Two-dimensional density profiles of the plasma stream propagating along a quasi-uniform magnetic field at 28 ns (a), 38 ns (b), 48 ns (c), and 68 ns (d) after the laser irradiation of the target. The spatial scale shown in (a) is the same for all the images. To demonstrate the evolution of the plasma cavity, the position of the target was shifted from shot to shot. Each panel in this figure is composed of a few such experimental snapshots.