# The saturation mechanism in a two-stream Free electron laser based upon a rectangular hybrid wiggler

Hosseinnezhad, A., Ostadi, A & Kordbacheh

(under review in the Physics of Plasmas)

Abstract:

Presented in this paper is a one-dimensional nonlinear simulation of a square hybrid two-stream free electron laser (TSFEL) consisting of an axial magnetic field guide. It is supposed that the two cold relativistic electron beams differ in energy, while the electron beam’s self-fields, and radiation wave slippage relative to electron beams are neglected. A set of differential equations of the first order of coupled nonlinearity, obtained from the combination of Maxwell’s equations and Lorentz’s equations, can be numerically solved using a Rang-Kutta algorithm of fourth order based on slowly varying amplitudes and wavenumbers approximation. According to the results of the calculations, the increase in the axial magnetic field will result in the efficiency in group I orbits increasing while the saturation length decreases. The results for group II orbits are different from those of group I, such that the efficiency decreases with increasing axial magnetic field. There is, however, an increase in saturation length. Furthermore, it is found that prebunching significantly reduces the length of saturation. A comparison of radiation saturation in an FEL and a TSFEL indicates that a TSFEL has a higher efficiency than an FEL. In contrast, the TSFEL has shorter saturation lengths.

Keywords: Two-stream free-electron Laser, rectangular hybrid wiggler, A Prebunched Beam, Raman regime