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Journal Articles

Pedestal conditions for small ELM regimes in tokamaks

Oyama, Naoyuki; Gohil, P.*; Horton, L. D.*; Hubbard, A. E.*; Hughes, J. W.*; Kamada, Yutaka; Kamiya, Kensaku; Leonard, A. W.*; Loarte, A.*; Maingi, R.*; et al.

Plasma Physics and Controlled Fusion, 48(5A), p.A171 - A181, 2006/05

 Times Cited Count:65 Percentile:90.57(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

The Roles of plasma rotation and toroidal field ripple on the H-mode pedestal structure in JT-60U

Urano, Hajime; Kamiya, Kensaku; Koide, Yoshihiko; Takizuka, Tomonori; Oyama, Naoyuki; Kamada, Yutaka; JT-60 Team

Plasma Physics and Controlled Fusion, 48(5A), p.A193 - A199, 2006/05

 Times Cited Count:10 Percentile:36.35(Physics, Fluids & Plasmas)

The characteristics of the H-mode pedestal structure were investigated by conducting the power scans for a variation of the toroidal momentum sources at different toroidal field ripple in JT-60U. It was found that the pedestal pressure is increased by reduced loss power of fast ions, independently of toroidal rotation. However, the energy confinement is improved with the CO-directed toroidal momentum source at H-mode plasmas with small ripple loss.

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:49.06(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

Small ELM regimes with good confinement on JET and comparison to those on ASDEX Upgrade, Alcator C-mod and JT-60U

Stober, J.*; Lomas, P. J.*; Saibene, G.*; Andrew, Y.*; Belo, P.*; Conway, G. D.*; Herrmann, A.*; Horton, L. D.*; Kempenaars, M.*; Koslowski, H.-R.*; et al.

Nuclear Fusion, 45(11), p.1213 - 1223, 2005/11

 Times Cited Count:31 Percentile:71.09(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Energy loss for grassy ELMs and effects of plasma rotation on the ELM characteristics in JT-60U

Oyama, Naoyuki; Sakamoto, Yoshiteru; Isayama, Akihiko; Takechi, Manabu; Gohil, P.*; Lao, L. L.*; Snyder, P. B.*; Fujita, Takaaki; Ide, Shunsuke; Kamada, Yutaka; et al.

Nuclear Fusion, 45(8), p.871 - 881, 2005/08

 Times Cited Count:107 Percentile:95.66(Physics, Fluids & Plasmas)

The grassy ELM is characterized by the high frequency periodic collapse up to $$sim$$kHz, which is $$sim$$15 times faster than that for type I ELM. A divertor peak heat flux due to grassy ELMs is less than 10% of that for type I ELMs. This smaller heat flux is caused by narrower radial extent of the collapse of temperature pedestal. The different radial extent between type I ELMs and grassy ELMs qualitatively agrees with the different radial distribution of the eigen function of the ideal MHD stability analysis. The ratio of ELM energy loss for grassy ELMs to the pedestal stored energy was 0.4-1%. In high triangularity regime, ELM amplitude, frequency and type can be changed from type I ELM to high frequency grassy ELM as counter plasma rotation was increased. In low triangularity regime, on the other hand, the complete ELM suppression (QH-mode) has been achieved, when the plasma position is optimized with CTR-NBIs. The existence of the edge fluctuations localized in pedestal region may reduce the pedestal pressure, and therefore the QH-mode can be sustained for long time up to 3.4s.

Journal Articles

Pedestal characteristics in JFT-2M HRS H-mode plasma

Kamiya, Kensaku; Oyama, Naoyuki; Miura, Yukitoshi; Hubbard, A. E.*

Plasma Physics and Controlled Fusion, 46(11), p.1745 - 1755, 2004/11

 Times Cited Count:13 Percentile:42.46(Physics, Fluids & Plasmas)

Recent experiments in the JFT-2M tokamak have concentrated on the studies of the access condition for the H-mode operation without any large ELMs, namely High Recycling Steady (HRS) H-mode regime in terms of the pedestal parameters. The HRS regime is more likely at the higher edge density and lower edge temperature, while the ELMy H-mode having large ELMs appears at the lower edge density and higher edge temperature. It is found that the ELMy/HRS operational boundary occurs at the normalized electron collisionality of $$nu$$*$$_{e}$$$$sim$$1 in the plasma edge region, depending slightly on q$$_{95}$$. A key feature of the HRS H-mode is the presence of the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz. It is suggested that the edge MHD activities may keep an edge pressure below a certain level needed to induce a large ELM.

Journal Articles

Fast dynamics of type I ELMs and transport of the ELM pulse in JT-60U

Oyama, Naoyuki; Asakura, Nobuyuki; Chankin, A. V.; Oikawa, Toshihiro; Sugihara, Masayoshi; Takenaga, Hidenobu; Itami, Kiyoshi; Miura, Yukitoshi; Kamada, Yutaka; Shinohara, Koji; et al.

