Effects of diamagnetic drift on MHD explosive bursts in reversed magnetic shear tokamak plasmas

The explosive bursts, induced by self-organized double tearing modes (DTMs) in reversed magnetic shear tokamak plasmas, are numerically investigated based on a set of reduced two-fluid equations. It is found that the diamagnetic drift has a destabilizing effect on the mode in the Rutherford phase but can effectively stabilize the explosive burst of the mode in the following nonlinear phase. The plasma viscosity mu is found to have an important effect on the critical ion skin depth delta(c) for completely suppressing the explosive bursts. In the low viscosity regime (i.e. mu < mu(c), where mu(c) is the critical viscosity), delta(c) increases with increasing mu, because the increase of mu can effectively reduce the velocity difference of islands between the two rational surfaces, which mainly result from zonal flow and electron diamagnetic flow. In the high viscosity regime (i.e. mu > mu(c)), however, delta(c) decreases with increasing mu, because the increase of mu can greatly stabilize the DTM instability. In addition, the dependences of critical viscosity mu(c) on viscosity and resistivity are obtained and the relevant mechanisms are analyzed.