Fusion Science and Technology / Volume 42 / Number 2,3 / September 2002 / Pages 357-367
The significance of real-time feedback control is emphasized in this paper as an indispensable method to improve and sustain the improved plasma characteristics in JT-60U high fusion performance discharges as well as to operate the fusion reactor under the optimal divertor conditions with respect to the heat load and exhaust pumping. In accordance, substantial improvement in the equivalent fusion amplification gain of over unity has been reproducibly 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 reliable internal transport barrier formation, and the magneto-hydrodynamic stability control was performed with the stored energy feedback. The feedback control techniques also demonstrated the effectiveness to produce quasi-steady-state 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 ELMy H-mode plasmas. Here, the matrix response function was evaluated to identify the limitations involved with the linear combination of independent controls. Other advanced feedback schemes, such as the feedback suppression of the neoclassical tearing mode required to sustain high plasma pressure in a steady-state, are also described. Finally, the controversial issues for the future intelligent plasma control necessary for the advanced steady-stated tokamak reactor are addressed.