Development of a real-time control system for NTMs suppression with ECRH/ECCD on EAST tokamak

Neoclassical tearing modes (NTMs) in tokamaks limit the achievable β and induce a major disruption in some cases. They should be stabilized to overcome the limit and therefore improve the efficiency of magnetic confinement. On EAST tokamak, ECRH/ECCD will be used as a main tool for NTMs suppression. In order to achieve more effective application of ECRH/ECCD, a real-time control system for NTM suppression is needed. In this paper, a feasible design of the control system is proposed. The real time algorithms of mode localization and phase tracking are developed. The allowed latency of the control system is evaluated based on the modeling of magnetic island dynamics. Control scheme, hardware, some technical parameters are discussed as well. Mode localization is a key problem for NTMs suppression with ECRH/ECCD due to its quite narrow power deposition. Depending on the character of the temperature perturbation associate with the island, ECE measurements are used to make a correlation analysis (Te fluctuation correlated with magnetic signals) to determine the mode radial location. Island phase tracking is necessary for NTMs suppression with modulated ECRH/ECCD power. The O and X point of the island is identified based on the features of magnetic perturbation associate with the island. Due to absence of magnetic measurements close to the gyrotron, a reference signal for controller is derived from the coil located at the midplane in the low field side. The real-time control system will be implemented in FPGA environment. Its maximum allowed latency is required to match the growth times of NTMs, which is predicted to be in order of 100 ms on EAST. (author)