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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:15.31(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:27.49(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

Dependence of pedestal structure on collisionality at fixed beta in JT-60U

Urano, Hajime; Aiba, Nobuyuki; Kamiya, Kensaku; Kamada, Yutaka; JT-60 Team

Nuclear Fusion, 56(1), p.016005_1 - 016005_8, 2016/01

 Times Cited Count:3 Percentile:73.33(Physics, Fluids & Plasmas)

Dependence of pedestal structure on collisionality at fixed beta has been investigated in JT-60U. In the ITER-relevant low collisionality regime, the pedestal width does not change with edge collisionality. In the high collisionality regime, the pedestal width broadens with increased edge collisionality. The pedestal pressure gradient and width are not significantly changed when the pedestal is close to an intermediate $$n$$ peeling-ballooning mode boundary at low collisionality. The experimental result indicates that conventional pedestal models where the pedestal width is independent of collisionality and is determined by $$beta_{rm p}$$ at the pedestal is not a bad assumption in the ITER-relevant low collisionality regime. On the other hand, the pressure gradient decreases and the pedestal width increases at high collisionality. The pedestal broadening becomes significant when the pedestal is marginal to be unstable at high $$n$$ ballooning mode in high collisionality regime.

Journal Articles

Integrated modelling of toroidal rotation with the 3D non-local drift-kinetic code and boundary models for JT-60U analyses and predictive simulations

Honda, Mitsuru; Satake, Shinsuke*; Suzuki, Yasuhiro*; Yoshida, Maiko; Hayashi, Nobuhiko; Kamiya, Kensaku; Matsuyama, Akinobu; Shinohara, Koji; Matsunaga, Go; Nakata, Motoki; et al.

Nuclear Fusion, 55(7), p.073033_1 - 073033_11, 2015/07

 Times Cited Count:5 Percentile:64.92(Physics, Fluids & Plasmas)

Journal Articles

On the spatial structure of solitary radial electric field at the plasma edge in toroidal confinement devices

Ito, Kimitaka*; Ito, Sanae*; Kamiya, Kensaku; Kasuya, Naohiro*

Plasma Physics and Controlled Fusion, 57(7), p.075008_1 - 075008_7, 2015/07

 Times Cited Count:18 Percentile:18.78(Physics, Fluids & Plasmas)

The solitary radial electric field in the edge of toroidal plasma is studied based on the electric field bifurcation model. Results are applied to tokamak and helical plasmas, and the dependence of the electric field structure on the plasma parameters and geometrical factors is analyzed. The order of magnitude estimate for tokamak plasma is not far from experimental observations. It is shown that, in helical plasmas, the height of electric field structure is reduced substantially owing to the ripple particle transport, while the width is influenced less. The implications of the results for the limit of achievable gradient in the H-mode pedestal are also discussed.

Journal Articles

Dependence of pedestal structure on collisionality in JT-60U

Urano, Hajime; Aiba, Nobuyuki; Kamiya, Kensaku; Kamada, Yutaka; JT-60 Team

Europhysics Conference Abstracts (Internet), 39E, p.P5.146_1 - P5.146_4, 2015/06

no abstracts in English

Journal Articles

Design study of a wide-angle infrared thermography and visible observation diagnostic on JT-60SA

Kamiya, Kensaku; Itami, Kiyoshi; Takeuchi, Masaki; Enokuchi, Akito*

Fusion Engineering and Design, 89(12), p.3089 - 3094, 2014/12

 Times Cited Count:1 Percentile:88(Nuclear Science & Technology)

Design study of a wide-angle infrared (IR) thermography and visible observation diagnostics for JT-60SA are reported. In order to image a large section inside the vacuum vessel (both in poloidal and toroidal directions), the optical system of endoscope is to provide a wide-angle view in the IR and visible range, which is being designed with a field of view of 106 degrees vertical and 63 degrees horizontal. The estimated spatial resolution is better than a few cm at a distance of 7.6 m from the front optics with a slit diameter of 4 mm.

