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Journal Articles

Review of recent steady-state advanced tokamak research and its further pursuit by reduction of TF ripple on JT-60U

Shinohara, Koji; JT-60 Team

Journal of the Korean Physical Society, 49, p.S56 - S62, 2006/12

The recent results of JT-60, such as the long discharge with the high normalized beta of 2.3 and the pulse length of 22.3 s which was 13 times longer than the current profile relaxation, and the observation of the increase of D$$alpha$$ emission and electron density as results of wall saturation will be reviewed. Additionally, the motivation and the design work will be reviewd on an on-going recent project of the ferritic insertion for the reduction of the toroidal field ripple. The pioneering works of JFT-2M in the ferritic insertion will be also reported.

Journal Articles

Observation of the interaction between the geodesic acoustic mode and ambient fluctuation in the JFT-2M tokamak

Ido, Takeshi*; Miura, Yukitoshi; Hoshino, Katsumichi; Kamiya, Kensaku; Hamada, Yasuji*; Nishizawa, Akimitsu*; Kawasumi, Yoshiaki*; Ogawa, Hiroaki; Nagashima, Yoshihiko*; Shinohara, Koji; et al.

Nuclear Fusion, 46(5), p.512 - 520, 2006/05

 Times Cited Count:77 Percentile:6.24(Physics, Fluids & Plasmas)

The electrostatic fluctuation spectrum and the fluctuation-induced particle flux of the JFT-2M tokamak were estimated using the hevy ion beam probe (HIBP) measurement. A geodesic acoustic mode (GAM) of the frequency about15kHz was identified in the L-mode. The GAM has its peak at about 3cm inside of the separatrix with the electric field of about 1.4kV/m. The estimated turbulent particle flux is found to be intermittent. It is found that the density fluctuation is modulated by the GAM in the wide frequency range and the coherence analysis shows that the flucruation-induced particle flux is partially contributed by the GAM. In the H-mode the GAM disappears and the fluctuation and the flux is much decreased.The mechanism of the large burst-like flux in the L-mode is not understood yet and left as the future problem.

Journal Articles

Comparisons of small ELM H-mode regimes on the Alcator C-Mod and JFT-2M tokamaks

Hubbard, A. E.*; Kamiya, Kensaku; Oyama, Naoyuki; Basse, N.*; Biewer, T.*; Edlund, E.*; Hughes, J. W.*; Lin, L.*; Porkolab, M.*; Rowan, W.*; et al.

Plasma Physics and Controlled Fusion, 48(5A), p.A121 - A129, 2006/05

 Times Cited Count:15 Percentile:49.68(Physics, Fluids & Plasmas)

Dedicated experiments were carried out to compare the properties, fluctuation behaviour and access conditions of these regimes. A common shape was developed which scaled the plasma boundary except for aspect ratio. Scans of density and input power were carried out at several values of q95, so as to achieve ranges of dimensionless parameters. A striking similarity of access conditions was seen. These results suggest common physical mechanisms for the H-mode regimes, which do not depend critically on aspect ratio over this range. On the other hand, several differences in the details of the edge fluctuations were found, and will be reported. The effect of wall conditioning via boronization on the H-mode regimes will also be discussed.

Journal Articles

Bispectral analysis applied to coherent floating potential fluctuations obtained in the edge plasmas on JFT-2M

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

Plasma Physics and Controlled Fusion, 48(4), p.S1 - S15, 2006/04

 Times Cited Count:33 Percentile:22.91(Physics, Fluids & Plasmas)

This paper presents the results of bispectral analysis of floating potential fluctuations in the edge region of ohmically heated plasmas in the JFT-2M tokamak. Inside of the outermost magnetic surface,coherent modes were observed around the frequency of geodesic acoustic mode which is a kind of the zonal flow. The squared bicoherence shows significant nonlinear couplings between the coherent fluctuations and the background fluctuations (which are likely to contain drift wave turbulent fluctuations). The experimental results that the total bicoherence is proportional to the squared amplitude of the coherent fluctuation, and that the biphase of the coherent modes localizes around a constant value $$pi$$, are consistent with the theoretical prediction on the drift wave - zonal flow systems based on the Hasegawa-Mima model.

