{N}$$ limit every 2 ms. The target $$beta$$$$_{N}$$ limit is artificially set by the operator in the first step training and is modified in the second step training using the output $$beta$$$$_{N}$$ limit from the trained network. To improve the prediction performance further, the difference between the estimated $$beta$$$$_{N}$$ limit and the measured $$beta$$$$_{N}$$ and the other 11 parameters are inputted to a main neural network to calculate the stability level. Major disruptions have been predicted with a prediction success rate of 80% at 10 ms prior to the disruption while the false alarm rate is lower than 4%. This 80% is much higher than about 10% previously obtained. A prediction success rate of 90% has been also obtained with a false alarm rate of 12% at 10 ms prior to the disruption. This 12% is about a half of previously obtained one.

Journal Articles

Electron density behavior during fast termination phase of post-disruption runaway plasma

Kawano, Yasunori; Nakano, Tomohide; Asakura, Nobuyuki; Tamai, Hiroshi; Isayama, Akihiko; Kondoh, Takashi; Hatae, Takaki; Takenaga, Hidenobu; Ide, Shunsuke

Purazuma, Kaku Yugo Gakkai-Shi, 81(10), p.743 - 744, 2005/10

Electron density of post-disruption runaway plasmas in JT-60U has been measured by the tangential CO$$_{2}$$ laser interferometer. Increases in electron density after the first drop of runaway plasma current have been observed during a fast termination phase of the runaway plasma. At the second current drop, an increase in electron density with multiple spikes or oscillation with the period of 1 ms has been found. It is suggested that the increased electron density seems to take part in the shorter current decay time after the second current drop.

Journal Articles

Role of bremsstrahlung radiation in limiting the energy of runaway electrons in Tokamaks

Bakhtiari, M.; Kramer, G. J.*; Takechi, Manabu; Tamai, Hiroshi; Miura, Yukitoshi; Kusama, Yoshinori; Kamada, Yutaka

Physical Review Letters, 94(21), p.215003_1 - 215003_4, 2005/06

 Times Cited Count:45 Percentile:83.09(Physics, Multidisciplinary)

Bremsstrahlung radiation of runaway electrons is found to be an energy limit for runaway electrons in tokamaks. The minimum and maximum energy of runaway electron beams is shown to be limited by collisions and Bremsstrahlung radiation, respectively. It is also found that a massive injection of a high-Z gas such as Xenon can terminate a disruption-generated runaway current before the runaway electrons hit the walls.

Journal Articles

Study of plasma termination using high-Z noble gas puffing in the JT-60U tokamak

Bakhtiari, M.; Tamai, Hiroshi; Kawano, Yasunori; Kramer, G. J.*; Isayama, Akihiko; Nakano, Tomohide; Kamiya, Kensaku; Yoshino, Ryuji; Miura, Yukitoshi; Kusama, Yoshinori; et al.

Nuclear Fusion, 45(5), p.318 - 325, 2005/05

 Times Cited Count:44 Percentile:79.14(Physics, Fluids & Plasmas)

In the previous works we had shown that injecting a mixture of large amounts of hydrogen and small amounts of argon can terminate a tokamak discharge quickly with avoiding runaway electron generation. In this work we have done the same experiments but with different gases in addition to argon. In fact we compared the effect of the puffing of argon, krypton, and xenon gases with and without simultaneous hydrogen gas puffing on disruption mitigation. We observed that injecting all impurities in the form of an admixture in hydrogen lead to faster plasma shutdowns with less runaway electron generation. We also found that injecting krypton gas (with or without hydrogen) seems to be a good candidate for plasma shutdown purposes since it induces low heat flux to divertor plates and avoids runaway electron generation more effectively.

Journal Articles

Overview of goals and performance of ITER and strategy for plasma-wall interaction investigation

Shimada, Michiya; Costley, A. E.*; Federici, G.*; Ioki, Kimihiro*; Kukushkin, A. S.*; Mukhovatov, V.*; Polevoi, A. R.*; Sugihara, Masayoshi

Journal of Nuclear Materials, 337-339, p.808 - 815, 2005/03

 Times Cited Count:63 Percentile:96.38(Materials Science, Multidisciplinary)

ITER is an experimental fusion reactor for investigation and demonstration of burning plasmas, characterised of its heating dominated by alpha-particle heating. ITER is a major step from present devices and an indispensable step for fusion reactor development. ITER's success largely depends on the control of plasma-wall interactions(PWI), with power and particle fluxes and time scales one or two orders of magnitude larger than in present devices. The strategy for control of PWI includes the semi-closed divertor, strong fuelling and pumping, disruption and ELM control, replaceable plasma-facing materials and stepwise operation.

