Yoshida, Maiko; Honda, Mitsuru; Narita, Emi*; Hayashi, Nobuhiko; Urano, Hajime; Nakata, Motoki; Miyato, Naoaki; Takenaga, Hidenobu; Ide, Shunsuke; Kamada, Yutaka
Nuclear Fusion, 55(7), p.073014_1 - 073014_9, 2015/07
Conditions without the increases in the thermal and particle transport with ECH have been experimentally investigated in positive magnetic shear (PS), weak magnetic shear (WS) and reversed magnetic shear (RS) plasmas with internal transport barriers (ITBs) on JT-60U. The ion heat diffusivity around an internal transport barrier in the ion temperature (-ITB) remains constant with ECH when a large negative toroidal rotation shear is formed before the ECH. The condition does not depend on the electron to ion temperature ratio (/) and ECH power. The electron heat diffusivity around a -ITB stays constant with ECH when the magnetic shear is negative around the Te-ITB region. Effective particle transport remains constant or reduces during ECH under the condition of negative magnetic shear.
Yoshida, Maiko; Ide, Shunsuke; Takenaga, Hidenobu; Honda, Mitsuru; Urano, Hajime; Kobayashi, Takayuki; Nakata, Motoki; Miyato, Naoaki; Kamada, Yutaka
Nuclear Fusion, 53(8), p.083022_1 - 083022_10, 2013/07
Time and special responses of electron channels and ion channels with central electron cyclotron heating (ECH) have been investigated in JT-60U positive shear H-mode and internal transport barrier (ITB) plasmas. The ion temperature reduces with ECH after the increase in the electron temperature where an increase in the ion heat transport with ECH accompanies an increase in the electron thermal transport. The core electron density decreases with ECH when the density profile is peaked before ECH injection. The counter intrinsic rotation with ECH is identified using H-mode plasmas with small torque input (BAL-NBI). The counter intrinsic rotation is generated after the increase in the electron temperature and correlates with the change in the electron temperature with ECH around the EC deposition. Time scale of the change in the toroidal rotation velocity is about 90-200 ms around the ECH deposition and the time scale is longer compared to those in and .
Yoshida, Maiko; Sakamoto, Yoshiteru; Honda, Mitsuru; Kamada, Yutaka; Takenaga, Hidenobu; Oyama, Naoyuki; Urano, Hajime; JT-60 Team
Nuclear Fusion, 52(2), p.023024_1 - 023024_9, 2012/02
Relation between the toroidal rotation velocities in the core and edge regions has been investigated in H-mode plasmas with small external torque input from the viewpoint of momentum transport. The toroidal rotation velocity in the core region gradually varies on a timescale after a rapid change in the toroidal rotation velocity in the edge region at the L-H transition. In steady state, a linear correlation between the core- and edge-rotation is observed in H-mode plasmas when the ion pressure gradient is small. The rotation profiles with a large have been reproduced in the core region by adopting a residual stress term proposed in this paper. Parameter dependencies of the edge-rotation are investigated at a constant ripple loss power, ripple amplitude and the plasma current. A reduction in the CTR-rotation is observed with decreasing the ion temperature gradient. Here CTR refers in the counter- direction.
Urano, Hajime; Saibene, G.*; Oyama, Naoyuki; Parail, V.*; de Vries, P.*; Sartori, R.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; Lnnroth, J.*; et al.
Nuclear Fusion, 51(11), p.113004_1 - 113004_10, 2011/11
The effect of TF ripple on the edge pedestal characteristics are examined in JET and JT-60U. By the installation of ferritic inserts, TF ripple was reduced from to in JT-60U. In JET, TF ripple was varied from to by feeding different currents to TF coils. The pedestal pressure was similar with reduced ripple in JT-60U. In JET, no clear difference of the pedestal characteristics was also observed. The edge toroidal rotation clearly decreased in counter direction by increased TF ripple. However, in JT-60U, the ELM frequency decreased by and the increased ELM loss power by with reduced ripple. In JET, ELM frequency increases only slightly with increased TF ripple. From this inter-machine experiment, TF ripple less than does not strongly affect the pedestal pressure. The effect of TF ripple on pedestal characteristics at lower collisionality close to ITER should be investigated as a next step study.
