Free electron lasers with static and dynamic plasma wigglers

In free electron lasers, plasma wigglers of static and dynamic types may be used. In the case of a static plasma wiggler a spatially modulated plasma density results in a periodic dielectric permittivity, but pumping electromagnetic fields are absent. A dynamic plasma wiggler arises when an electromagnetic wave propagating in a plasma is scattered by an electron beam. The wave fields act on beam electrons but modulate plasma particles also. Two mechanisms are responsible for the interaction between an electron beam and electromagnetic waves. One of them is analogous to that in usual FELs and exists only in dynamic plasma wigglers. Another mechanism is conditioned by space-temporal modulation of the density and velocity of plasma particles and exist in both static and dynamic plasma wigglers. The contributions of the two mechanisms into the interaction process may be comparable. Both types of magnetized plasma wigglers are considered in a linear approximation.