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Al
GaO
scintillators by gamma-ray-induced positron annihilation lifetime spectroscopyFujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
Times Cited Count：5 Percentile：32.24(Physics, Applied)To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAl
O, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg
ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Urano, Hajime; Nakata, Motoki; Aiba, Nobuyuki; Kubo, Hirotaka; Honda, Mitsuru; Hayashi, Nobuhiko; Yoshida, Maiko; Kamada, Yutaka; JT-60 Team
Nuclear Fusion, 55(3), p.033010_1 - 033010_9, 2015/03
Times Cited Count：41 Percentile：89.24(Physics, Fluids & Plasmas)Physics picture of improving energy confinement with argon seeding at high density has been investigated in JT-60U. Better confinement is sustained at high density by argon seeding accompanied by higher core and pedestal temperatures. Peaked density profiles are kept with argon seeding. Density peaking and dilution effects lower the pedestal density at a given averaged density. The pedestal density in the argon seeded plasmas which is relatively lower than that in a single deuterium puff enables the pedestal temperature to be higher. The density peaking is a key factor of sustaining better confinement in argon seeded H-mode plasmas.
Urano, Hajime; Nakata, Motoki; Aiba, Nobuyuki; Kubo, Hirotaka; Honda, Mitsuru; Yoshida, Maiko; Hayashi, Nobuhiko; Kamada, Yutaka; JT-60 Team
Europhysics Conference Abstracts (Internet), 38F, p.P4.018_1 - P4.018_4, 2014/06
This paper reports the analysis result of heat transport and pedestal structure in H-mode plasmas with and without argon seeding on JT-60U.
Luce, T. C.*; Challis, C. D.*; Ide, Shunsuke; Joffrin, E.*; Kamada, Yutaka; Politzer, P. A.*; Schweinzer, J.*; Sips, A. C. C.*; Stober, J.*; Giruzzi, G.*; et al.
Nuclear Fusion, 54(1), p.013015_1 - 013015_15, 2013/12
Times Cited Count：35 Percentile：83.31(Physics, Fluids & Plasmas)Shibanuma, Kiyoshi; Arai, Takashi; Hasegawa, Koichi; Hoshi, Ryo; Kamiya, Koji; Kawashima, Hisato; Kubo, Hirotaka; Masaki, Kei; Saeki, Hisashi; Sakurai, Shinji; et al.
Fusion Engineering and Design, 88(6-8), p.705 - 710, 2013/10
Times Cited Count：10 Percentile：60.97(Nuclear Science & Technology)Kamada, Yutaka; Barabaschi, P.*; Ishida, Shinichi; Ide, Shunsuke; Lackner, K.*; Fujita, Takaaki; Bolzonella, T.*; Suzuki, Takahiro; Matsunaga, Go; Yoshida, Maiko; et al.
Nuclear Fusion, 51(7), p.073011_1 - 073011_11, 2011/07
Times Cited Count：66 Percentile：92.02(Physics, Fluids & Plasmas)
plasmasMatsunaga, Go; Aiba, Nobuyuki; Shinohara, Koji; Sakamoto, Yoshiteru; Takechi, Manabu; Suzuki, Takahiro; Asakura, Nobuyuki; Isayama, Akihiko; Oyama, Naoyuki; Yoshida, Maiko; et al.
Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03
Kojima, Atsushi; Kamiya, Kensaku; Fujita, Takaaki; Kubo, Hirotaka; Iguchi, Harukazu*; Oyama, Naoyuki; Suzuki, Takahiro; Kamada, Yutaka; JT-60 Team
Plasma and Fusion Research (Internet), 5, p.015_1 - 015_7, 2010/04
A lithium beam probe (LiBP) has been developed for the measurement of electron density profiles with high spatial and temporal resolutions in JT-60U. Using an electron beam heating ion source with a capability of 10 mA extraction, a 5.5 mA beam has been injected to the plasmas. Using the LiBP, time evolutions of pedestal density profiles during type I and grassy edge localized modes (ELMs) have been obtained for the first time. After a type I ELM crash, the drop of the line-integrated density measured by an interferometer delays by 2 ms later than that of the pedestal density. Comparing the line-integrated density to the line integration of the edge density profile measured by the LiBP, it is found that the recovery from the type I ELM crash is correlated with the reduction of core plasma density. Compared with the type I ELM, grassy ELMs have smaller density crashes than that of type I ELMs, which is mainly derived from the narrower ELM affected area.
