Effect of the Electron-Beam Self-Fields on Gain in an Optical Wiggler Pumped Free-Electron Laser

摘要

The effects of self fields on gain for a free-electron lasers (FELs) with electromagnetic-wave wiggler and an axial guide magnetic field is presented. The relativistic equation of motion for a single electron for all relevant fields, including wiggler, self-fields and axial guide magnetic field has been solved. Two classes of possible single-particle trajectories in this configuration are found. Result of the numerical calculation shown that the relativistic part of group I (group H) orbits decreases (increases) monotonically with the axial field. The gain equations for the FEL configuration by adding the effect of self-fields have been derived. The numerical calculation has been employed to analysis the gain induced by the effects of the self-fields. It is shown that, for group I orbits the gain decreases in the presence of self-fields and the gain decrement increases with increasing axial guide magnetic field, while for group II orbits the self-fields enhances the gain. The gain decrement and enhancement are due to diamagnetic and paramagnetic effects of the self-magnetic field, respectively. The comparison of the gain for electromagnetic-wave wiggler with the gain in helical wiggler has been done.