Development of real-time measurement system of charge exchange recombination spectroscopy and its application to feedback control of ion temperature gradient in JT-60U

Real-time measurement system of the ion temperature profile has been developed for the feedback (FB) control of the ion temperature gradient (grad-Ti) with the filter charge exchange recombination spectroscopy (CXRS) system in JT-60U. The rapid analytical scheme without non-linear least square fitting enables us to calculate the ion temperature with four spatial points every 10 ms using a real-time processor system. The FB control experiment of grad-Ti has been demonstrated in ELMy H-mode plasmas by use of the neutral beam injectors having different deposition profiles as actuators. Grad-Ti was controlled to the reference value in the ramp-down phase, however, it did not recovered in the ramp-up phase because the internal transport barrier or transport was affected by the ramp-down of grad-Ti. From the transient response analysis of grad-Ti, the increase in the central Ti using the additional heating was required to recover the deteriorated grad-Ti. (author)