Reduction of undulator radiation and FEL small gain due to wiggler errors

A deterministic approach is taken to study the effect of errors in the wiggler magnet field on the spontaneous emission and the gain of free electron lasers (FELs). A 3-D formulation is used to derive the reduction in spontaneous emission due to changes in the time of flight of the electrons. A generalization of J.M.J. Madey's (1971) theorem to 3-D is then used to calculate the reduction in the FEL small gain.<<ETX>>