Nuclear Fusion, 44(5), p.582 - 592, 2004/05

 Times Cited Count:45 Percentile:81.82(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

High recycling steady H-mode regime in the JFT-2M Tokamak

Kamiya, Kensaku; Bakhtiari, M.; Kasai, Satoshi; Kawashima, Hisato; Kusama, Yoshinori; Miura, Yukitoshi; Ogawa, Hiroaki; Oyama, Naoyuki; Sato, Masayasu; Shinohara, Koji; et al.

Plasma Physics and Controlled Fusion, 46(5A), p.A157 - A163, 2004/05

 Times Cited Count:21 Percentile:59.14(Physics, Fluids & Plasmas)

A new operating regime, High Recycling Steady (HRS) H-mode regime, has been discovered on JFT-2M, which is easily reproduced under the wall fueling from the boronized first wall. Accompanying the HRS H-mode transition, the coherent magnetic and floating potential fluctuations are seen on magnetic probes at vessel wall and Langmuir probe in SOL, respectively. These coherent fluctuations have a frequency of the order of 10-100 kHz with significant variation, which is recognized to be important to enhance the particle transport. The HRS can be seen even at ${it q}$$$_{95}$$$$<$$3 with ${it n}$$$_{e}$$/${it n}$$$_{GW}$$$$>$$0.4 for the fixed delta$$sim$$0.4 in the standard single-null divertor configuration. Recent experimental results from JFT-2M show that the plasma shape also seems to play an important role in determining the type of ELMs. The HRS regime can be extended up to delta$$sim$$0.75 and ${it q}$$$_{95}$$$$sim$$2.6 in the double-null configuration, while lower delta boundary exists at delta$$sim$$0.3 with moderate ${it q}$$$_{95}$$$$sim$$4 even at high recycling and/or density condition of ${it n}$$$_{e}$$/${it n}$$$_{GW}$$$$>$$0.4.

Journal Articles

Overview of physics basis for ITER

Mukhovatov, V.*; Shimada, Michiya; Chudnovskiy, A. N.*; Costley, A. E.*; Gribov, Y.*; Federici, G.*; Kardaun, O. J. F.*; Kukushkin, A. S.*; Polevoi, A. R.*; Pustovitov, V. D.*; et al.

Plasma Physics and Controlled Fusion, 45(12), p.235 - 252, 2003/12

 Times Cited Count:46 Percentile:80.66(Physics, Fluids & Plasmas)

ITER will be the first magnetic confinement device with burning DT plasma and fusion power of about 0.5 GW. During the past few years, new results have been obtained that substantiate the confidence in achieving Q $$>$$ 10 in ITER with inductive H-mode operation. These include achievement of a good H-mode confinement near the Greenwald density at high triangularity of the plasma cross section; improvements in theory-based confinement projections for the core plasma; improvement in helium ash removal due to the elastic collisions of He atoms with D/T ions in the divertor predicted by modelling; demonstration of feedback control of NTMs and resultant improvement in the achievable beta-values; better understanding of ELM physics and development of ELM mitigation techniques; and demonstration of mitigation of plasma disruptions. ITER will have a flexibility to operate also in steady state and intermediate (hybrid) regimes. The paper concentrates on inductively driven plasma performance and discusses requirements for steady-state operation in ITER.

Journal Articles

Edge localized mode physics and operational aspects in tokamaks

B$'e$coulet, M.*; Huysmans, G.*; Sarazin, Y.*; Garbet, X.*; Ghendrih, P.*; Rimini, F.*; Joffrin, E.*; Litaudon, X.*; Monier-Garbet, P.*; An$'e$, J.-M.*; et al.

Plasma Physics and Controlled Fusion, 45(12A), p.A93 - A113, 2003/12

 Times Cited Count:83 Percentile:92.45(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Asymmetry of collapse of density pedestal by type I ELM on JT-60U

Oyama, Naoyuki; Miura, Yukitoshi; Chankin, A. V.; Takenaga, Hidenobu; Asakura, Nobuyuki; Kamada, Yutaka; Oikawa, Toshihiro; Shinohara, Koji; Takeji, Satoru

Nuclear Fusion, 43(10), p.1250 - 1257, 2003/10

 Times Cited Count:16 Percentile:48.5(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Scaling of H-mode edge pedestal pressure for a Type-I ELM regime in tokamaks

Sugihara, Masayoshi; Mukhovatov, V.*; Polevoi, A.*; Shimada, Michiya

Plasma Physics and Controlled Fusion, 45(9), p.L55 - L62, 2003/09

 Times Cited Count:37 Percentile:74.04(Physics, Fluids & Plasmas)

Improvement of the scaling of H-mode edge pedestal pressure for a Type-I ELM regime based on a simple analytical formula is achieved by introducing shaping factors into the scaling. The physics basis of these shaping factors is an enhancement of the critical pressure gradient by the magnetic well. With increasing the magnetic well, a high toroidal mode number ideal ballooning mode and peeling mode decouple and critical gradient is determined by intermediate mode number, which results in significant enhancement of the critical pressure gradient. The improved scaling can reproduce the pedestal pressure reasonably well for ASDEX-U, JET, DIII-D and JT-60U Type-I ELmy data archived in the ITER pedestal database.

