Control of SASE power and enhancement of FEL coherence by plasma wave dilation

A single transverse mode linear plasma response formulation of a free electron laser (FEL), including space-charge wave interaction, is used to describe the beam and radiation waves dynamics in radiating and non-radiating beam transport sections. This is employed to derive conditions for coherent operation of seeded high gain FELs. It is shown that the level of incoherent self-amplified spontaneous emission (SASE) radiation power can be controlled by adjusting the plasma oscillation phase in non-radiating sections, and that at X-UV wavelengths the theoretical FEL coherence will be ultimately limited only by quantum noise.