Tanaka, Yasunori*; Smirnov, R. D.*; Pigarov, A. Y.*; Takenaga, Hidenobu; Asakura, Nobuyuki; Uesugi, Yoshihiko*; Ono, Noriyasu*
Journal of Nuclear Materials, 415(Suppl.1), p.S1106 - S1110, 2011/08
Dust can be an important contributor to impurity contamination of the core and scrape-off-layer (SOL) plasmas in tokamak fusion devices. This is the first report about investigation of transport of carbon dust particles in case of JT-60U tokamak using the dust transport code (DUSTT). The DUSTT code takes into account various plasma-dust interaction processes. In the present report, background plasma parameters in JT-60U such as densities and temperatures of electron, ion and neutral atom were computed with the UEDGE code. Three dimensional trajectories, temperature evolution, and radius variation of dust particles launched from different positions at the inner divertor, the outer divertor and the dome structure in JT-60U tokamak were simulated numerically to study dynamics and transport of dust particles there. As a result, the lifetime of dust particles is dependent mainly on the ion density in trajectories in final term.
Litaudon, X.*; Sakamoto, Yoshiteru; de Vries, P. C.*; Salmi, A.*; Tala, T.*; Angioni, C.*; Benkadda, S.*; Beurskens, M. N. A.*; Bourdelle, C.*; Brix, M.*; et al.
Nuclear Fusion, 51(7), p.073020_1 - 073020_13, 2011/07
A variety of triggering mechanisms and structures of internal transport barrier (ITB) has been observed in various devices or depending on operation scenarios. Thus identity experiments on ITB in JT-60U and JET have been performed to shed light on the physics behind ITBs. Because of their similar size, the dimensionless parameters between both devices are the same. These experiments were performed with near identical magnetic configurations, heating waveforms and normalized quantities such as safety factor, magnetic shear, normalized Larmor radius, normalized collision frequency, beta, temperatures ratio. Similarities of the ITB triggering mechanism and the ITB strength have been observed when a proper match is achieved of the most relevant profiles of the normalized quantities. This paper will report on the detail comparison of transport properties of ITBs obtained in these JET/JT-60U identity experiments.
Oyama, Naoyuki; Takenaga, Hidenobu; Suzuki, Takahiro; Sakamoto, Yoshiteru; Isayama, Akihiko; JT-60 Team
Plasma and Fusion Research (Internet), 6, p.1402014_1 - 1402014_8, 2011/03
In JT-60U, the frequency hopping reflectometer has been developed to evaluate the poloidal rotation velocity as a Doppler reflectometer and the radial correlation of density fluctuations in plasmas. The system can measure the radial profile of density fluctuations or the profile of radial correlation at two spatial points by combining the fixed frequency reflectometer within 250 ms. The radial profiles of the poloidal rotation velocity evaluated from the Doppler-shifted frequency spectrum in density fluctuations show a positive radial electric field in co-rotating plasma and a negative radial electric field in counter-rotating plasma. The density fluctuation measurement at the internal transport barrier using a correlation reflectometer revealed that the long-range correlation was increased when the internal transport barrier was degraded with the central heating by electron cyclotron wave.
Takenaga, Hidenobu; Miyo, Yasuhiko; Bucalossi, J.*; Marty, V.*; Urano, Hajime; Asakura, Nobuyuki; Nishiyama, Tomokazu; Sasajima, Tadayuki; Masaki, Kei; Kaminaga, Atsushi
Nuclear Fusion, 50(11), p.115003_1 - 115003_10, 2010/11
The supersonic molecular beam injection (SMBI) was successfully operated in JT-60U. Frequent density jumps were clearly observed in the main plasma against the SMBI pulses with the background gas pressure () of 2-6 bar. Fuelling efficiency exhibited weak dependence on and the injection direction (high- and low-field-side injections). The amount of the fuelling necessary for achieving the same density level is much smaller for the SMBI than for the gas-puffing. It is comparable for the SMBI and the pellet injection even with shallower penetration of the SMBI as discussed below. The SMBI ionization area was estimated based on emission measured using the fast TV camera with a time resolution of 0.167 ms. The estimations indicated similar penetration position for = 6 and 2 bar, although the ionization area was larger for 6 bar. This result supports the weak dependence of the fuelling efficiency. The front of the ionization area moved between first and second frames of the fast TV camera and it reached just inside the separatrix in the second frame. The ionization area was significantly expanded from the expected SMB size and the expansion was also enhanced between two frames. These relatively slow changes between two frames suggest that interaction between SMB and plasma significantly influences the fuelling characteristics.