Journal Articles

Modeling of plasma current decay during the disruption

Owaki, Hirokazu; Sugihara, Masayoshi; Kawano, Yasunori; Lukash, V. V.*; Khayrutdinov, R. R.*; Zhogolev, V.*; Ozeki, Takahisa; Hatayama, Akiyoshi*

Europhysics Conference Abstracts (CD-ROM), 29C, 4 Pages, 2005/00

no abstracts in English

Journal Articles

Progress in physics basis and its impact on ITER

Shimada, Michiya; Campbell, D.*; Stambaugh, R.*; Polevoi, A. R.*; Mukhovatov, V.*; Asakura, Nobuyuki; Costley, A. E.*; Donn$'e$, A. J. H.*; Doyle, E. J.*; Federici, G.*; et al.

Proceedings of 20th IAEA Fusion Energy Conference (FEC 2004) (CD-ROM), 8 Pages, 2004/11

This paper summarises recent progress in the physics basis and its impact on the expected performance of ITER. Significant progress has been made in many outstanding issues and in the development of hybrid and steady state operation scenarios, leading to increased confidence of achieving ITER's goals. Experiments show that tailoring the current profile can improve confinement over the standard H-mode and allow an increase in beta up to the no-wall limit at safety factors $$sim$$ 4. Extrapolation to ITER suggests that at the reduced plasma current of $$sim$$ 12MA, high Q $$>$$ 10 and long pulse ($$>$$1000 s) operation is possible with benign ELMs. Analysis of disruption scenarios has been performed based on guidelines on current quench rates and halo currents, derived from the experimental database. With conservative assumptions, estimated electromagnetic forces on the in-vessel components are below the design target values, confirming the robustness of the ITER design against disruption forces.

Journal Articles

Edge safety factor at the onset of plasma disruption during VDEs in JT-60U

Sugihara, Masayoshi; Lukash, V.*; Khayrutdinov, R.*; Neyatani, Yuzuru

Plasma Physics and Controlled Fusion, 46(10), p.1581 - 1589, 2004/10

 Times Cited Count:11 Percentile:35.12(Physics, Fluids & Plasmas)

Detailed examinations of the value of the edge safety factor q at the onset of thermal quench during intentional VDE experiments in JT-60U are performed using two different reconstruction methods, FBI/FBEQU and DINA. Results by both methods are very similar and show that the thermal quench occurs when the q value is in the range between 1.5-2. This result suggests that the predictive simulations for VDEs should be performed within this range of q to examine the subsequent differences in the halo currents, plasma movement and other plasma behavior during the current quench.

Journal Articles

First measurement of time-resolved neutron yield on JT-60U using a microfission chamber

Hayashi, Takao; Nishitani, Takeo; Ishikawa, Masao

Review of Scientific Instruments, 75(10), p.3575 - 3577, 2004/10

 Times Cited Count:12 Percentile:53.99(Instruments & Instrumentation)

Micro fission chambers, which are pencil sized ionization chamber with fissile material inside, to be installed in the vacuum vessel as neutron monitor for the International Thermonuclear Experimental Reactor (ITER). The micro fission chamber has been installed inside toroidal field coils in JT-60U, in order to investigate the technical validity as neutron monitor in a magnetic field of about 2 T. Compared with the neutron yield measured by three $$^{235}$$U fission chambers which are used as neutron monitors in JT-60U, neutron yield measured by micro fission chamber has a good linearity with them. The influence of the magnetic field on the micro fission chamber has not been observed. However improper signals caused by plasma disruption and breakdown event of Neutral Beam Injection were observed, probably due to long wiring between the detector and the preamplifier. Therefore, by enhancement of noise protections, micro fission chambers can be available as neutron monitor for ITER.