Yoshida, Maiko; Sakamoto, Yoshiteru; Sueoka, Michiharu; Kawamata, Yoichi; Oyama, Naoyuki; Suzuki, Takahiro; Kamada, Yutaka; JT-60 Team
Fusion Engineering and Design, 84(12), p.2206 - 2213, 2009/12
Times Cited Count：17 Percentile：72.83(Nuclear Science & Technology)A fast charge exchange recombination spectroscopy (CXRS) system has been developed for the real-time measurement and feedback control of ion temperature (
) profile and toroidal rotation velocity (
) in JT-60U. In order to control and in real-time, the charge exchange recombination spectroscopy with high time resolution, the real-time processor system, and the real-time control system have been developed. Utilizing this system, real-time control of the gradient has been demonstrated with neutral beams at high beta plasmas. The strength of the internal transport barrier is controlled. Moreover, the real-time control of has been demonstrated from counter (anti parallel to the plasma current, 
) to co (parallel to the ) direction.
Kojima, Atsushi; Oyama, Naoyuki; Sakamoto, Yoshiteru; Kamada, Yutaka; Urano, Hajime; Kamiya, Kensaku; Fujita, Takaaki; Kubo, Hirotaka; Aiba, Nobuyuki; JT-60 Team
Nuclear Fusion, 49(11), p.115008_1 - 115008_8, 2009/11
Times Cited Count：21 Percentile：61.58(Physics, Fluids & Plasmas)In order to understand the physics of the ELM trigger and determining the ELM size, the fast ELM dynamics of type I and grassy ELMs have been studied in JT-60U, using new fast diagnostics with high spatial and temporal resolutions. The evolution of the ion pressure profile in the pedestal region is evaluated for the first time by detailed edge profile measurements. Type I ELMs observed in co-rotating plasmas exhibited larger and wider ELM affected area than ctr-rotating plasmas. Just before type I ELM crash, the pedestal ion pressure and its maximum gradient in co-rotating plasmas are 20% and 12% higher than those in ctr-rotating plasmas, respectively. It is found that the radial extent of the ion pressure gradient at the pedestal region in co-rotating plasmas is 14% wider than that in ctr-rotating plasmas. The experimental results suggest that the ELM size is determined by the structure of the plasma pressure in the whole pedestal region.
Matsunaga, Go; Takechi, Manabu; Aiba, Nobuyuki; Kurita, Genichi; Sakamoto, Yoshiteru; Koide, Yoshihiko; Isayama, Akihiko; Suzuki, Takahiro; Fujita, Takaaki; Oyama, Naoyuki; et al.
Plasma and Fusion Research (Internet), 4, p.051_1 - 051_7, 2009/11
no abstracts in English
Urano, Hajime; Sakamoto, Yoshiteru; Suzuki, Takahiro; Fujita, Takaaki; Kamiya, Kensaku; Isayama, Akihiko; Kamada, Yutaka; Takenaga, Hidenobu; Oyama, Naoyuki; Matsunaga, Go; et al.
Nuclear Fusion, 49(9), p.095006_1 - 095006_7, 2009/09
Times Cited Count：7 Percentile：27.5(Physics, Fluids & Plasmas)H-modes operated at higher 
with the current ramp down have shown higher energy confinement with higher density in JT-60U. The 
-factor evaluated for the core plasma depends strongly on with the relation of 
for the case without sawtooth activities. Center peaked profiles of electron density and electron temperature are obtained in high H-modes. The pedestal pressure is not significantly changed. The enhanced energy confinement in high H-modes is attributed to the core improvement with the peaked profiles of electron density and temperature. The electron heat diffusivity is reduced at the plasma core in high case, resulting in the center peaked 
profile while the 
profiles are approximately unchanged.
Sakamoto, Yoshiteru; Matsunaga, Go; Oyama, Naoyuki; Suzuki, Takahiro; Aiba, Nobuyuki; Takenaga, Hidenobu; Isayama, Akihiko; Shinohara, Koji; Yoshida, Maiko; Takechi, Manabu; et al.
Nuclear Fusion, 49(9), p.095017_1 - 095017_8, 2009/09
Times Cited Count：33 Percentile：73.96(Physics, Fluids & Plasmas)This paper reports the recent development of reversed shear plasmas with a high bootstrap current fraction towards reactor relevant regime, especially lower 
regime. By utilizing large volume configuration close to the conductive wall for wall stabilization, the beta limit of the reversed shear plasmas is significantly improved. As a result, high confinement reversed shear plasmas with high bootstrap current fraction exceeding no-wall beta limit are obtained in reactor relevant regime, where 
of 2.7, 
of 2.3 is achieved with reversed profile with 
of 2.3, and then HH
of 1.7, 
/
of 0.87 and 
of 0.9 are also obtained at of 5.3.
