A model for how induced reversed-currents form the 3-part CME structure

We report here a new model for explaining the three-part structure of CMEs consisting of a core prominence, a density cavity surrounding the prominence, and a shock-like leading edge feature. The model proposes that the cavity in a CME forms because a rising electric current in the core prominence induces an oppositely directed electric current in the background plasma; this eddy current is required to satisfy the frozen-in magnetic flux condition in the background plasma. The magnetic force between the inner core electric current and the oppositely directed induced eddy current propels the background plasma away from the core creating a density cavity and a density pileup at the cavity edge. The model is supported by laboratory experiments, 3D numerical MHD simulations, and can predict cavity widths to first order. This mechanism has broad applicability because the predicted widths are relatively independent of both the current injection mechanism and the injection timescale.