Tanaka, Kenji*; Kawahata, Kazuo*; Tokuzawa, Tokihiko*; Akiyama, Tsuyoshi*; Yokoyama, Masayuki*; Shoji, Mamoru*; Michael, C. A.*; Vyacheslavov, L. N.*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; et al.
Fusion Science and Technology, 58(1), p.70 - 90, 2010/07
Particle confinement processes were studied in detail on LHD. Diffusion coefficients (D) and convection velocities (V) were estimated from density modulation experiments. The magnetic configuration and collisionality were widely scanned in order to investigate parameter dependences of D and V. In order to study the effect of the magnetic configuration, magnetic axis positions (R) were scanned from 3.5 m to 3.9 m. This scan changed the magnetic ripples quite significantly, enabling the effects of neoclassical properties on measured values to be widely elucidated. Dependences of electron temperature (T) and helically trapped normalized collsionality (), where =1 indicates a rough boundary between the 1/ and plateau regimes, were examined using the heating power scan of neutral beam injection (NBI). It was found out that generally larger (or smaller) contributions of neoclassical transport resulted in more hollow (or peaked) density profiles. The larger neoclassical contribution was found to be situated at a more outwardly shifted R for the same T, and higher T or lower at each R. However, it is to be noted that R=3.5 m showed different characteristics from these trends in that this case showed a more peaked density profile at higher T.
Angioni, C.*; Fable, E.*; Greenwald, M.*; Maslov, M.*; Peeters, A. G.*; Takenaga, Hidenobu; Weisen, H.*
Plasma Physics and Controlled Fusion, 51(12), p.124017_1 - 124017_14, 2009/12
The physical processes producing electron particle transport in the core of tokamak plasmas are described. Starting from the gyrokinetic equation, a simple analytical derivation is used as guidance to illustrate the main mechanisms driving turbulent particle convection. A review of the experimental observations on particle transport in tokamaks is presented and the consistency with the theoretical predictions is discussed. An overall qualitative agreement, and in some cases even a specific quantitative agreement, emerges between complex theoretical predictions and equally complex experimental observations, exhibiting different dependences on plasma parameters under different regimes. By these results, the direct connection between macroscopic transport properties and the character of microscopic turbulence is pointed out, and an important confirmation of the paradigma of microinstabilities and turbulence as the main cause of transport in the core of tokamaks is obtained. Finally, the impact of these results on the prediction of the peaking of the electron density profile in a fusion reactor is illustrated.
Yoshida, Maiko; Kamada, Yutaka; Takenaga, Hidenobu; Sakamoto, Yoshiteru; Oyama, Naoyuki; Urano, Hajime; JT-60 Team
Nuclear Fusion, 49(11), p.115028_1 - 115028_8, 2009/11
Properties of the toroidal momentum diffusivity and the convection velocity in JT-60U H-mode plasmas have been obtained by plasma parameter scans such as the plasma current, neutral beam heating power and electron density. The toroidal momentum diffusivity increases with increasing heat diffusivity over a wide range of radii. The inward convection velocity increases with increasing the momentum diffusivity. It is found that the ratio increases with increasing ion temperature and decreases with increasing electron density.
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
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
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
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.
Yoshida, Maiko; Sakamoto, Yoshiteru; Takenaga, Hidenobu; Ide, Shunsuke; Oyama, Naoyuki; Kobayashi, Takayuki; Kamada, Yutaka; JT-60 Team
Physical Review Letters, 103(6), p.065003_1 - 065003_4, 2009/08
The role of electron cyclotron range of frequency (ECRF) wave on the toroidal rotation velocity profile has been investigated in JT-60U plasmas by separating the effects of the momentum transport, the intrinsic rotation by pressure gradient and the intrinsic rotation by ECRF. It is found that ECRF increases the toroidal momentum diffusivity and the convection velocity. ECRF drives the CO-intrinsic rotation inside the EC deposition and drives the CTR-intrinsic rotation outside the EC deposition. This CTR-rotation starts from the EC deposition radius and propagates to the edge region.