Journal Articles

Geodesic-acoustic-mode in JFT-2M tokamak plasmas

Ido, Takeshi*; Miura, Yukitoshi; Kamiya, Kensaku; Hamada, Yasuji*; Hoshino, Katsumichi; Fujisawa, Akihide*; Ito, Kimitaka*; Ito, Sanae*; Nishizawa, Akimitsu*; Ogawa, Hiroaki; et al.

Plasma Physics and Controlled Fusion, 48(4), p.S41 - S50, 2006/04

 Times Cited Count:113 Percentile:3.01(Physics, Fluids & Plasmas)

The potential and density fluctuations of Geodesic-Acoustic-Mode (GAM) were investigated through the direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe(HIBP). It was found that the amplitude of the fluctuation has a maximum inside of the plasma boundary and that it has an almost constant frequency. It was also found that the mode propagates in the radial direction and that the GAM affects the background turbulence. The influence to the background turbulence was found to be in consistent with a theoretical prediction.

Journal Articles

Characterization of coherent magnetic fluctuations in JFT-2M high recycling steady high-confinement mode plasmas

Kamiya, Kensaku; Oyama, Naoyuki; Ido, Takeshi*; Bakhtiari, M.*; JFT-2M Group

Physics of Plasmas, 13(3), p.032507_1 - 032507_9, 2006/03

 Times Cited Count:11 Percentile:59.35(Physics, Fluids & Plasmas)

Accompanying the HRS H-mode transition, the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz with significant variation are seen on the magnetic probes at the vessel wall. Above all, two types of edge MHD activities, which have associated toroidal mode number of n=1 and n$$sim$$7, respectively, seem to be more important for the HRS H-mode plasmas. To investigate their interaction, bi-spectral analysis is applied for the magnetic probe data. It is found to be a powerful tool, exhibiting the phase-coupled oscillations between two types of edge MHD activities having n=1 and n$$sim$$7.

Journal Articles

Blanket-plasma interaction in tokamaks; Implication from JT-60U, JFT-2M and reactor studies

Kikuchi, Mitsuru; Nishio, Satoshi; Kurita, Genichi; Tsuzuki, Kazuhiro; Bakhtiari, M.*; Kawashima, Hisato; Takenaga, Hidenobu; Kusama, Yoshinori; Tobita, Kenji

Fusion Engineering and Design, 81(8-14), p.1589 - 1598, 2006/02

 Times Cited Count:4 Percentile:66.27(Nuclear Science & Technology)

Blanket-plasma interaction is important for plasma performance enhancement and reliability of first-wall/ blanket. Typical examples are harminization of wall stabilization and reduction of EM force during current quench, error field effect by ferritic steel, neutral-wall interaction under wall saturation, etc. JAERI reactor studies, JT-60U and JFT-2M results on this topics will be described.

Journal Articles

Heating, current drive, and advanced plasma control in JFT-2M

Hoshino, Katsumichi; Yamamoto, Takumi; Tamai, Hiroshi; Oasa, Kazumi; Kawashima, Hisato; Miura, Yukitoshi; Ogawa, Toshihide; Shoji, Teruaki*; Shibata, Takatoshi; Kikuchi, Kazuo; et al.

Fusion Science and Technology, 49(2), p.139 - 167, 2006/02

 Times Cited Count:2 Percentile:81.05(Nuclear Science & Technology)

The main results obtained by the various heating and current drive systems, external coil system and divertor bias system are reviewed from the viewpoint of the advanced active control of the tokamak plasma. Also, the features of each system are described. The contribution of the JFT-2M in these areas are summarized.

