The effect of 2/1 pre-existing magnetic islands width on the suppression of runaway electrons in disruption simulations of J-TEXT

The suppression of runaway electrons (REs) is influenced by the size of pre-existing 2/1 magnetic islands. Simulations of argon (Ar) massive gas injection into J-TEXT plasmas with pre-existing 2/1 magnetic islands of different width are performed with the 3D magnetohydrodynamic code called NIMROD (Sovinecet al2004J. Comput. Phys.195355). Results show that the ratio of remaining REs is not monotonically dependent on the width of pre-existing 2/1 magnetic islands. Large enough pre-existing 2/1 magnetic islands can lead to strong magnetic perturbation and strong magnetic surface stochasticity to expel the REs. The critical width for the suppression of REs is to be 0.31 as the minor radius. Under the condition of suitable small pre-existing 2/1 magnetic islands width, with island width ranging from 0.07 to 0.11 times the minor radius, the mitigation of REs is achieved. The duration of magnetic perturbations delta B/B(n= 1) (exceeding (4 to 6) x 10(-3)) is a key for RE loss, and high amplitude of highnmodes plays an important role in RE loss.