Effects of m=0 Harmonics on Quasi-Linear Stage of m=1 Double Tearing Mode

Effects of the m = 0 harmonics on the early quasi-linear stage of m = 1 double tearing modes are investigated. The numerical calculation with the harmonics m = 0 included shows that the effect of the m = 0 harmonics on the mode is negligible in the linear stage. As the mode begins to grow nonlinearly, both the current and flow profiles are pinched due to the m = 0 harmonics. To make a comparison we also carry out the calculation with m = 0 harmonics turned off. The profiles of the total current, poloidal magnetic field, and poloidal shear velocity in the cases with or without the m = 0 harmonics are compared and discussed. In addition, the formation of a poloidal velocity shear is found and its mechanism is investigated.