Nonlinear evolution and control of neo-classical tearing mode in reversed magnetic shear tokamak plasmas

The reversed magnetic shear (RMS) configuration is believed to be one of the most promising advanced scenarios to achieve steady-state operation in the future large-scale tokamak devices. Nevertheless, the neo-classical tearing mode (NTM) is a detrimental threat to the steady-state operation and should be appropriately controlled by various effective strategies. This paper reviews recent numerical results on the nonlinear evolution and control of NTMs in RMS tokamak plasmas. The numerical results are mainly obtained through running initial value code MHD@Dalian Code. First, the nonlinear features of TMs/NTMs with RMS are introduced in comparison with the tokamak experimental results. Then, several effective control strategies on NTMs and on NTMs triggering explosive bursts are reviewed, including differential plasma rotation, electron cyclotron current drive (ECCD) and resonant magnetic perturbation (RMP), as well as the synergistic effect of ECCD and RMP. The introduced strategies are all feasible and effective to prevent the explosive bursts under the proper operations of control techniques. Finally, a two-fluid model is adopted to investigate the effect of diamagnetic drift flow on the nonlinear properties of TMs/NTMs with RMS. The evolution features and their dependence on key plasma parameters, such as plasma resistivity, ion viscosity and parallel/perpendicular transport coefficients, are all investigated and analyzed in detail. Moreover, the prospects of potential future intense topics in this area are given in the last section.