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 = τ E /τ 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 τ 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+fτ sw )l i 0.8 where τ sw < (c-Y)/f, and H sc = cl i 0.8 when τ sw > (c-Y)/f, where f = 10.0/q eff 2 , Y = c-0.96(r inv /a) and c = 0.92