  In a variety of magnetized plasma geometries, it has long been known that
highly charged impurities tend to accumulate in regions of higher density.
Here, we examine how this "collisional pinch" changes in the presence of
additional forces, such as might be found in systems with gravity, fast
rotation, or non-negligible space charge. In the case of a rotating,
cylindrical plasma, we describe a regime in which the radially outermost ion
species is intermediate in both mass and charge. We discuss implications for
fusion devices and plasma mass filters.
