A twisted magnetic flux rope embedded in the lower corona is thought to be a frequent ingredient of a coronal mass ejection(CME). We wish to study in a chromosphere-transition region-corona setup how a magnetic flux rope is formed, and evolves into the corresponding structure of a CME. We study the formation, evolution, and eruption of a magnetic flux rope by 2.5 dimensional resistive MHD simulation. We adopt an initial arcade-like linear force-free configuration in a rectangular simulation box, and drive the system by imposing slow motions which converge towards the magnetic inversion line on the bottom boundary. The convergence imposed to the footpoints of the magnetic arcades brings opposite-polarity magnetic flux to the polarity inversion. After a phase of quasi-static evolution, the convergence gives rise to the formation of a twisted flux rope by magnetic reconnection and finally to the eruption of a CME. In the eruptive phase, the closed magnetic field is severely stretched, leading to the formation of a current sheet, and this in turn enables fast reconnection. We observe the internal structure of the current sheet formed during the eruption process in our simulation. We confirm that the converging flow is a potential mechanism. for the formation of magnetic flux ropes, and a possible triggering mechanism for CMEs when a realistic atmosphere is included. Our simulation covers a wide range of scales, from the small-scale current sheet structure to the global-scale magnetic disruption, achieved by the use of the adaptive mesh refinement technique.
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