Effect of the edge current density on confinement and kink mode stability in H-mode and VH-mode discharges

摘要

The effect of the local current density in the outer portion of a tokamak discharge (J((rho) (approximately) a)) is discussed in three situations. In a H-mode discharge, a strong reduction of J((rho) (approximately) a) results in the loss of the H-mode pressure pedestal. A smaller reduction in J((rho) (approximately) a) can prevent the transition from H-mode to VH-mode. Finally, a sufficiently large value of J((rho) (approximately) a) accompanied by a sufficiently large value of the pressure gradient in the same region of the discharge, can destabilize low-n (e.g., n = 1 to 5) kink-type modes in a VH-mode discharge.