Takenaga, Hidenobu; Oyama, Naoyuki; Urano, Hajime; Sakamoto, Yoshiteru; Asakura, Nobuyuki; Kamiya, Kensaku; Miyo, Yasuhiko; Nishiyama, Tomokazu; Sasajima, Tadayuki; Masaki, Kei; et al.
Nuclear Fusion, 49(7), p.075012_1 - 075012_11, 2009/07
Characteristics of internal transport barrier (ITB) have been investigated under reactor relevant condition with edge fuelling and electron heating in JT-60U weak shear plasmas. High confinement was sustained at high density with edge fuelling by shallow pellet injection or supersonic molecular beam injection (SMBI). The ion temperature (T) in the central region inside the ITB decreased due to cold pulse propagation even with edge fuelling. By optimizing the injection frequency and the penetration depth, the decreased central T was recovered and good ITB was sustained with enhanced pedestal pressure. The T-ITB also degraded significantly with electron cyclotron heating (ECH), when stiffness feature was strong in the electron temperature (T) profile. The ion thermal diffusivity in the ITB region increased with the electron thermal diffusivity, indicating existence of clear relation between ion and electron thermal transport. On the other hand, T-ITB unchanged or even grew, when stiffness feature was weak in the T profile. Density fluctuation level at ITB seemed to be unchanged during ECH, however, correlation length became longer in the T-ITB degradation case and shorter in the T-ITB unchanging case.
Miyamoto, Seiji; Nakamura, Yukiharu*; Hayashi, Nobuhiko; Oyama, Naoyuki; Takenaga, Hidenobu; Sugie, Tatsuo; Kusama, Yoshinori; Yoshino, Ryuji
Proceedings of 36th European Physical Society Conference on Plasma Physics (CD-ROM), 4 Pages, 2009/07
The neutral dynamics including fueling, divertor pumping, charge exchange penetration, wall retention and so on would complicate the analysis of ITER plasma behavior such as H-L back transition during plasma current ramp-down. Recently, a relatively simple model of neutral dynamics was developed by us with TSC code to describe the plasma behavior during L-H and H-L transition phase. This model is compared with a JT-60U shot, in which it is possible to extract the effect of particle confinement change on neutral because H-mode discharge is switched on/off according to EC injection and thereby particle source density is kept constant during transition. It is shown that TSC simulation can account the behavior of neutral inferred from the experimental D signal. It is concluded that this model is applicable to scenario development of the ITER.
Takenaga, Hidenobu; Kawashima, Hisato; Nishio, Satoshi; Tobita, Kenji
Fusion Science and Technology, 57(1), p.94 - 102, 2009/06
A fuelling scenario in a fusion reactor has been investigated, where tritium is fuelled in the main plasma and deuterium is fuelled in both the main plasma and the edge plasma. The tritium fuelling in the main plasma minimizes the tritium fuelling rate necessary for sustaining the high tritium density in the main plasma, resulting in the minimum tritium recycling level at the fixed pumping fraction. The deuterium fuelling in the main plasma sustains the high deuterium density in the main plasma and the deuterium fuelling in the edge plasma enhances the deuterium recycling level for reducing the divertor temperature. Based on this scenario, particle balance was quantitatively investigated using the SlimCS design parameters at 2.95 GW fusion output with consideration of confinement times separately defined for the particles fuelled in the main plasma and the edge plasma.
Takenaga, Hidenobu; JT-60 Team
Journal of Nuclear Materials, 390-391, p.869 - 875, 2009/06
Particle control is important for burning plasma control, because fuel density is one of a few controllable parameters in a burning plasma. First, mechanisms responsible for determining density profiles and dependence of impurity transport on density profiles were investigated. Peakedness of density profiles increased with decreasing collisionality, which is consistent with ITG/TEM turbulence theory. However, other hidden parameters, such as toroidal rotation, existed. Metal impurity accumulation was observed with peaked density profile, while light impurity accumulation was not. Next, effects of fuelling on confinement was investigated using newly installed supersonic molecular beam injection (SMBI). SMBI directly affected the plasma parameters at r/a 0.8 as similar as pellet injection. However, confinement degraded with constant pedestal pressure in contrast to pellet injection. Using the burning plasma simulation scheme, it was demonstrated to reduce the simulated a-heating with SMBI due to confinement degradation and flattening of pressure profile.
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
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 ().