High-field limit for the Vlasov-Poisson-Fokker-Planck system

This paper is concerned with the analysis of the stability of the Vlasov-Po isson-Fokker-Planck system with respect to the physical constants. If the s caled thermal mean free path converges to zero and the scaled thermal veloc ity remains constant, then a hyperbolic limit or equivalently a high-field limit equation is obtained for the mass density. The passage to the limit a s well as the existence and uniqueness of solutions of the limit equation i n L (1), global or local in time, are analyzed according to the electrostat ic or gravitational character of the field and to the space dimension. In t he one-dimensional case a new concept of global solution is introduced. For the gravitational field this concept is shown to be equivalent to the conc ept of entropy solutions of hyperbolic systems of conservation laws.