Journal Articles

JFT-2M program

Kusama, Yoshinori; Yamamoto, Masahiro; JFT-2M Group

Fusion Science and Technology, 49(2), p.89 - 95, 2006/02

 Times Cited Count:8 Percentile:46.21(Nuclear Science & Technology)

The experimental program on the JFT-2M tokamak started with the first plasma on April 27, 1983 and was completed in March, 2004. In the series of experiments for 21 years, a lot of significant results leading the fusion energy research and plasma physics have been produced. As the first paper of this special issue on all aspect of JFT-2M, this paper reviews the JFT-2M program.

Journal Articles

Ripple reduction with ferritic insert in JFT-2M

Shinohara, Koji; Sato, Masayasu; Kawashima, Hisato; Tsuzuki, Kazuhiro; Suzuki, Sadaaki; Urata, Kazuhiro*; Isei, Nobuaki; Tani, Takashi; Kikuchi, Kazuo; Shibata, Takatoshi; et al.

Fusion Science and Technology, 49(2), p.187 - 196, 2006/02

 Times Cited Count:7 Percentile:50.67(Nuclear Science & Technology)

In JFT-2M, the toroidal field ripple was reduced by ferritic insert. Two kinds of ripple reduction were carried out. In the first case, ferritic steel was installed between toroidal field coil and vacuum vessel, just under toroidal field coil, outside vacuum vessel. In the second one, ferritic steel was installed inside vacuum vessel covering almost whole inside wall. The ripple was successfully reduced in the both cases. The temperature increment on the first wall measured by infrared TV was also reduced. A new version of OFMC code was also developed to analyze fast ion behavior in the complex structure of the toroidal field. The TF ripple reduction with ferritic insert in JFT-2M is summarized in this article.

Journal Articles

Plasma diagnostics in JFT-2M

Kasai, Satoshi*; Kamiya, Kensaku; Shinohara, Koji; Kawashima, Hisato; Ogawa, Hiroaki; Uehara, Kazuya; Miura, Yukitoshi; Okano, Fuminori; Suzuki, Sadaaki; Hoshino, Katsumichi; et al.

Fusion Science and Technology, 49(2), p.225 - 240, 2006/02

 Times Cited Count:3 Percentile:73.3(Nuclear Science & Technology)

The diagnostic system of JFT-2M has consisted of about 30 individual diagnostic instruments,which were used to study the plasma production, control, equilibrium, stability, confinement, plasma heating by NBI and/or RF (LH, ICRF, ECH) and current drive by RF. In these instruments, the motional Stark effect (MSE) polarimeter, charge exchanged recombination spectroscopy (CXRS), heavy-ion beam probe (HIBP), time of flight (TOF) neutral particle analyzer, etc. have contributed to make clear the improved mechanism of confinement such as H-mode and High Recycling Steady (HRS) H-mode, and to search the operational region of these modes.The infrared TV camera system and lost ion probe have played a very important role to investigate the heat load onto the walls due to ripple loss particles and escaping ions from core plasma, respectively.

Journal Articles

Engineering design, installation, and conditioning of ferritic steel plates/wall for AMTEX in JFT-2M

Yamamoto, Masahiro*; Shibata, Takatoshi; Tsuzuki, Kazuhiro; Sato, Masayasu; Kimura, Haruyuki; Okano, Fuminori; Kawashima, Hisato; Suzuki, Sadaaki; Shinohara, Koji; JFT-2M Group; et al.

Fusion Science and Technology, 49(2), p.241 - 248, 2006/02

 Times Cited Count:2 Percentile:81.05(Nuclear Science & Technology)

JFT-2M has been modified three times in the Advanced Material Tokamak Experiment (AMTEX) program to investigate compatibility of the low activation ferritic steel F82H with tokamak plasmas as a structural material for future reactors. The ferritic steel plate/wall was installed inside and/or outside of the vacuum vessel to reduce the ripple of toroidal magnetic field step by step through three modifications. This paper focuses on engineering aspects in these modifications; electromagnetic analysis to find a suitable way for fixing these plates, installation procedure to keep small tolerance, a three-dimensional magnetic field measurement device used to obtain information of the actual shape of the vacuum vessel used as a installation standard surface. To keep a good surface condition of the ferritic steel plate/wall that rusts easily, careful treatment was executed before the installation. To reduce oxygen impurities further, a boronization system with tri-methyl boron, which is safe and easy to operate, was developed.

