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To resolve concerns for heat/electromagnetic loads from vertical displacement events (VDEs), we developed an equilibrium controller, which can predict and control VDEs to an arbitrary direction and allows us to cope with either upward or downward unmitigated VDEs. Here we improve the prediction rate by parameterizing a power supplies voltage saturation rate with a newly developed adaptive voltage allocation (AVA) scheme. Furthermore, the AVA scheme also broadens accessible elongation by 0.3 in the presence of power supplies voltage saturation due to hybrid plasma current and shape/position control and unknown plasmas disturbances. In preparation for coming JT-60SA integrated commissioning, the VDE predictor and the AVA scheme are implemented in our equilibrium controller, and its performance is demonstrated by using MHD Equilibrium Control Simulator “MECS”.

We first propose an accurate and robust vertical instability predictor by using a support vector machine (SVM), one of the machine learning methods. The predictor is trained to detect precursor oscillation by using newly introduced classification parameters to measure the equilibrium controller performance, which is obtained by the adaptive voltage allocation scheme (Inoue et al 2021 Nuclear Fusion 61 096009). Furthermore, multi-layered preprocessing filters are newly introduced for the SVM training/prediction, which improves the prediction accuracy under highly imbalanced conditions, where ∼500 disruptive data while ∼3 × 106 non-disruptive data. The classification parameters can be calculated only by the current centroid, which suggests that the proposed predictor is robust against the extrapolation for the experiment and will be validated in JT-60SA experiments.

The plasma position and shaping, and the plasma current are controlled by poloidal field (PF) coils consisting of superconductors, and the fast plasma position change is controlled by in-vessel coils consisting of normal conductors on recent tokamaks. The coil current response for the voltage command value depends on the time constant of the coil. The in-vessel coils have a much faster coil current response than PF coils due to the short time constant. Therefore, the decoupling control between in-vessel coils and PF coils respecting each coil current response must be established. In this study, we introduce the issues given by the coupling of in-vessel and PF coils controls and demonstrate the improved control by the decoupling., 48th European Conference on Plasma Physics

An advanced ISO-FLUX equilibrium control scheme is developed and implemented in the JT-60SA equilibrium controller. For future fusion reactor, the VDE control by the active superconducting coils is essential due to the absence of in-vessel coils and stabilization plates, and the presence of large gap between plasmas and vacuum vessels with the tritium breeding blanket. Under the circumstances, the equilibrium controller should achieve plasma position/shape control and plasma current control by superconducting coils within limited power supply voltages, where plasma current control affects plasma position/shape control, and vice versa. The newly developed ISO-FLUX control scheme enhances the controllability under the above hybrid control of position/shape and plasma current circumstances. Furthermore, the new scheme also provides good controllability under large eddy currents conditions, which will also be expected in future superconducting tokamaks, such as JT-60SA, ITER, and DEMO due to its large inductance and high target plasma current. The JT-60SA equilibrium controller with the developed scheme is well verified by a magnetohydrodynamic equilibrium control simulator 'MECS' and ready for the integrated commissioning of JT-60SA.