EFFECTS OF THE SAFETY FACTOR AND THE INTERNAL INDUCTANCE ON MHD ACTIVITIES AND ENERGY CONFINEMENT IN JT-60U

On the basis of Ohmic and neutral beam heating experiments in JT-60U, the discharge regions in tokamaks are characterized in terms of the internal inductance l(i) and the effective safety factor at the edge, q(eff), in the low beta region. Stable discharges have medium l(i) values, and disruptive discharges occur both in higher and lower l(i) regions for a given q(eff). There is also a boundary of l(i) below which sawtooth free discharges occur. Another boundary of l(i) corresponds to the quasi-stationary current distribution profiles, along which the maximum value of r(inv)/a (sawtooth inversion radius/minor radius) is almost proportional to 1/q(eff). At a given q(eff) value, r(inv)/a increases with increasing l(i). Concerning L-mode confinement, the H-factor (H = tau(E)/tau(E)ITER89P) is almost proportional to l(i)0.8 over a wide range of q(eff) (q(eff) = 2-14). The degradation of confinement in the low q region (q(eff) < 4-5) in the L-mode is caused by the effects of l(i) and sawtooth activity. In the low q region, H/l(i)0.8 decreases with decreasing sawtooth period tau(SW) and with increasing r(inv)/a. The degradation due to sawteeth is stronger at lower q(eff). A new confinement scaling law for the H-factor (H(SC)) in the L-mode is obtained by including the effects of l(i) and sawteeth: H(SC) = (Y + ftau(SW)) l(i)0.8 where tau(SW) < (c - Y)/f, and H(SC) = cl(i)0.8 when tau(SW) > (c - Y)/f, where f = 10.0/q(eff)2, Y = c - 0.96(r(inv)/a) and c = 0.92.