Solve for scattered field - perturbation of the precise solution?

Hi everyone!

I have a question about scattered field.

If I have background field and \some particles(or some another objects) in it.
I should than solve for scattered field.
But will it be a precise solution or just a perturbation?
What would be if I than put my solution as a new background field and try to solve problem again? Like *making a perturbation theory*