On assumed boundary conditions at an interface between a dielectric and a compressible plasma

Some remarks are made concerning two assumed boundary conditions at the interface between a dielectric region and a compressible plasma. It is indicated that Fedorchenko´s double Laplace integral formulation, which invokes causality, is equivalent to the assumption of continuity of the normal electric field. In general, this differs from results derived on the basis of an assumed rigid boundary. It is shown that both expressions for the reflection coefficient in the dielectric region have the same form, but the temperature correction is different. Without appeal to the physics of the sheath, there is no reason to choose one condition over the other.