Journal Articles

Boundary condition for toroidal plasma flow imposed at the separatrix in high confinement JT-60U plasmas with edge localized modes and the physics process in pedestal structure formation

Kamiya, Kensaku; Honda, Mitsuru; Urano, Hajime; Yoshida, Maiko; Kamada, Yutaka; Ito, Kimitaka*; JT-60 Team

Physics of Plasmas, 21(12), p.122517_1 - 122517_8, 2014/12

 Times Cited Count:13 Percentile:33.25(Physics, Fluids & Plasmas)

Modulation Charge eXchange Recombination Spectroscopy (MCXRS) measurements with high spatial and temporal resolution have made the evaluation of the toroidal plasma flow of fully stripped carbon impurity ions in the JT-60U tokamak peripheral region (including in particular separatrix) possible with a better signal-to-noise ratio. Boundary condition of Vt imposed at the separatrix in ELMy H-mode plasmas has been identified, comparing between co- and counter-NBI discharges. The Vt value at the separatrix is not held fixed at the zero, varying with momentum input direction, but being not strongly affected by the ELM event. A non-zero Vt value at the separatrix might be connected to fast ion losses due to toroidal field ripple that results in formation of a negative radial electric field (Er) layer having almost zero (or very weak positive) Er-shear value at the separatrix. Improved understanding of physics process in pedestal structure formation for the Vt and Er is also discussed.

Journal Articles

Integrated modeling of toroidal rotation with the 3D non-local drift-kinetic code and boundary models for JT-60U analyses and predictive simulations

Honda, Mitsuru; Satake, Shinsuke*; Suzuki, Yasuhiro*; Yoshida, Maiko; Hayashi, Nobuhiko; Kamiya, Kensaku; Matsuyama, Akinobu; Shinohara, Koji; Matsunaga, Go; Nakata, Motoki; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

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:17.76(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

Edge radial electric field formation after the L-H transition on JT-60U

Kamiya, Kensaku; Matsunaga, Go; Honda, Mitsuru; Miyato, Naoaki; Urano, Hajime; Kamada, Yutaka; Ida, Katsumi*; Ito, Kimitaka*; JT-60 Team

Contributions to Plasma Physics, 54(4-6), p.591 - 598, 2014/06

 Times Cited Count:6 Percentile:61.05(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Report on ITPA (International Tokamak Physics Activity) meeting, 42

Yoshida, Maiko; Shinohara, Koji; Hayashi, Nobuhiko; Isayama, Akihiko; Kamiya, Kensaku

Purazuma, Kaku Yugo Gakkai-Shi, 89(12), p.887 - 889, 2013/12

ITPA (International Tokamak Physics Activity) meetings were held in Autumn 2013.

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:75 Percentile:5.11(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

Plasma boundary of 3D MHD equilibrium inferred from flow patterns

Ida, Katsumi; Kamiya, Kensaku; Suzuki, Yasuhiro*

Purazuma, Kaku Yugo Gakkai-Shi, 89(5), p.319 - 327, 2013/05

This paper provides and proposes a new technique to determine the location of the LCFS that is based on a characterization of the Er structure derived from CXS measurements in the LHD. We found that the spatial derivative in the Er structure had the local maximum value at the region very near, or possibly outside the vacuum LCFS location of vacuum magnetic field at the outer midplane in the low beta plasma.

Journal Articles

Characterization of edge radial electric field structures in the large helical device and their viability for determining the location of the plasma boundary

Kamiya, Kensaku; Ida, Katsumi*; Yoshinuma, Mikiro*; Suzuki, Chihiro*; Suzuki, Yasuhiro*; Yokoyama, Masayuki*; LHD Experimental Group*

Nuclear Fusion, 53(1), p.013003_1 - 013003_9, 2013/01

 Times Cited Count:15 Percentile:33.17(Physics, Fluids & Plasmas)

This paper provides and proposes a new technique to determine the location of the LCFS that is based on a characterization of the $$E$$$$_{r}$$ structure derived from CXS measurements in the LHD. We found that the spatial derivative in the $$E$$$$_{r}$$ structure had the local maximum value at the region very near, or possibly outside the vacuum LCFS location of vacuum magnetic field at the outer midplane in the low $$beta$$ plasma.