Journal Articles

Study of SOL/divertor plasmas in JFT-2M

Kawashima, Hisato; Sengoku, Seio; Uehara, Kazuya; Tamai, Hiroshi; Shoji, Teruaki*; Ogawa, Hiroaki; Shibata, Takatoshi; Yamamoto, Masahiro*; Miura, Yukitoshi; Kusama, Yoshinori; et al.

Fusion Science and Technology, 49(2), p.168 - 186, 2006/02

 Times Cited Count:2 Percentile:81.05(Nuclear Science & Technology)

Experimental efforts on JFT-2M have been devoted to understand SOL/Divertor plasmas and to investigate power and particle controllability. Open divertor configuration was used for the first decade of JFT-2M started in 1984. We found out the SOL/Divertor plasma properties such as in/out asymmetry, heat and particle diffusivities, and SOL current at ELMs. Handling of power and particle was demonstrated by active control methods such as local pumping, edge ergodization, divertor biasing, and edge heating. For improvement of power and particle control capability of divertor, it was modified to closed configuration in 1995, which demonstrated the baffling effects with narrower divertor throat. Dense and cold divertor state (n$$_{e}$$$$^{div}$$ = 4$$times$$10$$^{19}$$ m$$^{-3}$$ and T$$_{e}$$$$^{div}$$ = 4 eV), compatible with the improved confinement modes (e.g. H-mode), was realized by strong gas puffing. Being related with the core confinement at H-mode, the edge plasma fluctuations were identified by an electrostatic probe. These are reviewed in this paper.

Journal Articles

CT injection experiment in JFT-2M

Ogawa, Hiroaki; Ogawa, Toshihide; Tsuzuki, Kazuhiro; Kawashima, Hisato; Kasai, Satoshi*; Kashiwa, Yoshitoshi; Hasegawa, Koichi; Suzuki, Sadaaki; Shibata, Takatoshi; Miura, Yukitoshi; et al.

Fusion Science and Technology, 49(2), p.209 - 224, 2006/02

 Times Cited Count:3 Percentile:73.3(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas

Kamiya, Kensaku; Kawashima, Hisato; Ido, Takeshi*; Oyama, Naoyuki; Bakhtiari, M.*; Kasai, Satoshi; Kusama, Yoshinori; Miura, Yukitoshi; Ogawa, Hiroaki; Tsuzuki, Kazuhiro; et al.

Nuclear Fusion, 46(2), p.272 - 276, 2006/02

 Times Cited Count:3 Percentile:87.79(Physics, Fluids & Plasmas)

An attractive operational regime without any large ELMs, namely High Recycling Steady (HRS) H-mode, was found on JFT-2M during Y2000 campaign after boronization. Recent experiments have concentrated on the studies of the access conditions for the HRS regime, in terms of the pedestal parameters. The HRS regime was more likely at higher edge density and lower edge temperature, which corresponds to the normalized electron collisionality of 1 in the plasma edge region.

JAEA Reports

The Development of the boroncoating device for the JFT-2M

Yamamoto, Masahiro*; Okano, Fuminori; Tsuzuki, Kazuhiro; Ogawa, Hiroaki; Suzuki, Sadaaki; Shibata, Takatoshi

JAERI-Tech 2005-061, 11 Pages, 2005/09

JAERI-Tech-2005-061.pdf:0.94MB

Ferritic steel plates were installed in the JFT-2M vacuum vessel to conduct "the Advanced Material Tokamak Experiments (AMTEX)". A coating device with tri-methyl-bron(TMB)was developed to coat the ferritic steel surface with boron, since the ferritic steel is easy to rust and also has a property to absorb much impurity in the surface. The TMB gas used in the device was diluted with helium gas to 1% for ensuring workers themselves against the toxicity of the TMB. The uniformity and stability of the coated layer have been confirmed through sample tests with a microscope, whose samples had been set in the tokamak vacuum vessel. The coating thickness measured with X-ray photoelectron emission spectroscopy was roughly 130nm. In the plasma experiments after the boron coating, radiation loss in the plasma decreased to 1/3, and oxygen impurity also decreased to 1/10 compared to without the boron coating.

