Like the case previously (here), this is an example of the RDIs in magnetized gas. Specifically, the movie shows an xyz projection, with the initial magnetic field in the vertical direction (z), the acceleration of the grains in the x-z (width-height) direction, and the mutually perpendicular direction is depth (y). The colors show the logarithm of the gas density, relative to mean, measured on slices on the xyz surfaces in the periodic box, while the black points show the dust in the same slice. This particular box is motivated by parameters typical in HII regions, at roughly ~0.1 pc from a bright O star, with the box size being something like ~0.1 pc on a side. Here the dust is charged and feels both magnetic/Lorentz and drag/Coulomb forces, and it is drifting mildly super-sonically in a medium with plasma beta of ~10. The difference from the previous box[es] is that this includes a broad spectrum of grain sizes, a factor of ~100, from grains ~nanometer in size to ~0.1 micron. The different grains respond differently to various forces (here, the grain charge scales with grain size, but we assume the grains are all small in size relative to the incident radiation so the absorption efficiency scales with grain size, which in turn means that the radiative acceleration of the dust is independent of grain size).