Exploring SF- in-out asymmetry and detachment bifurcation in HL-2M with E × B by SOLPS

physical picture.Abstract In this paper, the SF- (with the second X-point located near the outer target surface) in-out asymmetry and detachment bifurcation in HL-2M were explored by the edge plasma code SOLPS5.1 including electric but neglecting magnetic drifts. The modeling results reveal that the radial electron drift component (Epol × B) can play a key role on inducing the SF- in-out asymmetry due to the effective carbon (C) screen capacity and high heat dissipation. The Epol × B drift can enhance the poloidal electron drift component (Er × B), and their synergistic effects can induce a marked in-out asymmetry. Besides, the results showed that the detachment bifurcation in SF- also could occur under given conditions. The presence of four factors (including E × B, C impurity, normal-Bt, and relatively small radial anomalous transport coefficients) forms the necessary conditions for producing the detachment bifurcation. The root reason for the detachment bifurcation formation is due to the strong interaction of Te, E × B, and C impurity radiation loss in the outer divertor region with normal-Bt direction. The detachment bifurcation could be removed or mitigated by weakening their interaction. Finally, the time-dependent detachment bifurcation process is simulated in this work to better understand its physical picture.