Journal Articles

Control of divertor heat load by Ar injection with keeping high performance in ELMy H-mode plasmas on JT-60U

Higashijima, Satoru; Asakura, Nobuyuki; Kubo, Hirotaka; Miura, Yukitoshi; Nakano, Tomohide; Konoshima, Shigeru; Itami, Kiyoshi; Sakurai, Shinji; Takenaga, Hidenobu; Tamai, Hiroshi; et al.

Journal of Nuclear Materials, 313-316, p.1123 - 1130, 2003/03

 Times Cited Count:15 Percentile:71.03(Materials Science, Multidisciplinary)

Reduction of steady-state heat load in the divertor and transient one by ELMs is a crucial issue for tokamak fusion devices. High radiation loss power is necessary for the heat load reduction, and the conventional gas puffing can increase the density and the radiation loss power, but it degrades the confinement. Core plasma with high confinement should be maintained simultaneously. Impurity seeding is a secure way to enhance the radiation loss power. In JT-60U, heat load is successfully reduced by Ar injection with keeping a high confinement in ELMy H-mode plasmas. In this paper, heat load reduction, radiation enhancement, and change of ELM activity are discussed.

Journal Articles

Overview of JT-60U results toward high integrated performance in reactor-relevant regime

Hatae, Takaki; JT-60 Team

Proceedings of 6th Japan-Australia Workshop on Plasma Diagnostics (CD-ROM), 13 Pages, 2002/00

The main purpose of JT-60U project is to make contribution to establishment of scientific basis of ITER and the demo tokamak reactor. Our ultimate goal is to achieve and sustain high integrated performance, namely high beta, high confinement, high bootstrap current fraction, full non-inductive current drive and heat/particle control, in a reactor-relevant regime. Toward this goal, we have developed weak magnetic shear ("high $$beta_{p}$$ mode") and reversed magnetic shear plasmas. In both regimes, the internal transport barrier (ITB) and the edge pedestal are obtained simultaneously. As a large-sized tokamak equipped with a variety of devices for heating, current drive and profile control, JT-60U has high ability to approach the conditions required in reactors (ITER or demo): low values of normalized Larmor radius and collisionality, high toroidal field, high temperature with Te$$>sim$$Ti, small central fueling, small ELM activities, etc. This paper reviews recent JT-60U results with the emphasis on the projection to the reactor-relevant regime.

Journal Articles

Comparison of edge pedestal parameters for JT-60U and DIII-D H-mode plasmas

Hatae, Takaki; Osborne, T. H.*; Kamada, Yutaka; Groebner, R. J.*; Takizuka, Tomonori; Fukuda, Takeshi; Lao, L. L.*

Plasma Physics and Controlled Fusion, 42(suppl.5A), p.A283 - A288, 2000/05

 Times Cited Count:8 Percentile:27.98(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

ITER Physics R&D Expert Group report

Wakatani, Masahiro*; Fukuda, Takeshi; Toi, Kazuo*; Takizuka, Tomonori; Miura, Yukitoshi; Ogawa, Yuichi*; Kamada, Yutaka; Oyabu, Nobuyoshi*; Hatae, Takaki

Purazuma, Kaku Yugo Gakkai-Shi, 76(2), p.175 - 177, 2000/02

no abstracts in English

Journal Articles

The Difference in H-mode confinement between co- and co+counter-neutral beam heating in the JFT-2M tokamak

Miura, Yukitoshi; *; Suzuki, Norio; *

Plasma Physics and Controlled Fusion, 40(5), p.799 - 803, 1998/05

 Times Cited Count:9 Percentile:33.14(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Characteristics of edge pedestal width in JT-60U ELM-free H-mode plasmas

Hatae, Takaki; Kamada, Yutaka; Ishida, Shinichi; Fukuda, Takeshi; Takizuka, Tomonori; Shirai, Hiroshi; Koide, Yoshihiko; Kikuchi, Mitsuru; Yoshida, Hidetoshi; Naito, Osamu

Plasma Physics and Controlled Fusion, 40(6), p.1073 - 1083, 1998/00

 Times Cited Count:40 Percentile:77.43(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Strain profile of plastic zone in dislocation-free niobium single crystal determined by X-ray topography


Japanese Journal of Applied Physics, 17(11), p.1915 - 1923, 1978/00

 Times Cited Count:2

no abstracts in English

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