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Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; Tachi, Yukio; Fukatsu, Yuta; Hamamoto, Shoichiro*; Siitari-Kauppi, M.*; Li, X.*
Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03
Times Cited Count：0 Percentile：0(Engineering, Civil)
(Copepoda) from a deep sediment-trap; Abundance and implications for ecological and biogeochemical studiesIkenoue, Takahito*; Otosaka, Shigeyoshi*; Honda, Makio*; Kitamura, Minoru*; Mino, Yoshihisa*; Narita, Hisashi*; Kobayashi, Takuya
Frontiers in Marine Science (Internet), 9, p.884320_1 - 884320_11, 2022/05
Times Cited Count：0 Percentile：0.01(Environmental Sciences)We studied seasonal variations of the mesozooplankton swimmer community collected by a sediment trap moored at 873 m in the Kuroshio & Oyashio Transition region off the east coast of Japan from 5 August 2011 to 23 June 2013. The total flux of mesozooplankton swimmers varied between 0 and 11.1 individuals m-2 d-1, with a mean of 3.1 individuals m-2 d-1 during the sampling period. Among the Copepoda, Neocalanus cristatus was the most dominant taxon. The species composition of the swimmers closely reflected the mid-depth mesozooplankton of the Oyashio region. The fluxes of Neocalanus species reflected ontogenetic vertical migration, but may have been overestimates of active fluxes if they included dormant individuals that accidentally entered the sediment trap.
Watanabe, Tadashi*; Katsuyama, Jinya; Mano, Akihiro
International Journal of Nuclear and Quantum Engineering (Internet), 13(11), p.516 - 519, 2019/10
The estimation of leak flow rates through narrow cracks in structures is of importance for nuclear reactor safety, since the leak flow could be detected before occurrence of loss-of-coolant accidents. The two-phase critical leak flow rates are calculated using the system analysis code, and two representative non-homogeneous critical flow models, Henry-Fauske model and Ransom-Trapp model, are compared. The pressure decrease and vapor generation in the crack, and the leak flow rates are found to be larger for the Henry-Fauske model. It is shown that the leak flow rates are not affected by the structural temperature, but affected largely by the roughness of crack surface.
Sakaki, Toshihiro*; Komatsu, Mitsuru*; Takeuchi, Ryuji
Vadose Zone Journal (Internet), 15(8), 7 Pages, 2016/08
Times Cited Count：2 Percentile：9.76(Environmental Sciences)In the Groundwater Recovery Experiment in Tunnel which is underway at the MIU, water saturation is one of the key parameters to monitor in order to understand the recovery processes. In this study, the process of saturation increase in the quasi-saturated zone where trapped discrete air phase affects saturation due to further increase in water pressure was studied. The relationship between the positive water pressure and saturation was measured by laboratory test using sands with trapped air bubbles and the effect of compression of bubbles on the changes in saturation was analyzed. The experimental results showed that the water pressure-saturation curves closely followed the relationship estimated solely based on the air bubble compression using Boyle's law. Based on this observation, a mathematical model was established to define the water pressure - saturation curve for the region where the water pressure is positive.
Idomura, Yasuhiro
Plasma and Fusion Research (Internet), 11, p.2403006_1 - 2403006_5, 2016/02
In this work, we address saturation mechanisms of decaying turbulence induced by the ion temperature gradient driven trapped electron mode. In the simulation, turbulent transport is quenched in the nonlinear quasi-steady phase, where temperature profiles exceeding linear critical temperature gradient parameters are formed. This kind of nonlinear critical temperature gradient is sustained by radial electric fields with strong shear, which is generated by corrugated density profiles. It is found that the density profile structure is related to electrons transport near low order mode rational surfaces, where non-adiabatic response of passing electrons becomes important.