Journal Articles

Neural-net disruption predictor in JT-60U

Yoshino, Ryuji

Nuclear Fusion, 43(12), p.1771 - 1786, 2003/12

 Times Cited Count:48 Percentile:79.99(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Examinations on plasma behaviour during disruptions on existing tokamaks and extrapolation to ITER

Sugihara, Masayoshi; Lukash, V.*; Kawano, Yasunori; Yoshino, Ryuji; Gribov, Y.*; Khayrutdinov, R.*; Miki, Nobuharu*; Omori, Junji*; Shimada, Michiya

Proceedings of 30th EPS Conference on Controlled Fusion and Plasma Physics (CD-ROM), 4 Pages, 2003/07

We examine plasma behaviours during plasma disruptions in detail in JT-60U and other tokamaks to derive appropriate physics guidelines for the behaviours. Their interpretations and their extrapolations to ITER are incorporated into the DINA code, which solves plasma transport and 2D free boundary plasma equilibrium simultaneously with circuit equations for the vacuum vessel and the PF coils. Sensitivity of the plasma behaviours and their impact on the EM force during disruptions due to the range of variation and uncertainty of the experimental data are examined.

Journal Articles

Wave form of current quench during disruptions in Tokamaks

Sugihara, Masayoshi; Lukash, V.*; Kawano, Yasunori; Yoshino, Ryuji; Gribov, Y.*; Khayrutdinov, R.*; Miki, Nobuharu*; Omori, Junji*; Shimada, Michiya

Purazuma, Kaku Yugo Gakkai-Shi, 79(7), p.706 - 712, 2003/07

The time dependence of the current decay during the current quench phase of disruptions, which can significantly influence the electro-magnetic force on the in-vessel components due to the induced eddy currents, is investigated using data obtained in JT-60U experiments in order to derive a relevant physics guideline for the predictive simulations of disruptions in ITER. It is shown that an exponential decay can fit the time dependence of current quench for discharges with large quench rate (fast current quench). On the other hand, for discharges with smaller quench rate (slow current quench), a linear decay can fit the time dependence of current quench better than exponential.

JAEA Reports

Trial manufacture of rotary friction tester and frictional force measurement of metals

Abe, Tetsuya; Kanari, Moriyasu; Tanzawa, Sadamitsu; Hiroki, Seiji

JAERI-Tech 2002-093, 17 Pages, 2002/12


no abstracts in English

Journal Articles

Axisymmetric disruption dynamics including current profile changes in the ASDEX-Upgrade tokamak

Nakamura, Yukiharu; Pautasso, G.*; Gruber, O.*; Jardin, S. C.*

Plasma Physics and Controlled Fusion, 44(8), p.1471 - 1481, 2002/08

 Times Cited Count:12 Percentile:38.48(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Neutral point validation studies on JT-60U, alcator C-Mod and ASDEX-upgrade tokamaks

Nakamura, Yukiharu; Yoshino, Ryuji; Granetz, R. S.*; Pautasso, G.*; Gruber, O.*; Jardin, S. C.*

Purazuma, Kaku Yugo Gakkai-Shi, 78(4), p.347 - 355, 2002/04

no abstracts in English

Journal Articles

Report of ITER physics R&D expert meeting

Ozeki, Takahisa; Takeji, Satoru; Iio, Shunji*

Purazuma, Kaku Yugo Gakkai-Shi, 77(11), P. 1165, 2001/11

The 13th ITER physics R&D expert meeting on MHD, Disruption and Control was held on Funchal of Madeira island, Portugal, in June 25-26 after 28th European Physical Society meeting. The eighteen members of the physics R&D experts and of Joint Central team of ITER were attened the meeting. They reconsidered the disruption data base and discussed recent progresses of the stability of long pulse discharges and the influence on the plasma confinement. They also give some suggestions to the ITER design. The report describes the summary of discussions.

Journal Articles

Present status of VDEs (Vertical Displacement Events) avoidance studies in Tokamak disruptions

Nakamura, Yukiharu

Purazuma, Kaku Yugo Gakkai-Shi, 77(9), p.843 - 856, 2001/09

no abstracts in English

Journal Articles

Characterization of disruption phenomenology in ITER

Yoshino, Ryuji; D.J.Campbell*; E.Fredrickson*; Fujisawa, Noboru; N.Granetz*; Gruber, O.*; T.C.Hender*; D.A.Humphreys*; N.Ivanov*; S.Jardin*; et al.

Fusion Energy 2000 (CD-ROM), 4 Pages, 2001/05

no abstracts in English

77 (Records 1-20 displayed on this page)