This box here is similar to that studied above [“Magnetic RDIs in a Piece of an HII Region: Larger Box with a Spectrum of Grain Sizes”] and this is an another 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 magnetic field strength, 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, as the previous case linked above. However, here we sample the properties an order-of-magnitude further away from the star. This means some are different: the radiation field is weaker so the acceleration of the grains via radiation is weaker, and their “terminal velocity” is significantly sub-sonic (~10x smaller than the gas sound speed).
Specifically, the parameters are representative of dust at roughly ~1 pc from a bright O star, with the box size being something like ~0.3 pc on a side. Here the dust is charged and feels both magnetic/Lorentz and drag/Coulomb forces, and it is drifting sub-sonically in a medium with plasma beta of ~10.
Note that the instabilities are not only still present, but they actually lead to more dramatic “clumping” of the dust in this case.