Ide, Shunsuke; JT-60 Team
Nuclear Fusion, 45(10), p.S48 - S62, 2005/10
Times Cited Count：53 Percentile：83.22(Physics, Fluids & Plasmas)no abstracts in English
Ikeda, Yoshitaka; Oikawa, Toshihiro; Ide, Shunsuke
Purazuma, Kaku Yugo Gakkai-Shi, 81(10), p.773 - 778, 2005/10
In steady-state tokamak fusion reactors, an efficient external current drive and a large fraction of the bootstrap current are required for non-inductive operation at low circulating power. NBI is a powerful and reliable actuator for current drive and heating. A negative ion-based NBI (N-NBI) with a high beam energy more than 350 keV has been installed in the JT-60U tokamak in order to study the NBI current drive and heating in an ITER relevant regime. This paper presents recent progress of N-NBI experiments and its system in JT-60U towards steady-state operation for ITER and tokamak fusion reactors.
Oikawa, Toshihiro; Suzuki, Takahiro; Isayama, Akihiko; Hayashi, Nobuhiko; Fujita, Takaaki; Naito, Osamu; Tsuda, Takashi; Kurita, Genichi; JT-60 Team
Nuclear Fusion, 45(9), p.1101 - 1108, 2005/09
Times Cited Count：4 Percentile：14.23(Physics, Fluids & Plasmas)Evolution of the current density profile associated with magnetic island formation in a neoclassical tearing mode plasma was measured for the first time in JT-60U by. As the island grew, the current density profile turned flat at the radial region of the island, followed by an appearance of a hollow structure. As the island shrank, the deformed region became narrower, and it finally diminished after the disappearance of the island. In an MHD-quiescent plasma, on the other hand, no deformation was observed. The observed deformation in the current density profile associated with the tearing mode is reproduced in a time dependent transport simulation assuming reduction of the bootstrap current in the radial region of the island. Comparison of the measurement with a calculated steady-state solution also explains the temporal behaviors of the current density and safety factor profiles with reduction and recovery of the bootstrap current. From the experimental observation and simulations, we reach conclusion that the bootstrap current decreases within the island O-point.
Hayashi, Nobuhiko; Takizuka, Tomonori; Ozeki, Takahisa
Nuclear Fusion, 45(8), p.933 - 941, 2005/08
Times Cited Count：13 Percentile：41.32(Physics, Fluids & Plasmas)We have investigated profile formation and sustainment of current hole (CH) plasma by 1.5D transport simulations with current limit model inside CH based on Axisymmetric Tri-Magnetic-Islands equilibrium. Sharp reduction of anomalous transport in RS region can reproduce JT-60U experiments. The transport becomes neoclassical-level in RS region, which results in autonomous profile formation of ITB and CH through large bootstrap current. ITB width determined by neoclassical-level transport agrees with that in JT-60U. Energy confinement inside ITB agrees with JT-60U scaling. The scaling means that core plasma inside ITB is governed by MHD equilibrium limit, i.e., autonomous limitation of energy confinement. The plasma with large CH is sustained with full current drive by bootstrap current. The plasma with small CH and small bootstrap current fraction shrinks due to penetration of inductive current. This shrink is prevented and CH size can be controlled by appropriate external CD. CH plasma is found to respond autonomically to external CD. Application of CH plasma to reactor is discussed.
Kishimoto, Hiroshi; Ishida, Shinichi; Kikuchi, Mitsuru; Ninomiya, Hiromasa
Nuclear Fusion, 45(8), p.986 - 1023, 2005/08
Times Cited Count：40 Percentile：28.81(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-
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-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.
simulations of microturbulenceIdomura, Yasuhiro
Purazuma, Kaku Yugo Gakkai-Shi, 81(8), p.581 - 592, 2005/08
A gyrokinetic particle simulation is a powerful tool in studying tokamak microturbulence. A method, which is a standard method in recent gyrokinetic particle simulations, dramatically improved an efficiency of a particle simulation by reducing a particle noise, and full torus turbulence simulations are enabled. In this paper, the method is reviewed, and issues in full torus gyrokinetic particle simulations are discussed.
