Multisection free-electron lasers with alternate undulator and dispersive sections

A free-electron laser (FEL) configuration, consisting of a large number of identical parts, is considered. Each part is divided into undulator and dispersive sections. A one-dimensional model is used to derive the dispersion equation describing the generation of radiation. A study is made of the dependence of the gain on the parameters of the dispersive sections. The conditions ensuring the maximum rate of rise of the gain are found. A three-dimensional simulation of multisection FELs is based on a modified form of the well-known TDA code. The parameters of the electron beam of the Stanford linear accelerator are used in the simulation. It is shown that an overall power gain of 4 × 10⁸ can be achieved at the wavelengths 4.2 — 4.3 nm when the total length of the magnetic system is 20 m. This gain is considerably higher than that attainable in uniform (free of dispersive sections) FELs.