Nonlinear wave interactions in a collisionless space and time dependent warm fluid plasma

Expressions for the current response operators of first and second order are calculated for a fluid plasma with isotropic pressure terms. The unperturbed state is an arbitrary space and time dependent solution of the basic equations. The response operators are given in a form which shows explicitly the mathematical structure behind the approximate conservation of wave energy in resonant wave interactions. The coefficients in the coupled mode equations are expressed in terms of these response operators.