Matsunami, Noriaki*; Fukuoka, Osamu*; Shimura, Tetsuo*; Sataka, Masao; Okayasu, Satoru
Nuclear Instruments and Methods in Physics Research B, 230(1-4), p.507 - 511, 2005/04
Times Cited Count：14 Percentile：67.9(Instruments & Instrumentation)no abstracts in English
Oikawa, Toshihiro; Isayama, Akihiko; Fujita, Takaaki; Suzuki, Takahiro; Tsuda, Takashi; Kurita, Genichi
Physical Review Letters, 94(12), p.125003_1 - 125003_4, 2005/04
Times Cited Count：10 Percentile：53.4(Physics, Multidisciplinary)Evolution of the current density profile associated with the magnetic island formation during a tearing mode was measured for the first time in the JT-60U tokamak. With the island growth, the current density profile turned flat at the radial region of the island, followed by appearance of a hollow structure. As the island shrank, the flat region became narrower, and it finally diminished after disappearance of the island. It was also observed that the local poloidal magnetic field fluctuated in correlation with the island rotation. This indicates that the observed deformation in the current density profile is localized in the O-point of the island. The result is the first experimental demonstration of theoretical predictions on the current density evolution in tearing modes.
100
systemsFujieda, Shinji*; Miura, Yoshinao*; Saito, Motofumi*; Teraoka, Yuden; Yoshigoe, Akitaka
Microelectronics Reliability, 45(1), p.57 - 64, 2005/01
Times Cited Count：11 Percentile：51.31(Engineering, Electrical & Electronic)To characterize the interface defects that are responsible for the negative-bias temperature instability (NBTI) of a thin plasma-nitrided SiON/Si system, we carried out inerface trap density measurements, electron-spin resonance spectroscopy and synchrotron radiation XPS. The NBTI was shown to occur mainly through the dehydrogenation of the interfacial Si dangling bonds (P
defects). Although we suggest that non- P defects are also generated by the negative-bias temperature stress, nitrogen dangling bonds do not seem to be included. The plasma-nitridation process was confirmed to generate sub-oxides at the interface and thus increase the interface trap density. Furthermore, it was found that the nitridation induces another type of P
defect than that at pure-SiO
/Si interfacec. Such an increase and structural change of the interfacial defects are likely the causes of the nitridation-enhanced NBTI.
Hayashi, Nobuhiko; Takizuka, Tomonori; Ozeki, Takahisa
Proceedings of 20th IAEA Fusion Energy Conference (FEC 2004) (CD-ROM), 8 Pages, 2004/11
Profile formation and sustainment of tokamak plasmas with current hole (CH) have been investigated by using 1.5D transport simulations. A current limit model inside CH based on the Axisymmetric Tri-Magnetic-Islands equilibrium is introduced. We found that the sharp reduction of anomalous transport in the reversed-shear (RS) region can reproduce JT-60U experiment. The transport becomes neoclassical-level in RS region, which results in the autonomous formation of internal transport barrier (ITB) and CH through large bootstrap current. ITB width determined by neoclassical-level transport agrees with that in JT-60U. Energy confinement inside ITB agrees with JT-60U scaling, which means autonomous limitation of energy confinement. The plasma with large CH is sustained with the full current drive by bootstrap current. The plasma with small CH and small bootstrap current fraction shrinks due to inductive current penetration. This shrink is prevented and the CH size can be controlled by appropriate external current drive (CD). The CH plasma is found to respond autonomically to external CD.
Sengoku, Seio
Purazuma, Kaku Yugo Gakkai-Shi, 80(11), p.940 - 943, 2004/11
Recent spherical tokamak (ST) experiments exhibit many advantageous results including plasma start-up without center solenoid, higher fraction of non-inductive current, formation of internal thermal-barrier as seen on conventional tokamak. In order to reflect these efforts on the design of so called "non-inductive steady-state (SS) operation scenario" and "current ramp-up scenario" of low-aspect reactor, fractions of bootstrap current and neutral-beam-driven current on VECTOR-OPT reactor are estimated. The operation with this SS scenario is shown to be feasible if the normalized beta, n, is raised to grater than 5 typical in ST.
Nakamura, Hiroo; Riccardi, B.*; Loginov, N.*; Ara, Kuniaki*; Burgazzi, L.*; Cevolani, S.*; Dell'Ocro, G.*; Fazio, C.*; Giusti, D.*; Horiike, Hiroshi*; et al.
