No abstract

No abstract

High-density disruptions and low-q disruptions have been investigated by soft-X-ray imaging on the JIPP T-II tokamak. Although an m = 3/n = 2 mode is identified together with a 2/1 mode before partial disruptions in high-density discharges, the resulting disturbance is limited and the central region is not affected. The growth of the 3/2 mode detected in low-q discharges leads to a rearrangement of the soft-X-ray profile by a 1/1 mode. The essential feature of major disruptions is the abrupt central thermal quench. Before major disruptions the predominant 2/1 mode is modulated by a central 1/1 component. The 1/1 mode is found to play an important role in the final stage of major disruptions, both in high-density discharges and in low-q discharges.

The neoclassical bootstrap current effect is investigated in the JT-60 tokamak. The experimental resistive loop voltages are compared with the calculations, using the neoclassical resistivity, with and without the bootstrap current, and the Spitzer resistivity for a wide range of plasma current (Ip = 0.5-2 MA) and poloidal beta (βp = 0.1-3.2). The neoclassical bootstrap current is calculated directly with the force balance equations for viscous and friction forces according to the Hirshman–Sigmar theory. The bootstrap current driven by the fast ion component is also included. The calculated resistive loop voltage is consistent with the neoclassical prediction including the bootstrap current. It is shown that up to 80% of total plasma current is driven by the bootstrap current in the regime with an extremely high poloidal beta value (βp = 3.2) while the beam driven current is negligibly small.

No abstract