Chaotic Electron Trajectories in Electromagnetic Wiggler Free-Electron Laser with a Guide Magnetic Field

The Hamiltonian for an electron travelling through a large-amplitude backward electromagnetic wave, an axial guide magnetic field and radiation field is formulated. Poincar~ surface-of-section plots show that this Hamiltonian is non-integrable, and leads to chaotic trajectories. Equilibrium conditions are derived in the limit where the radiation field approaches zero. Compared to conventional FEL, the total energy of the system at pondermotive resonance Ec is large, while the electron's critical energy Yc is low for electromagnetic wiggler FEL. Moreover, the threshold wave amplitude (A r = Ac) of beam chaoticity is found at lower values of the radiation field amplitude compared to magnetostatic wiggler FEL. Previous features confLrmed that electromagnetic wiggler FEL can operate more coherently and more efficiently at moderated particle's energy compared to magnetostatic wiggler FEL.