19th IAEA Fusion Energy Conference

Relationship between particle and heat transport in JT-60U plasmas with internal transport barrier

H. Takenaga¹⁾, S. Higashijima¹⁾, N. Oyama¹⁾, L. G. Bruskin¹⁾, Y. Koide¹⁾, S. Ide¹⁾, H. Shirai¹⁾, Y. Sakamoto¹⁾, T. Suzuki¹⁾, K. W. Hill²⁾, G. Rewoldt²⁾, G. J. Kramer²⁾, R. Nazikian²⁾, T. Takizuka¹⁾, T. Fujita¹⁾, A. Sakasai¹⁾, Y. Kamada¹⁾, H. Kubo¹⁾ and the JT-60 Team¹⁾
1) Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193, Japan
2) Princeton Plasma Physics Laboratory, Princeton, New Jersey, 08543-0451, U.S.A.

Abstract.
The relationship between particle and heat transport in an internal transport barrier (ITB) has been systematically investigated in reversed shear (RS) and high β_p ELMy H-mode plasmas in JT-60U. No helium and carbon accumulation inside the ITB is observed even with ion heat transport reduced to a neoclassical level. On the other hand, the heavy impurity argon is accumulated inside the ITB. The argon density profile estimated from the soft x-ray profile is more peaked, by a factor of 2-4 in the RS plasma and of 1.6 in the high β_p mode plasma, than the electron density profile. The helium diffusivity (D_He) and the ion thermal diffusivity (χ_i) are at an anomalous level in the high β_p mode plasma, where D_He and χ_i are higher by a factor of 5-10 than the neoclassical value. In the RS plasma, D_He is reduced from the anomalous to the neoclassical level, together with χ_i. The carbon and argon density profiles calculated using the transport coefficients reduced to the neoclassical level only in the ITB are more peaked than the measured profiles, even when χ_i is reduced to the neoclassical level. Argon exhaust from the inside of the ITB is demonstrated by applying ECH in the high β_p mode plasma, where both electron and argon density profiles become flatter. The reduction of the neoclassical inward velocity for argon due to the reduction of density gradient is consistent with the experimental observation. In the RS plasma, the density gradient is not decreased by ECH and argon is not exhausted. These results suggest the importance of density gradient control to suppress heavy impurity accumulation.