Active feedback control of steady-state improved confinement discharges in JT-60U

This paper emphasizes the significance of active feedback control as an indispensable method to improve and sustain the plasma performances as well as to operate the fusion reactor under the optimal divertor conditions. In accordance, the world record equivalent fusion amplification gain of 1.25 was lately achieved at the JT-60U tokamak in the reversed shear mode of operation with the robust feedback controls, where the value of target density was deliberately optimized for the reproducible internal transport barrier formation and the magneto-hydrodynamic stability control was performed with the neutron rate feedback. The feedback control techniques also demonstrated the effectiveness to produce a quasi-steady-state in high-performance plasmas. In addition, three major parameters associated with the fusion reactor instrumentations, namely the neutron production rate, operating density and divertor radiation power, were simultaneously feedback controlled in the H mode plasmas accompanied with the edge localized mode. Here, the matrix response function was evaluated to identify the limitations involved with the linear combination of independent controls. Finally, the controversial issues for the future ‘intelligent plasma control’, necessary for the advanced steady-state tokamak reactor is also addressed.