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Journal Articles

Core transport properties in JT-60U and JET identity plasmas

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

 Times Cited Count:8 Percentile:38.12(Physics, Fluids & Plasmas)

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.

Journal Articles

Spatio-temporal structure of the edge radial electric field during H-mode in JT-60U

Kamiya, Kensaku; Sakamoto, Yoshiteru; Matsunaga, Go; Kojima, Atsushi; Urano, Hajime; Oyama, Naoyuki; Koide, Yoshihiko; Kamada, Yutaka; Ida, Katsumi*; Kurki-Suonio, T.*; et al.

Nuclear Fusion, 51(5), p.053009_1 - 053009_3, 2011/05

 Times Cited Count:12 Percentile:51.33(Physics, Fluids & Plasmas)

We revisited to measure the edge impurity ion dynamic with new CXRS in the hot ion H-mode regime at the high magnetic field having two steps transition where a jump of Ti gradient precedes a jump of impurity Vp. Two discrete phases with different magnitude of Er in the H-phase have been observed. One is the intermediate H-phase having a large Ti gradients without significant Vp of impurity species with moderate magnitude of Er, and the other is the complete H-phase characterized by a large Er.

Journal Articles

Effects of edge collisionality on ELM characteristics in the grassy ELM regime

Oyama, Naoyuki; Kojima, Atsushi; Aiba, Nobuyuki; Horton, L. D.*; Isayama, Akihiko; Kamiya, Kensaku; Urano, Hajime; Sakamoto, Yoshiteru; Kamada, Yutaka; JT-60 Team

Nuclear Fusion, 50(6), p.064014_1 - 064014_10, 2010/06

 Times Cited Count:20 Percentile:65.34(Physics, Fluids & Plasmas)

The effect of the edge collisionality on ELM characteristics has been investigated in the grassy ELM regime on JT-60U. Both in high and low $$q$$ regimes ($$q_{95} > 6$$ and $$q_{95} sim 4.3$$), ELM amplitude becomes higher in plasmas with high edge collisionality. This collisionality dependence is opposite to the dependence observed in type I ELM regime, where the ELM amplitude decreases with increasing the edge collisionality. This collisionality dependence is favorable for next step devices such as ITER.

Oral presentation

Destabilization mechanism of edge-localized MHD mode by a toroidal rotation in tokamaks

Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji

no journal, , 

In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.

Oral presentation

Plasma rotation and momentum transport, and their relations to transport barriers

Sakamoto, Yoshiteru

no journal, , 

The studies of plasma rotation and momentum transport are the most-watched core- transport topics over the last few years. It is well known that plasma rotation can play an important role to achieve high confinement and high beta. The large rotational shear can produce an internal transport barrier (ITB) by suppression of turbulence, and the enough rotation speed can suppress resistive wall modes. Although fast toroidal rotation and its large shear can be obtained in present devises thanks to large toroidal momentum input from neutral beams, slow plasma rotation is foreseen in burning plasmas under the conditions of low momentum input and dominant alpha heating. Therefore it is important to accurately predict plasma rotation profile in ITER and DEMO reactor. In this paper, recent progresses in the studies of plasma rotation and momentum transport are reviewed especially in spontaneous or intrinsic toroidal rotation, momentum pinch, and their relations to transport barriers.

Oral presentation

Transport simulation on transport barriers associated with radial electric field and rotations

Honda, Mitsuru; Takizuka, Tomonori; Fukuyama, Atsushi*

no journal, , 

The relation among the pressure, toroidal and poloidal rotations and radial electric field $$E_r$$ is studied in a plasma with transport barriers by using a TASK/TX code. The neoclassical poloidal rotation driving mechanism driven by the ion temperature gradient $$T_i'$$, which is important especially in ITB plasmas with a steep $$T_i'$$, has been implemented in TASK/TX. Transport simulations with CDBM05 model clarifies that the toroidal rotation profile is governed by the profiles of the external torque and the anomalous perpendicular viscosity. Comparison between the ITB plasmas with and without the density barrier shows the clear difference in the profiles of $$E_r$$ and the resultant $$Etimes B$$ shear, due to the slight difference in the pressure gradient. In the steeper ITB plasmas, the clear notched structure is observed in $$E_r$$ profile, while not in the toroidal rotation profile. Even in that case, the toroidal rotation profile seems insensitive to the background plasma profiles.

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