Maximum particle density (ρ_p,max) for one of the 2D simulations and the two 3D simulations. The top plot compares run 3D.Z2 (blue) and a 2D run (red). The bottom plot compares run 3D.Z3 (blue) and the same 2D run (red). In each plot the purple line shows ρ_p,max for the 3D run after averaging along the azimuthal direction. The vertical dashed lines mark the places where the 3D runs transition from Z = 0.01 to Z = 0.019 (for 3D.Z2) or Z = 0.029 (for 3D.Z3). Similarly, the vertical solid lines mark the progressive increase of Z during the course of the 2D runs.