JAEA Reports

Development of the device for 3D-measurement of the magnetic field profile in the toroidal direction

Yamamoto, Masahiro*; Tsuzuki, Kazuhiro; Kimura, Haruyuki; Sato, Masayasu; Shibata, Takatoshi; Okano, Fuminori; Suzuki, Sadaaki

JAERI-Tech 2005-060, 16 Pages, 2005/09

JAERI-Tech-2005-060.pdf:2.83MB

The low activation ferritic steel is one of the candidate for structural material of a demo-reactor. However, it was afraid that the plasma confinement and stability might degrade due to the error field by the ferromagnetic property of the ferritic material. So, on JFT-2M tokamak Advanced Material Tokamak EXperiment program (AMTEX) has been carried out to investigate about the conformity with the plasma and ferritic steel. AMTEX was performed by introducing low activation ferritic plates (FPs) step by step. At the third stage, the FPs were installed to cover almost whole inside wall (FIW) of the vacuum vessel (VV) as a simulation of the blanket wall.In this experiment the accurate measurement of the distribution of the magnetic fields strength was required before and after the installation of the FIW.Therefore, the device for 3D-measurement of the magnetic field profile along the toroidal direction was developed.

JAEA Reports

Annual report of Naka Fusion Research Establishment from April 1, 2004 to March 31, 2005

Naka Fusion Research Establishment

JAERI-Review 2005-046, 113 Pages, 2005/09

JAERI-Review-2005-046.pdf:24.35MB

This annual report provides an overview of research and development activities at Naka Fusion Research Establishment, including those performed in collaboration with other research establishments of JAERI, research institutes, and universities, during the period from 1 April, 2004 to 31 March, 2005. The activities in the Naka Fusion Research Establishment are highlighted by researches in JT-60 and JFT-2M, theoretical and analytical plasma researches, research and development of fusion reactor technologies towards ITER and fusion power demonstration plants, and activities in support of ITER design and construction.

Journal Articles

Observation of nonlinear coupling between small-poloidal wave-number potential fluctuations and turbulent potential fluctuations in Ohmically heated plasmas in the JFT-2M tokamak

Nagashima, Yoshihiko*; Hoshino, Katsumichi; Ejiri, Akira*; Shinohara, Koji; Takase, Yuichi*; Tsuzuki, Kazuhiro; Uehara, Kazuya; Kawashima, Hisato; Ogawa, Hiroaki; Ido, Takeshi*; et al.

Physical Review Letters, 95(9), p.095002_1 - 095002_4, 2005/08

 Times Cited Count:95 Percentile:6.75(Physics, Multidisciplinary)

By a reciprocating electrostatic probe, two types of low frequency coherent electrostatic modes (about1kHz and 10-15kHz) are found,for the first time, in the edge region of ohmically heated plasmas in the JFT-2M tokamak. These modes exists in the last closed surface. The higher frequency mode has features of the geodesic acoustic mode (GAM), though the low frequency mode is not identified yet. A bispectral analysis revealed that significant nonlinear couplings (parametric modulation) between these coherent fluctuations and broadband background turbulent potential fluctuations occur. In the other words, the GAM and the back ground turbulence are modulated by the newly found low frequency electrostatic mode (further, the GAM modulates the background turbulence, also) for the first time. The newly found low frequency mode (frequency about 1kHz) is supposed to contribute to the turbulent diffusion nonlinearly.

Journal Articles

Recent technological progress for advanced tokamak research in JT-60U and JFT-2M

Hosogane, Nobuyuki; JT-60 Team; JFT-2M Group

Fusion Science and Technology, 47(3), p.363 - 369, 2005/04

 Times Cited Count:3 Percentile:73.42(Nuclear Science & Technology)

no abstracts in English

211 (Records 1-20 displayed on this page)