  In a variety of different systems, high-Z ion species show a marked tendency
to accumulate in regions of high plasma density. It has previously been
suggested that the apparent universality of this behavior could be explained
thermodynamically, in terms of the maximum-entropy state attainable when the
system must obey an ambipolarity condition. However, the previous treatment did
not allow for the possibility of temperature gradients. Here, tools from
non-equilibrium (Onsager) thermodynamics are used to show that ambipolarity
continues to play a key role in producing this behavior in the presence of
temperature gradients, and to recover well-known temperature screening effects
that appear in these cases.
