Snapshot of the simulation analyzed in this work. Left: Local average particle Lorentz factor ⟨γ⟩. Right: Angular velocity, $\mathrm{\Omega }=-E_{\theta }/\sqrt{h}{B}^r$, of magnetic field lines. Rotational shear along magnetic field lines causes the initially closed magnetic topology to partially open. A fully open topology is prevented by reconnection, which allows some closed loops to persist. Reconnecting current sheets are visible as sites of particle acceleration (left) and discontinuities in field-line angular velocity (right). A movie of this simulation is available online.