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Journal Articles

Cross-scale interactions between electron and ion scale turbulence in a tokamak plasma

Maeyama, Shinya*; Idomura, Yasuhiro; Watanabe, Tomohiko*; Nakata, Motoki*; Yagi, Masatoshi; Miyato, Naoaki; Ishizawa, Akihiro*; Nunami, Masanori*

Physical Review Letters, 114(25), p.255002_1 - 255002_5, 2015/06

 Times Cited Count:68 Percentile:95.12(Physics, Multidisciplinary)

Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and $$beta$$ value are realized for the first time, where the $$beta$$ value is given by the ratio of plasma pressure to magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real- mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. When the ion-scale modes are stabilized by finite-$$beta$$ effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport.

Journal Articles

A Possible breakthrough of power handling by plasma shaping in tokamak

Kikuchi, Mitsuru; Fasoli, A.*; Takizuka, Tomonori*; Diamond, P. H.*; Medvedev, S.*; Wu, Y.*; Duan, X.*; Kishimoto, Yasuaki*; Hanada, Kazuaki*; Pueschel, M. J.*; et al.

Proceedings of 8th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices (CD-ROM), 20 Pages, 2015/05

The standard D shaped H-mode operation showed excellent plasma confinement ut has important issues of transient and steady state heat flux. To solbe this issues, we proposed new scenario using plasma shaping as one of possible scenario of future tokamak reactor.

Journal Articles

Orbit-based analysis of resonant excitations of Alfv$'e$n waves in tokamaks

Bierwage, A.; Shinohara, Koji

Physics of Plasmas, 21(11), p.112116_1 - 112116_21, 2014/11

 Times Cited Count:19 Percentile:72.88(Physics, Fluids & Plasmas)

Journal Articles

Impact of wall saturation on particle control in long and high-power-heated discharges in JT-60U

Nakano, Tomohide; Asakura, Nobuyuki; Takenaga, Hidenobu; Kubo, Hirotaka; Miura, Yukitoshi; Shimizu, Katsuhiro; Konoshima, Shigeru; Masaki, Kei; Higashijima, Satoru; JT-60 Team

Nuclear Fusion, 46(5), p.626 - 634, 2006/05

 Times Cited Count:19 Percentile:56.94(Physics, Fluids & Plasmas)

In order to understand plasma-wall interactions in a long time scale, the discharge pulse length has been extended from 15 s to 65 s, with the NB-heating duration extended to 30 s. Nearly-saturation of the divertor plates was observed in the latter half of long pulse ELMy H-mode discharges. Particle sink into the divertor plates gradually decreased, and subsequently, wall-pumping efficiency became zero. This wall saturation resulted in a rise of the main plasma density without any auxiliary particle supply besides NB with divertor-pumping. Even when the total injected energy reached up to $$sim$$ 350 MJ in a discharge, neither sudden increase of carbon generation such as carbon bloom nor increase of the dilution of the main plasma was observed.

Journal Articles

Critical $$beta$$ analyses with ferromagnetic and plasma rotation effects and wall geometry for a high $$beta$$ steady state tokamak

Kurita, Genichi; Bialek, J.*; Tsuda, Takashi; Azumi, Masafumi*; Ishida, Shinichi; Navratil, G. A.*; Sakurai, Shinji; Tamai, Hiroshi; Matsukawa, Makoto; Ozeki, Takahisa; et al.

Nuclear Fusion, 46(2), p.383 - 390, 2006/02

 Times Cited Count:9 Percentile:33.28(Physics, Fluids & Plasmas)

It is shown that critical beta is decreased by ferromagnetic effect by about 8% for $$mu$$/$$mu$$$$_{0}$$$$sim$$2, $$mu$$ and $$mu$$$$_{0}$$ denoting the permeability of ferromagnetic wall and vacuum, respectively, for tokamak of aspect ratio 3. The existence of the stability window for resistive wall mode opened by both effects of the toroidal plasma rotation and the plasma dissipation, which was not observed for high aspect ratio tokamak, is found for tokamak of aspect ratio 3. The effect of ferromagnetism on them is also investigated. The critical beta analyses of NCT (National Centralized Tokamak) plasma using VALEN code are started with stabilizing plate and vacuum vessel geometry with finite resistivity, and the results for passive effect of stabilizing plate are obtained. The calculations including stabilizing effect of the vacuum-vessel and also active feedback control are also performed for present design of NCT plasma.

