A simple self-consistent model is proposed, which describes properties of the tail current sheet after the formation of a small plasmoid on the closed field lines in the magnetotail and its quick tailward retreat. Using a theory of forced magnetic reconnection, it is shown that the flux tube that contained a plasmoid becomes a plasma bubble, with the plasmoid being replaced by a thin current sheet embedded within the original thicker sheet. The model allows for an estimate of the decrease of the plasma entropy per unit magnetic flux within the bubble. It predicts that the bubble structure may also include bifurcated current sheets.