A collisionless plasma is described by the Vlasov-Poisson system. This system is considered in one space dimension in the case when there is one species of ions. Using the fact that the time evolution preserves a certain partial order of points in phase space, two theorems on large-time asymptotics are established.
"Large-time behavior of a one-dimensional monocharged plasma." Differential Integral Equations 20 (3) 277 - 292, 2007.