Journal of Nuclear Materials, 329-333(1), p.202 - 207, 2004/08
Times Cited Count：14 Percentile：66.01(Materials Science, Multidisciplinary)International Fusion Materials Irradiation Facility (IFMIF), being developed by EU, JA, RF and US, is a deuteron-lithium (Li) reaction neutron source for fusion materials testing. In the end of 2002, 3 year Key Element technology Phase (KEP) to reduce the key technology risk factors has been completed. This paper describes these KEP tasks results. To evaluate Li flow characteristics, a water and Li flow experiments have been done. To develop Li purification system, evaluation of nitrogen and tritium gettering materials have been done. Conceptual design of remote handling and basic experiment have been donde. In addition, safety analysis and diganostics design have been done. In the presentation, the latest design and future prospects will be also summarized.
Tamai, Hiroshi; Ishida, Shinichi; Kurita, Genichi; Shirai, Hiroshi; Tsuchiya, Katsuhiko; Sakurai, Shinji; Matsukawa, Makoto; Sakasai, Akira
Fusion Science and Technology, 45(4), p.521 - 528, 2004/06
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)The 1.5D time-dependent transport analysis has been carried out to investigate steady state operation scenarios with a central current hole by off-axis current drive schemes consistent with a high bootstrap current fraction for a large superconducting tokamak JT-60SC. A steady state operation scenario with HH
=1.4 and 
=3.7 has been obtained at I
=1.5 MA, B
=2 T and q
=5 where non-inductive currents are developed during the discharge to form a current hole with beam driven currents by tangential off-axis beams in combination with bootstrap currents by additional on-axis perpendicular beams. The bootstrap fraction increases up to nearly 75% of the plasma current and the current hole region is enlarged up to about 30% of the minor radius at 35 s from the discharge initiation. The current hole is confirmed to be sustained afterward for a long duration of 60 s. The stability analysis shows that the beta limit with the conducting wall can be about =4.5, which is substantially above the no wall ideal MHD limit.
Tamai, Hiroshi; Kurita, Genichi; Matsukawa, Makoto; Urata, Kazuhiro*; Sakurai, Shinji; Tsuchiya, Katsuhiko; Morioka, Atsuhiko; Miura, Yushi; Kizu, Kaname; Kamada, Yutaka; et al.
Plasma Science and Technology, 6(3), p.2281 - 2285, 2004/06
Times Cited Count：0 Percentile：0.02(Physics, Fluids & Plasmas)High performance steady-state operation for JT-60SC are evaluated by the TOPICS analysis. 
5 and bootstrap current fraction 86% is kept steady at I
=1.5 MA, B
=2 T by neutral beam power of 11 MW. The ERATO-J analysis shows that the external-kink mode with multiple toroidal mode numbers of n=1 and n=2 is stable at 
5.5 at the average ratio of conducting wall radius to plasma minor radius of about 1.2 with the wall stabilisation effect. Resistive wall modes, induced by a close location of the wall to plasma, is expected to be suppressed by the active feedback stabilisation with a set of non-axisymmetric field coils behind the stabilising plates. Further optimisation for the high- accessibility by the plasma shaping is performed with the TOSCA analysis. The plasma shaping factor defined as S=(I/aB)q
and strongly correlated to the plasma elongation and triangularity, is scanned from 4 to 6, which extends the availability of current and pressure profile control for the high performance plasma operation.
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
Journal of Plasma and Fusion Research SERIES, Vol.6, p.17 - 72, 2004/00
A global gyrokinetic toroidal particle code for a 3D nonlinear simulation (GT3D) has been developed for a comprehensive study of the ion and electron anomalous transport arising from the ion temperature gradient driven - trapped electron mode (ITG-TEM) turbulence in tokamak plasmas. In the preliminary linear ITG-TEM calculations, basic properties of ITG-TEM modes are confirmed. Adding trapped electrons not only increases the growth rate of the ITG mode, but also produces another unstable electron mode, the TEM mode, which is unstable even at 
. The dominant mode changes from the ITG mode to the TEM mode depending on 
and 
. In linear benchmark calculations using Cyclone base case parameters, eigenfrequencies obtained from GT3D, GTC(PPPL-UCI) and FULL(PPPL) show reasonable quantitative agreement.