Journal Articles

Method for detection of separatrix surface using differential double probe

Amemiya, Hiroshi*; Uehara, Kazuya

Japanese Journal of Applied Physics, Part 1, 45(1A), p.247 - 249, 2006/01

 Times Cited Count:4 Percentile:17.99(Physics, Applied)

A method for detecting the separatrix surface in the edge plasma in Tokamak is presented. Two sets of double probes whose front surfaces are shifted by a small distance are mounted and the difference of the currents is measured using a differential amplifier. When the separatrix surface reaches the probes, a current increment appears in the differential amplifier, giving a signal of the arrival of the separatrix. Procedures of obtaining plasma parameters including the ion temperature are described.

Journal Articles

Study of particle behavior for steady-state operation in JT-60U

Kubo, Hirotaka; JT-60 Team

Plasma Science and Technology, 8(1), p.50 - 54, 2006/01

 Times Cited Count:2 Percentile:7.57(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Electron capture processes in low energy collisions of C$$^{4+}$$ ions with excited H atoms

Shimakura, Noriyuki*; Homma, Mayumi*; Kubo, Hirotaka

Journal of Plasma and Fusion Research SERIES, Vol.7, p.199 - 202, 2006/00

no abstracts in English

Journal Articles

Design study of national centralized tokamak facility for the demonstration of steady state high-$$beta$$ plasma operation

Tamai, Hiroshi; Akiba, Masato; Azechi, Hiroshi*; Fujita, Takaaki; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; Hosogane, Nobuyuki; Ichimura, Makoto*; et al.

Nuclear Fusion, 45(12), p.1676 - 1683, 2005/12

 Times Cited Count:15 Percentile:48.09(Physics, Fluids & Plasmas)

Design studies are shown on the National Centralized Tokamak facility. The machine design is carried out to investigate the capability for the flexibility in aspect ratio and shape controllability for the demonstration of the high-beta steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor, and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced in consistent with the sufficient divertor pumping. Evaluations of the plasma performance towards the determination of machine design are presented.

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:35 Percentile:73.97(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

Nonlinear behaviour of collisionless double tearing mode induced by electron inertia

Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki*

Nuclear Fusion, 45(11), p.1264 - 1270, 2005/11

 Times Cited Count:12 Percentile:41.3(Physics, Fluids & Plasmas)

A gyrokinetic particle simulation is executed to clarify the effect of the electron inertia on the MHD phenomena in the reversed shear configuration (RSC) of a cylindrical tokamak plasma. It is found that the collisionless (kinetic) double tearing modes grow up at the Alfv$'e$n time scale, and nonlinearly induce the internal collapse when the helical flux at the magnetic axis is less than that at the outer resonant surface. After the internal collapse, the secondary reconnection is induced by the current concentration due to the $$m=2$$ convective flow. It is also clarified that a nonlinear dynamics accompanied with the elementary processes caused by the $$m=2$$ flow can generate a new RSC with resonant surfaces. In the presence of the density gradient, after the full reconnection induced by the $$m=2$$ mode, the radial electric field is found to be generated due to the difference of the $${bf E} times {bf B}$$ motion between ions and electrons. However, the intensity of the radial field is not so large as that induced by the collisionless kink mode.

Journal Articles

Conference summary; Progress in experiments on confinement, plasma-material interactions and innovative confinement concepts

Ninomiya, Hiromasa

Nuclear Fusion, 45(10), p.S13 - S31, 2005/10

 Times Cited Count:0 Percentile:0.01(Physics, Fluids & Plasmas)

This paper summarizes the results presented at the 20th IAEA Fusion Energy Conference 2004 in the sessions of confinement, plasma-wall interaction and innovative confinement concept. The highlights of the presentations are as follows. Long pulse operation with high beta and high bootstrap fraction much longer than the current diffusion time has been achieved. The discharge scenario optimization and its extrapolation towards ITER have progressed remarkably. Significant progress has been made in understanding of global confinement and transport physics.

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

Nonlinear acceleration of the electron inertia-dominated magnetohydrodynamic modes due to electron parallel compressibility

Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki

Physics of Plasmas, 12(9), p.092505_1 - 092505_7, 2005/09

 Times Cited Count:2 Percentile:7.25(Physics, Fluids & Plasmas)

The behavior of the collisionless magnetohydrodynamics modes is investigated by the gyro-kinetic particle simulation in a cylindrical tokamak plasma in the parameter region where the effects of electron inertia and electron parallel compressibility are competitive for magnetic reconnection. Although the linear growth of the $$m=1$$ internal kink-tearing mode is dominated by the electron inertia, it is found that the growth rate can be nonlinearly accelerated due to the electron parallel compressibility proportional to the ion sound Larmor radius $$rho_s$$. It is also found that, as decreasing the electron skin depth $$delta_e$$, the maximum growth rate before the internal collapse saturates independently of the microscopic scales such as $$delta_e$$ and $$rho_s$$. The acceleration of growth rate is also observed in the nonlinear phase of the $$m=2$$ double tearing mode.

