Suppression of explosive bursts triggered by neo-classical tearing mode in reversed magnetic shear tokamak plasmas via ECCD

The suppression of explosive bursts, triggered by the neo-classical tearing mode, in the reversed magnetic shear configuration tokamak plasmas by electron cyclotron current drive (ECCD) are numerically studied by making use of a reduced magnetohydrodynamic model including both bootstrap current and self-consistently evolving EC driven current. It is found that the ECCD with appropriate input power and switch-on time can effectively stabilize the neo-classical islands. In comparison with the classical one, it is far more difficult to control the neo-classical island due to the strong zonal magnetic field induced during the nonlinear evolution. This strong zonal field can lead to intense fluctuations of the magnetic surfaces once the ECCD is turned on, which can damage the steady deposition of the driven current. To avoid the strong zonal field, the switch-on time should be put forward, which is proved to be effective. By adopting this scheme, the explosive burst triggered by neo-classical current can also be effectively suppressed. Moreover, the steady-state distributions of driven current are displayed. The influence of the radial misalignment of ECCD is discussed in detail. Based on the numerical results in different fractions of bootstrap current, some suggestions are proposed for the tokamak experiments.