Focusing effect and modulation mechanism of the beam self-fields on the electron's Larmor rotation in a free-electron laser with an axial guide magnetic field

摘要

It is revealed that at anti-resonance in a free-electron laser with a reversed guide magnetic field, the beam self-fields can act to focus the beam transport and prevent the electrons from striking on the waveguide wall before the wiggler exit. It is found that the focusing function results from the modulation of the periodically-varying self-field tangential and normal components on the electron's Larmor rotation. As a potential application, substantial improvement of the wave gain and output power at anti-resonance could be expected, since the beam current loss can be obviated by using this modulation mechanism.