Ida, Katsumi*; Sakamoto, Yoshiteru; Yoshinuma, Mikiro*; Takenaga, Hidenobu; Nagaoka, Kenichi*; Hayashi, Nobuhiko; Oyama, Naoyuki; Osakabe, Masaki*; Yokoyama, Masayuki*; Funaba, Hisamichi*; et al.
Nuclear Fusion, 49(9), p.095024_1 - 095024_9, 2009/09
Times Cited Count：31 Percentile：71.94(Physics, Fluids & Plasmas)Dynamics of ion internal transport barrier (ITB) formation and impurity transport both in the Large Helical Device (LHD) heliotron and JT-60U tokamak are described. Significant differences between heliotron and tokamak plasmas are observed. The location of the ITB moves outward during the ITB formation regardless of the sign of magnetic shear in JT-60U and the ITB becomes more localized in the plasma with negative magnetic shear. In LHD, the low Te/Ti ratio (
1) of the target plasma for the high power heating is found to be necessary condition to achieve the ITB plasma and the ITB location tends to expand outward or inward depending on the condition of the target plasmas. Associated with the formation of ITB, the carbon density tends to be peaked due to inward convection in JT-60U, while the carbon density becomes hollow due to outward convection in LHD. The outward convection observed in LHD contradicts the prediction by neoclassical theory.
Kamada, Yutaka; Yoshida, Maiko; Sakamoto, Yoshiteru; Koide, Yoshihiko; Oyama, Naoyuki; Urano, Hajime; Kamiya, Kensaku; Suzuki, Takahiro; Isayama, Akihiko; JT-60 Team
Nuclear Fusion, 49(9), p.095014_1 - 095014_9, 2009/09
Times Cited Count：2 Percentile：8.15(Physics, Fluids & Plasmas)For understanding of the physics processes determining the radial profiles of the kinetic plasma parameters in the advanced tokamak plasmas, correlation between the edge and the internal transport barriers (ETB and ITB) has been studied. We fond that the edge pedestal beta, 
, increases almost linearly with the total 
, over a wide range of the plasma current for the type I ELMing H-mode, and the dependence becomes stronger with increasing triangularity. This dependence is not due to the profile stiffness. However, with increasing the stored energy inside the ITB radius (W
), the total thermal stored energy (W
) increases and then the pedestal stored energy (W) increases. With increasing W, the ELM penetration depth expands more inward and finally reaches the ITB-foot radius. At this situation, the ITB radius cannot move outward and the ITB strength becomes weak. Then the fractions of W and W to W become almost constant. We also found that the type I ELM expels/decreases edge toroidal momentum larger than ion thermal energy. The ELM penetration radius for toroidal rotation tends to be deeper than that for ion temperature, and can exceeds the ITB radius. The ELM affected area is deeper for CO rotating plasmas than CTR rotating ones. The ELM affected area is deeper in the order of the toroidal rotation (V
), the ion temperature (T
) and then the electron temperature (Te). The L-H transition also changes the V-profile more significantly than the Ti-profile. After the L-H transition, in the ELM-free phase, the pedestal V sifts into the CTR direction deeply and suddenly, and after that the pedestal V and T evolves in the similar timescale. The change in V by ELM and L-H transition may affect degradation / evolution of ITBs.
Suzuki, Takahiro; Oyama, Naoyuki; Isayama, Akihiko; Sakamoto, Yoshiteru; Fujita, Takaaki; Ide, Shunsuke; Kamada, Yutaka; Naito, Osamu; Sueoka, Michiharu; Moriyama, Shinichi; et al.
Nuclear Fusion, 49(8), p.085003_1 - 085003_8, 2009/08
Times Cited Count：8 Percentile：30.67(Physics, Fluids & Plasmas)Fully non-inductive discharge having a relaxed current profile and high bootstrap current fraction f
=0.5 has been realized in the high- ELMy H-mode discharge with weak magnetic-shear having q=5.8, qmin=2.1, and q(0)=2.4, where qmin and q(0) are the safety factor q at the minimum and the plasma center, respectively. The rest of the plasma current is externally driven by neutral beams (NBs) and lower-hybrid (LH) waves. The safety factor profile evaluated by the motional Stark effect (MSE) diagnostic is kept unchanged during 0.7 s at the end of the full current drive (CD) sustainment for 2 s (1.5 times the current relaxation time 
). The loop voltage profile is spatially uniform at 0 V at the end of the sustainment. This demonstration shows, for the first time, that the steady sustainment of ful-CD plasma is possible at high f=0.5 and reasonably low q=5.8 regime and is stably controlled by appropriate external current drivers. On the other hand, when the combination of bootstrap current and externally driven current does not match to the steady current profile, slight change in the current profile due to current relaxation resulted in appearance of magnetohydrodynamic (MHD) instability, e.g. neo-classical tearing mode (NTM), in a high beta plasma. This discharge clarifies importance of the demonstration of steady current profile developed here. These discharges contribute to the ITER steady-state operation scenario development.
