On Closure Conditions for the Moment Equations of a Bipolar Kinetic Model

We consider a bipolar kinetic model for charged media. In certain scalings the Debye length or the relaxation time are small. In addition different time scales are considered. These can be used in order to close the corresponding moment equations and leads to a (closed) set of macroscopic equations. We show three different scalings and obtain three completely different sets of macroscopic equations.