Journal Articles

Advanced tokamak research on JT-60

Kishimoto, Hiroshi; Ishida, Shinichi; Kikuchi, Mitsuru; Ninomiya, Hiromasa

Nuclear Fusion, 45(8), p.986 - 1023, 2005/08

 Times Cited Count:33 Percentile:25.42(Physics, Fluids & Plasmas)

The Japanese large tokamak JT-60 has been focusing its research emphases to develop a high performance plasma, namely high confinement, high temperature and high density, and to sustain it non-inductively for a long time with possible minimization of external power input. The first demonstration of high bootstrap current discharges in a high-poloidal-beta mode (high-$$beta$$p) and the concept development of a steady-state tokamak reactor SSTR based on this experimental achievement initiated the so-called "advanced tokamak research". The first observation of internal transport barriers in the JT-60 high-$$beta$$p mode was followed by the world-wide explorations of reversed shear discharges associated with internal transport barriers. The advanced tokamak research is now the major trend of the current tokamak development. A new concept of compact ITER was developed and proposed in the context of this advanced tokamak approach pursued on JT-60.

Journal Articles

Electron cyclotron heating assisted startup in JT-60U

Kajiwara, Ken*; Ikeda, Yoshitaka; Seki, Masami; Moriyama, Shinichi; Oikawa, Toshihiro; Fujii, Tsuneyuki; JT-60 Team

Nuclear Fusion, 45(7), p.694 - 705, 2005/07

 Times Cited Count:50 Percentile:82.9(Physics, Fluids & Plasmas)

Electron cyclotron heating (ECH) assisted start-up experiment was performed in JT-60U. The breakdown loop voltage, becoming the maximum value at the plasma start-up, successfully reduced from 30 V to 4 V (E = 0.26 V/m) by 200 kW ECH. This fulfills the value less than 0.3 V/m, which corresponds to the maximum electric field required in ITER. Moreover, in order to investigate properties of start-up plasmas, parameter scans of the ECH power, prefilled gas pressure, resonant position, polarization angle and injection position were carried out and the dependence on them were obtained. It was revealed that the properties have dependences on the injection position and polarization angle in large tokamaks although they seemed to have no dependence on them from the experiments in small and medium tokamaks. In addition, in experiments of the plasma start-up using second and third harmonic ECH, it was found that the plasma current was ramped by 800 kW second harmonic ECH and was not ramped by 1.6 MW third harmonic ECH even with 7 MW neutral beam injection heating.

Journal Articles

Intelligible seminor on fusion reactors, 3; Plasma heating system to generate high temperature fusion palsmas

Inoue, Takashi; Sakamoto, Keishi

Nihon Genshiryoku Gakkai-Shi, 47(2), p.120 - 127, 2005/02

no abstracts in English

Journal Articles

Intelligible seminor on fusion reactors, 1; Introduction to fusion reactors

Ueda, Yoshio*; Inoue, Takashi; Kurihara, Kenichi

Nihon Genshiryoku Gakkai-Shi, 46(12), p.845 - 852, 2004/12

no abstracts in English

Journal Articles

Divertor spectroscopy with molecular transport

Kubo, Hirotaka; Takenaga, Hidenobu; Nakano, Tomohide; Higashijima, Satoru; Shimizu, Katsuhiro; Sawada, Keiji*; Kobayashi, Shinji*; JT-60 Team

Nuclear Fusion Research; Springer Series in Chemical Physics, Vol.78, p.121 - 134, 2004/11

no abstracts in English

Journal Articles

Review of the history of experiments in the JFT-2M tokamak for 21 years

Miura, Yukitoshi; Hoshino, Katsumichi; Kusama, Yoshinori

Purazuma, Kaku Yugo Gakkai-Shi, 80(8), p.653 - 661, 2004/08

A series of experimental program on the JAERI Fusion Torus-2M (JFT-2M) was completed in March, 2004. In the experimental operation for 21 years since the first plasma on April 27, 1983, many significant results leading the fusion energy research and plasma physics have been produced in researches on high confinement mode (H-mode), heating and current drive, advanced plasma control, compatibility of low activation ferritic steel with improved confinement mode, etc. Among these results, some important results are presented.

119 (Records 1-20 displayed on this page)