25aE09P
JT-60U におけるトロイダル回転方向に関連した熱輸送変化の物理機構
Mechanisms of changes in heat transport due to toroidal rotation
direction in JT-60U
成田絵美, 本多充, 林伸彦, 浦野創, 吉田麻衣子, 井手俊介
Emi NARITA, Mitsuru HONDA, Nobuhiko HAYASHI, Hajime URANO Maiko YOSHIDA, andShunsuke IDE
原子力機構
JAEA
Toroidal rotation is the key to improve the energy confinement in tokamak plasmas. In JT-60U, it has
been reported that the higher confinement performance is observed with the steeper electron temperature
gradient of the internal transport barrier when rotation is in a co-direction with respect to the plasma
current than when rotation is in a counter- (ctr-) direction. The discharge in question was operated withthe plasma current Ip = 0.9 MA and the toroidal magnetic field BT = 1.6 T, and during the discharge,
the impurity density increases as rotation varies from co- to ctr-direction. The previous study using thegyrokinetic flux-tube code GS2 has shown that the impurity density causes a change in the real frequency
ω of the fastest growing mode; the mode tends to be more TEM-like with the increase in the impuritydensity [1]. The study has also shown that the eﬀects of the rotation shear on the linear growth rate γ
are not significant, but the study has not taken into account the rotation direction. This paper focuses on
the influence of the rotation direction on heat transport with the gyrokinetic flux-tube code GKW, which
includes the eﬀect of a rigid body toroidal rotation, unlike GS2.
This study uses the parameters of the experiment mentioned above: at the normalized minor radiusρ = 0.45, the normalized gradients of the electron density, the electron temperature, and the ion temperatureare 1/Lne = 1.6, 1/LTe = 3.4, and 1/LTi = 2.4, respectively, the safety factor is q = 1.3, the magnetic shear
is s = 0.71, and the eﬀective ion charge is Zeﬀ = 3.0. The linear calculations using GKW and GS2
including the eﬀects of collisionality and finite β show that the fastest growing mode is the ITG/TEM
hybrid mode, and that the linear growth rate γ has the maximum around the wavenumber kθ ρs ∼ 0.6 (seeFig. 1(a)). In addition, the dependence of γ on the toroidal angular frequency Ω = ⟨vϕ /R⟩ and on its
gradient Ω′ = −dΩ/dρ is investigated in the manner of [2]. As shown in Fig. 1(b), at Ω′ = 0, an increasein the absolute value of Ω suppresses γ due to the Coriolis drift and the equilibrium electrostatic potential
aﬀected by toroidal rotation. On the other hand, when a finite Ω′ is given, the change in the rotation
direction can aﬀect γ, since the value of Ω at which γ has the maximum shifts from zero. The qualitativechange in γ agrees with [2], although the experimental values of Ω and Ω′ , Ωexp = 1.01 × 104 s−1 andΩ′exp = −1.12 × 104 s−1 , have little eﬀects on γ. In this paper, the influence of Ω and Ω′ on the nonlinear
heat flux will also be presented.
Fig. 1 (a) Real frequencies ω (solid)
and linear growth rates γ (dotted)
predicted by GKW (circle) and GS2(square) at ρ = 0.45. (b) γ as a function of the toroidal angular frequency Ωand its gradient Ω′ at kθ ρs = 0.57. The
dashed line denotes the value of Ω atwhich γ becomes the maximum whenΩ′ is constant.
[1] E. Narita et al., Plasma Fusion Res. 10, 1403019 (2015).
[2] Y. Camenen et al., 42nd EPS conference on plasma physics (Proceedings), P5.106 (2015).