Journal Articles

Modifications to the edge radial electric field by angular momentum injection in JT-60U and their implication for pedestal transport

Kamiya, Kensaku; Honda, Mitsuru; Miyato, Naoaki; Urano, Hajime; Yoshida, Maiko; Sakamoto, Yoshiteru; Matsunaga, Go; Oyama, Naoyuki; Koide, Yoshihiko; Kamada, Yutaka; et al.

Nuclear Fusion, 52(11), p.114010_1 - 114010_12, 2012/10

 Times Cited Count:9 Percentile:55.06(Physics, Fluids & Plasmas)

Depending on the direction of the external tangential momentum input, substantial changes in not only toroidal but also poloidal flows for the carbon impurity ions are observed at around the $$E$$$$_{r}$$-well region. The shear in the edge $$E$$$$_{r}$$ becomes wider in the co-NBI case, while the edge $$E$$$$_{r}$$-well becomes deeper in the counter-NBI case.

Journal Articles

The Unified effect of counter-toroidal rotation and power across separatrix on type-I ELMs in JT-60U

Urano, Hajime; Oyama, Naoyuki; Kamiya, Kensaku; Aiba, Nobuyuki; Kamada, Yutaka; Fujita, Takaaki; JT-60 Team

Nuclear Fusion, 52(10), p.103012_1 - 103012_7, 2012/10

 Times Cited Count:2 Percentile:88.91(Physics, Fluids & Plasmas)

The unified effect of counter toroidal rotation and heating power on type-I ELMs was investigated in JT-60U tokamak. ELM frequency $$f_mathrm{ELM}$$ increased monotonically together with the power across the sepratrix $$P_mathrm{sep}$$ for all the cases of tangential NBs. However, dependence of $$f_mathrm{ELM}$$ on $$P_mathrm{sep}$$ was explicitly stronger than a proportional relation when the perpendicular NBs were injected. The toroidal rotation velocity at the H-mode pedestal $$V$$$$rm_T^{rm PED}$$ shifted continuously in counter direction when the perpendicular NBs were applied. At fixed values of $$V$$$$rm_T^{rm PED}$$, $$f_mathrm{ELM}$$ increased clearly in proportion to $$P_mathrm{sep}$$.

Journal Articles

Reduction of ion thermal diffusivity inside a magnetic island in JT-60U tokamak plasma

Ida, Katsumi*; Kamiya, Kensaku; Isayama, Akihiko; Sakamoto, Yoshiteru; JT-60 Team

Physical Review Letters, 109(6), p.065001_1 - 065001_4, 2012/08

 Times Cited Count:34 Percentile:15.17(Physics, Multidisciplinary)

The transport inside the magnetic island is investigated in the plasma during the transient phase after the back transition from $$H$$-mode to $$L$$-mode, where a sudden drop of temperature outside the magnetic island causes a peaking of ion temperature at the $$O$$-point inside the magnetic island.

Journal Articles

Report on ITPA (International Tokamak Physics Activity) meeting, 36

Oyama, Naoyuki; Shinohara, Koji; Isayama, Akihiko; Yoshida, Maiko; Kamiya, Kensaku

Purazuma, Kaku Yugo Gakkai-Shi, 88(5), p.282 - 285, 2012/05

no abstracts in English

Journal Articles

Observation of energetic particle driven axisymmetric mode in the JT-60U tokamak

Matsunaga, Go; Kamiya, Kensaku; Shinohara, Koji; Miyato, Naoaki; Kojima, Atsushi; Bierwage, A.; JT-60 Team

Europhysics Conference Abstracts (Internet), 36F, p.P2.062_1 - P2.062_4, 2012/00

131 (Records 1-20 displayed on this page)