Numerical analyses for nonlinear growths of tearing mode

The growths of nonlinear tearing mode and magnetic island width w have been calculated based on the unified analytical model (D. Li, Phys. Plasmas 2, 3275 (1995)) and by using TEXT parameters adopted in the island width measurements (Y. Z. Zhang et al., Phys. Rev. Lett. 65, 2877 (1990)). It is found that the Rutherford behavior like (Ψ tilde)1 ∝ t2 (i.e. w ∝ t) is dominant in the nonlinear phase if the linear mode is weekly unstable. However, the new behavior like (Ψ tilde)1 ∝ t (i.e. w ∝ t1/2) becomes dominant in the nonlinear phase when the linear mode is strongly unstable. It seems that synthetic effect of these two algebraic growths is more identical to the temporal evolution of (m/n=2/1) island width in TEXT discharges. Here (Ψ tilde)1 is the magnetic flux perturbation. (author)