Core and edge toroidal rotation study in JT-60U

摘要

The relation between toroidal rotation velocities (V_t) in the core and edge regions is investigated in H-mode plasmas with a small external torque input from the viewpoint of momentum transport. The toroidal rotation velocity in the core region (core-V_t) gradually varies on a timescale of ～20ms after a rapid change in the toroidal rotation velocity in the edge region (edge- V_t) at the L-H transition. This timescale of ～20 ms is consistent with a transport timescale using the momentum diffusivity (X_φ) and convection velocity (V_(conv))- In steady state, a linear correlation between the core- and edge-V_t is observed in H-mode plasmas when the ion pressure gradient (▽P_i) is small. This relation between core- and edge- V_t is also explained by momentum transport. The V_t profiles with a large ▽P_i are reproduced in the core region of r/a ～ 0.2-0.7 by adopting a residual stress term 'Π_(res) = α_(kχφ)▽P_i' proposed in this paper. Here r/a is the normalized plasma radius and α_(k1) is a radial constant. Using this formula, V_t profiles are reproduced over a wide range of plasma conditions. Parameter dependences of the edge- V_t are investigated at a constant ripple loss power, ripple amplitude and plasma current. A reduction in the CTR-rotation is observed with decreasing ion temperature gradient (▽T_i). Here CTR refers to the counter-I_p direction.