Sips, A. C. C.*; Casper, T.*; Doyle, E. J.*; Giruzzi, G.*; Gribov, Y.*; Hobirk, J.*; Hogeweij, G. M. D.*; Horton, L. D.*; Hubbard, A. E.*; Hutchinson, I.*; et al.
Nuclear Fusion, 49(8), p.085015_1 - 085015_11, 2009/08
Times Cited Count：53 Percentile：87.16(Physics, Fluids & Plasmas)Key parts of the ITER scenarios are determined by the capability of the proposed poloidal field (PF) coil set. They include the plasma breakdown at low loop voltage, the current rise phase, the performance during the flat top (FT) phase and a ramp down of the plasma. The ITER discharge evolution has been verified in dedicated experiments. New data are obtained from C-Mod, ASDEX Upgrade, DIII-D, JT-60U and JET. Results show that breakdown for 
0.23-0.33 V m
is possible unassisted (ohmic) for large devices like JET and attainable in devices with a capability of using ECRH assist. For the current ramp up, good control of the plasma inductance is obtained using a full bore plasma shape with early X-point formation. This allows optimization of the flux usage from the PF set. Additional heating keeps 
(3) 0.85 during the ramp up to = 3. A rise phase with an H-mode transition is capable of achieving (3) 0.7 at the start of the FT. Operation of the H-mode reference scenario at 
3 and the hybrid scenario at = 4-4.5 during the FT phase is documented, providing data for the (3) evolution after the H-mode transition and the (3) evolution after a back-transition to L-mode. During the ITER ramp down it is important to remain diverted and to reduce the elongation. The inductance could be kept 
1.2 during the first half of the current decay, using a slow ramp down, but still consuming flux from the transformer. Alternatively, the discharges can be kept in H-mode during most of the ramp down, requiring significant amounts of additional heating.
plasmas in the JT-60U tokamakMatsunaga, Go; Aiba, Nobuyuki; Shinohara, Koji; Sakamoto, Yoshiteru; Isayama, Akihiko; Takechi, Manabu; Suzuki, Takahiro; Oyama, Naoyuki; Asakura, Nobuyuki; Kamada, Yutaka; et al.
Physical Review Letters, 103(4), p.045001_1 - 045001_4, 2009/07
Times Cited Count：45 Percentile：84.91(Physics, Multidisciplinary)Oyama, Naoyuki; Isayama, Akihiko; Matsunaga, Go; Suzuki, Takahiro; Takenaga, Hidenobu; Sakamoto, Yoshiteru; Nakano, Tomohide; Kamada, Yutaka; Ide, Shunsuke; JT-60 Team
Nuclear Fusion, 49(6), p.065026_1 - 065026_10, 2009/06
Times Cited Count：42 Percentile：80.26(Physics, Fluids & Plasmas)The performance and sustained duration of long-pulse discharges for ITER hybrid scenario have been improved in JT-60U. The peaked density profile in the core plasma can be maintained with NBIs for central heating even when the density at the pedestal increased in the latter phase of the discharge due to the increase in the divertor recycling. High normalized beta (
) of 2.6 and high thermal confinement enhancement factor (
) was sustained for 25 s (
, where 
is the current diffusion time.) under the ITER relevant small toroidal rotation condition. High 
of 2.6 gives high G-factor (
) of 0.25 and peaked pressure profile gives large bootstrap current fraction (
).
Isayama, Akihiko; Matsunaga, Go; Kobayashi, Takayuki; Moriyama, Shinichi; Oyama, Naoyuki; Sakamoto, Yoshiteru; Suzuki, Takahiro; Urano, Hajime; Hayashi, Nobuhiko; Kamada, Yutaka; et al.
Nuclear Fusion, 49(5), p.055006_1 - 055006_9, 2009/05
Times Cited Count：63 Percentile：89.51(Physics, Fluids & Plasmas)no abstracts in English
